Space diversity performance prediction for earth-satellite paths using radar modeling techniques

Both single-terminal and two-terminal joint probability rain fade distributions for earth-satellite paths at 28.56 GHz are derived for Wallops Island, Virginia, by using radar modeling techniques. An array of parallel paths is modeled in the vertical plane which contained the COMSTAR satellite and a terminal receiving the 28.56 GHz COMSTAR beacon. The paths are displaced 1 km apart (8–100 km from the radar) at a fixed elevation angle (θo = 45°). They pass through the volume whose rain environment has been monitored as radar rain reflectivity levels and stored on magnetic tape. An attenuation at 28.56 GHz and a ground rain rate level is calculated for each path and for each radar scan. Both single and joint terminal conditional fade statistics are derived for an ensemble of such arrays, where the conditioning constant is the long-term rain rate distribution. The single and joint terminal distributions are calculated by multiplying the conditional fade statistics by the measured long-term rain rate distribution. As a partial check, the radar-derived single-terminal fade distribution at Wallops Island is compared with the directly measured levels obtained over a 3-year period showing very good agreement. A family of diversity gain curves is calculated from the joint probability distributions corresponding to different probability levels. These are demonstrated to be represented by a single diversity gain function defined as the ‘relative diversity gain.’ The radar-derived relative diversity gain is compared with those obtained from other investigations as well as with derived autocorrelation function results showing good agreement.