| Intelligence is an important trend in the development of global high-speed railways(HSR).Fifth Generation(5G)mobile communication technology,as a new generation of railway mobile communication systems,can meet the needs of future intelligent HSR wireless communication services.Massive Multiple-Input Multiple-Output(Massive MIMO)in 5G technology plays an important role in intelligent HSR vehicle-to-ground communication.The dynamic beamforming based on Massive MIMO can form beams with extremely high spatial division multiplexing gain.Through beam tracking,the narrow-beam communication between vehicles and ground can be built,which greatly improves the spectral efficiency and energy efficiency of the system.In order to support the effective design and evaluation of future intelligent HSR vehicle-to-ground communication systems,it is necessary to study narrow-beam channels in high-mobility scenarios.Channel measurement is the most direct and effective method to obtain channel characteristics and is a specific description of the wireless propagation channel.Channel modeling is an abstract description of the characteristics of wireless propagation channels.Accurate cognition of the propagation characteristics of wireless channels is crucial for planning wireless networks,selecting transmission technologies,and optimizing communication systems.At present,there is still a lack of research on narrow-beam channels in high-mobility scenarios at home and abroad.Therefore,in this paper,aiming at the application of Massive MIMO dynamic beamforming in vehicle-to-ground communication in high-mobility scenarios,the research on narrow-beam channel measurement and modeling in high-mobility scenarios is carried out.The main work of this paper is as follows:1)Carry out research on narrow-beam channel measurement in high-mobility scenarios.A set of narrow-beam channel measurement system suitable for high-mobility scenarios is built.The base station antenna of the channel measurement system adopts phased array technology,which can form narrow-beam with controllable beam direction and beamwidth.Through beam tracking,the base station and the mobile can establish narrow-beam channel communication.The digital acquisition and storage unit of the system can support high-speed acquisition and storage of signals in high-mobility scenarios.In the data processing step of the received signal,the Channel Impulse Response(CIR)of the narrow-beam channel is obtained through frame synchronization,system response acquisition and elimination,and sampling synchronization.The narrow-beam channel measurement in the high-mobility scenario was carried out on the highway,and the CIR of the dynamic narrow-beam channel was obtained.By extracting the characteristic parameters of CIR,the large-scale and small-scale fading characteristics of the channel are analyzed,and the effectiveness of the narrow-beam channel measurement in high-mobility scenarios is verified.2)The 3D non-stationary narrow-beam channel model in the high-mobility communication system is established through the geometric stochastic modeling method.The influence of beamforming based on Massive MIMO on the channel is considered at the base station,and the Gaussian beam mode is introduced to model the narrow-beam channel.Combined with the 3D geometric model,the broadband CIR of the model is derived.The dynamic evolution of scatterer clusters in space-time-frequency domain is also considered in the model.Through the correlation function in the space-time-frequency domain,formula derivation and simulation analysis are carried out for the correlation of single-link and multi-link in the channel model.The non-stationary characteristics of the narrow-beam channel and the effects of beamwidth and beam direction on the channel statistics are studied.Through the channel measurement data of HSR and highway,the fitting of the measured data and the simulation model is carried out,and the validity of the model is verified. |
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