Efficient feedback methods for MIMO channels based on parameterization

doi:10.1109/TWC.2007.05195

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Efficient feedback methods for MIMO channels based on parameterization

2007-01-01

PRE

Bhaskar D. Rao

DOI：10.1109/TWC.2007.05195

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Abstract

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In this paper, we propose two efficient lowcomplexity quantization methods for multiple-input multipleoutput (MIMO) systems with finite-rate feedback based on proper parameterization of the information to be fed back followed by quantization in the new parameter domain. For a MIMO channel which has multiple orthonormal vectors as channel spatial information, we exploit the geometrical structure of orthonormality while quantizing the spatial information matrix. The parameterization is. of two types: one is in terms of a set of unit-norm vectors with different lengths, and the other is in terms of a minimal number of scalar parameters. These parameters are shown to be independent for the i.i.d. flatfading Rayleigh channel, facilitating efficient quantization. In the first scheme, each of the unit-norm vectors is independently quantized with a finite number of bits using an optimal vector quantization (VQ) technique. Bit allocation is needed between the vectors, and the optimum bit allocation depends on the operating SNR of the system. In the second scheme, the scalar parameters are quantized. In slowly time-varying channels, the scalar parameters are also found to be smoothly changing over time, leading to the development of a simple quantization and feedback method using adaptive delta modulation. The results show that the proposed feedback scheme has a channel tracking feature and achieves a capacity very close to perfect feedback with a reasonable feedback rate.

Keywords:

channel information feedback

channel state information

MIMO systems

multiple antennas

parameterization

quantization

transmit beamforming

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