Improving Security of Communication Systems Using CHAOS

The principal design objective of this paper is to facilitate extremely secure digital communication using chaotic shift keying in existing frequency-hop spread spectrum systems. Generally in chaotic shift keying, the incoming digital bit stream is mapped onto one of the available chaotic signals. Our scheme proposes the use of antipodal chaotic signals, which means they are signals which are out of phase with each other by 180°. Data bits 0 and 1 can be mapped onto either of the antipodal signals using required convention. Also, in FH-spread spectrum (FH-SS) techniques, there exists a p-n code generator based on the output of which the frequency synthesizer selects a particular carrier frequency. Usual FH-SS systems use MFSK modulation in the stage following the frequency hopper. As our case involves the use of chaotic reference signals and their basic shapes need to be preserved throughout, we propose the use of binary frequency shift keying. The digital data, which is now in the form of chaotic signals, is turned into a BFSK signal. This resultant signal is mixed with a carrier frequency at the frequency synthesizer. This carrier is chosen by the frequency hopper, whose output, in turn depends on the output of a p-n sequence. We assume the transmission channel to contribute additive white noise. At the receiver, we propose to perform FSK demodulation as a first stage recovery to get back the chaotic signal. Now this recovered signal is either an exact copy of the chaotic reference signal or its inverse. To decide which of the two was sent by the transmitter, we can use a correlator receiver, which uses a locally generated chaotic reference signal. Keywords: Chaotic shift keying, orthogonal chaotic