Complex CDMA Versus FDMA/SCPC for Low and Medium Bit Rate Applications for Fixed Satellites Services

In this paper, the performance of a DS-CDMA asynchronous satellite communication system, using four-phase sequences with near-optimum correlation properties, is analysed and compared with the result achievable by adopting the FDMA/SCPC approach. The comparison is carried out on the basis of the number of the simultaneous active channels in the network and of spectral efficiency. In addition, a similar CDMA system using four-phase sequences, constructed by means of binary Gold sequences having the same family size, has been analysed, and notable performance differences have been found. In particular, the use of four-phase near-optimal sequences provides an increase of about 50 per cent in the spectral efficiency. This result expands the convenience of using CDMA over a wider set of bit rate values, even for fixed satellite communications. Convolutional coding and Viterbi soft decoding are also included in the system. Simulation results are shown for some values of bit error probabilities of practical interest.