Probability of error in the return link of a CDMA mobile satellite system

CDMA has been proposed as the multiple access technique for some future generation mobile satellite systems at the L-band. To enhance the coverage and the quality of service non-geostationary constellations are envisaged. This implies the presence of a large Doppler effect that combined with frequent mobile channel shadowing makes the uplink closure for handheld terminals a very challenging task. In this paper the performance of M-ary orthogonal convolutionally coded DS-CDMA is analyzed in depth and its performance compared to the simpler coded differential BPSK scheme. The bit error rate bounds with or without satellite diversity and equal gain combining are evaluated over typical LEO satellite fading channels. Different coding rates and soft metrics are considered to optimize the channel performance.