Reducing feedback load for proportional fair scheduling in MIMO OFDM systems

A feedback reduction scheme is proposed in multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. The proposed scheme can reduce the feedback load of channel quality indicator (CQI) required for proportional fair scheduling at base station (BS). The probability distributions of instantaneous rate and average rate are studied. Then the distribution of proportional fair (PF) priority is obtained. Each user predicts the probability of being scheduled on the condition that its own PF priority is known. To reduce the amount of feedback load, a hard threshold of PF probability is designed for the CQI feedback reduction. This threshold is broadcast to all the users and only the users whose instantaneous PF priorities are higher than the threshold will feed back the CQI. The amount of feedback load saved by implementing the hard threshold is determined and the effect on the system throughput is analyzed. The simulation results show that the proposed scheme can reduce the feedback overhead while minimize the throughput loss.