Selective Fading Radio Channels: Modeling and Prediction

Multipath fading is a major cause of impairment of highbit-rate digital line-of-sight transmission. This paper presents a characterization of the multipath propagation channel which is independent of any equipment consideration. The method is based on a modeling of the channel transfer function over a bandwidth of a few tens of megahertz. It is shown that several simple three-parameter mathematical models give a good representation of the transfer function. The experimental statistics of these parameters have been established on three experimental links. With two of the mathematical models, the parameters' joint statistics can be expressed in terms of classical probability laws depending on two coefficients whose values reflect the channel selectivity. The last part of the paper describes the application of such a channel modeling to the prediction of the quality on a given hop. This assumes that the values of the statistical coefficients have been obtained, which is possible from relatively simple radio propagation measurements, namely, the joint distribution of the levels at two frequencies spaced a few tens of megahertz apart.