TAPR spread spectrum update : tales from the rebel alliance
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Frequency Time Hopping Systems - A time hopping system is a spread spectrum system in which the period and duty cycle of a pulsed RF carrier are varied in a pseudorandom manner under the control of a coded sequence. Time hopping is often used effectively with frequency hopping to form a hybrid time-division, multiple-access (TDMA) spread spectrum system. ~'\).t~\

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Pulsed FM (Chirp) Systems - A pulsed PM system is a spread spectrum system in which a RFcarrier is modulated with a fixed period and fixed duty cyclesequence. At the beginning of each transmitted pulse, the carrier frequency is frequency modulated causing an additional spreading of the carrier. The pattern of the frequency modulation will depend upon the spreading function which is chosen. In some systems the spreading function is a linear PM chirp sweep, sweeping either up or down in frequency. Hybrid Systems - Hybrid systems use a combination of spread spectrum methods in order to use the beneficial properties of the systems utilized. Two common combinations are direct sequence and frequency hopping. The advantage of combining the two methods is to capitalize on characteristics that are not available from a single method.

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Why Spread Spectrum? To answer the question "why should I use spread spectrum" could easily degenerate into a simple listing of advantages and disadvantages. However, spread spectrum has many different unique properties that cannot be found in any other modulation technique. As radio amateurs, we should exploit these properties and search for useful applications. Think of spread spectrum as another useful tool in our repertoire of modulation methods toolbox. For completeness, I will list some advantages and disadvantages that you will see for typical spread spectrum systems. Bare in mind that these come about because of the nature of spread spectrum, not because they are direct attributes. Advantages: - Resists intentional and non-intentional interference - Has the ability to eliminate or alleviate the effect ofmultipath interference - Can share the same frequency band (overlay) with other users - Privacy due to the pseudo random code sequence (code division multiplexing) Disadvantages: - Bandwidth inefficient - Implementation is somewhat more complex.

Other Properties There are several unique properties that arise as a result of the pseudo random code sequence and the wide signal bandwidth that results from spreading. Two of these are selective addressing and code division multiplexing. Byassigning a given code to a single receiver or a group of receivers, they may be addressed individually or by group away from other receivers assigned a different code. Codes can also be chosen to minimize interference between groups of receivers by choosing ones that have low cross correlation properties. In this manner more than one signal can be transmitted at the same time on the same frequency. Selective addressing and Code Division Multiple Access (CDMA) are implemented via these codings. A second set of properties is low probability of intercept (LPI)and anti-jamming. When the intelligence of the signal is spread out over several megahertz of spectrum, the resulting power spectrum is also spread out. This results in the transmitted power spread out over a wide frequency bandwidth and makes detection in the normal sense (without the code), very difficult. Though LPI is not a typical application for radio amateurs, it would best to rename this property as "reduction of interference." Thus spread spectrum can survive in an adverse environment and coexists with other services in the band. The anti-jamming property results from the wide bandwidth used to transmit the signal. Recall Shannon's Information-rate theorem

c = W log (1 + SIN)

C = capacity in bits per second W = bandwidth S = signa l power N = noise power

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Introductory/Informative

where the capacity of a channel is proportional to its bandwidth and the signal-to-noise ratio on the channel. By expanding the bandwidth to several megahertz and even several hundred megahertz, there is more than enough bandwidth to carry the required data rate and have even more to spare to counter the effects ofnoise. Thisanti jamming quality is usually expressed as "processing gain." So for the radio amateur, the properties of code division multiplexing, coexistence in an adverse environment, and processing gain, are all excellent reasons to experiment with and find useful applications for spread spectrum in the amateur radio service . Coupled with these reasons, amateurs can also enjoy increased data rates in digital data (packet radio) that cannot be done with conventional amateur or commercial radios due to physical (i.e. bandpass filters) and rules restrictions. For example, narrowband systems in the 70 em band are limited to a maximum data rate of 56 kbps and a bandwidth of 100 kHz, there are no such restrictions in the 33 em band and up.

Perhaps one of the most important reasons to use spread spectrum is its ability discriminate against multipath interference. A RAKEl receiver implementation for direct sequence allows individual signal paths to be separately detected and the coherently combined with other paths. This not only tends to prevent fading but also provides a path diversity effect resulting in very rugged links in terrestrial mobile communications (ref. 2).

Building Blocks Spread spectrum signals are demodulated in two steps: 1) the spectrum spreading (direct sequence, frequency hopping) modulation is removed, and 2) the signal is demodulated. The process of despreading a signal is called correlation. The spread spectrum signal is despread when the proper synchronization of the spreading code between the transmitter and receiver is achieved. Synchronizationis the most difficultaspectofthe receiver. Moretime,research, effort, and money has gone into the development and improving of synchronization techniques than in any other area ofspread spectrum. The problem ofsynchronization is further broken down into two parts: initial acquisition and tracking. There are several methods to solve the synchronization problem. Many of these methods require a great deal of discrete components to implement. But perhaps the biggest break-through has been from Digital SignalProcessing (DSP) and Application Specific Integrated Circuits (ASIC). DSP has provided high speed mathematical functions that can slice up in many small parts and analyze the spread spectrum signal to synchronize and decorrelate it. ASIC chips drive down the cost by using VlSI technology and creating generic building blocks that can be used in any type of application the designer wishes. With the fast growing Part 15 and Personal Communications System (PCS) spread spectrum market, many ASIC manufactures have been designing and sellingASICchips that take care of the most difficultproblem in spread spectrum - despreading and synchronization. With a few extra components, the amateur can have a fully functioning spread spectrum receiver. 1 RAKE is not an acronym. It is called RAKE because the filter arrangement of the receiver is like a garden rake .

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One manufacture of a spread spectrum demodulator ASIC is UNISYSred. now Loral]. Their PA-100 performs the functions of despreading and demodulation, carr ier recovery loop (frequency or phase), Pseudo Noise (PN) code detection, PN code tracking loop, data synchronization, and automatic gain control. It is programmable and offers a wide ran ge of choices in data rates, modulation types, processing gains, PN codes, loop bandwidths, and tracking and acquisition procedures. It is capable of chipping rates up to 32 Mcps and data rates up to 64 Mbps. The PA-100 is controlled via a simple 8-bit inter face. The chip is a 208-pin plastic Metri x Quad Flat Package (MQFP). The cost of the chip is $167.00 in single qty and $67.00 in lots of 1000.

Where does Part 1.5 fit into all this? Many of the spread spectrum devices on the market today are listed as Part 15 devices . This refers to the device operating under the provisions of Title 47 Section 15.247of the Code of Federal Regulations (CFR). There are three frequency bands allocated to this service: 902 - 928 MHz (26 MHz bandwidth) 2400 - 2483.5 MHz (83.5 MHz bandwidth) 5725 - 5850 MHz (125 MHz bandw idth)

Operation under this provision of this section is limited to frequency hopping and direct sequence spread spectrum. No other spreading techniques are permitted. Section 15.247defines the technical standards that these systems must operate under. For example, the maximum peak output power of the transmitter shall not exceed 1 watt. If transmitting antennas of directional gain greater than 6 dBi are used, the power shall be reduced by the amount in dB that the directional gain of the antenna exceeds 6 dBi. This equates to a maximum transmitter EIRP of +6dBW (1w att into a 6 dBi gain antenna) Part 15equipment operates on a secondary basis. Users must accept interference from other transmitters operating in the same band and may not cause interference to the primary users in the band. Primary users are government systems such as airborne radiolocation systems that emit a high EIRP; and Industrial, Scientific, and Medical (ISM) users. Thus the Part 15 device manufacturer must design a system that will not cause interference with and be able to tolerate the noisy primary users of the band. And this is where spread spectrum systems excel because of their low noise transmissions and ability to operate in an adverse environment. Amateurs should realize that under the present Part 97 rules and regulations governing amateur spread spectrum today, taking a Part 15spread spectrum device and adding an amplifier to it would break the rules . Even though it would be transmitting within the amateur spectrum, it more than likely would not be using one of the specified spreading codes assigned to amateur operation (refer to Sec. 97.311 Section (d) - SS emission types). However, this should not deter the radio amateur from using Part 15 devices in their experimentation or use in the amateur service. The device should be monitored to ensure that it remains under the

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Introductory/Informative

Part 15 regulations and as such, no Part 97 regulations apply. Amateur traffic can flow though Part 15 devices, and they do not require a callsign since they do not require a license. However, the radio amateur should realize that when the traffic enters the amateur bands, for example, through a gateway, then Part 97 rules begin to apply.

Further Part 97 Rules and Regulations Any radio amateur contemplating experimentation of spread spectrum in the amateur bands (excluding Part 15 devices) should become familiar with the present Part 97 rules and regulations governing it. Here are some excerpts that bare emphasizing: Sec. 97.119 Station identification

(a)(5) By a CW or phone emission during 55 emission transmission on a narrow bandwidthfrequenojsegment. Alternatively, by thechanging ofone ormore parameters of the emission so that a conventional CW or phone emission receiver can be used to determine the station call sign. Sec. 97.305 Authorized emission types.

Spread Spectrum is permitted on thefollowing bands (over the entire band unless otherwise indicated): UHF: 70 em (420-450 MHz), 33 em (902-928 MHz) , 23 em (1240-1300 MHz), 13 em (2300-2310 and 2390-2450 MHz*) SHF: 9 em (3.3-3.5 GHz), 5 em (5.650-5.925 GHz), 3 cm (10.00-10.50 GHz), 1.2 em (24.00-24.25 GHz) EHF: 6 mm (47.0-47.2 GHz), 4 mm (75.5-81.0 GHz), 2.5 mm (119.98-120.02 GHz), 2 mm (142-149 GHz), Lmm (241-250 GHz), Above 300 GHz Operation on all of the above bands are on a secondary basis. No amateur station transmitting in these bands shall cause harmful interference to, nor is protected from interference due to the operation of the primaru service. (*Note: Recent rule making has allocated 2390-2400 MHz and 2402-2400 MHz to the Amateur community on a primary basis.)

Sec. 97.311 SS emission types [Note: Sections (a) through (d) set the technical standards for spread spectrum emissions.]

(e) The station records must document all 55 emission transmissions and must be retainedfor a period ofl yearfollowing thelastentry. Thestation records must include sufficient information to enable the FCC, using the information contained therein, to demodulate all transmissions. Thestation records must contain at least thefollowing: (1) A technical description of the transmitted signal; (2) Pertinent parameters describing the transmitted signal including the frequency orfrequencies ofoperation and,where applicable, thechip rate, thecode rate, thespreadingfunction, the transmission protocol(s) including the method ofachieving synchronization, and the modulation type;

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(3) A general description of the type of information being conveyed, (voice, text, memoru dump,facsimile, television, eic.); (4) The method and, if applicable, thefrequency orfrequencies usedfor station identification; and (5) Thedate ofbeginning and thedate ofending useofeach type of transmitted signal. if) When deemed necessanJ by an EIC to assure compliance with this part, a station licensee must: (1) Cease SS emission transmissions; (2) Restrict SS emission transmissions to the extent instructed; and (3) Maintain a record, convertible to the original information (voice, text, image, etc.) of all spread spectrum communications transmitted. (g) The transmitter power must not exceed 100 W.

Rules Reform Needless to say,by today's standards, practices, and improvements in technology, the above Part 97 rules and regulations on amateur spread spectrum are extremely restrictive especially in the case of the few fixed spreading codes dictated by section 97.311 (d)(l). The ARRL is reviewing the suggestions from the ARRL Futures Committee for changes to these rules and regulations to allow less restriction and freer experimentation.

Getting Around the Rules· Legally In the mean time there is a Special Temporary Authority (STA) to allow amateur spread spectrum experimentation being handled by TAPR. Under the TAPR SS STA97.119(b)(5),to remove the requirement to transmit station identification signals by a CW or phone emission; Section 97.305(c), to permit spread spectrum emissions on amateur radio bands 50-54 MHz, 144-148 MHz, 219-220 MHz and 222-225 MHz; Section97.311(c),to provide for transmission ofhybrid spread spectrum emissions; and Section 97.311(d), to permit the use of other spreading codes. To get involved in the STA, please visit the TAPR SS Web page http:/ /www.tapr.org/ ss . TAPR expects: Stations to maintain the highest standards in operational practices. Stations must submit a report before the end of each STA period that will be used in the final report. Stations must have a dependable Internet e-mail service so that information and discussion regarding the STA can be held. Stations must hold at least a Technician Class license. Stations must be aware that any transmissions conducted pursuant to the requested STA will be secondary in nature, and must cease immediately in the event of harmful interference. Stations must be a current member of TAPR.

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Introductoryllnformative

The information that you collect through your experimentation will be helpful in the advancement of Amateur spread spectrum but will also be useful for justification for rules changes before the FCC.

Areas to expand and researc:h Typical 55 applications such as wireless ethernet use point-to-point communications. They link two subnets over distances of several miles with external Yagi antennas and less than one watt of power. Amateurs would rather use the traditional C5MA/CA technique they are familiar with in today's packet radio. However, with the requirement of correlating the spreading code it would require a network node to have multiple receivers to listen in on the channel and detect when an outlying node is trying to communicate with it. Here's where amateur radio experimentation can advance the art of spread spectrum, by creating a CDMA spread spectrum packet radio network. Byusing the techniques employed by CPS, relatively short codes can be use to minimize receiver acquisition time . These codes would also need to have good cross-eorrelation properties to minimize multiple access interference between nodes. Power control is required to control the reuse of the frequency beyond code division multiplexing. It also behooves us to explore good power control to limit interference and to reduce the power consumption and drain on batteries. Routing of packets through a network is typically a software issue, but with the ability to do code division multiplexing, how do we route packets from one subnet to another when they do not use the same code sequence? Driving cost down has always been a top goal of any designer, and even more so since the Amateur is experimenting with their own money. Amateurs tend to be a frugal lot and will find any means available to build a system that costs as little as possible. This spawns innovative and creative methods to achieve this means. Then these means tend to be passed back to the commercial sector and benefit everybody. CDMA is not the exclusive province of direct sequence systems; CDMA can also be used with frequency hopping. TDMA is not the exclusive province of narrowband systems; TDMA can also be used with direct sequence or frequency hopping.

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This isn't new In the 1982 AMRAD letter (reprinted on page 4-11 of the ARRL SS Handbook), Hal Feinstein, WB3KDU, wrote,

Spread spectrum hasfound its way into packet radio. Spread spectrum allows each node to have a uniquecode whichacts as a hard address. Another node in the system can send data to that node by encoding that data with the spread spectrum addressfor thereceiving node. Trafficfor other nodes does notinterfere because it would have a different code. Among thereasons citedfor employing spread spectrum for packet switching are privacy, selected addressing, multipath protection and band sharing. But it is interesting to note that a load is taken off the contention collision approach because now a singlefrequency is not in contention among the nodes wishing to transmit. The load is divided among the nodes addresses, and each that is interested in sendingdata toa target node competes for that node only. This is the CDMApart ofSS. This is one of those areas the FCC really wants hams to experiment with. I think the paper has a lot of insight and it was even written over 13 years ago.

PANSAT . A Spread Spectrum Satellite The Space Systems Academic Group (SSAG) at the Naval Postgraduate School (NPS) in Monterey, California is actively designing and building an amateur satellite named PANSAT. PANSAT is the acronym for Petite Amateur Navy Satellite. PANSAT is to become a packet digital store-and-forward satellite vary similar in capabilities as the existing PACSATs in orbit today. PANSAT is expected to get launched as a Get Away Special (GAS) payload from the Space Shuttle. Solar Panels (17)

Electrical Power Subsystem (EPS) Digital Contr ol (DCSA & B)

Communications Subsystem

Battery Box B

Battery BoxA DipoleAntennas (4) in turnstile

Launch \ehicle Interface

Cylindrical Support

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Introductory/Informative

One big difference between today's PACSATs and PANSAT is that PANSAT will use direct sequence spread spectrum as the communications up and downlink. PANSAT is being designed from the ground up as an amateur satellite. The only military mission of PANSAT is as a training vehicle for the education of military officers in the Space Systems Curricula by the design, fabrication, testing and operation of a low-eost, low earth orbit (LEO), digital communications satellite. One of the engineering objectives of PANSAT includes the evaluation and performance of spread spectrum packet radio communications using the Amateur community as the user base. In order to facilitate the evaluation of spread spectrum performance the SSAG is designing a low cost spread spectrum modem and RF package to be presented to the amateur community in a kit form. The goal is to have the design of the spread spectrum radio /modem available before the launch of PANSAT to allow Amateurs to build and become operational via terrestrial means. This presents an exciting exchange of technology and the ability for the Amateur to build a low cost unit to experiment with. As the design and development progresses they will be presented in the Amateur press.

Future and Summary Now is the time to begin experimenting with spread spectrum communications on a wider scale. Technology has advanced to the point where Amateurs can afford to build systems. The building blocks are available now in the form of Application Specific Integrated Circuits. The recent flood of consumer devices that employ spread spectrum has also driven the price down. In many cases the Amateur can either use these devices under their present type acceptance or modify them for Amateur operations. However, the Amateur should remain aware of the rules and regulations governing the particular device whether it falls under Part 15 or Part 97 of the FCC Rules and Regulations and remain within their guidelines. If the Amateur wishes to expand beyond the present Part 97 rules in bonafide experimentation, they are encouraged to join in the Special Temporary Authority. Spread spectrum systems exhibit unique qualities that cannot be obtained from conventional narrowband systems. There are many research avenues exploring these unique qualities. Amateurs in their inherent pioneering nature can and will find new and novel applications for spread spectrum communications that the commercial sector may not even think of. And due to the frugal propensity of the Radio Amateur, they will certainly find the least expensive way to implement it, thus driving down the cost. Amateurs should realize that there is plenty of room to explore spread spectrum techniques. All that remains now is to pick up a few good books on the subject and warm up the soldering iron. And as you progress upon this road less traveled, make sure you take notes along the way. Then share your discoveries with your fellow Amateur to help all of us expand the horizon with this exciting mode of communications call spread spectrum. It is no longer shrouded in secrecy and it's not just for breakfast anymore!

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WEB Crawling I've started a general amateur radio SS page, http://www.tapr.org/ss. See also thePANSAT page at http :/ / www.sp.nps.navy.mil/pansat/ pansat.html

Selected Bibliography Extensive research oriented analysis

M.K. Simon, J.Omura, R Scholtz, and K. Levitt, Spread Spectrum Communications Vol. I, Il, Ill. Rockville, MD . Computer Science Press, 1985. Intermediate level

J.K Holmes, CoherentSpread SpectrumSystems,New York, NY. Wiley Interscience, 1982. D], Torrieri, Principlesof Secure Communication Systems. Boston. Artech house, 1985. Introductory to intermediate levels

G.R Cooper and CD.McGillem, Modem Communications and Spread Spectrum, New York, McGraw-Hill, 1986. RE. Ziemer and RL. Peterson, Digital Communications and Spread Spectrum Systems, New York, Macmillan, 1985. RE. Ziemer and RL. Peterson, Introduction to Digital Communications, New York, Macmillan, 1985. Practical

RC Dixon, Spread Spectrum Systems, John-Wiley & Sons, 1984. Journals There have been several special issues of IEEE publications that are devoted to spread spectrum systems. IEEE Transactions on Communications: August 1977 and Ma y 1982. IEEE Journal of Selected Areas in Communications: May 1990, June 1990, and May 1992. References (1) RC Dixon, Spread Spectrum Systems, John-Wiley & Sons, 1984, page 7. (2) K. Gilhousen, Qualcomm Inc., USENET newsgroup discussion.

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Introductoryllnformative

A Short History of Spread Spectrum by Steven R. Bible, N7HPR ([email protected]) reprinted from TAPR PSR #62 , April 1996.

"Whuh? Oh," said the missile expert. "I guess I was off base about the jamming. Suddenly it seems to me that's so obvious, it must have been tried and it doesn't work." "Right, it doesn't. That's because the frequency and amplitude of the control pulses make like purest noise they're genuinely random. So tr yin g to jam them is like trying to jam FM with an AM signal. You hit it so seld om, yo u might as well not try." "What do you mean, random? You can't control an ything with random noise." The captain thumbed over his shoulder at the Luanae Galaxy. "They can. There's a synchronous generator in the missiles that reproduces the same random noise, peak by peak. Once you do that, modulation's no problem. I don't know how they do it. They just do. The Luanae can't explain it; the planetoid developed it." England put his head down almost to the table. "Th e sa me random," he whispered from the very edge of sanity. -from "The Pod in the Barrier" by Theodore Sturgeon, in Galaxy, Sept. 1957; reprinted in A touch of Strange (Doubl eday, 1958).

Science fiction or science fact? It's uncanny how science fiction writers can glimpse the future . However, spread spectrum's beginnings date back to the 1920's with the advent of RADAR. Spectrum spreading for jamming avoidance and resolution, be it for location accuracy or signal discrimination, was a concept familiar to radar engineers by the end of the war. Spread spectrum wa s a natural result of the Second World War battle for electronic supremacy, a war waged with jamming and anti-jamming tactics [1]. In trying to combat this threat, scientists determined that: ...it can be stated that the best anti-jamming is simply good engineering design and the spread of the operating frequencies. In the military, spread spectrum techniques were primarily used to combat enemy jamming since they tolerate much more interference than conventional means. Jamming of communication and navigation systems was attempted by both sides and the need for reliable communication and accurate navigation in the face of this threat was real. One major AJ tactic of the war was to change carrier frequency often and force the jammer to keep looking for the right narrow band to jam.

Cloaked in secrecy and shrouded in mystery, spread spectrum has become one of the most misunderstood modulation techniques today. Perhaps because of spread spectrum's lineage from intensive research during and after World War II. Many people equate spread spectrum with an obscure modulation technique that cannot be understood and used predominantly for secrecy. Perhaps no other technology

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developed out of the post WWII era carries such a stigma.Spread spectrum's stigma can be likened to the Manhattan Project. But as the Manhattan Project had many beneficial spin-offs that we take ad vantage of today, spread spectru m came out of its cloak of secrecy in the late 1970's when the Federal Communications Commission began exploring the concept of using w ide band spread spectrum techniques for commercial uses. So began a new paradigm in thinking concerning communications techniques. Now a third dimension, coding, w as introduced in addition to frequency and time. Communications engineers had to rethink how information was transmitted over wire and wireless. It was Claude Shannon that introduced the concept of statistical concepts to information transfer. Thus was born a new area of research we know today as Information Technology.

Poisson, Shannon, and the Radio Amateur In 1959 John Costas, K2EN, wrote a canonical paper [2] that challenged the conventional wisdom of the day that relief from congestion in the radio frequency spectrum was by dividing the available bandwidth into channels as small as possible. This is a principle we know today as frequency allocation and he argued that this principle was not based on any fundamental physical principles. "The inherent communication capacity of the spectrum can be shared in ways other than by frequency allocation and for many applications the frequency division approach represents a very poor choice indeed." Costas, using statistical me thods applied to communications pioneered by Claude Shannon first suggested that the best way to improve spectrum crowding was to use wide band techniques. "The frequency diversity [55] system is intuitively ridiculous because it apparently "wastes" bandwidth rather indiscriminately. As we shall see, intuition is a poor guide in these matters. The feeling that we should always try to "conserve bandwidth" is no doubt caused by an environment in which it has been standard practice to share the RFspectrum on a frequency basis. Our emotions do not alter the fact that bandwidth is but one dimension of a multidimensional situation." Costas knew about the chaotic use of amateur frequencies. Strangely enough, the only other communications service that closely resembles the amateur service is the military. The amateur bands are similar to military uses of the spectrum not so much in intentional jamming, but simply casual interference when two opposing forces attempt to operate independently using the electromagnetic spectrum.

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Introductoryllnformatlve

Non-military Uses of Spread Spectrum Given that spread spectrum techniques have evolved largely in response to military requirements, and in view of the fact that they require large bandwidths (relative to the information bandwidth), it is reasonable to ask why anyone would consider spread spectrum techniques for non-Government applications. Specifically,only the anti-jamming property of spread spectrum seems to be unique to military environments. The other uses, including resistance to unintentional interference, resistance to interception, discrete addressing, multipath resistance, multiple access and pulse compression all have potential civilian applications. In general terms, it is possible to identify four potential motivations for introducing a new communications or radiolocation technology [3]: Reduced Cost - Because of the performance improvements that are possible with spread spectrum, it is conceivable that under certain conditions, a particular spread spectrum system could be less costly due to reduced transmitter power or the elimination of ancillary circuits than a narrowband system offering the same level of communication of ranging performance. Improved Communication of Radiolocation Performance - Spread spectrum systems can provide significant resistance to unintentional interference and multipath fading. Tothe extent that error correction coding is used, spread spectrum systems provide improved performance against additive white Gaussian noise. Expanded Capabilities - Spread spectrum systems can provide user privacy, discrete addressing, and multiple access on a transmit-at-will basis. Improved Spectrum Utilization - The notion that spread spectrum techniques could provide improved utilization may be at first surprising. J. P. Costas was the firstto raise this possibility. More recently,Cooper and Nettleton [4]have predicted improved spectrum efficiency for high-capacity spread spectrum mobile radio systems.

Amateur Experimentation Amateur experimentation started innocently enough, with a short note in the June 1980AMRAD newsletter. Paul Rinaldo, W4RI,spread the word that the FCC had some interest in amateur radio experimenting with wide band techniques. Soon a special interest group formed for the purpose of exploring spread spectrum techniques in the amateur bands. The next step was to obtain a Special Temporary Authority (STA) which was granted on March 6,1981. AMRAD experimentation is chronicled in The ARRL Spread Spectrum Sourcebook. AMRADs experimentation lead to the granting of spread spectrum emissions to amateurs on May 1985 from Report and Order GEN Docket No. 81-414.

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Unlicensed Spread Spectrum One of the most rapidly developing and hotly contested areas of wireless data involves the use of spectrum that does not require the user to be licensed. In 1985, the FCC opened up three bands for unlicensed uses (data and other types of communications) based on a set of regulations designed to minimize interference and encourage the development of new services. Since then 130 companies have developed more than 200 systems and products for use in these bands the 900 MHz band being the most popular and more than 3 million devices are now in use by consumers and businesses [5]. Unlicensed systems and devices are widely known as Part 15 devices because they operate according to Part 15 of the FCCs rules. Some of the services that operate under Part 15 include automated utility readers, wireless LANs, cordless phones, wireless audio speakers, home security systems, and medical monitoring devices . The FCC Part 15 rule has been a catalyst for innovative wireless applications and has stimulated the development of many new forms of low-cost spread spectrum radios. Perhaps the best protection for spread spectrum radios is their inherent robustness against interference and large multipath delays. The FCC Part 15 rule has been adopted in part or completely by many other countries. Generally, North, Central, and South American countries have adopted this same rules. Most countries worldwide allow some form of unlicensed spread spectrum radios for commercial applications [6]. Part 15 is under revision by the FCC. On February 5,1996, the FCC released ET Docket No. 96-8 (also known as FCC 96-36). Information is available from http://www.sss-mag.com/fcc1.html.

Wireless LANs Wireless LANs closely approximate amateur packet radio. It is perhaps this technique that amateurs will have the most interest. Wireless LANs operate in the 900 MHz, 2.4 GHz, and 5.7GHz bands. They offer speeds up to 5.3 Mbps, although actual throughput is usually 1 to 2 Mbps. They use either direct sequence or frequency-hopping, spread spectrum transmission techniques. A number of wireless LAN products operate in the unlicensed bands, and the IEEE is currently developing industry standards for LANs as well as standards that will allow users' computers to communicate with each other directly "ad hoc" or "peer-to-peer" networking. Development of products for the 2.4 GHz band has reportedly accelerated in anticipation of the IEEE standard for wireless LANs, the increasing congestion of the 902 to 928 MHz band, and the greater amount of bandwidth available compared to the 900 MHz band.

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Introductoryllnformative

Conclusion The history of spread spectrum dates back to the 1920s when scientist and engineers began using noise techniques to enhance ranging and resolution. Spread spectrum then became the natural engineering result of trying to solve the problem of reliable communications in an intentional jamming environment. Cloaked in secrecy until the late 1970s, spread spectrum came into the commercial realm in the 1980s. Amateurs began experimenting in 1981and Part 97 of the rules permitted spread spectrum emissions for the amateur service in 1985. The FCC also created Part 15 in 1985 to encourage development of new services for commercial uses. Part 15 devices today account for many of spread spectrums uses. For further reading on the fascinating subject of the origins of spread spectrum communications, readers should consult reference [1]. For the history of amateur spread spectrum, The ARRL Spread Spectrum Sourcebook is a good guide.

References [1] R. A. Scholtz, "The Origins of Spread-Spectrum Communications," IEEETrans. Commun., COM-30, pp. 822-854,May 1982. [2] J. P. Costas, "Poission, Shannon, and the Radio Amateur," Proc. IRE, vol. 47, no . 12, pp. 2058-2068,Dec. 1959. [3]W. C. Scales, "Potential Use of Spread Spectrum Techniques in Non-Government Applications," MTR-80W335, The MITRE Corporation, McLean, Virginia, Dec. 1980. [4] G. R. Cooper and R. W. Nettleton, "A Spread Spectrum Technique for High-Capacity Mobile Communications," IEEE Trans. Vehicular Technology, Vol. VT-27,No.4, November 1978. [5]U.S. Congress, Office of Technology Assessment, Wireless Technologies and the National Information Infrastructure, OTA-ITC-622 (Washington, DC: U.S. Government Printing Office, July 1995). [6] M. K. Simon, et al, Spread Spectrum Communications Handbook, McGraw-Hill, New York, 1994.

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Spread Sp~trum and the Amateur Radio Servi~e • R~ent Developments by: Dewayne Hendricks WA8DZP reprinted from TAPR PSR #60, October 1995.

Backin 1989,AIBroscius,N3FCT,[1]discussed the use of commercially available Part 15SSdevices that were becoming available in the market, for use in the amateur radio service (ARS) for packet radio operations. He identified several commercial systems that were then available and made the following recommendation: "To responsibly address this technology, we feel amateur operators should experiment with the commercial systems now available in establishing long distance communication paths using high-gain antenna systems coupled with the maximum legal power of one watt, determining interference levels seen by weak signal receivers attributable to spread spectrum transmissions, and carefully introducing this technology to computer bulletin board operators who could financially support development of an unlicensed computer Internet." Tothe author's knowledge, to date very little effort has been made by the amateur radio community to pursue this recommendation. For instance, although there have been reports by various hams of their experiences with such devices on various USENET newsgroups over the last several years, there has been no written report of such experiences in ARS publications such as QEX, PSR or DCC proceedings. So while there are now millions of SS devices out in the world today in the hands of the average consumer, SS remains an unrealized technology in the world of amateur radio.

Commerc:ial 55 Ac:tivities Since the Broscius article in 1989,there has been a lot of activity in the commercial sector regarding SS. As a result of the request and feedback of many manufacturer's of Part 15 devices, the FCC changed the rules in 1990in order to make it possible to product devices under Part 15 which could operate at higher data rates and to close up some of the holes in the previous version of the regulation that had been issued in 1985. In January, 1991,Apple Computer filed the now famous Data-PCS petition with the FCC which asked for the allocation of 40 MHz in the 1850-1990 MHz band for a new radio service to be used for high-speed, local area network services. Some important points of the petition include: • be accessibleto users of personal computers without imposition of licensing obligations, network connection fees, or air-time charges; • be open to any computer manufacturer's products and any network access and usage scheme that complies with the regulatory requirements.

20

Introductory/lnformative

• •

be regulated in a manner that assures non-discriminatory access to assigned frequencies by compatible devices for like purposed; and have flexibility built into the initial regulatory scheme to encourage innovation in and the evolution of Data-PCS technologies and services.

In 1993, the FCC allocated 20 MHz for this new service, in the 1910-1930 MHz band. In addition, ten additional MHz were allocated this year by the FCC for this service in the 2390-2400 MHz band. Lest you forget, this ten MHz of spectrum is part of the current ARS allocation which runs from 2390-2450 MHz. The ARS was made primary in this band by the FCC and the Data-PCS service now shares this band with the ARS on a secondary non-interference basis. Finally, Apple Computer this May '95 petitioned the FCC for yet another new service called the NIl Band (National Information Infrastructure). In this case, they are asking the FCC to: •

allocate for use as part of the NIl Band the 5150-5300 MHz band, a shared private-government band that currently is not heavily used within the United States and has been allocated throughout most of Europe for unlicensed wireless local area networks;



allocate for use as part of the NIl Band the 5725-5875 MHz band, a shared private-government band that currently is used by unlicensed Part 15 technologies, industrial, scientific and medical ("ISM") devices, and Amateur radio operators;

This comes to a total of 300 MHz!! Again, lest you forget to notice, about 150 MHz of this is coming out of the ARS allocation at 5.7 GHz. Apple describes the essential characteristics of this new service as follows: "The NIl Band will be fundamentally different from any other wired, licensed-wireless, or unlicensed service. Unlike licensed-wireless services, no single entity will have an exclusive license to provide service using the spectrum. Unlike both licensed-wireless and wired services, availability will not be determined by a service providers deployment plan or the economics of a fee-for-service offering. Unlike traditional Part 15 operation, NIl Band devices will not have to contend with unpredictable and uncontrollable interference, a host of different devices employing a variety of modulation schemes and power levels, and the continuing threat of giving way to incompatible services. Unlike Data-PCS offerings, the NIl Band will support very high-bandwidth transmissions and communications over longer distances. Unlike the proposed unlicensed bands above 40 GHz, the NIl Band will support certain in-building and longer-distance communications that are not feasible using very high frequencies and will be amenable to more rapid product deployment.

21

The NIl Band would promote the full deployment of a National Information Infrastructure ("NIl"), extending the effective reach of the NIl by making possible high-bandwidth access and interaction throughout a limited geographic area - where mobility is key - both on a peer-to-peer, ad hoc basis and through wireless local area networks. Moreover, it would provide for unlicensed, wireless, wide area "community networks" connecting communities, schools, and other groups under served by existing and proposed telecommunications offerings. The NIl Band would advance a host of public policy objectives, including assuring that all segments of society have accessto the "information superhighway;" extending advanced telecommunications offerings to schools, libraries, hospitals, and government agencies; and promoting the participation of small businesses, businesses owned by women or minorities, and pioneering firms in tomorrow's telecommunications marketplace." As you can see this is a very ambitious proposal. If it makes it thru the rulemaking process at the FCC, then in the near future the average consumer will have in their hands communications facilities which will make the current technologies and practices of the ARS look like something from the age of 'spark gap' transmitters. To date, it is estimated that there are about 60 million Part 15 devices out in the world. Of these, about eight million are SS devices. One can expect to see lots of exciting wireless products announced and SS technologies will be a major part of many of these new offerings .

Amateur Radio 55 Activities Little has changed in the amateur radio service as far as high-speed SS packet radio is concerned in the period since 1989. Most of the commercial SSequipment available today on the market cannot be operated under the current Part 97 rules . One event of note however, was the publishing by the ARRL of the "Spread Spectrum Sourcebook" [2]. This was an excellent attempt by the League to acquaint the average ham with the technology of spread spectrum. Another excellent reference on packet radio technology and the use of SS appears in [3]. About the time of Apple's Data-PCS petition, Robert Buaas, K6KGS, submitted a request for an STA (Special Temporary Authorization) to amend Part 97 to allow relaxed usage of SStechnology in the ARS. Buaas' request was granted by the FCC in 1992and he was awarded an STAthat had been renewed several times and remains in effect as of today. There is a recent QEX article which covers the STA and 55 technology [4]. An earlier QEXarticle which describes the STAappears in [5].

22

Introductoryllnfo rma tive

Since the original STA was granted, Buaas and the other hams who are authorized to experiment under the STA have perf ormed many experim en ts using SS technology both with existing Part 15 SS devices and homebrew hardware that was developed for the purpose of the experiments. This work formed the basis for theARRL Board of Director's to pass a motion in January, 1994to have their counsel submit to the FCC a petition for rul emaking to modify the SS rules in Part 97. Nothing was filed with the Commission in 1994, however the League's Board reaffirmed its decision this year at their January meeting. At this time, the author can report that both the League and TAPR will be submitting petitions for rulemaking to the FCC to change the SS rules. This filing will be the joint effort of both organizations during the past year to come up with a set of rule changes which will allow the amateur community to make the most effective use of SS technology in the ARS. Future issues of PSR w ill provide more information on the petitions and how they are moving thru the formal rulemaking process. In addition, in the coming year TAPR will be launching an initiative to better acquaint the average ham with this technology and make it possible for them to experiment with it thru the availability of new hardware. To sum up, the ARS has a lot of catching up to do with the commercial sector in this area. SS technology is not ma gic and is by no means the solution to all of the world's problems. However, it can make possible some new avenues for the deployment and availability of high-speed packet radio systems to the amateur radio community in the future.

References [1] Broscius, A. "License-Free Spread Spectrum Packet Radio," 8th ARRL Computer Networking Conference Proceedings, p .16 [1989] [2] American radio Relay League "Spread Spectrum Sourcebook," ARRL, [1991] [3] Lynch, c.x. and Brownrigg, E.B. "Packet Radio Networks -Architectures, Protocols, technologies and Applications," Pergamon Press [1987] [4] Price, H. "Digital Communications", QEX, p. 22 June, [1995] [5] Rinaldo, P. "CDMA Spread Spectrum STA", QEX, p. 2 June, [1992]

23

The Trip So Far in High Speed Digital Communication Via Spread Spredrum John Hansen, W2FS ([email protected]) Director,Academic Information Technology, State University ofNew York- Fredonia Reprinted/rom TAPR PSR #61, January 1996.

"Any sufficiently advanced technology is indistinguishable from magic." - Clarke's Third Law. I've been following developments in high speed data transmission via spread spectrum radio devices for a number of years. However, since I was intially interested in it as a hobbyist and since the prices were considerably more than my toy budget, about all I did was read and wonder. A couple of things happened in the last year to change this dramatically. First I became Director of Academic Information Technology at a local college, which put me in charge of bringing connectivity to campus. This also provided me with a significant budget allegedly for connectivity, but also, to more limited extent for research and development. Secondly, I attended this year's Networld-Interop in Atlanta. There I ran into a company called BreezeCom (formerly Lannair) which seemed to be selling 2.4 Ghz spread sprectrum devices that could push 3 mbits/sec over distances (they claimed) of over 3500feet. They were actually demonstrating this equipment and it did appear to work. There were a number of places on campus where I thought this technology had potential, thoug h I wasn't exactly sure where it would go in first. So I figured the next step was to acquire some of it and cart around campus to see how it would perform over various paths. The BreezeCom product is not designed to be a bridge. A number of companies have prod ucts out like this. The theory is you put up an "access point" that is hooked directly into the ethemet network and then you buy a "station adapter" for each of the computers that you want to have access the system. A campus could have multiple access points and users could cruise between them, essentially the way cellular telephones do . What you are not supposed to be able to do with this type of technology is provide Ian to Ian links. A number of manufacturers I talked to, in fact, insisted it was impossible to hook a hub up to the station unit and have it w ork. This is a key point, because while I have some uses that will clearly involve the single unit access paradigm, I also have some pressing needs for point to point, Ian to Ian links. On our campus, this would often involve very low data rates. An example would be a group of 30 computers set up in one room to submit registration information for students. Veryvery little data is involved, but I would not want to buy a "station unit" for each of the 30 computers. The cheapest vendor of equipment that is designed as a "wireless bridge" that I could find would cost close to $5000 for one link. While this would be cheaper than buying a "station unit" for each of the computers, it still was more than I really wanted to pay.

24

Introductoryllnformatlve

I got to talking with the President of BreezeCom about this and he said they were aboutto come out with firmware that would allow bridging, but that it wasn't available yet. He offered to let me beta test it. In the meantime, I asked if the bridging function was all that was required, wouldn't it be possible to use and outboard bridge or perhaps even a Windows NT box that had routing functions built in. He paused for a moment and allowed that it might work. That was enough for me to want to try it. Access units from BreezeCom come in two flavors but the price is the same in either case. The AP-10 is a unit with two integrated antennas in the transmitter that look a bit like rubber duck antennas. These are designed for distribution of ethernet within buildings. The second flavor is the AP-10D. It has no antennas, but comes with a pair of SMA connectors on it for installing external antennas. The company makes several external antennas. The simplest is a patch antenna in a plastic case somewhat larger than a pack of cigarrettes. The company initially recommended hooking up two of these to the AP-10D.Only one of the two antennas is actually used at a time and the unit samples to see which provides the best connection. In practice, I have found virtually no difference in performance between using one and two antennas. Thus I would recommend using one. This is now the company's recommendation as well, unless you are in a place with lots of buildings and multipath problems. The patch antenna claims to have an h-plane beamwidth of 165 degrees and a gain of 8.5dBi. It is clearly directional, but I have no means of verifying this claim. My experimentation leads me to think it may be somewhat narrower. The company also makes an omni antenna that has (if I remember correctly), a gain of about 6 dBi). If you are contemplating putting the antenna in a high location (We have a building in the center of campus that is 9 stories tall... the next tallest building is 3 stories), there is a potential problem with the omni because it does not radiate down (or up) well. The retail list price of the AP-lO or 10D is $1295, and the retail on the patch antenna and feedline (it comes with about 8 feet of cable) is $125. I asked about educational discounts (as I always do) and was told to check with their distributors. At that time, they had very few distributors and BreezeCom agreed to sell to me for 10% off list. The station units come in three flavors. First, there is a 1 port adapter (SA-10 and SA-lOD,depending on whether it has integrated antennas or SMA connectors). This unit has one RJ-45 twisted pair connector. Second, there is a four port adapter (SA-40 and SA-40D) which has 4 RJ-45 twisted pair connectors. There is also a very interesting PCMCIA card for laptops. This is a really cute device that sticks out of a PCMCIA slot only about 1/2 inch and lets you cruise while being connected. The antenna is embedded in the card, and its range is rather limited (something like 300-400 feet) and its top data rate is 1 mbit/sec. Noneless, if one had an appropriate application it would be truly cool. It took a long time (like 21/2 months) for me to actually get my hands on this equipment. Part of this is due to the fact that it is all imported from Israel (and this was about the time of the asassination there, though I have no idea whether this disrupted business enterprises or not) but part of it appears to be related to FCC approval. This is only my guesswork here based on indirect statements I've gotten

25

from BreezeCom. It appears, however, that the FCC isn't keen on the SMAconnector approach. I have heard from a number of manufacturers that the FCC is requiring "proprietary" connectors on this type of unit so people won't buy them and hook up BigKahuna antennas and violate the law. As I understand it (my reference here is Steve Bible's excellent article ... see www.tapr.org) you can run 4 watts erp from one of these stations without violating the law. Since the BreezeCom unit has a power output of 50 milliwatts, you could legally get away with something around 19-20dBi gain in the antenna system without violating the law. However, even a modest sized dish can generate more gain than this. BreezeCom is trying a number of approachs to pacify the FCC.. apparently one being to require a "professional" antenna installer, whatever that means. Anyway, right now it is possible to get "sample units" but larger quantities are unlikely to be available until this gets worked out with the feds. My equipment showed up just after Christmas (how nice!). We got it up and running very quickly. There is a serial port on each of the units and you connect it to your PC running a terminal program to manage it. Start by putting an IP address in it, beyond that there is little to manage, at least initially. We first set up both units in the same room, but then moved them progressively further and further apart. Finally, we mounted the access point on the 9th floor of the tallest building on campus and taped the antennas to the inside of the window with McGuiver Tape. Further experimentation leads me to believe this system will perform better if we can get the antenna outside (it is really designed to be mounted on the exterior of a building. We carted the station unit around campus with my laptop (which has an ethernet card in it) to test various paths. This was interesting because the unit runs off a 5 volt cube tap . If we had had a good sized 5 volt battery we could have literally gone anywhere and had a truly portable internet browser. Testing from several locations on campus led me to conclude that we simply would not be able to find a clear path on campus that was far enough to really tax the capabilities of the unit. So the next step was to move off campus. Fortunately my house is located on a street that is adjacent to campus on the same side of the 9 story building that we put the antenna (gee, what a coincidence). It is close to a half mile away from the access point. We took the equipment to my kitchen and taped the antenna to my glass patio door. There are pine trees in my back yard that block the line of site path to the access point, but it worked anyway. A note or two on signal strength and speed is probably in order. There are six lights on the station adapter. One is for power. One lights up when you have a link to an access point. One flickers as data moves over the link. The other three show you the speed at which data is moving. One of the nice things about BreezeCom's units is that if the path is not good enough to support 3 mbit/sec it will ratchet down to 2 mbit/sec. If that's no good it will go to 1 mbit /sec and if that doesn't work it will fall back to .5 mbit/sec. If all three lights are lit you have 3 mbit/sec. Two lights and one light represent 2 and 1 mbit/sec respectively. If the link light is on and there is one signal strength light flashing, that means you are at .5 mbit/ sec. With the setup described above, I get 1 light solidly on and a second one flashing .

26

Introductory/Informative

BreezeCom advised me that if I went in through the serial link and locked the speed at 1 mbit/ sec under these circumstances, throughput would actually go up, since it would no longer be switching back and forth between one and two mbit/sec. In fact when I did this throughput rose by about 20 percent. Over this path I can pass a 1 MByte filein under 9 seconds. When I take the antennas outside (just beyond the glass door) I get 2 lights. I took them to my attic, and after I peeled back the metal backing on the insulation, I got one light even though there was about 8 inches of snow on the roof. We've had some pretty serious snowstorms during this testing period (on occasion I can't even see the building that has the access point on it) and I've not seen any degredation in throughput as a result. 50 we come to the bridging issue. I bought a small hub and hooked two computers to it and ran the uplink port to the transciever. It performed flawlessly even when I downloaded large files on both computers at the same time. Clearly the only barrier to Ian to Ian connections with this is that the unit will choke on too much data. I wouldn't want to try this on a Ian with an application server running, certainly. BTW, the unit contains 8 megsof memory for buffering.

Frankly, the results astound me (hence the Clarke quote). I sit at home and treat my officemachine hard drive as if it were just any other network asset. The campus link to the Internet is a T-1 connection (my first act as Director of Academic Information Technology was to upgrade this) and I cruise the net at a very respectable speed on this system from my home. When I used to dial up with a 28.8 modem and download a file, Netscape would report in the vicinity of 2.8 K/ sec. Now I see numbers like 35k/sec. The bottleneck is clearly no longer between me and campus. Are we having fun yet? Well, 8.5 dBi gain on 50 milliwatts is considerably below the legal limit. 50 the next step was to look into higher gain antennas. I called BreezeCom about it and they said they were coming out with a parabolic antenna shortly for just this purpose. One of their employees said they tested this successfully at a range of 20 miles . The president of the company later claimed 5-6 miles. They offer a 2 by 3 foot dish that has about 23 dBi gain for $395list. They put 30 feet of RG-8 coax on it to bring the gain down to the legal limit. However, I am aware of other sources of antennas. The company that was formerly DownEast Microwave sells loop yagis and claims they have actually sold some for precisely this purpose. They make a 1 foot yagi with 11dB gain for about $50, a 3 foot yagi with 17 dB gain for $85 and a 6 foot loop yagi with 20 db gain (I don't have the price handy). These might be good choices for use with this system. However, I also knew that Bob Myers Communications was marketing an 5 band 2 by 3 foot parabolic antenna that sounds extremely similar to the BreezeCom unit (except I believe BreezeCom said their's was Magnesium). Advertised mostly as an Oscar 13 mode 5 downlinke antenna, Bob says the gain of his unit is 25 dB and the price is only about $75 including shipping ...so I ordered one. At that point I'll push the envelope and see how far we can get.

27

Please understand that I am in no way affiliated with either of these companies and I don't know them well enough to personally vouch for their solvency or integrity. My initial impression is quite favorable, but please understand that it is my initial impression based on a relatively short relationship thus far. All of this has led me to think considerably more broadly about the applications for this technology both as a pure part 15 device (I've contemplated selling really high speed internet access to local companies and individuals, for example) and as in the amatuer radio service.

Postscript: Two and a Hall Years and Counting by John Hansen, W2FS (june, 1998) The link described in the above article has been providing me with reliable internet access now for over two and a half years . There have been no equipment failures, despite the fact that we moved the access point outside to the roof of the campus' 9 story building. I installed the Bob Myers dish in my attic and now obtain solid access even when there is a foot or two of snow on the roof. Heavy rain storms attenuate the signal somewhat, but never enough to prevent a solid connection. We took the Myers dish to a location 5 miles out of town and found we could access the network at that distance with a line of sight path. Time has not permitted further experiments to test the limits of the range of these units. We discovered that you cannot simply plug an access point into an NT box and put an entire subnet on the network. This is because the access point reads the MAC address of the unit hooked up to it and only allows packets from that MAC address to pass. There are several possible ways around this. First, BreezeCom has come out with a bridge product that has space for 255MAC addresses. Thus if you use their bridge, you can hook up a subnetwork of up to 255 units. This device costs about $2000. Secondly it is has been suggested to me that if you hook a Linux box up to the access point and configure the Linux box to do IF masquerading, this should work. I suspect that it will, since the BreezeCom unit would only actually see the MAC address of the Linux box, but since we went ahead and purchased the BreezeCom bridge, we have not had a need to actually try this. I remain as amazed by this technology as the day I put it up. Perhaps the biggest advantage of this approach is not the speed itself, but the convenience. I never have to dial up an internet provider.... any computer in my house that's on, is always on the net.

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Introductoryllnformatlve

W"'Jre1ess In VIaan Bataar· Learning Fro.l. A True-ure Mongolian Network Adventure By :Dewayne Hendricks, WA8DZP (dewayne®warpspeed.com) Reprin ted from 16th ARRL and TAPR Digital Communications Conference, Baltimore, Maryland, October 1997

In Ulaan Baatar, Mongolia, severe weather conditions prevail, the wired telecommunications infrastructure is very poor, advanced telecommunications technology expertise is limited (although there is considerable local computer expertise), and US access to Mongolian scientific and research facilities is highly constrained by lack of normal Internet connections. Last year, some of us went to Mongolia to integrate a series of data radios into a wireless network, and then field-test them. Our purpose was to build on and apply knowledge being gained from the "WirelessField Test(WFT) Projectfor Education," funded by the National Science Foundation (NSF) and run by Dave Hughes of Old Colorado City Communications, in Colorado Springs, CO.

The Problem The expedition's mission was an attempt to remedy the lack of a suitable wired telecommunications infrastructure in Mongolia, including across its capital city-a problem typical of thousands of cities in underdeveloped countries. "Suitable," in this case, means public or private circuits capable of carrying data with the reliability and bandwidths necessary for scientific research between institutions, increasingly equipped with advanced in-house computer and even local area networks. As a result of this deficiency, the primary institutions in Mongolia, such as the Mongolian Technical University, the MongolianAcademy of Sciencesand the many other educational facilities which reside in the capital city are inaccessible (via data link) to US scientific institutions, researchers and students. What exists is a poor and obsolete government postal, telephone, and telegraph voice-telephone system, a holdover from when the Soviet Union controlled Mongolia. Efforts to use even late model error-correcting phone datamodems to link the computers in the various institutions is only partially successful, since the non-digital circuits are so old. It is difficult to maintain even a 14.4Kbps connection without the line dropping many times in an hour. As a result of the first step to provide Internet access to Mongolia, NSF funded the establishment of a costly ($72K/yr) satellite Internet link. This 128K link, provided by Sprintlink, only reached one set of computers in a single building, in the central part of the city, by direct wiring. The PIT has neither the resources nor the expertise to provide even the lowest speed (56Kbps) wired circuits to connect the numerous other institutions. The "last mile" problem of connecting this satellite link to the institutions (actually about one to ten kilometers from the satellite ground station), which must then

29

distribute the signal to their own wired intranets, had so far defeated efforts to link it by local telephone facilities. In this respect, Mongolia is typical of scores of underdeveloped nations with a poor telephone infrastructure, too limited to adapt to modem requirements for institutional datalinks to and from other nations, especially the US. Wireless datalinks provide one possible general solution to this problem, not only in Mongolia, but in many other countries.

Challenges A number of challenges made this a difficult project, as well as one from which valuable lessons and techniques were learned for application elsewhere: •

The weather is more severe in Ulaan Baatar than in the areas in Southern Colorado where our wireless field-test project has been implemented. High winds and average temperatures from -15° to -25°C for entire winter months will subject the radios, connectors, shielding materials, and antennas to extremes of cold and wind.

The question was whether or not economical commercial-grade radios and systems could handle the weather and give similar MTBF (mean time between failure) times to those systems operating in milder climates . •

Whether the electromagnetic environment from the equipment that exists in Mongolia today, some from systems developed and deployed by the Soviet Union in the past, in a different technological regulatory environment, will affect the spread-spectrum dataradios that we intended to deploy, which were developed in the US and operate in environments controlled by FCC rules.



Could the wireless network be integrated into networks made up of a mish-mash of US and foreign computer and peripheral equipment, and would interoperability be a problem?



Given the level of in-country expertise able to help install and maintain the wireless network, could local personnel be trained sufficiently in a short period of time to handle the network in the future, with only the assistance of remote expertise to call upon for help?

Groundwork The Mongolian government had permitted a group of Russian-trained Mongolian engineers to form a private technology company, DataCom Co., Ltd, headed by Dr. Dangaasuren Enkhbat, using facilities at a technical center once occupied by Soviet engineers. The NSF had turned to this company-with limited liquid assets, but in a suitable central facility in the capital-to provide the critical organizational link between the satellite-based Internet feed and in-eountry institutions. In return for being

30

Introductoryllnformative

able to eventually provide Internet service to private companies in Mongolia, and being given control of the satellite groundstation, DataCom agreed to provide links to Mongolian public, scientific, educational, government, and library institutions for at least two years, at no cost. With initial funding from various sources, and with help from groups such as Sprint, PanAmSat, Comstream, NSF and the US ambassador to Mongolia at the time, Donald C. Johnson, DataCom became the first Internet Service Provider in Mongolia in December of 1995. (The top-level domain name for Mongolia is MN. DataCom maintains a Web site at http://www.magicnet.mn/). Once the project was approved by NSF, our first task was to determine what would be required for the expedition and what we'd have to do once we arrived in Ulaan Baatar to deploy the wireless network. We made use of maps, videos and communications with the staff of DataCom, in order to determine exactly what types of radios would work in their environment, and what configurations and physical distributions of sites would be required for distribution of Internet services from the DataCom location . The plan was to install a basic wireless Metropolitan Area Network that would consist of eight sites: the DataCom site, and seven sites selected by DataCom. These were all universities, with the exception of the US Embassy. Based upon our experience in the WFT project, we had made a preliminary decision to use unlicensed Part 15 dataradios developed and marketed in the US by a small Boulder, CO company called FreeWave Technologies, Inc. (http://www.freewave.com/). They make a spread-spectrum radio that can send data at 170Kbps over the air and interfaces to a computer via a serial data interface (RS-232) at 115.2Kbps. The radio operates in the 902-928MHz part of the spectrum, one of three bands utilized by Part 15 devices in the US.These radios put out 1 watt of power; using various antenna configurations we have been able to obtain/send data with them distances of up to 60 miles. (For more information on the use of these sorts of unlicensed spread-spectrum radios, check out our WFT project Web site at http://wireless.oldcolo.com/). We learned that the 902-928MHz band was not completely available for our use in Mongolia, since the commercial cellular telephone network there used GSM

technology which operated in a portion of the band from 902-915 MHz. In order to use the FreeWave radios in Mongolia, we had to make two things happen. We first got DataCom to obtain from the Mongolian government permission to operate the radios in the 915-928MHz part of the spectrum, avoiding the conflict with the GSM cellular network. We next got FreeWave to provide us with a special version of their radio which would operate in this smaller portion of the 902 MHz band. As it turns out, this was not difficult-they had already encountered the same problem when they first entered the Australian market, which uses GSM cellular in the same band. In order to connect each site's radio to the local LAN we determined that we needed a low-eost Internet router that could be installed and maintained at each location. For the WFT project, we had already developed such a router based upon

31

the widely available Linux operating system and a low-cost Pc. We decided to use this approach in Mongolia, as we already had a great deal of experience with this router and an attached FreeWave radio. Aside from Linux, all a PC needed to function as a special purpose IP router was a high-speed serial card that would support an interface speed of 115.2Kbps and enough RAM to allow Linux to function properly (in this case we used 16MB). Also important were the antennas and feedlines. It was clear that we needed an omni-directional antenna for the DataCom site, since it was the point-of-presence (POP) for all Internet services and each remote site would have to connect to it. For the remote sites, we would require a directional antenna that could focus all of the available energy from the radio on the POP. Although the distances involved in the Ulaan Baatar network would be a good deal less than we had been used to in the US (average about 20 miles), we decided to use the same high-gain omni and directional antennas that had used here rather then taking the time to find lower-gain alternatives-it's better to have more antenna gain than you need than to get there with less and find out that you need more. We also decided to use the same low-loss coax feedline (LMR-400) to connect the radio to the antenna that we had been using in the WFT project. Even with all the up-front analysis of each site's requirements, we still had no idea of the exact amount of feedline that we would require.As a result, we decided to take three times as much as we thought we'd need. Finally, there was the issue of electrical power. In Mongolia, they use 220 VAC; we had to obtain the necessary power adapters and connectors to insure that the radios and routers could all operate on local AC power. As is common practice with an expedition of this sort to a remote part of the world, we made sure that we had spares for all of the key equipment, especially routers and radios. When it came to just how we were going to get all of the equipment to Mongolia, the NSF intervened and made arrangements with the US ambassador in Mongolia that allowed us to ship everything via diplomatic channels (the famous" diplomatic pouch"). Thus we were able to avoid the normal problems encountered using commercial shipping firms and dealing with customs procedures. It turns out that spread-spectrum radios cannot be exported to countries such as Mongolia without a special export permit from the US government. Obtaining such a permit can take anywhere from three to six months. As we were trying to get the expedition completed before the harsh Mongolian winter started (December-March) we were fortunate in being able to bypass that requirement by shipping the radios the way that we did.

The downside in using the diplomatic channel for shipping is that once you put your shipment into the system, you only have a rough idea when it is going to arrive at its destination. Thus we had to use estimates on the time it took other

32

Introductoryllnformative

items to arrive in Mongolia as the basis for determining just when the expedition team itself should arrive. As it turned out, we were lucky in that most of the equipment arrived before we arrived in Mongolia, with the exception of a few pieces that arrived after we had been in-country about a week.

Installation A team consisting of Glenn Tenney, AA6ER (of Fantasia Systems, San Mateo) and myself left for Mongolia in October of last year. After we had arrived, made the initial visit to DataCom, and inventoried our equipment that had arrived (except for the few missing items), the first order of business was to survey all of the chosen sites in order to determine just what would be needed to deploy the equipment. We were shocked to find that DataCom was surrounded by high-rise buildings that effectively blocked line-of-sight to all of the sites where installations were to have taken place. One of the key factors in getting this type of low-power radio to work properly is to have a clear line-of-sight path to any location that you wish to contact.Without major obstructions, it is possible to establish communications over fairly long distances; with obstructions it is usually not possible to go more than a few hundred feet. Given what we saw from the DataCom site, it looked like it was time to wrap things up and get on the way back home. However, we decided to make the best of a bad situation, attempt to proceed anyway, and see just what could be accomplished. First, we installed the first radio and router at the DataCom site. In order to maximize the power output to the antenna from the radio, we mounted the radio on the roof of the building just a few feet from the antenna in a small equipment shed. This approach allowed us to use just a short coax feedline to the antenna and then a rather long serial-data cable to the router which was on the second floor of a four-story building. Since this location was the main hub for the wireless network, we used an omnidirectional antenna. We next set up a mobile radio so that it could be powered by batteries and carried about in a car with one of the directional antennas. We decided that we wanted to travel around town and see if it was possible to receive the signal at any distance from the POP location. To our surprise, we were able to get a good signal at most of the sites where we were to have installed a radio-all without having line-of-sight to the POP. After some analysis, we were able to determine that even though Ulaan Baatar is populated with a large number of high-rise buildings, the materials used in their construction are such that they appear to be effectively transparent at the frequency of the radio emissions that we were using. This windfall allowed us to proceed with installation at each site as planned. The most difficult part of the installation is the proper placement of the antenna and its connection to the radio. The major goal is to minimize the length of feedline used to connect the radio to the antenna-the basic rule being that the longer the feedline, the less power actually gets to the antenna, and hence the lower the signal quality at the remote location. This is where we spent most of our time during the next two and a half weeks. Each site had to be surveyed; then we had to work with the local people in charge of that site to convey to them what needed to be done and make sure that the proper permissions obtained to do the work.

33

At some sites, nothing major was required, as the antenna and the radio / router ended up being in the same room. In other sites, such as the US Embassy, the antenna had to be mounted on the roof and feedline run several floors to get to the radio and the router. Once the site preparation was complete, it was a very simple matter to install the radio and router. One major problem developed, once we were over the site preparation issues and got to testing the radios. We found the PCS we selected were unable to have their serial ports run at speeds over 19.2Kbpswithout data overruns; as soon as we tried to send data to the radios at any speed over 19.2Kbps, nothing worked. After a few days spent in investigating the cause of the problem, we discovered that even though the technical specifications of the PCS indicated that the on-board serial hardware could be run at speeds up to 115.2Kbps, this was not the case. DataCom has some new Pentium PCS that arrived while we were there, intended for a public Internet access center. When we installed Linux on those machines, configured it as a router, and set the serial interface to the 115.2Kbps speed, everything functioned properly. As luck would have it, we were able to contact someone coming over from the US to Mongolia. This person brought the necessary number of high-speed serial cards over; we were able to install them in the PCS that we had and get them to function properly at the higher datarate. As a result, we were finally able to leave Mongolia, after a slightly longer stay than we'd planned, with the wireless network installed and good connections to the seven remote sites. The network that we installed is still up and running today.The staff at DataCom has been able to maintain the network and even extend it with additional sites.

Lessons Learned Here is a summary of some of the key things we learned as a result of this effort: • A good site survey ahead of installation is the key to the installation's success. The specificsof a survey require people with a good deal of expertise in several areas. If you can't get those people to the site ahead of time to perform the survey, success can be in serious doubt in such remote locations as Mongolia. •

Always make sure that you test the equipment that you're using before you ship it to a remote location.Never believe the specifications for a product until you've tested it yourself!!!



Radio is still something like a black art (i.e., magic). There is always something new to be learned. Until we had gone to Mongolia and did this installation, we would have never believed that you could deploy such a wireless network in a dense urban area without having line-of-sight to all locations.



Low-cost spread-spectrum radio products that are being used in increasing numbers in the US to deliver access to the Internet can be successfully deployed in developing countries with limited expertise in both radio and Internet technologies.

In closing, we'd like to take this opportunity to acknowledge the help and assistance of Steve Goldstein of the NSF, without whose caring and wisdom this effort would not have been possible.

34

Introductoryllnformative

License -Free Spread Spectrum Packet Radio Albert G. Broscius, N3FCT Distributed Systems Lab, CIS Dept., University of Pennsylvania Reprinted from 8th Computer Networking Conference, Colorado Springs, CO, October 1989

Amateur experiments with spread spectrum techniques under an STA have provided a basis for FCC rule changes in 1986 allowing restricted forms of spread spectrum modulation on the amateur bands. Only frequency hopped (PH) and direct sequence (DS) spreading has been authorized, though, prohibiting hybrid spreading techniques which are often preferred in modern designs. The pseudo-noise (PN) code sequences available for DSare also restricted by the amateur rules to a set of three linear feedback shift register (LFSR) sequences. Further, transmitted power is restricted to one-hundred watts and a technical log of all spread spectrum activity must be kept. Unfortunately, work in this area has not yet yielded commercial or even kit-form amateur spread spectrum transceivers in spite of the fine engineering effort spent on this technique by several groups around the county. Deciding to bring industrial resources to bear on the technology transfer from the military to consumer electronics, the FCC added Part 15.126 of its Rules in June, 1985 in order to speed along the development efforts already authorized for several amateur groups under a 1981 STA. This new section of the low-power communications devices regulations mandates only the power distribution uniformity, the occupied bandwidth for DS transmitters, and the bandwidth and number of hopped channels for PH transmitters. The FCC's attitude toward this technology appears to foster commercial applications which are capable of taking advantages of "wasteland" properties used by Industrial, Scientific(ISM) equipment for non-communications purposes and by high EIRP radiolocation systems [4] without undue interference to amateur transmissions on these shared bands. The ability of spread spectrum systems to improve signal-to-noise ratio should enable communication transceivers to overcome the high floor resulting from RF sources operating on these bands. Narrowband interference sources such as amateur transmissions on these shared bands would also by combated by a properly designed spread spectrum system.

Commercial Systems The commercial system currently approved for operation under this Part have centered so far on data communications requirements although some wireless alarm type applications have been discussed. One system marketed by O'Neill Communications Inc. claims to have a channel transmission rate of 38.4Kbps and a radio-eomputer transmission rate of 9.6kbps [1]. It also claims to use AX.25 as it communication protocol between radio nodes. With a transmit power of 20 milliwatts, this system states an indoor range 100 feet and an outdoor range in

35

excess of 500 feet. For range extension, the manufacture suggests the use of up to two of the radio units in repeater operation. With an estimated cost of approximately $500 per node, this is one of the less expensive systems being marketed. The other data communication system now marketed is call ARLAN and is sold by a Canadian firm, Telesystems SLW of Ontario. There are two versions of the ARLAN: one supports asynchronous communication between terminal ports of standalone radio units, the other consists of an ruM PC-type circuit board with an antenna connection at the rear of the card. Shipped with a stub antenna, the card uses the 902-928MHz band to connect computers together using the Novell Netware protocols at 200Kbps and up to 1 watt of transmitted power. Interestingly, the company claims to have tested a pair of the ruM PC-type machines together with beam antennas successfully at a distance of six miles. The price on these units, however, is approximately $1500 per node which may be prohibitive for use by individuals.

ImpUcations for the Radio Amateur While it may be disheartening that commercial systems have become available before their amateur counterparts, it should be mentioned that these license-free systems may be used to augment or supplement our communications abilities even though they are not regulated under Part 97 of the Rules. It is also possible that a system which qualifies under 15.126 could be modified to be pursuant to Part 97 spread spectrum rules and thus allowed to operate at the higher power limit, one hundred watts, available for amateur spread spectrum as long as the control operator satisfied all appropriate requirements of the rules. And of course, placing a 15.126 unit on a Microsat-class vehicle [5] could pave the way for license-free space operation although there may be other restrictions which come into play in that situation. The design of a power-limited spread spectrum network with realistic inter-node distances would require substantial antenna engineering skills which could be provided by amateur operators familiar with propagation conditions on these bands. However, the resulting network would be free of Part 97 restrictions in the spirit of the pre-Commission Ham activities. Realistically, a Wild Westscenario of competing BBS networks and CB-style chaos could make this non-Ham world an unpleasant environment. Unfortunately, unless a pro-active position on this technology is taken, we may see a digital CB world forming around our shared allocations. Neglecting intentional interference to amateur transmissions and power-limit abuses, there is still the issue of a high noise floor on the weak signal portions of the shared bands. Although these bands now suffer from their shared status, some feel that an influx of consumer electronics items which may each transmit up to one watt will cause unacceptable degradation on the "quite regions" of the band plan. Considering the possible density to be tens of radiators per city block, the argument of RF pollution seems credible.

36

Introductory/Informative

Recommendations To responsibly address this technology, we feel amateur operators should experiment with the commercial systems now available in establishing long distance communications paths using high-gain antenna systems coupled with the maximum legal power of one watt, determining interference levels seen by weak signal receivers attributable to spread spectrum transmissions, and carefully introducing this technology to computer bulletin board operators who could financially support development of an unlicensed computer internet.

References 1. Information from "Computer Shopper," September 1989, pp. 448-450, relayed to the [email protected] Internet mailing list by N6PLO 2. "Spread Spectrum Communications," Vol 1, Simon, Omura, Sholtz, and Levitt, Computer Science Press, 1985. 3. "The ARRL 1985 Handbook for the Radio Amateur," Edited by Mark Wilson, ARRL, 1985. 4 . See "NOTE" in Appendix concerning high EIPR radiolocation; See Chapter 38 [3] concerning the ISM status of these bands. 5. "AMSAT's MicrosatJPacsat Program," Tom Clark , W3IWI, ARRL 7th Computer Networking Conference Proceedings, October 1988.

Appendix Refer to document: Code of Federal Regulations Title 47, Volume 1, Parts to 19 From the U.S. Government Printing Office via GPO Access CITE: 47CFR15 Page 610-676 TITLE 47-TELECOMMUNICATION CHAPTER I-FEDERAL COMMUNICATIONS COMMISSION PART 15-RADIO FREQUENCY DEVICES

°

http://www.access .gpo.gov/nara/cfr/cfr-table-search.html

37

The Markey/ Antheil Spread Spectrum Patent [Beaum ont, C. (1997) . Secret Communi cations Devic e: The Markey-Antheil spread spectrum pat ent [ 1 web page]. Available Web: http://www.ncaje.com/chris/patent/index.html]

Many years ago, on the eve of World War II, a well-known actress of the day and a avant-garde American composer, while at a dinner party, thought up an interesting scheme to control armed torpedoes over long distances without the enemy detecting them or jamming their transmissions. While they had the foresight to patent their invention, the term of the patent lapsed without either of them realizing any money from their invention, which formed the basis of what was to become spread-spectrum communications. This invention becomes even more incredible when you consider that it came before the invention of digital electronics..however, it makes very substantial use of digital concepts. Yes, indeed the term "ahead of its time" would apply here, because over 60 years later, as high-speed microprocessors become inexpensive, spread-spectrum communications, Hedy 'Lamarr ' and my father, George Antheil's "secret communications technique" - adapted to use today's ultrafast microprocessors is coming into its own as an effective and inexpensive way to communicate over long distances, privately and efficiently. In fact, the same characteristics that made their technique jam-proof, also, through a mathematical phenomenon which can easily be documented, creates an extraordinary efficiencyof transmission such that extremely low-power transmitters can be used over extraordinary distances, and most significantly,many transmitters and receivers can occup y the same band of frequencies at the same time . This extraordinary efficiency has the potential, indeed, it is already enabling inexpensive wireless access to high-bandwidth Tep-IP telecommunications, frequently radically altering the economics of setting up Intemet-eonnected LANs for community organizations. Hedy Lamarr and George Antheil's invention of spread-spectrum has recently received the EFF Pioneer award. The complete patent is available at: http://www.ncafe.com/chris/patent/patentl.htrnl

.

38

Introductory/lnformative

George Antheil

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After this initial procedure the power and pre-amplifiers can be added for free-space checks (provided radio regulations permit). Some minor adjustments particularly of the VCXO frequency may be required to ensure reliable acquisition and locking. If the VCXO frequency offset is too great then the receiver will initially acquire the signal, but will be unable to track it. A degree of trial and error may be necessary to arrive at a receiver clock offset which provides rapid synchronisation and reliab le tracking performance. The prototype took less than two seconds from power-up to synchronise and would remain in lock provided the signal was not lost. The Radiocommmunications Agency (the UK radio regulatory authority) granted special authority to the author to experiment with spread spectrum techniques on the 70 em band under his amateur radio service licence. At present the UK amateur radio licence does not permit the use of spread spectrum modulation. It is hoped that in the future the standard UK licence w ill permit spread spectrum modes of operation as is allowed in the USAby the Federal Communications Commission. The design and circuitry in this article is held in copyright by Jam es A. Vincent, 1993.

136

TechnicaVTheory

TUF1, RK3 and MAR series devices are manufactured by Mini-Circuits (from Cirkit in the UK and Dale Electronics, Camberley) FX609J from Consumer Microcircuits, Witham, Essex, England. Crystals are available from IQD Ltd, Crewkeme, Somerset, England. RFFM2 DBM comes from Walmore Electronics, London, England.

References 1. Convert NRZ to Biphase. John T. McGaughey. Electronic Design April 12 1990 2. HighPerformance 70cm Pre-Amp. Timothy Edwards. Radio and ElectronicsWorld March

1982 3. Appendix 4 - Multiplication ofDirect Sequence Signals. Spread Spectrum Systems Second Edition Robert C. Dixon. Wiley Interscience. 4. Communication in the Presence of Noise. C.E. Shannon. Proc.IRE, vol.37, No1,(pplO-21) Jan 1949. 5. The Synchronous Oscillator: A Synchronisation and Tracking Network. Vasil Uzunoglu & MarvinH. White. IEEE Joumal of Solid-StateCircuits. Vol. SC-20, No.6December 1985. 6. Synchronous and the Coherent Phase-Locked Synchronous Oscillators: New Techniques in Synchronisation andTracking. VasilUzunoglu & Marvin H. White. IEEE Transactions on Circuits and Systems. Vol.36, No7, July 1989. 7. A Practical Direct-Sequence Spread Spectrum UHF Link. Andre Kesteloot, N4ICK. QST magazine. [ Re-printed in the ARRLSpread Spectrum Handbook (pp 8-47- 8-54)The American Radio Relay League. ]. 8. United States Patents: 4 335404,4 274 067 and 4 356456.

Bibliography Spread Spectrum Systems Second Edition. Robert C Dixon, Wiley Interscience, ISBN 0-471-88309-3.

The ARRL Spread Spectrum Sourcebook. Editors Andre, Kesteloot N4ICK and Charles Hutchinson K8CH. The American Radio Relay League. ISBN 0-87259-317-7. Spread Spectrum Communications Volume 1, 2 and 3. Marvin K Simon, Jim K Omura, Robert A Scholtz and Barry K Levitt. Computer Science Press. ISBN 0-88175-017-7 (Set).

Coherent Spread Spectrum Systems. Jack K Holmes. Wiley Interscience. ISBN 0-471-03301-4.

Digital Communication btJ Satellite. James J. Spilker Jr. Prentice-Hall. ISBN 0-13-214155-8.

137

Detection and Estimation of Covert DS/SS Signals using Higher Order Statistical Processing Mamdouh Gouda +, Ernest R Adams,& Peter C J Hill Reprinted from 16th ARRL and TAPR Digital Communications Conference, Baltimore, Maryland, October 1997 (http://www.tapwrg/ss)

Conventional linear and non-linear receivers are generally ineffectivein detecting direct-sequence spread spectrum (DS/SS) signals if the spreading sequences are unavailable. An investigation into using correlation-based processing is reported showing that the cyclostationary property of DSISS provides detection capability. Finally we describe with results an emerging technique based on higher-order statistics where triple correlation analysis is used, leading to the detection and estimation of DS/SS length and its code generating function g(X).

Introduction Modem civil and military electronic communication systems are becoming ever smarter, more complex and in some cases also very difficult to intercept because the nature of the design leads to a covert signal structure. In fact some transmitted waveforms are intentionally designed to make the detection process virtually impossible. Such low-probabilities-of-intercept (LPI) signals have very wideband extremely low power spectral density signatures based on a hidden code structure; moreover they can operate in a complex radio environment of high noise, interference, jamming and other co-channel signals. A particularly difficult threat signal to intercept is direct-sequence spread spectrum (DS/SS) and in this case the problem is exacerbated when such systems operate in multiple access mode using code division multiple access (CDMA). Moreover, if the pseudo-noise spreading codes are very long and the intercept window is short including an unknown number of aperiodic data modulations then standard signal processing methods based on second order statistics are severely limited. State of the art techniques for communications signal detection which are based on second-order (i.e. variance) spectral processing are considerably limited by CEphase blindness, and the inability to easily separate out wanted signals from background noise[l]. Our study, however, is focused on higher-order statistical processing which specifically uses the cyc1ostationary signal property but is combined with the suppression of Gaussianity [2,3] in order to improve the SNR of the detection process. This was the key motivation for our attack on the problem of detecting DS/SS using correlation analysis and also spectral processing for detecting CDMA and chip-code characterisation respectively. The paper discusses the theory of triple correlation function analysis as applied to the detection of DS/SS PN chip code sequences in some detail and then describes the various

.

138

TechnicaVTheory

methods which have been investigated for estimating the basis code polynomials of DS/SS signals in the presence of channel noise. Attention is given to the importance of the doubling technique which improves SNR and reduces the dimensionality of tef characterization.

Higher-order moment signal processing techniques The proposed detector for covert DS/SS signals uses third order cumulants in the form of triple correlation analysis, bispectral processing and an associated characterisation process[4]. HOM/HOStechniques should be better able to exploit the non-gaussian cyclostationarity of the signal against the channel noise and interference. For example, the shift-and-add property of the m-sequences[S], i.e. uEElu p = u q. where EEl is binary addition of sequence elements, with an equivalent polynonual representation, g(X) + XPg(X)mod(XL + 1) = Xqg(X)mod(XL + 1), leads to the delta function response for the periodic autocorrelation function (ACF) C,)'t) = E[v('t)v(t+ 't)]and this ACF is no more than the second order cumulant in HOM terms. Higher-order cumulants simply extend the averaging process by considering additional time-shifted versions of the same m-sequence signal. In particular, the third-order cumulant or triple correlation is defined as

where t, = pTeand 't2 = qTefor Cxxx sampled at the chip rate liTe Hz. In practice, m-sequences use the values ± 1 rather than 0 and 1: (O,l)~(l,-l). The previously defined binary addition of sequences, EEl, is equivalent to multiplication, *, in this new domain.

Triple correlation of complete m-sequences The discrete version of Cxxx('t l , 't2) is evaluated as L

C(p,q)

=.l L

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i=l

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139 L

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In the original equation for C(p,q), v (i) = v(i+p) and v (i)=v(i+q), i.e. those sequences are advanced in time or shiftedto the left (LS). Thei-e is a corresponding delayed or right-shifted (RS) version of C. Substituting i+q=n and assuming L>q~p~O, v(i+q)=v(n), v(i+p)=v(n-(q-p)) and v(i)=v(n-q). Thus C(p,q) may be written in terms of RS versions of v: C(p,q)

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For each peak at (p,q) there is a corresponding peak at (L-q,L-(q-p));reflections are also peaks. E.g. as sequence a ,with generating polynomial g(X)=X5+X2+1,(L=31) has peak (p,q)=(1)8), it also has peak (13)4); (18)) and (14)3) are also peaks as shown in Fig 1. 30 r--.....~,..---!"'""""---,.

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.

140

TechnicaVTheory

Determination of g(X) from triple correlation peak locations The theory developed so far assumes the m-sequence length L is known. In particular, knowledge of L is necessary to evaluate the triple correlation C(p, q). However, there is evidence that sufficiently long partial m-sequences produce good estimation of peak locations. L may be derived from the peak locations (i, j), (2i, 2j), . . ., (2ki, r) for i < j Assuming the last pair is the first for which r < 21, r =21 mod(L), or L =2kj - r. As an example, the pairs (1, 18),(2,5) would produce L = 36 - 5 = 31. As peaks may be displaced, several such sequences should be examined.

If L is known, it is possible to determine g(X), and thus the tap weights of its LFSR, from a single triple correlation peak location. This follows from the fact that, for a given L, different primitive g(X) produce no common peaks. As an illustration, consider the m-sequences of length 31 generated by g(X) = Xs + X2 +1 (45 octal). If, for example,as shown in Fig 1, the peak location (1, 18) is known, the following peak locations may be predicted: (1, 18), (2, 5), (4, 10), (8, 20), (16, 9). From the one peak such as (2,5) we can derive g(X):

Thus a is a solution of g(X) = 0, where g(X) must be of ord er 5 and include 1:

Coset summing for better detection Although the effects of noise may be reduced by averaging the tcfs from several short signal samples, this process is computationally costly and assumes persisting m-sequences. Coset summing is an alternative or complementary technique which improves SNR and reduces the dimensionality of tcf characterization. It may lead either to powerful multivariate discrimination of fragments of known m-sequences or to the blind determination of an m-sequence from the detection of a single tcf peak.

141

Coset summing involves searching NxN partial tcfs for peaks by using the doubling property of peak locations. Each feasible tcf location is visited, beginning (p,q)=(1,2),(1,3),...,(2,3),(2,4),..., and the following sum of non-repeated tcf values calculated: S

= C(p,q) + C(2p mod L, 2q mod L) + ... + c (2'p mod L , 2'q mod L)

where p=2 r +1p mod Land q=2r +1q mod L. Each doubled location, (Z'p mod L, 2iq mod L) for 1$ i $ r, is excluded from the future search as its coset is represented by the initial location (p,q). Thus each coset present in the partial tcf is represented by a single peak, called the coset leader. Clearly,all the peaks of a coset will not generally be present in the partial tcf. When doubled locations lie outside the partial tcf (p',q'>N) no contribution is made to the sum but doubling is continued, and further values for locations within the partial window summed, until the original (p,q) results. Coset summing is illustrated in Fig 1, the tcf of a 31 length m-sequence [45]. Assuming only a 16x16partial window is available, the peak at (2,5) would be the first peak encountered in the search. The other coset peaks added would be at (4,10) and (16,9): doubling would generate the other coset members (8,20) & (1,18) lying outside the partial window. However, the peaks at (4,10) & (16,9) would be excluded from the search and their contributions included at (2,5), the coset leader. Clearly,in addition to reducing dimensionality, the use of coset sums of available tcf values will improve the detectability of actual peaks. Actual peaks of partial tcfs of m-sequences in noise have average values of 1 while the average non-peak values are -1/L. If the search begins with a non-peak location, other locations generated by doubling will also be non-peak. Thus all the coset sums will consist of exclusively peak values or exclusively non-peak values. These summed values may be tested against a threshold to decide whether they arise from a coset of actual peaks.

Conclusions Triple correlation analysis provides a powerful means of searching for and detecting the presence of covert wideband signals such as D5/55.The results show that the tcf is an excellent basis for detection and identification of m-sequences. The doubling process (coset sum)improves the detectability of actual triple correlation peak and reduce non-peak values. However higher-order statistical processing can extract more information than that conveyed by second-order power spectral density or autocorrelation function.

142

TechnicaVTheory

References 1. Stephens J.P., CEAdvances in signal processing technology for electronic warfare, Journal of Electronic Defense, September 1995. 2. Gardner W.A., CESignal interception: a unifying theoretical framework for feature detection" IEEE Trans on Comms, 36, 1988. 3. Nikias C. L. & Petropulu A. P., CEHigher-order spectra analysis - a nonlinear signal processing framework" PTR Prentice-Hall Inc., 1993. 4. E R Adams, M Gouda & P C J Hill, CEDetectionand characterisation of DSjSS signals using higher-order correlation" Proceedings of IEEE4th ISSSTA, Mainz, Germany,Sep 1996, pp27-31. 5. S.W.Golomb, Shift Register Sequences, Rev.Ed.(Aegean Park Press,1982).

Address for communication MrMGouda Communications Electro-optics & Signal Processing Group (CESPG) School of Engineering & Applied Science (SEAS) Cranfield University - RMCS Shrivenham, Swindon, Wilts SN6 8LA, England, UK Phone +44 (0)1793 785211 Fax +44 (0)1793 78366 E-mail [email protected]

143

VHF/UHF/Microwave Radio Propagation: A Primer for Digital Experimenters By : Barry McLarnon, VE3JF ([email protected]) Reprinted from 16th ARRL and TAPR Digital Communications Conference, Baltimore, Maryland, October 1997 (http://www.tapr.org/ss)

This paper attempts to provide some insight into the nature of radio propagation in that part of the spectrum (upper VHF to microwave) used by experimenters for high-speed digital transmission. It begins with the basics of free space path loss calculations, and then considers the effects of refraction, diffraction and reflections on the path loss of Line of Sight (LOS) links. The nature of non-LOS radio links is then examined, and propagation effects other than path loss which are important in digital transmission are also described.

Introduction The nature of packet radio is changing. As accessto the Internet becomes cheaper and faster, and the applications offered on the "net" more and more enticing, interest in the amateur packet radio network which grew up in the 1980s steadily wanes. To be sure, there are still pockets of interest in some places, particularly where some infrastructure to support speeds of 9600 bps or more has been built up, but this has not reversed the trend of declining interest and participation. Nevertheless, there is still lots of interest in packet radio out there - it is simply becoming re-focused in different areas. Some applications which do not require high speed, and can take advantage of the mobility that packet radio can provide, have found a secure niche -APRS is a good example. Interest is also high in high-speed wireless transmission which can match, or preferably exceed, landline modem rates . With a wireless link, you can have a 24-hour network connection without the need for a dedicated line, and you may also have the possibility of portable or mobile operation. Until recently, most people have considered it to be just too difficult to do highspeed digital. For example, the WA4DSY 56 Kbps RF modem has been available for ten years now, and yet only a few hundred people at most have put one on the air. With the new version of the modem introduced last year, 56 Kbps packet radio has edged closer to plug 'n play, but in the meantime, landline modem data rates have moved into the same territory. What has really sparked interest in high-speed packet radio lately is not the amateur packet equipment, but the boom in spread spectrum (SS) wireless LAN (WLAN) hardware which can be used without a licence in some of the ISM bands. The new WLAN units are typically integrated radio / modem/ computer interfaces which mimic either ethernet interfaces or landline modems, and are just as easy to set up. Many of them offer speeds which landline modem users can only dream of. TAPR and others are working on bringing this type of SStechnology into the amateur service, where it can be used on different bands, and without the Effective Radiated Power (ERP) restrictions which exist for the unlicenced service. This technology will be the

.

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ticket to developing high-speed wireless LANs and MANs which, using the Internet as a backbone, could finally realize the dream of a high-performance wide-area AMPRnet which can support the applications (WWW, audio and video conferencing, etc.) that get people excited about computer networking these days. Although the dream as stated above is somewhat controversial, the author believes it represents the best hope of attracting new people to the hobby, providing a basis for experimentation and training in state-of-the-art wireless techniques and networking, and, ultimately, retaining spectrum for the amateur radio service. One problem is that most of the people attracted to using digital wireless techniques have little or no background in RF. When it comes to setting up wireless links which will work over some distance, they tend to lack the necessary knowledge about antennas, transmission lines and, especially, the subtleties of radio propagation. This paper deals with the latter area, in the hopes of providing this new crop of digital experimenters with some tools to help them build wireless links which work. The main emphasis of this paper is on predicting the path loss of a link, so that one can approach the installation of the antennas and other RF equipment with some degree of confidence that the link will work. The focus is on acquiring a feel for radio propagation, and pointing the way towards recognizing the alternatives that may exist and the instances in which experimentation may be fruitful. We'll also look at some propagation aspects which are of particular relevance to digital signaling.

Estimating Path Loss The fundamental aim of a radio link is to deliver sufficient signal power to the receiver at the far end of the link to achieve some performance objective. For a data transmission system, this objective is usually specified as a minimum bit error rate (BER). In the receiver demodulator, the BER is a function of the signal to noise ratio (SNR). At the frequencies under consideration here, the noise power is often dominated by the internal receiver noise; however, this is not always the case, especially at the lower (VHF) end of the range. In addition, the "noise" may also include significant power from interfering signals, necessitating the delivery of higher signal power to the receiver than would be the case under more ideal circumstances (i.e., back-to-back through an attenuator). If the channel contains multipath, this may also have a major impact on the BER. We will consider multipath in more detail later - for now, we will focus on predicting the signal power which will be available to the receiver.

Free Space Propagation The benchmark by which we measure the loss in a transmission link is the loss that would be expected in free space - in other words, the loss that would occur in a region which is free of all objects that might absorb or reflect radio energy. This represents the ideal case which we hope to approach in our real world radio link

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(in fact, it is possible to have path loss which is less than the "free space" case, as we shall see later, but it is far more common to fall short of this goal). Calculating free space transmission loss is quite simple. Consider a transmitter with power P, coupled to an antenna which radiates equally in all directions (everyone's favorite mythical antenna, the isotropic antenna). At a distance d from the transmitter, the radiated power is distributed uniformly over an area of 4nd 2 (i.e. the surface area of a sphere of radius d), so that the power flux density is: p

s= --'- 2 4n d

(1)

The transmission loss then depends on how much of this power is captured by the receiving antenna. If the capture area, or effective apertureof this antenna is Ar' then the power which can be delivered to the receiver (assuming no mismatch or feedline losses) is simply

Pr =sA r

(2)

For the hypothetical isotropic receiving antenna, we have

(3)

Combining equations (1) and (3) into (2),we have

P, = p' (~ )2 4n d

(4)

The free space path loss between isotropic antennas is P, I P, Since we usually are dealing with frequency rather than wavelength, we can make the substitution A = clf (where c, of course, is the speed of light) to get

(5)

This shows the classic square-law dependence of signal level versus distance. What troubles some people when they see this equation is that the path loss also increases as the square of the frequency. Does this mean that the transmission medium is inherently more lossy at higher frequencies? While it is true that absorption of RF by various materials (buildings, trees, water vapor, etc.) tends to increase with frequency, remember we are talking about "free space" here. The

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frequency dependence in this case is solely due to the decreasing effectiveapertureof the receiving antenna as the frequency increases. This is intuitively reasonable, since the physical size of a given antenna type is inversely proportional to frequency. If we double the frequency, the linear dimensions of the antenna decrease by a factor of one-halt and the capture area by a factor of one-quarter. The antenna therefore captures only one-quarter of the power flux density at the higher frequency vers us the lower one, and delivers 6 dB less signal to the receiver. However, in most cases we can easily get this 6 dB back by increasing the effective aperture, and hence the gain, of the receiving antenna. For example, suppose we are using a parabolic dish antenna at the lower frequency. When we double the frequency, instead of allowing the dish to be scaled down in size so as to produce the same gain as before, we can maintain the same reflector size. This gives us the same effective apertureas before (assuming that the feed is properly redesigned for the new frequency, etc.),and 6 dB more gain (remembering that the gain is with respect to an isotropic or dipole reference antenna at the same frequ ency). Thus the free space path loss is now the same at both frequencies; moreover, if we maintained the same physical aperture at both ends of the link, we would actually have 6 dB less path loss at the higher frequency. Youcan picture this in terms of being able to focus the energy more tightly at the frequency with the shorter wavelength. It has the added benefit of providing greater discrimination against multipath - more about this later. The free space path loss equation is more usefully expressed logarithmically:

LP

= 32 .4+ 20log f

+ 20logd dB (f ill i MHz; d iIn k m )

(6a)

or

L p = 36.6+ 20log f + 20logd dB (f in MHz, d in miles)

(6b)

This shows more d early the relationship between path loss and distance: path loss increases by 20 dB/ decade or 6 dB/ octave,so each time you double the distance, you lose another 6 dB of signal under free space conditions. Of course, in looking at a real system, we must consider the actual antenna gains and cable losses in calculating the signal power P, which is available at the receiver input: (7)

where Pt

L

=

=

c: =

Gr Lt

Lr

=

=

=

transmitter power output (dBm or dBW, same units as P) free space path loss between isotropic antennas (dB) transmit antenna gain (dBi) receive antenna gain (dBi) transmission line loss between transmitter and transmit antenna (dB) transmission linelossbetween receiveantenna and receiverinput (dB)

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A table of transmission line losses for various bands and popular cable types can be found in the Appendix. Example 1. Suppose you have a pair of 915 MHz WaveLAN card s, and wa nt to use them on a 10 km link on which you believe free space path loss conditions will apply. The transmitter power is 0.25 W, or +24 dBm. You also have a pair of yagi antennas with 10 dBi gain, and at each end of the link, you need about 50 ft (15 m) of transmission line to the antenna. Let's say you're using LMR-400coaxial cable, which will give you about 2 dB loss at 915 MHz for each run. Finally, the path loss from equation (6a) is calculated, and this gives 111.6 dB, which we'll round off to 112 dB. The expected signal power at the receiver is then, from (7):

t; = 24 -112 + 10 + 10 -2 -

2 = -72 dBm

According to the WaveLAN specifications, the receivers require -78 dBm signal level in order to deliver a low bit error rate (BER). So, we should be in good shape, as we have 6 dB of margin over the minimum requirement. However, this will only be true if the path really is equivalent to the free space case, and this is a big if'. We'll look at means of predicting whether the free space assumption holds in the next section.

Path Loss on Line of Sight Links The term Line of Sight (LOS) as applied to radio links has a pretty obvious meaning: the antennas at the ends of the link can "see" each other, at least in a radio sense . In many cases, radio LOSequates to optical LOS:you're atthe location of the antenna at one end of the link, and with the unaided eye or binoculars, you can see the antenna (or its future site) at the other end of the link. In other cases, we may still have an LOS path even though we can't see the other end visually. This is because the radio horizon extends beyond the optical horizon. Radio waves follow slightly curved paths in the atmosphere, but if there is a direct path between the antennas which doesn't pass through any obstacles, then we still have radio LOS. Does having LOS mean that the path loss will be equal to the free space case which we have just considered? In some cases, the answer is yes, but it is definitely not a sure thing. There are three mechanisms which ma y cause the path loss to differ from the free space case:



refraction in the earth's atmosphere, which alters the trajectory of radio waves, and which can change with time.



diffraction effects resulting from objects near the direct path.



reflections from objects, which may be either nea r or far from the dire ct path.

We examine these mechanisms in the next three sections.

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Atmospheric Refraction As mentioned previously, radio waves near the earth's surface do not usually propagate in precisely straight lines, but follow slightly curved paths. The reason is well-known to VHF/UHF DXers: refraction in the earth's atmosphere, Under normal circumstances, the index of refraction decreases monotonically with increasing height, which causes the radio waves emanating from the transmitter to bend slightly downwards towards the earth's surface instead of following a straight line. The effect is more pronounced at radio frequencies than at the wavelength of visible light, and the result is that the radio waves can propagate beyond the optical horizon, with no additional loss other than the free space distance loss. There is a convenient artifice which is used to account for this phenomenon: when the path profile is plotted, we reduce the curvature of the earth's surface. If we choose the curvature properly, the paths of the radio waves can be plotted as straight lines. Under normal conditions, the gradient in refractivity index is such that real world propagation is equivalent to straight-line propagation over an earth whose radius is greater than the real one by a factor of 4/3 - thus the often-heard term"4/3 earth radius" in discussions of terrestrial propagation. However, this is just an approximation that applies under typical conditions - as VHF/UHF experimenters well know, unusual weather conditions can change the refractivity profile dramatically. This can lead to several different conditions. In superrefraetion, the rays bend more than normal and the radio horizon is extended; in extreme cases, it leads to the phenomenon known as dueting, where the signal can propagate over enormous distances beyond the normal horizon. This is exciting for DXers, but of little practical use for people who want to run data links. The main consequence for digital experimenters is that they may occasionally experience interference from unexpected sources. A more serious concern is subrefraetion, in which the bending of the rays is less than normal, thus shortening the radio horizon and reducing the clearance over obstacles along the path. This may lead to increased path loss, and possibly even an outage. In commercial radio link planning, the statistical probability of these events is calculated and allowed for in the link design (distance, path clearance, fading margin, etc.). We won't get into all of the details here; suffice it to say that reliability of your link will tend to be higher if you back off the distance from the maximum which is dictated by the normal radio horizon. Not that you shouldn't try and stretch the limits when the need arises, but a link which has optical clearance is preferable to one which doesn't. It's also a good idea to build in some margin to allow for fading due to unusual propagation situations, and to allow as much clearance from obstacles along the path as possible. For short-range links, the effects of refraction can usually be ignored

Diffraction and Fresnel Zones Refraction and reflection of radio waves are mechanisms which are fairly easy to picture, but diffraction is much less intuitive. To understand diffraction, and radio propagation in general, it is very helpful to have some feeling for how radio waves behave in an environment which is not strictly "free space". Consider Fig. 1, in which a wavefront is traveling from left to right, and encountering an obstacle which absorbs or reflects all of the incident radio energy. Assume that the

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incident wavefront is uniform; i.e., if we measure the field strength along the line A-N, it is the same at all points. Now, what will be the field strength along a line B-B'on the other side of the obstacle? Toquantify this, we provide an axis in which zero coincides with the top of the obstacle, and negative and positive numbers denote positions above and below this, respectively (we'll define the parameter (used on this axis a bit later).

8

A

• •



• •• • •

Advancing Wavefront

AI

-2

-1 0 1 2

3

8

1

Figure 1 Shadowing of Radio Waves by an Object

Intuition may lead one to expect the field strength along B-B' to look like the dashed line in Fig. 2, with complete shadowing and zero signal below the top of the obstacle, and no effect at all above it. The solid line shows the reality: not only does energy "leak" into the shadowed area, but the field strength above the top of the obstacle is also disturbed. At a position which is level with the top of the obstacle, the signal power density is down by some 6 dB, despite the fact that this point is in "line of sight" of the source. This effect is less surprising when one considers other familiar instances of wave motion. Picture, for example, tossing a rock in a pond and watching the ripples propagate outward. When they encounter an object such as a boat or a pier, you will see that the water behind the object is also disturbed, and that the waves traveling past, but close to, the object are also affected somewhat. Similarly, consider a distant source of sound waves: if the sound level is well above the ambient level, then moving behind an object which absorbs the incident sound energy completely does not result in the sound disappearing completely - it is still audible at a lower level, due to diffraction (as an aside, it is interesting to note that the wavelength of a 1 KHz sound wave is nearly the same as a 1 GHz radio wave). So much for analogies -let's get back to radio waves.

-

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I

-25 '-:c----'::----',:---'t~-~-~--" -1 -3 -2 o 2 3

v (position on line 8-8') Figure 2 Signal Levels on the Far Side of the Shadowing Object

The explanation for the non-intuitive behavior of radio waves in the presence of obstacles which appear in their path is found in something called Huygens' Principle. Huygens showed that propagation occurs as follows: each point on a wavefront acts as a source of a secondary wavefront known as a wavelet, and a new wavefront is then built up from the combination of the contributions from all of the wavelets on the preceding wavefront. The secondary wavelets do not radiate equally in all directions - their amplitude in a given direction is proportional to (1 + cos a), where ( is the angle between that direction and the direction of propagation of the wavefront. The amplitude is therefore maximum in the direction of propagation (i.e.,normal to the wavefront), and zero in the reverse direction. The representation of a wavefront as a collection of wavelets is shown in Fig. 3.

Radio energy from wavelets enters shadowed region Figure 3 Representation ofRadio Waves as Wavelets

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At a given point on the new wavefront (point B), the signal vector (phasor) is determined by vector addition of the contributions from the w avelets on the preceding wavefront, as shown in Fig.4. The largest component is from the nearest wavelet, and we then get symmetrical contributions from the points above and below it. These latter vector s are shorter, due to the angular reduction of amplitude mentioned above, and also the greater distance traveled. The greater distance also introduces more time delay, and hence the rotation of the vectors as shown in the figure . As we include contributions from points farther and farther away, the corresponding vectors continue to rotate and diminish in length, and they trace out a double-sided spiral path, known as the Cornu spiral.

A +2

Vector +2 I

I I I I

Vector +1

oI

~

.,~

I

Vector Sum

,~ I

+ " Vector 0 I

I I I

I I I

" I

"~B

·2

I I I

I

, I

Vector-1

(vector-2 Figure 4 Buildin g of a New Wavefront by Vector Summation

The Cornu spiral, shown in Fig. 5, provides the tool we need to visualize what happens when radio waves encounter an obstacle. In free space, at every point on a new wavefront, all contributions from the wavelets on the preceding wavefront are present and unattenuated, so the resultant vector corresponds to the complete spiral (i.e., the endpoints of the vector are Xand Y). Now, consider again the situation shown in Fig. I, and for each location on the wavefront B-B', visualize the makeup of the Cornu spiral (note that the top of the obstacle is assumed to be sufficiently narrow that no significant reflections can occur from it). At position 0, level with the top of the obstacle, we will have only contributions from the positive half of the preceding wavefront at A-A:, since all of the others are blocked by the obstacle. Therefore, the received components form only the upper half of the spiral, and the resultant vector is exactly half the length of the free space case, corresponding to a 6 dB reduction in amplitude. As we go lower on the line B-B', we start to get blockage of components from the positive side of the A-A: wavefront, removing more and more of the vectors as we go, and leaving only the tight upper spiral. The resulting amplitude diminishes monotonically towards zero as we move down the new wavefront, but there is still signal present at all points behind the obstacle, as shown in the graph in Fig. 2. How about the points along line B-B' above the

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obstacle, where the graph shows those mysterious ripples? Again, look at the Cornu spiral: as we move up the line, we begin to add contributions from the negative side of the A-A' wavefront (vectors -1, -2, etc.). Note what happens to the resultant vector - as we make the first tum around the bottom of the spiral, it reaches its maximum length, corresponding to the highest peak in the graph of Fig. 2. As we continue to move up B-B' and add more components, we swing around the spiral and reach the minimum length for the resultant vector (minimum distance from point Y). Further progression up B-B' results in further motion around the spiral, and the amplitude of the resultant oscillates back and forth, with the amplitude of the oscillation steadily decreasing as the resultant converges on the free space value, given by the complete Cornu spiral (vector X-Y) .

v = +1

v =-1 Figure 5 The Cornu Spiral

So, in a nutshell, to visualize what happens to radio waves when they encounter an obstacle, we have to develop a picture of the wavefront after the obstacle as a function of the wavefront just before it (as opposed to simply tracing rays from the distant source). Now we're in a position to talk about Fresnel zones. A Fresnel zone is a simpler concept once you have some understanding of diffraction: it is the volume of space enclosed by an ellipsoid which has the two antennas at the ends of a radio link at its foci. The two-dimensional representation of a Fresnel zone is shown in Fig. 6. The surface of the ellipsoid is defined by the path ACB, which exceeds the length of the directpathAB by some fixed amount. This amount is M/2, where n is a positive integer. For the first Fresnel zone, n = 1 and the path length differs by A/2 (i.e.,a 180(phase reversal with respect to the direct path). For most practical purposes, only the first Fresnel zone need be considered. A radio

153

path has first Fresnel zone clearance if,as shown in Fig. 6, no objects capable of causing significant diffraction penetrate the corresponding ellipsoid. What does this mean in terms of path loss? Recall how we constructed the wavefront behind an object by vector addition of the wavelets comprising the wavefront in front of the object, and apply this to the case where we have exactly first Fresnel zone clearance. We wish to find the strength of the direct path signal after it passes the object. Assuming there is only one such object near the Fresnel zone, we can look at the resultant wavefront at the destination point B. In terms of the Cornu spiral, the upper half of the spiral is intact, but part of the lower half is absent, due to blockage by the object. Since we have exactly first Fresnel clearance, the final vector which we add to the bottom of the spiral is 180( out of phase with the direct-path vector - i.e., it is pointing downwards. This means that we have passed the bottom of the spiral and are on the way back up, and the resultant vector is near the free space magnitude (a line between X and Y in Fig. 5). In fact, it is sufficient to have 60% of the first Fresnel clearance, since this will still give a resultant which is very close to the free space value.

----------_.-.-.-B.....'

~---=::::::==~::::4

. ./

Figure 6 Fresnel Zone for a Radio Link

In order to quantify diffraction losses, they are usually expressed in terms of a dimensionless parameter (, given by:

(8)

where L\d is the difference in lengths of the straight-line path between the endpoints of the link and the path which just touches the tip of the diffracting object (see Fig. 7, where L\d = d. + d, - d). By convention, v is positive when the direct path is blocked (i.e., the obstacle has positive height), and negative when the direct path has some clearance ("negative height"). When the direct path just grazes the object, v = O. This is the parameter shown in Figures 1 and 2. Since in this section we are considering LOS paths, this corresponds to specifying that v ::; O. For first Fresnel zone clearance, we have L\d = ').,,/2, so from equation (8), ( = -1.4. From Fig. 2, we can see that this is more clearance than necessary - in fact, we get slightly higher signal level (and path loss less than the free space value) if we reduce

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the clearance to v = -1, which corresponds to ~d = A/4. The v = -1 point is also shown on the Cornu spiral in Fig. 5. Since ~d= A/4, the last vector added to the summation is rotated 900 from the direct-path vector, which brings us to the lowest point on the spiral. The resultant vector then runs from this point to the upper end of the spiral at point Y. It's easy to see that this vector is a bit longer than the distance from X to Y, so we have a slight gain (about 1.2 dB) over the free space case. We can also see how we can back off to 60% of first Fresnel zone clearance ( v "" -0.85)without suffering significant loss. But how do we calculate whether we have the required clearance? The geometry for Fresnel zone calculations is shown in Fig. 7. Keep in mind that this is only a two-dimensional representation, but Fresnel zones are three-dimensional. The same considerations apply when the objects limiting path clearance are to the side or even above the radio path. Since we are considering LOS paths in this section, we are dealing only with the "negative height" case, shown in the lower part of the figure. We will look at the case where h is positive later, when we consider non-LOS paths.

P

T~R a) h pos itive

T....,.-

d

---,...-_ _-...:::d

~

R

h

P b) h negative

Figure 7 Fresnel Zone Geometry

For first Fresnel zone clearance, the distance h from the nearest point of the obstacle to the direct path must be at least

(9)

where d. and d, are the distances from the tip of the obstacle to the two ends of the radio circuit. This formula is an approximation which is not valid very close to the endpoints of the circuit. For convenience, the clearance can be expressed in terms of frequency:

155

(lOa) where f is the frequency in GHz, d. and d, are in krn, and h is in meters. Or:

(lOb) where f is in GHz, d. and d, in statute miles, and h is in feet. Example 2. We have a 10 krn LOS path over which we wish to establish a link in the 915 MHz band. The path profile indicates that the high point on the path is 3 krn from one end, and the direct path clears it by about 18 meters (60 ft.) - do we have adequate Fresnel zone clearance? From equation (lOa), with d. = 3 krn, d, = 7 krn, and f = 0.915 GHz, we have h = 26.2 m for first Fresnel zone clearance (strictly speaking, h = -26.2 m) . A clearance of 18 m is about 70% of this, so it is sufficient to allow negligible diffraction loss. Fresnel zone clearance may not seem all that important - after all, we said previously that for the zero clearance (grazing) case, we have 6 dB of additional path loss . If necessary, this could be overcome with, for example, an additional 3 dB of antenna gain at each end of the circuit. Now it's time to confess that the situation depicted in Figures 1 and 2 is a special case, known as "knife edge" diffraction. Basically, this means that the top of the obstacle is small in terms of wavelengths. This is sometimes a reasonable approximation of an object in the real world, but more often than not, the obstacle will be rounded (such as a hilltop) or have a large flat surface (like the top of a building), or otherwise depart from the knife edge assumption. In such cases, the path loss for the grazing case can be considerably more than 6 dB - in fact, 20 dB would be a better estimate in many cases. So, Fresnel zone clearance can be pretty important on real-world paths. And, again, keep in mind that the Fresnel zone is three-dimensional, so clearance must also be maintained from the sides of buildings, etc. if path loss is to be minimized. Another point to consider is the effect on Fresnel zone clearance of changes in atmospheric refraction, as discussed in the last section. We may have adequate clearance on a longer path under normal conditions (i.e.,4/3 earth radius), but lose the clearance when unusual refraction conditions prevail. On longer paths, therefore, it is common in commercial radio links to do the Fresnel zone anal ysis on something close to "worst case" rather than typical refraction conditions, but this may be less of a concern in amateur applications. . Most of the material in this section was based on Ref. [2], which is highly recommended for further reading.

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Ground ReDections An LOS path may have adequate Fresnel zone clearance, and yet still have a path loss which differs significantly from free space under normal refraction conditions. If this is the case, the cause is probably multipath propagation resulting from reflections (multipath also poses particular problems for digital transmission systems - we'll look at this a bit later, but here we are only considering path loss).

One common source of reflections is the ground. It tends to be more of a factor on paths in rural areas; in urban settings, the ground reflection path will often be blocked by the clutter of buildings, trees, etc. In paths over relatively smooth ground or bodies of water, however, ground reflections can be a major determinant of path loss. For any radio link, it is worthwhile to look at the path profile and see if the ground reflection has the potential to be significant. It should also be kept in mind that the reflection point is not at the midpoint of the path unless the antennas are at the same height and the ground is not sloped in the reflection region - just the remember the old maxim from optics that the angle of incidence equals the angle of reflection. Ground reflections can be good news or bad news, but are more often the latter. In a radio path consisting of a direct path plus a ground-reflected path, the path loss depends on the relative amplitude and phase relationship of the signals propagated by the two paths. In extreme cases, where the ground-reflected path has Fresnel clearance and suffers little loss from the reflection itself (or attenuation from trees, etc.), then its amplitude may approach that of the direct path. Then, depending on the relative phase shift of the two paths, we may have an enhancement of up to 6 dB over the direct path alone, or cancellation resulting in additional path loss of 20 dB or more. If you are acquainted with Mr. Murphy, you know which to expect! The difference in path lengths can be estimated from the path profile, and then translated into wavelengths to give the phase relationship. Then we have to account for the reflection itself, and this is where things get interesting. The amplitude and phase of the reflected wave depend on a number of variables, including conductivity and permittivity of the reflecting surface, frequency, angle of incidence, and polarization. It is difficult to summarize the effects of all of the variables which affect ground reflections, but a typical case is shown in Fig. 8 [2]. This particular figure is for typical ground conditions at 100 MHz, but the same behavior is seen over a wide range of ground constants and frequencies. Notice that there is a large difference in reflection amplitudes between horizontal and vertical polarization (denoted on the curves with "h" and "v", respectively), and that vertical polarization in general gives rise to a much smaller reflected wave. However, the difference is large only for angles of incidence greater than a few degrees (note that, unlike in optics, in radio transmission the angle of incidence is normally measured with respect to a tangent to the reflecting surface rather than a normal to it); in practice, these angles will only occur on very short paths, or paths with extraordinarily high antennas. For typical paths, the angle of incidence tends to be of the order of one degree or less - for example, for a 10 km path over smooth earth with 10 m antenna heights,

157

the angle of incidence of the ground reflection would only be about 0.11 degrees. In such a case, both polarizations will give reflection amplitudes near unity (i.e.,no

reflection loss). Perhaps more surprisingly, there will also be a phase reversal in both cases. Horizontally-polarized waves always undergo a phase reversal upon reflection, but for vertically-polarized waves, the phase change is a function of the angle of incidence and the ground characteristics.

Reflection

0.5

amplitude

0 0

10

0

20

30

40

30

40

(0

Degrees

Reflection

-100

../

-200 0

10

phase

h

20

Angle of Incidence (degress) Figure 8 Typical Ground Reflection Parameters

The upshot of all this is that for most paths in which the ground reflection is significant (and no other reflections are present), there will be very little difference in performance between horizontal and vertical polarization. For very short paths, horizontal polarization will generally give rise to a stronger reflection. If it turns out that this causes cancellation rather than enhancement, switching to vertical polarization may provide a solution. In other words, for shorter paths, it is usually worthwhile to try both polarizations to see which works better (of course, other factors such as mounting constraints and rejection of other sources of multipath and interference also enter into the choice of polarization). As stated above, for either polarization, as the path gets longer we approach the case where the ground reflection produces a phase reversal and very little attenuation. At the same time, the direct and reflected paths are becoming more nearly equal. The path loss ripples up and down as we increase the distance, until we reach the point where the path lengths differ by just one-half wavelength. Combined with the 180( phase shift caused by the ground reflection, this brings the direct and reflected signals into phase, resulting in an enhancement over the free space path loss (theoretically 6 dB, but this will seldom be realized in practice).

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Thereafter, it's all downhill as the distance is further increased, since phase difference between the two paths approaches in the limit the 1800 phase shift of the ground reflection. It can be shown that, in this region, the received power follows an inverse fourth-power law as a function of distance instead of the usual square law (Le.,12 dB more attenuation when you double the distance, instead of 6 dB). The distance at which the path loss starts to increase at the fourth-power rate is reached when the ellipsoid corresponding to the first Fresnel zone just touches the ground. A reasonably good estimate of this distance can be calculated from the equation

d = 4h/~ A

(11)

where h. and h, are the antenna heights above the ground reflection point. For example, for antenna heights of 10 m, at 915 MHz (A. = 33 cm) we will be into the fourth-law loss region for links longer than about 1.2 km. So, for longer-range paths, ground reflections are always bad news. Serious problems with ground reflections are most commonly encountered with radio links across bodies of water. Spread spectrum techniques and diversity antenna arrangements usually can't overcome the problems - the solution lies in siting the antennas (e.g., away from the shore of the body of water) such that the reflected path is cut off by natural obstacles, while the direct path is unimpaired. In other cases, it may be possible to adjust the antenna locations so as to move the reflection point to a rough area of land which scatters the signal rather than creating a strong specular reflection.

Other Sources 01 ReDections Much of what has been said about ground reflections applies to reflections from other objects as welL The"ground reflection" on a particular path may be from a building rooftop rather than the ground itself, but the effect is much the same. On long links, reflections from objects near the line of the direct path will almost always cause increased path loss - in essence, you have a permanent "flat fade" over a very wide bandwidth. Reflections from objects which are well off to the side of the direct path are a different story, however. This is a frequent occurrence in urban areas, where the sides of buildings can cause strong reflections. In such cases, the angle of incidence may be much larger than zero, unlike the ground reflection case. This means that horizontal and vertical polarization may behave quite differently - as we saw in Fig. 8, vertically polarized signals tend to produce lower-amplitude reflections than horizontally polarized signals when the angle of incidence exceeds a few degrees. When the reflecting surface is vertical, like the side of a building, a signal which is transmitted with horizontal polarization effectively has vertical polarization as far as the reflection is concerned. Therefore, horizontal polarization will generally result in weaker reflections and less multipath than vertical polarization in these cases.

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Effects of Rain, Snow and Fog The loss of LOS paths may sometimes be affected by weather conditions (other than the refraction effects which have already been mentioned). Rain and fog (clouds) become a significant source of attenuation only when we get well into the microwave region. Attenuation from fog only becomes noticeable (i.e.,attenuation of the order of 1 dB or more) above about 30 GHz. Snow is in this category as well. Rain attenuation becomes significant at around 10 GHz, where a heavy rainfall may cause additional path loss of the order of 1 dB/km.

Path Loss on Non-Line of Sight Paths We have spent quite a bit of time looking at LOS paths, and described the mechanisms which often cause them to have path loss which differs from the"free space" assumption. We've seen that the path loss isn't always easy to predict. When we have a path which is not LOS, it becomes even more difficult to predict how well signals will propagate over it. Unfortunately, non-LOS situations are sometimes unavoidable, particularly in urban areas. The following sections deal with some of the major factors which must be considered.

Diffraction Losses In some special cases, such as diffraction over a single obstacle which can be modeled as a knife edge, the loss of a non-LOS path can be predicted fairly readily. In fact, this is the same situation that we saw in Figures 1 and 2, with the diffraction parameter v > O. This parameter, from equation (8), is

To get (d, measure the straight-line distance between the endpoints of the link. Then measure the length of the actual path, which includes the two endpoints and the tip of the knife edge, and take the difference between the two. The geometry is shown in Fig. 7(a), the "positive h" case. A good approximation to the knife-edge diffraction loss in dB can then be calculated from

L(v) = 6.9+ 20 log [.Jv 2+l +v]

(12)

Example 3. We want to run a 915 MHz link between two points which are a straight-line distance of 25 km apart. However, 5 km from one end of the link, there is a ridge which is 100 meters higher than the two endpoints. Assuming that the ridge can be modeled as a knife edge, and that the paths from the endpoints to the top of ridge are LOS with adequate Fresnel zone clearance, what is the expected path loss? From simple geometry, we find that length of the path over the ridge is 25,001.25 meters, so that ild = 1.25 m. Since A. = 0.33 m, the parameter v, from (8),

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is 3.89. Substituting this into (12), we find that the expected diffraction loss is 24.9 dB. The free space path loss for a 25 km path at 915 MHz is, from equation (6a), 119.6 dB, so the total predicted path loss for this path is 144.5 dB. This is too lossy a path for many WLAN devices. For example, suppose we are using WaveLAN cards with 13 dBi gain antennas, which (disregarding feedline losses) brings them up to the maximum allowable EIRP of +36 dBm. This will produce, at the antenna terminals at the other end of the link, a received power of (36- 144.5 + 13) =-95.5 dBm. This falls well short of the -78 dBm requirement of the WaveLAN cards. On the other hand, a lower-speed system may be quite usable over this path. For instance, the FreeWave 115Kbps modems require only about -108 dBm for reliable operation, which is a comfortable margin below our predicted signal levels. To see the effect of operating frequency on diffraction losses, we can repeat the calculation, this time using 144 MHz, and find the predicted diffraction loss to be 17.5 dB, or 7.4 dB less than at 915 MHz. At 2.4 GHz, the predicted loss is 29.0 dB, an increase of 4.1 dB over the 915 MHz case (these differences are for the di ffraction losses only, not the only total path loss). Unfortunately, the paths which digital experimenters are faced with are seldom this simple. They will frequently involve diffraction over multiple rooftops or other obstacles, many of which don't resemble knife edges. The path losses will generally be substantially greater in these cases than predicted by the single knife edge model. The paths will also often pass through objects such as trees and wood-frame buildings which are semi-transparent at radio frequencies. Many models have been developed to try and predict path losses in these more complex cases. The most successful are those which deal with restricted scenarios rather than trying to cover all of the possibilities. One common scenario is diffraction over a single obstacle which is too rounded to be considered a knife edge. There are different ways of treating this problem; the one described here is from Ref. [3]. The top of the object is modeled as a cylinder of radius r, as shown in Fig. 9. To calculate the loss, you need to plot the profile of the actual object, and then draw straight lines from the link endpoints such that they just graze the highest part of the object as seen from their individual perspectives. Then the parameters D s' d., d, and ( are estimated, and an estimate of the radius r can then be calculated from

R I ~loC I 1-0-1



Figure 9 Diffraction by a Rounded Obstacle

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(13) Note that the angle a is measured in radians. The procedure then is to calculate the knife edge diffraction loss for this path as outlined above, and then add to it an excess loss factor Lex, calculated from

flO-

Lex = l1.7a ~-:i dB

(14)

There is also a correction factor for roughness: if the object is, for example, a hill which is tree-eovered rather than smooth at the top, the excess diffraction loss is said to be about 65% of that predicted in (14). In general, smoother objects produce greater diffraction losses . Example 4. We revisit the scenario in Example 3, but let's suppose that we've now decided that the ridge blocking our path doesn't cut it as a knife edge (ouch !). From a plot of the profile, we estimate that Ds = 10 meters. As before, d) = 20 km, d, = 5 km and the height of the ridge is 100 meters. Dusting off our high school trigonometry, we can work out that a = 1.43°, or 0.025 radians. Now, plugging these numbers into (13), we get r = 188 meters. Then, with A = 0.33 m, we can calculate the excess loss from (14):

L = 11.7 X 0.025 x ~7r X188 = 12.4 dB ex 0.33 So, summed with the knife edge loss calculated previously, we have an estimated total diffraction loss of 37.3dB (assuming the ridge is "smooth" rather than "rough"). This is a lot, but you can easily imagine scenarios where the losses are much greater: just look at the direct dependence on the angle a in (14) and picture from Fig. 9 what happens when the obstacle is closer to one of the link endpoints. Amateurs doing weak signal work are accustomed to dealing with large path losses in non-LOS propagation, but such losses are usually intolerable in high-speed digital links .

Attenuation from Trees and Forests Trees can be a significant source of path loss, and there are a number of variables involved, such as the specific type of tree, whether it is wet or dry, and in the case of deciduous trees, whether the leaves are present or not. Isolated trees are not usually a major problem, but a dense forest is another story. The attenuation depends on the distance the signal must penetrate through the forest, and it increases with frequency. According to a CCIR report [10],the attenuation is of the order of 0.05 dB/m at 200 MHz, 0.1 dB/m at 500 MHz, 0.2 dB/m at 1 GHz, 0.3 dB/m at 2 GHz and 0.4 dB/m at 3 GHz. At lower frequencies, the attenuation is somewhat

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lower for horizontal polarization than for vertical, but the difference disappears above about 1 GHz. This adds up to a lot of excess path loss if your signal must penetrate several hundred meters of forest! Fortunately, there is also significant propagation by diffraction over the treetops, especially if you can get your antennas up near treetop level or keep them a good distance from the edge of the forest, so all is not lost if you live near a forest.

General Non-LOS Propagation Models There are many more general models and empirical techniques for predicting non-LOS path losses, but the details are beyond the scope of this paper. Most of them are aimed at prediction of the paths between elevated base stations and mobile or portable stations near ground level, and they typically have restrictions on the frequency range and distances for which they are valid; thus they may be of limited usefulness in the planning of amateur high-speed digital links . Nevertheless, they are well worth studying to gain further insight into the nature of non-LOS propagation. The details are available in many texts - Ref. [3] has a particularly good treatment. One crude, but useful, approximation will be mentioned here: the loss on many non-LOS paths in urban areas can be modeled quite well by a fourth-power distance law. In other words, we substitute d' for d 2 in equation (5). In equation (6), we can substitute 40l0g(d) for the 20l0g(d) term, which would correspond to the assumption of square-law distance loss for distances up to 1 km (or 1 mile, for the non-metric version of the equation), and fourth-law loss thereafter. This is probably an overly optimistic assumption for heavily built-up areas, but is at least a useful starting point. The propagation losses on non-LOS paths can be discouragingly high, particularly in urban areas. Antenna height becomes a critical factor, and getting your antennas up above rooftop heights will often spell the difference between success and failure. Due to the great variability of propagation in cluttered urban environments, accurate path loss predictions can be difficult. If a preliminary analysis of the path indicates that you are at least in the ballpark (say within 10 or 15 dB) of having a usable link, then it will generally be worthwhile to give it a try and hope to be pleasantly surprised (but be prepared to be disappointed!).

Software Tools for Propagation Prediction Although there is no substitute for experience and acquiring a "feel" for radio propagation, computer programs can make the job of predicting radio link performance a lot easier. They are particularly handy for exploring "what if" scenarios with different paths, antenna heights, etc. Unfortunately, they also tend to cost money! If you're lucky, you may have access to one of the sophisticated prediction programs which includes the most complex propagation models, terrain databases, etc. If not, you can still find some free software utilities that will make it easier to do some of the calculations discussed above, such as knife edge diffraction losses. One very useful freeware program which was developed specifically for short-range VHF/UHF applications is RFProp, by Colin Seymour, G4NNA. Check Colin's Web page at http://www.users.dircon.co.uk/-rietking/freesw.htm for more information and downloading instructions. This is a Windows (3.1,95 or NT)

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program which can calculate path loss in free space and simple diffraction scenarios. In addition to calculating knife edge diffraction loss, it provides some correction factors for estimating the loss caused by more rounded objects, such as hills. It also allows changing the distance loss exponent from square-law to fourth-law (or anything else, for that matter) to simulate long paths w ith ground reflections or obstructed urban paths. There is also some provision for estimating the loss caused when the signals must penetrate buildings. The program has a graphical user interface in which the major path parameters can be entered and the result (in terms of receiver SNR margin) seen immediately. There is also a tabular output which lists the detailed results along with all of the assumed parameters.

Special Considerations for Digital Systems We have previously looked at the effect of multipath on path loss. When reflections occur from objects which are very close to the direct path, then paths have very similar lengths and nearly the same time delay. Depending on the relative phase shifts of the paths, the signals traversing them at a given frequency can add constructively to provide a gain with respect to a single path, or destructively to provide a loss. On longer paths in particular, the effect is usually a loss. Since the path lengths are nearly equal, the loss occurs over a wide frequency range, producing a "flat" fade . In many cases, however, reflections from objects well awa y from the direct path can give rise to significant multipath. The most common reflectors are buildings and other manmade structures, but many natural features can also be good reflectors. In such cases, the propagation delays of the paths from one end of the link to the other can differ considerably. The exten t of this time spreading of the signal is commonly measured by a parameter known as the delay spread of the path. One consequence of having a larger delay spread is that the reinforcement and cancellation effects will now vary more rapidly with frequency. For example, suppose we have two paths with equal attenuation and which differ in length by 300 meters, corresponding to a delay difference of 1 (sec. In the frequency domain, this link will have deep nulls at intervals of 1 MHz, with maxima in between. With a narrowband system, you may be lucky and be operating at a frequency near a maximum, or you may be unlucky and be near a null, in which case you lose most of your signal (techniques such as space diversity reception may help, though). The path loss in this case is highly frequency- dependent. On the other hand, a wideband signal which is, say,several MHz wide, would be subject to only partial cancellation or selective fading. Depending on the nature of the signal and how information is encoded into it, it may be quite tolerant of having part of its energy notched out by the multipath channel. Tolerance of multipath-induced signal cancellation is one of the major benefits of spread spectrum transmission techniques .

Longer multipath delay spreads have another consequence where digital signals are concerned, however: overlap of received data symbols with adjacent symbols, known as intersymbol interference or lSI. Suppose we try to transmit a 1 Mbps data stream over th e two-path multipath channel mentioned above . Assuming a modulation scheme with 1 (sec symbol length is used, then the signals arriving over the two paths will be offset by exactly one symbol period. Each received

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symbol arriving over the shorter path will be overlaid by a copy of the previous symbol from the longer path, making it impossible to decode with standard demodulation techniques. This problem can be solved by using an adaptive equalizer in the receiver, but this level of sophistication is not commonly found in amateur or WLAN modems (but it will certainly become more common as speeds continue to increase). Another way to attack this problem is to increase the symbol length while maintaining a high bit rate by using a multicarrier modulation scheme such as OFDM (Orthogonal Frequency Division Multiplex), but again, such techniques are seldom found in the wireless modem equipment available to hobbyists. For unequalized multipath channels, the delay spread must be much less than the symbol length, or the link performance will suffer greatly. The effect of multipath-induced lSI is to establish an irreducible error rate - beyond a certain point, increasing transmitter power will cause no improvement in BER, since the BER vs E/No curve has gone flat. A common rule of thumb prescribes that the multipath delay spread should be no more than about 10% of the symbol length. This will generally keep the irreducible error rate down to the order of 10-3 or less. Thus, in our two-path example above, a system running at lOOK symbols/ s or less may work satisfactorily. The actual raw BERrequirements for a particular system will of course depend on the error-control coding technique used. Delay spreads of several microseconds are not uncommon, especially in urban areas. Mountainous areas can produce much longer delay spreads, sometimes tens of microseconds. This spells big trouble for doing high-speed data transmission in these areas. The best way to mitigate multipath in these situations is to use highly directional antennas, preferably at both ends of the link. The higher the data rate, the more critical it becomes to use high-gain antennas. This is one advantage to going higher in frequency. The delay spread for a given link will usually not exhibit much frequency dependence - for example, there will be similar amounts of multipath whether you operate at 450 MHz or 2.4 GHz, if you use the same antenna gain and type. However, you can get more directivity at the higher frequencies, which often will result in significantly reduced multipath delay spread and hence lower BER. It may seem strange that high-speed WLAN products are often supplied with omnidirectional antennas which do nothing to combat multipath, but this is because the antennas are intended for indoor use. The attenuation provided by the building structure will usually cause a drastic reduction in the amplitude of reflections from outside the building, as well as from distant areas inside the building. Delay spreads therefore tend to be much smaller inside buildings - typically of the order of 0.1 (sec or less. However, as WLAN products with data rates of 10 Mbps and beyond are now appearing, even delay spreads of this magnitude are problematic and must be dealt with by such measures as equalizers, high-level modulation schemes and sectorized antennas.

Conclusions Radio propagation is a vast topic, and we've only scratched the surface here. We haven't considered, for example, the interesting area of data transmission involving mobile stations - maybe next year! Hopefully, this paper has provided some insight into the problems and solutions associated with setting up digital links in the VHF to microwave spectrum. To sum up, here are a few guidelines and principles:

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Always strive for LOS conditions. Even with LOS, you must pay attention to details regarding variability of refractivity, Fresnel zone clearance and avoiding reflections from the ground and other surfaces. Non-LOS paths will often lead to disappointment unless they are very short, especially with the high-speed unlicenced WLAN devices. Their low ERP limits and high receive signal power requirements (due to large noise bandwidths, high noise figures and sometimes, significant modem implementation losses) leave little margin for higher-than-LOS path losses. Hams are not encumbered by the low ERP limits, but it can be very expensive to overcome excessive path losses with higher transmitter powers.



Use as much antenna gain as is practical. It is always worthwhile to try both polarizations, but horizontal polarization will often be superior to vertical. It will generally provide less multipath in urban areas, and may provide lower path loss in some non-LOS situations (e.g., attenuation from trees at VHF and lower UHF). Also, interfering signals from pagers and the like tend to be vertically polarized, so using the opposite polarization can often provide some protection from them.



There are advantages to going higher in frequency, into the microwave bands, due to the higher antenna gains which can be achieved. The tighter focusing of energy which can be achieved may result in lower overall path loss on LOS paths (providing that you can keep the feedline losses under control), and less multipath. Higher frequencies also have smaller Fresnel zones, and thus require less clearance over obstacles to avoid diffraction losses. And, of course, the higher bands have more bandwidth available for high-speed data, and less probability of interference. However, the advantage may be lost in non-LOS situations, since diffraction losses, and attenuation from natural objects such as trees, increase with frequency.

Radio propagation is seldom 100% predictable, and one should never hesitate to experiment. It's very useful, though, to be equipped with enough knowledge to know what techniques to try, and when there is little probability of success . This paper was intended to help fill some gaps in that knowledge. Good luck with your radio links!

A cknowled gem ents The author gratefully acknowledges the work of his daughter Kelly (http://hydra.carleton.ca/ -klm) in producing the figures for this paper. WaveLAN is a registered trademark of Lucent Technologies, Inc.

Referen ces [1] ARRL UHF/Microwave Experimenter's Manual (American Radio Relay League, 1990). [2] Hall, M.P.M.,Barclay, L.w. and Hewitt, M.T. (Eds.), Propagation ofRadiowaves (Institution of Electrical Engineers, 1996). [3] Parsons, J.D., The Mobile Radio Propagation Channel (Wiley & Sons, 1992). [4] Doble, J., Introduction toRadio Propagation for Fixed andMobile Communications (Artech House, 1996).

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[5] Bertoni, H .L., Honcharenko, W., Maciel, L.R. and Xia, H.H., "UHF Propagation Prediction for Wireless Personal Communications", Proceedings of the IEEE, Vol. 82, No.9, September 1994, pp. 1333-1359. [6] Andersen, J.B., Rappaport, T.S. and Yoshida, S., "Propagation Measurements and Models for Wireless Communications Channels", IEEE Communications Magazine, January 1995, pp. 42-49. [7] Freeman, R.L., Radio System Design for Telecommunications (Wiley & Sons, 1987). [8] Lee, W.c.Y., Mobile Communications Design Fundamentals, Second Edition (Wiley & Sons, 1993). [9] CCIR (now ITU-R) Report 567-4, "Propagation data and prediction methods for the terrestrial land m obile service using th e fre quency range 30 MHz to 3 GHz" (International Telecommunication Union, Geneva, 1990). [10] CCIR Report 1145, "Propagation over irre gular terrain with and w ithout vegetation" (International Telecommunication Union, Geneva, 1990).

Transmission Line Attenuation Chart The following table shows coax type and the attenuation (measured in db) you can expect by frequency of use per 100 feet of cable. Coax LDF 6-5 0 LMR- 1700 He 1 1 iax LDF5 LMR-1 200 LMR-900 LMR-600 HEL IAX FS J4 LMR-500 HELIAX F SJ 4 LMR-400 Beldon 991 3 Ul tra- Link RG213 /RG214 HELIAX FSJ1 LMR-240 ProF lex 800 Be ldon RG8X LMR- 2 00 Ultra-L ink RG-5 8 LMR-1 0 0

size 1. 5 5 0"

1. 6 70 " 1. 090" 1. 200 " 0 .870 " 0 . 590 " 0 .630" 0 . 500" 0. 520" 0 .40 5 " 0.40 5 " 0 .405 " 0 .405 " 0.300" 0.240" 0.242 " 0.2 4 2 " 0. 1 9 5 " 0 .195 " 0 . 195 " 0 . 1 50 "

15 0MHz 22 0MHz 45 0MHz 0 .6 17 0 .34 0 .34 7 0 .427 0 .42 7 0 .45 8 0 . 834 0 .4 81 0. 864 0 .5 89 0 .755 1.10 0 .6 19 1.1 8 1. 72 0 .964 0 . 845 1. 51 1. 22 2 .17 1.49 1. 29 2.32 1.5 1. 8 2 .7 1.6 1.9 2. 8 1. 5 2 .7 2.8 3.5 5 .2 2 .23 3.93 3 .0 3 .7 5.3 7.8 4 .7 6.0 8.6 4 .0 4 .8 6 .9 5 .1 9.5 6 .2 7 .4 10 .6 10 . 9 8 .9 1 5 .8

900MHz 1 . 5GHz 0.907 1. 22 1. 267 0.632 1. 23 1. 66 1. 26 1. 69 1. 60 2 .12 2.50 3.31 2 .20 2 .93 3.13 4 .1 3 3 .3 8 4.50 3 .9 5.1 4 .2 5 .6 4 . 19 8.0 10.1 5 .687 7.47 7 .6 9 .9 12 . 8 9. 9 14 .0 16 . 5 22 .8

15 . 9 12 . 9 2 1. 1 30.0

2GHz 5.8GHz 1. 45 2 . 50 1. 50 1. 9 7 1. 99 2. 4 9 3 .90 7. 3 3 .45 4. 84 5. 31 6 .0 10.8 6.7 13 . 8 6 .7 15 .2 2 8.6 8 .73 11. 5 20.4 23.1 15 . 0 36 32 .2 3 5.0

40 .9

5 1.6

Data gathered from : • Hutton An tenna Supply Catalog, 1997, p. 144 • Barry McLamon, VE3JF, Attenuation of Coaxial Transmission Lines in the VHF /UHF/ Microwave Amateur and ISM Bands Other Info: • The LMR series is manufactured by Times Microwave. • 9913 is manufactured by Belden Corp. • RG-series cables are manufactured by Belden and many others. • The LDF series are foam dielectric, solid corrugated ou ter conductor cables, bes t known by the brand name HELIAX (®Andrew Corp.). • Attenuation at any frequency = (K1 x SqRt(Fmhz) + K2 x Fmhz)

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Chapter 4 Regulatory This chapter covers some of the issues related to regulatory issues. It begins with the current Part 97 rules for the amateur radio service with regard to spread spectrum operations. These rules are currently under review for change, and the Notice Proposed Rule Making (NPRM-8737) issued in March of 1997that outlines what the FCC has proposed for changes to the rules is also included. Current details regarding the amateur radio service rules and regulations for spread spectrum are kept on the TAPR Spread Spectrum web pages (http: / /www.tapr.org/ ss). The pages include comments and reply comments from most of the filings on the NPRM . TAPR's comments and reply comments to NPRM-8737 are presented in this chapter. TAPR supports the request to modify Part 97.311(b) as it pertains to the unintentional triggering of repeater inputs. This section is redundant with other parts of the Commission's rules and, therefore, is unnecessary. TAPR supports the requestto delete sections 97.311(c) and (d), in order to permit SS emissions and spreading codes that are not currently authorized. Elimination of the rule that dictates specific spreading codes is necessary to facilitate further experimentation and to match the provisions allowed under an existing amateur service SSSTA, discussed below. In addition, it would facilitatethe use and adoption by amateur radio operators of Part 15 SSequipment and hardware. TAPR differs with respect to the question of which frequencies should be authorized for SS emissions. In the Petition, the ARRL proposes that brief test transmissions of SSemissions be permitted only on those frequency bands in which SSemissions currently are authorized. TAPRbelieves that SSemissions should be allowed on all frequency bands. The Commission should not impose any restriction on the length of time SS emissions are transmitted. Ample time already has been provided for the experimental phase of SSusage in the amateur service (five years of experimentation under the 1980AMRAD STAand ten years under the current Part 97 rules), and it is now time to allow SS use without restriction. TAPR also differs on how station identification and documentation should be handled under a revised set of rules . The ARRL in its petition did not ask the Commission to delete sections 97.311(e) and 97.119(b)(5) of the rules, even though it questioned the practicality of the requirements set forth in these sections. TAPR, in contrast, recommends that the Commission delete these subsections of the rules. The interference and harm to the band in which an SS station is operating that would be caused by a requirement to use a CW identification outweighs the benefits that would accrue for monitoring purposes from the use of the ill.

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597.31155 emission types (a) 55 emission transmissions by an amateur station are authorized only for communications between points within areas where the amateur service is regulated by the FCC. 55 emission transmissions must not be used for the purpose of obscuring the meaning of any communication. (b) Stations transmitting 55 emission must not cause harmful interference to

stations employing other authorized emissions, and must accept all interference caused by stations employing other authorized emissions. For the purposes of this paragraph, unintended triggering of carrier operated repeaters is not considered to be harmful interference. (c) Only the following types of 55 emission transmissions are authorized (hybrid 55 emission transmissions involving both spreading techniques are prohibited): (1) Frequency hopping where the carrier of the transmitted signal is modulated with unciphered information and changes frequency at fixed intervals under the direction of a high speed code sequence. (2) Direct sequence where the information is modulo-Z added to a high speed code sequence. The combined information and code are then used to modulate the RF carrier. The high speed code sequence dominates the modulation function, and is the direct cause of the wide spreading of the transmitted signal. (d) The only spreading sequences that are authorized are from the output of one binary linear feedback shift register (which may be implemented in hardware or software). (1) Only the following sets of connections may be used: Number of stages Taps used in shift register in feedback 7 7, l. 13 13,4,3, and l. 19 19,5,2, and 1. (2) The shift register must not be reset other than by its feedback during an individual transmission. The shift register output sequence must be used without alteration. (3) The output of the last stage of the binary linear feedback shift register must be used as follows: (i) For frequency hopping transmissions using x frequencies, n consecutive bits from the shift register must be used to select the next frequency from a list of frequencies sorted in ascending order. Each consecutive frequency must be selected by a consecutive block of n bits. (Where n is the smallest integer greater than log2X.)

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(ii) For direct sequence transmissions using m-ary modulation, consecutive blocks of log2 m bits from the shift register must be used to select the transmitted signal during each interval. (e) The station records must document all 55 emission transmissions and must be retained for a period of 1 year following the last entry. The station records must include sufficient information to enable the FCC, using the information contained therein, to demodulate all transmissions. The station records must contain at least the following: (1) A technical description of the transmitted signal; (2) Pertinent parameters describing the transmitted signal including the frequency or frequencies of operation and, where applicable, the chip rate, the code rate, the spreading function, the transmission protocol(s) including the method of achieving synchronization, and the modulation type; (3) A general description of the type of information being conveyed (voice, text, memory dump, facsimile, television, etc.); (4) The method and, if applicable, the frequency or frequencies used for station identification; and (5) The date of beginning and the date of ending use of each type of transmitted signal. (f) When deemed necessary by an ErC to assure compliance with this Part, a station licensee must:

(1) Cease 55 emission transmissions; (2) Restrict 55 emission transmissions to the extent instructed; and (3) Maintain a record, convertible to the original information (voice, text, image, etc.) of all spread spectrum communications transmitted. (g) The transmitter power must not exceed 100 W.

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FCC Proposed Amateur Radio Service Spread Spectrum Rule Making (RM-8737) Before the Federal Communications Commission Washington, D. C. 20554 In the Matter of Amendment of the Amateur Service Rilles to Provide For Greater Use of Spread Spectrum Communication Technologies

) WT Docket No. 97-12 ) ) RM-8737 ) ) ) )

NOTICE OF PROPOSED RULE MAKING Adopted: January 9, 1997

Released: March 3,1997

Comment date: May 5, 1997 Reply comment date: June 5, 1997 By the Commission: I. INTRODUCTION AND EXECUTIVE SUMMARY 1. On December 12, 1995, the American Radio Relay League, Inc. (ARRL) filed a petition for rule making ("Petition") requesting amendment of the rules to allow amateur stations to transmit spread spectrum ("55") type emission technologies employing additional spreading sequences. It also requests that each 55 transmitter be required to incorporate a device to automatically limit its power to that actually necessary to carry out the communications. The ARRL believes that these rule changes would facilitate the ability of the amateur service to contribute to the development of 55 communications. 2. This Notice of Proposed Rule Making ("Notice") proposes to amend the Commission's rules for the Amateur Radio Services to authorize amateur stations to make greater use of 55 type emission technologies. We believe that our proposed rule changes will allow amateur operators to develop innovations and improvements to communications products, and develop new communications technologies. We believe these proposed rule changes also would allow amateur operators more flexibility to use current and future communications technologies, encourage the amateur service community to expand its experimental activities with 55, and allow amateur stations to transmit 55 type emissions that presently are transmitted by other communications devices. These proposed changes also are consistent with our general policy of allowing licensees flexibility to develop more effective and efficient uses of the radio spectrum.

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II. BACKGROUND

3. Spread spectrum is a technique whereby the energy of the transmitted signal is distributed over a wide segment of spectrum. The signal power density can be very low and the duration of a transmission on any frequency in the segment of the spectrum can be but a fraction of a second. SS systems, therefore, can evenly share all of the spectrum in the available frequency segment, despite a number of stations transmitting simultaneously. They can often share the same spectrum unobtrusively with non-55 systems because the transmissions may not be noticeable to a casual listener. 4. Special Temporary Authority to experiment with SS transmissions was granted to 25 amateur stations affiliated with the Amateur Radio Research and Development Corporation 16 years ago. These experiments involved on-air evaluation of different spreading rates, frequency ranges, and interference to stations transmitting other emission types . On the basis of these tests, two types of spreading techniques -- frequency hopping and direct sequence -- were authorized by our rules. Under our current rules, SS transmissions may be made on authorized amateur service frequencies above 420 MHz with transmitter powers up to 100 watts. Since introduction of SSin the amateur radio service, numerous commercial applications of SShave also evolved, including personal communications services, remote meter reading and position locating. III. DISCUSSION

5. Comments. The Petition was placed on Public Notice January 26, 1996. In response to the Public Notice requesting statements opposing or supporting the Petition, we rece ived 32 comments and reply comments. The majority of commenters support additional SS communications because of the benefits that may come from experimentation, but suggest that SSbe limited to specificspectrum segments of the amateur service frequency bands to protect stations engaged in other types of communication. Some commenters oppose SSdue to concerns that greater use of SSwill result in interference to amateur stations engaging in satellite communications, weak signal terrestrial and Earth-Moon-Earth communications, and repeaters. In reply, the ARRLargues that the interference potential would not significantly increase because the rules already authorize SSon these amateur service bands. Also, the ARRL points out that concern regarding interference to repeaters is unfounded because most repeater usage occurs on the amateur bands below 420 MHz. 6. Two commercial Part 15interests, Metricom and Symbol Technologies,request that new types of amateur SS transmissions in the 902-928 and 2400-2450 MHz amateur frequency bands be prohibited or alternatively, that radiated power limits for new SStypes be limited to those governing the unlicensed Part 15 devices with which these bands are shared. Metricom, a service provider using unlicensed devices, acknowledges that spread spectrum experimentation accomplished in the amateur radio service enabled it to develop what it describes as its own technologically leading edge SS systems. However, Metricom also argues that

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172 . Regulatory

increasing the flexibility for amateur operators to experiment with new types of spread spectrum designs in these two bands would disturb the balance in sharing these bands among different users . Metricom expresses particular concern regarding the 902-928MHz band, citing our recent Report and Orderestablishing rules for Automatic Vehicle Monitoring Systems . In an Ex Parte filing, Metricom also expresses concern that amateurs operators will obtain commercial Part 15 SS devices and modify them for use under our Part 97 rules. Symbol, a manufacturer of unlicensed devices that operate in these two bands, argues that the disparity between authorized power for amateur stations (100watts with unlimited antenna gain) and authorized power for unlicensed devices (1 watt with 6 dBi antenna gain) will affect the operation of unlicensed devices in the vicinity of amateur stations. 7. In reply, the ARRL argues that the potential for interference in these bands would not increase significantly because SS has been authorized at the proposed power levels for more than a decade. The ARRL goes on to note, however, that in its petition it proposed to control power by proposing to require automatic transmitter power control to limit radiated power to that level necessary to maintain communications. The ARRL acknowledges the underlying concern that amateur operators might purchase and modify commercial SSproducts. In response to this concern, ARRL contends that even if this were to occur, interference would be unlikely because such products likely will be designed to use different spreading codes and sequences so that they will not interact with each other when used as unlicensed devices. ARRLfurther contends that this design feature will minimize interference whether used as unlicensed devices or as amateur stations. Finally, the ARRL notes that the amateur radio service is a licensed service entitled to protection from interference, whereas unlicensed Part 15 devices have no interference protection rights under our rules and no domestic or international allocation status. 8. Webelieve that the amendments requested would increase spectrum efficiency and allow amateur operators to contribute to technological advances in communications systems and equipment. Experiments conducted by amateur operators have shown that stations transmitting SS emissions can co-exist with other amateur stations, and in many cases these spread spectrum emissions are undetectable by other amateur stations. SS publications in the amateur service community, and the comments of the ARRL, show that the effect of restricting amateur stations to using two spreading techniques has been to prevent amateur service licensees from incorporating into their operations technical advances that have been developed in other services. We agree that the current rule prohibits amateur stations from using SS emission types that are routinely used in other communication services, and that such a prohibition is inconsistent with the experimental purpose of the amateur service. As requested by the ARRLand Part 15 equipment providers, we propose to require that automatic power control circuitry which reduces the radiated power of an amateur station transmitting an SS emission to the minimum level necessary to conduct communications, be included in SS equipment. Additionally, we solicit comments, regarding other methods that are available to minimize any potential interference between amateur

173

station operations and Part 15 devices. Accordingly, we tentatively conclude that these amendments are appropriate and consistent with the underlying purposes of the amateur service. We propose, therefore, to facilitate the desire of amateur operators to experiment with, develop, improve, and test practical SS systems. 9. In view of the foregoing, we propose to amend the amateur service rules to allow amateur stations greater flexibility in transmitting SS communications. Specifically, we propose to eliminate the rules that restrict amateur stations to transmitting only frequency hopping and direct sequencing spreading techniques. These proposed rule changes are consistent with our policy of encouraging greater spectrum flexibility by enabling licensees to introduce innovative technologies and to respond quickly to demands for new and different services and applications, without administrative delays. IV: PROCEDURAL MATIERS Regulatory Flexibility Act 10. As required by Section 603of the Regulatory FlexibilityAct, the Commission has prepared an Initial Regulatory Flexibility Analysis (IRFA) of the expected significant economic impact on small entities by the policies and rules proposed in this Notice. Written public comments are requested on the IRFA. Comments must be identified as responses to the IRFA and must be filed by the deadlines for comments on the Notice provided below. Initial Regulatory Flexibility Analysis 1. Need for and Objectives of the Proposed Rule: The need for and objective of this rule making proceeding is to eliminate technical restrictions that amateur radio operators claim hamper their flexibility to experiment with SS emission types.

II. Legal Basis: Authority for this action can be found in Sections 4 (i), and 303(a), (1)(1), and (r) of the Communications Act of 1934, as amended, 47 USc. 154(i),and 303(a), (1)(1), and (r), III. Description and Estimate of the Number of Small Entities To Which Rule Will Apply: None. The rules in Part 97 of the Commission's Rules, 47 c.F.R. Part 97, apply to individuals who are qualified to be licensees and/or control operators of amateur radio stations. Small businesses are not eligible to be licensees in the amateur service, and amateur radio operators are prohibited from transmitting communications for compensation, for their pecuniary benefit, and on behalf of their employers. See 47 c.F.R. 97.113. IV. Description of Projected Reporting, Recordkeeping and Other Compliance Requirements: None. This rule making proceeding does not impose any new or additional recordkeeping, reporting or compliance requirement on amateur service licensees.

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Regulatory

V. Significant Alternatives To Proposed Rule Which Minimize Significant Economic Impact on Small Entities and Accomplish Stated Objectives: None. This proceeding will effect only amateur stations that choose to transmit a spread spectrum emission using a spreading technique that is not permitted under the currently effective rules . Small businesses are not eligible to be licensees in the amateur service, and amateur radio operators are prohibited from transmitting communications for compensation, for their pecuniary benefit, and on behalf of their employers. See 47 CER. 97.113.

VI. Federal Rules that May Duplicate, Overlap, or Conflict With the Proposed Rule: None. Ex Parte Rules - Non-Restricted Proceeding

11. This is a non-restricted notice and comment rule making proceeding. Ex Partepresentations are permitted, except during the Sunshine Agenda period, provided that they are disclosed as specified in the Commission's Rules. See generally 47 CER. 1.1202,1.1203,and 1.1206(a). Comment Dates

12. Pursuant to applicable procedures set forth in Sections 1.415 and 1.419 of the Commission's Rules, 47 CER. 1.415 and 1.419, interested parties may file comments on or before May 5,1997, and reply comments on or before June 5,1997. To file formally in this proceeding, you must file an original and four copies of all comments and reply comments. If you want each Commissioner to receive a personal copy of your comments, you must file an original plus nine copies. You should send comments and reply comments to Office of the Secretary, Federal Communications Commission, Washington, DC 20554. Comments and reply comments will be available for public inspection during regular business hours in the FCC Reference Center of the Federal Communications Commission (Room 239), 1919 M Street, N. W., Washington, DC 20554. Ordering Clauses

13. Accordingly, IT IS ORDERED that, pursuant to Sections 4 (i), and 303(a), (1)(1), and (r) of the Communications Act of 1934, as amended, 47 U.s.C 154 (i), and 303(a), (1)(1), and (r), notice is hereby given of proposed amendments to Part 97 of the Commission's Rules, 47 CER. Part 97, in accordance with the proposals, discussions, and statement of issues in this Notice of Proposed Rule Making. Comment is sought regarding such proposals, discussions, and statements. 14. IT IS FURTHER ORDERED that the Secretary shall mail a copy of this document to the Chief Counsel for Advocacy of the Small Business Administration in accordance with paragraph 605(b) of the Regulatory Flexibility Act. Pub . L. No . 96-354,94 Stat. 1164,5 U.s.C 601-612 (1980).

175

Contact Person

15. For further information concerning this proceeding, contact William T.Cross, Wireless Teleconununications Bureau, (202)418-0680. FEDERAL COMMUNICATIONS COMMiSSION William F. Caton Acting Secretary APPENDIX A Comments Mid-America Coordination Council, Inc. SouthEastern Repeater Association, Inc. Wisconsin Association of Repeaters Southern California Repeater and Remote Base Association The San Bernadino Microwave Society The Indiana Repeater Council The Central States VHF Society Mike Cheponis John Mock George R. Isely HenryB.Ruh N ational Conununications System Tucson Amateur Packet Radio Corporation Robert A. Buaas Charles M. Albert, Jr. Reply Comments American Radio Relay League, Inc. Naval Postgraduate School Radio Amateur Satellite Corporation Manager, National Conununications System Metricom, Inc. Tucson Amateur Packet Radio Corporation Robert S. Larkin James E. Mitzlaff Robert Brown Paul H. Trotter Ronald Klimas Mike Cheponis Philip R. Karn Robert A. Buaas Robert J. Carpenter Steven R. Bible William A. Tynan

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Regulatory

APPENDIXB

Part 97 of Chapter I of Title 47 of the Code of Federal Regulations is proposed to be amended as follows: Part 97 - Amateur Radio Service 1. The authority citation for Part 97 continues to read as follows: Authority citation: 48Stat. 1066,1082,as amended; 47 U.s.c. 154,303. Interpret or apply 48 Stat. 1064-1068, 1081-1105, as amended; 47 u.s.c 151-155,301-609, unless otherwise noted. 2. In Section 97.3, paragraph (c)(8) is revised to read as follows: 97.3(c)(8) Definitions. (a) *** (c) ***

(8) SS. Spread-spectrum emissions using bandwidth-expansion modulation emissions having designators with A, C, 0, F,G, H, J or R as the first symbol; X as the second symbol; X as the third symbol. * * * * *

3. Section 97.305(b) is revised to read as follows: 97.305 Authorized emission types. ****

(b) A station may transmit a test emission on any frequency authorized to the control operator for brief periods for experimental purposes, except that no pulse or SSmodulation emission may be transmitted on any frequency where pulse or SS emissions are not specifically authorized. * * * * *

4. Section 97.311 is revised by revising paragraphs (a) and (b) and redesignating paragraphs (c) and (d) as "Reserved" to read as follows: 97.311 SS emission types. (a) SS emission transmissions by an amateur station are authorized only for communications between points within areas where the amateur service is regulated by the FCC and between an area where the amateur service is regulated by the FCC and an amateur station in another country that permits such communications. SS emission transmissions must not be used for the purpose of obscuring the meaning of any communication.

177

(b) A station transmitting SS emissions must not cause harmful interference to stations employing other authorized emissions, and must accept all interference caused by stations employing other authorized emissions.

(c) Reserved. (d) Reserved. (e) *****

(f) *****

(g) The transmitter power must not exceed 100 W under any circumstances. If more than 1 W is used, automatic transmitter control shall limit output power to that which is required for the communication. This shall be determined by the use of the ratio, measured at the receiver, of the received energy per user data bit (Eb) to the sum of the received power spectral densities of noise (NO) and co-channel interference (10). Average transmitter power over 1 W shall be automatically adjusted to maintain an Eb/ (NO + 10) ratio of no more than 23 dB at the intended receiver.

Current Information on Amateur Spread Sp~trum Rule Changes Visit http://www.tapr.org/ssfor a list of comments and reply comments available on-line to RM-8737. Latest information regarding Amateur Radio Service Spread Spectrum rule making can also be found.

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Regulatory

TAPR Comments to NPRM on Amateur Radio Service Spread Spectrum Rule Making (RM-8737) Before the Federal Conununications Commission Washington, D. C. 20554 In the Matter of

) WT Docket No. 97-12 )

Amendment of Part 97 of the Commissions Rules Governing the Amateur Radio Service to Facilitate Spread Spectrum Conununications

) RM-8737 ) ) ) )

COMMENTS OF TUCSON AMATEUR PACKET RADIO CORPORATION The Tucson Amateur Packet Radio Corporation ("TAPR") submits these conunents in response to the above-referenced petition for rule making (the "Petition") filed by the American Radio Relay League, Incorporated ("ARRL"). BACKGROUND AND STATEMENT OF INTEREST

TAPR is a non-profit (501(c)(3)) scientific and educational organization w ith more than 2,500 members worldwide. It is chartered to engage in three principal activities: scientific testing and research into the development and improvement of technological systems for use in the amateur radio service including, but not limited to, digital packet radio conununications; research and testing of systems, hardware, and software for packet radio local area networks and computer network systems; and disseminating to the public the information obtained as a result of such research and testing. TAPR was founded in 1982 as a national organization with interests in the areas of packet and digital conununications. It grew out of a 1981 effort to design a packet radio Terminal Node Controller, or "TNC," that would be available to amateurs at a modest cost. From these initial designs emerged what is now the de facto standard in amateur and many conunercial packet radio operations. Today, TAPR continues as an international, membership-supported research and development organization for the amateur radio conununity. TAPR continues to develop new conununications technology, provide kits for the amateur conununity, and promote the advancement of the amateur art through publications, meetings, and conununications standards. TAPR also maintains a web site (http: / /www.tapr.org), which includes a page specifically addressing current amateur spread spectrum issues (http:/ / www.tapr.org/ss).

179

DISCUSSION

TAPR generally supports the recommendations made by the ARRL in its Petition. Spread Spectrum ("SS") teclmology has not made great advances in the amateur radio service since it was first permitted in 1985,in part due to the fact that, by today's standards, the Part 97 regulations on amateur spread spectrum are extremely restrictive. In particular, the small number of fixed spreading codes permitted under Section 97.311(d)(1) inhibits the use and development of SSby amateur radio stations. TAPR believes that it is in the public interest, and in the interest of the amateur radio service, to change the rules for SS in order to accelerate the adoption of SS by the general amateur community. TAPR also supports many of the specific recommendations made by the ARRL. First, TAPR supports the ARRL's request to modify Part 97.311(b) as it pertains to the unintentional triggering of repeater inputs. This section is redundant with other parts of the Commission's rules and, therefore, is unnecessary. Second, TAPR supports the ARRL's request to delete sections 97.311(c) and (d), in order to permit SS emissions and spreading codes that are not currently authorized. Elimination of the rule that dictates specific spreading codes is necessary to facilitate further experimentation and to match the provisions allowed under an existing amateur service SSSTA, discussed below. In addition, it would facilitate the use and adoption by amateur radio operators of Part 15 SSequipment and hardware. Third, TAPR supports the ARRL's proposed change to 97.311(g), which would provide for automatic transmitter power control to limit the output power of an SS station to that which is required for communication, when more than one watt of output power is used. TAPR, however, differs with the ARRL as to just how simple this requirement would be to implement technically. While TAPR agrees that technically it is simple to control the output power of a transmitter, it is quite another matter to make this control automatic and foolproof. If the Commission decides to proceed with this particular change to the rules, it should phase the change in over some reasonable period of time, in order to give the amateur community the opportunity to develop and deploy SS equipment that properly can meet this requirement. While, as noted above, TAPRagrees with many of the ARRL's recommendations, it disagrees with a few of the proposals contained in the Petition. In particular, TAPR differs with the ARRL with respect to the question of which frequencies should be authorized for SS emissions. In the Petition, the ARRL proposes that brief test transmissions of SS emissions be permitted only on those frequency bands in which SS emissions currently are

.

180

Regulatory

authorized. TAPR believes that 55 emissions should be allowed on all frequency bands covered by the 55 5TAcurrently held by Mr. Robert Buaas K6KG5 (6m and 2m, in addition to the frequency bands currently authorized by Part 97). In addition, the Commission should allow 55 emissions in the 219-210MHz band, which was authorized for use by the amateur radio service after the Buaas 55 5TAwas originally granted in 1992. Finally, the Commission should not impose any restriction on the length of time 55 emissions are transmitted. Ample time already has been provided for the experimental phase of 55 usage in the amateur service (five years of experimentation under the 1980AMRAD 5TA and ten years under the current Part 97 rules), and it is now time to allow 55 use without restriction. TAPR also differs with the ARRL as to how station identification and documentation should be handled under a revised set of rules. The ARRL in its petition did not ask the Commission to delete sections 97.311(e) and 97.119(b)(5) of the rules, even though it questioned the practicality of the requirements set forth in these sections. TAPR, in contrast, recommends that the Commission delete these subsections of the rules . The interference and harm to the band in which an 55 station is operating that would be caused by a requirement to use a CW identification outweighs the benefits that would accrue for monitoring purposes from the use of the ro. As a result, the amateur radio community should be permitted to develop an approach for handling the necessary functions of monitoring and identification. TAPR already is working on possible resolutions to this problem and in the near future will be in a position to make a proposal to the Commission on this matter. CONCLUSION

55 technology can provide many useful benefits to the amateur radio community if its use becomes more widespread and mainstream. In order to accomplish this, however, certain changes must be made to the Commission's rules governing the use of 55 in the amateur radio service. By making these changes, the Commission will create a regulatory environment that will give members of the amateur radio service enough flexibility to develop innovative equipment and hardware employing 55 technology For these reasons, TAPR urges the Commission promptly to issue a notice of proposed rule making to facilitate spread spectrum communications in the amateur radio service, as proposed in the Petition and as modified herein. Respectfully submitted, THE TUC50N AMATEUR PACKET RADIO CORPORATION

181

TAPR Reply Comments to NPRM on Amateur Radio Service Spread Spectrum Rule Making (RM-sn7) Before the Federal Communications Commission Washington, D. C. 20554 In the Matter of

) WT Docket No . 97-12 )

Amendment of Part 97 of the Commissions Rules Governing the Amateur Radio Service to Facilitate Spread Spectrum Communications

) RM-8737 ) ) ) )

REPLY COMMENTS OF TUCSON AMATEUR PACKET RADIO CORPORATION

The Tucson Amateur Packet Radio Corporation ("TAPR") submits the following reply comments regarding the Petition for Rulemaking (the "Petition") filed by the American Radio Relay League CARRL"), which proposed certain changes in the rules governing spread spectrum operation in the Amateur Radio Service CARS"). I. PERMITTING MORE WIDESPREAD SPREAD SPECTRUM OPERATION IN THE ARS WOULD SERVE THE PUBLIC INTEREST.

A number of the comments recognized the benefits that could be provided by more widespread use of spread spectrum technologies in the ARS (1). In addition to those that would accrue to ARS operators, as described in the Petition, increased use of spread spectrum in the ARS would contribute to the overall development of spread spectrum communications (2) and, as a result, would provide benefits indirectly to commercial users as well. Expanded use of spread spectrum in the ARS also would further the Commission's objective of promoting efficient spectrum use. At the FCC's March 5,1996 en bane hearing on spectrum policy, Paul Barens, the "father" of one of the technologies that forms the basis of the Internet, made the following statement: "What do we see today if we tune a spectrum analyzer or a radio receiver across most of the scarce spectrum bands? Mostly nothing. Dead air. This strongly suggests that most of our limited spectrum space is not being fully utilized and is going to waste. Specifically, with digital technology, spectrum bands can be more efficiently packed without interfering with existing services."

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182

Regulatory

By increasing the ability of ARS operators to use spread spectrum technologies, the Commission would enhance their ability to use digital technologies to enhance spectrum efficiency,as recommended in the above passage. In tum, the Commission also would make it possible for the ARS better to accommodate the many new users seeking to use ARS bands, which are already congested due to the widespread use of non-digital equipment. Although spread spectrum is not a panacea, it offers the promise of increased spectrum efficiency, reduced interference, and improved communication performance without adversely affecting other spectrum users. As a result, the Commission's rules governing spread spectrum operation should be modified to enable these technologies to flourish within the amateur service community.

II. EXPANDED SPREAD SPECTRUM OPERATIONS WILL NOT ADVERSELY AFFECT OTHER ARS OPERATIONS. Several repeater coordinating organizations, who are responsible for the coordination of repeater operations in their regional areas of activity, filed comments opposing to the Petition. These entities generally alleged that adoption of ARRL's proposals would cause widespread interference to, and disruption of, existing operations. The fears and concerns expressed in these comments defy the proven ability of properly designed and implemented spread spectrum systems to operate in harmony with other spectrum users, are based upon "worst-case" scenarios, and reflect a desire to maintain the status quo even at the cost of stifling new technologies and services. As a result, they should not be permitted to prevent the development of spread spectrum in the ARS. First, as discussed by Robert Buaas, claims that spread spectrum operation will raise the noise floor ignore the fact that few real systems operate near the noise floor, and those that do would profit from applying spread spectrum technology (3). Second, in the ten years since the Commission first allowed limited spread spectrum operation in the ARS,a great deal of work has been done to address concerns that more flexiblespread spectrum operationwould adversely affect other types ofARSoperations. Inparticu1ar,the 1991Buaas spread spectrumSTAhas made it possible for experimenters to engage in widespread use of spread spectrum technologies in the amateur band allocations below 450 MHz. Notably, operation under the existing spread spectrum rules and experimentation under the spread spectrum STA have not generated substantiated claims of objectionable interference (4). Finally, the successful operation of Part 15 spread spectrum systems provide substantial evidence of the ability of these devices to co-exist with other users. Today, millions of spread spectrum devices operating under Section 15.247 of the Commission's rules are being used to support end-user solutions in areas such as cordless phones, location monitoring devices, and local and metropolitan-area

183

networking. These devices have been deployed across the United States without any local coordination and without any licensing by the Commission. Yet despite this flexibility and extensive use, spread spectrum Part 15 devices have almost universally operated without causing objectionable interference to other Part 15 devices or to others operating in shared spectrum (5). This success story provides ample proof that when spread spectrum devices are properly designed, manufactured, and deployed, they can coexist successfully with many diverse applications and, in addition, can facilitate frequency reuse. In light of this history of successful, non-interfering operation, the Commission should not permit unsubstantiated claims of potential interference to thwart the introduction and use of new spread spectrum technologies in the ARS (6). III. SECTION 97.119(B)(S) OF THE RULES SHOULD BE DELETED, AS SUGGESTED BY NCS.

TAPR supports the suggestion made by the Manager of the National Communications System ("NCS")to delete Part 97.119 (b)(5),which deals with the requirement for CW identification. TAPR agrees that no currently available commercial equipment implements such a function, and that deletion of this requirement will act to speed the rapid adoption of this equipment into use in the ARS.

CONCLUSION

TAPR congratulates the ARRL for its forward-looking proposal to liberalize the spread spectrum rules in the ARS. ARRL's proposal, if adopted, could provide a variety of benefits to both members of the amateur service community and to the wider public. Proposals to modify the status quo often generate opposition by those who are adequately served by it. Like the turmoil that occurred in the ARS during the transition from AM to SSB, the growing use of spread spectrum in the service will not be without incidents of disagreement and misunderstanding. For this reason, TAPR intends to use its resources during the rulemaking process to educate the ARS community on the theory, application, and practice of spread spectrum technology. Yetwhile fear and opposition are understandable, they should not be permitted to stifle new developments. In light of spread spectrum's strong track record and proven benefits, unsubstantiated claims of potential interference should be discounted and the Commission should act promptly to issue a Notice of Proposed Rulemaking proposing to implement the changes sought by ARRL, modified as discussed in TAPR's earlier comments.

184

Regulatory

Respectfully submitted, THE TUCSON AMATEUR PACKET RADIO CORPORATION

By: Dewayne Hendricks Tucson Amateur Packet Radio Corporation 8987-309 E Tanque Verde Rd #337 Tucson, Arizona 85749-9399 (817)383-0000 (1) See, e.g., Comments of Robert A. Buaas ("Buaas Comments"); Comments of the Manager of the National Communications System ("NCS Comments"); Comments of John Mock; Comments of Henry B. Ruh; see also ARRL Petition. (2) See NCS Comments at p. 3. (3) Buaas Comments at p. 2. (4) Buaas Comments at P: 3. (5) See Comments of the Part 15 Coalition, PR Docket No. 93-61 (1995). (6)TAPRbelieves that a program of continuing education to the ARScommunity on the merits and benefits of spread spectrum technology coupled with a wider use and deployment of equipment by amateurs in various applications will go a long way towards resolving the concerns of many of the commenters who have filed in opposition. TAPR intends to use its resources to perform this function and service for the amateur radio community in much the same fashion that it helped start the packet radio revolution in the ARS during the mid-1980's.

185

Wireless LAN/MAN Modem Product Compiled by Barry McLarnon, VE3JF. http://hydra.carleton.ca/info / wlan.html

Introduction This is a survey of currently available wireless RF modem products suitable for w ireless LAN and MAN applications. At the moment, this survey includes only those products which are suitable for unlicenced operation in the ISM bands: 900 MHz (902-928 MHz), 2.4 GHz (2400-2483.5 MHz) and 5.8 GHz (5725-5850MHz). Some of these products are intended for very short range wireless applications, while others are designed to be used as longer-haul point-to-point wireless bridges, and some can be used in either role. No attempt has been made to differentiate between these usages in this survey. Also, I don't necessarily list every product in each vendor's wireless product line. Some product lines have many different variants, and the tables would get too unwieldy if I tried to list them all, but I try to include some representative products from each manufacturer. I tend to omit the "access point" products, and products in which the WLAN modem is integrated into something else, such as a portable computer. The vast majority of the products listed u se spread spectrum modulation techniques, since that is where my main interest lies. Most of the information presented here was taken from manufacturers' literature, so the figures concerning data rates and ranges are subject to specmanship. Caveat emptor! Accurate pricing information is also hard to come by, and subject to inaccuracies, so don't take what you see here as gospel. It's possible that some of the products listed are actually "vaporhardware". If you have any information along these lines, please let me know. This survey covers only complete wireless modem products (i.e., plug-in cards or standalone units). It does not cover chip sets, amplifiers, etc. Many of these other products can be found in Lee Fry's Spread Spectrum Device Compendium (http:/ /www.mindspring.com/~lfry/part15.htrn). Infrared wireless technology is a viable alternative for some WLAN applications.

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Product

Type

Data Rate

Power

Cylink

AirPro T1

DS

1.544 Mbps

-

-

35 km

standalone (DSX-l)

Glenayre

Lynx.sc Model 31000

DS

1.544 Mbps

23 dBm

-

80 km

standalon e (DSX-l)

Glenayre

Lynx.sc Model 31600

DS

2 X 1.544 Mbps

23 dBm

-

80 km

standalon e (DSX-l)

P-COM

Model 100-5

DS

56 Kbps to 2.048 Mbps

100mW

-

50 km

"standalone (V.35, DSX-I, G.703)"

RadioLAN

Model 101 Wireless ISA CardLINK

NB

10 Mbps

50mW

36 m

91m

ISA card

RadioLAN

Model PIOI Wireless PC CardLINK

NB

10 Mbps

50mW

36 m

91 m

PCMCIA card

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Vendor

Product

Type

Data Rate

Power

RadioLAN

Model lOA Wireles s NetworkLINK

NB

10 Mbps

50mW

36 m

91 m

ISAcard

RadioLAN

Model BL208 Wireless BackboneLINK

NB

10 Mbps

50mW

36 m

91 m

standal one (ethernet)

Windata

FreePort

DS

5.7 Mbps

I WERP

80 m

-

standal one (ethernet)

Windata

AirPort II

DS

5.7 Mbps

I WERP

-

2.9 km

standalone (ethernet)

2.4 GHz Wireless LAN/MAN Modem Produ Maximum Range Indoor I Outdoor

Vendor

Product

Type

Data Rate

Power

Aerotron

NLR-2.4T

DS

19.2 Kbps

500mW

450 m

2.4 km

Airon et

ARLAN 6552400

DS

1-2 Mbps

100mW ERP

150 m

5 km

Aironet

ARLA N 6902400

DS

1-2 Mbps

100mW ERP

150 m

5 km

PCMCIA Type II

Altvater

WIM ANline

FH

625 Kbps*

100mW (US: IW)

-

5 km (US: 30 km)

standalone (RS232, X.2IN.II )

Breezecom

AP- IO Access Point

FH

1-3 Mbps

10/100 mW

100 m

500 m

standal one (IOBaseT )

Breezecom

AP- IO PRO Access Point

FH

1-3 Mbps

10/100 mW

150 m

I km

standalone (IOBaseT)

Bree zecom

SA-IO Station Adapter

FH

1-3 Mbps

10/100 mW

100 m

500 m

standalone (IOBaseT)

Bree zecom

SA- IO PRO Station Adapter

FH

1-3 Mbps

10/100 mW

150 m

I km

standa lone (IOBaseT)

Breezecom

SA-40 Station Adapter

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1-3 Mbps

10/100 mW

100 m

500 m

standalone (4X JOBaseT)

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2.4 GHz Wireless LAN/MAN Modem Prod Vendor

Product

Type

Data Rate

Power

Maximum Range IndoorI Outdoor

Configuration

Breezecom

SA-40 PRO Station Adapter

FH

1-3 Mbps

10/100 mW

150 m

1 km

standalone (4X lOBaseT)

Breezecom

SA-PX PCMCIA Adapter

FH

1 Mbps

50mW

70m

300m

PCMCIA

Breezecom

SA-PC PRO PC Card

FH

1-3 Mbps

10/100 mW

-

600 m

PCMCIA

Breezecom

WB-IO Wireless Bridge

FH

1-3 Mbps

0.1-4 W ERP

200m

1-10 km

standalone (10BaseT)

FH

56 Kbps 2.048 Mbps

50mW

-

1-32 km

(TIIEI, V.35,

Breezecom

BreezeLINK-121 Wireless EltTl

standalone

RS-530, X.21)

Clarion

MlO

DS

10 Mbps

-

100m

8 km*

standalone (ethernet AU!)

CRL

DS 16-24/1SA

DS

1 Mbps

60mW

50 m

1 km

ISA card*

C-SPEC

WaveLAN PCAT Wireless Adapter

DS

2 Mbps

88mW

240m

-

ISA card

2.4 GHz Wireless LAN/MAN Modem Produ Vendor

Product

Type

Data Rate

Power

Maximum Range Indoor I Outdoor

C-SPEC

WaveLAN PCMCIA Wireless Adapter

DS

2 Mbps

88 mW

240m

-

PCMCIA Type II

C-SPEC

OverLAN Wireless BridgelRouter

DS

2 Mbps

88mW

150 m

8 km

standalon e (ethernet)

C-SPEC

OverLAN RF10 Wireless BridgelRouter

DS

10 Mbps

-

-

24 km*

standalon e (ethernet)

Cylink

AirLink 64SMP

DS

64 Kbps

650mW

300m

48 km

standalon e (RS232/422, V.35)

Cylink

AirLink 128S

DS

128 Kbps

650 mW

300 m

48 km

standal one (RS232/422 , V.35)

Cylink

AirLink 256S

DS

256 Kbps

650mW

300 m

48 km

stand alone (RS232/422, V.35)

Cylink

AirLink 384S

DS

384 Kbps

650mW

300 m

48 km

standal one (RS232/422 , V.35)

Configuration

2.4 GHz Wireless LAN/MAN Modem Prod Maximum Range Indoor I Outdoor

Vendor

Product

Type

Data Rate

Power

Cylink

AirLink 512S

DS

512 Kbps

650mW

300m

48 km

standalone (RS232/422, V.35)

DATA-LINC

SRM6000H

FH

Up to 115.2 Kbps

-

450m

30-50 km

standalone (RS232/422/48 5)

DCT

VLl28

DS

128 Kbps*

18 dBm

-

48 km

standalone (RS232/422N 35)

DCT

VL256

DS

256 Kbps*

18 dBm

-

48 km

stand alone (RS232/422N. 35)

DCT

VirtualNet PCMCIA Adapter

DS

1-4 Mbps

18 dBm

125 m

1.1 km

PCMCIA Typ II

DCT

VirtualNet ISA PC Adapter

DS

1-4 Mbps

18 dBm

125 m

1.1 km

ISA card

DCT

VirtualNet Access Point

DS

1-4 Mbps

18 dBm

125 m

1.1 km

standalone (ethernet)

DEC

Roamabout 2400 FH/ISA NIC

FH

1.6 Mbps

100mW

150 m

300m

ISA card

Configuratio

2.4 GHz Wireless LAN/MAN Modem Prod Maximum Range Indoor I Outdoor

Vendor

Product

Type

Data Rate

Power

DEC

Roamabout 2400 FHlPC Card

FH

1.6 Mbps

IOOmW

150 m

300m

PCMCIA Type II

DEC

Roamabout 2400 DS/ISA NIC

DS

2 Mbps

88mW

240m

-

ISA card

DEC

Roamabout 2400 DS/PC Card

DS

2 Mbps

88mW

240 m

-

PCMCI A Type II

Digital Wireless

WIT2400M

FH

115.2 Kbps

-

300 m

Ikm

OEM module (RS232)

DTS

Skyplex I

DS

1.2 - 512 Kbps*

-

-

100 km*

Configuration

standalone (RS232/RS422

EIA530N.35)

DTS

Skyplex II

DS

1.544 Mbps*

8 or 28 dBm

-

-

standalone (DSX-I )*

Glenayre

Lynx cp2

DS

1.544 Mbps

Up to 1 W

-

48 km

standalone (DSX-I)

GRE

GINA 8000NVK

DS

64 Kbps

725mW

240 m

19 km

(RS232/44 9,

standalone V.35)

2.4 GHz Wireless LAN/MAN Modem Prod Vendor

Product

Type

Data Rate

Power

Maximum Range Indoor / Outdoor

IBM

Wireless LAN ISAlMicro Chann el

FH

0.5-1.2 Mbps

IOOmW

250 m

-

ISAlMi cro Channel card

IBM

Wireless LAN PCMCI A

FH

0.5-1.2 Mbps

100mW

250 m

-

PCMCI A Type II

IBM

Wireless LAN Entry 8227 Access Point

FH

350 Kbps

IOOmW

180 m

-

standalon e (ethernet)

IBM

Wireless LAN Entry PCMCIA

FH

350 Kbps

100mW

180 m

-

PCMCIA Type II

InTalk

ST500

OS

2 Mbps

-

60-90 m

915 m

PCMCIA car

InTalk

WRIOOO Access Point

OS

2 Mbps

-

60-90 m

9 15 m

standal one (ethernet)

KarlNet

WaveLAN PCAT Wireless Adapter

OS

2 Mbps

88mW

240 m

-

ISA card

KarlNet

WaveLAN PCMCIA Wireless Adapter

OS

2 Mbps

88mW

240 m

-

PCMCIA Type II

Configuratio

2.4 GHz Wireless LAN/MAN Modem Prod Maximum Range Indoor I Outdoor

Vendor

Product

Type

Data Rate

Power

IBM

Wireless LAN ISA/Micro Channel

FH

0.5-1.2 Mbps

100mW

250 m

-

ISA/Mic ro Channel card

IBM

Wireless LAN PCMCIA

FH

0.5-1.2 Mbps

100mW

250 m

-

PCMCI A Type II

IBM

Wireless LAN Entry 8227 Access Point

FH

350 Kbps

100mW

180 m

-

standalone (ethernet)

IBM

Wireless LAN Entry PCMCIA

FH

350 Kbps

100mW

180 m

-

PCMCIA Type II

InTalk

ST500

DS

2 Mbps

-

60-90 m

9 15 m

PCMCIA card

InTalk

WRIOOO Access Point

DS

2 Mbps

-

60-90 m

9 15 m

standalone (ethernet)

KarlNet

WaveLAN PCAT Wireless Adapt er

DS

2 Mbps

88mW

240 m

-

ISA card

Configuration

2.4 GHz Wireless LAN/MAN Modem Prod Vendor

Product

Type

Data Rate

Power

Maximum Range Indoor I Outdoor

KarlNet

WaveLAN PCMCIA Wireless Adapter

DS

2 Mbps

88mW

240 m

-

PCMCIA Type II

KarlNet

Wireless KarlBridge

DS

2 Mbps

88mW

150 m

8 km

standalone (ethernet)

KarlNet

Wireless KarIBridge BridgelRouter

DS

2 Mbps

88mW

150 m

8 km

standalone (ethernet)

Lucent

WaveLAN PCAT Wireless Adapter

DS

2 Mbps

88mW

240 m

-

ISA card

Lucent

WaveLAN PCMCIA Wireless Adapter

DS

2 Mbps

88mW

240 m

-

PCMCIA Type II

MikroTik

MicroTik Wireless Router Package

-

2 Mbps

100mW

-

-

standalone (ethernet)

Configuratio

2.4 GRz Wireless LAN/MAN Modem Produ Maximum Range Indoor I Outdoor

Vendor

Product

Type

Data Rate

Power

Multicap

Serial-Wave

FH

1.6 Mbps *

100mW

150 m

18 km

standalone (RS232)

Multipoint Networks

RAN64s s

DS

64 Kbps

18 dBm

-

-

standalone (RS2 32/EIA5 3ON .35)

Multipoint Network s

RANI 28ss

DS

128 Kbps

18 dBm

-

-

standalone (RS232/EIA53ON. 35)

Mult ipoint Networks

RAN2048ss

FH

2.048 Mbps

18 dBm

-

Up to 30 km

standalone (G.703)*

Netwave

AirSurfer Wireless PC Card

FH

I Mbps

25mW ERP

45 m

200m

PCMCIA Type II

Netwave

AirSurfer Access Point

FH

I Mbps

25mW ERP

45 m

200 m

standalone (IOBaseT, WBase2)

Nomadic

Mercury RF-I

FH

1.6 Mbps *

100mW

150 m

300 m

standalone (RS232)

Configuration

2.4 GHz Wireless LAN/MAN Modem Prod Maximum Range Indoor / Outdoor

Configuration

-

75 km

standalone (V.35, DSX-I , G.703)

100mW

150 m

300m

ISA card

1.6 Mbps

100mW

150m

300 m

PCMCIA Type II

FH

1.6 Mbps

100mW

-

4.8 km

standalone (ethernet)

Wireles s Remote Office Link

DS

256 Kbps (or more)

-

-

32 km

standalone ( IOBaseT ethern et*)

Solectek

AIRLAN/Bridge 200E

DS

2 Mbps

4WERP

-

40 km

stand alone (ethernet)

Solectek

AIRLAN/Bridge Ultra

DS

2 Mbps

4 WERP

-

40 km

standalone (ethernet)

Solectek

AIRLANlRo uter 200E

DS

2 Mbp s

4 W ERP

-

40 km

standalone (ethern et)

Vendo r

Product

Type

Data Rate

Power

P-COM

Model 100-2

DS

56 Kbps 2.048 Mbps

6 mw or 500mW

Prox im

RangeLAN 2 7100ISA

FH

1.6 Mbps

Proxim

RangeLAN2 7400 PC Card

FH

Proxim

RangeLink

RadioC onnect

2.4 GHz Wireless LAN/MAN Modem Prod Maximum Range Indoor I Outdoor

Vendor

Product

Type

Data Rate

Power

Solectek

AIRLAN/Bridge 1000

DS

10 Mbps

4WERP

-

40 km*

standalone (ethernet)

Symbol

Spectrum24 LA 2400

FH

I Mbps

100-500 mW

55-75 m

300m

PCMCIA Type II

Raytheon

Raylink PC Card

FH

2 Mbps

100mW

150 m

300 m

PCMCIA Type II

RDC

PortLAN

FH

I Mbps

-

150 m

830 m

PCMCIA Type II

Utilicom

LongRanger 2020/lSM2.4-4TS256

DS

Up to 256 Kbps

0.25 - 4 WERP

-

50 km*

standalone (RS232/RS422/ EIA530N .35)

WaveAccess

Jaguar DS 132

FH

3.2 Mbps*

50 mW

-

1.5 km

Standal one (IOBaseT ethernet)

WaveAccess

WaveLyNX BR 132 Wireless Bridge

FH

3.2 Mbps

50mW

-

32 km*

Standalon e (IOBaseT ethernet)

WaveAccess

Jaguar PCI32

FH

3.2 Mbps*

50mW

100 m

150 m

PCMCIA Type II

Configuration

2.4 GHz Wireless LAN/MAN Modem Produ Vendor

Product

Type

Data Rate

Power

Maximum Range Indoor I Outdoor

WaveAcce ss

Jaguar API32

FH

3.2 Mbp s*

50mW

100 m

1.5 km

standalone (ethernet)

Wave Wireless

SPEEDLAN 3

FH

3 Mbp s

4WERP

550 m

8 km

standalone (ethern et)

Wave Wireless

SPEEDLAN 5

DS

3-8 Mbps

4 WERP

-

16 km

standalone (ethernet)

Wave Wireless

SPEEDLAN 10 BRouter

DS

8 Mbps

4WERP

-

16 km

standalone (ethern et)

Wi-LAN

Hopper Plus Wireless Ethernet Bridge

DS

1.9 Mbp s

100mW

-

9 km

standalone (ethernet)

Wi-LAN

Hopper FD Wirele ss Modem

DSIFH

19.2 Kbps*

16 mW

-

-

standal one (RS232)

Wind ata

FreePort

DS

5.7 Mbp s

I WERP

80 m

-

standalone (ethernet)

Wind ata

AirP ort II

DS

5.7 Mbp s

I WERP

-

2.9 km

standalone (ethernet)

Young Design

Model 2400

FH

115.2 Kbps

100mW

-

50 km

stand alone (RS232)

Configuration

2.4 GHz Wireless LAN/MAN Modem Prod Vendor

Product

Type

Data Rate

Power

Maximum Range Indoor I Outdoor

Z-COM

WL2420 LANE scape/ ISA

DS

2 Mbps

50mW

150 m

8 km

ISA card

Z-COM

WL2430 LANE scapelPCMCIA

DS

2 Mbps

50mW

150 m

8 km

PCMCIA Type II

Z-COM

WL2410 LANEscape Access Point

DS

2 Mbps

50mW

150 m

8 km

standalone (ethernet)

Zenith

CruiseLAN/ISA

FH

1.6 Mbps

IOOmW

150 m

300 m

Zenith

Crui seLAN/ PCMCIA

FH

1.6 Mbps

100mW

150 m

300 m

Configuration

ISA card (1/2 size)

PCMCIA Type II

::>

900

~

1\

'c'"": ~

MHz Wireless LAN/MAN Modem Prod

Product

Type

Data Rate

Power

Aerotron

NLR- 900T

OS

19.2 Kbps

725mW

450 m

2.4 km

standalone (RS23 2)

Airon et

ARLAN 655900

OS

215/860 Kbps

1WERP

300 m

10 km

ISA card (1/2 size)

Airon et

ARLAN 690900

OS

215/860 Kbps

I WERP

300m

10 km

PCMCIA Typ e II

C-SPEC

Wa veLAN PCAT Wi reless Adapter

OS

2 Mbps

250mW

240 m

-

ISA card

C-SPEC

Wav eLAN PCMCIA Wireless Adapter

OS

2 Mbps

250mW

240 m

-

PCMCIA Type II

C-SPEC

OverLAN . Wirel ess BridgelRouter

OS

2 Mbps

250mW

240 m

16 km

standalone (ethern et)

Cylink

AirLink 19MPE

OS

1.2-19.2 Kbps

800mW

-

-

standalone (RS232/422, V.35)

Cyl ink

AirLink 64MP

OS

1.2 - 64 Kbps

800 mW

-

48 km

standalone (RS232/422, V.35)

......

~

I

)

Maximum Range Indoor I Outdoor

Vend or

,, )

.... >

~

::;J

'>"

~

'"

'" )

l..

D

~

o

I )

:-, ,. )

Configuration

900

MHz Wireless LAN/MAN Modem Prod Maximum Range Indoor I Outdoor

Vendor

Product

Type

Data Rate

Power

Cylink

AirLink 128

DS

128 Kbps

800mW

-

-

standalone (RS232/422, V.35)

DATA-LINC

SRM6000

FH

Up to 115.2 Kbps

0.1-1 W

450m

30-48 km

standalone (RS232/422/485

DEC

Roamabout 915 DS/ISA

DS

2 Mbps

250mW

240 m

-

PCMCIA Type II

Digital Wireless

WIT915

-

38.4 Kbps

lW

-

-

OEM module (RS232)

FreeWave

DGR -115

FH

2.4 - 115.2 Kbps

lW

-

32 km

standalone (RS232)

GRE

GINA 6000NVK

DS

64 Kbps

725mW

240 m

19 km

standalone (RS232/449, V.35)

Inficom

Infilink Tl

-

1.544 Mbps

100mW

-

16 km

standalone (V.35)

Inficom

Infilink ATM

-

25.6 Mbps

100mW

-

16 km

standalone (ATM)

KarlNet

WaveLAN PCAT Wireless Adapter

DS

2 Mbps

250mW

240 m

-

ISA card

Configuration

900 MHz Wireless LAN/MAN Modem Prod Maximum Range Indoor I Outdoor

Configuration

Vendor

Product

Type

Data Rate

Power

KarlNet

WaveLAN PCMCIA Wir eless Adapter

DS

2 Mbps

250mW

240m

-

PCMCIA Typ e II

KarlNet

Wirel ess KarIBridge

DS

2 Mbps

250mW

-

16 km

standalone (ethernet)

KarlNet

Wirel ess KarIBridgelRouter

DS

2 Mbps

250mW

-

16 km

standal one (ethernet)

Luce nt

WaveLAN PCAT Wireless Adapter

DS

2 Mbps

250 mW

240m

-

ISA card

Lucent

WaveLAN PCMCIA Wir eless Adapter

DS

2 Mbps

250mW

240 m

-

PCMCIA Type II

Metricom

Ricochet Wir eless Mod em

PH

100 Kbp s*

-

-

500 m

standalone (RS232)

Microhard

MRX-900

PH

2.4-115.2 Kbps

lW

-

> ;30 km

stand alone (RS232)

900

MHz Wireless LAN/MAN Modem Prod Maximum Range Indoor I Outdoor

Vendor

Product

Type

Data Rate

Power

Momentum Microsystem s

Aviator Wireless

NB

150 Kbps

0.7mW

25 m

-

standalone (parallel port)

Norand

RB4020 Wireless Netw ork Radio Base

DS

192 Kbps

IW

-

-

standalone (RS485)

Norand

RCB4000 Wir eles s Netw ork Inte grated ControllerlBase

DS

192 Kbps*

IW

-

-

standalone (RS2 32)

Nu -Metrics

RFM-915

DS

9.6 Kbps

40mW

-

48 km

standalone (RS232/485)

O'Neill

Law nII-232

DS

38.4 Kbps

40mW

90m

9 15 m

standalone (RS232)

OTC Telecom

AirEZY 900

DS

I Mbps

100mW

150 m

240 m

standalone (ethernet: BNC or RJ-45 )

Per soft

Intersect Remote Bridge

DS

2 Mbp s

IOOmW

240 m

8 km

standalon e (ethernet)

Solectek

AIRLAN Brid ge Plus

DS

2 Mbp s

up to 4 WERP

-

5 km

stand alone

Configuration

900

MHz Wireless LAN/MAN Modem Prod Maximum Range Indoor I Outdoor

Configuration

Vendor

Product

Type

Data Rate

Power

UNICOM

RF 915

DS

Up to 38.4 Kbps

I mW - I W

-

5 km

standalone (sync /async ser ial)

Utilicom

LongRanger 2020/lSM900-4TS256

DS

Up to 256 Kbp s

0.25 - 4 WERP

-

50 km *

standalone (RS232/RS422 EIA5 30N.35

W i-LA N

Hopper DS Wireless Modem

DS

19.2 Kbp s

0.5W

-

10 km

standal one (RS232)

W i-LA N

Hopper FD Wireless Modem

DSfFH

19.2 Kbp s*

0.5 W

-

9.5 km

standalone (RS232)

W i-LA N

Hopper Plus Wireles s Eth ernet Bridge

DS

1.45 Mbps

0.5 W

-

9.5 km

standalone (ethernet)

Xe tron

Hummingbird 902

FH

19.2 Kbp s

IW

240 m

8 km

OEM card (RS232/4 85)

Youn g Design

RM 910 -INT

DS

78.4 Kbps

20mW

100 m

200 m

standalone (RS232)

200m

I Km (with Yagi A nt.)

standalone (RS232)

Yo ung Design

RM 91O-EXT

DS

78.4 Kbp s

20mW

206

Appendix A

WLAN Vendor Information Aerotron-Repco Sales, Inc. 2400 Sand Lake Road Orlando, FL 32809-7666 Tel: 800-950-5633 or 407-856-1953 Fax : 407-856-1960 Aironet Wireless Communications, Inc. 367 Ghent Road, Suite 300 Akron, OH 44334-0292 Tel: 800-394-7353 or 330-665-7900 Fax: 330-665-7922 Email: [email protected] Airdata WIMAN Systems 2950 Tamiami Trail N . Suite 16 Naples, FL. 34103 Tel: 941-261-1633 Fax: 941-261-5325 Email: [email protected] Breeze Wireless Communications 2195 Faraday Ave, Suite A Carlsbad, CA 92008 Tel: 619-431-9880 Fax: 619-431-2595 Cabletron Systems 35 Industrial Way Rochester, NH 03867-5005 Tel: 603-332-9400 Fax: 603-337-2211 Clarion 2-22-3, Sibuya, Sibuya-ku Tokyo 150, Japan Tel: 201-818-1166 Fax: 201-818-1317 C-SPEC Corp. 20 Marco Lane Dayton, OH 45458 Tel: 8DO-GOCSPECor 937-439-2882 Fax: 937-439-2358 Email: [email protected]

DATA-LINC Group 2635 151st Place N.E. Redmond, WA 98052-5562 Tel: 206-882-2206 or 425-882-2206 Fax: 206-867-D865 or 425-867-D865 Email: [email protected] Digital Equipment Corp. Maynard,MA Tel:508-493-5111 Digital Transmission Systems, Inc. 3000 Northwoods Parkway (Bldg. 330) Norcross, GA 30071 Tel: 770-798-1300 F a x : 770-798-1325 E-mail: info@dtsx .com Digital Wireless Corp. One Meca Way Norcross, GA 30093 Tel: 770-564-5540 Fax: 770-564-5541 Email: [email protected] Glenayre Western Multiplex Corp. 1196 Borregas Avenue Sunnyvale, CA 94089-1302 Tel:408-542-5200 Fax: 408-542-5300 GRE America, Inc. 425 Harbor Blvd. Belmont, CA 94002 Tel: 800-233-5973 or 415-591-1400 Fax: 415-591-2001 Email: [email protected] IBM Wireless 700 Park Office Road, Highway 54 Building 662 Research Triangle Park, NC 27709 Tel: 919-543-7708 Fax: 919-543-5568

Cylink Corporation 910 Hermosa Court Sunnyvale, CA 94086 USA Tel: 408-735-5800 Fax: 408-735-Q643 Email: [email protected]

Inficom, Inc. 645 Southcenter, Suite 343 Seattle, WA, USA 98188-2836 Tel: 206-865-9753 Fax: 206-562-6066 Email: [email protected]

Data Communications Technologies 2200 Gateway Centre Blvd, Suite 201 Morrisville, NC 27560-9122 USA Tel: 1-800-344-1395 Fax: 919-462-D3OO Email: [email protected]

InTalkInc. P.O. Box 2181 Melbourne, FL, USA 32901 Tel: 800-510-1516 or 407-724-7972 Fax: 407-724-7886 Email: sales®intalk.com

207 .

Karlnet, Inc. 5030 Postlewaite Rd. Columbus, OH 43235-3450 Tel: 614-457-5275 Fax: 614-442-7599 Email: [email protected] Lucent Technologies Inc. WaveLAN Commercial Sales Room IH62, 5 Wood Hollow Road Parsippany, NJ 07054 Tel: 201-581-4296/4297 or 1-800 WAVELAN Fax: 201-581-4282 Email: [email protected] Metricom, Inc. 980 University Ave. Los Gatos, CA 95030 Tel:800-556-6123 or 408-399-8200 Email: [email protected] Microhard Systems Inc. #209,12 Manning Close N.E. Calgary, AB, Canada TIE 7N6 Tel:403-248-0028 Fax: 403-248-2762 Email: [email protected] Momentum MicroSystems, Inc. 2864 S. Circle Drive, Suite 401 Colorado Springs, CO 80906 Tel: 719-540-8338 or 800-894-5280 Fax: 719-540-8361 Email: [email protected] Multicap Antwerpsesteenweg 124/19 8-2630 Aartselaar, Belgium Tel: ++32 (0)3 877.44.80 Fax: ++32 (0)3 887.10.16 Email: [email protected] Multipoint Networks Inc. 19 Davis Drive Belmont, CA 94002 Tel: 650-595-3300 Fax: 650-595-2417 Email: [email protected] Netwave Technologies, Inc. 6663 Owens Drive Pleasanton, CA 94588 Tel: 510-737-1600 or 800-NETWAVE (sales) Fax: 510-847-8744 Email: [email protected] Nomadic Technologies 2133 Leghorn Street Mountain View, CA 94043 Tel: 415-988-7200 Fax: 415-988-7201 Email: [email protected]

Norand Corporation 550 2nd Street SE Cedar Rapids, IA 52401 Tel:319-369-3100or 800-553-5971 Fax: 319-369-3453 Email: [email protected] Nu-Metrics Box 518 University Drive Uniontown, PA 15401 Tel: 412-438-8750or 800-346-2025 Fax: 412-438-8769 Email: [email protected] O'Neill Connectivities, Inc . 607 Horsham Road Horsham, PA 19044 Tel:800-624-5296or 215-957-5408 Fax:215-957~33

OTCTelecom 2036 Bering Drive San Jose, CA 95131 Tel: 800-770~98 or 408-245-6888 Fax: 408-245-8886 Email: otcsales@ezylink. com P-COMInc. 3175 S. Wmchester Blvd. Campbell, CA 95008 Tel: 408-866-3666or 1-80D-646-PCOM(7266) Fax: 408-866-3655 Persoft, Inc. 465 Science Dr PO Box 44953 Madison, WI 53744-4953 Tel:800-368-5283or 608-273-4357 Proxim, Inc. 295 North Bernardo Ave. Mountain View, CA 94043 Tel: 800-229-1630or 415-960-1630 Fax: 415-960-1984 Email: [email protected] RadioConnect Corporation 6041 Bristol Parkway Culver City, California 90230 Tel: 310-338-3388 Fax: 310-338-3399 Email: [email protected]

208

Appendix A

RadioLAN 455 DeGuigne Drive, Suite 0 Sunnyvale, CA Tel: 408-524-2600 or 888-2RadioLAN Fax: 408-524-0600 Email: [email protected] Raytheon Electronics 362 Lowell Street Andover, MA 01810 Tel: 508-470-9011 Fax: 508-470-9452 Email: [email protected] RDC Networks Inc. 1160 Chess Drive, Suite #1 Foster City, CA 94404 Tel: 415-577-8075 Fax: 977-8-977-7050 Email: [email protected] Solectek Corporation 6370 Nancy Ridge Drive, Suite 109 San Diego, CA 92121-3212 Tel: 800-437-1518 or 619-450-1220 Fax : 619/457-2681 Symbol Technologies, Inc. 116 Wilbur Place Bohemia, NY 11716 Tel: 800-SCAN 234 or 516-563-2400 Fax : 516-563-2831 Telxon Corp. 3330 West Market Street Akron, OH 44334-0582 Tel: 800-800-8008 Email: [email protected] UNICOMInc.

no Box 184

Wmter Springs, FL, USA 32708 Tel: 888-696-5517 or 407-696-5517 Fax: 407-696-5526 Email: [email protected] Utilicom Inc. 323 Love Place Goleta, CA 93117 Tel: 805-964-5848 Fax: 805-964-5706 Wave Wireless Networking 1748 Independence Boulevard, C-5 Sarasota, FL 34234 Tel: 800-721-9283 Fax: 941-355-0219 Email: sales®the-wave-wireless.com

WaveAccess Wireless Communications One Apple Hill, Ste. 203 Natick, MA 01760 Tel: 508-653-3646 or 508-653-3306 Email: [email protected] Wi-LAN Inc. #300-801 Manning Rd. N .E. Calgary, AB, Canada TIE 8J5 Tel: 800-258-6876 or 403-273-9133 Fax : 403-273-5200 Email: wi-Ian©Wi-lan.com Windata Corp. 543 Great Rd. Littleton, MA 01460 Tel: 508-952-0170 or 800-553-8008 Fax : 508-952-0168 or -0169 Email: [email protected] Note:The Wmdata products are also available from Cabletron Wireless Scientific 1890 South 14th Street Building 100, Suite 105 Amelia Island, FL 32034 Tel: 904-261-6977 Fax: 904-261-2129 Email: [email protected] Xetron Corporation 460 West Crescentville Rd. Cincinnati, OH 45246 Tel: 513-881-3500 Fax: 513-881-3379 Email: [email protected] Young Design, Inc 103 Rowell Court Falls Church, VA22046 Tel: 703-237-9090 Fax: 703-237-9092 Email: [email protected] Z-COM,Inc. Hsinchu, Taiwan Tel: +886-3-5W364 Fax: +886-3-5773359 Email: center®zcomwireless.com Zenith Data Systems 2150 East Lake Cook Road Buffalo Grove, IL 60089 Tel: 800-416-7591 or 708-808-5000 Fax: 708-808-4434 Email: [email protected]

209

Index Symbols 70. 1.54Mb p s 71, 99, 100, 102, 105. 10-base-T 57, 64, 66, 99. 1200 baud 1240-1300MH z 8. 28,57. 14.4Kbps 2400 - 2483.5MHz 7-8. 2400-2450MHz 171. 57. 28.8Kbps 5725 - 5850MH z 7. 7-8, 30, 35, 902 - 928MH z 101, I, 172, 185. 57, 99. 9600 baud

A AMRAD

2-3, 11, 16, 62, 68, 167, 180. Antenna 7, 10, 19, 24-26, 29-33, 35-36, 45, 60, 101-102, 144, 147, 152, 155, 156, 158, 160, 162, 164-165, 172. Antheil, George I , 37-38. Antijamming 121. ARRL 3, 9, 11, 16, 18, 21-22, 28, 36, 41, 45-46, 50, 53, 55, 59, 62, 66-68, 70-71, 99, 106, 136-137, 143, 165, 167, 170-172, 178-184. ARRLSpread Spectrum Sourcebook 3, 16, 18, 136. Auto-correlation 121. Availability 20, 22, 71, 95-98, 101.

B Bandwidth

3, 5-8, 15-17, 20-21, 28, 34, 37, 43, 48, 53, 72-77, 81-82, 86-93, 107-110, 117, 120-122, 158, 165, 176.

Baran, Paul 67-68. BER 72, 144, 147, 164. Bible, Steve, N7HPR I , 2, 44, 49. Biphase Shift Keying See also BPSK Bit Error Rate See also BER BPSK 110, 117, 121-122, 124-126, 133. BreezeCom 23-27. Broad Band 72, 80-81, 89-91, 93. Broscius, Albert, N3FCT I, 19, 34, 45.

c Carrier Sense Multiple Access/Carrier Avoidance See also CSMA/CA CDMA 2, 5, 10-11, 22, 46, 50, 121, 137. Channelized 71-72. Channelized Access 71. Chip See also Chip Rate Chip Rate 8, 121, 138, 169. Code Division 5-6, 10, 137. Code Division Multiple Access See also CDMA Code Sequence 3-5, 10, 34, 111, 123, 137, 168. Coexist I , 3, 5-6, 42. 46-48, 65, 183. Communications Act of 1934 43, 48, 60, 173-174. Congested 76, 81, 92-94, 182. Congestion 15, 17, 72, 81, 92. Conserving Bandwidth 81, 93. Continuously Variable Slope Delta Modulation See also CVSD Cornu Spiral 151-154. Correlation 5, 6, 10, Ill, 121, 122, 126, 129, 137-138, 140-142. Correlation Based 137. Correlator 121. Costas 15, 16, 18, 71-72, 102, 105, 113. Costas, John, K2EN 15. Cos tas Loop 122. Cross-Correlation 122. CSMA /CA 10. CVSD 115.

210

D

G

DCC. See also Digital Communications Conference Delay Locked Loop 122, 128. Delta Modulation 115, 122. Delta modulation 113-115. Despreading 6-7, 120. Dewayne Hendricks, WA8DZP I, 28, 41, 44-45, 49. 100. DHCP 143, 147-149, 152-153, Diffraction 155, 159-163, 165. Digital Communications Conference 19, 28, 41, 45, 50, 53, 59, 62, 71, 99, 106, 137, 143. 122. Diphase 3, 122, 136. Direct Sequence 3-4, 6-7, 10, Direct sequence 12, 17, 34, 71, 107, 109-111, 115-117, 120-122, 124, 129, 133, 168-169, 171. Direct-sequence 137. Distributed 42, 48, 74, 76, 145, 171. DownEast Microwave 26. DSB 72-73, 75-77, 80, 93. Dwell time 110.

Gaussian Noise Gilder, George Global Position Service GPS Ground Reflections

E Effective aperture EME

145-146. 55, 69, 178.

F Feedline

24, 31-33, 101,. 145, 160, 165 FEC 43, 49, 54, 71, 99. Forward Error Correction See also FEC Frequency coordination 65. Frequency coordinator 64-65. Frequency Hopping 4, 6-7, 10, 34, 71, 99, 101, 109-111, 120, 122,168, 171, 173. Frequency-Selective Filter 93. Frequency Shift Keying See also FSK Fresnel Zone 152-156, 158-159, 165. FSK 71, 99, 102.

16, 107. 67-68. See also GPS 2, 10, 107. 156.

H Hansen, John, W2FS I, 23, 27. High-Capacity 16. High-Speed I, 19, 21-22, 31, 33, 37, 43, 46, 49, 67, 99, 143-145, 161-162, 164-165. Hop Rate 110. Huygens' Principle 150. Hybrid 4, 9, 34, 50, 110, 168.

I IEEE 13, 17, 18, 136, 142, 166. Industrial, Scientific, Medical Freq. See also ISM Interference 5-10, 14-17, 19-20, 34-36, 42-43, 45, 48-50, 67-69, 73, 75-77, 80-81, 91-92, 110, 115, 120-122, 137-138, 148, 157, 163, 165, 167-168, 171-172, 177, 180, 182-183. Internet 9, 19, 25-31, 33, 36-37, 41-42, 45, 48, 51, 54, 56-59, 62, 64, 67, 70, 99-100, 143-144, 181. Intersymbol Interference 163. IP Masquerading 27. ISM 7, 20, 34, 36, 143, 166, 185.

J Jamming

5, 6, 14-16, 18, 37, 72-73, 89-90, 120-122, 137. Jamming Margin 118, 120. Jones, Greg, WD5IVD 41, 44-45, 49, 51, 56, 67.

211

L

o

37-38. Lamarr, Hedy 28. Last Mile 34, 140, 178. LFSR See also LOS Line of Sight 122. Linear Codes Linear Feedback Shift Register See also LFSR 27, 31, 33. Linux 58, 99. Long Haul 143, 147, 152-156, LOS 159, 161-162, 165. 12, 17, 30-31, 33, 100. Low Cost

Overlay

M Maximal Code 122. McLarnon, Barry, VE3JF 44, 49, 71, 143, 166, 185. Mean Time Between Failures. See also MTBF Mean Time To Restore. See also MTTR 35, 36. Microsat 26, 71, 117, 141, Microwave 157, 162-164, 173. 5, 10, 17, 32, 43, 49, Minimize 67, 101, 105, 153, 170. 1, 28-33. Mongolia 29, 95-97. MTBF 95-97. MTTR 100. Multi-point 99. Multiple-hop

N Narrowband

3, 6, 10, 12, 16, 72, 80-81, 90-92, 101, 111, 121, 133, 163. National Science Foundation. See also NSF Naturalistic Inquiry 55. Noise 3, 5-7, 14, 16, 18, 34-35, 68, 75, 77, 80, 82, 86, 89, 90-91, 94, 105, 107-110, 113, 117, 120, 122-124, 137-138, 140-141, 144, 165, 177, 182. Noise Floor 3, 35, 182. Notice of Proposed Rule Making. See also NPRM NPRM 47, 67, 167, 170, 174, 178, 181. NPRM-8737 167. NSF 28, 29, 30, 31, 33.

5.

p Packet Status Register See also PSR PANSAT 11-13. Paradigm 15, 23, 41, 51-54, 64, 67. Part 15 1, 6-8, 12, 17-22, 27, 30, 34, 45-47, 58, 167, 171-172, 179, 182-184. Part 97 1, 2, 7-9, 12, 18, 21-22, 35, 44, 46, 49, 58, 65-66, 68, 167, 172-174, 176, 178-181, 183. Patch Antenna 24. Path Loss 144, 147, 159. PCS 2, 6, 19, 20, 21, 33, 46, 51. Personal Communications System. See also PCS Phase Reversal Keying Seealso PRK PN code 7, 110-111, 117, 121, 129-131, 133. Point-to-point 10, 100, 183. Poisson 15, 71-72, 74-76. Power Control 10, 43, 49, 172, 179. Power Flux Density 145-146. Power Spectral Density 120. Power-limited 35. Prism 100. Privacy 11, 16, 111. PRK 110. 120, 122. Process Gain Propagation 35, 71, 143-144, 148, 150, 156, 161-166. Protocols 35, 42-43, 48-49. Pseudo-noise 34, 110, 122-123, 137. Pseudo-random 3-5, 109, 110-111, 115-117, 120-124. Pseudo-random generator 3. PSR 14, 19, 22-23, 45, 51, 54, 56, 59, 64, 67, 70, 95. Public service 58, 60, 61. Pulsed FM 4.

Q QEX 2-3, 19, 21-22, 45, 46, 50. QPSK 71, 99, 101-102, 105, 121. Quadature Phase Shift Keying See also QPSK

212

R

SSB

14, 68. Radar 7, 16, 34, 36. Radiolocation 99. Reed, Bill, WDOETZ 139, 143, 147, Reflections 151, 156-158, 163-165. 143, 147-148, Refraction 155-156, 159. 2, 7-9, 12, 17, 19, 34, Regulation 36, 46, 52, 54, 60, 67, 105, 134, 167, 176, 179. 28, 77-81, 96, 99, 146. Reliability 35, 54, 64-65, 69, Repeater 167-168, 171, 179, 182. Rinaldo, Paul, W4RI 16. RM-8737 46-47, 50, 52, 55, 168, 177-178, 181. Robert Buaas, K6KGS 21, 46, 53. Router 30-33.

T

5 Satellites 61, 69. SAW filter 101, 105. Shannon, Claude 5, 15, 18, 71-72, 82, 84-86, 94, 107-108, 136. Share 5, 12, 15, 20, 34-35, 42-43, 48-49, 60, 65, 67-69, 73, 93, 171, 183. Signal to Noise Ratio 75-77, 85, 87-89, 92, 107-109, 113, 120, 137-138, 140, 144, 163. Signal-to-noise 6, 34, 68, 75, 120. Smart Radio 41, 67, 70. Smart Transmitters 42, 48. SNR. See also Signal to noise ratio Space-division-multiple-access-devices 68. Special Temporary Authority 9, 12, 16, 169. Spectrum Utilization 6, 9, 71-72. Spread Spectrum Sourcebook 3, 16, 18, 21-22, 46, 50, 68, 134. Spreading code 6-7, 9-10, 50, 54, 111-112, 114-115, 121, 137 167, 172, 179. Squaring Loop 122. SS emission 7-9, 167-169, 172-177, 179-180 .

51, 70, 72-77, 80, 93, 183. STA 9, 16, 21-22, 34, 46-47, 50, 65, 140, 167, 178:-180, 182. Stricklin, Bob, N5B 99. Sumner, David 70. Synchronization 6-8, 101-102, 105-106, 169.

TAPR

9, 14, 19, 22-23, 28, 41-51, 53-56, 59, 62, 65-67, 69, 71, 95, 99, 106, 137, 143, 167, 178-181, 183-184. TCPjIP 1, 37. TDMA 4, 10. Technicians 58, 60, 61. Time hopping 4. Time Domain Multiple Access See also TDMA Tom McDermott, N5EG 71, 95, 99.

u Unlicensed

17, 19-21, 30, 36, 45, 171, 172.

v Videoconferencing Vincent, James A., G1PVZ

99. 107, 123.

w Warehouse Warehousing Wavelet Weak signal

65, 70. 67-68. 146-149. 19, 35, 36, 45, 55, 80, 161, 171. Weak-signal 69. White-noise 82, 89. Wireless 1-2, 10, 15, 17, 20-21, 23, 28-30, 32-34, 37,42, 44, 48, 56, 58, 69, 99, 100, 143-144, 164, 185, 207-208.