The Study Of Encode And Decode Technology Based On Down Hole Pressure Continuous Signal

MWD is the most important technique for down hole data acquisition,and using mud pressure continuous wave to transmit data is a new method.Through the analysis and studies on some modes of wirelesstransmission as acoustic wave, electromagnetic wave and mud pulse, the mudpulse has bright future for application. Continuous wave transmission hasstrong anti-interference ability, high transmitting rate and is fit for deep welldrilling and the low ROP situation compared to positive and negative impulseof mud pressure. The paper presents the study on encode and decode methodand modulate techniques based on continuous wave transmission. Accordingto some key parameters for signal transmission quality measurement astransmission rate, error rate, dependability, signal-to-noise ratio andemphasized on the aspect of data transmission dependability, with theconsideration of drilling condition, the Golay code down hole encode methodwhich has error control ability has been designed. The Golay code wasdecoded by the method for amending error code which has been proposedwith the encode-decode rules and the encode-decode electrical circuit isshowed in this paper. Second, it was fund that the phase ambiguity problemcould be exist when the code is decoded only by using absolute phase modulation techniques through derivation, analysis on space mathematicalmodel of modulation signal, so the paper indicates that modulation signalscan be demodulated in well surface with differential coherent detectionmethod. In addition, according to the study on serial data transmission style,the paper also presents the analysis on structure and function of down holecommunication apparatus, the constitution of bus standard andcommunication protocol between them.