Performance of chip-synchronous and chip-asynchronous OCDMA in presence of fiber optic dispersion and optical hard-limiter

The bit error rate (BER) performance of chip-synchronous and chip-asynchronous direct sequence optical code division multiple access (DS-OCDMA) is investigated using Gaussian shaped optical orthogonal code (OOC) as signature sequence and avalanche photodiode (APD) receiver. In this analysis, mainly two basic impairments, fiber optic dispersion and multiple access interference (MAI) are taken into consideration along with APD shot noise, surface leakage current, bulk dark current, amplifier noises and electric circuit noise to evaluate signal to noise ratio (SNR) and hence to calculate BER performance. The system performance is determined as a function of fiber optic length, chip rate and number of simultaneous user. The numerical results depict that chip-asynchronous OCDMA improves system performance and reduces power penalty significantly by using erbium doped fiber amplifier (EDFA) and optical hard-limiter in comparison to chip-synchronous OCDMA.