Trellis-coded DS/CDMA multiuser communications

We investigate trellis coding with multiuser detection (MUD) applied in direct-sequence code-division multiple-access (DS/CDMA) communications. A generalized model called multi-sequence model is applied to systematically design the transceivers. In multi-sequence model, each user can be assigned more than one spreading sequence and the coding, modulation, and spreading sequences are jointly considered based on the extended Ungerboeck´s set partitioning principle to maximize free distance. We derive the optimum detector under the maximum likelihood criterion. To measure the influence on the bit-error-rate due to coding and multiple-access interference, asymptotic multiuser coding gain (AMCG) is defined to provide lower and upper bounds for transceivers. The numerical experiments justify the precision of AMCG to evaluate system performance. Verified by numerical analysis, a transmitter designed by multi-sequence model can achieve significant coding gain over uncoded systems while applying optimum detector, and the performance of coded systems is severely degraded without MUD. Therefore, these facts not only demonstrate the value to jointly design coding, modulation, and spreading sequences in trellis-coded DS/CDMA communications but also emphasis the needs of MUD to optimize the system performance.