Multi-user receivers for synchronous and asynchronous transmissions for chaos-based multiple-access systems

This paper addresses the problem of multi-user detection for a multiple-access system based on chaotic communications. In particular, one considers the differential chaos shift keying (DCSK) modulation. Two kinds of transmissions are considered: synchronous transmissions, where the bit epochs are aligned at the receiver, and asynchronous transmissions. Different detectors are studied for both kinds of transmissions: (i) an optimal receiver, which minimizes a least-squares criterion; this detector requires the knowledge of many user characteristics; (ii) an adaptive LMS detector, which converges to the previous detector without any a priori knowledge concerning the chaotic sequences; this detector is then better suited for practical applications; (iii) detectors based on the estimation of the chaotic sequences. Theoretical performance results are derived for all these detectors. Simulation results are reported, which confirm the theoretical analysis and allows one to compare the proposed detectors. These results show that the chaotic-sequence estimation (CSE)-based detectors are only fitted for synchronous transmissions, but give poor results for asynchronous transmissions. At the contrary, LMS-based receivers, which could also be used for standard direct-sequence spread-spectrum systems, present the best practical performance. In particular, the performances obtained for asynchronous transmissions remain close to those obtained for synchronous transmissions.