| Summary: | The major part of the work described in the thesis is a study of a novel technique for the demodulation of two level phase shift keyed signals. Its advantage over conventional coherent demodulation methods is that it uses a free running oscillator as the local oscillator in the receiver, which is not locked to the transmitted carrier signal. Thus this novel system does not require the complex synchronisation techniques used in conventional phase shift keyed demodulators. This new demodulator like conventional coherent demodulators has not got the fixed speed disadvantage of differential phase shift keying. This new demodulator also referred to as a Quasi-Coherent demodulator has been characterised both theoretically and experimentally and compared with conventional coherent and differential phase shift-keyed systems. The possibility of extending this technique to multiphase phase shift keyed system is also discussed. The performance of a multilevel coherent phase shift keyed system in the presence of interference can be predicted by computing the exact mathematical equation for the error rate. In the thesis an approximate, but quick and simple method has been developed to, predict the performance of multilevel coherent phase shift keyed system from the well known result of a two level coherent phase shift keyed system. In all the interference analysis so far done by other authors, it is assumed that the reference at the receiver is coherent with the received signal. However, it is evident that in the presence of a strong interference, a phase locked loop derived reference will in general be coherent with the composite signal (i.e. signal plus interference plus noise) and not with the signal as assumed by previous authors. The effect of such a reference i.e. coherent with the composite signal on the performance of a two level system has been discussed fully in chapter four. The performance of a digital system also depends on the receiving filter characteristic and on the sampling jitter that is inevitably present in the sampling pulse in the decision circuitry of the receiver. The effect of these two factors on the performance of a two level coherent phase shift keyed system has been fully discussed in chapter five..
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