12.1 Introduction

It is expected that, during the first decade of the 21st century, digital mobilecommunications systems of the current generation will have stimulated themarket in such a way that it will not be possible to satisfy users' requirementsin terms of capacity, services, coverage, and quality.

This will be the appropriate moment to introduce the so-called third-generation (3G) systems whose main characteristics will be their vocation foruniversality and their multifunction capability. These types of systems willmake extensive use of digital techniques and the technology developed duringthis decade. Given that the main feature of mobile communications systemsis their capability to set up calls while the user is on the move or traveling, itis obvious that the final objective of these types of systems will be to providethe user with a light, inexpensive personal telephone terminal that can be usedanywhere by means of terrestrial or satellite radio links. These are called personalcommunications systems, and they are the basis of the ITU's concept ofuniversal personal telecommunications (UPT).

These systems are based on the fact that most communications are initiatedor addressed to a specific person. The basic objective of these systems is toallow each person to be able to communicate anytime and anywhere.

In fact, this would fulfill the utopia of total communication. Althoughsuch a utopia is probably not achievable in its entirety, it is expected that, forthe first time in history, technology puts at the disposal of mankind the meansto get close to the intended objective.

It must be stressed that an important...