Mitigating error propagation in CDMA multiuser DFE

Robust measures via constraining the filter weight vector are applied to the decision-directed decision feedback equalization (DFE) detectors to alleviate the error propagation problem in CDMA wireless systems. These constraints are constructed from the spreading codes of the desired user to preserve its output energy. The constrained portion of the weight vector is able to curb the effect of incorrect past decisions and provide the leverage to prevent error propagation and maintain a stable transmission. The use of signal-preserving constraints also improves the multiple access interference suppression capacity. Efficient adaptive RLS algorithms for nonlinear DFE filters are developed, and the achievable steady state SINR performance of both the unconstrained and constrained DFE is derived.