What is the value of limited feedback for MIMO channels?

TLDR

Feedback enables a transmitter to adapt to channel conditions, and in MIMO systems it can specify a precoding matrix to activate the strongest modes, but limited feedback raises questions about quantization and achievable performance gains. The paper reviews recent research on limited feedback for MIMO channels. The authors propose constructing a finite set of precoding matrices and selecting one to send to the transmitter. Results indicate that a few bits of feedback yield performance near that of full channel knowledge.

Abstract

Feedback in a communications system can enable the transmitter to exploit channel conditions and avoid interference. In the case of a multiple-input multiple-output channel, feedback can be used to specify a precoding matrix at the transmitter, which activates the strongest channel modes. In situations where the feedback is severely limited, important issues are how to quantize the information needed at the transmitter and how much improvement in associated performance can be obtained as a function of the amount of feedback available. We give an overview of some recent work in this area. Methods are presented for constructing a set of possible precoding matrices, from which a particular choice can be relayed to the transmitter. Performance results show that even a few bits of feedback can provide performance close to that with full channel knowledge at the transmitter.