This article presents a novel four-dimensional autonomous fractional-order chaotic system (FOCS) with multi-nonlinearity terms. Several dynamics, such as the chaotic attractors, equilibrium points, fractal dimension, Lyapunov exponent, and bifurcation diagrams of this new FOCS, are studied analytically and numerically. Adaptive control laws are derived based on Lyapunov theory to achieve chaos synchronization between two identical new FOCSs with an uncertain parameter. For these two identical FOCSs, one represents the master and the other is the slave. The uncertain parameter in the slave side was estimated corresponding to the equivalent master parameter. Next, this FOCS and its synchronization were realized by a feasible electronic circuit and tested using Multisim software. In addition, a microcontroller (Arduino Due) was used to implement the suggested system and the developed synchronization technique to demonstrate its digital applicability in real-world applications. Furthermore, based on the developed synchronization mechanism, a secure communication scheme was constructed. Finally, the security analysis metric tests were investigated through histograms and spectrograms analysis to confirm the security strength of the employed communication system. Numerical simulations demonstrate the validity and possibility of using this new FOCS in high-level security communication systems. Furthermore, the secure communication system is highly resistant to pirate attacks. A good agreement between simulation and experimental results is obtained, showing that the new FOCS can be used in real-world applications.

A new fractional-order chaotic system with its analysis, synchronization, and circuit realization for secure communication applications

In this paper biometric feature systems and multimodal databases for biometric recognition systems are analyzed on the basis of scientific publications in IEEE Xplore digital library. It is shown that wavelet transform coefficients are the most universal feature used in biometric person recognition systems – it is among five frequently used features used in all five popular traits. Moreover, face is the most frequently used trait in multimodal person recognition systems – it is used along with 48 % of iris, 44 % of fingerprint, 33 % of voice and 24 % of signature multimodal systems. Analysis of 15 multimodal databases reveals the fact, that older multimodal databases, e. g., XM2VTS, are still widely used for comparison. However databases such as Biosecure are more versatile and should become more popular soon if a free access will be provided.

Development of Biometric Systems for Person Recognition: Biometric Feature System

The current work presents a study of the implementation of a quadrature chaos phase-shift keying communication system (QCPSK) based on the employment of different chaos oscillators. The research takes two directions, with one being the study of the chaos synchronization’s noise immunity for several chaos oscillators that are the potential core blocks of the QCPSK system. The correlation coefficient over time is used to estimate the synchronization noise immunity. The second direction is the estimation of the QCPSK system’s baseband model performance in the AWGN propagation channel using the bit error ratio (BER) as the estimation method for several chaos oscillators employed as the core of the QCPSK system’s model.

https://www.mdpi.com/2079-9292/10/6/640/pdf

Impact of the Chaotic Synchronization’s Stability on the Performance of QCPSK Communication System

The current work presents the application of the substitution method - based chaos synchronization for a pair of Vilnius chaos oscillators. The core idea of this synchronization technique is to replace the one of the state variables of the response (slave) chaos oscillator with a similar state variable from the drive (master) chaos oscillator, resulting in two chaos oscillators behaving similarly. One of the potential applications of synchronized chaos oscillators is employment for secure communication system, which uses chaotic signals as for data transmission, as for oscillator synchronization. For this reason, the study of the noise immunity of synchronization between the two chaos oscillators is relevant. The research presented in this paper involves both the simulation and the experimental hardware approaches. Both approaches use correlation coefficient estimation as a measure for the synchronization evaluation between two chaos oscillators.

Noise Immunity of Substitution Method – based Chaos Synchronization in Vilnius Oscillator

A vast amount of different electronic oscillators with chaotic behavior have been proposed in the literature, but for this study a Vilnius chaotic oscillator (VCO) has been chosen. The low cost of such a circuit makes it attractive for secure communication between wireless sensor nodes. The chaotic signal is characterized by its high sensitivity to parameter offset. That is why oscillator element nominal value deviation and a supply voltage influences the behavior of the chaotic oscillator and synchronization between distinct circuits is needed to be studied. Theoretical analysis was performed using an LTspice simulation environment and experimental analysis was performed on a breadboard using Analog Discovery 2. MATLAB software was selected to process signals. 0 -1 test was selected to evaluate oscillator dynamics, to rate synchronization correlation coefficient calculation was used. The most sensitive elements were identified, and the regions of stable operation revealed.

Experimental Study of the Impact of Component Nominal Deviations on the Stability of Vilnius Chaotic Oscillator

The paper presents a computationally efficient and accurate numerical approach to evaluating RF–DC power conversion efficiency (PCE) for energy harvesting circuits in the case of multi-tone power-carrying signal with periodic envelopes. This type of signal has recently received considerable attention in the literature. It has been shown that their use may result in a higher PCE than the conventional sine wave signal for low to medium input power levels. This reason motivated the authors to develop a fast and accurate two-frequency harmonic balance method (2F-HB), as fast PCE calculation might appreciably expedite the converter circuit optimization process. In order to demonstrate the computational efficiency of the 2F-HB, a comparative study is performed. The results of this study show that the 2F-HB significantly outperforms such extensively used methods as the transient analysis (TA), the harmonic balance method (HB), and the multidimensional harmonic balance method (MHB). The method also outperforms the commercially available non-linear circuit simulator Keysight ADS employing both HB and MHB. Furthermore, the proposed method can be readily integrated into commonly used commercially available non-linear circuit simulation software, including the Keysight ADS, Ansys HFSS, just to name a few—minor modifications are required. In addition, to increase the correctness and reliability of the proposed method, the influence of PCB is considered by calculating Y parameters of its 3D model. The widely employed voltage doubler-based RF–DC converter for energy harvesting and wireless power transfer (WPT) in sub-GHz diapason is chosen to validate the proposed method experimentally. This RF–DC converter is chosen for its simplicity and capability to provide sufficiently high PCE. The measurements of the PCE for a voltage doubler prototype employing different multi-tone waveform signals were performed in laboratory conditions. Various combinations of the matching circuit element values were considered to find the optimal one in both—theoretical model and experimental prototype. The measured PCE is in very good agreement with the PCE calculated numerically, which attests to the validity of the proposed approach. The proposed PCE estimation method is not limited to one selected RF–DC conversion circuit and can also be applied to other circuits and frequency bands. The comparison of the PCE obtained by means of the proposed approach and the measured one shows very good agreement between them. The PCE estimation error reaches as low as 0.37%, and the maximal estimation error is 32.65%.

/pdf/fast-and-accurate-approach-to-rf-dc-conversion-efficiency-2bqiskzh.pdf

Fast and Accurate Approach to RF-DC Conversion Efficiency Estimation for Multi-Tone Signals

A vast amount of different electronic oscillators with chaotic behavior have been proposed in literature, but for this study a simple two transistor oscillator has been chosen. The low cost of such a circuit makes it attractive for secure communication between wireless sensor nodes. However, for practical use it is necessary to know, how the deviation of nominals of circuit elements and a supply voltage influences the behavior of the chaotic oscillator and synchronization between distinct circuits. Theoretical analysis was performed using simulations of chaotic oscillators in LTspice program, and MATLAB software has been selected to analyze the obtained data. To evaluate the chaotic behavior of the system, the MATLAB 0–1 test function was employed, and the autocorrelation function was used to evaluate the synchronization of the system. The most sensitive elements were identified, and the regions of stable operation revealed.

Ruslans Babajans

Papers

Impact of the Chaotic Synchronization’s Stability on the Performance of QCPSK Communication System

Noise Immunity of Substitution Method – based Chaos Synchronization in Vilnius Oscillator

Experimental Study of the Impact of Component Nominal Deviations on the Stability of Vilnius Chaotic Oscillator

Fast and Accurate Approach to RF-DC Conversion Efficiency Estimation for Multi-Tone Signals

Influence of Element Nominal Values on Chaos Oscillator Dynamics and Synchronization