Robust measures for decision feedback equalization in CDMA systems

Decision feedback equalization (DFE) is a very effective receiver component that cancels intersymbol interference without inducing noise amplification. However, it suffers from error propagation in the start-up phase and when the environment undergoes a sudden change. For DS-CDMA wireless systems, we develop robust measures to mitigate the catastrophic error propagation effect using appropriate constraints on the receiver weight vectors. These constraints are constructed from the spreading codes of the desired user to preserve its output energy. By doing so, a desirable level of signal output power is maintained to keep the error probability low, thus preventing decision errors from occurring or propagating. Moreover, the introduction of signal-preserving constraints offers capacity of multiple access interference suppression. Efficient adaptive implementations are developed, and simulations performed to verify the effectiveness of the proposed constrained DFE detectors. It is demonstrated that the constructed constraints can eliminate the training overhead, offering complete blind implementations for multiuser decision-directed DFE filters