Long-Haul SAC-OCDMA over FSO channel using random diagonal code: performance comparison under various weather conditions

This paper analyse the performance of a three-user Spectral Amplitude Coding Optical Code Division Multiple Access system over a Free Space Optical channel, addressing the need for a simple, interference-free multi-user optical link that remains viable under changing weather conditions. The system uses the Random Diagonal (RD) code with parameters user ( K = 3), code weight ( W = 5), and code length ( N = 10). Ten chip wavelengths are assigned from 1,550.0 nm to 1,557.2 nm. Results show that all three users achieve bit error rate below 10 −9 up to approximately 3.5 km under clear conditions and beyond 2.1 km under light mist at 3 × 2.5 Gbps. Within the target range, the q factor exceeds 6 for all users. It is also analysed that the cross-correlation within the data segment of the RD code is always zero, thereby removing Multiple Access Interference and suppressing Phase-Induced Intensity Noise without any subtraction circuit at the receiver. A direct detection receiver with a rectangular filter per user placed at the data segment chip wavelength. As compared to exiting work, this design offers better performance in terms of high data security, high quality factor and low error rate, less complexity and low cost.