Measurements and modelling of wireless channel for satellite mobile/personal communication systems

Propagation channel plays an important role in the overall design of any mobile communication system, even more so for a satellite-based mobile system. Signal propagation mechanisms such as shadowing of the line-of-sight (LOS) signal and multipath reception are the most significant issues of concern to systems designers. Estimation of additional link margin, necessary for low gain low directivity mobile terminal, to provide reasonable service availability is usually a first step towards understanding the propagation impairments. Satellite-mobile link quality to a great extent is determined by the propagation channel characteristics. The propagation channel characteristics are believed to be most significantly dependent upon the mobile surrounding environment. Signal amplitude variations of the order of several dBs may be experienced mainly due to the obstruction of the line-of-sight (LOS) path between a satellite and a mobile over a relatively short duration of time. This effect is known as shadowing. In general, a mobile terminal is not capable of discriminating between the LOS signal and its various reflected replicas. This causes degradation in the received signal due to multipath. For broadband systems, the differential delays of different incoming replicas cause further problems and therefore distort the signal. The paper discusses various aspects of a mobile satellite propagation channel. It outlines CSER activities in modelling the narrowband characteristics, and wideband measurements, of the channel