Mạng và viễn thông P16

Cordless Telephony and Radio in the Local Loop (RILL)The rapid deregulation of telephone network services taking place during the 1990s has brought a large number of new public network operators to the market, each of which has an interest in optimizing the cost of customer connection to network. Much interest, in particular, has been his channelled into radio technologies(so-called‘radio-in-the-localloop’ or ‘wireless localloop’, WLL), as these are seen as aquickandeconomic way to create newaccess infrastructure, bypassing the dependence on the established monopoly operators for ‘last-mile’ connections....
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Mạng và viễn thông P16 Networks and Telecommunications: Design and Operation, Second Edition. Martin P. Clark Copyright © 1991, 1997 John Wiley & Sons Ltd ISBNs: 0-471-97346-7 (Hardback); 0-470-84158-3 (Electronic) Cordless Telephony and Radio in the Local Loop (RILL) The rapid deregulation of telephone network services taking place during the 1990s has brought a large number of new public network operators to the market, each of which has an interest in optimizing the cost of customer connection to network. Much interest, in particular, has been his channelled into radio technologies(so-called‘radio-in-the-localloop’ or ‘wireless localloop’, WLL), as these are seen as aquickandeconomic way to create newaccess infrastructure, bypassing the dependence on the established monopoly operators for ‘last-mile’ connections. In this chapter we discuss some of the most important technologies in this sector. We also discuss cordlesstelephone technology a asmeans providing for access to fixed ‘limited mobility’ networks.16.1 THE DRIVE FOR RADIO IN THE LOCAL LOOP It was historically the casethat a monopoly existed on both the public telephone service and the construction and operation of telecommunications transmission networks. The state-owned monopoly carrier had the sole right to lay cables in the street or construct radio transmission links. Although competition in public telephone network services may have been introduced manyin countries, there not has necessarily been a relaxation of the transmission network monopoly. In consequence, the new telephone carriers(networkoperators)maybedependentontheirstrongestcompetitorsfor the supply of all transmission links. Thankfully for thenew operators, if a little slowly, the national transmission monopolies are alsobeing removed. Unfortunately, however, thisdoes not immediatelyremovethedependence of the new operators on the ex- monopoly carrier, because the large base of established lineplant and investment is difficult for the new carriers to duplicate quickly. The best hope for them lies in the rapid construction of an overlay, radio-based infrastructure. 319320 CORDLESS TELEPHONY AND RADIO IN THE (RILL) LOCAL LOOP16.2 FIXED NETWORKS BASED ON RADIO TECHNOLOGY Figure 16.1 illustratesthetypicalconfiguration of a new telephonenetworkbased largely on radio transmission links. Traditional point-to-point ( P T P ) microwave radio technology ideally suitedfor the is long point-to-point links between switching centres (i.e. between local exchanges and regionalswitching centres and for the trunks between regional switching centres). There may be some regulatory and administrative matters to be resolvedwithrespect to on a licensing of the required radio frequencies, but as the frequencies are requiredstrict point-to-point basis and not over wider areas, this should be achievable both from a regulatory and planning point of view, because the number of links of this type is relatively small. By contrast, there has been relatively little attention paid to radio connection end of customers by the monopoly network players, so that new effort needs to be applied to develop economic technology and to finding suitable radio frequency bands for this new application. Here, the nature of the connection is point-to-multipoint ( P M P ) , requiring potential cdnnection of many thousands of endstations with dynamic allocation of radio bandwidth. The radio path length need only extend to about 5 km and the endpoints are fixed, so this removes the need for much of the complexity of the GSM system(e.g.for roaming and h a n d - o f ) but the radio designis complicated by the physical properties of available radio bands (most having relatively short range and maybe requiring line ofsight (LOS)).Further problems are posed the difficult radio by operating conditions of urban environments (radio shadows, multipath, interference). For heavily used lines with bitrates above 2 Mbit/s, point-to-point ( P T P ) microwave remainsthepredominantmethodbecause of thestrong signalstrengthneededto support high bitrates reliably over appreciable distances. This is best achieved with highly dir ...