Research On Electromagnetic Simulation Of Through-the-earth Communication With Its Parallel Algorithms

Through-the-earth communication system is a safe and reliable communication system used in minecoal production and disaster relief, which is designed and developed based on the basic research of electromagnetic (EM) propagation in the complex stratum media. When analytical methods is used to study the radio wave propagation in the earth medium, only the reflection and transmission coefficients can be calculated in a simplified model.And test method can be used to provide some EM propagation parameters in a particular region only. With the development computer technology, the research of EM issues by numerical calculation becomes a hotspot. Although the EM numerical calculation was successfully applied to many areas of EM problem, it is also carried out to research the EM propagation in a complex stratum based on the simplified stratum model. Because the whole stratum media is approximation to the homogeneous medium in the simplified model, the EM parameters are get by averaging the value of parameters of study region with ignoring the difference of the stratum, and there are errors between the computing result in simplified model and the EM transmission in the real world. This thesis achieves the estimation of the EM parameters distribution in stratum and the modeling of stratum media using an improved Kriging interpolation based on the borehole data by absorbing and analyzing the 3D stratum modeling, spatial interpolation and EM numerical computation, and uses the finite difference time domain (FDTD) to simulate the process of EM transmission in the real world stratum. Furthermore, this thesis makes a thorough study on the parallel computing in the stratum media modeling and FDTD in order to improve the computing speed for large area with a plenty of layers and Yee grids. Finally, an integration system is developed by analyzing the process of EM simulation.The study results provide an advance and effective way to studying the propagation characteristics in a complex stratum media ,these studis are as follows:The characteristics of the stratum and wireless wave theory are presented, the EM parameters of stratum media tied closely to transmission of the radio wave are analyzed. Based on the model of parallel multi-layer stratum, the mathematic expressions of reflection and transmission coeficients of the radio wave transmitting through the multi-layer stratum medium are deduced.An improved Kriging interpolation is adopted to setup a stratified stratum medium model and estimate the distribution of the electromagnetic parameters in the mutant stratum media. In Kriging interpolation algorithm, the determination of parameters of a correlation model is a key issue to construct the regression model, the computing accuracy rely on the initialization when using the conventional numerical optimization methods such as pattern search method when computing the parameters, which result in the instability of the optimization solution,a modified binary particle swarm optimization (GPSO), independent of the initialization of parameters, is presented to compute the global optimums of correlation model parameters, the experimental results show that the proposed GPSO significantly improves the search efficacy and stability compared to the exiting optimization algorithm. By this interpolation method, the high precise media model and electromagnetic parameters can be provided during the electromagnetic numerical computing.A through-the-earth EM simulation approach integrated with stratum media modeling by Kriging and FDTD is proposed. The issue of ignoring the difference of the stratum in the simplified model is overcome by using the Kriging to model the strum media, the EM features of stratum media are reflected by assigning the values of EM parameters to each Yee grid belong to the different stratum, the radio wave's propagation process in complex stratum is carefully described using the proposed EM simulation approach.In order to improve the computing speed of spatial interpolation used for stratified stratum, and to achieve the load balancing within the different number of stratum layers and computing nodes , a novel parallel Kriging interpolation with multi-granularity is developed based on the strategy of dynamic adjustment of the parallel granularity. In this algorithm, according to the quantitative relationship between the number of CPUs with this of stratum layer, the parallel granularity is adaptively adjusted, in which the coarse granularity Kriging interpolation is priority used while the medium granularity Kriging is adopted to balance the computing load.In order to improve the computing efficiency of the parallel FDTD based on MPI, the technologies such as space decomposition, load balace, topologic configuration and data transmission are carefully analyzed and improved. Finally, the parallel media modeling and parallel FDTD are combinated to form an integrative parallel EM simulation system for studying the through-the-earth communication.