Coexistence of chaos-based and conventional digital communication systems of equal bit rate

Chaos-based communication systems represent a new category of spread-spectrum communication systems, whose working principle differs significantly from conventional direct-sequence and frequency-hopping spread-spectrum systems. However, like all other kinds of spread-spectrum systems, chaos-based systems are required to provide reasonable bit error performance in the presence of a narrow-band signal which can be generated from an intruder or a coexisting conventional communication system. In particular, the frequency band of this foreign narrow-band signal can fall within the bandwidth of the chaos-based system in question. Such a scenario may occur in normal practice when chaos-based systems are introduced while the conventional systems are still in operation. It is therefore important to examine the coexistence of chaos-based and conventional systems. The objective of this paper is to evaluate the performance of the chaos-based system when its bandwidth overlaps with that of a coexisting conventional system. In particular, the chaos-based systems under study are the coherent chaos shift keying (CSK) system and the noncoherent differential CSK (DCSK) system, whereas the conventional system used in the study employs the standard binary phase shift keying scheme. Also, both the chaos-based and conventional systems are assumed to have identical data rates. Analytical expressions for the bit-error rates are derived, permitting evaluation of performance for different noise levels, power ratios and spreading factors. Finally, results from computer simulations verify the analytical findings.