85 research outputs found
The role of synchronization in digital communications using chaos - part I: fundamentals of digital communications.
In a digital communications system, data is transmitted from one location to another by mapping bit sequences to symbols, and symbols to sample functions of analog waveforms. The analog waveform passes through a bandlimited (possibly time-varying) analog channel, where the signal is distorted and noise is added. In a conventional system the analog sample functions sent through the channel are weighted sums of one or more sinusoids; in a chaotic communications system, the sample functions are segments of chaotic waveforms. At the receiver, the symbol may be recovered by means of coherent detection, where all possible sample functions are known, or by noncoherent detection, where one or more characteristics of the sample functions are estimated. In a coherent receiver, synchronization is the most commonly used technique for recovering the sample functions from the received waveform. These sample functions are then used as reference signals for a correlator. Synchronization-based receivers have advantages over noncoherent ones in terms of noise performance and bandwidth efficiency. These advantages are lost if synchronization cannot be maintained, for example, under poor propagation conditions. In these circumstances, communication without synchronization may be preferable. The main aim of this paper is to provide a unified approach for the analysis and comparison of conventional and chaotic communications systems. In Part I, the operation of sinusoidal communications techniques is surveyed in order to clarify the role of synchronization and to classify possible demodulation methods for chaotic communication
The role of synchronization in digital communications using chaos - Part II: Chaotic modulation and chaotic synchronization.
For pt. I see ibid., vol. 44, p. 927-36 (1997). In a digital communications system, data are transmitted from one location to another by mapping bit sequences to symbols, and symbols to sample functions of analog waveforms. The analog waveform passes through a bandlimited (possibly time-varying) analog channel, where the signal is distorted and noise is added. In a conventional system the analog sample functions sent through the channel are weighted sums of one or more sinusoids; in a chaotic communications system the sample functions are segments of chaotic waveforms. At the receiver, the symbol may be recovered by means of coherent detection, where all possible sample functions are known, or by noncoherent detection, where one or more characteristics of the sample functions are estimated. In a coherent receiver, synchronization is the most commonly used technique for recovering the sample functions from the received waveform. These sample functions are then used as reference signals for a correlator. Synchronization-based coherent receivers have advantages over noncoherent receivers in terms of noise performance, bandwidth efficiency (in narrow-band systems) and/or data rate (in chaotic systems). These advantages are lost if synchronization cannot be maintained, for example, under poor propagation conditions. In these circumstances, communication without synchronization may be preferable. The theory of conventional telecommunications is extended to chaotic communications, chaotic modulation techniques and receiver configurations are surveyed, and chaotic synchronization schemes are describe
The role of synchronization in digital communications using chaos - part III: performance bounds for correlation receivers
For pt. II, see ibid., vol. 45, p. 1129-40 (1998). In a digital communications system, data is transmitted from one location to another by mapping bit sequences to symbols, and symbols to sample functions of analog waveforms. The analog waveform passes through a bandlimited (possibly time-varying) analog channel, where the signal is distorted and noise is added. In a typical conventional system, the analog sample functions sent through the channel are weighted sums of one or more sinusoids, called basis functions; in a chaotic communications system, the sample functions are segments of chaotic waveforms. This three-part paper shows in a tutorial manner how the theory of conventional telecommunications systems can be applied to chaotic modulation schemes. In addition, it discusses the latest results in the field of chaotic communications. In Part III, examples are given of chaotic communications schemes with and without synchronization, and the performance of correlator-based systems is evaluated in the context of noisy, bandlimited channel
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
A simple circuit realization of the tent map
We present a very simple electronic implementation of the tent map, one of
the best-known discrete dynamical systems. This is achieved by using integrated
circuits and passive elements only. The experimental behavior of the tent map
electronic circuit is compared with its numerical simulation counterpart. We
find that the electronic circuit presents fixed points, periodicity, period
doubling, chaos and intermittency that match with high accuracy the
corresponding theoretical valuesComment: 6 pages, 6 figures, 10 references, published versio
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 Rosensteinâs algorithm. We obtain positive values for the largest
Lyapunov exponent (â0.2) 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 â 25
GHz at both ports. This ultra wideband nature of chaos obtained has potential applications in high speed
random number generation and communication
Discrete-time synchronization of chaotic systems for secure communication
This paper deals with the problem of designing an exact nonlinear reconstructor for discrete-time chaotic encrypted messages. More precisely, we investigate the problem of designing a discrete-time dead-beat observer for nonlinear systems with unknown inputs. The application of the proposed observer in the context of secure communication and data transmission is also investigated
Time Scaling of Chaotic Systems: Application to Secure Communications
The paper deals with time-scaling transformations of dynamical systems. Such
scaling functions operate a change of coordinates on the time axis of the
system trajectories preserving its phase portrait. Exploiting this property, a
chaos encryption technique to transmit a binary signal through an analog
channel is proposed. The scheme is based on a suitable time-scaling function
which plays the role of a private key. The encoded transmitted signal is proved
to resist known decryption attacks offering a secure and reliable
communication.Comment: 15 pages, 7 figure
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