Feedback Strategies for MIMO-OFDM Communication Systems

by Prof. Robert W. Heath, Jr., Assistant Professor, Department of Electrical and Computer Engineering, University of Texas at Austin

 :  01 Jun 2005 (Wed)
 :  2:00pm - 3:00pm
Venue  :  Room 1401, 1/F (Lifts 25-26), HKUST

Channel state information can be used by the transmitter to improve quality and capacity in MIMO-OFDM communication systems. In most communication systems the transmitter will obtain channel state information through a feedback control channel. The number of channel parameters, however, is proportional to the product of the number of transmit antennas, receive antennas, and multi-paths. In real systems it can be difficult to inform the transmitter about the channel in a timely fashion. In this presentation we describe a cross-layer approach to reducing feedback in MIMO-OFDM communication channels.

First we discuss a strategy called quantized precoding that reduces the feedback requirements for each user. This approach sends back the precoding matrix for a cluster of subcarriers then uses interpolation to restore the precoders for the missing subcarriers. Second we propose a feedback protocol that uses a contention channel consisting of a fixed number of feedback minislots to feedback channel state information. This protocol allows use to exploit multi-user diversity gain without requiring each user to be assigned a dedicated feedback control slot. Users initiate feedback when the channels in their subbands exceed a threshold. The feedback threshold is optimized based on the number of subbands and number of users to maximize throughput. Numerical examples compare feedback requirements, error rates, and achievable throughputs.


Robert W. Heath, Jr. is an Assistant Professor in the Department of Electrical and Computer Engineering at The University of Texas at Austin and is a member of the Wireless Networking and Communications Group where he directs the Wireless Systems Innovations Laboratory. He received his B.S.E.E. (1996) and his M.S.E.E. (1997) degrees from the University of Virginia, and the Ph.D.E.E. (2002) degree from Stanford University. He is also president of MIMO Wireless Inc, a consulting company dedicated to the advancement of MIMO technology. Dr. Heath's research interests include wireless communication theory and signal processing. Currently he is focusing on all aspects of MIMO communication including antenna design, practical receiver architectures, limited feedback techniques, mobility management, and scheduling algorithms. He is an Associate Editor for the IEEE Transactions for Communications and the IEEE Transactions on Vehicular Technology.


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