Theoretical Wireless Channel Modeling And Simulation In Confined Space Scenarios

Wireless electromagnetic wave is an important method for wireless communication in tunnel environment, therefore it is of much importance for the development of underground rail transportation to study the wireless channel in tunnel scenarios. Aiming at the feature of NLOS tunnel scenarios, some modifications are done on the conventional propagation-graph channel modeling theory by the operation of dividing scattering points sets and introduction of transfer probability among points sets, which can refine the transfer function among points sets, the accuracy of wireless channel modeling can be prompted by the adjustment of channel impulse response (CIR) taps by the times of transfer probability among different points sets.In the scheme proposed in this paper, the geometric model is constructed according to the actual tunnel size firstly, then the geometrical model is divided into M scattering points sets based on the proposed algorithm of dividing geometric model. Calculate the transfer probability among different points sets according to the definition of transfer probability. The transfer function of every single propagation routine can be obtained by the times of sub-transfer functions among points sets which can be acquired by the conventional propagation-graph theory, and the whole system transfer function can be deducted by the sum of all possible routines’transfer function. The maximum routine number is MN given that maximum reflection number is N.The transfer probability matrix is deducted by the definition of transfer probability. And sub-transfer function between two points sets can be deduced by conventional propagation-graph theory. The transfer function of some routine is the product of sub-transfer function of two adjacent points sets. The CIR in time domain is finally obtained by the inverse fourier transform of all routines’transfer function.Then the broadband wireless channel measurement system is introduced in this paper and the measurement result power delay profile (PDP) is shown when bandwidth is 150MHz in different frequency point and different position. The comparison work between simulation and empirical research are present to demonstrate the verification and rationality of the proposed method since two results trends are similar and values both are close within the range of allowable error-10dB.On this basis, some work are done to analyze multiple antennas’channel parameters, e.g. the antennas’ correlation coefficient, angle of arrival (AOA), angle of departure (AOD), channel capacity. Some conclusions can be drawn that angle spread of AOA is much larger than AOD’s, RX’s antennas’ correlation coefficient fluctuates more frequently than TX’s. When the scenario is stationary the gap between Rayleigh channel’s capacity and simulation scenario’s capacity increases as the antenna number increases, this can be explained by the degradation of channel matrix.In other scenarios, as tunnel bending angle increases, the tunnel environment is gradually approaching to LOS scenario from NLOS scenario, and it can be found that transfer probability matrix shows a certain change trend:the transfer probability between two sets belonging to same part is relatively high, while it is gradually reduced between sets belonging to different parts.Peak CIR taps on the delay coordinates with the principle of geometry, antenna correlation coefficient fluctuates more and more frequently, angle spread gradually becomes larger, channel capacity decreases, the number of effective channel matrix’s singular value decreases.