Successive Interference Cancellation for Optical CDMA Systems: Fundamental Principles

In this paper successive interference cancellation (SIC) based on optical code division multiple access (O-CDMA) systems has been investigated. SIC scheme refers to a family of low complexity multi-user detection (MUD) methods for direct sequence CDMA systems. Performance of optical CDMA system is influenced by multiple access interference (MAI) resulted from the overlapping between the users. This kind of noise is became a primary concern in optical CDMA systems. To overcome this problem, we applied successive interference cancellation technique to a spectral amplitude coding (SAC) system that uses modified quadratic congruence (MQC) codes as signature sequence codes, taking into account the effect of all major noise sources, such as phaseinduced intensity noise (PIIN), shot noise, and thermal noises. Furthermore, in SIC scheme we have taken into account the impact of imperfect interference cancellation. The system is analyzed for two cases: same effective power for all the users and different effective power from each user. We have successfully shown that under ideal effective power the SIC/SAC optical CDMA systems have potential to suppress the intensity noise and mitigate multiple access interference. Hence, using SIC/SAC cancellation scheme, the system can accommodate much more number of users as compared to the one without cancellation. Further, under ideal power the system using SIC scheme with direct sequence encoding (SIC/DS) shows much lower BER performance as compared to the one without cancellation (i.e. conventional receiver) or to SIC/SAC cancellation scheme. Hence, much more number of users can be accommodated by SIC/DS receiver system. Furthermore, SIC/DS scheme still shows much lower BER performance as compared with SIC/SAC scheme under different effective power.