Research On OOK Signal’s Modulation And Demodulation Algorithm Of Drilling Mud Pulse Telemetry

Drilling mud pulse telemetry system transmits orientation data, formation data and drilling parameter to the surface in real-time. In the downhole, pressure waves are generated by pressure change from restricting the flow of drilling mud, which is caused by the relative oscillations between the stator and rotor in the continuous-wave pulse generator. The communication channel is extremely harsh so that the mud pulse signals passing through are attenuated and distorted. On the surface, real-time data is demodulated from the received signal.In this paper, a linear time invariant system model is presented during a certain time window, which is based on signal superposition caused by bit reflection, channel delay analyzed through the experiment data of discrete pulses and constant physical characteristics of the drilling channel. The modulation of on-off keying (OOK) with the control logic of oscillating shear valve in the pulse generator is analyzed. Coherent detection method is utilized to demodulate the received signal based on the channel delay characteristics. Numerical simulations are employed to obtain the error margin of OOK signal amplitude, OOK symbol period and signal-noise-ratio at certain bit error rate.In the experiments through 3000-meter circular pipeline, the applied demodulation method of coherent detection is verified successfully, as well as composition of the noise, signal-noise-ratio of the signal and channel delay.The experiment results revealed that the noise is mainly composed of periodic noise and Gaussian white noise, the signal-noise-ratio (SNR) is in conformity with the simulation, and channel delay also exists. The experiment data are demodulated with a data rate of 11.43 bits per second (bps), achieving corresponding requirements.