Research On Through-the-earth Communication System For Mines Based On Current Field Propagation

As a part of the safety communication,through-the-Earth(TTE)mine communication systems can achieve minimum communication in the mine,and thus play a crucial role in ensuring the safety of life.The vital importance of TTE mine wireless communication appears especially when an accident occurs.Conventional communication methods are very susceptible to damages to wires and may become paralyzed under such circumstances.In order to employ an effective and timely rescue operation,there is an urgent need to size up the situation and locate the underground worker that should be carried out by communications in emergency conditions.Due to the serious attenuation of the signal through the rock and soil stratums,the communication distance is greatly restricted.In this paper,we study a direct-sequence spread spectrum(DSSS)communication system based on current field,which can improve the receiver sensitivity.The main research contents and innovations can be summarized as follows:1.The channel model of the rock and soil stratums is proposed and analyzed.By analyzing the channel from both perspectives of impedance model and electrostatics theory based current field propagation model,the method of reducing the impedance to increase the communication distance is obtained.Moreover,the attenuation of the received signal with the communication distance is calculated theoretically.2.A realization scheme for TTE communication system combining both hardware and software is designed.The scheme uses hardware to realize signal preprocessing and sampling,and uses C language programming to realize high-gain orthogonal M-ary DSSS,broadband pulse baseband modulation,RS coding,narrowband interference suppression and so on.This scheme not only ensures real-time requirements but also increases the flexibility of implementation.3 A signal acquisition algorithm is proposed,and both theoretical analysis and simulation verification are provided.16 points are sampled for each chip,so the signal can be divided into 16 ways by serials-parallel conversion.Sliding correlation despreading is carried out by using the same correlator.Take the group with the largest difference between the two signals as the decision quantity.Theoretical analysis and simulation results show that the required signal-to-noise ratio can be reduced by 7.2d B compared to the traditional sliding correlation acquisition algorithm.4.The software part of both the transmitter and receiver is implemented and tested.An algorithm for calculating the correlation value is proposed which is applicable to the software receiver.Both the signal frame structure and the local code structure are optimized to improve the method for calculating the correlation between them.In addition,the correlation value of two m-sequences is calculated by FFT,which makes the calculation complexity of the acquisition and despreading significantly reduced.