A Hybrid Feedback Protocol for Multiuser MIMO Downlink with Per-Antenna Scheduling

A novel hybrid feedback protocol is proposed for the multiuser multiple-input multiple-output downlink system. In the system under consideration, per-antenna scheduling is utilized. The base station (BS) employs spatial multiplexing and the users utilize zero-forcing receivers, creating multiple parallel spatial channels. For each spatial channel, exactly one user is scheduled at the BS, based on the feedback information from users. The hybrid feedback protocol is proposed to reduce the feedback overhead. It combines contention-based feedback and best-one feedback, in which each user competes to send information only about his best spatial channel. According to the channel quality of their best spatial channels, users are classified into three classes. Users in different classes have different probabilities to send feedback information on each feedback slot. The parameters that control the feedback process are jointly optimized to maximize the average sum-rate capacity. Simulation results show that the hybrid feedback protocol reduces the feedback overhead significantly with negligible sum-rate capacity loss compared to conventional feedback protocols.