Research On The Radio Wave Coverage Characteristics Along Railway Based On Vector Parabolic Equation Method

The stable wireless communication system along the railway is one of the important factors for the safe operation of trains.The terrain along China's railways is complicated.In order to avoid the interference between the wireless communication signals of the train and the external signals,the wireless communication signals of the trains are usually controlled to propagate in the limited space along the railway.Therefore,the realization of efficient coverage of radio waves along the railway in a limited area is an important means to improve the quality of wireless communication and thus ensure the safe operation of the railway wireless control system.The research of radio wave coverage along the railway mainly focuses on the single scene of the tunnel,there is very little research on radio wave coverage in the open space along the line and the mixed space including the continuous area of the open space and the restricted space.Aiming at the shortcomings of existing research,this paper studies the characteristics and laws of radio wave coverage in the mixed space along the railway,hoping to provide a theoretical basis for the design of the railway wireless communication system in the central and western regions of China.The main work and innovations of this paper are as follows:(1)On the basis of the original alternating direction implicit parabolic equation method,the impedance boundary conditions of the tunnel were studied and simulated,and the bidirectional parabolic equation method in the tunnel environment is derived.With this method,the backscattered radio waves in the presence of trains can be considered,so the electric field distribution in the tunnel can be simulated more realistically.In order to verify the correctness of the method,the results of the parabolic equation method were verified by the ray tracing method.(2)The parabolic equation method was applied to the study of radio wave coverage characteristics in open space.There is no clear physical boundary for this kind of environment,and it is difficult to use the calculation method for full space calculation.Therefore,the window function was used to set the boundary of the calculation area of the parabolic equation method in the open space,and the radio waves at the boundary were absorbed,thereby simulating the calculation area as an open space.In order to verify the correctness of the method,the results of the parabolic equation method were verified using the free space radio wave propagation empirical formula and the two-raymethod.(3)The parabolic equation method was used to study the influence of various factors in the mixed space along the railway on the radio wave coverage.A multi-scenario radio wave coverage model such as open space-tunnel was established,and the propagation characteristics of radio waves in different scenarios were simulated.Using the two indicators of field strength median and flatness factor to study the effect of antenna position on radio wave coverage,the most suitable area for antenna installation was obtained.In addition,the influence of the tunnel's own medium on radio wave coverage was studied,the law of the influence of dielectric constant and conductivity on radio wave coverage was given.(4)From the theoretical and experimental aspects,the radio coverage of different antenna positions and obstacles in the corridor environment was studied,and the received power distribution law at different antenna positions was measured and compared with the results obtained by parabolic equation model analysis.