Crosstalk Noise Suppressed for Multi-frequency φ-OTDR Using Compressed Sensing

The frequency division multiplexing (FDM) is an effective method to improve the detection ability of high-frequency disturbance in phase-sensitive optical time domain reflectometer (phi-OTDR). However, as the probe channels increase, crosstalk between channels will be generated. As a result, the recovery phase signal-to-noise ratio (SNR) will be deteriorated, which will reduce the detection capability of phi-OTDR. Therefore, a novel method for suppressing crosstalk noise by compressed sensing under multi-frequency phi-OTDR is proposed in this paper. The band-limited characteristics of vibration are deeply analyzed, and the frequency domain is chosen as the sparse domain. Noise without sparsity is discarded in the compression process. Furthermore, the noise cannot be recovered in the reconstruction process which uses the critical information containing the global property of phase signal. Consequently, the influence of crosstalk noise is reduced effectively. In experiments, compared with the restored signals without the proposed method, the average SNRs of the reconstructed 12 kHz sinusoidal vibration are respectively enhanced by 18.57 dB, 40.47 dB, and 41.67 dB in the sensing system with 6, 7, and 8 channels. In addition, the 24 kHz triangular wave signal and the disturbance composed of several different frequencies with random amplitudes can be detected and reconstructed. The proposed crosstalk noise suppression method provides a potential choice for phi-OTDR performance enhancement.