| Along with the development of petroleum industry, mining and test of deep oil wells has become increasingly important. Logging is an important part of mining deep wells. Wireless transmission of logging system, cost saving and simple operation, naturally becomes the present research hotspot.The thesis use ultrasound to transmit information to ground through oil tube wall. Underground oil tube wall is a special, high temperature, high pressure and strong reverberation channel, which makes ultrasonic communication system demanding. The communication rate of 2FSK communication mode is low, but the mode can be used in the underground complex environment with its stable, reliable, and strong multipath effects. The following is the content of the thesis. At first, the thesis studied the 2FSK modulation and demodulation principle, proposing to generate the 2FSK signal by direct digital frequency synthesizer and demodulate it by differential detection method at the receiver. Low-pass filter is an important part of differential detection method, so the thesis focused on FIR low-pass filter realized by distributed algorithm. For exact delay of the delay unit in 2FSK differential detection demodulator, the thesis introduced fractional delay filter to address it. Secondly, use DSP Builder to design DDS module in 2FSK modulation system, and delay, multiplier and FIR low-pass filter modules in 2FSK demodulation system.2FSK modem was carried out on the Simulink platform. Thirdly, the thesis expanded ADC and DAC modules on DE2 board, then use Verilog HDL to design modules in 2FSK modem system, and these modules were synthesized and simulated. Finally, the modules above were integrated, synthesized and downloaded on DE2 board to realize 2FSK modem system, which was tested. The result was that:when the voltage P-P of 2FSK signal was greater than 0.85V, the modem can achieve 0～19200bps adjustable transmission rate, and it can be used in the low rate ultrasonic communication system. |
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