Adaptive Opportunistic Transmission in MU-MIMO Downlink with Reduced Feedback

In this paper we proposed two threshold-aided adaptive opportunistic transmission strategies in multiuser multiple-input multiple-output (MU-MIMO) downlink with limited feedback. Threshold scheme in company with transmission mode adaptation are employed to handle feedback cost and improve system performance. In one time slot, each mobile station (MS) carries out channel estimation, selects appropriate transmission mode and feeds back adaptively. With feedback information the base station (BS) schedules one user out of candidate MSs and transmits to it. One of the proposed strategies employs single-level threshold. However, proper design of the threshold is difficult. Since a tight one would result in high outage probability whereas a loose one could not reduce feedback load effectively. Thus the other method employs double-level threshold. In this scheme, the primary threshold is used for feedback reduction, the secondary one is employed to guarantee the outage performance. In evaluating the strategies, statistical analysis and Monte-Carlo simulation are used. Results show that with properly designed thresholds, the proposed schemes can greatly reduce the feedback load, achieve high throughput and good outage performance.