Research On Resource Allocation In NOMA-based UAV Communication Network

In response to the lack of terrestrial infrastructure in disaster areas or remote areas,the Internet of Things terminals cannot work continuously and effectively.An Unmanned Aerial Vehicle(UAV)-assisted Wireless Powered Communication(WPC)system based on Non-Orthogonal Multiple Access(NOMA)is studied in this thesis,where UAV can quickly cover the target area,while meeting the requirements of Internet of Things terminals on battery life and spectrum efficiency.Due to high mobility,flexible maneuverability and fast deployment,UAV can serve as aerial Base Station and play an important role in the deployment of Internet of Things in emergency scenarios.WPC provides an effective solution to the contradiction between information transmission and energy consumption for Internet of Things terminals,which can extend the battery life effectively.NOMA is capable of serving multiple terminals over the same resource block,which can effectively enhance spectrum efficiency and meet the large-scale connection requirements in the Internet of Things scenario.Therefore,this thesis combines UAV-assisted communication with WPC and NOMA,while designs resource allocation and trajectory optimization schemes for the hovering and flying states of UAV,respectively.The performance of the proposed scheme is theoretically derived and simulated.Firstly,the related theories and technical basis of NOMA-based UAV-assisted WPC are analyzed.For the principle of UAV-assisted communication,the UAV communication model and channel model are explained emphatically.For the wireless information and energy transmission,the principle of Radio Frequency energy harvesting and the system model of two typical paradigms: Simultaneous Wireless Information and Power Transfer and WPC are analyzed.For the access mode,the basic principle of NOMA is analyzed,which includes the implementation process of the Successive Interference Cancellation as well as the system model analysis of uplink and downlink NOMA.In addition,the basic theory of convex optimization and bisection method are analyzed to solve the optimization problem of resource allocation in this thesis.Then,considering the scenario where the emergency area is small,a NOMA-based UAV-assisted WPC system in hovering state is proposed.In this system,a clustered NOMA access mode is designed to realize the tradeoff between NOMA spectrum efficiency and complexity.In the downlink,UAV transfers RF energy to all terminals.In the uplink,terminals transmit information to UAV by utilizing the harvested energy,and the information is decoded with different decoding orders.Our goal is to maximize the uplink achievable sum rate,while meeting the constraints of UAV maximum transmit power and total transmission timeslot.The Lagrange Multiplier and bisection method are jointly used to solve this optimization problem.Simulation results demonstrate that,the proposed scheme can achieve higher uplink achievable sum rate,and different decoding orders will directly affect the fairness between terminals.Finally,considering the scenario where the emergency area is larger,a NOMA-based UAV-assisted WPC system in flight state is proposed.In this system,a joint trajectory design and resource allocation scheme is proposed,while the two modes of UAV in periodic flight and one flight are considered respectively.The UAV flight cycle is divided into several equal timeslots.Each timeslot is divided into downlink and uplink subslots corresponding to energy harvesting and information transmission,respectively.The aim is to maximize the uplink average achievable sum rate of all terminals by jointly optimizing subslot allocation and UAV trajectory,subject to the UAV mobility constraint and uplink sum rate of all terminals in each time slot.In order to solve this optimization problem,an efficient alternative iteration algorithm is proposed.Simulation results demonstrate that the optimized trajectory flies as close to each terminal as possible and can be adjusted with the position of terminals.In addition,the scheme proposed in this thesis is effective for different flight modes.