There have been a number of papers focusing on fiber distributed sensing with coherent Rayleigh backscattering
published. However, up to now, very limited research articles on investigation of coherent Rayleigh backscattering signal
waveform and its physical mechanism have been reported. This paper first proposes a theoretical derivation to illustrate
coherent Rayleigh backscattering waveform. The theoretical model is then proved with numerical simulation and
experimental measurement. In addition, signal processing method is an important factor on the performance of a phasesensitive
OTDR system. An improvement of signal processing method, which is consisted of digital average, moving
average and interval subtraction, with good effect on locating external perturbation is also introduced.