On the Achievable Throughput of Per Chunk User Scheduling for MIMO-OFDM Downlink Using Opportunistic Feedback

Abstract

Future mobile communication systems will adopt the multiple antennas at both transmitter and receiver to improve system capacity and spectral efficiency. In our proposed system a Per-chunk user scheduling with opportunistic feedback for multiple-input–multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) is considered. In this system we provide a solution for achievable throughput by grouping adjacent subcarriers into chunks, the amount of required feedback information is reduced. Based on the net throughput criterion, which accounts for the reduction in sum rate due to the feedback overhead, it is shown that there exists an optimal chunk size that maximizes the net throughput.  In which, for each chunk, only users with achievable rates higher than a predetermined threshold report back their rates. Analytical expressions for the net throughput are derived, which enable finding the optimum threshold that maximizes the average net throughput. The results show that increasing the total number of users in the system results in the net throughput of most existing MIMO-OFDM downlink schemes decreasing to zero for moderate-size user pools, whereas the net throughput of per-chunk user scheduling with opportunistic feedback increases with the total number of users even that number is very large.