TDD-CDMA Downlink precoding with Channel Mismatch Error

Recently research has been focused on techniques that simplify the mobile receiver structure in CDMA systems by means of precoding. It is known that when channel state information (CSI) is available at the transmitter a large performance gain can be achieved. In a system employing time-division duplexing (TDD), CSI can be obtained at the base station if there is reciprocity between the forward and reverse channels. In any case, channel estimation errors are inevitable due to the presence of background noise in the estimated signal and due to the finite number of feedback bits used in a limited-rate feedback system model. In this paper, MMSE based precoding technique has been derived by considering channel estimation errors as an integral part of the system design. Simulation results are provided which demonstrate significant performance improvement when compared to the chip-wise linear precoding.