TCM, TTCM, BICM and BICM-ID assisted MMSE multi-user detected SDMA-OFDM using Walsh-Hadamard spreading

Space division multiple access (SDMA) aided orthogonal frequency division multiplexing (OFDM) systems assisted by efficient multi-user detection (MUD) techniques have recently attracted intensive research interests. Forward error correction (FEC) schemes and frequency-domain spreading techniques can be efficiently amalgamated with SDMA-OFDM systems for the sake of improving the achievable performance. A coded modulation (CM) assisted and minimum mean-square error (MMSE) multi-user detected SDMA-OFDM system combined with Walsh-Hadamard-transform-spreading (WHTS) across a number of subcarriers is proposed. The various CM schemes used are trellis coded modulation (TCM), turbo TCM (TTCM), bit-interleaved coded modulation (BICM) and iteratively decoded BICM (BICM-ID); they constitute bandwidth efficient schemes that combine the functions of coding and modulation. Invoking the WHTS technique makes possible further improvement of the average bit error rate (BER) performance of the CM-SDMA-OFDM system, since the bursty error effects imposed by the frequency-domain fading encountered are spread over the entire WHT block length, therefore increasing the chances of correcting the transmission errors by the CM decoders.