A new path-gain/delay-spread propagation model for digital cellular channels

We derive a statistical model for the distribution of rms delay spread (tau(rms)) within a cellular environment, including the effects of base-to-mobile distance, environment type (urban, suburban, rural, and mountainous areas), and the correlation between delay spread and shadow fading, We begin with intuitive arguments that tau(rms) should be lognormally distributed at any given distance d; that the median of this distribution should grow as some (weak) power of d and that the variation about the median should be negatively correlated with shadow fading gain. We then present empirical evidence, drawn from a wide array of published reports, which gives strong support to these conjectures. Finally, we combine our findings with the widely used model for path gain in a cellular environment, The result is a compact statistical model for the joint distribution of path gain and delay spread. The model lends itself readily to Monte Carlo simulation and is useful for performance studies of cellular systems with bandwidths up to tens of kilohertz.