Secure OFDM transmission scheme based on chaotic encryption and noise-masking key distribution

In this Letter, we propose a secure orthogonal frequency division multiplexing (OFDM) transmission scheme based on chaotic encryption and noise-masking key distribution. With the implementation of a three-dimensional digital chaotic system, the security performance is effectively enhanced by scrambling the phase, symbol, and subcarrier frequency of the OFDM signal. The proposed noise-masking key distribution can mask the key information of the chaotic system into noise and transmit it with the chaotic encrypted signal simultaneously. By this mechanism, the legal receiver can realize uninterrupted authentication and decryption even if the key is constantly updated. Transmission of a 62.2-Gb/s quadrature phase shift keying (QPSK) and 124.4-Gb/s 16 quadrature amplitude modulation (16QAM) OFDM signal over a 2-km 7-core fiber using the proposed scheme is experimentally demonstrated. The results show that the proposed scheme can realize security enhancement and cost-effective key distribution without significant bit error ratio (BER) performance degradation.

Experimental synchronization of chaos in a large ring of mutually coupled single-transistor oscillators: phase, amplitude, and clustering effects

In this paper, experimental evidence of multiple synchronization phenomena in a large (n = 30) ring of chaotic oscillators is presented. Each node consists of an elementary circuit, generating spikes of irregular amplitude and comprising one bipolar junction transistor, one capacitor, two inductors, and one biasing resistor. The nodes are mutually coupled to their neighbours via additional variable resistors. As coupling resistance is decreased, phase synchronization followed by complete synchronization is observed, and onset of synchronization is associated with partial synchronization, i.e., emergence of communities (clusters). While component tolerances affect community structure, the general synchronization properties are maintained across three prototypes and in numerical simulations. The clusters are destroyed by adding long distance connections with distant notes, but are otherwise relatively stable with respect to structural connectivity changes. The study provides evidence that several fundamental synchronization phenomena can be reliably observed in a network of elementary single-transistor oscillators, demonstrating their generative potential and opening way to potential applications of this undemanding setup in experimental modelling of the relationship between network structure, synchronization, and dynamical properties.

Experimental dynamical characterization of five autonomous chaotic oscillators with tunable series resistance

In this paper, an experimental characterization of the dynamical properties of five autonomous chaotic oscillators, based on bipolar-junction transistors and obtained de-novo through a genetic algorithm in a previous study, is presented. In these circuits, a variable resistor connected in series to the DC voltage source acts as control parameter, for a range of which the largest Lyapunov exponent, correlation dimension, approximate entropy, and amplitude variance asymmetry are calculated, alongside bifurcation diagrams and spectrograms. Numerical simulations are compared to experimental measurements. The oscillators can generate a considerable variety of regular and chaotic sine-like and spike-like signals.

INFLUENCE OF SYSTEM NON-UNIFORMITY ON DYNAMIC PHENOMENA IN ARRAYS OF COUPLED NONLINEAR NETWORKS

In this paper we investigate the influence of system non-uniformity on the existence and stability of synchronous motion in an array of bi–directionally coupled electronic circuits. In computer simulations we find the level of non-uniformity for which synchronous behavior is sustained. We also present several examples of attractors, which appear when the synchronous motions is no longer stable.

Synchronization, re-entry, and failure of spiral waves in a two-layer discrete excitable system

A three-dimensional structure composed of two coupled discrete excitable lattices is considered. Each lattice (layer) is a discrete excitable subsystem and using a local model of excitation transfer and failure we have estimated the sufficient conditions for it to exhibit spiral waves. Then we show how interlayer synchronization of all motions is possible. Various effects of spiral wave synchronization, re-entry and failure are also investigated.