On multiuser receiver performance analysis and code design for space-time coded DS-CDMA systems

The combination of space-time coding (STC) techniques and multiuser detection is a promising approach to increase the spectral efficiency of multiple-access channels. We present a theoretical performance analysis of multiuser receivers for space time coded DS-CDMA systems. We study the performance of the maximum-likelihood multiuser receiver (MLMR) for a set of asynchronous independent users communicating with the base station. The framework of space-time coding is used to analyze the jointly coded users' signals. Based on the joint codeword distance matrix, we derive a new performance criterion for constructing codes. We prove that when the proposed criterion is satisfied, the MLMR for space-time coded DS-CDMA achieves the single user bound. We present numerical results that agree closely with the theoretical analysis. Moreover, due to the prohibitive complexity of the MLMR, we examine the performance of a suboptimal scheme, derived from MLMR, which was previously proposed (see Corral-Briones, G. et al., Proc. IEEE WCNC 41, p.94-8, 2002). Simulation results show that this scheme retains the asymptotic performance of the MLMR for space-time coded systems.