Enhancements in chaos-based digital communication systems

Abstract

Use of chaos as a fast and convenient mean to spread the spectrum of a signal has received much attention in communication engineering in the past few years. The advantages of spread-spectrum communications include the robustness against multipath fading, resistance to jamming and high secrecy due to low probability of detection. On the other hand, many problems are there to overcome in chaos communication. They include the synchronization problem for coherent demodulation and the estimation problem due to the random-like property of chaos. Moreover in a spread-spectrum system, the issue of bandwidth efficiency must be considered. For instance, multiple users should be able to use the same frequency band without interfering with each other. This thesis studies the modulation-demodulation methods in chaos communications. The study is centered on the previously proposed chaos-shift-keying (CSK) and differential chaos-shift-keying (DCSK) systems. The thesis includes the study of detection methods of CSK and a multiple access system based on DCSK. Also, an M-ary scheme for chaos communications is proposed. The performances of the digital communication systems in this thesis are measured by their bit error rates (BER). The channel is assumed to be of additive white Gaussian noise (AWGN). Computer simulations are carried out and analyses are given. Overall evaluations are also presented.