Performance and Confidentiality Comparison of Different Hybrid SAC/OCDMA-WDM Overlay Schemes

Code pulses of a spectral amplitude coding/optical code division multiple-access (SAC/OCDMA) system are overlaid onto a multichannel wavelength division multiplexing (WDM) system. Modified quadratic congruence (MQC) codes are developed as the signature codes for the SAC/OCDMA system. The developed code is to avoid the overlapping between signals of both systems with no use of notch filters. In addition, performance and confidentiality results of this scheme are compared to our previous hybrid SAC/OCDMA-WDM overlay scheme which utilizes normal MQC codes with notch filters. The system performance and data confidentiality are evaluated in terms of bit-error rate (BER) and eye diagrams. The eavesdropper’s interceptor that is based on a simple energy detector can scan all corresponding SAC/OCDMA wavelengths to detect an entire coded signal of an authorized user. Our results indicate that the performance and confidentiality have inverse relationship between the two hybrid systems. For a first hybrid scheme that does not adopt notch filters, the BER performance, when a data rate is 622Mbps, for OCDMA users is about 10−15 at 4 dB of an optical attenuator, and BER for eavesdropper detection values vary from 10−6 to 10−15 due to different overlapping effects between WDM interferes and OCDMA pulses. On the second hand for a hybrid scheme that contains notch filters, the BER performance for OCDMA users is about 10−12 at 4 dB of an optical attenuator, and for eavesdropper detection values are mostly about 10−2. However, it is concluded that an eavesdropper faces immunity from SAC/OCDMA system in both cases because WDM channels act as a partial masking over encoded signals in a hybrid scheme. Furthermore, the tradeoff between the performance and confidentiality for authorized SAC/OCDMA users is considered.