What is the Value of Limited Feedback for MIMO Channels?¤ David J. Lovex, Robert W. Heath Jr.y, Wiroonsak Santipachz, Michael L. Honigz x School of Electrical and Computer Engineering Purdue University 465 Northwestern Ave. West Lafayette, IN 47907 USA
[email protected] y Wireless Networking and Communications Group Department of Electrical and Computer Engineering The University of Texas at Austin Campus Mail Code: C0803 Austin, TX 78712 USA
[email protected] z Department of Electrical and Computer Engineering Northwestern University 2145 Sheridan Road Evanston, IL 60208 USA fsak,
[email protected] July 6, 2004 Abstract Feedback in a communications system can enable the transmitter to exploit chan- nel conditions and avoid interference. In the case of a multiple-input multiple-output (MIMO) channel, feedback can be used to specify a precoding matrix at the transmit- ter, 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. Perfor- mance results show that even a few bits of feedback can provide performance close to that with full channel knowledge at the transmitter. Index Terms- Limited feedback, Quantized precoding. ¤D. J. Love was supported by a Continuing Graduate Fellowship and a Cockrell Doctoral Fellowship through The University of Texas at Austin.