raction of the code tree needs to be reserved services with rapidly varying resource requirements. This page intentionally left blank Chapter 4.7 Propagation modelling and channel characterisation Pierre Degauque, Emmanuel Van Lil, Vittorio Degli-Espositi, Pertti Vainikainen, Filipe Cardosa, Wim A. Th. Kotterman, and Luis M. Correia 4.7.1 Introduction decreasing the computation time of ray models is also an important issue, techniques for speeding up ray The development and application of new signal processing launching models have also been developed. Simplified algorithms and, more generally, the optimisation of mobile or hybrid models, which introduce statistical elements communication systems are strongly related to the sta- into the deterministic approach, have also been pro- tistical properties of the propagation channel. New coding posed, although they may produce less precise results. techniques, such as space-time coding algorithms, have Examples of applications are used throughout the been developed as a result of the fast growth in indoor chapter to highlight the advantages and drawbacks of the communications coupled with a never-ending need for different methods. Given an assumption of an ideal and higher and higher data transmission rates. At the time that complete description of the environment, the hypothesis the previous COST 273 Action ended, the existing of smooth surfaces is often implied. However, in many knowledge of channel characteristics was essentially based cases, and especially at high frequencies, the roughness or on data pertaining to path loss, delay spread and coherence the size of irregularities of a wall surface is on the same bandwidth. However, because this knowledge proved to order of magnitude as the wavelength, and thus diffuse be incomplete for new systems, intensive research has scattering must be taken into account. This scattering, been conducted concerning the deterministic propagation which plays a fundamental role in time and angle dis- modelling and the estimation of 