1.1 The Need for Wireless Data Transmission

Since the final decades of the twentieth century, data networks have known steadily growing success. After the installation of fixed Internet networks in many places all over the planet and their now large expansion, the need is now becoming more important for wireless access. There is no doubt that by the end of the first decade of the twentieth century, high-speed wireless data access, i.e. in Mb/s, will be largely deployed worldwide.

Wireless communication dates back to the end of the nineteenth century when the Maxwell equations showed that the transmission of information could be achieved without the need for a wire. A few years later, experimentations such as those of Marconi proved that wireless transmission may be a reality and for rather long distances. Through the twentieth century, great electronic and propagation discoveries and inventions gave way to many wireless transmission systems.

In the 1970s, the Bell Labs proposed the cellular concept, a magic idea that allowed the coverage of a zone as large as needed using a fixed frequency bandwidth. Since then, many wireless technologies had large utilisation, the most successful until now being GSM, the Global System for Mobile communication (previously Groupe Sp&eUcial Mobile), originally European second generation cellular system. GSM is a technology mainly used for voice transmission in addition to low-speed data transmission such as the Short Message Service (SMS).

The GSM has evolutions that are already used in many countries. These evolutions are destined to facilitate relatively high-speed data communication in GSM-based networks. The most important evolutions are:

• GPRS (General Packet Radio Service), the packet-switched evolution of GSM;

• EDGE (Enhanced Data rates for GSM Evolution), which includes link or digital modulation efficiency adaptation, i.e. adaptation of transmission properties to the (quickly varying) radio channel state.

In addition to GSM, third-generation (3G) cellular systems, originally European and Japanese UMTS (Universal Mobile Telecommunication System) technology and originally American cdma2000 technology, are already deployed and are promising wireless communication systems.

Cellular systems have to cover wide areas, as large as countries. Another approach is to use wireless access networks, which were initially proposed for Local Area Networks (LANs) but can also be used for wide area networks.