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The problem of adopting space-time block coding (STBC) in the uplink of direct sequence code division multiple access (DS-CDMA) systems is addressed. A novel system architecture is proposed for space-time (ST)-coded uplink transmissions over multipath fading channels with multiple user interference (MUI)-free reception. This proposed system is a combination of single-carrier time-reversal zero-padding (SC-TR-ZP)-based STBC with chip-interleaved block-spread (CIBS)-CDMA. Simulation results show that a substantial performance improvement can be achieved by adopting ST coding compared to the original CIBS-CDMA scheme without ST coding. Optimal maximum likelihood sequence estimation (MLSE) may be computationally prohibitive for long channels and/or with high-level modulation. Hence, the performance of different decision feedback sequence estimation (DFSE) schemes is investigated for the proposed ST-coded uplink system. In the case of whitened DFSE (WDFSE), a linear prediction (LP)-based approach is adapted for designing a whitening prefilter. Furthermore, a new scheme, which is a combination of linear equalization (LE) and modified unwhitened DFSE (MUDFSE) is proposed. The proposed combined LE-MUDFSE (Comb. LE-MUDFSE) scheme is very attractive as error-floor behavior appearing in other unwhitened DFSE schemes is eliminated. The simulation results indicate that a substantial performance improvement over the minimum mean-square error (MMSE) equalizer can be achieved by using either Comb. LE-MUDFSE scheme or WDFSE scheme.
Date of Publication: Nov. 2005