Chaotic Communication Research Articles

Estimating Optimal Synchronization Parameters for Coherent Chaotic Communication Systems in Noisy Conditions

It is known, that coherent chaotic communication systems are more vulnerable to noise in the transmission channel than conventional communications. Among the methods of noise impact reduction, such as extended symbol length and various digital filtering algorithms, the optimization of the synchronization coefficient may appear as a very efficient and simple straightforward approach. However, finding the optimal coefficient for the synchronization of two chaotic oscillators is a challenging task due to the high sensitivity of chaos to any disturbances. In this paper, we propose an algorithm for finding the optimal synchronization parameter K_opt for a coherent chaos-based communication system affected by various noises with different signal-to-noise ratios (SNR). It is shown, that under certain conditions, optimal $K$ provides the lowest possible bit error rate (BER) during the transmission. In addition, we show that various metrics applied to the message demodulation task propose different noise immunity to the overall system. For the experimental part of the study, we simulated and physically prototyped two chaotic communication systems based on well-known Rossler and Lorenz chaotic oscillators. The microcontroller-based prototype of a chaotic communication system was developed to investigate the influence of noise in the real transmission channel. The experimental results obtained using the designed hardware testbench are in good correspondence with the theoretical propositions of the study and simulation results. The suggested evaluation metrics and optimization algorithms can be used in the design of advanced chaos-based communication systems with increased performance.

Chaotic Systems-Based Secure Communication Scheme for Detection of Wind Turbines

With the popularity of the Industrial Internet of Things, there are huge security challenges in the storage and transmission of image information. How to ensure that transmitted images from malicious attacks and random tampering have become a hot topic of information security. In this paper, a new secure communication scheme is proposed in consideration of the security requirements of transmitted images during the detection of wind turbines process. The scheme is based on the image diffusion method of chaotic systems. By utilizing the sensitivity of the chaotic systems to the initial conditions and parameters, and using the parameters as the key to realizing the encryption and decryption of the image. Furthermore, a large amount of image information will be acquired in real-time during the inspection process of the fan blades by UAVs. Due to the limited computing and storage resources of UAVs, C-E-D three-layer architecture is adopted, which can effectively offload the complex tasks to the edge and cloud to significantly reduce UAVs latency and energy consumption. Test and analysis results show that the proposed encryption scheme is effective and reliable for image security communication applications.

Secure WDM communication based on second order differential feedback electro-optical chaotic mutual injection synchronization

An optical phase chaos and mutual injection chaos synchronization scheme based on second order differential feedback electro-optical loop is proposed for chaotic communication. The filtered chaotic waves for mutual injection synchronization and multi-channel signals are transmitted through wavelength division multiplexing (WDM) to realize large-capacity confidential communication. The results show that the bandwidth of the optical chaos is 41.38 GHz, the normalized permutation entropy is 0.999, and the chaos has the performance of time delay suppressing (TDS). This scheme achieves up to 7-channel 25 GBaud 16QAM with the multi-modulus algorithm (MMA) algorithm at OSNR of 25 dB after 100 km transmission. The bit-rate distance of 280,000 Gb/s km is successfully realized by 500 km transmission of 4-channel 35 GBaud 16QAM signals at 25 dB OSNR. The analysis proves that the performance of the second order digital differential electro-optical phase feedback (2nd order DEOP) chaos is better than that of the 1st order DEOP chaos and 3rd order DEOP chaos. The 2nd order DEOP chaos can be generated at a smaller feedback coefficient, the bandwidth of radio frequency chaos is wider, and the TDS suppression is better. This scheme realizes high-speed and large-capacity secure optical chaos communication, which can be widely used in WDM networks and has practical feasibility and application value.

Coupling Projection Synchronization of Three Chaotic Systems and Its Multilevel Secure Communication via DNA CRNs

The complete synchronization of two chaotic systems and its secure communication have been considered based on DNA chemical reaction networks (DNA CRNs). There are concerns about the security of the single-level chaotic secure communication system. Thereby a multi-level secure communication scheme is put forward via DNA CRNs in this work. Firstly, a three-variable chaotic system that consists of catalysis, double, fasciation, and annihilation modules is constructed using DNA CRNs. Secondly, according to the stability principle of nonlinear systems, DNA CRNs are adopted to realize the coupling projection synchronization of three chaotic systems, and the synchronization results are discussed. Finally, sine and cosine signals are designed using DNA CRNs. These signals are added into three systems to realize multi-level encryption and decryption. Furthermore, the interference terms are taken into consideration to test the robustness of the system. The results show that the proposed scheme has high security, and can efficiently encrypt and decrypt biological signals through multi-level transmission in the presence of interference.

The influence of noise and frequency distortions in the communication channel on a communication circuit based on a hyperbolic chaos generator.

The analysis of the possibility of using a chaotic communication scheme based onsynchronization of the receiver and transmitter, which used hyperbolic chaos generators. It is shown that useful information nonlinearly mixed into the transmitter signal can be detected by the receiver if it is in stable synchronization with the transmitted signal. Research has been conducted to confirm the hypothesis that the roughness, strong chaotic properties and noise-like broadband spectrum of this type of generator provide greater reliability and stability of transmission. The influence of noise and frequency distortions of the signal in the communication channel on the quality of information detection by the receiver is also shown.

Influence of Noise and Frequency Distortions in a Communication Channel on a Communication Scheme Based on a Hyperbolic Chaos Generator

The article analyses the effectiveness of a chaotic communication scheme based on synchronization of hyperbolic chaos generators used as a receiver and a transmitter. It is shown that useful information nonlinearly mixed into the transmitter signal can be detected by the receiver if the receiver has stable synchronization with the transmitted signal. Research, aimed to confirm the hypothesis that robustness, strong chaoticity and noise-like wideband spectrum of this type of oscillators provide reliability and stability of transmission, has been carried out. This study also shows the effect of noise and frequency distortion of the signal in a communication channel on the quality of information detection.

Signal-to-noise ratio degradation analysis for optoelectronic feedback-based chaotic optical communication systems.

Chaotic optical communication encrypts transmitted signals through physical noise; this ensures high security while causing a certain decrease in the signal-to-noise ratio (SNR). Thus, it is necessary to analyze the SNR degradation of decrypted signals after chaotic encryption and the minimum requirements for the SNR of the fiber channel to meet the required bit error rate (BER) performance. Accordingly, an SNR model of decrypted signals for optoelectronic feedback-based chaotic optical communication systems is proposed. Under different channel SNRs, the SNR degradation of 40 Gbit/s phase chaos and intensity chaos models is investigated by simulation and experiment, respectively, with a 15 GHz wideband chaotic carrier. Comparing decrypted signals with original signals, the simulation results show that there is a 2.9 dB SNR degradation for both intensity chaos and phase chaos. Further, in experiments, SNR degradation from 4.5 dB to 5.6 dB, with various channel SNRs for intensity chaos, is analyzed, while there is an SNR degradation from 7.1 dB to 8.3 dB for phase chaos. The simulation and experimental results provide guidance for long-distance transmission chaotic optical communication systems.

100Gb/s coherent optical secure communication over 1000 km based on analog-digital hybrid chaos.

In recent years, the transmission capacity of chaotic secure communications has been greatly expanded by combining coherent detection and multi-dimensional multiplexing. However, demonstrations over 1000 km fiber are yet to be further explored. In this paper, we propose a coherent optical secure transmission system based on analog-digital hybrid chaos. By introducing an analog-digital converter (ADC) and a bit extraction into the feedback loop of entropy source, the broadband analog chaos is converted into a binary digital signal. This binary digital signal is then mapped to a 65536-level pulse amplitude modulation (PAM) signal and injected into the semiconductor laser (SL) to regenerate the analog chaos, forming a closed loop. The binary digital signal from the chaos source and the encrypted signal are transmitted via wavelength division multiplexing (WDM). By using conventional digital signal processing (DSP) algorithms and neural networks for post-compensation, long-haul high-quality chaotic synchronization and high-performance secure communication are achieved. In addition, the probability density distribution of the analog chaotic signal is effectively improved by adopting the additional higher-order mapping operation in the digital part of the chaos source. The proof-of-concept experimental results show that our proposed scheme can support the secure transmission of 100 Gb/s quadrature phase shift keying (QPSK) signals over 1000 km of standard single-mode fiber (SSMF). The decrypted bit error rate (BER) reaches 9.88 × 10-4, which is well below the 7% forward error correction (FEC) threshold (BER = 3.8 × 10-3). This research provides a potential solution for high-capacity long-haul chaotic optical communications and fills the gap in secure communications based on analog-digital hybrid chaos.

FPGA implementation of orthogonal hyperchaotic sequences generator based on the CNN: application in multi-user chaotic communications

In this article, we propose an efficient orthogonal hyperchaotic sequences generator for application in multi-user chaotic communication systems. The proposed generator consists of two blocks. The first block generates binary hyperchaotic sequences of varying lengths using a 6-Dimensional Cellular Neural Network (CNN) system, offering a wide range of sequence length choices. The second block uses an optimized selection method to generate multiple sets of orthogonal sequences with interesting correlation properties. The method is based on the balance and correlation properties, where zero cross-correlation between any two sequences is considered. A FPGA-based implementation of the proposed generator is presented. The hardware architecture is designed in VHDL and deployed on a Xilinx Virtex-6 FPGA ML605 evaluation kit. The generator is then analyzed and compared with the existing generator in terms of logic area consumption, throughput, latency, and randomness quality. The comparative analysis results show the effectiveness of the proposed generator, which can achieve a high throughput, low latency, and successfully pass all NIST statistical tests. Moreover, the generated orthogonal hyperchaotic sequences exhibit promising performance in a multi-user Differential Chaos Shift Keying (MU-DCSK) system, outperforming the Walsh-Hadamard sequences in terms of bit-error rate under various channel conditions.

Multistable dynamics and attractors self-reproducing in a new hyperchaotic complex Lü system.

Multistable dynamics analysis of complex chaotic systems is an important problem in the field of chaotic communication security. In this paper, a new hyperchaotic complex Lü system is proposed and its basic dynamics are analyzed. Owing to the introduction of complex variables, the new system has some structurally distinctive attractors, such as flower-shaped and airfoil-shaped attractors. In addition, the evolution process of the limit cycle is also investigated. Next, the multistable coexistence behavior of the system is researched by the method of attraction basins, and the coexistence behavior of two types of hyperchaotic attractors and one type of chaotic and periodic attractors of the system are analyzed. The coexisting hyperchaotic attractors also show flower and airfoil shapes, and four types of coexistence flower-shaped attractors with different structures are perfectly explored. Moreover, the variation of coexistence attractors in the plane and space with parameters is discussed. Then, by introducing a specific piecewise function determined by a two-element method into the new high-dimensional system, the self-reproduction of the attractor can be realized to generate the multistability, and the general steps of attractors self-reproducing in the higher dimensional system are given. Finally, the circuit design of the new system is implemented, which lays a foundation for the application of complex chaotic systems.

Моделирование энергетического приемника для систем сверхширокополосной хаотической радиосвязи

The problem of modeling an energy receiver of ultra-wideband chaotic radio pulses for chaotic radio communications is studied. As is shown, a combination of numerical and analytical modeling completes the problem of calculating characteristics of ultra-wideband chaotic communication systems. On the one hand, the numerical method is effective for calculating receiving systems with short radio pulses, and with an increase in the duration of radio pulses Tp the rate of the method decreases proportionally, whereas technical requirements for the computing equipment increase proportionally, so the operation time increases faster than Tp. On the other hand, the accuracy of the analytical solution, which is insufficient in the case of short radio pulses, grows proportion-ally with an increase in the duration of the radio pulses. Thus, in this problem, the numerical and analytical methods ideally complement each other. It is shown that the accuracy of the approximate analytical solution for the optimal threshold and the error probability becomes sufficient for engineering calculations at the values of the number of freedom degrees (processing gain) of chaotic radio pulses B  200. The combination of numerical and analytical modeling methods can significantly simplify tiresome modelling of chaotic communication systems, for example, those that provide maximum range by increasing the signal length.

Тенденции развития сверхширокополосных прямохаотических средств связи

The report discusses the development trends in the development of ultra-wideband wire-less communications based on chaotic signals. For the first time, direct chaotic communications were proposed in 2000 as a way to use noise-like (chaotic) signals for communication systems. The idea was to generate information-carrying signals directly in the region of radio or microwave frequencies where transmission takes place, and to modulate and demodulate these signals there without resorting to frequency transfer operations. In the basic version of the scheme, chaotic radio pulses were used as an information carrier, which made it possible to use “on-off” modulation and modulation of the positions of chaotic radio pulses. An envelope detector matched with the transmitted signal was used as a receiver. Another variant of the direct chaotic system is the recently proposed relative transmission scheme based on chaotic radio pulses. The report examines the characteristics and specifics of both schemes when used in ultra-wideband wire-less communication in the centimeter and decimeter wavelength ranges.

High-speed chaos-based secure optical communications over 130-km multi-core fiber.

Chaotic optical communication is of great significance for secure data transmission. Despite rapid development over the decades, high-speed (>100 Gbps) and long-distance (>100 km) chaotic optical communication in a single fiber is still full of challenges. Here, we propose and experimentally demonstrate high-speed and long-distance chaos-based secure optical communications using mutual injection of semiconductor lasers and space-division multiplexing (SDM) techniques. The encrypted signals are transmitted through all seven core channels of the multi-core fiber (MCF), which effectively expands the aggregate transmission capacity of a single fiber. A pair of source and synchronization devices based on mutual injection of semiconductor lasers are employed to effectively encrypt and decrypt signals. Chaos-based secure optical communications with 70-Gbps on-off keying (OOK) and 140-Gbps quadrature phase-shift keying (QPSK) signals over a 130-km MCF are successfully demonstrated in the experiment with favorable performance. The demonstration may pave the way for future ultrahigh capacity and ultra-long distance chaotic optical communications by fully exploiting multi-dimensional resources of light waves, including the spatial dimension.

Optical transmitter fingerprint construction and identification based on chaotic phase space reconfiguration.

An optical transmitter identification scheme based on optical chaotic phase space reconfiguration for secure communication is proposed to target injection attacks in the physical layer of optical networks. First, a feature fingerprint construction method based on reconfigured phase space of optical chaos is proposed. Then the fingerprint is controlled by the feedback intensity and filtering bandwidth of chaos. The in-phase and quadrature-phase encryption (IQE)/decryption (IQD) ensures the loading of fingerprints and realizes the confidential communication. In the experiment, the recognition rate of three transmitters is up to 99.3%. In the simulation, the recognition rate of five optical transmitters reaches 100% after 600 km transmission. The bit error rate of 25 GBaud QPSK signal after 300 km transmission at 25 dB OSNR is 1.6 × 10-3. Compared with the traditional optical transmitter identification methods, the fingerprint of this scheme is controllable. The IQE and IQD not only realize the chaotic fingerprint loading but also ensure the secure transmission of the signal avoiding the synchronization and time delay exposure problems in traditional chaotic communication systems. It is robust to device parameters, with low implementation difficulty and low cost. Therefore, this scheme has research and application value for secure communication in the physical layer of optical networks.

Effect of Lateral Alignment Error on Communication Performance of Space Chaotic Optical Communication System

In space chaotic optical communication system, when chaotic signal is coupled into the fiber at receiving terminal, it will be affected by the lateral alignment error. To study the influence of it on space chaotic optical communication system, this paper analyzed two kinds of mismatches brought by lateral alignment error, then we give a calculation model of bit error rate under lateral alignment error. Based on the model, we conducted numerical simulations. Results show that the effect of lateral alignment error on external mismatch is greater than the effect of it on internal mismatch and the system will be affected more by lateral alignment error which caused by random angular jitter than caused by static bias error. Besides, further analysis found that in high-precision space chaotic optical communication system, compensating for internal mismatch can effectively reduce the effect of lateral alignment error on system. The results will be helpful for optimizing the design of space chaotic optical communication system.

Investigation of Doppler Frequency Shift Effect on the Performance of Four-Channel Space Chaotic Laser Communication

In this article, the wavelength division multiplexing (WDM) technology is applied to the space chaotic laser communication system. We deduce the bit error rate (BER) model of multi-channel space chaotic laser communication with Doppler frequency shift. Based on the BER model, the effect of Doppler frequency shift on the performance of four-channel space chaotic laser communication systems on the synchronous orbit(GEO)-low earth orbit(LEO) and GEO-mid earth orbit(MEO) has been discussed in detail. The numerical simulation results indicate that the effect of Doppler frequency shift on GEO-LEO system is much less than GEO-MEO system. Therefore, the Doppler frequency shift effect of GEO-LEO system can be overcome by redundant design, and the Doppler frequency shift effect of GEO-MEO system must be paid more attention to the optimum design. Besides, the relationship between the performance of communication system and frequency shift under different channels are similar. The result has an important implication for reducing the complexity of the system design. These results of the article are significant for the design of the four-channel space chaotic laser communication system.

Ultra-wideband chaotic optical communication based on electro-optic differential feedback loop

A differential feedback electro-optical phase chaotic system is proposed to generate ultra-wideband optical chaos and realize high-speed long-distance chaotic communication. The nonlinear dynamics of this differential feedback loop are studied in detail. The numerical results show, firstly, in terms of chaos complexity, the highest permutation entropy of 0.993 and the largest spectral entropy of 0.945 are achieved. Regarding the key hiding, the time delay signature of phase chaos on both the autocorrelation function and delayed mutual information can be completely suppressed, so security can be guaranteed. Secondly, the maximum bandwidth of the radio spectrum is 46.75 GHz in the range of 50 GHz, and the minimum flatness is 1.62 dB/GHz. Finally, the reception of format-transparent messages can be realized by combining co-drive synchronization and coherent demodulation. The 50 GBaud QPSK signal can transmit 2400 km and the 25 GBaud 16 QAM signal can transmit 1500 km at an OSNR of 25 dB. This system realizes ultra-wideband high-complexity chaos and chaotic communication, which can greatly improve the security, transmission distance, and transmission rate of chaotic optical communication.

Complete Bifurcation Analysis of the Vilnius Chaotic Oscillator

The paper is dedicated to the numerical and experimental study of nonlinear oscillations exhibited by the Vilnius chaotic generator. The motivation for the work is defined by the need for a comprehensive analysis of the dynamics of the oscillators being embedded into chaotic communication systems. These generators should provide low-power operation while ensuring the robustness of the chaotic oscillations, insusceptible to parameter variations and noise. The work focuses on the investigation of the dependence of nonlinear dynamics of the Vilnius oscillator on the operating voltage and component parameter changes. The paper shows that the application of the Method of Complete Bifurcation Groups reveals the complex smooth and non-smooth bifurcation structures, forming regions of robust chaotic oscillations. The novel tool—mode transition graph—is presented, allowing the comparison of experimental and numerical results. The paper demonstrates the applicability of the Vilnius oscillator for the generation of robust chaos, and highlights the need for further investigation of the inherent trade-off between energy efficiency and robustness of the obtained oscillations.

Electro-optical chaotic communication system based on additional chaotic phase-shift with time-delay signature concealment

We propose and demonstrate an electro-optical chaotic communication system with additional chaotic phase-shift based on the mutual coupling structure. Under the condition of complete concealment of time-delayed signatures (TDSs), the key space of the system is greatly enhanced and highly reliable chaotic communication is finally realized. The additional-phase introduced by the new branch is nonlinearly superimposed on the phase generated by the chaotic signal of the original branch, which improves the complexity and aperiodicity of chaos. For security performance, the system only needs a very small feedback gain (i.e., βi = 2.5) to conceal TDSs. Moreover, since the system has only one chaotic signal transmitted in the transmission link, it overcomes the exposure of TDSs caused by the cross-correlation characteristics between different links. At the same time, the system has strong synchronization robustness and can achieve high-quality communication when the parameters are well-matched. To sum up, the proposed system can effectively resist eavesdropping, which provides security for the physical layer of optical networks.

Even and odd Laguerre-Gaussian chaoticons in nematic liquid crystal

This paper investigated the propagations of odd and even Laguerre-Gaussian beams in nematic liquid crystal, and found that only the (0, 0) mode of Laguerre-Gaussian beams can form a soliton. As for the other modes of Laguerre-Gaussian beams, many of them will evolve into unbounded states with scattered remnants of energy, while some high order modes can form chaoticons, of which intensity are localized well with little scattering, and propagate over long distance. Additionally, unlike solitons, chaoticons are not sensitive to the power. Even if the incident power deviates from the critical power, some beams can still form chaoticons within a certain deviation range. These results may provide new ways to control the propagation of unstable beams. The evolution and formation of chaoticons have great value to the applications of chaotic synchronization and chaotic secure communication.