Αλγόριθμοι και τεχνικές συγχρονισμού ασύρματων ψηφιακών δεκτών ορθογώνιας γραμμικής διαμόρφωσης

Abstract

This thesis addresses critical algorithmic and architectural design issues concerning digital receivers for high-capacity radio communication systems. The results presented herein, in effect, provide a comprehensive approach in optimal pulse shaping networks, channel estimation and synchronization techniques from the basic theoretical concept up to implementation choices. The thesis is composed of three main parts. First, a composite optimization methodology based on the steepest-descent and the quasi-Newton minimax algorithms is developed for the prompt design of physically realizable biquadratic pulse shaping filters for data transmission. Current work has proved that cascaded pulse shaping realizations can meet stringent in-band requirements in an optimal manner while inexpensively guarantee performance robustness under implementation. Next, a unified algebraic treatment that tackles directly in a systematic and mathematically effective manner the synchronization errors estimation problem variations is composed. The proposed synthesis methodology contributes further to the optimality of the symbol-rated polarity estimation algorithms, since it proves that the ensuing error signal is based on optimal algebraic expressions constituted by a minimum set of prime-implicants and therefore is characterized by maximum noise immunity. The third and largest part of the thesis introduces the novel concept of soft loop diversity via adaptive statistical loop filtering; this innovative technique is applied to the class of binary quantized digital phase locked loop (DPLL) synchronizers to obtain both fast acquisition and reliable steady state tracking simultaneously. The proposed loop is analyzed by exercising Markovian analytical techniques on a simplified two-dimensional (2-D) Markov chain approximation. All things considered, it is claimed that the synchronization diversity enigma is optimally resolved by exercising a hybridized adaptation/verification algorithm on the statistical confidence requirements of the discrete phase corrections in closed loop synchronization schemes.