Turbo Equalization and its Applications

In communication systems, the transmitted signals often experience various forms of corruption, and a very destructive one is the inter-symbol interference (ISI), resulting from the signals travelling through multiple paths and arriving with different delays. To compensate for the multipath propagation effect, equalization is often required at the receiver and as a very powerful candidate, the turbo equalization technique iteratively exchanges soft information between the equalizer and the decoder, offering excellent performance. Meantime, single-carrier frequency domain equalization (SC-FDE) and orthogonal frequency division multiplexing (OFDM) have become two of the most important modulation schemes in communications. Both schemes are based on guard interval assisted block transmissions and both can be implemented by fast Fourier transform/inverse fast Fourier transform (FFT/IFFT) operations, featuring very low complexity. Cyclic prefix (CP), as a commonly used guard interval, is typically discarded at the receiver. However, the fact that it is a repetition of part of the data suggests that it contains useful information and can be exploited for enhancing the system performance. This thesis considers the application of turbo equalization in SC-FDE and OFDM systems and based on the linear minimum mean square error (LMMSE) principle, various equalization algorithms are proposed with the aim of exploiting the prefix redundancy for data detection and channel estimation. To facilitate the description