A reduced rank decorrelating RAKE receiver for CDMA communications over frequency selective channels

Abstract

CDMA systems need simultaneous multiple access interference suppression and adaptive interference suppression filters that may span three symbols. Thus, a large number of filter coefficients need to be estimated. By the use of reduced rank filtering, it is possible to lower the number of required filter coefficients with a small decrease in performance. Honig (see Proc. IEEE Asilomar Conf. Signals, Syst. Comput., Pacific Grove, CA, p.1106-10, 1998) made a successful attempt to develop a reduced rank algorithm based on the multistage Wiener (MSW) filter of Goldstein and Reed (see IEEE Tran. on Information Theory, vol.44, no.7, p.2943-59, 1998) for non-dispersive CDMA signals. In this paper, motivated by MSW we propose a reduced rank decorrelating RAKE receiver for dispersive CDMA signals. The proposed receiver is blindly implemented in a lower dimensional space, relative to the full-rank receivers, without the aid of training sequences and the channel information. By exploiting the structure of the user signature waveform, the proposed receivers exhibit performance close to that of the reduced rank MMSE receiver implemented with the desired user's known channel information.