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.

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.

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.