EM-based multiuser detections for optical CDMA networks

We introduce several EM-based multiuser detectors for an optical CDMA system. The detectors have soft and hard stages. In the soft stage, a soft estimation of the interference is obtained by solving an unconstrained maximum-likelihood (ML) problem via an iterative expectation-maximization (EM) algorithm. Then, the hard stage detects the user information bit by solving a one-dimensional Boolean constrained problem conditioned on knowing the interference. Our results reveal that the proposed detectors have very low complexity and are robust against changes in parameters. Moreover. the numerical results illustrate that, despite their simplicity, our detectors substantially outperform other well-known suboptimum detectors, such as multistage and decorrelating detectors.