Method to Develop Coded Excitation for Velocimetry in Downhole Drilling

Background: In this paper, the phase modulation coding/decoding technology is discussed for the application in the high attenuation medium based on the simulation and the experiment. Methods: For the decoding perspective, the matched filter and the inverse filter are compared. An extra processing is introduced right after the matched filtering to restrain the range sidelobes. Furthermore, in the latter part of this paper, the factors to cause a degeneration in signal-noise ratio are quantitatively evaluated by simulation beam pattern and Doppler signal. Results: Based on the experiments and simulation in this paper, it´s found that the signal amplitude get significant boosted (30dB) while the range resolution is compatible with the span of a single pulse. It´s also proved that the frequency dependent phase distortion from attenuation will cause more degeneration than Doppler effect, but even this influence can be compensated by the equalization.