Generalization Of Widely Linear Filtering Concepts For Equalization And Interference Suppression In PAM/QAM Systems
Kuchi, Kiran Kumar
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In PAM/QAM transmission systems, standard Minimum Mean Square Error (MMSE) linear (LE) or Decision Feedback Equalization (DFE) equalization methods are often used to suppress the detrimental effects inter-symbol and/or co-channel interference (ISI/CCI) effects of the channel. In this thesis we show the benefits of a new signal processing concept called Widely Linear (WL) filtering for equalization applications in wireless systems. In particular, we introduce generalized WL MMSE/MMSE-DFE equalization structures for both PAM systems that use real constellations and QAM (that use complex modulation alphabets) with multiple antennas and multiple co-channel interferers. In this thesis we first show that WL equalizers offer lower noise enhancement and better performance than conventional equalizers for PAM systems with ISI. In CCI limited systems, we show that WL methods offer a significantly higher IC gain especially in the presence of non-circular interference (e.g. PAM-type CCI). Our results indicate that the proposed concepts can be applied to enhance performance of existing/emerging cellular type systems with a small increase in system complexity.