Hybrid chaos communication with Code Index Modulation

Hybrid chaos communication (HCC) is promising for covert transmission by delivering confidential information via chaotic signals. To enhance the transmission rate and the energy efficiency while maintaining a low probability of interception, in this paper, we propose a code index modulation-aided HCC (CIM-HCC) scheme. Specifically, the input bit stream is split into the chaotic signaling stream, the modulating stream, and the code indexing stream. The chaotic signaling stream is modulated by the hybrid chaos signal and the code indexing stream is mapped onto the Walsh codes. The modulating stream is multiplied to the Walsh codes. Thus, the proposed CIM-HCC achieves higher data rate and lower power consumption than that of the conventional HCC. Another advantage is that, since part of the information bits are conveyed by the indices of the Walsh codes, the CIM-HCC outperforms the conventional HCC, and binary phase-shift keying (BPSK) in terms of reliability. In particular, when the number of indexing bits equals to that of the signaling bits, the proposed CIM-HCC doubles the data rate and saves about 50% power consumption. In addition, the numerical results show that the proposed scheme outperforms the code index modulation differential chaos shift keying in terms of bit error rate over both the additive white Gaussian noise channel and the multipath Rayleigh fading channels.