In a digital communications system, data are transmitted from one location to another by mapping bitsequences to symbols, and symbols to sample functions of analog waveforms. The analog waveformpasses through a bandlimited (possibly time-varying) analog channel, where the signal is distorted andnoise is added. In a conventional system the analog sample functions sent through the channel areweighted sums of one or more sinusoids; in a chaotic communications system the sample functionsare segments of chaotic waveforms. At the receiver, the symbol may be recovered by means ofcoherent detection, where all possible sample functions are known, or by noncoherent detection,where one or more characteristics of the sample functions are estimated. In a coherent receiver,synchronization is the most commonly used technique for recovering the sample functions from thereceived waveform. These sample functions are then used as reference signals for a correlator.Synchronization-based coherent receivers have advantages over noncoherent receivers in terms ofnoise performance, bandwidth efficiency (in narrow-band systems) and/or data rate (in chaoticsystems). These advantages are lost if synchronization cannot be maintained, for example, underpoor propagation conditions. In these circumstances, communication without synchronization maybe preferable. In Part I, the theory and operation of conventional communications systems weresurveyed and possible fields of application of chaotic communications were identified. In Part II, thetheory of conventional telecommunications is extended to chaotic communications, chaoticmodulation techniques and receiver configurations are surveyed, and chaotic synchronizationschemes are described. In Part III, examples will be given of chaotic communications schemes withand without synchronization, and the performance of these schemes is evaluated in the context ofnoisy, bandlimited channels.
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