DIFFERENTIAL CHAOS SHIFT KEYING: A ROBUST CODING FOR CHAOS COMMUNICATION G´ eza Kolumb´ an*, B´ ela Vizv´ ari**, Wolfgang Schwarz*** and Andreas Abel*** *Department of Measurement and Instrument Engineering Technical University of Budapest H-1521 Budapest, Hungary E-mail: kolumban@mmt.bme.hu on leave with Department of Electrical Engineering, Circuits and Systems Group Swiss Federal Institute of Technology **Department of Operations Research E¨ otv¨ os Lor´ and University of Budapest E-mail: vizvari@cs.elte.hu **Institute for Fundamentals of Electrical Engineering and Electronics Dresden University of Technology E-mail: schwarz@iee1.et.tu-dresden.de Abstract The statistical attributes of the received chaotic signal are evaluated in the noncoherent chaos shift keying (CSK) modulation scheme in order to perform the demodulation. This approach offers a very simple circuit configuration, but like the other solutions proposed before, it is sensitive to the channel noise and imperfections. In the differential chaos shift keying (DCSK) approach every incoming information bit is encoded into two bits. The first signal serves as a reference, while the second one carries the information. If the binary information to be transmitted is ”1” then first the reference signal is transmitted and after it that signal is repeated. For a ”0”, the inverted version of the reference signal is transmitted. The receiver has a storage capability and the demodulation is performed by evaluating the cross-correlation of the two signals. The effect of noise is reduced by averaging and proper design of the channel filter. The effect of channel imperfections is also reduced, because both the signal and its reference are sent via the same channel. The DCSK approach offers a very robust solution for the chaos communication and it can be implemented with very simple circuitry even in the microwave frequency region. 1 Introduction The chaos communication systems will offer a cheap alternative of the conventional spread spectrum telecommunication systems in many applications if robust modulation methods will be available. In the real telecommunication channel, the received signal is corrupted by noise and interferences, moreover it suffers from channel imperfections. The conventional coherent receivers use the correlation technique or matched filter approach for demodulation [1]. The exact copy of the signal set used for the transmission of the different symbols has to be known in the correlation receiver. The elements of the signal set are recovered 1