Abstract-A new non-coherent scheme called Permutation Index Differential Chaos Shift Keying (PI-DCSK) modulation is proposed in this paper. This original design aims to enhance data security, energy and spectral efficiencies, compared to its rivals. In the proposed PI-DCSK scheme, each data frame is divided into two time slots in which the reference chaotic signal is sent in the first time slot and a permuted replica of the reference signal multiplied by the modulating bit is sent in the second time slot. In particular, the bit stream is divided at the transmitter into blocks of n + 1 bits, where n mapped bits are used to select one of the predefined reference sequence permutations, while a single modulated bit is spread by the permuted reference signal just mentioned. At the receiver side, the reference signal is recovered first, then all permuted versions of it are correlated with the data-bearing signal. The index of the correlator output with maximum magnitude will estimate the mapped bits, while the output content of the corresponding correlator is compared to a zero threshold to recover the modulated bit. Moreover, a new multiple access (MA) method based on the proposed scheme is described and analysed. Analytical expressions for the error performance in single-user and multi-user environments are derived for additive white Gaussian noise (AWGN) and multipath Rayleigh fading channels, respectively. Furthermore, the performance of the proposed PI-DCSK system is analysed and compared with other non-coherent chaotic modulation schemes and is found to be promising.Index Terms-Chaos-based communication systems, permutation index differential chaos shift keying (PI-DCSK), bit error rate (BER), non-coherent detection, multiple access (MA).

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Abstract-In this work, a novel non-coherent modulation system named 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 (BER) are derived for both additive white Gaussian noise (AWGN) 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.

An initial condition-index chaos shift keying modulation is proposed. This design aims to increase the spectral and energy efficiencies to unprecedented levels. The proposed scheme exploits the initial conditions to generate different chaotic sequences to convey extra bits per transmission. In the proposed design, the input data stream is formed in blocks of p tot = n + 1 bits. In this architecture, n bits are mapped into N = 2 n predetermined initial conditions that are used to generate unique chaotic sequences at the transmitter. At the receiver side, the predetermined initial conditions are used to generate a set of N chaotic sequences that are correlated with the received signal. The index of the initial condition for which the chaotic sequence produces a maximum correlation with the received signal is selected to recover the mapped bits, and the corresponding sequence is used to despread the transmitted modulated bit. To validate the proposed scheme, the bit error rate over fading channels is analysed and formulated and the proposed system performance is compared with other conventional and index modulation schemes. In comparison to rival modulation schemes, the results obtained in the proposed work show a competitive performance.

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