Experimental demonstration of 25 GHz wideband chaos in symmetric dual port EDFRL

We study dynamics of chaos in dual port erbium-doped fiber ring laser (EDFRL). The laser consists of two erbium-doped fibers, intracavity filters at 1549.30 nm, isolators, and couplers. At both ports, the laser transitions into the chaotic regime for pump currents greater than 100 mA via period doubling route. We calculate the Lyapunov exponents using Rosenstein’s algorithm. We obtain positive values for the largest Lyapunov exponent (≈0.2) for embedding dimensions 5, 7, 9 and 11 indicating chaos. We compute the power spectrum of the photocurrents at the output ports of the laser. We observe a bandwidth of ≈ 25 GHz at both ports. This ultra wideband nature of chaos obtained has potential applications in high speed random number generation and communication

Adaptive sliding mode observers in uncertain chaotic cryptosystems with a relaxed matching condition

We study the performance of adaptive sliding mode observers in chaotic synchronization and communication in the presence of uncertainties. The proposed robust adaptive observer-based synchronization is used for cryptography based on chaotic masking modulation (CM). Uncertainties are intentionally injected into the chaotic dynamical system to achieve higher security and we use robust sliding mode observer design methods for the uncertain nonlinear dynamics. In addition, a relaxed matching condition is introduced to realize the robust observer design. Finally, a Lorenz system is employed as an illustrative example to demonstrate the effectiveness and feasibility of the proposed cryptosyste

Spreading of wave packets in disordered systems with tunable nonlinearity

We study the spreading of single-site excitations in one-dimensional disordered Klein-Gordon chains with tunable nonlinearity $|u_{l}|^{\sigma} u_{l}$ for different values of $\sigma$. We perform extensive numerical simulations where wave packets are evolved a) without and, b) with dephasing in normal mode space. Subdiffusive spreading is observed with the second moment of wave packets growing as $t^{\alpha}$. The dependence of the numerically computed exponent $\alpha$ on $\sigma$ is in very good agreement with our theoretical predictions both for the evolution of the wave packet with and without dephasing (for $\sigma \geq 2$ in the latter case). We discuss evidence of the existence of a regime of strong chaos, and observe destruction of Anderson localization in the packet tails for small values of $\sigma$.Comment: 9 pages, 7 figure

Physics and Applications of Laser Diode Chaos

An overview of chaos in laser diodes is provided which surveys experimental achievements in the area and explains the theory behind the phenomenon. The fundamental physics underpinning this behaviour and also the opportunities for harnessing laser diode chaos for potential applications are discussed. The availability and ease of operation of laser diodes, in a wide range of configurations, make them a convenient test-bed for exploring basic aspects of nonlinear and chaotic dynamics. It also makes them attractive for practical tasks, such as chaos-based secure communications and random number generation. Avenues for future research and development of chaotic laser diodes are also identified.Comment: Published in Nature Photonic

Contributions à l’amélioration des systèmes de communication multi-utilisateurs par\ud chaos : synchronisation et analyse des performances

Les radiocommunications constituent actuellement un domaine en plein essor. Depuis quelques années, de nombreux chercheurs étudient la possibilité d'utiliser des signaux chaotiques pour transmettre des données, en particulier dans un contexte multi-utilisateurs. Parmi les différentes techniques d'accès multiple, le CDMA (Code Division Multiple Access) permet à différents utilisateurs de transmettre simultanément sur la même bande de fréquence. Les séquences utilisées actuellement pour l'étalement du spectre sont des séquences dites pseudo-aléatoires binaires à faible intercorrélation générées sur la base d'un registre à décalage (les séquences de Gold) ou bien des séquences binaires orthogonales (les séquences de Walsh).\ud \ud \ud \ud Cette thèse porte sur l’étude d’un système de communication multi-utilisateurs par étalement de spectre utilisant des générateurs de chaos. Les signaux chaotiques peuvent être générés par des systèmes itératifs discrets modélisés par des transformations ponctuelles. \ud \ud \ud Dans un premier temps, nous avons étudié les signaux chaotiques issus de différents systèmes dynamiques, /a priori/ définis par des fonctions classiques continues ou continues par morceaux. En se basant sur les propriétés de corrélation et sur les distributions des énergies des signaux chaotiques, une étude comparative entre les différentes séquences chaotiques a été faite dans le cadre d’une transmission DS-CDMA par séquence chaotique. Le but de cette comparaison est de fournir des éléments permettant de choisir la séquence la mieux adaptée à l’étalement du spectre. Une méthode simple rapide et précise pour prédire le taux d’erreurs binaires pour des systèmes DS-CDMA basé sur le chaos a été proposée en mode mono et multi-utilisateur. Une étude plus poussée sur la distribution de l’énergie a permis d’établir une expression analytique du taux d’erreurs binaires. Ces calculs de performances ont été étendus à un canal de transmission à multi-trajets en mode multi-utilisateurs.\ud \ud Nous avons exploré ensuite le processus de synchronisation des systèmes dynamiques chaotiques. Tout d’abord, nous avons porté notre attention sur l’étude des différentes méthodes d’intégration numérique afin de déterminer une méthode adaptée permettant de réaliser la synchronisation chaotique par couplage avec une faible charge de calcul.\ud \ud Enfin, toujours dans l’idée d’établir la synchronisation du chaos pour les systèmes de transmission de type DS-CDMA. Nous avons proposé des récepteurs intégrant des unités de synchronisation similaires aux unités de synchronisations (/acquisition et poursuite/) utilisées dans les systèmes classiques à étalement du spectre. Ces unités de synchronisations utilisent simultanément une séquence binaire pseudo-aléatoire classique et une séquence chaotique pour établir et maintenir la synchronisation. Ces techniques ont été comparées à une méthode similaire de la littérature, ce qui a permis de montrer l’amélioration de la performance des systèmes proposés, et notamment le fait qu’ils soient opérationnels en mode asynchrone.-------------------------------------------------------------------------------Radiocommunications field is currently in full development. In recent years, many researchers have explored the possibility of using chaotic signals to transmit data, especially in a multi-user case. Among the various multiple access techniques, the CDMA (Code Division Multiple Access) allows different users to transmit simultaneously on the same frequency band. The sequences currently used for classical spread spectrum are the sequences known as pseudo-random binary sequences with low cross-correlation generated on the basis of a shift linear register (Gold sequences) or binary orthogonal sequences (Walsh codes).\ud \ud This thesis has focused on the study of a communication system with multi-user spread spectrum using chaotic generators as spreading sequences. The chaotic signals can be generated by iterative discrete systems modelled by discrete transformations.\ud \ud \ud In a first step, we have studied various chaotic signals from different dynamical systems, / a priori / defined by traditional functions continuous or piece wise linear functions. Relying on the correlation properties and the energy distribution of chaotic signals, a comparative study between different chaotic sequences was made in the framework of chaos-based DS-CDMA systems. The purpose of this comparison is to provide necessary elements to choose the best sequence for a spread spectrum system under an Additive White Gaussian Noise (AWGN) channel. A simple method to rapidly and accurately predict the bit error rate for chaos-based DS-CDMA was proposed in single and multi-user cases. Further study on the energy distribution has resulted in an analytical expression of the bit error rate. These performances have been also been studied and extended to the multi-user case.\ud \ud In a second part, we have explored the synchronization process of chaotic dynamical systems. After reviewing the existing approaches in the literature, we have focused our attention on the study of different methods of digital integration in order to determine an appropriate method to achieve synchronization using coupling with a low a low computing charge.\ud \ud \ud Finally, we have studied the synchronization process for chaos-based DS-CDMA system. We have proposed receivers incorporating synchronization units similar to the synchronization units (/ acquisition and tracking /) used in conventional spread spectrum systems. These synchronization units are using simultaneously a classical binary pseudo-random sequence together with a chaotic sequence in order to achieve and maintain synchronization. These techniques were compared to a similar existing method recently proposed in literature. We have demonstrate the improvement in performance brought by our proposed system, including the fact that this system is also operational in the asynchronous case.\ud \u

Variations of Boundary Surface in Chua’s Circuit

The paper compares the boundary surfaces with help of cross-sections in three projection planes, for the four changes of Chua’s circuit parameters. It is known that due to changing the parameters, the Chua’s circuit can be characterized in addition to a stable limit cycle also by one double scroll chaotic attractor, two single scroll chaotic attractors or other two stable limit cycles. Chua’s circuit can even start working as a binary memory. It is not known yet, how changes in parameters and conseqently in attractors in the circuit will affect the morphology of the boundary surface. The boundary surface separates the double scroll chaotic attractor from the stable limit cycle. In a variation of the parameters presented in this paper the boundary surface will separate even single scroll chaotic attractors from each other. Dividing the state space into regions of attractivity for different attractors, however, remains fundamentally the same

Design of nonlinear observer for chaotic message transmission

Thesis (Master)--Izmir Institute of Technology, Electronics and Communication Engineering, Izmir, 2013Includes bibliographical references (leaves: 60-64)Text in English; Abstract: Turkish and Englishx, 64 leavesChaos is an interesting nonlinear phenomena that occurs in wide variety of fields. A significant amount of research was devoted to understanding chaos and its properties. After that, researchers focused on searching for possible application areas for chaos to utilize its properties. The need to increase the security of a communication system is considered as a perfect match for chaos and its several properties, yielding chaotic communication. In this thesis, chaotic communication is approached from a control theory perspective. Specifically, three nonlinear observers are designed to extract message encrypted in a chaotic communication signal. The design and stability analysis is presented for the first observer, and the other observers are presented as modifications to the first one. Extensive numerical simulations are performed to demonstrate the viability of the proposed observers. Robustness of the observers to noise, additive disturbances, and parametric mismatch, and security of the observers are demonstrated numerically

New Media and the Arab Spring of 2011

About media and the Arab sprin

Bit error performance of diffuse indoor optical wireless channel pulse position modulation system employing artificial neural networks for channel equalisation

The bit-error rate (BER) performance of a pulse position modulation (PPM) scheme for non-line-of-sight indoor optical links employing channel equalisation based on the artificial neural network (ANN) is reported. Channel equalisation is achieved by training a multilayer perceptrons ANN. A comparative study of the unequalised `soft' decision decoding and the `hard' decision decoding along with the neural equalised `soft' decision decoding is presented for different bit resolutions for optical channels with different delay spread. We show that the unequalised `hard' decision decoding performs the worst for all values of normalised delayed spread, becoming impractical beyond a normalised delayed spread of 0.6. However, `soft' decision decoding with/without equalisation displays relatively improved performance for all values of the delay spread. The study shows that for a highly diffuse channel, the signal-to-noise ratio requirement to achieve a BER of 10−5 for the ANN-based equaliser is ~10 dB lower compared with the unequalised `soft' decoding for 16-PPM at a data rate of 155 Mbps. Our results indicate that for all range of delay spread, neural network equalisation is an effective tool of mitigating the inter-symbol interference