This book is dedicated to the science and engineering of mobile communication systems. Mobile communication is, at this stage, already one of the biggest segments of information technology and every technology fore caster predicts a seemingly endless growth. Why is it that mobile communication now seems to be an essential part of society, and with an equally strong market demand for both personal users and professional users?

A total adaptivity and match between required services and channel characteristics can only be approximated by developing realistic user ambitions based on knowledge of the radio channel and careful design. This chapter takes a first look at some of the expected characteristics of the transmission medium, both natural and man-made.

As discussed in Section 2.2.1, the traditional method for providing communication services to mobile users is to equip the user terminal with a radio and locate the switching function in centralised fixed equipment. An example of such a system is GSM. Here, the routing and relaying functions are located in the base stations and in the infrastructure that interconnects the base stations. A network where the switching function is distributed and located in the equipment carried by the network users provides an alternative to the traditional telecommunication systems. The first challenge met in such mobile radio systems is a highly dynamic network topology. The network operates under the direct influence of the users which set the operating conditions by deciding the operating terrain, spatial distribution and traffic distribution. The spatial distribution is a function describing where the users are located within the network coverage area. They can be located at fixed positions, at random locations specified by a random distribution, or at positions which alter over time. The traffic distribution characterises the user's packet stream to be served. This stream is specified by three components: the packet interarrival distribution, the packet length distribution and the traffic pattern distribution (a matrix showing the probability of addressing each destination within the addressing domain).