A general route diversity model for convergent terrestrial microwave links

Abstract

This research examines route diversity as a fade mitigation technique in the presence of rain for convergent, terrestrial, microwave links. A general model is derived which predicts the joint distribution of rain attenuation on arbitrary pairs of convergent microwave links, directly from the link parameters. It is assumed that pairs of links have joint rain attenuation distributions that are bilognormally distributed. Four of the five distribution parameters can be estimated from International Telecommunication Union recommendation models. A maximum likelihood estimation method was used in a previous paper to estimate the fifth parameter, that is, the covariance or correlation. In this paper an empirical model is reported, linking the correlation of log rain fade with the geometry and radio parameters of the pair of links. From these distributions, the advantage due to route diversity may be calculated for arbitrary fade margins. Furthermore, the predicted diversity statistics vary smoothly and yield plausible extrapolations into low‐probability scenarios. Diversity improvement is calculated for a set of example link scenarios.