Quantized transmit beamforming with antenna selection in a MIMO channel

Abstract

For a point-to-point multi-input multi-output (MIMO) wireless channel, we propose a feedback scheme, which consists of transmit-antenna selection algorithm and beamforming quantization. A feedback, which is relayed from a receiver to a transmitter via a feedback channel, specifies a set of active transmit antennas and associated beamforming vector, which contains transmit antenna coefficients. Assuming perfect channel knowledge, the receiver selects the set of transmit antennas that maximizes the largest eigenvalue of a channel covariance matrix and then, chooses the beam-forming vector that maximizes the capacity, from a random vector quantization (RVQ) codebook. Entries in the RVQ codebook are independent isotropically distributed and was previously shown to perform close to the optimum. We derive capacity bounds for the proposed scheme, which are functions of feedback bits, and number of active transmit antennas. The bounds are shown to approximate the actual performance well. Also complexity of the scheme can be reduced with fewer activated transmit antennas.