Code-shifted Differential Chaos Shift Keying Research Articles

DESIGN AND PERFORMANCE ANALYSIS OF ORTHOGONAL MULTI-LEVEL CODE-SHIFTED DIFFERENTIAL CHAOS SHIFT KEYING COMMUNICATION SYSTEM

Based on Orthogonal Chaotic Vector Shift Keying (OCVSK) system and Multilevel Code-Shifted Differential Chaos Shift Keying (MCS-DCSK) system, a new Multilevel Code-Shifted Differential Chaos Shift Keying (OMCS-DCSK) modulation system is proposed and designed in this paper. New orthogonal chaotic signal sets are generated using Gram-Schmidt algorithm and Walsh code function then these signals are used for bearing information bits to achieve higher data rate and better bandwidth efficiency compared with the conventional DCSK communication system. The bit error rate (BER) analysis of the OMCS-DCSK system over additive white Gaussian noise (AWGN) and multipath Rayleigh fading channel is derived and compared with the simulation results. Also, the spectral and complexity analysis of the system are presented and compared with the conventional DCSK systems. The results show that the proposed system outperforms OCVSK and MCS-DCSK in BER performance and spectral efficiency

A Multilevel Code-Shifted Differential Chaos Shift Keying System With Reference Diversity

In this brief, a multilevel code-shifted differential chaos shift keying system with reference diversity (MCS-DCSK-RD) is proposed. In the proposed system, the reference signal with several replicated versions (called reference diversity) are transmitted to reduce the interference of channel noise on the reference signal. We derive the theoretical bit error rate (BER) of the proposed system over the AWGN and multipath Rayleigh channels, and verify its accuracy by simulations. Then, the optimal reference diversity quantity is determined via the theoretical BER. Compared with the multilevel code-shifted differential chaos shift keying (MCS-DCSK) system, the proposed scheme with optimal reference diversity quantity can effectively reduce noise, thus obtain much better BER performance over the additive white Gaussian noise (AWGN) and multipath Rayleigh channels. Also, we further reduce the noise by averaging the received demodulated signals at the receiver, thereby further improving the BER performance of the MCS-DCSK-RD system.

Multi‐carrier chaotic communication scheme for underwater acoustic communications

Multi-carrier (MC) and spread-spectrum (SS) are two good technologies for underwater acoustic (UWA) communications. In this study, the authors propose a novel MC chaos modulation scheme, which combines code-shifted differential chaos shift keying (CS-DCSK) with orthogonal frequency division multiplexing (OFDM), namely MC-CS-DCSK. The proposed scheme exploits the orthogonal characteristic of the Walsh code to superimpose the chaotic reference chips and the information bearing chips in the same time/frequency unit. Besides, a cyclic-shift interleaver is used on chips to harvest frequency diversity. To the in-depth understanding of the proposed system, the bit error rate (BER) of the proposed system under Gaussian channels and multipath Rayleigh fading channels are derived and verified by simulation. Furthermore, the spectral efficiency of the proposed system is analysed and compared with some existing chaos-based communication systems. Finally, they study BER performance of the system under UWA channels and compare it with traditional MC direct sequence SS and OFDM-based MC-DCSK systems. Simulation results show that the system has good robustness under time-varying UWA channels.

A Novel Multiple-Access Correlation-Delay-Shift-Keying

In Correlation-Delay-Shift-Keying (CDSK), the reference signal and the information-bearing signal are added together during a certain time delay. Because the reference signal is not strictly orthogonal to the information-bearing signal, the cross-correlation between the adjacent chaotic signal (Intra-signal Interference, ISI) will be introduced into the demodulation at the receiver. Therefore, the Bit-Error Ratio (BER) of CDSK is higher than that of Differential-Chaos-Shift-Keying (DCSK). To avoid the ISI component and enhance the BER performance of CDSK in multiuser scenario, Multiple-Access CDSK with No Intra-signal Interference (MA-CDSK-NII) is proposed. By constructing the repeated chaotic generator and applying the Walsh code sequence to modulate the reference signal, in MA-CDSK-NII, the ISI component will be eliminated during the demodulation. Gaussian approximation method is adopted here to obtain the exact performance analysis of MA-CDSK-NII over additive white Gaussian noise (AWGN) channel and Rayleigh multipath fading channels. Results show that, due to no ISI component and lower transmitting power, the BER performance of MA-CDSK-NII can be better than that of multiple-access CDSK and Code-Shifted Differential-Chaos-Shift-Keying (CS-DCSK).

Code-Shifted Differential Chaos Shift Keying with Code Index Modulation for High Data Rate Transmission

In the general code-shifted differential chaos shift keying (GCS-DCSK) system, multiple bit-streams are simultaneously carried by CS-DCSK signal using Walsh codes. However, its data rate is limited by the available Walsh codes in the Walsh code matrix due to orthogonality constraint of GCS-DCSK signal. In this paper, we propose a new GCS-DCSK scheme with code index modulation (CIM-CS-DCSK), which can achieve higher spectrum efficiency using code index modulation to carry additional bits. In the proposed scheme, the reference chaotic signal is the same as that of GCS-DCSK, and the multiple information bearing signals are simultaneously modulated by the information symbols and the selected Walsh codes with specific indices, which are determined by an integer sequence mapped from information symbols via the natural numbers to $k$ -combinations mapping method. We derive bit error rate of the proposed scheme over the additive white Gaussian noise channel. The numerical results not only verify our analysis but also show the advantage of the proposed scheme over GCS-DCSK. Through analyzing and comparing the numbers of carried bits per transmitted symbol of CIM-CS-DCSK and GCS-DCSK, it is shown that the proposed scheme can obtain higher data rate than GCS-DCSK with the same resource constraints.

A Simplified GCS-DCSK Modulation and Its Performance Optimization

In this paper, a simplified Generalized Code-Shifted Differential Chaos Shift Keying (GCS-DCSK) whose transmitter never needs any delay circuits, is proposed. However, its performance is deteriorated because the orthogonality between substreams cannot be guaranteed. In order to optimize its performance, the system model of the proposed GCS-DCSK with power allocations on substreams is presented. An approximate bit error rate (BER) expression of the proposed model, which is a function of substreams’ power, is derived using Gaussian Approximation. Based on the BER expression, an optimal power allocation strategy between information substreams and reference substream is obtained. Simulation results show that the BER performance of the proposed GCS-DCSK with the optimal power allocation can be significantly improved when the number of substreams [Formula: see text] is large.

Performance Analysis of the CS-DCSK/BPSK Communication System

As a spread spectrum communication system, code-shifted differential chaos shift keying (CS-DCSK) is required to provide reasonable bit error performance in a coexisting scenario where the conventional communication system is an interferer. Meantime, the bit error performance of the conventional communication system should not deteriorate dramatically in the presence of a CS-DCSK signal, which is as an interferer. This paper studies the performances of the CS-DCSK/BPSK coexisting system. By comparisons on the bit error rate (BER) of two coexisting systems, i.e, CS-DCSK/BPSK and DCSK/BPSK systems, in different channel environments at the same interference signal ratio, it reveals that CS-DCSK/BPSK has better performances than DCSK/BPSK. The BER expression of the CS-DCSK sub-system is derived in the presence of BPSK interference signals when two sub-systems are synchronized. Also derived is the BER expression of the BPSK sub-system in the presence of CS-DCSK signals when two sub-systems are asynchronized and synchronized, respectively. For the synchronization case, the BER expression of the BPSK sub-system is independent of the strengths of CS-DCSK signals. As a new interferer, CS-DCSK has less effect on the conventional communication system. It is shown that numerical simulations are in good agreement with the analytic results.

A Novel Chaotic Modulation Scheme in a Cooperative Relaying System

In recent years, the demand for new-generation wireless networks has spurred research on cooperative communication, a powerful physical layer technique to combat fading in wireless relaying scenario. Recently, chaos based communication has been proved to exhibit excellent features which suits better for the emerging wireless networks. Different chaos based modulation schemes has been analyzed with the recent literatures, of which the code shifted differential chaos shift keying (CS-DCSK) and Quadrature chaos shift keying (QCSK) schemes are proved to be the better schemes. By combining the advantage of aforementioned CS-DCSK and QCSK scheme, a novel modulation scheme called code shifted Quadrature chaos shift keying (CS-QCSK) is reported in our earlier work [21] and its suitability in a cooperative relaying scenario with a single relay node is tested in this paper. The novel CS-QCSK scheme is implemented in the nodes of the cooperative relaying system to upgrade the system performance. The simulation results have validated the effectiveness of the proposed scheme by offering better BER performance, minimum outage probability and increased spectral efficiency compared to the non-cooperative transmission method.

Multiuser BER Analysis Of CS-QCSK Modulation Scheme in a Cellular System

In recent years, chaotic communication is a hot research topic and it suits better for the emerging wireless networks because of its excellent features. Different chaos based modulation schemes have evolved, of which the CS-DCSK modulation technique provides better BER performance and bandwidth efficiency, due to its code domain approach. The QCSK modulation technique provides double benefit: higher data rate with similar BER performance and same bandwidth occupation as DCSK. By combining the advantage of code shifted differential chaos shift keying (CS-DCSK) and Quadrature chaos shift keying (QCSK) scheme, a novel modulation scheme called code shifted Quadrature chaos shift keying (CS-QCSK) is proposed and its suitability in a multiuser scenario is tested in this paper. The analytical expressions for the bit-error rate for Multi-user CS-QCSK scheme (MU-CS-QCSK) under Rayleigh multipath fading channel is derived. The simulation result shows that, in multiuser scenario the proposed method outperforms classical chaotic modulation schemes in terms of bit error rate (BER).

Analytical Evaluation of a Hybrid Chaotic Shift Keying [CS-QCSK] in a CDMA System

recent years, various chaos based modulation schemes were evolved, of which the CS-DCSK modulation technique provides a better BER performance and bandwidth efficiency, due to its code domain approach(10). The QCSK modulation technique provides double benefit, namely: higher data rate with similar BER performance and same bandwidth occupation as DCSK. By combining the advantage of code shifted differential chaos shift keying (CS-DCSK) and Quadrature chaos shift keying (QCSK) scheme, a novel CS-QCSK modulation scheme called code shifted Quadrature chaos shift keying is proposed. The noise performance of CS-QCSK is better to most conventional modulation schemes and also provides an increased data transmission rates with greatly improved robustness. Analytical expressions for the bit-error rates are derived for both AWGN channel and Rayleigh multipath fading channel. The simulation result shows that the proposed method outperforms the classical approaches in terms of bit error rate and spectral efficiency.

A NEW DATA RATE ADAPTION COMMUNICATIONS SCHEME FOR CODE-SHIFTED DIFFERENTIAL CHAOS SHIFT KEYING MODULATION

In a binary Transmitted Reference (TR) system each bit is encoded into two wavelets of finite duration. The information is transmitted by the sign of correlation measured between the two wavelets. The Code-Shifted Differential Chaos Shift Keying (CS-DCSK) modulation scheme transmits the two wavelets in the same time slot and applies two Walsh code sequences to keep the wavelets separated. The CS-DCSK modulation scheme is generalized here by transmitting more than one information bearing wavelets with one reference. The orthogonality of wavelets is assured by different Walsh code sequences. The new Generalized CS-DCSK (GCS-DCSK) scheme is a multilevel modulation where the symbol period is kept constant but the data rate can be varied in an adaptive manner by adding new or removing existing information bearing wavelets, each of them is isolated by Walsh code. Exploiting the Gaussian approximation, an analytical expression is derived for the noise performance of GCS-DCSK modulation. Its accuracy is verified by computer simulation.

Design of a High-Data-Rate Differential Chaos-Shift Keying System

In a differential chaos-shift keying (DCSK) system, the reference and information chaotic bearing signals are transmitted in two consecutive time slots and require the presence of delay components in the modulator and demodulator circuits. This system design requires a difficult-to-implement radio-frequency delay line that limits the data rate. The code-shifted DCSK (CS-DCSK) system proposes a solution for these problems by spreading the two chaotic slots by Walsh codes instead of using a time delay and sending them during the same time interval. In this brief, we extend the study of the CS-DCSK system, and we design two versions of a high-data-rate CS-DCSK system, which increase the data rate and can also perform in a multiuser case. The idea to achieve a high data rate is to get the information bits to share the same reference chaotic slot, where their separation is assured and maintained by different chaotic signals. In addition, this new design is not limited to a restricted number of Walsh codes such as CS-DCSK and provides from the properties of the chaotic signal in terms of security and good correlation properties. Finally, the performances of the systems are analyzed.