COMPLEX CDMA VERSUS FDMA SCPC FOR LOW AND MEDIUM BIT-RATE APPLICATIONS FOR FIXED SATELLITE SERVICES/

In this paper, the performance of a DS-CDMA asynchronous satellite com munication system, using four-phase sequences with near-optimum correl ation properties, is analysed and compared with the result achievable by adopting the FDMA/SCPC approach. The comparison is carried out on t he basis of the number of the simultaneous active channels in the netw ork and of spectral efficiency. In addition, a similar CDMA system usi ng four-phase sequences, constructed by means of binary Gold sequences having the same family size, has been analysed, and notable performan ce differences have been found. In particular, the use of four-phase n ear-optimal sequences provides an increase of about 50 per cent in the spectral efficiency. This result expands the convenience of using CDM A over a wider set of bit rate values, even for fixed satellite commun ications. Convolutional coding and Viterbi soft decoding are also incl uded in the system. Simulation results are shown for some values of bi t error probabilities of practical interest.