ABSTRACT
In this paper, we analyse the performance of the downlink of a Non-Geostationary Earth Orbits (NGEO) mobile satellite channel based on Direct Sequence-Code Division Multiple Access (DS-CDMA) in the presence of shadowing, fading and interference from other satellites visible at the same time. In particular, the performance of QPSK convolutionally coded DS-CDMA over a Rice-Lognormal channel is analysed in depth. The provision of such a service requires that the user must have sufficient link quality for the duration of call. To have sufficient link quality, the user must have an adequate power to overcome the path loss and other physical impairments and maintain the performance of the system. The most important factor in determining the performance is the probability of signal shadowing which depends both on the user environment and on the constellation.
The paper addresses the exploitation of satellite diversity in the Rician-Lognormal channel. In particular, we focus on the impact of satellite diversity on service availability, path blockage, call dropping and system capacity, considering the effects of imperfect power control, shadowing and voice activity. Concatenated codes are used to provide different bit error probabilities for different services.
We show that satellite diversity is an essential in providing service availability especially in urban and suburban areas. Also we show the impact of satellite diversity on the system capacity under different environments, which is related to elevation angle, latitude and the nature of the user terminal environment.