The fifth generation (5G) mobile communication has been envisioned to enable Internet of Things (IoT) in the future, however, supporting the IoT functionality in 5G networks is a challenging task since low power consumption and low-cost requirements of equipments of IoT. As an especial wireless communication, underwater acoustic (UWA) communications have attracted considerable attention in recent few decades due to the special economic and military strategic value in ocean which involves the interests and developments of various countries. However, UWA channel is a typical harsh and complex environment for information transmission. The performance of UWA communications is affected significantly by low propagation speed, large propagation delays, variation of the channel impulse response and so on. The multipath transmission combined with lager propagation delays of UWA channels cause serious inter-symbol-interference (ISI) which may influence dozens of symbols. Variation of the channel impulse response results in severe Doppler spread. Therefore, how to design transmission signal is an essential issue for physical layer of underwater acoustic communication systems. Chaotic modulation based on non-coherent detector has low implement complexity and excellent performance over severe selective fading channels. Therefore, chaotic modulation may be a good candidate for the IoT and UWA networks.
In this talk, we will present research progress of chaotic modulation of wireless communications and underwater acoustic communications. Especially, in order to improve the BER performance and transmission efficiency of chaotic modulation, differential chaos shift keying (DCSK) with index modulation is presented and extensively discussed. For examples, DCSK combined code index modulation and DCSK combined time slots index modulation will be presented. On the other side, to make DCSK modulation fit to underwater acoustic transmission environment, DCSK-based system should be redesigned. Therefore, we present two DCSK-based systems which own robustness over time-varying and underwater acoustic channels. The proposed scheme combines code-shifted differential chaos shift keying (CS-DCSK) with orthogonal frequency division multiplexing (OFDM), namely MC-CS-DCSK. The proposed scheme firstly utilizes the orthogonal characteristic of the Walsh code to make the chaotic reference chips and the information bearing chips superimposed in time/frequency domain. Then the chips from CS-DCSK modulators, which form a multiple carrier symbol, are shifted by a cyclic-shift interleaver. Then, the shifted chips are loaded onto different sub-carriers by the use of inverse discrete Fourier transform (IDFT). Simulated results show that the proposed system has robust performance over doubly selective fading channel and underwater acoustic channels.