SUMMARYThis paper applies perfect difference code (PDC) to develop an optical code-division multiple-access (OCDMA) system with spectral amplitude coding (SAC). The differential receiver of the proposed systems exploits the cross-correlation property of PDC to remove the multiple-access interference (MAI) without reducing the power of the received signal. The threshold applied in the data decision process has a crucial influence on the bit error rate (BER). Hence, this study investigates the effects of several different decision rules. The numerical results show that the BERs of the synchronous OCDMA system using PDC proposed by Weng and Wu are 100 times and 17 times greater than those of the current system for code sizes of 183 and 307, respectively, under conditions of equal power budgets. To achieve the same BERs, the theoretical analysis reveals that the transmission power required by the Weng's system is around k=ðk À 1Þ times greater than that of the current system, where k denotes the code weight of the signature code employed. Additionally, under conditions of reliable communication (i.e. BER 4 10 À 9 ), the capacity of the proposed system is almost one and half times greater than that of Weng's system. Regarding the data decision threshold, this study proposes a realisable sub-optimal decision threshold as a replacement for the optimal decision threshold. The performance of the proposed system using this sub-optimal threshold is found to be only marginally poorer than that obtained when the optimal decision threshold is employed. Therefore, the proposed sub-optimal threshold provides a suitable means of improving the system performance of SAC OCDMA systems using signature codes with a fixed in-phase cross-correlation property.

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