Multi-level threshold opportunistic transmission in MU-MIMO downlink with reduced feedback

In this paper we introduced a multi-level threshold opportunistic transmission scheme in multiuser MIMO (MU-MIMO) downlink with reduced feedback. In the strategy two thresholds are employed. The tight one is used for feedback load reduction, and the loose one is to guarantee low outage probability. Mobile station (MS) whose channel gain exceeds one of the thresholds is eligible for feeding back information. We also introduce transmission mode adaptation, including beamforming (BF) and spatial multiplexing (SM) at each MS. User can select proper transmission scheme based on its channel estimation. With feedback channel state information (CSI), base station (BS) schedules one user out of candidate MSs in each time slot. In evaluating the strategy, statistical analysis is employed in company with Monte-Carlo simulation. Results show that with properly designed thresholds, the proposed scheme can greatly reduce the feedback load and achieve high throughput as well as good outage performance.