Resource Allocation And Spatial Planning In UAV-Assisted Wireless Communication Systems

In recent years,due to the characteristics of low cost,high mobility and flexible deployment,unmanned aerial vehicles(UAVs)have been found widespread in civilian applications.Compared with traditional ground communication,UAV-assisted communication,which is regarded as a leading hotspot in the future wireless communication research,can significantly improve the system's quality of service due to its high possibility of line-of-sight(LoS)links.Aiming at UAV-assisted communication system,this thesis mainly focuses on research for system performance optimization in different communication scenarios that involve resource allocation and trajectory design.The main contributions of the thesis are presented as follows:First,a UAV-assisted cooperative communication system with one pair of source and destination is investigated,where the UAV is deployed as a mobile relay following Ampify-and Forward(AF)protocol.With simultaneous wireless information and power transfer(SWIPT),the UAV's transmission capability is powered exclusively by radio signal transmitted from the source via time-sharing mechanism.By jointly optimizing UAV's decision profile,transmission power allocation and UAV's trajectory design,an alternative algorithm based on dual decomposition and successive convex approximation is proposed to maximize the end-to-end cooperative throughput.Second,a UAV-assisted wireless powered communication network is investigated,where the UAV is deployed as a hybrid mobile access point for both power and information transfer and the ground users share the spectrum via NOMA for uplink.By jointly optimizing up-and-donwlink time allocation,user's uplink transmission power allocation and UAV's trajectory design,an alternative algorithm based on successvie convex approximation and logistic function approximation is proposed to improve the system common throughput.Last but not least,since the actual transmission rate needs to meet the quality of service requirements in practical modulation schemes,actual throughput optimization of a UAV-assisted downlink communication system is investigated,where the UAV is deployed as mobile basestation to serve ground users.By jointly optimizing transmission power allocation and UAV's trajectory,an algorithm based on penalty method and successive convex approximation is proposed to improve the system's quality of service.