MLSE and MAP detectors for high-data-rate DS-CDMA reception in dispersive channels

A maximum likelihood sequence estimation (MLSE) and a maximum a posteriori (MAP) detector for DS-CDMA are proposed. The proposed receivers are attractive when the desired signal is in multi-code reception scenarios and when propagation channels are dispersive. Multipath results in loss of orthogonality among own-cell signals in the downlink and among same-user signals in the uplink. In these cases, receiver performance is limited by self-interference from the desired signal itself and interference from all other signals. The generalized RAKE (C-RAKE) receiver can be used to suppress both forms of interference, treating them as colored noise. To improve receiver performance further, we use an MLSE or a MAP detector to alleviate self-interference. The MAP detector can be used with the outer code decoder to form a turbo equalizer to further improve the receiver performance. Our numerical results show that gains larger than 2 dB over G-RAKE can be achieved by the proposed receivers for a WCDMA radio-access bearer of 4.6 Mbps using a 64-state sequence detector.