In this work the authors thoroughly investigated a digital information transmission system using discrete chaotic signal over cable. As an example in their work the authors consider the non-autonomous 2nd order non-linear oscillator system presented in Tamaševicious, Cenys, Mycolaitis, and Namajunas (1998) which is particularly suitable for digital communications and present the experimental results regarding synchronization. The effect of noise (internal or external) on the synchronization of the drive-response system (unidirectional coupling between two identical systems) is analyzed and since in every practical implementation of a communication system, the transmitter and receiver circuits (although identical) operate under slightly different conditions the case of the mismatch between the parameters of the transmitter and the receiver is considered. Moreover, there is a study of the robustness of the system with reference to the desired security, proposing a more sophisticated approach, which combines the simplicity in the implementation of a chaotic system with an enhanced encoding scheme that will overall increase security.
Top1. Introduction
The significance of private and secure communications is very clear in a world, which increasingly relies on rapid transmission of large amounts of information. The current solutions for secure communications are the public key cryptosystems using software techniques to achieve computational complexity while quantum cryptography has the potential to render such techniques obsolete. However, hardware complexity is another method of increasing security in communications by hiding or masking the message on a chaotic carrier (Pecora, et. al. 1990; Ott, et. al. 1990; Carroll, et. al. 1993; Chua et. al. 1996; Wu et. al. 1996; Kolumban, et. al. 1998; Tamaševičious, et. al. 1998; Mycolaitis, et. al. 1999; Pikovsky, et. al. 2003; Yang, 2004).
The introduction of non-linear chaos theories has offered several new applications and performance enhancements to existing communication systems. A chaotic generator can produce non-linear and non-repeating sequences and it is very hard to predict chaotic patterns and sequences even when the chaotic function is known to the interceptors. This is because different estimation of the initial condition will lead to a very different chaotic sequence.
Chaotic communication systems are simpler, by means of circuit engineering implementation, as compared to traditional spread spectrum systems. Two key features of chaos are a noise-like time series and sensitive dependence on initial conditions and control parameters, which cause chaotic transmissions to have low probability of detection as an information-bearing signal and low probability of interception, respectively (Chambers, & Frey, 1993; Ogorzalek, 1993; Frey, 1993; Dedieu, et. al. 1993; Short, 1994; Wu, & Chua, 1994; Murali, & Lakshmanan, 1994; Chua, et. al. 1996; Yang, & Chua, 1996; Yang, Wu & Chua, 1997; Yang, & Chua, 1997; Yang, & Chua, 1997; Yang, et. al. 1997; Yang, & Yang, 1997; Yang, Sharuz, 1997; He, & Vaidya, 1998; Chien, & Liao, 2005).