Channel Measurement And Model At Low Elevation Angle In Mountainous Areas

The low elevation angle area refers to the area where the angle between the communication platform and the receiver of the signal is less than 10°.Low elevation angle communication generally occurs in the following situations: First,when satellite communication covers the global or near space,the communication coverage radius of the high-altitude platform is relatively large.The edge of the coverage area is generally in the low-elevation communication area.Second,in the process of approaching and descending from a high-altitude platform in space,communication between the high-altitude platform and the ground will be partly at a low elevation angle.Third,when the low-altitude unmanned aerial vehicle is in investigation and tracking,the communication between the unmanned aerial vehicle and the operator will experience low-elevation communication.With the continuous development of near-space communications and unmanned aerial communications,there will be more and more low-angle communications in China.China's mountainous area accounts for more than one-third of the country's total area,so mountainous terrain will become a typical scene for low-elevation communication.The low elevation angle region of the mountain has very obvious influence on the characteristics of the wireless channel.In the low elevation region of the mountainous region,the mountains are densely forested and the terrain is complex.It has characteristics such as large path loss,severe shadow fading,and strong ground clutter and multipath effects.In order to fully grasp the channel characteristics of low elevation angles in mountainous terrain,this thesis is in accordance with the requirements of the National Natural Science Foundation of China's major research project in fostering the project's ‘Analysis and Optimization on Network Capacity of Near Space Communication Network with Dynamic Topology'.Do the following main tasks:(1)According to the wireless signal propagation principle and channel measurement method,a set of mountain low elevation angle channel measurement system was designed based on the existing conditions of the laboratory.The system uses LabVIEW software to design a signal launch control platform that can change the signal frequency and gain.Based on this,a signal transceiver system based on LabVIEW software,U-center software,NI USRP 2900 platform,HZPA10247 broadband RF power amplifier,U-blox GPS module and Anritsu MS2713 E spectrum analyzer was established.(2)A field trip to Chongqing Tieshanping Park,Geleshan Forest Park and Chongqing University was conducted.Based on the investigation,Chongqing University campus,Shapingba Binjiang Road and Geleshan suburbs were selected as measurement sites.Planning the measurement path,designing the measurement plan,and measuring the channel in the above-mentioned three typical scenarios through the built measurement platform.(3)Through the compilation and analysis of the recorded measurement data,the path loss curves and shadow effect parameters in the three situations of open campus,Binjiang Road and Geleshan suburbs were fitted.And compared with the path loss of the free space loss model and the COST-231 Walfisch-Ikegami model,the large-scale fading model of the channel under three scenarios was obtained.By comparing the large-scale fading channel models of the three scenarios,it can be found that in the case of line-of-sight,the influence of the low altitude elevation environment on the signal propagation is not prominent.In the non-line-of-sight environment,the low elevation angle of the mountain environment will make the signal attenuation worse.