Research On Long-Distance Magnetic Induction Through-the-Earth Wireless Communication Technologies For Emergency Rescue

As a communication technology for underground emergency communication scenarios,wireless through-the-earth(TTE)communication is a key link in emergency rescue after underground accidents.The development of wireless TTE communication technology can greatly reduce the difficulty of underground rescue and improve the survival rate of miners after underground accidents.This can provide a huge guarantee for the life safety of miners in the mine,and also make a significant contribution to the successful mining of mineral resources.At present,the commonly used wireless TTE communication solutions include electromagnetic wave communication,elastic wave communication,electrode communication and magnetic induction(MI)communication.MI communication shows obvious advantages in communication scenarios due to its stable channel state,no multipath effect,and small wire size.However,the research of MI TTE communication started late,and there are still many shortcomings in the research of domestic and foreign scholars in this field,especially for long-distance TTE communication scenarios,so it is urgent to carry out research on long-distance direct MI TTE communication.Aiming at the long-distance direct TTE communication scenario,firstly,this thesis established the MI TTE communication system and the MI TTE communication model using single-axis coil for the transceiver antenna,and proposed an equivalent circuit analysis method for the transceiver circuit of the MI TTE communication system.Using the equivalent circuit analysis method of the transceiver circuit of the MI TTE communication system,the calculation formula of the MI TTE communication channel capacity was derived.The received induced electromotive force and TTE channel capacity under different TTE communication distances are simulated and calculated,and the communication rate under different TTE distances was determined,which provided theoretical support and feasibility verification for the establishment of longdistance MI TTE communication system.Aiming at the problem that the position and attitude of the receiving coil in the single-axis coil receiving scheme have some randomness,this thesis proposed a TTE signal analysis method for the transceiver coil at any relative position.The TTE signal strength when the receiving coil is in an arbitrary tilted state was analyzed,and it was found that the single-axis receiver had a receiving dead zone with zero received signal strength when the plane of the receiving coil was parallel to the direction of magnetic induction intensity.In order to solve this problem,this thesis further proposed a triaxial MI TTE orthogonal receiving scheme through three two-two orthogonal receiving coils for diversity reception,then the mutual inductance between the triaxial receiving coils was modeled and analyzed.Theoretical analysis proved that there was no crosstalk between the receiving coils of the triaxial orthogonal receiving scheme,and the receiving power can be kept at more than 3 / 3 of the ideal receiving power in the current position,which not only solved the problem of receiving dead zone in the single-axis coil receiving scheme,but also greatly improved the TTE communication performance and application scope of the long-distance MI TTE communication system.The ground structure of the actual TTE communication scene is complex,so this thesis established the transmission function of the ground penetration channel when the parameters of the ground penetration medium are not the same,and analyzed the noise characteristics of the ground penetration channel.So that the channel amplitude frequency response,channel impulse response and channel bandwidth of the MI TTE communication system under different TTE medium and TTE communication distance can be obtained,which can provide theoretical guidance for the design of the subsequent MI TTE communication system.Using the established TTE channel model,a MI TTE communication simulation platform was constructed,and the TTE communication performance under different TTE channels using BPSK and QPSK modulation methods was compared,and the corresponding maximum modulation order was given under different TTE communication distances and different TTE medium parameters.