Reduced-complexity receivers for space-time coded DS-CDMA systems

GRACIELA CORRAL BRIONES; CARMEN E. RODRIGUEZ

Digital Commun. Res. Lab., Univ. Nacional de Cordoba, Argentina

Conferencia; GLOBECOM '02. IEEE Global Telecommunications Conference, 2002.; 2002

The combination of space-time coding and multiuser detection is an effective way to increase the spectral efficiency of multiple access systems. In this paper we propose a new multiuser decoder for space-time coded asynchronous DS-CDMA systems over Rayleigh fading channels. The proposed scheme is an extension of the one introduced in Corral-Briones et al. (2002). Complexity is reduced exploiting the fact that the trellis for the entire decoder can be decomposed into a set of trellises for subsets of users with a lower total state count. Different tradeoffs between performance and complexity can be achieved by adjusting the number of users decoded by each trellis. We investigate the behavior of the proposed receiver for a few users with moderate and high correlation. Simulation results show that the new scheme achieves an order of magnitude lower error rate than the conventional receiver (i.e., a single-user decoder that ignores multiuser interference) at almost the same complexity. Moreover, doubling the complexity, the proposed receiver performs near the single user bound. We also address the performance and complexity of the new scheme in high bandwidth efficiency situations, which are of high practical interest. It is found that performance close to the single user bound is achieved with our scheme at practical frame error rates with significantly lower complexity than the receiver proposed in Corral-Briones.