OCDMA-based sensor network for monitoring construction sitesaffected by vibrations

Due to increasing demands for the more accurate structural health monitoring of large-scale facilities, e.g. modern high-speed railways and bridges, there is a huge uptake in the development of optical sensor networks (OSN), which can help mitigate issues with conventional electric sensors, especially their sensitivity to electromagnetic interference and size. The existing fibre optic infrastructures are not widely used by OSNs, due to the lack of appropriate multiplexing techniques. Aiming at addressing the implementation issues of optical sensors in urban areas, this study proposes an efficient and cost-effective system for supporting the vibration sensing of unequally distributed points. The proposed system takes advantages of the spectral amplitude encoding optical code division multiple access (SAC-OCDMA) technique in providing differentiated services in the physical layer with varying code weights. This system utilises more wavelengths (i.e. higher power) in more distant sensing points in order to retrieve vibration signals properly. The mechanism of SAC for OSN is elaborated using simulation results, including the impact of transmission distance and the procedure for allocating codes to different zones. These results indicate the suitability of the proposed system for implementation in existing fibre optic infrastructures. Moreover, the numerical analysis shows a high capacity of the sensor network deploying SAC. The proposed system contributes to the construction research and practice by addressing the implementation issues of structural health monitoring of large-scale facilities in urban areas.