STATISTICAL OBSERVATIONS OF DATA-TRANSMISSION OVER LAND MOBILE SATELLITE CHANNELS

A satellite system communicating directly to a mobile terminal requires the basic link analysis of a small fixed terminal, but will have additional channel characteristics due to the motion of the terminal. This motion introduces spectral changes in the transmitted waveforms that can provoke future degradations relative to those of fixed-point systems. The effects are primarily originated by the time-varying multipaths that appear in trying to transmit an electromagnetic field from a satellite to a moving terminal or vehicle. The multipath fading severely restricts the accurate data transmission over land-mobile satellite networks. The fading plagues the propagation medium by imposing random amplitude and phase variations on the transmission signal. However, the relative effect of an undesired random variation is reduced by the presence of a strong line-of-sight (LOS) component. In this paper, to analyze the data transmission performance of the satellite-to-ground mobile channel, a Rician fading model is used. For this model, the received multipath signal consists of the sum of a direct or LOS component and a fading component due to reflections from objects adjacent to the transmission path. Generally, when a data packet encounters a fade, it most likely contains errors and will have to be retransmitted. Thus, the size of the packet is crucial to determine the performance of the channel. The present study finds for the first time the optimum packet size by applying an analytical model of the dynamics of the Rician channel. The performance criterion is based on the rate of information transfer through the network, the vehicle speed, and the modulation fade margin.