I/Q uncorrelation methods for quadrature signals correlated in multipath channel

Abstract

In this thesis, an I/Q uncorrelation method is proposed for efficient equalization of quadrature signals. The I/Q uncorrelators for both Forney and Ungerboeck receivers are proposed, both of which transforms complex valued filters into real valued ones, making the in-phase and quadrature-phase channels uncorrelated with each other. The receiver which utilizes the I/Q uncorrelators shows BER performance equal to that of the optimum receivers that are formulated by Forney and Ungerboeck only in a specific channel which is symmetric with reference to a carrier frequency in frequency domain. The I/Q uncorrelation methods drastically reduces effective intersymbol interference (ISI) delay spreads. Because In-phase and Quadrature-phase signals through I/Q uncorrelator are uncorrelated each other, when signaling is M-ary and the equivalent low pass channel spreads the ISI over L symbol intervals, the Viterbi algorithm under the proposed scheme considers two groups of $\sqrt{M}$ -ary signals independently , which means that only $2ㆍM^{(L+1)/2}$ branch metrics for each new received symbol may computed, whereas the conventional whitened matched filter based Viterbi algorithm requires $M^{L+1}$ metrics. Unfortunately, however, it makes he noise samples colored which brings severe performance loss compared with optimum receivers in $10^{-3}$ BER in three-ray multipath channels. Per-Survivor Processing (PSP) provides a general framework for the approximation of maximum likelihood sequence estimation (MLSE) algorithms whenever the presence of unknown quantities prevents the precise use of the classical Viterbi algorithm. This principle stems from the idea that data-aided estimation of unknown parameters may be embedded into the structure of the Viterbi algorithm itself. Because noise samples though I/Q uncorrelator are colored, the Euclidean distance in branch metrics is not optimal. To lessen the performance loss, we introduce a new distance metric in PSP fashion using a c...