Efficient Channel Quantization and Feedback Strategies for Multiuser MIMO-OFDM Systems

Multiuser diversity can significantly improve wireless system performance by exploiting the feedback information that conveys the channel quality. In multiple input-multiple output and orthogonal frequency division multiplexing (MIMO-OFDM) systems, the per subcarrier on per antenna feedback induces a substantial amount of feedback overload and requires high computational complexity. This paper addresses the channel quality information (CQI) quantization and feedback strategies for resolving this problem. First, a quantization method is proposed by quantized values indicating the modulation level instead of the full values of CQI. A close-form expression of the achievable spectrum efficiency is obtained and shows no loss compared with perfect CQI. Secondly, three partial feedback approaches are proposed in order to reduce the amount of CQI feedback at the expense of slight decrease of spectrum efficiency, named opportunistic, best and hybrid feedback respectively. Finally, extensive simulations are presented to evaluate the performance of feedback strategy. The results indicate that hybrid feedback combined with the proposed quantization method performs best in comparison with other schemes. In this case, the feedback overload can be greatly reduced without compromising the multiuser diversity gain, as long as a proper choice of the strategy parameters is executed.