Quantized feedback scheduling for MIMO-OFDM broadcast networks with subcarrier clustering

Abstract

Feedback of user channel quality information (CQI) to base station (BS) is essential for efficient scheduling of multi-user (MU) multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) broadcast networks. This feedback overload increases linearly with the cardinality of users, transmit antennas and subcarriers present in MIMO-OFDM systems. Hence, clustering of adjacent subcarriers has been considered in literature for reduction in feedback load. Here users communicate the CQI of the center subcarrier of the clusters assuming that subcarriers of a cluster experience similar channel conditions. However, this method leads to inefficient resource scheduling for higher cluster sizes as it does not take advantage of CQI of other subcarriers that experience non-uniform channel conditions. This reason motivated us to develop a new limited feedback scheduling scheme where quantization of CQI with multiple bits is implemented along with clustering of adjacent subcarriers. In this scheme, the multi-bit quantized CQI of all the subcarriers of a cluster are examined for the efficient scheduling along with further reduction in the feedback overhead. Moreover, we proposed a less time consuming method to find the optimum quantization thresholds that play significant role in multi-bit quantization process by using genetic algorithm (GA). This GA methodology is computationally more efficient than exhaustive search process.