Tanei Channel Models For High-speed Train Wireless Communication Systems

As a typical scenario of the fifth generation(5G)communication system,high mobility scenarios,such as high-speed trains(HSTs),have achieved rapid developments in recent years and consequently,HST communications are also blooming.There is large number of users inside train.With the increasing demands of the HST users,numerous communication data need to be transmitted.However,these data transmission has far exceeded the capacity of the current high-speed rail communication system.Therefore,new generation HST.communication system,which can provide high-capacity and high-reliability commnucation services,is essential.HSTs may encounter many scenarios when traveling,such as:open space,viaduct,cutting,station,and tunnels.For the tunnel scenario,due to its own structural features,propagation characteristics of signals inside tunnels are quite different from those in other HST scenarios.For the design and evaluation of future HST tunnel wireless communication system,an accurate channel model which can mimic the large-scale and small-scale channel characteristics,is indispensable.Some existing tunnel channel models focused on the analysis of large-scale fading characteristics,and ignored that of small-scale fading characteristics.Therefore,accurate and comprehensive channel models and analysis of the corresponding channel statistical properties are still missing currently.This thesis will be devoted to the study of non-stationary multiple-input multiple output(MIMO)HST tunnel channel models.In the thesis,HST tunnel channel models are first reviewed comprehensively.The channel measurements,which have been carried out,are also provided.Then,some existing tunnel channel models according to different modeling methods are classified,and the corresponding channel characteristics are listed.Considering the limited visibility of tunnels,long and narrow space inside tunnel,and the waveguide effect,HST tunnel channel models are developed from the following aspects.Firstly,in order to make up for the deficiencies of the existing two dimentional(2D)channel model,more accurate three dimentinal(3D)non-stationary wideband tunnel channel models,which consider the influence of elevation angels,are necessary.Secondly,the non-stationarity of HST tunnel channel should be taken into account.Most of the existing tunnel channel models are under the wide-sense stationary assumption which is not established due to the fast movement of the transmitter and/or the receiver.Then,radio signals inside tunnels will suffer more reflections and scattering.Therefore,the combination of single-bounced(SB)and multiple-bounced(MB)components is first considered to mimic the signal propagation inside tunnels.Finally,small-scale fading characteristics are studied emphatically.Most of the current modeling works are focused on the large-scale fading characteristics,and simplified the analysis of small-scale fading characteristics.The small-scale fading channel models also play an important role in system design and cannot be ignored.In conclusion,accurate tunnel channel models which can mimic the channel characteristics are essential.From the aspect of deterministic tunnel channel modeling,the mode-based tunnel channel models are proposed for the first time to study the influences of small-scale fading characteristics and power distribution.Based on the exsiting multi-mode model,time-dependent multi-mode tunnel channel model is further proposed.Then,some corresponding channel characteristics,such the temporal autocorrelation function(ACF),the power spectrum density(PSD),and the receiver power,are investigated.Meanwhile,the influences of different operating frequencies,tunnel size,and propagation modes inside tunnel on ACF are studied.Moreover,the impact of different parameters on channel characteristics in a HST ray tracing tunnel channel model,is analyzed.From the aspect of stochastic tunnel channel modeling,we proposed geometry-based stochatical model considering the influence of tunnel size and tunnel shape.For rectangular tunnel and horseshoe tunnel,the signal propagation space can be abstracted as cuboid shape.It is assumed that there is large number of scatterers randomly distributed on the closed tunnel space.Combining the WINNER ? model and the confined propagation space,these scatterers can be classified as a series of clusters randomly distributed inside tunnel.Based on this modeling method,3D non-stationary GBSM theoretical tunnel channel model is proposed by considering single-cluster case with the SB components and twin-cluster case with the MB components.The corresponding simulation model is then developed using the modified method of equal area(MMEA)in order to obtain discrete angular parameters.Finally,based on the proposed model,a series of channel statistical properties are investigated,the non-stationarity of channel is analyzed,and a good validation is presented by comparing with relevant measurement data.In the existing HST tunnel scenarios,circular tunnels or arched tunnels also occupy a certain proportion.The cross sections of these tunnels are approximately cylinder shape,the corresponding calculation is simplified,and the modeling work is developed based on the clusters distribution.Firstly,it is assumed that there are some clusters randomly distributed on the tunnel walls.The position of cluster can be determined by the mean angle of cluster and the cylinder itself.Once the angles are determined,the positions of clusters can be obtained.Then,the position of Tx,Rx,and cluster can be presented,all the channel information can be obtained,such as angle of arrival,angle of departure,delay,and propagation distance.Therefore,a 3D non-stationay tunnel wideband circular channel model is established.Moreover,considering the azimuth and elevation angles are dependent,the corresponding simulation model is developed using the method of equal volume(MEV)to joint calculate discrete angular parameters.Based on the proposed GBSMs,important small-scale fading channel characteristics are investigated and futher verified by relevant measurement data finally.To summarize,we have developed 3D tunnel channel models considering the influence of elevation angles,and mimic the multiple reflections and scattering by SB and MB cases.Moreover,non-stationary HST tunnel theoretical and simulation channel models considering the time-variant angles are proposed,and verified by measurement data.The proposed channel models are important for the design,test,and performance evaluation of HST tunnel communication within the framework of 5G networks.