The object of the work reported in this thesis is to construct and examine the performance of a direct-sequence spread-spectrum system and to investigate the feasibility of introducing the technique into the land mobile radio services, by means of bandsharing with the existing television services, as a means of improving spectrum utilisation. For comparative purposes, conventional modulation systems are also considered to be contenders for the scheme. Chapter 1 summarises the concepts of spread-spectrum systems. It introduces the modulation techniques that fall under this heading and describes the fundamental parameters associated with their operation. Chapter 2 indicates the reason behind the need to investigate spread-spectrum systems for adoption into the land mobile radio service and gives a general survey of the work previously carried out towards realising this aim. Chapter 3 examines the choice of initial design parameters and base modulation technique for an experimental direct-sequence system and describes the component sections used. Performance figures are presented for operation under both Gaussian and 'other-user' interference. Chapter 4 is devoted to the synchronisation aspect of a direct-sequence spread-spectrum system. It gives a survey of the techniques available for obtaining initial synchronisation and experimentally compares the operation of various delay lock loop implementations with respect to their ability to maintain accurate synchronisation. Chapter 5 covers the subjective assessment of television picture quality, as dictated by untrained observers, when subjected to various forms of modulation interference. Chapter 6 presents a feasibility study into the use of direct-sequence spread-spectrum or conventional modulation methods as possible contenders for a mobile service operating on a bandsharing basis with the television broadcast services in London and the South-East. Chapter 7 gives a final summary of all the conclusions.
|Date of Award