System Aspects of Cellular Radio System Planning in First-and Second-generation Systems Cell Qusters

Engmcenng, Nnlronol Unrversuy o f Slngupore. ublic cellular radio systems are less than two decades old. The concepts of cellular radio are much older, rooted in the O OS, when technology was far too immature to support such complex systcms. There are two main components in mobile radio systems.Theradiointerface,whichallowsuserstowander while communicating via radio from a mobile station (MS) to the other component, a fixed network that interworks with the public switched telephone network (PSTN) or the integrated services digital nctwork (ISDN). Privatc mobile radio communication systems have been present throughout most of this century, as exemplified by the marine, police, and military services. What makes public cellular radio complex is the control structure that enables the network to know where an MSiscurrently located, and to track it irrespective of whether the MS is making a call, with the proviso that the mobile equipment is switched on. Thc control mechanism is made possible by a sct of protocols that enables MSs to register on the network, facilitates call set-up and clear-down, switches MSs between base stations (BSs) as they travel, controls the radiated power levels, provides security (in some systems). and perform a myriad of other vital functions. However,thenumber of 8 ;ersa networkcan support is fundamentally dependent 011 the common air interface (CAI) overwhich userscommunicate. User capacity is dependent on many factorb, but the cardinal ones are the amount of spectrum the regulators allocate. the size of the radio coverage area from a BS. and the amount of interference a particular radio link can tolerate. In this article we are primarily concerned with the system aspects associated with the CAI. We do not consider the subsystem of the radio link, such as speech codccs, channcl codccs, modems, nor propagation issues. Multiple access method5 that enable many users to access the network are of interest. but we refrain from in-depth discussions of the two major multiple access methodscurrentlyinvogueastheyareconsideredinother articles in this issue. We will focus on the critical importance of BS siting. Starting with existing large cells, we will deliberate on the problems that might arise in siting BSs in three dimensional microcells, in order to consider suitable multiple access methods for future cellular environments. In keeping with this magazine, our treatment will be general and light in touch,identifyingissuesrather than solving them.