Multi-stage MMSE/MOE receivers for frequency selective fading channels in DS-CDMA systems

A multi-stage minimum mean square error filter bank (MS-MMSE-FB) and a minimum output energy filter bank (MS-MOE-FB) for the detection of DS-CDMA (Direct-Sequence Code-Division Multi-Access) signals under a dynamic multi-path fading environment are presented. The output signal-to-interference plus noise ratios (SINRs) for both MS-MMSE-FB and MS-MOE-FB are derived. The analytical results reveal how the output SINRs of reduced-rank MS-MMSE-FB and MS-MOE-FB vary with the rank of filters. The findings coincide with results in [1], namely, the rank needed to achieve a target performance does not scale with the system loading in an additive white Gaussian noise (AWGN) channel. The derivation shows that, with the aid of desired user's channel information, the rank of the receivers can be drastically dropped without affecting the steady state SINR, an important factor for interference suppression in a dynamic fading channel with adaptive MS-MMSE-FB/MS-MOE-FB detections.