Observational analysis improved signal-to-noise ratio by 6.97 dB using quasi-distributed acoustic sensing, indicating effective coding methods.
In this paper, a quasi-distributed acoustic sensing (QDAS) system based on P4-code modulation is proposed for signal-to-noise ratio (SNR) enhancement. The P4-code modulated signal is generated by an acousto-optic modulator (AOM) and injected into ultra-weak fiber Bragg grating (UWFBG) array. At the receiver, coherent detection is adopted for optical-to-electrical conversion. Then the optical time-domain reflectometry (OTDR) trace is retrieved based on pulse compression technology. The vibration information is obtained after differential phase demodulation process. Experimental results show that the noise floor is suppressed by 15.27 dB ref rad2/Hz and the demodulated SNR is improved by 6.97 dB compared with the conventional single pulse interrogation scheme. The effect of the coding length on the noise floor is investigated. Moreover, the frequency response is measured, and the power spectrum densities (PSDs) of the vibration signals are obtained with high SNR over 24.83 dB. Vibrations with different voltages can be demodulated quantitatively with excellent linearity, and the sensitivity is 1.026 rad/V at 3 kHz.
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Li et al. (2025) studied this question.
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