Distributed Optical Fiber Perimeter Security Technology Based on Φ-OTDR with Interference Fading Suppression

Distributed optical fiber vibration sensor based on phase-sensitive optical time-domain reflectometry (Φ-OTDR) has important application prospects in railway perimeter security. In order to reduce the influence of inherent interference fading in Φ-OTDR on phase demodulation and improve the recognition rate of disturbance signals, an interference fading suppression method based on moving vector rotating average (MVRA) was proposed. Firstly, the detected signal was characterized by a complex vector, and the complex vector signals at each position were rotated and aligned according to their initial phase angles. Then, the moving average method was used to improve the signal-to-noise ratio by mitigating the fluctuation of the signal amplitude and reducing the power of the detected noise, thereby suppressing interference fading. Next, the disturbance signal was demodulated from the suppressed fading signal. MVRA was compared with spectrum extraction and remix (SERM) and digital phase-shift transform (DPST) methods, and the anti-fading effect was verified by the standard deviation of the differential phase. Finally, an experimental platform for distributed optical fiber perimeter intrusion detection was built to simulate four kinds of protective disturbance signals, including environmental noise, stress damage, climbing, and net shearing. The demodulated phase grayscale image was taken as the feature image, and then a convolutional neural network was used for pattern recognition. The experimental results show that MVRA can suppress fading more efficiently than SERM and DPST. When the sliding window length is 50 ns, the signal-to-noise ratio is improved by 11.2 dB, and the recognition rate of disturbance signals is increased from 88% before fading suppression to 92% after fading suppression.