N. Khaled, B. Mondal, Robert W. Heath Jr, G. Leus and F. Petre
Accepted to IEEE Vehic. Tech. Conference, Dallas, TX, USA, September 25-28, 2005.
Multiple-input multiple-output (MIMO) wireless systems can achieve significant diversity and array gain by using transmit beamforming and receive combining techniques. In the absence of full channel knowledge at the transmitter, the transmit beamforming vector can be quantized at the receiver and sent to the transmitter using a low-rate feedback channel. In the literature, quantization algorithms for the beamforming vector are designed and optimized for a particular channel distribution, commonly the uncorrelated Rayleigh distribution. When the channel is not uncorrelated Rayleigh, however, these quantization strategies result in a degradation of the receive signal-to-noise ratio. In this paper, switched codebook quantization is proposed where the codebook is dynamically chosen based on the channel distribution. The codebook adaptation enables the quantization to exploit the spatial and temporal correlation inherent in the channel. The convergence properties of the codebook selection algorithm are studied assuming a block-stationary model for the channel. In the case of a non-stationary channel, it is shown using simulations that the selected codebook tracks the distribution of the channel resulting in improvements in signal-to-noise ratio. Simulation results show that in the case of correlated channels, the SNR performance of the link can be significantly improved by adaptation, compared to non-adaptive quantization strategies designed for uncorrelated Rayleigh fading channels.
This preprint is available here.