Optimized quantization resolution for limited CSI feedback with outage

Abstract

In mobile slow fading scenarios, channel state information (CSI) is required at the transmitter to adapt the data transmission strategy to the current channel state. In this regard, precoding in multiuser-multiple-input-multiple-output (MU-MIMO) downlink systems is a prominent example. In frequency division duplex, channel observations are quantized and fed back via the uplink, protected by an error correction code. The quantization resolution together with the code strength correspond to a certain amount of feedback bits. For a limited number of uplink signaling resources, there is a trade-off between investing bits for increasing the quantization resolution or for improving the error correction capability. While existing feedback schemes use a fixed quantization resolution, this work proposes a scheme which finds the optimal number of quantization bits for minimizing the channel uncertainty at the transmitter. Simulation results verify the proposed solution and apply it to precoded transmission in a MU-MIMO downlink system.