MIMO Precoding of CDMA Systems

Because of the independency of the MIMO Rayleigh channels, the capacity of a MIMO CDMA network is often limited by co-channel interference. In the uplink, sophisticated multiuser detection (MUD) can be implemented at the base stations (BS) to counter the co-channel interference. However, on the downlink, the receivers at the mobile stations (MS) are usually required to be simple, therefore complex interference suppression/cancellation techniques are not always possible at the receiver side. In this paper, MIMO precoding at the transmitter side is proposed as an means to improve system performance. CDMA BSs can cooperate to determine the signals to be transmitted on the downlink, effectively realizing an orthogonal transmitting scheme. Theory analysis and simulations show that good capacity and BER performance have been achieved by the proposed scheme, though the MIMO CDMA of only two antennas and the Rayleigh channel to be not fully noncoherent