Effects of hard-limiter and error correction coding on performance of direct-detection optical CDMA systems with PPM signaling

We analyze the effects of an optical hard-limiter and error correction coding on the performance of direct-detection optical synchronous CDMA systems with pulse position modulation (PPM) signaling; Reed-Solomon (RS) codes and convolutional codes (CC's) with soft-decision Viterbi decoding are employed. We analyze the upper bound on the performance under the assumption of Poisson shot noise model for the receiver photodetector and the noise due to the detector dark currents is considered. We analyze the performance under average power and bit rate constraints. Our results show that the upper bound on the performance of the system with the optical hard-limiter becomes tighter as M is increased. Moreover, RS codes are shown to be more effective to reduce an asymptotic floor to the error probability of the system with large M, while CC's with soft-decision Viterbi decoding is more effective for the system with small M.