Spectral efficiency of unipolar SAC-OCDMA system considering noise effects

In this paper, we evaluate the spectral efficiency of unipolar spectral-amplitude coding optical code-division multiple access (SAC-OCDMA) system operating with incoherent sources in the present of intensity, shot, and receiver thermal noises. The spectral efficiency achievable by four SAC codes such as Hadamard, modified quadratic congruence (MQC), balanced incomplete block design (BIBD) and zero cross-correlation (ZCC) is evaluated and compared against the number of active users and code length for a bit error rate (BER) of 10^-10. Analytical results indicated that ZCC code can support more users and leads to the best achievable spectral efficiency than other SAC codes considered. Moreover, the effect of shot and receiver thermal noise degrades the SAC-OCDMA system performance, e.g., when the number of users equal to 80, ZCC has 1.8 dB spectral efficiency penalty by considering these noises as additional to intensity noise.