Analysis of a DS-CDMA return link for mobile satellite communications

Coded non-coherently demodulated DS-CDMA (Direct-Sequence Code Division Multiple Access) schemes are well suited for the uplink of forthcoming satellite-based personal communication systems. To enhance the coverage and the quality of service low Earth ortbiting (LEG) constellation are usually selected. This implies the presence of large Doppler effect that combined to the frequent mobile channel shadowing makes the uplink closure for hand-held 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 withouth 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.