An Enhanced Space-time Equalizer for MIMO Multi-code CDMA Systems

This paper proposes an enhanced chip-level linear space-time equalizer for multiple-input-multiple-output (MIMO) multi-code CDMA systems. In the MIMO multi-code CDMA systems, the reuse of the same spreading codes in different transmit antennas significantly degrades the equalization performance if the space-time equalizer uses a weighting vector that minimizes the mean squared error of the equalizer output chip sequence. As the CDMA despreader concatenated to a space-time equalizer distorts inter-stream interference components differently from multipath interference and background noise components, the traditional chip-level minimum mean squared error (MMSE) weighting vector usually steers in a sub-optimal direction in the signal space. Therefore, we propose a new MMSE weighting vector that takes the despreading effect into account in this paper. Simulation results show a substantial performance improvement through the new weighting vector