Design of a Dual Index PPM-DCSK Transceiver for Covert Wireless Communications

In this paper, we propose a novel dual index pulse position modulation differential chaotic shift keying (DI-PPM-DCSK) system for wireless covert communication. Unlike conventional PPM schemes, at the transmitter, we propose to modulate index bits with the positions of both the reference and information-bearing signals, thereby incorporating more index bits into each symbol. Thus both energy efficiency and data rate can be improved. Besides, the information-bearing modulated signals are hidden with the artificial noise to enhance the covertness of communications. At the receiver, we propose to demodulate the information bits by calculating the coherence of adjacent symbols. Moreover, we derive analytical expressions for the bit error rate (BER) and covert performance of the system, which are validated through numerical simulations. The results demonstrate that the proposed system achieves superior data rate and BER performance compared to existing counterparts over fading channels. Furthermore, the covertness is validated with both theoretical analysis and simulation results.