UMTS: Origins, Architecture and the Standard

Sincethe beginning of the 1990s,cellular communication services have been enjoy- ing an unprecedented level of development, made possible by the existence of the so-called second generation digital technologies, GSM (Global System for Mobile communication) being one of the most popular. These technologies, generally incompatible with each other, are the result of standards created at the start of the 1980s. After some years of evolution and successive improvements, these different standards have today reached the limits of their possibilities. In order to permit the creation of new services and to offer users real mobility on a global scale, it has become necessary to make a technological jump and cross the threshold to third generation cellular networks. Anumber ofpartners (telecom- munications equipment suppliers and operators) have therefore been working together for some years to define the future technology, trying to reconcile the requirements of new services (high quality wireless Internet, multimedia, etc.) with the necessity of guaranteeing to users and network operators the smoothest possible transition to the new generation. Despite the unification efforts of the International Telecommunications Union, through its IMT-2000 program, there exist not one, but several third generation technologies, the main one being the Universal Mobile Telecommunication System (UMTS).Since January 1999,the 3GPP (Third Generation Partnership Project), in charge of the development of the UMTS standard, has carried out a substantial amount of work, whose concrete expression consists of several tens of thousands of pages of specifications spread over more than 300documents.