Performance Comparison of Wavelength Spreading and Synchronous OCDMA Systems Using Perfect Difference Codes with Interference Cancellation

Abstract

In this paper, we adopt the perfect difference codes in the spectral-amplitude-coding (SAC) optical code-division multiple-access (OCDMA) systems to overcome the disadvantages of the synchronous optical code-division multipleaccess (SOCDMA) systems proposed in [1]. Due to the properties of perfect difference codes, the SOCDMA system [1] can only perform well in synchronous mode. But the proposed OCDMA systems using the same signature codes can perform well in asynchronous mode and fully remove multiple access interference (MAI) by differential receivers. At the receiver end, we adopt different decision thresholds to make decisions for the received data bits. We evaluate the performances of the proposed systems under consideration of shot noise, thermal noise, avalanche photodiode (APD) bulk, and surface leakage currents. The numerical results reveal that the proposed systems have better performance and larger system capacities than the SOCDMA system [1]. Moreover, with enough power budget, the proposed wavelength spreading OCDMA system is one system free of MAI limit.