THE ROLE OF SYNCHRONIZATION IN DIGITAL-COMMUNICATIONS USING CHAOS .1.FUNDAMENTALS OF DIGITAL-COMMUNICATIONS

In a digital communications system, data is transmitted from one locat ion to another by mapping bit sequences to symbols, and symbols to sam ple functions of analog waveforms, The analog waveform passes through a bandlimited (possibly time-varying) analog channel, where the signal is distorted and noise is added, In a conventional system the analog sample functions sent through the channel are weighted sums of one or more sinusoids; in a chaotic communications system, the sample functio ns are segments of chaotic waveforms, At the receiver, the symbol may be recovered by means of coherent detection, where all possible sample functions are known, or by noncoherent detection, where one or more c haracteristics of the sample functions are estimated, In a coherent re ceiver, synchronization is the most commonly used technique for recove ring the sample functions from the received waveform, These sample fun ctions are then used as reference signals for a correlator. Synchroniz ation-based receivers have advantages over noncoherent ones in terms o f noise performance and bandwidth efficiency, These advantages are los t if synchronization cannot be maintained, for example, under poor pro pagation conditions, In these circumstances, communication without syn chronization may be preferable, The main aim of this paper is to provi de a unified approach for the analysis and comparison of conventional and chaotic communications systems, In Part I, the operation of sinuso idal communications techniques is surveyed in order to clarify the rol e of synchronization and to classify possible demodulation methods for chaotic communications, In Part II, chaotic synchronization schemes a re described in detail and proposed chaotic communications techniques are summarized, In Part III, examples of chaotic communications scheme s with and without synchronization are given, and the performance of t hese schemes is evaluated in the context of noisy, bandlimited channel s.