WiMax Operator's Manual

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CHAPTER 3 ■ STRATEGIC PLANNING OF SPECTRUM AND SERVICES 41 a metro hub. The great error of the telecom bubble was to assume that demand for bandwidth was insatiable and would drive the rapid adoption of faster and faster access technologies regardless of cost or other limitations. In fact, carriers have not found a great deal of demand for optical wavelength services in the range of 1Gbps to 10Gbps. It remains to be demonstrated whether demand would be more intense for a wireless service of comparable speed. The other point of divergence between FSO and millimeter microwave has to do with distance. While some manufacturers of FSO equipment have claimed transmission distances of up to several miles, no commercial deployment yet shows that. Sending an infrared signal over great distances is not infeasible, but the power levels necessary to permit long-distance links render the transmitter unsafe to birds and to the eyes of any animal including Homo sapiens unlucky enough to blunder into the path of the beam. Higher power levels are also had at the price of throughput since laser modulators suffer the same trade-offs in terms of frequency and power level afflicting microwave output transistors. To date, FSO systems have been costly, high maintenance, and critically short in useful range. Costs are coming down, and, at the same time, auto-alignment systems are reducing maintenance requirements substantially. Distance limitations will not be so easily solved, though, and these limitations will confine FSO to niche applications for the foreseeable future. RF Orphans: The Low ISM Band and Ultrawideband The first unlicensed frequency band was established by the FCC in the late 1980s, covered the range from 902MHz to 928MHz, and was dubbed the industrial, scientific, and medical (ISM) band. A friend of mine with a degree in RF engineering from Georgia Tech calls it the “dogs and cats” band because a host of rather incompatible devices occupy it, including garage-door openers, cordless phones, remote-controlled toys, and so on. Incidentally, the FCC has since authorized several additional ISM bands, and, the name notwithstanding, none has been much used in industrial, scientific, or medical settings. Transmissions within this first ISM band penetrate walls with ease, and thus there are no line-of-sight issues with which to contend. On the other hand, the band is extremely crowded and has been almost since its inception, and it does not afford the network operator a great deal of bandwidth with which to work. This band has been used by a number of wireless Internet service providers (WISPs), most notably Metricom, but is used relatively little today. However, a modest revival of interest in it appears to be under way. Transceivers are available from certain manufacturers, including Redline, Alvarion, and Trango. The best that one can say is that it represents an option, a means of eking out more bandwidth for a network or giving a network operator some wiggle room in a particularly interference-prone 2.4GHz environment. Ultrawideband (UWB), touched on briefly earlier, is, in its pure form, a carrierless radio technology where the signal consists of a series of low-intensity pulses that themselves may span several gigahertz of spectrum and in theory encompass every frequency within that span. Recently the term has also been appropriated by an industry group touting a multiband Orthogonal Frequency Division Multiplexing (OFDM) technology that spans a considerable amount of spectrum but does in fact utilize carriers. UWB radios are supposed to coexist with radios occupying fixed bands, and, in theory, the UWB signal will appear as only a slight increase in background noise to a conventional receiver. The FCC has concluded that interference at levels needed for broadband access are in fact objectionable, though, and has limited
42 CHAPTER 3 ■ STRATEGIC PLANNING OF SPECTRUM AND SERVICES the power of UWB equipment to a point where transmissions of much beyond 100 feet are impractical. Originally conceived as a basis for ground- and foliage-penetrating radar systems, UWB has more recently figured in experimental stealth radios employed by the armed forces. Commercial prototypes intended for use in public access networks have shown a number of singular virtues including throughputs in the hundreds of megabits per second, near immunity to multipath distortion, and pronounced ability to penetrate buildings and dense foliage. Over-the-air UWB may ultimately play a prominent role in high-speed public communications networks, but it is going to have to clear some formidable regulatory hurdles before that happens. And given that powerful lobbies representing broadcast and telecommunications incumbents are vehemently opposed to it, those hurdles are not apt to be cleared any time soon, at least not in the United States. Recently Southern California–based Nethercomm has developed a very interesting UWB system that could in fact play in metropolitan public networks. The Nethercomm system revives the old idea of waveguides whereby radio transmissions are sent through metal pipes that contain interference and permit senders to use as much bandwidth as they want. In this case the metal pipes are preexisting gas lines. Nethercomm claims that technology will support throughputs of several tens of gigahertz and will best any residential fiber-optic system. In theory, the notion should work, but we have not examined any actual implementations. Licensed vs. Unlicensed Spectrum: The Operator’s Dilemma The licensing of radio spectrum has been in effect since the very dawn of commercial radio in the early 1920s, and the underlying notions informing such licensing are threefold. First, it sequesters generous allocations of spectrum for purely governmental use. Second, it further serves the government by deriving abundant revenues from the licensing process. And third, it prevents commercial users from interfering with one another by restricting each to a specific portion of the band. Such considerations still exist today, though, at least in the United States, the second has assumed paramount importance. Assuming that you can afford to pay for the license, licensed spectrum would appear to be a better medium in which to operate. The spectrum itself is a tangible asset with a real financial value, and the exclusivity of use provisions would seem to be a positive protection from interference. The issue is not so simple as appearances suggest, however, as the following sections illustrate. The Unlicensed Frequencies: A Matter of Peaceful Coexistence Beginning in the late 1980s a number of nations, including the United States, began to explore a new concept, sometimes known as Open Spectrum, that called into question the whole rationale behind the licensing of spectrum, or, in effect, making it the property of the license holder. The concept of Open Spectrum led more or less directly to the creation of the unlicensed bands. This concept is that spectrum, rather than being private property, should be a commons— a shared resource available to all. To avoid the tragedy of the commons—that is, the mutual
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WiMax Operator’s Manual Building
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This book is dedicated to my wife.
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Contents About the Author . . . . .
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■CONTENTS ix Performing Site Surv
Page 12: ■CONTENTS xi Cyberwarfare . . . .
Page 16: About the Technical Reviewer ■ROB
Page 20 and 21: Introduction Broadband wireless has
Page 22 and 23: CHAPTER 1 ■ ■ ■ Wireless Broa
Page 24 and 25: CHAPTER 1 ■ WIRELESS BROADBAND AN
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Page 35 and 36: 14 CHAPTER 2 ■ ARCHITECTING THE N
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92 CHAPTER 4 ■ SETTING UP PHYSICA
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100 CHAPTER 4 ■ SETTING UP PHYSIC
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102 CHAPTER 5 ■ STRATEGIES FOR SU
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CHAPTER 6 ■ ■ ■ Beyond Access
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CHAPTER 6 ■ BEYOND ACCESS 133 Rou
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CHAPTER 6 ■ BEYOND ACCESS 135 (Qo
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CHAPTER 6 ■ BEYOND ACCESS 137 The
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CHAPTER 6 ■ BEYOND ACCESS 139 ins
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Figure 6-4. Wireless public network
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CHAPTER 6 ■ BEYOND ACCESS 143 sto
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Specialized Content Distribution Pl
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Beyond the Central Office CHAPTER 6
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CHAPTER 6 ■ BEYOND ACCESS 149 out
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CHAPTER 6 ■ BEYOND ACCESS 151 som
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CHAPTER 7 ■ ■ ■ Service Deplo
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CHAPTER 7 ■ SERVICE DEPLOYMENTS O
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178 CHAPTER 8 ■ NETWORK MANAGEMEN
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CHAPTER 9 ■ ■ ■ Network Secur
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CHAPTER 9 ■ NETWORK SECURITY 189
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Index ■Numbers 2.4GHz to 928MHz b
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asic access and best-effort deliver
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■D dark fiber, features of, 75-76
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harmonics, impact on AC power, 188
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challenges to, 85-86 and NLOS, 121
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PONs (passive optical networks), fe
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signal diversity, providing with ad
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■V VDSL and entertainment service
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