WiMax Operator's Manual

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CHAPTER 3 ■ STRATEGIC PLANNING OF SPECTRUM AND SERVICES 47 Latin America and Europe, as well as in North America, though exact frequency allocations differ from country to country. LMDS spectrum is only spottily available today in the marketplace in the United States. Some scattered independents in secondary and tertiary markets own such spectrum and may be induced to sell it in some instances, but the largest players, though all bankrupt now, disposed of their holdings in blocs, or else were rescued and refinanced. LMDS bands have the capacity to support a great deal of traffic, but they are strictly line of sight, and the links are undependable beyond a couple of kilometers. I think LMDS can provide the basis of profitable services in selected markets, but I am skeptical as to the viability of point-to-multipoint architectures at these frequencies. Provisioning very fat point-to-point pipes to high-value customers and using these frequencies for cellular backhaul probably makes more sense. The next licensed frequency of interest is located in two bands in the 38GHz region and provides more than 500MHz of bandwidth in the United States and in Canada. The 38GHz frequency is widely used in Latin America as well as in the United States, but frequency allocations are quite different there from those in North America. This is a region of deep water vapor attenuation, and ranges are even shorter than is the case for LMDS. To date this spectrum has been used for point-to-point and point-to-consecutive point services. ART and Winstar purchased great numbers of local licenses several years ago, but neither established a nationwide footprint, and both in fact went bankrupt. Some 38GHz licenses are available today as distressed assets. Most of the strictures applying to LMDS also apply to 38GHz except that the useful range is considerably less. Another licensed band is available at 39GHz, and for all practical purposes it is similar to the 38GHz band. First Avenue () has bought a great deal of this spectrum and leases it, primarily for backhaul, to other carriers. A further band extending from 75GHz to 85GHz has been allocated to a single carrier, Loea, on an experimental basis. Recently the FCC has allocated additional licensed spectrum in the region extending from 70GHz to 90GHz and has made it available on an expedited basis, as has been the case with 18GHz and 23GHz. Different Uses for Different Frequencies Frequency and bandwidth are major factors affecting the scope of the services that the network can deliver and the customers who can be reached. The band one selects for one’s airlink has a considerable bearing on the market one can address. Lower Microwave: Primarily a Residential and Small Business Play The lower microwave frequencies, are, as you have seen, governed by the 802.16a standard that actually extends to 11Ghz. Still, in my estimation, typical lower microwave deployments are best not attempted at frequencies much above 6GHz, and in the United States no commercial spectrum is available between 6GHz and 18GHz that is authorized for broadband access applications. Spectral allocations of course vary from one nation to another, but generally the region between 6GHz and 10GHz has been little used for providing broadband access anywhere in the world.
48 CHAPTER 3 ■ STRATEGIC PLANNING OF SPECTRUM AND SERVICES Although spectral allocations in the lower microwave region vary from one nation to another, most bands are under 200MHz in width and often under 100MHz. Moreover, most antenna systems designed for use in these regions simply will not allow the entire bandwidth to be reused within a few degrees of arc, so network operators must allocate their assigned spectrum—be it 30MHz, 50MHz, 100MHz, or 200MHz—to a number of contiguous users who will all be encompassed within the same transmission beam and thus will all be presented with the full allocated spectrum. Coincidentally, those same users will also be exposed to every transmission occurring over that spectrum within the sector defined by the antenna beam. The practical implications are numerous. First, users are going to get a fairly small allocation of spectrum for their own use, perhaps no more than a few hundred kilohertz in a fully subscribed network. Second, for reasons of security, the network operator cannot depend entirely on channelization or modulation coding to segregate transmissions from one another and to ensure privacy. Instead, further privacy measures are advisable, preferably ones that entail the encryption of each transmission and the installation of an encryption key management system to make the encryption process both transparent to the user and extremely difficult to penetrate on the part of interlopers. Chapters 6, 8, and 9 discuss such security and encryption methods at length. The relatively small amounts of bandwidth that can be accorded individual users in the lower microwave bands restrict the network operator’s ability to court large enterprise customers, and the basic service offerings end up competing with DSL and cable services for the small business customer and the small office home office (SOHO) customer. Residential customers for high-speed access may also be served, but there the wireless operator is apt to enjoy no particular advantage in markets where DSL and cable are already well entrenched. Addressing the Bandwidth Problem in the Lower Microwave Regions It should be noted that some radios do permit simultaneous operation in two different bands, significantly increasing the amount of bandwidth available to the network operator and ultimately to the subscriber. Most commonly, dual-band radios will use one band for the uplink and another for the downlink. One may, for instance, use the 2.4GHz unlicensed band for an uplink and the MMDS licensed bands (2.5GHz to 2.7GHz) for a downlink. Downlinks, it should be understood, normally utilize far more bandwidth than uplinks; in other words, the network is asymmetrical—the theory being that most residential and small business users tend to download far larger files than they transmit, and that the Web browsing experience will be greatly enhanced by a faster downlink as well. It is possible to design radios that can span more than two bands; one could, for example, build a radio that could operate in the lower ISM band (902MHz to 928MHz), the unlicensed band centered at 2.4GHz, and all three of the three unlicensed bands between 5GHz and 6GHz. A company called Wireless Inc. put out just such a product a few years ago but was unable to find a market for it and ceased production. The basic concept remains valid, however, and I predict that as demands for bandwidth grow among 802.16a network operators, it will be revived. In the midterm, radios will begin to appear that are not bound to fixed bands at all and will enable the network to use almost any frequency desired; that is, the radio would not have to be factory tuned to just a few bands but would have the flexibility to select any band and
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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
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■CONTENTS xi Cyberwarfare . . . .
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About the Technical Reviewer ■ROB
Page 20 and 21: Introduction Broadband wireless has
Page 22 and 23: CHAPTER 1 ■ ■ ■ Wireless Broa
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98 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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