Transmitter precoding for space time CDMA system in multiuser communication

The desire to reduce complexity at mobile unit in cellular system has led to the investigation of signal processing techniques that move the complexity from the mobile unit to the base station. Transmitter precoding is one such technique and it represents a linear transformation of transmitted signals, such that mean squared error at all receivers is minimised. In this paper, we investigate the performance of transmitter precoding technique for the downlink of multiple input single output (MISO) DS CDMA system over fading channel. Our receivers are constrained to simple matched filters and complete channel information (CSI) at the transmitter is assumed. This is feasible under the time division duplex (TDD) mode of the 3G UMTS system where channel is assumed to be the same on uplink and downlink and can be estimated from the uplink at the base station. It is seen that transmitter precoding for MISO system offers reasonable advantage over single antenna system precoding along with transferring computational complexity to the base station from mobile station.