Gabor Kis

Chaotic communications with correlator receivers: theory and performance limits

This paper provides a review of the principles of chaotic digital communications using correlator receivers. Modulation schemes using one and two chaotic basis functions, as well as coherent and noncoherent correlation receivers, are discussed. The performance of differential chaos shift keying (DCSK) in multipath channels is characterized. Results are presented for DCSK with multiuser capability and multiple bits per symbol.

Performance evaluation of FM-DCSK modulation in multipath environments

G. Kolumban [2000] has shown that, under specified conditions, the noise performance of frequency-modulated differential chaos shift keying (FM-DCSK) in a single-ray additive white Gaussian noise channel is independent of the shape of the underlying waveform. This paper discusses the qualitative features of the FM-DCSK system and characterizes the performance of this system in standard reference multipath channels.

FM-DCSK: a novel method for chaotic communications

In binary Differential Chaos Shift Keying (DCSK), each information bit is mapped to the correlation between two pieces of a chaotic waveform. The receiver determines the correlation (which is proportional to the energy per bit) in order to demodulate the received signal. Since a chaotic signal is not periodic, the energy per bit is not constant and can only be estimated, even in the noise-free case. This estimation has a non-zero variance that limits the attainable data rate. This problem can be avoided if the energy per bit is kept constant. In this paper, the DCSK technique is combined with frequency modulation in order to achieve two properties: the excellent noise performance of DCSK is maintained; in addition, the energy per bit is kept constant in order not to limit the data rate. A low-pass equivalent model that significantly speeds up the simulation of an FM-DCSK system is also developed. Finally the noise performance of the proposed FM-DCSK system is given.

Recent advances in communicating with chaos

The past few years have witnessed rapid growth in the field of mobile and indoor radio applications. Chaotic communications schemes are potentially suitable for these applications, offering simpler and cheaper solutions that currently available Spread Spectrum (SS) techniques. This paper presents an overview of the most promising chaotic communications schemes which have been developed recently and proposes some multilevel extensions of these methods to increase the data rate.

Optimum noncoherent FM-DCSK detector: application of chaotic GML decision rule

A new detector configuration is proposed for the detection of FM-DCSK signals with improved noise performance. Since the new detector configuration is developed directly from the chaotic GML decision rule, it offers the best noise performance in AWGN channel in the category of noncoherent detection if the reception of a single isolated symbol and memoryless modulation scheme is considered. The paper shows how the a priori information on chaotic signals may be exploited in waveform communication to maximize the noise performance.

Chaotic modulation for robust digital communications over multipath channels

This tutorial work identifies the characteristic properties of chaotic digital modulation schemes and shows how the unique features of chaotic basis functions can be exploited to competitive advantage in selected application domains. Two robust noncoherent chaotic digital modulation schemes (DCSK and FM-DCSK) are described in detail and the performance of FM-DCSK is examined critically for communication channels where systems using conventional coherent and narrow-band modulation schemes fail. Since the FM-DCSK signal is a wide-band signal and its demodulation is performed without synchronization, the FM-DCSK modulation scheme is especially suitable for operation in multipath channel such as Wireless Local Area Networks (WLANs).

Application of noise reduction to chaotic communications: a case study

Over the past few years, several methods have been proposed for decontaminating noisy chaotic signals by exploiting the short-term predictability of chaotic signals. This work evaluates the effectiveness, for a differential chaos shift keying (DCSK) telecommunications system, of a noise reduction approach using a deterministic optimization technique. Noise reduction is governed by a cost function which consists of two terms: the first gives the distance between the noisy and enhanced orbits, while the second one checks the dynamics of the cleaned signal. These two terms are weighted by a scalar /spl Gamma/. The effect of this factor on the noise reduction performance is also studied. Evaluation of the noise performance of a telecommunication system by computer simulation requires a very long simulation time. We propose a computationally-efficient criterion for quantifying the performance improvement of a DCSK system. We show that the noise reduction technique improves the overall noise performance only if the energy per bit-to-noise spectral density (E/sub b//N/sub 0/) exceeds a certain threshold. The effect of code length on this threshold level is also evaluated. Finally, the effect of parameter mismatch, which is present in every practical system, is analyzed.

Multipath performance of FM-DCSK chaotic communications system

In Frequency-Modulated Differential Chaos Shift Keying (FM DCSK) modulation scheme, the digital information to be transmitted is mapped to an inherently wide-band chaotic signal rather than to a sinusoidal carrier. In this sense, the FM-DCSK system offers a new solution to spread spectrum communications. The FM-DCSK can be used in every application where multipath propagation rather than thermal noise limits the overall system performance. Because there is no need for synchronization at the FM-DCSK demodulator, this modulation scheme is very robust against channel disturbances and distortion. This paper evaluates the multipath performance of the FM-DCSK system in WLAN application by computer simulation.

Simulation of the multipath performance of FM-DCSK digital communications using chaos

In binary FM-differential chaos shift keying (FM-DCSK), each information bit is mapped to the correlation between two pieces of a constant-amplitude frequency-modulated waveform. The receiver determines the correlation (which is proportional to the energy per bit) in order to demodulate the received signal. Since the application of FM ensures constant energy per bit, the noise performance and data rate of FM-DCSK are superior to any other chaotic modulation technique in the literature. Because of their broadband nature, chaotic modulation schemes have potentially better performance in multipath environments than modulation schemes based on sinusoids. This work compares the simulated performance of BPSK and FM-DCSK in typical multipath configurations. The previously conjectured advantage of a broadband chaotic signal in the presence of deep selective fading is verified.

On the effectiveness of noise reduction methods in DCSK systems

Many different methods to decontaminate noisy chaotic signals have been proposed over the past few years. A possible application of these techniques is chaotic communications, where an unwanted additive channel noise has to be removed from the received chaotic signal. Until now, the noise performance of differential chaos shift keying (DCSK) could not be improved significantly using these noise reduction algorithms. Recent investigations suggest that noise reduction techniques can be used only if the signal-to-noise ratio (SNR) of the received signal exceeds a certain threshold. The objective of this work is to introduce an adequate performance measure based on correlation. Using this performance measure the reason for the threshold effect is explained.