CDMA with Transmit Antenna Diversity Technique for Broadband Propagation Systems

The combination of CDMA and space time block coding (STBC) has been proposed for indoor environment where the delay spreads are very small and the channel is flat fading. However, these schemes are not valid for the outdoor situation where the delay spreads are significantly large and the channel is frequency selective fading. Therefore, in our paper, we propose CDMA with space-time block coding with three transmit antennas for frequency selective fading channels (outdoor situation) without loss of diversity order. In the proposed scheme, Orthogonal Frequency Division Multiplexing (OFDM) technique is used to mathematically change the frequency selective fading channel to multi flat fading channels. It is worthy of noting that our scheme provides very low decoding complexity compared to CDMA with space time trellis coding. Also, the proposed scheme provides high performance and high bandwidth efficiency. Simulation results are provided to show the significant improvement in the performance achieved by the proposed scheme.