10.1 Introduction

In the European countries with more developed mobile communications, cellularsystems since their outset have experienced a substantial increase in thenumber of users. This gave rise for the need to find more sophisticated andevolved technologies able to handle high volumes of traffic.

In the United Kingdom, for example, the analog TACS system wasused. Cellular telephony service was provided by two operators with separatenetworks. Both networks have been in operation since January 1985, withsuch an increase in users that, in June 1989, figures rose to a total of 600,000.Already in the early 1990s subscriber figures were well over one million onboth networks [1]. One of the common characteristics of all analog cellularsystems has been their exponential grown in the number of users, to such anextent that some networks were on the brink of saturation. Hence, there wasa real need for a more efficient system in terms of users per MHz.

A further relevant characteristic in Europe was the great diversity ofexisting systems varying from country to country with no operative compatibility.To sort out this problem the global system for mobile communications(GSM) was developed in Europe in the 1980s, with commercial operationstarting in the early 1990s. GSM belongs to the so-called second-generationpublic cellular mobile communications systems.

The first generation, represented by analog systems such as NMT, C,AMPS, and TACS, was characterized by the use of frequency modulation forthe voice signal and the solution of important technical problems such asefficient use of the RF spectrum, location of users on a national scale,...