Multiple Access Interference Bit Error Rate Evaluation Technique for Direct Detection FFH-OCDMA Bragg Gratings Based Channels

This paper proposes a more realistic optical code division multiple access (OCDMA) sequence bit error rate (BER) evaluation technique for multiple access interference (MAI) during transmission over optical fiber. The technique provides a filter for all possible non-zero correlations events that may occur during transmission, leaning on all positive time-frequency intervals for a 2-D OCDMA, or all positive time intervals for 1-D OCDMA. As a wavelength hopping/time sequence (WH/TS) suggests, this MAI evaluation on a 2-D OCDMA consists of one-coincidence frequency hopping code optical orthogonal code (OCFHC-OOC) Bragg gratings encoded signals. For a better assessment of the timeintervals, we also investigate the 1-D OCDMA OOC since the OOC is the time spreading component of the OCFHCOOC sequence. In both cases, the signals of interest are transmitted using simple On-Off keying with non-returnto-zero signalling and direct detection at the receiver. The received signal contains multiple access interference from other users’ coincidence correlations and the inband random correlations from the photodiode due to square detection. The MAI mean and variance are analysed over all possible non-zero wavelength-time interval pairs of sequences and the standard Gaussian approximation is used to evaluate the bit error rate. Further, the resulting bit error rate is then compared with that of the user coincidence-based evaluation technique.