CIM-DCSK: A differential chaos shift keying scheme with code-index modulation

In this paper, we propose a new chaos modulation scheme which combines differential chaos shift keying (DCSK) with code index modulation (CIM) using Walsh codes, namely CIM-DCSK. We consider two CIM-DCSK communication systems that have different executable methods. In the first system, the reference chaos signal is the same with the conventional DCSK, and the information bearing signal is simultaneously modulated by an information symbol and a Walsh code with a specific index which is selected according to an extra information symbol. By index modulation on information bearing signal, additional information bits are carried. In the second system, referring to short reference DCSK (SR-DCSK), a short reference signal is transmitted at first, then a P replicas of the reference signal, which is served as information bearing signal, is simultaneously modulated by information symbol and Walsh code with a specific index like the first system. By computer simulation, the BER performances of the two proposed systems are compared with those of DCSK and SR-DCSK, respectively. Simulated results show that the proposed systems outperform the DCSK and SR-DCSK.