Transmit-preprocessing techniques with simplified receivers for the downlink of MISO TDD-CDMA systems

Time-division-duplex code-division multiple-access (TDD-CDMA) systems have recently gained attention with their inclusion in third-generation mobile systems. In this paper, we introduce two optimized transmit preprocessing techniques to reduce multiple access interference in the downlink of TDD-CDMA systems with multiple transmit antennas that are employed at the base station (BS). In these systems, signal preprocessing is performed at the BS, so that a simplified receiver structure that consists of a one-finger correlator can be utilized at the mobile station. Analytic solutions for both of the optimized transmit preprocessing techniques are derived by minimizing the transmit mean square error. Numerical results are also provided, which demonstrate significant performance improvement when compared to the conventional RAKE system and the pre-RAKE maximum ratio combining transmit diversity system. In particular, transmit antennas can be used to increase the system capacity.