Research On Radio Coverage Characteristics In Confined Environment Based On Hybrid Method

In confined environments,safety operation of railway transportation systems is guaranteed by stable and effective wireless communication systems.Radio wave is the carrier of signals in wireless communication system.High efficient radio coverage in confined environment builds the fundamental factor for wireless communication systems.Numerical methods have been widely applying to study radio coverage in confined environments.However,single numerical method is difficult to independently model radio coverage in confined environment due to radio wave is easily affected by parameters of transmitting antennas,physical structures in confined environment and complex electromagnetic environments.Based on the studies on numerical methods,this dissertation presented hybrid method and it was applied to study radio coverage issues in confined environments.Additionally,measurement was conducted and lots of measurement data were obtained.Then,this dissertation proposed a new thought for the desiging of radio coverage solutions in confined environments.Main innovated aspects of this dissertation are as follow:1.Numerical methods including vector parabolic equation(VPE),ray tracing(RT)and finite difference time-domain(FDTD)were studied and applied to model radio wave propagation in confined environments with hard boundaries.The paper presented a wide angle VPE scheme in order to expand its simulation angle.A distribution analysis of transmitting antennas in a curved tunnel was also investigated by using VPE method.Additionally,radio coverage in a real subway tunnel was modeled with RT as well.2.Hybrid numerical methods including hybrid VPE/FDTD method and hybrid RT/FDTD method were proposed.The hybrid methods achieved a tradeoff between computational efficiency and accuracy.The hybrid methods were validated by comparing with measurement data,it offered a new kind of solution for radio coverage in confined environments.3.Hybrid methods were used to address radio coverage problems in a tunnel with complex environments.In this study,a real train model and receiving antenna model were adopted,then the received voltages of antennas for different situations in tunnels were analyzed.Received voltages properties in different cases were obtained and compared.Additionally,impacts of antenna relays and obstacles in the tunnel were also studied.4.Hybrid methods were applied to model radio coverage in complex subway environments.Electric field distribution of co-frequency antennas were simulated and its potential impacts on radio coverage of train control systems were studied.The location of the co-frequency antenna was also optimized by finding a least influence position.Then influences of trains on radio coverage in subway tunnels were also analyzed with hybrid methods.5.Impacts of antenna parameters on radio wave propagation in a semi-circle cross section tunnel was measured.The parameters includeing locations of transmitting antennas,antenna types and polarization styles,respectively.Measured data was analyzed by empirical model and electromagnetic field theorems.Guidances for antenna design and distribution was proposed at the same time.