| As a new type of air mobile terminal,unmanned aerial vehicle(UAV)has low cost,easy deployment,and high mobility characteristics,and is widely used in data transmission,remote sensing,patrol inspection,virtual reality,and other applications.Using cellular infrastructure to provide coverage support for UAV users and establish a cellular-connected UAV communication network has become one of the most promising UAV communication solutions and has the advantage of wide coverage and low cost.However,the traditional deployed ground base station(GBS)antenna is tilted downward,and the network focuses on serving ground users.As a result,UAV can only obtain services through the side lobes of the base station antenna,which cannot meet their requirements for highly reliable and large-capacity communication services.At the same time,the introduction of high-mobility cellular-connected UAV has greatly changed the interference pattern of networks,resulting in incomplete theoretical analysis frameworks for network performance.Given this,this article will consider the three-dimensional mobility characteristics of UAV and build a performance analysis model for cellular-connected UAV communication networks,providing a theoretical basis for UAV communication technology.The main research content of this article is as follows:(1)For the frequent handover problem caused by the high mobility characteristics of UAV,a three-dimensional random waypoint movement model is used to model and analyze the moving and handover process of UAV equipped with the directional antenna by using the stochastic geometry theory.Considering the nearest association strategy and the strongest average received signal strength(RSS)association strategy respectively,the theoretical expressions of the association probability and the handover probability of the cellular-connected UAV are derived,and the effects of the ground base station density and the directional antenna beamwidth on the handover performance of the UAV are further analyzed.(2)For the new characteristics of network interference distribution caused by the threedimensional mobility of UAV and the fading characteristics of air-to-ground channels,a performance analysis method for cellular-connected UAV communication networks is studied.Using the stochastic geometry theory,considering the nearest association strategy and the strongest average RSS association strategy,the network performance analysis framework is constructed,the coverage probability theoretical expression of UAV user with directional antenna is derived,and the impact of association strategies,UAV mobility models,antenna models,ground base station density,etc.on UAV user coverage probability is quantified.Under the same association strategy,compared with the omnidirectional antenna,the coverage probability of UAV equipped with the directional antenna can be improved by 20% maximum.(3)For the limitations of traditional ground base station down-tilted antenna models that focus on serving ground users,a hybrid antenna model with an up-tilted antenna and a downtilted antenna is considered to improve the quality of service for UAV aerial users.In the scenario where UAV aerial users and ground users coexist,the handover probability of threedimensional mobile UAV users and ground users,as well as the coverage probability theoretical expressions of UAV users and ground users,were derived using the stochastic geometry theory.The effects of the power ratio of the up-tilted antenna to the down-tilted antenna,antenna beam-width,ground base station density,and UAV height on handover probability and coverage probability were quantified,the impact of hybrid antenna models on the performance of cellular-connected UAV communication networks was measured.The ground base station equipped with a hybrid antenna model can increase UAV coverage probability by 15%compared to the traditional down-tilted antenna. |
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