Power Allocation And Trajectory Optimization For UAV-Enabled Multi-Link Relay Communication Systems

Unmanned aerial vehicles(UAVs)have the characteristics of cost-effective,flexible mobility and on-demand deployment,equipping the communication equipment,they can establish a high-probability line-of-sight(LoS)communication link with ground communication devices by artificially controlling or adaptively changing their trajectories,which lead to their wide applications in the field of wireless communication.UAV relay is a major application of UAVs in the field of wireless communication.Compared with traditional static relays on the ground,a UAV relay can take full advantage of its high mobility,adaptively and quickly adjust the trajectory to obtain better channel condition between itself and the target communication node and can establish a reliable and low-latency communication link between source nodes and their destination nodes.This thesis mainly focuses on the research of UAV-enabled relay system and UAVenabled Io T system.Based on the different communication performance requirements such as throughput and information delay,etc.,this thesis proposes an algorithm of joint optimization of UAV trajectory and the resource allocation of the entire communication system,to design the optimal UAV flight trajectory and resource allocation for optimal performance.The thesis includes the following two aspects:(1)In order to support the rapidly growing data requirements,we consider a UAV enabled multi-link communication system,in which multiple sources communicate with their destinations with the assistance of the corresponding UAV relay.Since all links communicate sharing the same spectrum at the same time,there is co-channel interference between each link.Thus,this thesis proposed to jointly optimize the UAV relay 3D trajectory and the power allocation of the UAV and the source for maximizing the throughput performance of the whole system by coordinating interference.The resulting problem is a non-convex optimization problem and contains severely coupled variables.To tackle this difficulty,this thesis proposes a method based on the block coordinate descent technology,the successive convex approximation technology and introducing slack variables technology,to alternately and iteratively solve the non-convex problem.The simulation results show that our proposed algorithm can effectively improve the minimum throughput of all source-UAV relaydestination links,and prove that in the UAV-enabled multi-link relay communication system,the necessity to weaken the co-channel interference by jointly optimizing the 3D trajectory and the transmit power of the UAV.(2)The existing works usually assume that the channel between the UAV and the ground communication node is a LoS channel,but it is not suitable for the actual communication environment.Thus,we study a multiple UAV-enabled data collection system based on the more realistic Rician fading channel model,where one UAV is deployed as a data collection UAV to collect the data from ground sensor nodes,and the other UAV is deployed as a relay to forward the data collected by data collection UAV to the data fusion center,so as to realize long-distance data collection and analysis.To improve the communication efficiency of the UAV and reduce the information delay,this subject proposed to minimize the UAV’s flying duration by jointly optimizing the orizontal trajectory and vertical altitude of UAVs,the bandwidth and transmite power of the sensor nodes and UAVs.We also use methods such as block coordinate descent method to solve this joint optimization problem alternately and iteratively.The comparison of simulation results shows that our proposed joint optimization algorithm based on the Rician fading channel model can better coordinate the communication between the links,improve the communication efficiency of the communication system,and effectively reduce the task completion time of the UAV.