MIMO Broadcast Channels with Finite Rate Feedback

TL;DR

This paper analyzes the impact of finite rate feedback on MIMO broadcast channels, revealing that feedback rate must increase linearly with SNR to maintain multiplexing gains, contrasting with point-to-point MIMO systems.

Contribution

It provides simple expressions for throughput degradation due to finite rate feedback and highlights the linear feedback rate increase needed with SNR for full multiplexing.

Findings

Feedback rate must increase linearly with SNR to achieve full multiplexing gain.

Finite rate feedback causes throughput degradation, quantified by derived expressions.

Contrasts with point-to-point MIMO where feedback rate does not need to increase with SNR.

Abstract

Multiple transmit antennas in a downlink channel can provide tremendous capacity (i.e. multiplexing) gains, even when receivers have only single antennas. However, receiver and transmitter channel state information is generally required. In this paper, a system where each receiver has perfect channel knowledge, but the transmitter only receives quantized information regarding the channel instantiation is analyzed. The well known zero forcing transmission technique is considered, and simple expressions for the throughput degradation due to finite rate feedback are derived. A key finding is that the feedback rate per mobile must be increased linearly with the SNR (in dB) in order to achieve the full multiplexing gain, which is in sharp contrast to point-to-point MIMO systems in which it is not necessary to increase the feedback rate as a function of the SNR.