Generalized data estimate refinement techniques for iterative multiuser detection in TD-CDMA including higher order modulation

Due to complexity reasons the employment of optimum nonlinear multiuser detection in TD-CDMA is prohibitive. Therefore, in the past the preferred detection scheme in both the uplink and the downlink of TD-CDMA was linear multiuser detection based on the zero forcing or minimum mean square error estimation. Unfortunately, especially in scenarios with high system loads linear multiuser detection has the disadvantage of an undesirably small asymptotic efficiency which can only be overcome by nonlinear detection schemes as e.g. iterative nonlinear multiuser detection schemes. Iterative nonlinear multiuser detection schemes benefit from exploiting a priori information which is generally evaluated by data estimate refinement schemes. Data estimate refinement schemes have only been studied systematically for BPSK and QPSK modulation yet. In this paper, generalized optimal and suboptimal data estimate refinement schemes which support any kind of modulation scheme will be proposed and analyzed.