Transmit and receive techniques for MIMO-OFDM systems

Abstract

This thesis is concerned with the designs of transmit and receive techniques for a multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system in wideband frequency selective MIMO block fading channels. Several space-time pre-coding schemes are studied. Their ergodic and outage capacity performances are analyzed and their tradeoff between capacity and diversity gains is investigated. A two-dimensional linearly transformed MIMO-OFDM system is proposed which can achieve full diversity and full capacity. For the receiver, we focus on the iterative turbo receiver algorithms. Simplification of the soft decision functions has been proposed that introduces only marginal performance degradation. More importantly, a family of Bayesian minimum mean squared error (MMSE) turbo receivers are proposed, which can significantly improve the BER and FER performance over conventional turbo receivers. The proposed Bayesian turbo receivers can also improve the convergence speed, hence effectively reducing the processing delay. The extrinsic information transfer (EXIT) chart of the proposed Bayesian turbo receiver is derived and compared with the conventional turbo receivers, which verify the superior performance of the proposed Bayesian turbo receiver over the conventional receivers. The preamble design for training sequence assisted channel estimation is also studied. Both the time domain and frequency domain channel estimation algorithms are looked into, and the corresponding preamble design is proposed which can optimize the mean squared error (MSE) of the channel estimates.