Ray-tracing Based Wireless Coverage Analysis For Subway Tunnels

With the continuous development of economy and urbanization,the traffic pressure in urban interior increases significantly,which has promoted people’s exploration of underground space.In particular,the rapid development of subway has greatly reduced the traffic burden in the city and ensured the continuous growth of urban economic vitality.Wireless communication system,as an important foundation for subway safety operation and information service,has always been the focus of subway construction.The subway tunnel scene is significantly different from the outdoor railway scene,and the internal test tasks are difficult to carry out,which makes it difficult to obtain the measured data.The lack of measured data and the diversity of tunnel scenes make the empirical model less accurate.All of these increase the difficulty of wireless coverage prediction and network planning.At present,the phenomenon of weak communication signal,low transmission rate and waste of resources often occurs in the subway tunnels.This research aims to realize the wireless coverage prediction of the distributed antenna system in the subway tunnels by studying the radio propagation characteristics,and to provide a theoretical basis for the internal wireless network planning and optimization.The research contents mainly include: design and development of simulation software for radio propagation in subway tunnels,the radio propagation characteristics in subway tunnels and the influence of the tunnels geometric parameters on the radio propagation characteristics,and the wireless coverage prediction and evaluation of the actual subway tunnel scenes.By using the ray-tracing(RT)technology to carry out high-precision channel simulation in the subway tunnels,the key channel parameters are extracted and analyzed from the simulation results,and the influence of tunnel geometric parameters on the internal radio propagation characteristics is obtained,which can provide suggestions for the layout of distributed antenna schemes in the subway tunnels.This paper develops a subway tunnels coverage prediction simulation software based on the ray tracing simulator kernel,which can be used for the study of the radio propagation characteristics and the wireless coverage prediction in the subway tunnels.The received signal power distribution prediction in subway tunnels with different geometries is completed,and the effects of cross-sectional size,degree of bending and degree of fluctuation on the large-scale and small-scale fading of the signal are proved.The channel parameters such as Rice K-factor,angle spread and root mean square delay spread in subway tunnels with different geometric structures are extracted and characterized.Based on the actual subway tunnel scenes of Dongpu-Sanxi-Yuzhu on Guangzhou Metro Line 5,this research achieves the wireless coverage prediction when the receiving antenna is located inside and outside the train body respectively.Comprehensively considering the wireless coverage effect and system stability,the Access Point(AP)deployment optimization of the 5th Generation Mobile Communication System(5G)with a frequency band of 4.9 GHz is completed on the basis of the original AP site of the tunnels.This paper provides theoretical basis and data support for wireless network planning and optimization in the subway tunnel scenes,which is helpful for the design and performance evaluation of its internal wireless communication system.