Space-time coding for frequency selective fading channels with underwater acoustic communication applications

This dissertation focuses on error correction coding and channel equalization for time varying, intersymbol interference (ISI) multiple input multiple output (MIMO) systems with applications in high data rate underwater acoustic communications.; In the first part of the dissertation, a Kalman filter based soft input, soft output MIMO equalizer for quasi-static Rayleigh fading radio channels is proposed. This iterative equalizer provides considerable complexity reduction compared to the optimum maximum a-posteriori probability (MAP) equalizer at a competitive performance. A low-complexity, approximate version of the above equalizer is also proposed which provides further complexity reduction. It is shown that for high data rate systems using a large number of transmitters or large constellation sizes or both, the complexity of the proposed structure is significantly less than the MAP equalizer.; The second part of the dissertation focuses on underwater acoustic (UWA) communications. In an effort to fundamentally increase the achievable data rates and spectral efficiencies of the UWA channel, the use space-time coding and sophisticated iterative processing, along with multi-carrier communications is proposed. To realize the benefits of MIMO communication systems several specialized iterative receiver algorithms are proposed, that are tailored for the UWA channel. These algorithms are iterative and adaptive in nature and are well suited for efficient online implementation in real time MIMO modems. The proposed algorithms are validated via simulation; and also by successfully applying them on shallow water, medium range experimental data obtained from ONR, (Office of Naval Research) sponsored experiments conducted off the coast of Elba island. Italy (2003) and Kauaii island, Hawaii (2005). Using the proposed algorithms, significantly higher data, rates and bandwidth efficiencies are demonstrated as compared to the existing UWA modems.