QoS-based space-frequency prefiltering for TDD MC-CDMA systems in slowly time-varying channels

This work presents a space-frequency prefiltering scheme for slowly time-varying TDD MC-CDMA downlink communications with multiple antennas at the base station (BS). Unlike the conventional spatially uncorrelated block fading channel model, both channel variation in each packet and spatial correlation are considered in the design. In the TDD mode, the mobile terminals (MTs) transmit training signals at the end of each uplink packet. In the following downlink packet, the BS computes the signal weights on different antennas and subcarriers for each MT in each symbol period based on the channel state predicted from the received training signals. The goal is to minimize the total required transmit power while keeping the received signal-to-interference-plus-noise ratio (SINR) as the target for each MT Moreover. the maximum packet length for satisfying the SINR requirements has been determined. The results indicate that the total required transmit power call be reduced by a lower mobile speed or more BS antennas. As a result, the maximum packet length call be extended in virtue of the power reduction. Copyright (C) 2008 John Wiley & Sons. Ltd.