Experiments on Rf Band Communications Using Chaos

A number of approaches to the design of communications systems with chaos have recently been proposed [Kocarev et al., 1992; Belsky & Dmitriev, 1993; Cuomo et al., 1993; Dedieu et al., 1993; Halle et al., 1993; Volkovskii & Rul’kov, 1993]. Low-frequency physical experiments demonstrating a principle possibility of such system realization have also been made [Kocarev et al., 1992; Bohme et al., 1994; Dmitriev et al., 1994, 1995; DelgadoRestituto et al., 1995]. The main element of the mentioned systems is a chaotic module devoted to form the chaotic signal and to introduce information into the transmitter signal, and at the same time, to retrieve the information in the receiver. One of the most important operation requirements to the majority of the known systems is the equality of the chaotic module parameters in the transmitter and receiver [Belsky & Dmitriev, 1995]. This is associated with the necessity to obtain in the receiver an exact copy of the signal formed in the transmitter (synchronous response) [Pecora & Carroll, 1990]. A question then arises: Can the synchronous response, hence, information retrieval, be achieved in real conditions, i.e. by using developed chaotic modules in RF-band communications systems? The problem is that in such systems the signal undergoes a number of additional manipulations (modulation, heterodyning, detection, amplification, etc.) which can lead to distortions, regarding the complex structure of the formed signal and essentially nonlinear characteristics of system functional elements. This paper describes the experiments on speech signal transmission in RF band on example of a chaotic module with nonlinear information mixing [Dmitriev et al., 1994, 1995]. The structure of the paper is as follows. First we describe the structure of a communications system employing dynamic chaos. Then we derive a mathematical model of the communications system and analyze computer modeling results. The last section is devoted to experiments on communications in the RF band.