A concatenated coded modulation scheme for spread spectrum multiple access system

This paper presents a concatenated coded modulation scheme for error control as applied to a spread spectrum multiple access system. A system model is proposed that allows one to apply modulation code (block) and a pseudo-noise (PN) spreading sequence to the data symbols to be transmitted. Gold sequences are employed for the purpose of PN spreading. Some good inner codes were chosen from Kasami (1990). Performance of those codes in an additive Gaussian noise channel is investigated with 5-30 users transmitting simultaneously. The performance of the system for coded 8-PSK were compared with uncoded QPSK under similar environment. The coded modulation scheme showed significant performance improvement with little or no bandwidth increase. The short modulation code is used as the inner code and a relatively powerful Reed-Solomon (RS) code is used as the outer code. Soft decision Viterbi decoding can be used for inner code. The proposed scheme is attractive for high speed satellite communications for file transfer applications where great reliability is desired