Direct-detection optical synchronous CDMA systems with double optical hard-limiters using modified prime sequence codes

An optical code-division multiple-access (CDMA) system with double optical hard-limiters is proposed where the optical hard-limiters are placed before and after an optical correlator. Moreover, the effect of the optical hard-limiter on the performance of the optical synchronous CDMA systems using modified prime sequence codes as signature codes is analyzed under the assumption of Poisson shot noise model for the receiver photodetector where the noise due to the detector dark currents exists. We evaluate the performance under average power and bit rate constraints. Our results show that using the single optical hard-limiter slightly degrades the performance of the optical CDMA systems under the assumption of Poisson shot noise model for the receiver photodetector where the noise due to the detector dark currents exists. Moreover, we show that the optical CDMA systems with double optical hard-limiters have better performance than other conventional CDMA systems with and without the optical hard-limiter when the number of simultaneous users is not so large.