A mobile channel model is a set of mathematical expressions into which channel characteristics obtained from field measurements can be inserted in order to predict the performance of a proposed mobile communication system. The basis for a model may be either theoretical or empirical, or a combination of these two. Theoretical propagation models allow a recognition of the fundamental relationships that apply over a broad range of circumstances. They also allow definition of relationships that exist among any combination of input parameters. Empirical models are derived from measurements and observation, and offer a major advantage in that all environmental influences are implicit in the result regardless of whether or not they can be separately recognised and theoretically studied. The validity of empirical models is limited only by the accuracy with which individual measurements are made, and by the extent to which the environment of the measurements adequately represents the physical environment in which the model is to be applied. The Universal Mobile Telecommunication Service (UMTS) will provide a personal communication service and will be composed of several different types of subnetworks; for example, cellular networks, microcellular networks, wireless PABXs etc. The UMTS terminals will have the capability to access any of these subnetworks. Accurate characterisation and modelling of the UMTS 1.7 mobile channel is a necessity. The required information for this characterisation includes knowledge of the statistics for signal fading, of the dispersive nature of the medium, and of the additive noise that can be expected in a mobile radio environment. UMTS channel models are discussed.
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