Research On Electromagnetic Wave Wireless Transmission Technology Of Near Bit

In a rotary steerable drilling system,the downhole information was collected by near-bit sensors needs to be transmitted to the surface in real time for analysis and monitoring on the surface.Therefore,the wireless short-distance transmission technology of near-bit was a key technology,the information was collected by the tool was transmitted to the MWD(Measure While Drilling)system is possible.This paper designs a near-bit wireless short-range communication system based on FPGA and transmits the near-bit information wirelessly to the MWD system through electromagnetic induction.The overall structure design of near-bit wireless short-range communication system was designed and the transmitting system and the receiving system were designed and implemented.Finally,a ground-based test was conducted to select the optimal carrier frequency.(1)In the design of the launch system,the power spectrum simulation of FSK was performed by MATLAB.The CPFSK modulation method with faster sidelobes was selected.The DDS generator is designed using Verilog hardware description language.The I~2C protocol was used to read and write E~2PROM,and the data in E~2PROM was encoded and CRC was implemented.Verification,2FSK modulation was implemented with the DDS generator.D/A conversion and 7th-order Butterworth filter circuit,signal conditioning circuit,and the same proportion amplifier circuit are designed,design and implementation of the launch system are completed.(2)In the design of the receiving system The optimal low-pass and band-pass filters were designed by MATLAB,and the generated filter tap coefficients were imported into the FIR IP core.Using 2FSK incoherent demodulation principle,2FSK demodulation was implemented based on FPGA,and Modelsim simulation and data decoding were performed.Pass valid data through the FIFO buffer and send it to PC serial port debugging assistant(instead of MWD system)with UATR.The A/D conversion and signal attenuation circuit and the analog amplification circuit were designed to complete the receiving system.(3)A ground simulation test was conducted.Using FPGA's hardware programmable advantage,the optimal carrier frequency was selected and the development cycle was shortened without changing the hardware design.Ground experiment results show that when the selected carrier is 20KHz and 40KHz,the transmission distance of short-range communication can reach 6.2m(error rate is 0),which can meet the requirements of downhole near-field communication.