Study On The Large Scale Propagation Models And Handover Optimization In High-Speed Railway

With the development of the High-speed Railway all over China and the world, the research of wireless propagation theory in the High-speed Railway is more and more important. As the Railway special digital mobile communication system, GSM-R supplies wireless communication and control information transmission for the the train. The reliability of the GSM-R network is directly related to the safety of train. High-speed railway propagation scenario has its particularity, so only applying the existing model simply is not feasible. Suitable large-scale propagation model for the High-speed railway propagation scenario can supply theory basis to the wireless network planning and the research on the interference and frequency allocation. This paper proposes large-scale propagation models in several scenarios of the High-speed railway, which are based on the receiving power testing and data analysis in the real network.Handover performance is one of the most important parts of the system. The handover of GSM-R network is a hard handover, so there will be short communication interruption in the process. And ping-pang handover will occur if the handover parameters are not set reasonablely. Ping-pang handover not only takes up system resources, but also leads to transmission errors and dropping calls for the communication interrupt. This paper makes handover simulation under the conditions of different speed, shadow fading standard deviations and others, which is based on the High-speed railway Hardware-in-loop simulation platform in the lab. And this paper proposes optimization of the handover parameters settings and makes verification through simulation.The innovations of this paper are listed as follows:First, the antenna is modeled. And the gains of transmitting antenna at different receiving points are analyzed and calculated, which are based on the real transmitting antenna in the High-speed railway.Second, based on the propagation scenarios classification, large-scale propagation characterisitics are analyzed in viaduct, cutting and open area scenarios, and tuning models based on the HATA open area scenario are proposed in viaduct and open area in High-speed railway. The shadow fading distribution is analyzed. And the auto-correlation of the shadow fading is modeled. Third, this paper proposes the clutter loss calculation method in the High-speed railway. And the referenced clutter loss values are shown based on the geography information.Last, ping-pang handover probability under the conditions of different speed, handover margin and timer to inhibit back handover is analyzed based on the Hardware-in-loop simulation. Two handover optimization methods are proposed, one method is that the handover margin should be set according to the shadow fading standard deviation of the home cell, and the other one is that the timer to inhibit back handover is statically or dynamically based on the mobile speed.