Soft output interference suppression in TDMA wireless communications

We present a novel symbol-by-symbol Bayesian multiuser detector for cochannel interference cancellation in TDMA cellular communications. To begin with, we present the usual composite signal model consisting of the desired signal, interferer, channel parameters and channel noise. Then, we derive the soft output interference cancellation algorithm (SICA) to compute fixed-lag maximum a posteriori (MAP) estimates of the data symbols of the desired user, using a fixed lookahead of D observations. In the process, the interferer symbols are treated as nuisance parameters and averaged out. The complexity of the SICA is exponential in the length of the combined channel at the receiver. Subsequently, we present a simple, yet effective, technique for complexity reduction without significant performance degradation. We apply the algorithm to some typical scenarios, using the IS-136 TDMA standard, to demonstrate its interference suppression capabilities. In this paper, we assume that all relevant channel parameters are known. Hence, our results should be viewed as representing the best possible performance that can be obtained with the SICA in the scenarios considered.