Fig. 1. Autocorrelation and summation results for 32-bit Golay code^[41]

Fig. 2. Demodulation results for external perturbations^[37]. (a) Single-pulse result; (b) single pulse result after four times averaging; (c) 128-bit Golay coding result

Fig. 3. Demodulation results for linear chirp signals^[37]. (a) (c) Time domain spectrum and STFT result of single pulse result after four times averaging; (b) (d) time domain spectrum and STFT result of 128-bit Golay coding

Fig. 4. External perturbation of fiber tail demodulation^[39]. (a) (c) Time-domain profile and power spectral density of unipolar code demodulation; (b) (d) time-domain profile and power spectral density of bipolar code demodulation

Fig. 5. Intensity profiles and differential phase profiles of scattered signals^[40]. (a) Intensity profile and (e) differential phase profile of original signal; (b) intensity profile and (f) differential phase profile after using the filtering method; (c) intensity profile and (g) differential phase profile after using Fourier integration method; (d) intensity profile and (h) differential phase profile after using SERM method

Fig. 6. Schematic of distributed frequency drift compensation^[41]

Fig. 7. Diagram of experimental setup^[41]

Fig. 8. Processing flow^[59]

Fig. 9. Demodulation perturbation of PZT1 and PZT2 before compensation^[59]. (a) Time domain spectrum of PZT1; (b) frequency domain spectrum of PZT1; (c) time domain spectrum of PZT2; (d) frequency domain spectrum of PZT2

Fig. 10. Compensated demodulation perturbation of PZT1 and PZT2^[59]. (a) Time domain spectrum of PZT1; (b) frequency domain spectrum of PZT1; (c) time domain spectrum of PZT2; (d) frequency domain spectrum of PZT2

Fig. 11. Orthogonal coding autocorrelation decoding principle^[60]

Fig. 12. Q-DAS system structure with long-range and large-bandwidth^[54]

Fig. 13. Autocorrelation function and cross-correlation function for 20 sets of orthogonal multicode^[61]. (a) Autocorrelation function; (b) cross-correlation function

Fig. 14. PSD plots of perturbed signals at different frequencies^[61]