Land Mobile Communications: Cellular Radio, Paging, and Personal Communication Services

Abstract

AbstractLand mobile communications dates back to the 1920s; and it has served well, although comparatively inconspicuously, ever since. In that period, the majority of land mobile systems were used for public safety and vehicle dispatching. Only since the mid‐1980s have land mobile systems started to really take their place in the business community. Cellular radio began the explosive march. The kickoff event was a description of an analog FM system called AMPS (advanced mobile phone system) in a 1979 issue of Bell System Technical Journal. Since then, it seems, the number of cellular radio subscribers doubles every year. Paging has seen equivalent acceptance as universal worldwide.PCS (personal communication services) is currently experiencing eruptive emergence. From our perspective, it seems no more than an outgrowth of the cellular radio concept with shorter ranges and lower power. Both face the problem of building penetration. Some cordless telephone systems are truly evolving into the PCS category, such as the DECT (digital European cordless telephone). Another application of PCS with great promise is the wireless local loop (WLL). In this case, instead of connecting the local serving exchange to the subscriber by wire pair, a radio technique is employed. Such systems can be implemented very rapidly at about half the cost of an equivalent wired system. Where competition is permitted in the local serving area, it would be advisable to avoid the additional wired approach and use radio instead. [Note:The current popular press uses the wordwireless. The term was widely used in Great Britain. In North America its connotation is slightly different. All of the applications discussed in this chapter would be called wireless. However, we will use the traditional, more meaningful term:radio.]Cellular radio is chronically short of bandwidth and has turned to using many different means to conserve bandwidth (i.e., achieve more users per unit of bandwidth). PCS, although assigned four times as much bandwidth, will eventually suffer the same demise.A drawback of present cellular radio is the lack of a universal standard. Europe is further along in this regard with its GSM, which is digital, uses a TDMA access technique, and is fairly bandwidth conservative. It is even making inroads in North America. Currently, North America has two different TDMA systems, two CDMA systems, and two analog systems (i.e., AMPS and N‐AMPS).Multipath reception has the potential to corrupt performance in both PCS and digital cellular radio. Its corruptive effects increase as bit rate increases. These harmful effects can be mitigated by using direct sequence spread spectrum transmission along with digital signal processing.