Security enhancement for spectral amplitude coding OCDMA based on hybrid EDW/M seq. code systems

This paper presents the security enhancement for spectral amplitude coding optical CDMA. The eavesdropper probability of error-free code detection based on hybrid code system is investigated. Enhancement Double Weight (EDW) optical CDMA scheme and M-sequence codes are used as a hybrid code system. The eavesdropper performance is based on observing the authorized transmitted signal based on classical detection theory. The eavesdropper taps a coded transmission of a particular user and performs the necessary calculations to derive the transmitter´s code word from these transmissions. If an eavesdropper could be forced to tap code pulses with low SNRs, a security enhancement can be obtained. An eavesdropper would need SNR of 9.2 dB to correctly detect encoded pulses with a probability of 50 % for the hybrid scheme, which is 5 and 3 dB higher than M-sequence and EDW schemes respectively. The difference in performance of the eavesdropper´s receiver with envelope detection is getting small, especially at higher SNRs.