Research On Optimized Transmission Strategy For UAV-assisted Wireless Communication Systems

Due to the high mobility and low cost as well as good line-of-sight(LoS)links,unmanned aerial vehicles(UAV)assisted wireless communication systems are considered as promising techniques in the next generation wireless communication systems.It can be acted as aerial communication platform such as mobile base station(BS),mobile relaying for information collection and dissemination,which has been widely applied in various communication scenarios,such as coverage enhancement,secure communication,mobile edge computing and caching.However,UAV-assisted communication systems are still confronted with many challenges,in which the most severe one is the endurance of UAV.In UAV-assisted information collection scenario,due to the limited battery capacity,UAV must fly back to recharge or replace the battery during the task,which makes the UAV's energy quite precious,and people have to consider to reduce UAV's propulsion energy consumption so as to prolong the UAV's duration time and energy utilization efficiency,based on the premise of task accomplishment.In UAV-assisted communication systems,UAV-assisted relaying is considered as a promising technology.Compared with traditional terrestrial fixed relaying system,UAV-assisted relaying can better meet system requirements and improve communication quality as well as enlarge communication coverage.Nevertheless,many problems,such as UAV's deployment and information-causality condition,lead to more complex to study this scenario than the traditional terrestrial fixed scenario.In addition,multi-UAV cooperative communication is also of significance in UAV-assisted communication systems.On the one hand,multi-UAV cooperation can create larger system gains and wider coverage compared with single UAV communication system.Also,multi-UAV cooperation system is able to adapt the different requirements of heterogeneous communication networks so that fit the future development direction of the networks.On the other hand,the problems including scheduling between UAVs and ground users and secure flight among UAVs would be important consideration factors in multi-UAV cooperative scenario,which increases the network design complexity to some extent.This paper focuses on the above aspects,and the main study contents and innovation points are summarized as the following scenarios:1.Optimized transmission strategy research on UAV-assisted information col-lection systemsBased on UAV's endurance problem caused by UAV's propulsion energy consumption,an energy-efficient UAV communication system is designed.In the multiple ground terminals(GTs)scenario,a UAV is dispatched to collect the information from GTs,meanwhile ensure each GT's communication quality of service(QoS).By using the Dinkelbach fractional programming theory and successive convex optimization(SCA)technique,an iterative algorithm is proposed to jointly optimize GTs scheduling and UAV trajectory.Eventually,the optimal UAV's energy efficiency(EE)is obtained,and the UAV's energy utilization efficiency is efficiently improved as well.2.Optimized transmission strategy research on UAV-assisted relaying communication systemsAimed to rotary-wing UAV-assisted relaying scenario,a throughput maximization design with multiple GTs is studied.In this system,UAV needs to receive the information from the source nodes,and then transmit the received information to a destination node.The rotary-wing UAV energy consumption is modeled,and the limited flight energy and information-causality constraint are considered in the research problem.Also,a fairness of information transmit is considered.By adopting convex optimization theory,under the constraints of UAV mobility and information causality,the optimal resource allocation scheme and UAV trajectory are obtained under the joint design for multiple variables.3.Optimized transmission strategy research on multi-UAV cooperative com-munication systemsAimed to the scenario of multiple GTs,a multi-UAV cooperation is adopted to receive the information of GTs.We consider the difference design among multiple UAVs for the first time,and achieve the communication design for each individual UAV so as to meet the specifical requirements.Besides,an efficient secure flight scheme is designed,which effectively guarantees the UAV's flight security.For inter-ference avoidance between links,orthogonal time slot scheme is proposed.Finally,by using convex optimization theory and SCA technique,time slot scheduling and power allocation as well as flight trajectory are jointly optimized,and the goal of the difference design among UAVs under the security condition is achieved.