Adaptive MC-CDMA and MC-DS-CDMA receivers for multiuser and multipath fading communications

OFDM is a promising scheme for multicarrier (MC) transmission, since it has the advantage of high spectral efficiency, robustness to frequency selective fading, and feasibility of low-cost transceiver implementation. The combination of OFDM and CDMA, referred to as OFDM-CDMA, recently attracted most research interests in wireless communications. In this paper, adaptive receivers for OFDM-CDMA communication systems are developed based on the least mean square (LMS) algorithm. We evaluate the down-link performance for two forms of OFDM-CDMA schemes which are MC-CDMA and MC-DS-CDMA in multipath fading channels. A drawback of OFDM schemes is the rate reduction due to the cyclic prefix (CP) overhead, which significantly affects the channel utilization in MC-DS-CDMA systems. Thus we propose adaptive receiver structure that exploits both frequency-domain and time-domain equalization to improve the performances of MC-DS-CDMA systems with shorter or no CP. Simulation results show performance comparisons between MC-CDMA and MC-DS-CDMA systems, which also verify the performance improvement of our proposed receiver for MC-DS-CDMA systems exploiting shorter or no CP.