Efficient minimum probability of error demodulation for DS-CDMA systems

Demodulators based on the minimum mean squared error (MMSE) criterion are optimal for ´ideal´ AWGN channels. However, in the case of wireless multipath channels, wherein ISI is inherent, MMSE based algorithms do not offer the optimal framework for demodulation. Minimum probability of symbol error (MPOSE) based detectors have been shown to perform significantly better than MMSE based approaches in these scenarios under a variety of modulation and multiplexing schemes. High computational complexity, however, prohibits the use of these algorithms in practical communication systems. The major challenge now is to reduce the computational burden of the MPOSE algorithms. This paper, as a step in this direction, discusses two already published MPOSE algorithms and proposes a modification to them whereby we not only achieve significant gains in computational complexity but also improve the BER performance. The system is also found to be robust to error propagation due to wrong estimation of the ISI term.