WiMax Operator's Manual

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CHAPTER 4 ■ SETTING UP PHYSICAL INFRASTRUCTURE 77 Hybrid Fiber Coax In a few locations, mostly in the United States, a new type of hybrid fiber-cable system operator known as an overbuilder may offer packet services capable of speeds in the 10–30Mbps range, sufficient for backhaul in some instances. Few such operators guarantee quality of service, however, and here again the cable operator is likely to be competing for the same access customer as the broadband wireless operator. VDSL VDSL, with speeds in excess of 50Mbps in some cases, might also be considered for backhaul where available, but availability is limited as yet. Even more limited opportunities exist for utilizing a power line carrier for backhaul, a technology where data is transmitted over AC power lines at throughput speeds as high as 30Mbps. One New England–based company named Amperion is pursuing a strategy of combining powerline carrier backhaul with wireless broadband access, but to date it has achieved few commercial deployments. Bear in mind that any such arrangement requires the active participation of the local electrical utility, and while such entities have long evinced interest in gaining a stake in the communications business, few have made major commitments to doing so. Wireless Bridge Connections Wireless broadband operators, can, if they so choose, pursue a wireless pure play in regard to backhaul and utilize wireless point-to-point “bridge” connections from the base station to a central office. They can do so using their own spectrum, or they may elect to use another wireless service provider, preferably one utilizing millimeter microwave equipment or freespace optics. Such bridge connections can utilize either low microwave or millimeter wave frequencies and will normally employ the full available spectrum in the one airlink. Very high-gain, narrow-beam antennas are the rule here, and maximum transmission distances are multiples of the radii of the cells being backhauled. Wireless bridge backhaul connections exceeding 30 miles are feasible in some instances. The same spectrum can be used for backhaul as is used for access, but the prevailing practice is to use a dedicated band to avoid interference since the backhaul has the potential to interfere with every subscriber in the cell inasmuch as it reuses all of the spectrum. The 5.8 U-NII band is frequently assigned to backhaul and offers a good combination of bandwidth and range—100 megahertz (MHz) and more than 20 miles, best case. Other frequencies favored for backhaul purposes include the 18GHz and 23GHz licensed bands where licenses are fairly easily obtainable in the United States, the 24GHz unlicensed band, the 28GHz–31GHz Local Multipoint Distribution Service (LMDS) bands, the 38GHz and 39GHz bands, and the unlicensed band at 60GHz. In all of these bands at least 100MHz of spectrum is available and interference is minimal. Range is an issue, however, especially as one goes higher in frequency, and in the highest band, centered at 60GHz, distance should not exceed a kilometer. The cost of radios for the millimeter wave regions is significantly higher than for the lower microwave bands, and bridge links are minimally several thousand dollars apiece. In the case of LMDS, 38GHz, and 39GHz, the cost is apt to be much higher, approaching $100,000, though that must be balanced against the generous allocations of bandwidth and resultant high throughputs and the fact that the bridge equipment represents a one-time capital cost along with the generally fairly minimal recurrent costs associated with roof rights.
78 CHAPTER 4 ■ SETTING UP PHYSICAL INFRASTRUCTURE THE NETHERCOMM SOLUTION A unique wireless broadband technology has been recently introduced by a California company called Nethercomm. At this point its possible impact on the market cannot be determined, but the technology forms an interesting option that may provide real benefits in certain networks. Nethercomm’s system is based on ultrawideband (UWB) radio technology where the whole available radio spectrum from the low kilohertz to the tens of gigahertz is utilized. Unlike more conventional over-theair UWB systems, Nethercomm’s radios transmit over waveguides, closed metal pipes that contain the signal and prevent interference with other radios. The idea of using waveguides for propagating radio transmissions is not new, and beginning in 1947 much of the long-distance telephone traffic in the United States took place over underground waveguides. What’s different about the Nethercomm system is the use of UWB in lieu of conventional modulation techniques and the notion of employing infrastructure that is already in place, namely gas lines. Nethercomm claims that their prototype systems are capable of outputs of several gigabits per second, faster than most passive optical systems, and that the outlay for equipment is far less. If these claims are true, the system could succeed, though it is arriving in the marketplace critically after many rival technologies have already established themselves. Of course, such a network depends on forging an agreement with the local natural gas utility, a process fraught with uncertainties. As is, most gas utilities with an interest in broadband have opted to exploit dark fiber or install new types of armored fiber inside the gas lines. Free-Space Optics Pure Plays and Hybrid Networks for Backhaul The final option for wireless backhaul is free-space optical, briefly alluded to previously in the text. Free-space or free-air optical is a technology for transmitting information by means of infrared laser pulses without the medium of optical fiber. Speeds equivalent to those of fiber are attainable in theory, though existing systems are not much faster than millimeter microwave. Free-space optical equipment does not require a license to operate and, while generally more expensive than low frequency microwave, has been coming down in price. A single point-to-point link can run as little as a few thousand dollars or as much as several tens of thousands of dollars. Free-space optical equipment can be tricky to set up and maintain because transceivers must be precisely aligned with one another, and something as minor as the settling of a building can severely misalign a link. Autoaligning equipment does exist, but it tends to be expensive. Condensation on the lens, dust, and soot can also be problems. As with other wireless transceivers, siting is critical, and roof rights are generally required. Some systems can be operated through window glass, though distance is critically reduced in such instances, and metalized window coatings effectively prevent such transmissions altogether. Free-space optical systems can be used in tandem with millimeter microwave—the combination of 60GHz and free-space is especially intriguing because the two are well matched in speed and have complementary attenuation characteristics. Obviously such a ploy is expensive, but it provides the highest speed and best availability of any wireless link.
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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
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Introduction Broadband wireless has
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CHAPTER 1 ■ ■ ■ Wireless Broa
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CHAPTER 1 ■ WIRELESS BROADBAND AN
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14 CHAPTER 2 ■ ARCHITECTING THE N
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Page 47 and 48: 26 CHAPTER 2 ■ ARCHITECTING THE N
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128 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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