Low Complexity MIMO-LDPC CDMA Systems over Multipath Channels

This paper develop a low complexity composite CDMA system based on MIMO (Multiple-Input-Multiple-Output) processing and LDPC(low-density parity-check) codec based CDMA systems, involved the complicated case of multipath, multiusers and short length LDPC codes. To explore the practical application, the mobile user in the composite CDMA systems is with only two antennas and adopts short length irregular LDPC codec, each user’s data has been divided two LDPC encoded substreams being sent to two transmitter antennas at base station. Since the LDPC encoded substreams of reaching the mobile user are orthogonal each other in space and time, the CDMA system performances (BER and SINR) can be improved much, but the multipath may ruin the orthogonal property. To solve the problems, the paper provides the algorithms of main function modules of transmitter and receivers, gives a simple method to test the girth of LDPC codes, and analyzes the performance of MIMO-LDPC CDMA systems theoretically and experimentally. The simulation results show that the hybrid CDMA systems can be of better performance than the conventional CDMA systems based on single transmitted antenna at a base station.