Design and Analysis of Asynchronous Incoherent Optical-CDMA Systems Using a New Code-Shifting Technique

Abstract

In this paper, a novel code-shifting technique, which can be added atop asynchronous incoherent optical code-division multiple-access systems without complex modifications, is proposed and studied. The new technique divides the time-slot (or chips), in which the optical pulses of codewords are located, into $g$ equal-width sub-chips; every pulse is randomly and independently shifted to start at one of the $g$ sub-chips of its own chip, where $g > 1$ is a positive integer. The effects of this random $g$ -shift to the cross-correlation property and performance of asynchronous optical codes (of periodic cross-correlation functions of at most one) are formulated. Although it is found that the periodic cross-correlation functions are worsened to $3-2/g$ , our theoretical and computer-simulation results show an unconventional finding that code performance improves as $g$ increases.