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Design and analysis of MIMO systems with practical channel state information assumptions

Abstract

Using multiple antennas at both the transmitter and the receiver is one of the most promising techniques that can offer significant increases in channel capacity of a communication system in a wireless fading environment. However, the performance of the MIMO system depends heavily upon the availability of the channel state information (CSI) at the transmitter (CSIT) and at the receiver (CSIR). In this dissertation, we focus our attention on the design and analysis of MIMO systems over wireless fading channels with practical CSI assumptions, which can broadly be divided into the following two categories. The first part considers the development of a general framework for the analysis of multiple antenna systems with finite-rate feedback, wherein the CSI is quantized at the receiver and conveyed back to the transmitter through a rate-constrained reverse link. Inspired by the results of classical high resolution quantization theory, the problem of finite rate quantized communication system is formulated as a general fixed-rate vector quantization problem with side information available at the encoder (or the quantizer) but unavailable at the decoder. The framework of the quantization problem is sufficiently general to include quantization schemes with general non-mean square distortion functions, and constrained source vectors. Asymptotic distortion analysis of the proposed general quantization problem is provided by extending the vector version of the Bennett's integral. Specifically, tight lower and upper bounds of the average asymptotic distortion are provided together with useful insights from a source coding perspective. The proposed general methodology provides a powerful analytical tool to study a wide range of finite-rate feedback systems which includes both MISO systems over spatially correlated fading channels and MIMO systems over i.i.d. fading channels. The established framework is also versatile enough to provide analysis of sub-optimal mismatched CSI quantizers and quantizers with transformed codebooks. The second part of this dissertation is focused the on the design and analysis of MIMO systems over fading channels with CSI unavailable both at the transmitter and at the receiver. To be specific, we first provide an improved capacity lower bound for MIMO systems with unknown CSI. By analyzing (and optimizing) the proposed capacity lower bound with respect to different system parameters, we improve our intuition and understanding of the effects of training on the overall performance of MIMO systems under unknown CSI assumptions. Moreover, based on the capacity analysis results, we also provide the design of practical LDPC-coded MIMO systems under the same unknown CSI assumption at both component level and structural level. We first propose at the component level several soft-input soft-output MIMO detectors whose performances are much better than the conventional MMSE-based detectors. At the structural level, an unconventional iterative decoding scheme is proposed whose structure leads to a simple and efficient LDPC code degree profile optimization algorithm with proven global optimality and guaranteed convergence from any initialization

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