Chaotic Shift Keying Research Articles

Optical chaotic communication system based on time-delayed shift keying and common-signal-induced synchronization

Aiming at the difficulty of traditional chaotic-shift-keying (CSK) systems in resisting return map attacks, we propose an optical chaotic communication system based on time-delayed shift keying and common-signal-induced synchronization. This scheme combines amplified spontaneous emission (ASE) noise, phase modulator (PM), and fiber Bragg grating (FBG) to achieve dual masking in both intensity and phase fields, achieving 10Gb/s information transmission. A common-signal-induced method is used to achieve the synchronization of the system. Moreover, by shifting the time delay as the message-feeding method, the return map attack is effectively resisted, to prevent the amplitude and frequency information of the chaotic attractor from being exposed. In terms of confidentiality and communication performance, this scheme demonstrates good performance of time delay signatures (TDSs) concealment and long-distance transmission capability. In addition, this scheme maintains high sensitivity to key parameters and achieves better confidentiality while increasing the key space.

Chaotic Spread-Spectrum Communication: A Comparative Study between Chaotic Synchronization and Matched Filtering

This publication investigates the performance of demodulation methods utilized in spread spectrum chaotic communication systems in order to understand conditions at which advanced demodulation methods, such as chaotic synchronization, provide tangible benefits over classical, matched filtering-based approaches. We conduct simulations and comparisons of three different communication systems: classic direct sequence spread spectrum (DSSS), chaotic signal fragment-based pseudo-chaotic spread spectrum (PCSS), and chaotic synchronization-based antipodal chaos shift keying (ACSK). These systems possess similar spectral and time domain characteristics, allowing us to shed light on their fundamental differences and limitations in chaos-based communication. Additionally, we assess the impact of frequency modulation (FM) on these modulation methods, as FM allows the creation of simplified non-coherent modulation schemes. Our findings, based on the analysis of bit error ratio (BER) curves, demonstrate that in the case of a non-dispersive communication channel, the utilization of chaotic synchronization does not allow to achieve performance of correlation-based receivers. Additionally, the utilization of chaotic synchronization for multiple access poses certain challenges due to malicious synchronization between users. As a supplementary finding, we show that in systems with matched filter-based demodulation, discrete-time quantized spreading sequences confer an advantage over analogous, continuous-time spreading waveforms.

Security Analysis of Differential Chaotic Keying in Optical Communication

Space free optical communication (FSO) has the advantages of wide bandwidth resources, less susceptibility to attacks, strong resistance to interference, and low losses. The FSO system itself has high security, with the realization of single photon detection technology, the stealer can obtain information without blocking the beam propagation. So using chaotic encryption methods can further improve the security performance of communication systems. This article uses a gamma gamma turbulence model and utilizes the differential chaotic shift keying (DCSK) method of communication systems to improve the system’s resistance to attacks. The theoretical expression of the system error rate under this model is derived, and the security performance of the system is further analyzed. Through experimental simulation, it is proved that the system has better resistance to attacks and lower bit error rates.

Design and Analysis of a Multi−Carrier Orthogonal Double Bit Rate Differential Chaotic Shift Keying Communication System

A new multi−carrier orthogonal double bit rate differential chaotic shift keying (MC−ODBR−DCSK) communication system is presented in this paper. With two composite signals generated by an orthogonal chaotic signal generator as reference signals, 2M bits of information data are transmitted on M−channel subcarriers, improving transmission speed and energy efficiency. In addition, the receiver does not require a radio frequency (RF) delay circuit to demodulate the received data, which makes the system easier to implement. This paper analyzes Data−energy−to−Bit−energy Ratio (DBR) of the system. The bit error rate performance of the system is simulated to verify the impact of parameters such as chaotic maps, semi-spread spectrum factor, and sub-carrier number. At the same time, the bit error rate performance of the MC−ODBR−DCSK system is compared with traditional DCSK systems in Rician fading and additive Gaussian white noise (AWGN) channels.

Statistical Characteristics of Differential Communication Scheme Based on Chaotic Radio Pulses

The aim of this paper is to analyze statistical characteristics of the new differential communication scheme based on chaotic radio pulses in the presence of additive white noise (Gaussian) and using various distributions of instantaneous values of the chaotic signal. The characteristic feature of the presented scheme is the usage of significantly shorter time delays compared to the classical differential chaotic shift keying (DCSK) scheme. In order to investigate noise immunity of the direct chaotic differential communication (DC2) scheme, numerical statistical simulation is performed in terms of the bit error probability (BER) of the transmitted information. Then, the results of this simulation are compared to the results of analytical research. It is shown that due to the inherent internal noises of the scheme, the bit error probability (BER) for arbitrarily large values of the ratio of the signal energy to the Gaussian noise spectral density (Eb/N0) is higher than 10−3 for the values of processing gain K < 30 for any distribution of instantaneous values of the chaotic signal. With the increase of the K values, there is a rapid decrease in BER in a system with a channel without white noise. Numeric simulation is performed, which verifies and clarifies the analytical estimates obtained earlier regarding the bit error probabilities as functions of processing gain and ratio of the signal energy to the Gaussian noise spectral density. The minimum values of Eb/N0 are obtained, which provide necessary error probabilities with the processing gain set. It is shown that with a high processing gain (K > 30), the communication scheme considered here operates effectively both in a channel without fluctuation noises and in a channel with additive white Gaussian noise. The statistical characteristics of the proposed scheme do not depend on the choice of a particular distribution of instantaneous values of the chaotic signal. Taking into account that the scheme uses short delays, which do not depend on the processing gain of the used signal and are easily implemented, for example, on fragments of a high-frequency cable, the results obtained show good prospects for its implementation in a physical experiment.

Secure Mimo Communication System with Frequency Hopping Aided OFDM-DCSK Modulation

In this paper, a multiple-input multiple-output (MIMO) communication system with frequency hopping (FH) aided orthogonal frequency division multiplexing differential chaotic shift keying (OFDM-DCSK) modulation is proposed. Our objective is to improve the security of MIMO communication system which is encoded by space time block coding (STBC). In order to combat the eavesdropping or malicious attacks due to the broadcast characteristics of wireless communication system, we propose to use DCSK and FH modules to encrypt the information, and hide the user data in the chaotic sequences, where the initial value of chaotic sequences and the method of generating FH module are only shared among legitimate users. Moreover, we derive the bit error rate (BER) and the secrecy capacity of the scheme in additive white Gaussian noise (AWGN) channel and Rayleigh fading channel. Simulation results show that the proposed scheme can effectively improve the security of MIMO communication system, which can be seen from the BER of eavesdroppers and legitimate users, and the secrecy capacity of the proposed scheme and the benchmark schemes.

Discovering Chaos-Based Communications by Recurrence Quantification and Quantified Return Map Analyses

Many studies show the possibility of transmitting messages in a protected and covert manner using a noise-like chaotic waveform as a carrier. Among popular chaotic communication system (CCS) types, one may distinguish chaotic shift keying (CSK) and parameter modulation (PM) which are based on the manipulation of the transmitting chaotic oscillators. With the development of direct digital synthesis (DDS), it became possible to modulate chaotic signals by varying the properties of the numerical method used in digital chaos generators. The symmetry coefficient modulation (SCM) is such an approach potentially able to provide higher secrecy. However, the actual security of chaos-based communications is still a questionable and controversial feature. To quantitatively evaluate the CCS security level, a certain numerical metric reflecting the difficulty of breaking a communication channel is needed. Return maps are commonly used to attack chaotic communication systems, but the standard algorithm does not involve any kind of quantification. In this study, we propose a new method for estimating the differences between two return maps based on a two-dimensional (2D) histogram. Then, we investigate the resistance of chaotic shift keying, parameter modulation, and SCM communication schemes against three types of attacks: the proposed quantified return map analysis (QRMA), recurrence quantification analysis (RQA), which had not been previously reported for attacking chaos-based communications, and the classical approach based on spectral analysis. In our experiments we managed to recover the plain binary message from the waveform in the channel when transmitted using all three chaos-based messaging techniques; among them, SCM appeared to be the most secure communication scheme. The proposed QRMA turned out to be the most efficient technique for message recovery: the sensitivity of the QRMA appeared to be 2–5 times higher than that in the case of spectral analysis. The proposed QRMA method can be efficiently used for evaluating the difficulty of hacking chaos-based communication systems. Moreover, it is suitable for the evaluation of any other secure data transmission channel.

Design and Analysis of a Short Reference Orthogonal Double Bit Rate Differential Chaotic Shift Keying Communication Scheme

With the broadband, noise-like, and non-periodic characteristics of chaotic signals, chaotic digital modulation schemes have received extensive attention. A new short reference orthogonal double bit rate differential chaotic shift keying (SR-ODBR-DCSK) communication scheme is proposed in the paper. The modulation technology generates two orthogonal chaotic signals by using the orthogonality of the chaotic signals acting on the Walsh function and modulates the continuous two-bit data information respectively to achieve the simultaneous transmission of two signals at the same time slot. Odd information bits and even information bits are modulated to two orthogonal signals so as to reach a double transmission rate on the basis of the original channel. In this paper, the performance of SR-ODBR-DCSK in the additive white Gaussian noise (AWGN) channel is analyzed, and a Monte Carlo simulation test is carried out. The bit error rate of this modulation method is compared with that of SR-DCSK. The results show that the SR-ODBR-DCSK system is excellent and promising.

Secure collaborative cognitive radio based on chaotic modulation and compressive sensing

Cognitive radio (CR) is a wireless technology that is used to overcome the spectrum scarcity problem. CR includes several stages, spectrum sensing is the first stage in the CR cycle. Traditional spectrum sensing (SS) techniques have many challenges in the wideband spectrum. CR security is an important problem, since when an attacker from outside the network access the sensing information this produces an increase in sensing time and reduces the opportunities for exploiting vacant band. Compressive sensing (CS) is proposed to capture all the wideband spectrum at the same time to solve the challenges and improve the performance in the traditional techniques and then one of the traditional SS techniques are applied to the reconstructed signal for detection purpose. The sensing matrix is the core of CS must be designed in a way that produces a low reconstruction error with high compression. There are many types of sensing matrices, the chaotic matrix is the best type in terms of security, memory storage, and system performance. Few works in the literature use the chaotic matrix in CS based CR and these works have many challenges: they used sample distance in the chaotic map to generate a chaotic sequence which consumes high resources, they did not take into consideration the security in reporting channel, and they did not measure their works using real primary user (PU) signal of a practical application under fading channel and low SNR values. In this paper, we propose a chaotic CS based collaborative scenario to solve all challenges that have been presented. We proposed a chaotic matrix based on the Henon map and use the differential chaotic shift keying (DCSK) modulation to transmit the measurement vector through the reporting channel to increase the security and improve the performance under fading channel. The simulation results are tested based on a recorded real-TV signal as PU and Compressive Sampling Matching Pursuit (CoSaMP) recovery algorithm under AWGN and TDL-C fading channels in collaborative and non-collaborative scenarios. The performance of the proposed system has been measured using recovery error, mean square error (MSE), derived probability of detection (Pdrec), and sensitivity to initial values. To measure the improvement introduced by the proposed system, it is evaluated in comparison with selected chaotic and random matrices. The results show that the proposed system provides low recovery error, MSE, with high Pdrec, security, and compression under SNR equal to −30 dB in AWGN and TDL-C fading channels as compared to other matrices in the literature.

Secured Medical Image Hashing Based on Frequency Domain with Chaotic Map

Recently, online-medicine got increased global interest, particularly during COVID19 pandemic. Data protection is important in the medical field since when promoting telemedicine applications, it is necessary to protect the patient data and personal information. A secured process is needed to transmit medical images over the Internet. In this paper hash algorithm is employed to protect the data by using powerful features from the coupled frequency domains of the Slantlet Transformation (SLT) and the Discrete Cosine Transform (DCT). The Region of Interest (ROI) is localized from an MRI image then extraction of a feature set is performed for calculating the hash code. Then, hash code is enciphered to maintain security by employing a secure Chaotic Shift Keying (CSK). The suggested method of security is ensured by the strength of the CSK and the encryption key secrecy. A detailed analysis was conducted using 1000 uncompressed images that were chosen randomly from a publicly available AANLIB database. The proposed methodology can be useful for JPEG compression. Also, this method could resist many attacks of image processing likes filtering, noise addition, and some geometric transforms.

An Encryption Architecture Suitable for on Chip Integration With Sensors

This paper demonstrates a hardware encryption algorithm that can be integrated directly with sensors on the same chip. In contrast to using power-hungry microprocessors and software implementations, the encryption algorithm was based on a Lorenz chaotic system and was implemented as time scaling chaotic shift keying (TS-CSK). The coupled differential equations of TS-CSK were implemented using low power integrators, multiplexers, switches, and passive components. Both a single-ended and differential system was developed. The single-ended based system showed no oscillation, while the differential based system demonstrated oscillation. Experimental measurements of the differential system with an integrated temperature sensor demonstrated the ability to encrypt and decrypt the transmitted signal. The differential encryption/decryption system was implemented in 180 nm technology and operated with a 1.8 V power supply and 1.5 mW of power.

Design and optimization of multi user OFDM orthogonal chaotic vector shift keying communication system

This paper study and present, power allocation strategy on sub-carriers of multiuser OFDM employed for orthogonal chaotic vector shift keying (MU OFDM-OCVSK) over multipath frequency selective fading channels. firstly, the MU OFDM-OCVSK system is modeled with power allocated on reference and information bearing subcarriers. Then, the computed bit error rate equation of the power allocation MU OFDM-OCVSK system is derived. The optimal power allocation strategy on subcarriers is obtained using convex optimization. Finally, compared with the traditional MU OFDM-DCSK and MU OFDM-OCVSK without power allocation system the proposed system can achieve an excellent BER performance under multipath Rayleigh fading channels. Numerical and Simulation results emphasize the remarkable features of the proposed optimal power allocation strategy.

Secure Verifiable Scheme for Biometric System based on Secret Sharing and CSK

Biometric templates stored in a database introduce a number of security and privacy risks. The requirements for an architecture that does not suffer from these risks are needed. Therefore, the reference information that is stored in the database must not give sufficient information to make successful impersonation possible. Also, the reference information must be retrieved as little as possible about the original biometrics; in particular it reveals no sensitive information. The proposed system introduces a novel method for template protection and a verification using the merging techniques of chaotic shift keying (CSK) and secret image sharing (SIS). The proposed architecture assures a complete protection framework for the biometric templates, which involves two phases: the first phase is to protect the ID image; a watermark ID image that includes the personal information embedded in the template using a novel watermarking algorithm to generate two shares, and then it is utilized to verify the accuracy of the revealed template. The second phase is for template protection, where the generated shares are encoded separately using CSK and then one share is stored in the database and the other kept with the user. The experimental and comparative results demonstrate that the proposed framework retains the protection of the template and preserves robustness to malicious attacks, while it does not have a discernible effect on the quality of the template.

Energy Efficient Parallel Concatenated Index Modulation and $M$-ary PSK Aided OFDM-DCSK Communications With QoS Consideration

In this paper, we propose a parallel concatenated index modulation and $M$ -ary phase shift keying (MPSK) to integrate with carrier interferometry (CI) codes into the orthogonal frequency division multiplex (OFDM) differential chaotic shift keying (DCSK) communication system. Our objective is to meet different quality of service (QoS) user demands while achieving higher energy efficiency and retaining reliable communications with low peak-to-average power ratio (PAPR). In our design, one input bit set is modulated by the index of the CI codes matrix whose rows are rotated circularly, another bit set is mapped to the MPSK symbols to realize the $M$ -ary modulation. Subsequently, the resultant MPSK symbols are modulated by reference chaotic sequences and spread by the information-bearing rotated CI codes matrix at the transmitter. After the OFDM modulations, the information bearing symbols are transmitted over multiple subcarriers. At the receiver, after the non-coherent chaotic correlation demodulation, the maximum likelihood detection method is firstly applied to attain the estimates of the index modulated bit set, which are then used to recover the phases of chaotic sequences for further evaluation of another MPSK modulated symbols. Since no additional energy is required while more bits can be transmitted via the $M$ -ary modulation and index modulation, the energy efficiency can be improved. In addition, thanks to the orthogonality of the CI codes matrix and the spreading in the frequency domain, the PAPR could be suppressed and reliability performances can be improved. Then theoretical analysis is conducted and simulation results validate the theoretical analysis. Moreover, the results demonstrate the superior bit error rate (BER) performances to benchmarks and flexible data rate could be provided for user terminals via different combinations of the index modulation and the $M$ -ary modulation.

Robust chaotic-shift-keying scheme based on electro-optical hybrid feedback system.

A chaotic-shift-keying (CSK) scheme is designed based on a chaos system with electro-optical hybrid time delayed feedback structure. By switching the time delay parameter as a message feeding method, the generated chaotic signal is no longer suffered from return map attack, which is an innate vulnerability of traditional CSK. When the coupling of the seed electrical chaotic system and the nonlinear optical time delay feedback loop is carefully weighed, this CSK scheme shows a good robustness in terms of handling noise for transmitting digital signals. By demodulating the digital signals with the chaotic coherent detection method, a bit error rate of 6×10-4 is achieved at the signal-to-noise ratio of 10dB in the simulation. The proposed method has a promising application prospect in some harsh environments.

Efficient and Secure Non-Coherent OFDM-Based Overlapped Chaotic Chip Position Shift Keying System: Design and Performance Analysis

In this paper, we propose a novel non-coherent orthogonal frequency division multiplex (OFDM) based overlapped chaotic chip position shift keying (OCCPSK) system. Different from traditional non coherent chaotic systems, this system endeavors to achieve efficient and secure performances with no need to transmit reference chaotic sequences. At the transmitter, information bits are grouped into multiple subsets and respectively modulated by the position of chaotic chips. Then iterative chaotically shift-aided shuffling and overlapping operations are performed on the resultant multi-ary signals to enhance the security. Subsequently, OFDM modulations are performed and information-bearing signals are transmitted. At the legitimate receiver, with the known key parameters, reverse operations are carried out. Then the positions used for modulations can be formulated out to recover information bits via maximizing the Euclidean norm of received symbols. Since no reference chaotic signals are required to be transmitted, both efficiency and security performances are improved. Moreover, we derive the analytical symbol error rate (SER) and bit error rate (BER) expressions over fading channels, and theoretical spectrum efficiency, energy efficiency and security performances are analyzed. Simulation results verify the effectiveness of derivations, and demonstrate the high efficiency and security of this design.

THE M-ARY SECURITY DIFFERENTIAL CHAOTIC FREQUENCY SHIFT SYSTEM BASED ON THE MIMO MODEL

To improve the data security and efficiency of the multi-input multi-output (MIMO)-based differential chaotic shift keying (DCSK) system under the wireless multipath fading channel, a new non-coherent modulation solution, i.e., the M-ary security differential chaotic shift keying (MS-DCSK), is proposed in this study. The scrambling matrix and shift matrix are used to construct a scrambling matrix group in this system, enabling the scrambling matrix to enhance the security of chaotic signals while carrying the M-ary bit information. By doing so, the security, energy efficiency, and spectral efficiency of the system are improved. In addition, by taking advantage of the quasi-orthogonal characteristics of chaotic sequences, the system receiver can effectively utilize the multipath diversity and space diversity of the multi-antenna transmitter and receiver system, without requiring the channel state information (CSI).

Study the Effect of Spreading Factor value on the Performance of Chaotic Modulation Schemes

High data rate and bandwidth efficiency are the requirements of modern wireless systems. Most studies introduce different ways to develop communication systems to meet these requirements. The researches in the last few years focused on the chaotic system as a chaotic modulation due to its nature. So that the performances of various chaotic modulation schemes (Initial Condition Modulation (ICM) and Chaotic Shift Keying (CSK)) in terms of bit error rate (BER), for different spreading factors are implemented in this article and simulated using MATLAB 2016b simulation. The main objective of this paper is to make a comparison of various chaotic modulation schemes under AWGN channel and study the effect of the spreading factor (β) on the performance of different chaotic modulation schemes, where the spreading factor (β) is the number of generated chaotic signal samples during the bit period (Tb). Different values of spreading factor (12,16, 20, 40, 60, 80, and 100) samples are selected to implement various chaotic modulation schemes. The results show that the spreading factor value of (100) achieves good performance for all types of chaotic modulation schemes which are implemented here. Increasing the value of spreading factor over (100) such as (120, 140, and 180) will add a little bit enhancement to the system, whilst the processing time will increase dramatically.

Design and Processing of a Novel Chaos-Based Stepped Frequency Synthesized Wideband Radar Signal.

The linear stepped frequency and linear frequency shift keying (FSK) signal has been widely used in radar systems. However, such linear modulation signals suffer from the range–Doppler coupling that degrades radar multi-target resolution. Moreover, the fixed frequency-hopping or frequency-coded sequence can be easily predicted by the interception receiver in the electronic countermeasures (ECM) environments, which limits radar anti-jamming performance. In addition, the single FSK modulation reduces the radar low probability of intercept (LPI) performance, for it cannot achieve a large time–bandwidth product. To solve such problems, we propose a novel chaos-based stepped frequency (CSF) synthesized wideband signal in this paper. The signal introduces chaotic frequency hopping between the coherent stepped frequency pulses, and adopts a chaotic frequency shift keying (CFSK) and phase shift keying (PSK) composited coded modulation in a subpulse, called CSF-CFSK/PSK. Correspondingly, the processing method for the signal has been proposed. According to our theoretical analyses and the simulations, the proposed signal and processing method achieve better multi-target resolution and LPI performance. Furthermore, flexible modulation is able to increase the robustness against identification of the interception receiver and improve the anti-jamming performance of the radar.

Turbo Trellis-Coded Differential Chaotic Modulation

In this brief, a novel turbo trellis-coded differential chaotic modulation (TTC-DCM) system is proposed, where parallel concatenated trellis codes are combined with the M-ary differential chaotic shift keying (M-ary DCSK) scheme. An extrinsic information transfer chart is employed to analyze the convergence over additive white Gaussian noise channel and multipath Rayleigh channels. Simulation results show that the new scheme can obtain considerable coding gains without impairing the bandwidth efficiency in comparison with the M-ary DCSK scheme and the trellis-coded differential chaotic modulation scheme. Moreover, compared to the direct-sequence spread-spectrum turbo trellis-coded modulation scheme, TTCDCM has lower complexity and better robustness in the absence of channel state information over multipath Rayleigh channels. Overall, because of the merits of promising performance, high bandwidth efficiency, robustness to poor channel conditions, and an easy-to-implement property, the TTC-DCM scheme is suitable for bandlimited communication applications under poor channel conditions.