The asymptotic multiuser efficiency of two-stage detection in mismatched AWGN channels

This paper investigates the loss of near-far resistance for two multiuser detectors due to imperfect channel estimation in the additive white Gaussian noise multiple access channel. The symbol error rates and the Asymptotic Multiuser Efficiencies (AMEs) of the two-stage hard-limiting detector are determined for imperfect channel knowledge in the two-user asynchronous channel. The degradation of the AME due to channel mismatch is described for a variety of mismatch conditions, including errors in estimation of timing and complex amplitude. It is shown that when perfect knowledge of the channel does not exist, the two-stage detector becomes near-far limited. Also presented is a comparison of the exponentially complex maximum likelihood sequence detector and the hard-decision two-stage detector with imperfect knowledge of the channel