Estimating the selectivity of a radio channel from routine measurements on operational links

Multipath propagation is one of the main causes of outage on high-bit-rate digital line-of-sight links. These impairments are due mainly to the selectivity of the propagation channel. Predictive methods have been devised to estimate this effect. In most of them, the behaviour of the atmospheric propagation channel is represented by a statistical propagation model and that of the transmission equipment by a set of signature curves. The propagation model consists of both a mathematical model representing the transfer function (TF) of the channel over the frequency bandwidth of interest (generally a few tens of MHz) and the associated probability distribution of the model parameters. To get a general predictive method applicable to any link, a critical point is to know how this probability distribution changes with the relevant characteristics of the link (frequency, hop length, antenna aperture etc.). The authors show how this knowledge can be obtained from routine measurements on operational links, and present some experimental results obtained this way