Prediction of coverage for a LEO system in mid- and high-latitude urban areas using a photogrammetric technique

The performance of a Globalstar-like low-Earth-orbit system is predicted based on hemispherical photographs taken in Ottawa, Canada, and Lillestrom, Norway. The pictures are sorted into three states: vegetation, solid obstacles and clear sky. The simulated satellite look angles are combined with the digital pictures to determine the path state for each satellite, i.e., shadowed, blocked or clear line-of-sight. Cumulative distributions of narrowband fading at L-band are developed for the case when the receiver utilizes one (best or highest) satellite, and up to three-fold diversity with either switching or coherent combining of the received signals. By selecting the best satellite instead of the highest, a significant reduction in fading is obtained. For Lillestrom, the necessary fade margin to obtain 1% outage is reduced by 13 dB when using 3-fold coherent combining diversity instead of the single best satellite.