PERFORMANCE ANALYSIS OF SINGLE-USER AND MULTIUSER DETECTORS FOR OPTICAL CODE-DIVISION MULTIPLE-ACCESS COMMUNICATION-SYSTEMS

Code division multiple access (CDMA) is a powerful multiplexing scheme, particularly suited to the optical domain with its broad spectrum, Unfortunately, analysis of optical CDMA (OCDMA) systems has been almost exclusively restricted to systems employing a correlation detector, which suffer high degradation when received user powers are dissimilar. This study examines the performance of an optimum single-user detector and two multiuser detectors for OCDMA in the presence of additive light intensity noise and Poisson detection. The optimized single-user detector is the maximum likelihood detector given the interference from other users is a random process with known distribution, One multiuser detector is based on a local search algorithm for maximizing the likelihood function. The second multiuser detector is a generalization of the optical multistage detector to accept soft-decision from the previous stage, Approximations to the error probabilities of the OCDMA system based on either random signature sequences or deterministic codes are derived for each detector using a large deviations theory approach, The asymptotic multiuser efficiency is found to be related to the large deviations rate function, The analysis shows that the correlation detector performance decreases rapidly as the number of users increases, while the optimized single-user detector and the two multiuser detectors proposed perform considerably better and show less sensitivity to unequal received user powers.