Hasler M.

Synchronization of chaotic systems and transmission of information
M. Hasler
Department of Electrical Engineering, Swiss Federal Institute of Technology,
1015 Lausanne, Switzerland

The different methods to synchronize chaotic systems in a master-slave configuration are presented. They include:

• Synchronization of an autonomous system by imposing a state partially (special case: Pecora-Carroll synchronization)
• Synchronization of an autonomous system by linear feedback
• Synchronization of the invese of a driven system

The synchronization is then used to transmit information via a chaotic signal. The purpose of this approach is to broaden the spectrum of the information signal and to hide the information contained in it. The approach has some resemblance with conventional spread spectrum techniques, but the advantage is that some basic encryption and spectrum spreading are achieved simultaneously with simple circuitry. We will introduce briefly the following methods to modulate and demodulate a chaotic signal:

• Chaotic masking
• Chaotic switching
• Direct modulation and demodulation by the inverse system
• Modulation by predictive control

Engineering aspects of these methods will be discussed. They include the influence of parameter mismatch between the transmitter and the receiver and the influence of channel imperfections, such as additive noise and finite bandwidth. A method will also be presented that allows for several transmitter-receiver pairs to share the same channel, as is the case for CDMA (Code Division Multiple Access) systems in the conventional spread spectrum approach.

1. M. Hasler, Phil. Trans. R. Soc. Lond. A, 353 (1995) 115.
2. U. Feldmann, M. Hasler, W. Schwarz, "Communication by chaotic signals, the inverse system approach", accepted for publication in International Journal on Circuit Theory and Design.
3. J. Schweizer, M.P. Kennedy, Physical Review E, 52 (1995) 4865.
4. J. Schweizer, M. Hasler, "Multiple access communications using chaotic signals", to appear in Proc. ISCAS'96, Atlanta.