A reduced-rank MMSE-DFE receiver for space-time coded DS-CDMA systems

A reduced-rank, minimum mean square error decision feedback estimator (MMSE-DFE) is proposed for the downlink, space-time coded, direct-sequence (DS) code division multiple access (CDMA) system. This new technique combines the multistage Wiener filter (MSWF) (Goldstein and Reed (1998)) with the decision feedback estimator (DFE). The primary requirement of MSWF-DFE is the knowledge of channel state information (CSI), which is feasible by using a pilot signal. Since there is no need for eigendecomposition or covariance matrix inversion, MSWF-DFE achieves a lower computation complexity via the rank reduction process. Moreover, in MSWF-DFE the commonality of the feedforward filter and the feedback filter is fully explored in order to share in computations. Thus, no or negligible extra computational load is required by the decision feedback. Our simulation results show that the proposed MSFW-DFE successfully maintains a near full-rank MMSE-DFE performance with the low rank forward and backward filters and can reduce the computational cost dramatically.