Sequence Synchronisation in Chaos-based Direct Sequence Spread Spectrum Communication Systems

Abstract

This thesis presents an investigation into the modelling and performance of sequence synchronisation in Chaos-based Direct Sequence Spread Spectrum (CDS-SS) communication systems with the aims of identifying the existing gaps in research and suggesting a new and accurate modelling approach. The CDS-SS systems offer physical layer security without the need for a significant increase in computation or power requirements. This is significant when conventional encryption techniques cannot be used on secure communication systems because of their high power requirements as well as computational intensity. The main focus of this thesis is the problem of synchronising chaos-based spreading sequences. The modelling approaches previously used for chaos-based spreading codes do not take their non-binary nature into account and are not accurate as a result. This thesis extends the existing analysis in the literature to include CDS-SS synchronisation in presence of channel fading. Subsequently, an accurate approach is developed for modelling the synchronisation block of a CDS-SS system. This approach is based on the statistical description of chaos-based spreading codes cross- and auto-correlation functions and is termed chaos correlation statistics (CCS). To verify the validity of this approach, the acquisition stage of a CDS-SS synchronisation block is modelled using three scenarios: noise, fading and interleaving. It has been shown that the CCS method makes an accurate prediction of the acquisition phase performance for all three scenarios considered. The CCS method is also used to model a CDS-SS tracking loop statistically with high accuracy as verified by comparison with numerical analysis results. The effects of tracking loop errors and timing jitter on the probability of error have been derived for the same three scenarios mentioned above. These newly derived probability of error equations are verified by extensive simulation results. Overall it is concluded that sequence synchronisation for CDS-SS systems is possible and the CCS method is a suitable tool for accurate prediction of synchronisation performance in CDS-SS systems. Also, the CCS approach can be used in any scenario in which accurate modelling of the correlation function of non-binary spreading sequences is needed.