Differential Pulse-Position Modulation for Multi-User Chaotic Communication

In this paper, we propose a joint differential pulse position modulation and differential chaos shift key modulation (DPPM-DCSK), where one bit modulates the reference PPM signal by chaotic signal, and the other $m_{c}$ bits are mapped by the position index of this chaotic pulse in the information signal. In particular, in the DPPM-DCSK, the information-carrying PPM signal for the current symbol also serves as the reference for the next symbol. It can avoid the energy and rate wastes in the conventional PPM-DCSK. Moreover, we redesign the differential Walsh codes (WC) for DPPM-DCSK to enable multi-user communications. The numerical bit-error-rate (BER) performance of the proposed DPPM-DCSK-WC over multipath Rayleigh fading channels are derived and then verified by simulations. The results demonstrate that the DPPM-DCSK-WC can achieve performance gains of more than 2 dB over the conventional PPM-DCSK and DDCSK-WC for multi-user scenarios, and this gain can be up to 5 dB in the high-delay channels at a BER of ${{10}^{-4}}$ . In addition, the superior performance of the proposed scheme is proved over ultra-wideband (UWB) wireless channels, which indicates its great potential for chaotic-based wireless applications.