Research And Design Of Wireless Underground Magnetic Induction Communication System

With the development and utilization of underground space and resources,collection and transmission of underground information has been becoming more and more important.Different from the space on the ground,the underground transmission medium is composed of air,water,soil,sand and stone,which is more complex and changeable.In underground environment,the traditional wireless communication technology using electromagnetic wave has such problems as high path loss,unstable channel and large antenna size,which is hard to meet the requirements of practical application.Wireless magnetic induction communication(WMIC)technology transmits information through a coupled magnetic field,which is very stable in underground environment without magnetic materials,providing a new way for the effective transmission of underground information.Considering the practical application requirements of wireless underground sensor network(WUSN),the application design and performance optimization of wireless underground magnetic induction communication(WUMIC)system are studied in this thesis.Firstly,this thesis systematically reviews the latest research of the WUMIC system and its applications at home and abroad,and summarizes the existing problems in the current research.Besides,the transmission principle of magnetic signal,model and transmission characteristics of WUMIC system are introduced in detail,which is the theoretical basis for the research of application design and performance optimization.Secondly,the intensity and distribution characteristics of the transmitting magnetic field are analyzed by calculation and finite element simulation,considering the characteristics of underground environment.On this basis,a design scheme of WUMIC system based on coupling coils is proposed.The system transmits information through a coupled magnetic field between coils and selects 2ASK signal modulation and demodulation.The design includes two parts: hardware design and software design,the hardware design is composed of transceiver circuit design and transceiver coils design and the software design is composed of communication protocol design and transceiver strategy design.Then the experimental platform is set up to test the feasibility of the design scheme.The experimental results show that the design of the WUMIC system proposed in this thesis is working well in underground environment.Finally,in order to solve the problems of limited bandwidth,small channel capacity and low speed of transmission,considering the combination of MIMO technology and WUMIC technology,a design scheme of WUMIC system based on MIMO technology is proposed.The design scheme selects orthogonal coils as transceiver antennas,the crosstalk is solved through the orthogonal relation between coils,and several independent transceiver links are established.Based on Shannon's theorem,channel capacity of the system is calculated,and the performance of the system is further improved by the power optimization allocation algorithm.Then the feasibility of the crosstalk cancellation scheme is verified by experimental tests.Meanwhile,simulation results show that the MIMO technology can significantly improve the capacity of the WUMIC system under the appropriate power allocation algorithm.The research work in this thesis provides a reference for the design and performance improvement of the WUMIC system and has guiding and facilitating effects on the practical application of WUMIC technology in underground environment.