Multi-Carrier $M$-ary DCSK System With Code Index Modulation: An Efficient Solution for Chaotic Communications

A new multi-carrier <inline-formula><tex-math notation="LaTeX">$M$</tex-math></inline-formula>-ary differential chaos shift keying system with code index modulation, referred to as <italic>CIM-MC-<inline-formula><tex-math notation="LaTeX">$M$</tex-math></inline-formula>-DCSK</italic>, is proposed in this paper. In the proposed CIM-MC-<inline-formula><tex-math notation="LaTeX">$M$</tex-math></inline-formula>-DCSK system, the reference and information-bearing signals for each subcarrier can be transmitted simultaneously by using the orthogonal sinusoidal carriers, where the information-bearing signal adopts the <inline-formula><tex-math notation="LaTeX">$M$</tex-math></inline-formula>-DCSK modulation to further increase the data rate. With an aim to making full use of the system energy resources, the reference signals in all subcarriers are coded by a Walsh code to carry additional information bits. The analytical bit-error-rate (BER) expressions of the proposed CIM-MC-<inline-formula><tex-math notation="LaTeX">$M$</tex-math></inline-formula>-DCSK system are derived over additive white Gaussian noise as well as multipath Rayleigh fading channels. Furthermore, a noise-reduction scheme and a hierarchical-modulation scheme are designed for the proposed system. In particular, the former scheme can significantly improve the BER performance while the latter scheme can provide different quality of service for the transmitted bits according to their different levels of importance. Simulation results verify the accuracy of the analytical expressions and the superiority of the proposed systems.