Efficient and robust M-ary differential chaos shift keying scheme with code index modulation

In this study, a new chaos modulation scheme which combines M-ary differential chaos shift keying (DCSK) with code-index modulation (CIM-MDCSK) is proposed. In the CIM-MDCSK scheme, the two Walsh codes that are used to generate two orthogonal chaos components are selected from the candidate codes, whose code indices are determined by information symbols. Thus, the information bits are conveyed not only by M-ary DCSK signal but also by the indices of the Walsh codes. Theoretical symbol error rate (SER) and bit error rate (BER) of the proposed scheme are derived and confirmed by simulations. Furthermore, by applying the noise-reduction to reference signals of CIM-MDCSK, the SER/BER expressions are also derived. Simulation results show that the proposed CIM-MDCSK outperforms DCSK and M-ary DCSK based on Hilbert transform. Especially, the CIM-MDCSK with noise-reduction shows significant advantages. Moreover, the performance of CIM-MDCSK scheme is compared with direct sequences spread-spectrum system with code-index modulation over flat and frequency selective fading channel. The proposed CIM-MDCSK can offer good performance over frequency selective fading channel with a low complexity non-coherent receiver which does not require any channel state information and channel equalisation.