Modelling, measurement and analysis of narrowband fast fading on relay channels

A procedure for the analysis of narrowband fast fading data with statistically non-stationary characteristics is proposed and applied to data obtained from wideband radio propagation experiments involving two-hop relay channels at 2.25 GHz. The reported experiments were conducted from two channel sounder base station sites in Ottawa to enable a study of the characteristics of relay links in urban microcell environments and of vehicle-to-vehicle communications in relay-based cellular networks. It is shown that empirically-derived cumulative probability distributions for narrowband fast fading on relay links during time intervals when such fading exhibits quasi-stationary characteristics conform closely to a Double-Rician model, the derivation of which is detailed. Analysis of the Double-Rician distribution shows that Double-Rician fading is deeper than Rician fading, unless the K-ratios of the Rician links comprising the relay link are highly dissimilar (having 10 dB difference or more). In such cases, fading on the relay link has a distribution that is very similar to that of the constituent link with the smallest K-ratio. While, in general, relaying is meant to increase average received SNR, it is shown that when the fast fading on the links constituting a relay channel is i.i.d., N-hop relaying reduces the specular-to-random power ratio on the relay link by N times, or significantly increases the depth of fading. This result indicates a need for significant gains at relay stations in some cases.