| Amongst linear filters, which are use in a wide variety of domains, we find a class of time variant filters. The purpose of this thesis is to explore a particular case of these filters which are linear periodical time variant filters.; Our work is presented in four chapters.; The first chapter introduces the elementary notions related to time variant systems (LTV). It presents a re-writing of the relations describing those systems using the notion of time-frequency duality.; The second chapter defines what a linear periodic time varying filter is and presents a study of the characteristics of these filters. It also demonstrates how these filters can be used in two types of applications. The first one being information scrambling and the later, a new type of spectral spreading using a band limited signal.; The third chapter deals with the reconstruction process of a signal submitted to a linear periodic filter. We display some examples including an examination of the effects of noise in the reconstruction process of the signal.; In the last chapter, we present a new multi-user transmission method. This method is an extension of the previously explored topics and enables us to show that it is in fact a generalization of the code division multiple access techniques (CDMA). |
