Capacity approaching and efficient signaling schemes for wideband wireless communication systems

The goal of this dissertation is to provide an thorough understanding of the constant trade-offs between spectral efficiency of information transmission, fidelity of message reconstruction and computational complexity of system implementation that are required for a modern wideband wireless communication system design. In particular, this dissertation examines four areas of wideband wireless communication in which the mobile radio channel's time, frequency and spatial diversity have not yet been exploited to maximum advantage: (1) Efficient linear detector design for wideband multiple-input multiple-output (MIMO) communication system over dynamic channels. (2) Turbo equalizer design for high mobility wideband single-input single-output (SISO) communication system. (3) Joint channel estimation and data recovery in high mobility wideband SISO communication system. (4) Channel estimation and data detection for high mobility wideband MIMO communication system.;Chapter 1 provides an in-depth introduction to numerous common themes in modern wideband wireless communication systems. Cost-effective and high data rate wireless communication systems are of great interests in numerous commercial applications. The demands for wireless systems that are reliable and have high spectral efficiency are pushed by the desires of people to have ubiquitous digital life style. Consequently, such demands have motivated the use of wideband wireless channels in order to provide larger bandwidth and spectrally more efficient communication system among other signaling schemes for the wireless wideband channel, orthogonal frequency division multiplexing (OFDM), multiple-input multiple-output (MIMO) and iterative processing are the key components for systems that provide good performance, high spectral efficiency with manageable complexity.;Chapter 2 is concerned with the design of efficient linear front-end detectors in the iterative detection-decoding MIMO OFDM systems. Despite the availability of a priori information feedback from time outer channel decoder, conventional front-end linear minimum mean square error (LMMSE) based detectors allocate fixed amount of computational resources uniformly throughout the iterative detection-decoding process. This chapter provides two linear front-end detectors which not only achieve a significant amount of complexity reduction, more importantly they offer the same performance as their conventional full complexity counterpart LMMSE based detectors.;Chapter 3 discusses the optimal and near optimal turbo equalizer designs of wideband SISO OFDM system in a high mobility environment. OFDM systems suffer performance degradation in fast fading channels due to intercarrier interference (ICI). Combining frequency domain equalization and bit interleaved coded modulation (BICM), the iterative receiver is able to harvest both temporal and frequency diversity. Traditionally, either sub-optimum LMMSE based equalizers or heuristic two-stage trellis based equalizers are used to combat ICI in OFDM systems. Realizing that ICI channels are intrinsically 1ST channels, this chapter derives an optimum soft-in soft-out maximum a posteriori (MAP) equalizer by extending Ungerboeck's maximum likelihood sequence estimator (MLSE) formulation to ICI channels.;Chapter 4 explains efficient and very effective techniques to obtain channel state information (CSI) in the high mobility wideband SISO OFDM systems. In order to perform coherent detection and estimation, CSI is indispensable. Being able to accurately and effectively acquire CSI in the time varying channel is critical. Conventional frequency domain channel estimation (CE) methods have an irreducible error floor at high normalized Doppler frequency fdTs, since ICI corrupts the orthogonality among subcarriers. Considering that the fast time-varying channel is also a source of temporal diversity, CE ought to take place in the pre-FFT time domain. Realizing channel variations in time are often smooth, this paper proposes a time domain channel estimator using pilot symbol assisted modulation (PSAM) with complexity O(N), where N is the FFT size. With soft a priori information about the data symbols becomes available, this paper further proposes a turbo channel estimator (TCE) structure which provides a way to consistently improve the bit error rate (BER).;Chapter 5 is concerned with channel estimation and data detection for wide-band MIMO OFDM system in a high mobility environment. Deploying MIMO OFDM in a mobile digital communication system is a way to achieve reliability, high-data rate and spectral efficiency. With the goal of designing practical systems that can provide high-quality of service in such dynamic environment, several challenges arise. Among these challenges, rapid channel time-variation mainly due to users mobility is certainly an important one. While cyclic prefixed OFDM systems have strong immunity to time-invariant frequency-selective channels, they suffer severely from time-varying channels mainly due to ICI. This chapter examines the design of the optimum demodulation structure and provides an efficient channel estimation algorithm in the high mobility coded MIMO OFDM systems.