Use of cell-site diversity in millimeter-wave fixed cellular systems to combat the effects of rain attenuation

An examination of potential advantages of cell-site diversity with selection combining in the context of mm-wave fixed cellular systems is reported. The study involved simulation of converging radio links over weather radar images of the radar reflectivity factor, from which the specific attenuation of rain at 30 GHz was derived. The average correlation of attenuation on two converging links as a function of their angular separation is shown to indicate the potential benefits in the use of cell-site diversity, especially in heavy rain. Results show that diversity gain exhibits a dependence on angular separation θ in the general form of sin ^k (θ/2). For links of identical lengths the model reduces to a root-sinusoidal shape (k = 0.5), whereas links of unequal lengths lead to the ITU-R recommended model (k = 1). Based on the sin ^k (θ/2) model and observation of the length ratio of the links, a set of criteria for determining the benefit of cell-site diversity for a given subscriber location is proposed.