MIMO Broadcast Channels With Finite-Rate Feedback

TLDR

Multiple transmit antennas can yield large capacity gains in a downlink, but both transmitter and receiver channel state information are generally required. The authors analyze a system in which receivers have perfect channel knowledge while the transmitter receives only quantized channel information. They employ zero‑forcing transmission and derive simple expressions for throughput degradation caused by finite‑rate feedback. The study finds that to achieve full multiplexing gain, the feedback rate per mobile must increase linearly with SNR in dB, unlike point‑to‑point MIMO where the feedback rate need not grow 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 correspondence, 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 signal-to-noise ratio (SNR) (in decibels) in order to achieve the full multiplexing gain. This is in sharp contrast to point-to-point multiple-input multiple-output (MIMO) systems, in which it is not necessary to increase the feedback rate as a function of the SNR