Spectral efficiency analysis of bipolar spectralamplitude coding optical code-division multipleaccess systems using different one-dimensional codes

In this study, the spectral efficiency (SE) of bipolar spectral-amplitude coding optical code-division multiple-access (SAC-OCDMA) systems operating with incoherent sources is analysed. The analytical expressions of the model were derived to assess the performance of SAC-OCDMA systems, taking into account the intensity noise as the primary source of noise. Four different SAC codes were used to evaluate and compare the SE against the number of active users and code length for a bit-error rate (BER) of 10^-11. The investigated codes are Hadamard, modified quadratic congruence (MQC), balanced incomplete block design (BIBD) and zero cross-correlation (ZCC). Our analytical results revealed that ZCC code has the ability to support more users at a high data rate up to 2.5 Gbps and offers significant SE enhancement in bipolar SAC-OCDMA system over other SAC codes under investigation. In addition, bipolar encoding improves the SE compared with unipolar technique, for example bipolar ZCC has 7.7-dB SE advantage than unipolar ZCC. Furthermore, when BER requirement of the system decreases, the SE can be increased.