Analysis of noise suppression for OCDMA systems with fixed in-phase cross-correlation codes and single O/E converter

Performance of the non-coherent spectral amplitude coding optical code division multiple access (SAC-OCDMA) systems is primarily degraded by the presence of noise sources generated during the process of optical-to-electrical (O/E) conversion at the receiving photodiode (PD). Phase induced intensity noise (PIIN) is generated by limitations in the coding scheme that leads to the mixing of adjacent spectrum's commonly known as multiple access interference (MAI). While, shot and thermal noise sources are generated at PD during the conversion of signal from O/E domain for further processing. This paper investigates and compares the performance of two detection techniques with reference to the received power units and suppression of noise sources while recovering and decoding enhanced multi diagonal (EMD) code. Both techniques namely spectral direct detection (SDD) and single PD detection (SPD) use one PD for O/E conversion to reduce the effect of shot and thermal noise. Numerical analysis using Gaussian approximation shows that SPD technique provides better performance for an acceptable bit error rate (BER) of 10(-9) as compared with SDD technique, due to maximum recovery of power units in the received spectrum. Simulation analysis through a highly recognized software called Optisystem also validates the mathematical formalism and shows the EMD and SPD based SAC-OCDMA system is able to support 64 subscribers communication simultaneously beyond 1 Gbps of data while -10 dBm power is maintained at the receiving PD.