Research On Symbol Synchronization Algorithm In Drilling Mud Pulse Telemetry

MPT(mud pulse telemetry)is currently the most widely used wireless data transmission technology in MWD(measurement while drilling)systems.In a MPT system,drilling fluid passes a moving valve controlled by a dowhole motor that generates pressure waves which traval to the surface.The surface data acquisition system collects data and transmits it to the demodulation system,which decode data in real-time using digital signal processing methods.Timing synchronization and symbol synchronization(or bit synchronization)are both important steps in a demodulation system.The former is to obtain the accurate arriving time of data frame,while the later is to determine the correct time duration of each symbol.In this paper,timing synchronization and symbol synchronization techniques in MTP systems are studied.Time synchronization procedure in this paper can be devided into two steps:LFM(linear frequency modulation)synchronization and m sequence synchronization,which based on the autocorrelation characteristic of LFM signal and m sequence respectively.Thus the arriving time of the signal can be obtained through correlation calculation.In the process of time synchronization,the result might be affected by various factors such as modulation methods,signal distortion,signal attenuation,position of the receiver,etc.Solutions to those problems are also discussed in this paper.Symbol synchronization plays an important roll in a high-speed mud pulse data decoding system by handling problems caused by inaccurate symbol periods.With the improvement of data transfer rate,symbol synchronization is becoming more and more important.This paper studies the influence of waveform distortion and imprecise motor control on symbol synchronization.Symbol synchronization process based on Gardner algorithm and early-late-gate algorithm are applied in the analysis of field experimental data respectively.Both results are analyzed and compared.This study is supported by the project:Data modulation/demodulation algorithm and drilling fluid numerical analysis in MWD systems.The field experimental data uesd in this paper are collected from a field test held in Xinjiang Province,October 2016.