Research On The Filtering And Decoding Technology Of Continuous Wave Mud Pulser Signal

Continuous wave mud pulse transmission technology has become the forefront of current downhole information transmission due to its high transmission rate and strong antiinterference ability.Therefore,it is an important research topic on effective demodulation and decoding of continuous wave signal under the background of complex noise.In this dissertation,the noise suppression method and decoding technology applied to continuous wave signal is studied,and the main tasks and results are as follows:The current research status of measurement information transmission technology and signal processing technology while drilling are introduced.The generation mechanism and transmission characteristics of continuous wave mud pulse signals are described.The influence of various noises on signal detection during continuous wave transmission is discussed.And the generation principle and characteristics of pump noise are analyzed.All the works in this thesis is based on the experimental data of a hydraulic circulation system.The signal characteristics from the time domain and the frequency domain are analyzed,and the signal demodulation and decoding method based on adaptive filtering is used for suppressing the strong and time-varying noise in continuous wave signals.From the basic theory of adaptive filtering,the method and principle of adaptive filtering are deeply studied.A signal processing method combining an adaptive notch filter and an adaptive filter is proposed.First,an adaptive notch filter filters out useful signals,then the filter output of the notch filter is used as a reference signal of the adaptive filter.At the same time,the reference signal is independent of the useful signal,and the adaptive filter has a good effect on filtering.The empirical mode decomposition method is used for the noise filtering.Three de-noising methods are used for the signal processing and simulation experiments based on Intrinsic Modality Function.It is proved that the de-noising method based on the frequency spectrum analysis of the intrinsic modal function has an effect on de-noising and is available for continuous wave signals.The cross-correlation method is used to improve the accuracy of the continuous wave mud pulse signal decoding results.The reference signal of the conventional cross-correlation method is a single frequency useful signal,a new reference signal is used and tested in this thesis,which is a combination of two different frequency sine functions.This method changes the reference signal in the cross-correlation.The experimental data processing results of relevant code elements,which are decoded by determining the waveform change during decoding.The result of experimental data analysis shows that after the cross-correlated signals pass through lowpass filtering,sampling decision,and other decoding processes,valid code element sequences can be obtained.This method is feasible and simple,which can improve the signal processing rate effectively.