Coded Performance of Spread Space-Spectrum Multiple Access for the MIMO Forward Link Transmission

In this paper, the coded performance of a previously proposed space-time multiuser multiplexing scheme called the spread space-spectrum multiple access (SSSMA) is investigated for the forward link MIMO system. The key feature of SSSMA is that the number of user-channels is increased by exploiting additional degrees of freedom offered by multiple antennas. The large MIMO data pipe is divided and allocated to multiple coded user-channels over the entire transmission time interval and bandwidth. Thus, unlike the orthogonal multiple access scheme, the spatial multiple access interference (MAI) exists in SSSMA and is mitigated through the use of the space-time diagonal (STD) spreading sequences. When coding is introduced, each user may employ a user-specific optimal inter-leaver. It is theoretically shown that for two transmit antennas and optimal interleaving, the full diversity criterion is satisfied for all multiuser codeword pairs, thereby suggesting that spreading is an effective means to achieve spatial diversity at high bandwidth-efficiency. With suboptimal detector such as interference-cancelling receiver based on turbo processing, it is shown that the SSSMA offers near-capacity performance that is superior to many well-known MIMO transmission schemes.