Maximum MIMO System Mutual Information with Antenna Selection and Interference
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Maximum MIMO System Mutual Information with Antenna Selection and Interference Rick S. Blum Department of Electrical and Computer Engineering, Lehigh University, Bethlehem, PA 18015-3084, USA Email: [email protected] Received 31 December 2002; Revised 13 August 2003 Maximum system mutual information is considered for a group of interfering users employing single user detection and antenna selection of multiple transmit and receive antennas for flat Rayleigh fading channels with independent fading coefficients for each path. In the case considered, the only feedback of channel state information to the transmitter is that required for antenna selection, but channel state information is assumed at the receiver. The focus is on extreme cases with very weak interference or very strong interference. It is shown that the optimum signaling covariance matrix is sometimes different from the standard scaled identity matrix. In fact, this is true even for cases without interference if SNR is sufficiently weak. Further, the scaled identity matrix is actually that covariance matrix that yields worst performance if the interference is sufficiently strong. Keywords and phrases: MIMO, antenna selection, interference, capacity.
1.
INTRODUCTION
Multiple-input multiple-output (MIMO) channels formed using transmit and receive antenna arrays are capable of providing very high data rates [1, 2]. Implementation of such systems can require additional hardware to implement the multiple RF chains used in a standard multiple transmit and receive antenna array MIMO system. Employing antenna selection [3, 4] is one promising approach for reducing complexity while retaining a reasonably large fraction of the high potential data rate of a MIMO approach. One antenna is selected for each available RF chain. In this case, only the best set of antennas is used, while the remaining antennas are not employed, thus reducing the number of required RF chains. For cases with only a single transmit antenna where standard diversity reception is to be employed, this approach, known as “hybrid selection/maximum ratio combining,” has been shown to lead to relatively small reductions in performance, as compared with using all receive antennas, for considerable complexity reduction [3, 4]. Clearly, antenna selection can be simultaneously employed at the transmitter and at the receiver in a MIMO system leading to larger reductions in complexity. Employing antenna selection both at the transmitter and the receiver in a MIMO system has been studied very recently [5, 6, 7]. Cases with full and limited feedback of information from the receiver to the transmitter have been considered. The cases with limited feedback are especially attractive in that they allow antenna selection at the transmitter without requiring a full description of the channel or its eigenvector
decomposition to be fed back. In particular, the only information fed back is the selected subset of transmit antennas to be employed. While cases with this limited feedback of information from the receiver
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