THE ROLE OF SYNCHRONIZATION IN DIGITAL-COMMUNICATIONS USING CHAOS - PART II - CHAOTIC MODULATION AND CHAOTIC SYNCHRONIZATION

In a digital communications system, data are transmitted from one loca tion to another by mapping bit sequences to symbols, and symbols to sa mple functions of analog waveforms, The analog waveform passes through a bandlimited (possibly time-varying) analog channel, where the signa l 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 coherent receivers have advantages over noncoherent receiv ers in terms of noise performance, bandwidth efficiency (in narrow-ban d systems) and/or data rate (in chaotic systems). These advantages are lost if synchronization cannot be maintained, for example, under poor propagation conditions, In these circumstances, communication without synchronization may be preferable. In Part I, the theory and operatio n of conventional communications systems were surveyed and possible fi elds of application of chaotic communications were identified. In Part II, the theory of conventional telecommunications is extended to chao tic communications, chaotic modulation techniques and receiver configu rations are surveyed, and chaotic synchronization schemes are describe d, In Part III, examples will be given of chaotic communications schem es with and without synchronization, and the performance of these sche mes is evaluated in the contest of noisy, bandlimited channels.