| With the continuous advancement of urban construction in China,the underground tunnels were built to enable the maintenance and operation works of utilities,as well as reduce the impact within the city center.As the increasingly mature technology of the Internet of Things and further deployments of network construction,the wireless communication of sensor monitoring and operational system will become increasingly urgent to support underground utility tunnels.To ensure the telecommunication coverage quality in the utility tunnel,it is particularly necessary to establish a suitable channel model for the complex environment of the underground utility tunnels,and to conduct efficient and accurate simulation calculation.At present,the suitable channel prediction methods for tunnel environment include ray tracing method,parabolic equation method and finitedifference time-domain method.However,the above three models will encounter the problems of poor calculation accuracy or low calculation efficiency due to the influence of calculation scope when applied to the scene of utility tunnel.In order to solve the above problems,according to the radio wave propagation characteristics of different areas of underground utility tunnel and the idea of hybrid channel modeling method,this thesis considers the advantages and disadvantages of each channel model,and makes deeply research on hybrid numerical channel modeling method for underground utility tunnel scene.The main work can be divided into the following parts:Firstly,the basic theory of wireless channel modeling in underground utility tunnels is introduced,including characteristics of radio wave propagation in the tunnel environment and existing channel modeling theories or methods.The wireless channel model includes ray tracing method,parabolic equation method and finite-difference time-domain method,are introduced respectively,which lays the foundation for the establishment of the mixed channel model.Secondly,in order to improve the computational efficiency of parabolic equation method,the alternate direction implicit parabolic equation method is derived based on CN difference method.In order to improve the accuracy of parabolic equation method and the efficiency of ray tracing method,a hybrid model based on three-dimensional ray tracing method was derived to correct parabolic equation method.The hybrid numerical model is used to calculate the radio wave coverage issues in the underground utility tunnel,and the results are compared with the finitedifference time-domain method to verify the effectiveness of the hybrid simulation method.The influence of different position of transceiver antenna and closed tube cabin on simulation calculation of different channel models is discussed and the stability and necessity of calculation accuracy of mixed model is verified.It provides an accurate and efficient method for channel simulation calculation in underground utility tunnels.Thirdly,in order to improve the calculation accuracy of ray tracing method in the free space propagation region near the transmitting antenna,a hybrid numerical model based on ray tracing method and finitedifference time-domain method is derived.The hybrid model is used to calculate the electromagnetic wave coverage characteristics of the transmitting antenna attached to the nearby region,and the results are compared with the finite-difference time-domain method to verify the effectiveness of the hybrid simulation method.The influence of different pipeline deployment on the simulation calculation of channel model is discussed,and the efficiency and stability of calculation accuracy of the mixed model are verified.It provides a more accurate method for the simulation calculation of free propagation area in underground utility tunnels.Finally,we combined the above two hybrid numerical models,and the wireless channel simulation calculation of underground utility tunnel environment is computed by MATLAB.The efficiency and accuracy of the comprehensive hybrid model calculation are verified by the results,which were compared with those of ray tracing method and finite-difference timedomain method. |
