Precoding Design and Optimization for Multi-Antenna Systems With Limited Feedback

Abstract

We consider a multi-antenna wireless system consisting of a source transmitting to its destination with limited feedback, where the channel state information (CSI) is considered to be quantized and fed back from the destination to the source in the face of channel quantization errors (CQE). We propose a multi-antenna precoding (MAP) scheme to mitigate an adverse effect of the CQE, which is called the CQE oriented MAP and denoted CQE-MAP for short. Typically, using more channel quantization bits enhances the accuracy of quantized CSI acquired at the source and improves the data rate of the source-destination transmission, which, however, results in an increase of the CSI feedback overhead. We define an effective throughput as the difference of the data transmission rate and the CSI feedback rate that is used for characterizing the system overhead of sending the quantized CSI. An optimization analysis of the CQE-MAP scheme is carried out in terms of maximizing the effective throughput with regard to the number of quantization bits per channel. It is proved that the conventional maximal ratio transmission (MRT) based MAP method denoted by MRT-MAP could be a special case of the proposed CQE-MAP scheme for centralized antenna systems. Simulation results demonstrate that the CQE-MAP generally achieves a higher effective throughput than the MRT-MAP for distributed antenna systems, especially in the high signal-to-noise ratio (SNR) region. It is also illustrated that the effective throughput of CQE-MAP scheme can be further maximized through an optimization of the number of quantization bits per channel. Moreover, with an increase of the SNR or a decrease of the terminal moving speed, an increased number of quantization bits per channel is needed for the sake of maximizing the effective throughput.