Commutation Code Index DCSK Modulation Technique for High-Data-Rate Communication Systems

In this brief, a novel non-coherent modulation system called commutation code index differential chaos shift keying (CCI-DCSK) is presented. In the proposed scheme, the benefits of index modulation (IM) are exploited so that the system energy and spectral efficiencies are improved. We are putting forward a CCI-DCSK scheme in which the reference sequence along with its corresponding data bearing orthogonal version are sent within the same time slot to enhance spectral efficiency. Specifically, at the transmitter ${p}$ additional bits are mapped into the index of the repetition commutation, which is performed on the reference signal for the sake of forming its orthogonal version. Furthermore, the modulated bit is spread by the corresponding commutated replica of the reference signal. The reference and orthogonal data bearing signals are then summed within the same time slot prior to transmission. At the receiver, the received signal is first correlated with all possible combinations of the commutated replicas in order to find the index of the correlator output with the maximum magnitude. Subsequently, the maximizing index is then used to estimate the mapped bits, while the output of the corresponding correlator is used to despread the modulated bit via a zero-threshold comparator. To complete the study, analytical expressions for the bit error rate are derived for both additive white Gaussian noise and multipath Rayleigh fading channels. Finally, performance results of the proposed CCI-DCSK scheme is compared with the state-of-the-art IM-based non-coherent chaotic modulations and is found to be superior and competitive.