6
Physical Layer
6.1 Introduction
In this chapter the Wideband Code Division Multiple Access (WCDMA—Universal Terrestrial Radio Access (UTRA) Frequency Division Duplex (FDD)) physical layer is described. The physical layer of the radio interface typically has been the main discussion topic when different cellular systems were compared. The physical layer structures naturally relate directly to the achievable performance issues, when observing a single link between a terminal station and a base station. For the overall system performance the protocols in the other layers, such as handover protocols, also have a great deal of impact. Naturally it is essential to have low Signal-to-Interference Ratio (SIR) requirements for sufficient link performance with various coding and diversity solutions in the physical layer, since the physical layer defines the fundamental capacity limits. The performance of the WCDMA physical layer is described in detail in Chapter 11.
The physical layer has a major impact on equipment complexity with respect to the required baseband processing power in the terminal station and base station equipment. As well as the diversity benefits on the performance side, the wideband nature of WCDMA also offers new challenges in its implementation. As third-generation systems are wideband from the service point of view as well, the physical layer cannot be designed around only a single service, such as speech; more flexibility is needed for future service ...
