Canceling Co-Channel Interference for MIMO CDMA Systems*

According to MIMO idea, the CDMA systems with MIMO technique can increase system capacity, each mobile station in a cell can get at least two spatial communication channels if it equip more than two antennas. The idea is based on the assumption of the MIMO channels of base station (BS) to mobile stations (MSs) to be fully non-coherent, which means that the row vectors of MIMO channels´ matrix should be orthogonal each other. However, this paper shows that, for general application scenes, the row vectors of MIMO channels´ matrix are not orthogonal each other, the MIMO system can only keep the channel matrix to nonsingular, which leads to great co-channel interference existing in the spatial MIMO channels allocated to mobile stations, and the caused BER degradation can not satisfy the communication specifications. To solve the problem, different from classical MIMO approach, this paper proposes utilize inversed channel matrix to decode the spatial signal, instead of transposed channel matrix. Theory analysis and simulations show that good capacity and BER (error bit rate) performance can be achieved by the proposed scheme, though the MIMO CDMA of only two antennas and the MIMO channels are not fully non-coherent