Performance of multistage interference cancellers in space-time coded CDMA systems

In this paper, we investigate the bit error performance of multistage interference cancellers in a K-user asynchronous/synchronous space-time coded CDMA system under near-far conditions. We consider orthogonal space-time block codes with M, 1 ≤ M ≤ 8 transmit antennas. We develop a generalized discrete time vector model for the received signal at the output of the matched filters, and use this model to evaluate the bit error performance of multistage interference cancellers (IC). Our performance results show that: (a) when accurate fade amplitude and timing estimates are available, the IC are less near-far resistant at low near-far ratios (NFR) compared to,that at high NFR, due to the unreliability of the interfering users´ data estimates in the initial stages of the IC at low NFR; and (b) in the high NFR region, the near-far resistance is degraded due to inaccuracies in fade amplitude estimates. This indicates that that some amount of transmit power control is desired in IC to counter the loss of near-far resistance due to the above reasons.