The Digital Signal Processing Lab @ UCSD


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Thesis Title

Multiple-Antenna Communication Systems with Finite Rate Feedback

Thesis Abstract

Using multiple antennas at both ends of a communication link, we can significantly improve the achievable date rate and the link reliability in fading environments. The link performance can be even more improved, when the transmitter has channel state information (CSI). In this dissertation, we study various transmission strategies and feedback methods for CSI in multiple antenna systems with a finite-rate feedback channel.

We first consider multiple-input multiple-output (MIMO) channels with a small number of principal eigen-modes of the channel available at the transmitter. We proposed a novel transmission strategy and a new multiple antenna system concept which enables better use of the MIMO channel. We also derive the channel capacity of the MIMO systems employing the proposed beamforming and feedback methods by solving the associated optimization problem for the optimal power allocation.

Next, we investigate various quantization methods for feeding back the multi-dimensional channel information through a finite-rate feedback channel. For multiple-input single-output (MISO) systems, we propose a new quantizer design criterion for capacity maximization and develop an iterative vector quantization (VQ) design algorithm. The performance of systems with quantized beamforming is analyzed for the independent fading case in terms of the capacity loss, the outage probability and the symbol error probability.

The methodology employed in MISO systems is then extended to MIMO systems. Assuming equal power allocation, we propose a new criterion and develop an iterative algorithm for designing the codebook of beamforming matrices. Under the independent fading channel and high SNR assumption, the effect on channel capacity of quantized beamforming is analyzed. To compensate for the degradation due to the equal power allocation, we propose a multi-mode spatial multiplexing transmission strategy that allows for effective utilization of the feedback bits.

Finally, we propose two efficient feedback methods based on parameterization. The parameterization has two forms of output: 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. The first form of parameterization leads to a sequential VQ method for beamforming matrix feedback, and the scalar parameters to a simple differential feedback method for slowly time-varying MIMO channels.

Year of Graduation: 2005