Chaos In Circuits And Systems
With a combination of overview, tutorial and technical articles, this book describes state-of-the-art research on significant problems in the field of chaos in circuits and systems.
TABLE OF CONTENTS Chaos In Circuits And Systems
22.2: Chaotic Modulation and Demodulation
22.2 Chaotic Modulation and Demodulation
Chaotic digital modulation is concerned with mapping symbols to analog chaotic waveforms. In CSK [3], information is carried in the weights of a combination of basis functions which are derived from chaotic signals. Differential chaosshift keying [4] is a variant of CSK where the basis functions have a special structure and the information can be recovered from the correlation between the parts of the basis functions.
In this work, we concentrate on the transmission and reception of a single isolated symbol; problems arising from the reception of symbol streams are not treated here.
22.2.1 Modulation
Assume that one symbol belonging to an alphabet of M symbols is emitted by a message source every T seconds. Using the notation introduced in [5], the elements of the CSK signal set are defined by
where m denotes the symbol to be transmitted, the weights s mj are the elements of the signal vector and the basis functions g j( t) are chaotic waveforms. The signals s m( t) may be produced conceptually as shown in Fig. 22.1.
Figure 22.1: Generation of the elements of the signal set.
Note that the shape of the basis functions is not fixed in chaotic communications. This is why the signal s m( t) which is transmitted through the channel has a different shape during every symbol interval of duration T, even if the same symbol is transmitted repeatedly.
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