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Wireless Access Networks


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Wireless Access Networks



The Motivation for Wireless Networks



Reference Architecture for Wireless Networks



Wireless Characteristics



Spectrum Management



Unlicensed Usage






Spectrum Management Issues



Frequency Assignment



Direct Broadcast Satellite



Low Earth Orbit Satellites



Multichannel Multipoint Distribution Service



Local Multipoint Distribution Service



Third-Generation Cellular



Wireless Issues







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Residential Broadband, Second Edition

From: Residential Broadband, Second Edition
Author: George Abe
Publisher: Cisco Press (53)
More Information

6. Wireless Access Networks

This chapter covers the following topics:

  • The Motivation for Wireless

  • Reference Architecture for Wireless Networks

  • Wireless Characteristics

  • Spectrum Management

  • Frequency Assignment

  • Direct Broadcast Satellite

  • Low Earth Orbit Satellite

  • Multichannel Multipoint Distribution Service

  • Local Multipoint Distribution Service

  • Third-Generation Cellular Telephony

  • Wireless Issues

  • Summary

The previous chapters pointed to the tremendous strides recently made on wired networks. Copper and fiber networks are becoming more ubiquitous, easier to use, less costly, and, most of all, faster. Furthermore, the transmission capacity of wired networks is considered infinite because carriers can manufacture bandwidth as demand increases.

The Motivation for Wireless Networks

Cables and wires are not without their problems. Digging trenches or climbing poles for installation can involve difficulties, including problems of construction permits and easements, aesthetics of aerial cables, and backhoes that can inadvertently dig up cables—all of this can add up to high installation costs. Furthermore, the cable may be installed in the wrong place, such as an area with a disappointing market for services. In addition, air doesn't rust or fall down in bad weather, as cable and wiring can. To some observers—including the operators themselves—the fixed networks of wired systems look like vulnerable high-capital assets in a world of fast-changing technologies.

Most importantly perhaps is the need for facilities-based bypass by new market entrants who wish to offer competitive voice or Internet service but who don't want to use existing telephone or cable infrastructure. Wireless is the quickest way to start a company, particularly when the distribution of initial customers is sparse.

Each nation's airwaves historically have been a tightly regulated commodity for a variety of reasons. Spectrum allocation is governed not only by commercial interest but also by public interest (public safety, scientific research), technical characteristics, and, of course, a heavy dose of industry input. Spectrum often is underutilized because, unlike today's digital modulation schemes, older modulation techniques used bandwidth inefficiently. In the United States, the FCC granted spectrum licenses for free until 1993, so there was little incentive to develop new modulation technology. Moreover, a good portion of the available spectrum is reserved for either high-priority uses by local agencies such as fire and police departments, or national uses such as Federal Aviation Administration air traffic control, deep satellite telemetry, and military communications. Broadcast TV and radio also consume choice swaths of spectrum. Finally, very high-frequency spectrum (above 20 GHz) was deemed too difficult for commercial use.

Enter technology. With the advent of digital technologies, frequencies above 20 GHz became commercially viable. Secondly, frequencies lower than 20 GHz can support more users at higher speeds, primarily because of digital modulation and compression techniques. Added to these technological advances, policy changes that relocate incumbent license users to less-valued spectrum force both the new bandwidth services and the present license holders to use spectrum more wisely. The recent auctioning of spectrum by the FCC puts a price on bandwidth and thereby creates incentive for efficient use. All these forces conspire to make wireless the technology of choice for new entrants to broadband access. These new entrants include big service providers who want to enter someone else's market.

In the last few years, the U.S. government and world spectrum authorities have authorized many new wireless services. Among these are direct broadcast satellite (DBS), Personal Communications Services (PCS, second-generation digital cellular telephony), Local Multipoint Distribution Service (LMDS), Multichannel Multipoint Distribution Service (MMDS), digital TV spectrum, Low Earth Orbit (LEO), 24 GHz licenses (Teligent), 38 GHz licenses (Winstar, Advanced Radio), Global System for Mobile Communication (GSM) telephony, Wireless Communications Service (WCS), and third-generation cellular telephony (3G).

The sum of these services indicates that over the last few years, the FCC has auctioned, liberalized the use of, or otherwise licensed more than 3 GHz of spectrum for nongovernmental, nondefense, consumer and business services. This compares favorably with the 1 GHz capacity of coaxial cable or the 1 MHz capacity of a twisted-pair copper loop. Furthermore, spectrum holders now enjoy fewer restrictions on what services they can provide. Because voice service requires so little bandwidth, plenty of bandwidth is left over for video and Internet access services. Finally, there will be a tremendous overhang of analog TV spectrum in the low-frequency ranges of 54 MHz up to 700 MHz when TV broadcasters go digital and the government reclaims the analog TV spectrum. This is prime spectrum property.

Finally, the key marketing advantage of wireless is that consumers are willing to pay more for a lower-quality service, if it is wireless. Satellite television services are higher priced than cable and do not have local content programming. Yet, there are more than 9 million subscribers in the United States. Likewise, cellular telephones have poor voice quality, high prices, and low connectivity. Yet, in the fourth quarter of 1998, more than 33 million GSM, cdmaOne, and TDMA handsets were sold worldwide. By the end of 1999, there will be more than 300 million digital telephony users (and this is an addition to analog handsets), far exceeding the number of Internet subscribers. Mobile access also is not just for telecommuters. Even soccer moms value their pagers and cell phones as means to keep in touch with kids and provide peace of mind while traveling.

The question of wireless networks is whether or not they work at a reasonable—not necessarily lower—cost. Wireless networks use even higher frequencies than a wired infrastructure, so doubts about its robustness and cost-effectiveness for high-speed data service continue.

However, the convenience of wireless, its proven appeal to consumers, the current plethora of spectrum, the promise of more spectrum, and technical innovations that permit the more aggressive use of spectrum all conspire to position wireless as a key access option.

This chapter discusses the various options for wireless access from the carrier to the home. These technologies include DBS, MMDS, LEO, LMDS, and 3G. Other similar technologies, such as 38 GHz licenses (Winstar [Nasdaq: WCII], Advanced Radio Telecommunications [Nasdaq: ARTT]) and a 24 GHz service called Teligent (Nasdaq: TGNT), are viewed as extensions of these and will not be covered. Other wireless technologies are used within the home, such as IEEE 802.11, Bluetooth, and HomeRF. These will be discussed in the following chapter on home networking.


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Just Published

Residential Broadband, Second Edition
by George Abe

Introduces the topics surrounding high-speed networks to the home. It is written for anyone seeking a broad-based familiarity with the issues of residential broadband (RBB) including product developers, engineers, network designers, business people, professionals in legal and regulatory positions, and industry analysts.


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