Abstract:
In this thesis, sequence synchronization techniques for single and multiple-access chaotic communication systems are investigated. In particular, the techniques of sequence synchronization studied include those based on the principles of Pecora-Carroll (PC) chaotic synchronization and those based on the principles of traditional direct sequence code division multiple access (DS-CDMA) synchronization. Based on the principles of PC chaotic synchronization, novel approaches to chaotic synchronization are proposed and used to design new single-user chaotic communication systems. These new chaotic communication systems include those based on the chaotic parameter modulation (CPM) and the initial condition modulation (ICM) techniques. Furthermore, the principles of time division multiplexing (TDM) are used to obtain the CPM and ICM based multi-user TDM systems. The performance of all of the proposed and the existing systems is evaluated in terms of the bit error rate (BER) in the additive white Gaussian noise (A WGN) and the Rayleigh fading channels. Furthermore, it is shown that by implementing certain linear and wavelet filters, one can improve the BER performance of the ICM based systems in the AWGN channel. The sequence synchronization of chaotic communication systems based on the DSCDMA principles is then proposed. Both phases of the sequence synchronization process, namely the code acquisition and the code tracking, are proposed and investigated. It is shown that in terms of BER the chaos based DS-CDMA system outperforms the CPM and ICM based TDM systems for low number of users in the A WGN channel and vice versa for large number of users. In addition, it is found that the chaos based OS-CDMA system outperforms the ICM and CPM based TDM systems in the Rayleigh fading channel. However, in the Rayleigh fading channel, they all fail to satisfy the adopted highest acceptable BER level of 10⁻³. In addition to the CPM and ICM based TDM systems and the chaos based DS-CDMA system, the chaos based TDM system with the DS-CDMA correlator receiver is also proposed. It is shown that this system outperforms the CPM and ICM based TDM systems for any number of users. However, the system is outperformed by the chaos based DS-CDMA system for low number of users and vice-versa for large number of users. In order to mutually exploit the OS-CDMA and TDM benefits, a generalized chaos based TDM communication system with more than one DS-CDMA user per TDM branch is proposed and evaluated in the A WGN channel. In this way, the bandwidth efficiency of a DS-CDMA system is combined with the inter-user interference immunity of a TDM system, to allow for an increased number of users in the system while improving the BER performance. In general, it is shown that the multi-user chaotic communication systems based on the acquisition and tracking synchronization scheme, are more robust to A WGN and Rayleigh fading than those based on the principles of chaotic synchronization. Finally, the security of the proposed, as well as of the existing chaotic communication systems, is evaluated in terms of newly proposed measures termed the 'Bit Power Parameter Spectrum' (BPPS) and the 'Bit Power Initial Condition Spectrum' (BPICS). Using these measures, it is shown that chaotic communication systems can be optimized in terms of security.