Coexistence of Chaos-Based and Conventional Narrowband Digital Communication Systems

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 narrowband signal which can be generated from an intruder or a coexisting conventional communication system. In particular, the frequency band of this foreign narrowband 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 chapter 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 non-coherent differential CSK (DCSK) system, whereas the conventional system used in the study employs the standard binary phase-shift-keying (BPSK) scheme [Proakis and Salehi (1994), Ziemer and Tranter (1995)].