Linear multiuser precoding with transmit antenna diversity for DS/CDMA systems

For the downlink of direct-sequence (DS) code-division multiple access (CDMA) systems, the demand for high data rate transmission and the constraint of low-complexity mobile stations have led to the investigation of transmitter (Tx)-based multiple access interference (MAI) cancellation techniques. In this paper, we propose two linear MAI cancellation techniques, preRAKE linear decorrelating preceding (preRAKELDP) and multipath decorrelating preceding (MDP). The multipath diversity and antenna diversity are utilized in these transmitter designs. In the PreRAKELDP method, the PreRAKE combiner is preceded by a linear precoding filter. We illustrate two different transmit power control strategies for preRAKELDP, the zero-forcing (ZF)-based with individual user power scaling and the minimum-mean-square-error (MMSE)-based under total power constraint. The MMSE solution achieves lower error probability while the ZF solution has lower computational complexity. Compared to the preRAKELDP, the MDP method employs a simpler precoding filter but has modestly higher error rate. By theoretical analysis and numerical experiments, it is shown that the preRAKELDP and MDP outperform the existing linear transmitter precoding methods with similar complexity. In addition, the two proposed schemes result in very simple channel-independent receiver structure. Thus, they are suitable for the downlink of CDMA systems.