Digital implementation and parameter tuning of adaptive nonlinear differential limiters

Master of ScienceDepartment of Electrical and Computer EngineeringAlexei NikitinBalasubramaniam NatarajanIt has been shown that the performance of communications systems can be severely limited by non-Gaussian and impulsive interference from a variety of sources. The non-Gaussian nature of this interference provides an opportunity for its effective mitigation by nonlinear filtering. In this thesis, we describe blind adaptive analog nonlinear filters, referred to as Adaptive Nonlinear Differential Limiters (ANDLs), that are characterized by several methodological distinctions from the existing digital solutions. When ANDLs are incorporated into a communications receiver, these methodological differences can translate into significant practical advantages, improving the receiver performance in the presence of non-Gaussian interference. A Nonlinear Differential Limiter (NDL) is obtained from a linear analog filter by introducing an appropriately chosen feedback-based nonlinearity into the response of the filter, and the degree of nonlinearity is controlled by a single parameter. ANDLs are similarly controlled by a single parameter, and are suitable for improving quality of non-stationary signals under time-varying noise conditions. ANDLs are designed to be fully compatible with existing linear devices and systems (i.e., ANDLs’ behavior is linear in the absence of impulsive interference), and to be used as an enhancement, or as a simple low-cost alternative, to state-of-the-art interference mitigation methods. We provide an introduction to the NDLs and illustrate their potential use for noise mitigation in communications systems. We also develop a digital implementation of an ANDL. This allows for rapid prototyping and performance analysis of various ANDL configurations and use cases

Low-Complexity Iterative Receivers

La tesi affronta il problema delle comunicazioni digitali su canali con memoria, ponendo particolare enfasi su canali affetti da interferenza intersimbolica e canali affetti da rumore impulsivo. In particolare, l'analisi e il progetto vengono rivolti ai ricevitori ad oggi considerati come i più efficaci in tali scenari, ossia i ricevitori iterativi. Il fattore di qualità cruciale per un sistema di comunicazione viene considerato, nell'intera tesi, un conveniente compromesso tra complessità e prestazioni, piuttosto che le sole prestazioni. Il maggiore contributo del lavoro di tesi consiste in un insieme di ricevitori in grado di offrire, a parità di complessità, prestazioni migliori rispetto alle soluzioni di letteratura.The thesis addresses the problem of providing reliable communications over channels with memory, with particular emphasis on channels impaired by intersymbol interference and channels impaired by impulse noise. In particular, the receivers to date considered as the most effective for such scenarios, namely the iterative receivers, are investigated. Throughout the work, a convenient performance/complexity tradeoff, rather than the performance only, is considered as the key quality figure for a communication system. The main contribution the thesis provides is a set of low-complexity receivers that impressively outperform the existing receivers with similar complexity