Research On Wireless Channel Measurement?Characteristic Analysis And Modeling In Tunnel Scenarios

With the accelerated pace of urbanization in China,the development of city traffic space is strictly restricted,city rail traffic can alleviate the traffic pressure in the city and improve urban economic vitality to realize the sustainable development of society,economy and environment.The increasing number of passenger puts forward higher requirements for the operation of urban rail,the density of trains,the automation and intelligentization of train operation.In addition,the effective utilization and development of urban underground space has also brought more problems such as the fire prevention,security monitoring,passengers' communication needs,while hiding a huge economic and social benefits.These undoubtedly need to be carried on the wireless communication system with high transmission rate and reliability,and put forward new requirements for the application of the new wireless communication technology in the underground space.Wireless channel is the foundation of wireless communication system design,and accurate cognition of the propagation characteristics of wireless channel is the precondition of designing wireless communication system.Scholars in China and abroad have made a great deal of research on the characteristics of radio wave propagation in tunnels,but the research on MIMO channel characteristics is not enough,especially the research of angle characteristics in tunnels.By means of joint analysis of angle,delay and power of the multipath,we can intuitively understand the reflection,diffraction and scattering in tunnel,and further understand the cause of waveguide and keyhole effect.In addition,there is no standardized model in the underground railway tunnel scenarios at present.The accuracy of the channel model is mainly reflected in whether we can select the appropriate modeling method according to the particularity of the environment,thus we should have a better understanding of the characteristics of the measured environment during the establishment of the model.It is different from any kind of ground cellular system and other rail traffic mobile communication environment,tunnel is a main scenario in urban rail transit.Compared with other scenes,the particularity of tunnel scenario is mainly limited by narrow and long span,changeable and fixed scene.Through the analysis of previous literature,the existing channel model has some limitations in applicability.In view of the above problems,this paper studies in the following aspects:1)A SISO measurement platform based on commercial instruments and a self-made virtual MIMO measurement system were established.The extraction methods of channel characteristic parameters in tunnel environment were summarized.And validation measurements were carried out in a curved tunnel laboratory.The channel characteristics at different frequency in the transition from LOS to NLOS in the curved tunnel were given in the aspect of path loss,CIR,RMS delay spread,angle,the amplitude of MIMO matrix,the channel matrix singular value and channel capacity.And also the contrast basis for the subsequent long straight tunnel channel measurement was provided.2)Using SISO and virtual MIMO measurement platform,the propagation characteristics in LOS condition and characteristics of MIMO channel in long straight tunnel were measured and analyzed.Parameters such as path loss,CIR,RMS delay spread,angle,MIMO amplitude matrix,channel matrix singular value and channel capacity were obtained.Through the joint analysis of the angle,delay and power of multipath signals and compared with the measured results in the curved tunnel,the signal reflection and scattering laws in the tunnel were summarized,which provides the basis for the establishment of the channel model.3)The particularity of tunnel environment channel is analyzed,and the advantages and disadvantages of using statistical model,semi-deterministic model and deterministic model in tunnel environment are enumerated.It is pointed out that the deterministic model and the semi-deterministic model are the most suitable modeling methods for the tunnel scenarios.Ray tracing method was used to model the channel characteristics of long straight tunnel.Based on the measured number of reflections in the tunnel,the simulation parameters were adjusted,and the simulation results were compared with the measured data.The feasibility of ray tracing method in modeling of the tunnel scenario was discussed,and the advantages and disadvantages of this method were analyzed to improve further.A modified propagation graph model based on the surface splitting method was adopted to model the channel characteristics of long straight tunnels.The original scattering points were improved into the set of scattering points in plane,which makes it more consistent with the reflection law,reduces the computation of the visual matrix,and increases the practicability of the model.A hybrid model of ray tracing method and propagation graph method was adopted to model the channel characteristics of long straight tunnels.The advantages and disadvantages of the ray tracing method and the propagation graph method in the modeling of the tunnel scenario channel were analyzed.Taking advantage of the two methods,a hybrid model with better accuracy and flexibility was proposed,and the accuracy of the model was verified by comparing with the measured data.