A novel structure of MIMO-Turbo CDMA system

A novel structure of CDMA system is proposed in this paper. Combined with MIMO technique, Turbo en-decoding is used based on the CDMA system, which works well under the enviroments of multiuser and multipath. In this improved CDMA system, the data flow transmitted to one mobile user is divided into two substreams, and each substream is encoded by different Turbo encoder and spread by the same spreading code respectively. The spread data flows are sent to two transmit antennas at base station; while the mobile user despreads and decodes two data flows received from two receive antennas by the same matched filters and two corresponding Turbo decoders respectively. Although Turbo coding will decrease transmit code ratio, MIMO technique compensates the loss of frequency efficiency caused by Turbo codec with channel multiplexing, so the good BER performance is obtained as well as the full transmit rate without much more additional complexity. The paper analyzes the performance of MIMO-Turbo CDMA systems theoretically and experimentally under such conditions of multiuser and multipath. The simulation results show that the novel CDMA systems can be of better performance than the conventional CDMA systems based on single transmit antenna at a base station.