Joint Uplink And Downlink Optimization Of UAV-assisted Non-orthogonal Multiple Access Systems

With the rapid development of communication technology,the era of the fifth generation of mobile communication has arrived.In the new era of communication,not only new requirements for wireless mobile communication networks,such as spectrum efficiency,energy efficiency,etc.,but also new and powerful complements to future mobile networks,including unmanned aerial vehicle(UAV),high-altitude platform,and even a network of satellite systems.In addition,future communications will place more emphasis on personalized scenarios,such as the network needs of the hotspots studied in this dissertation(large gatherings,shows,events,etc.).In such a scenario,not only users are gathered,but their needs are also diverse.What is more noteworthy is that with the rise of social networks,the communication characteristic that the uplink is gradually valued and even as important as the downlink of these regions is prominent,rather than the traditional downlink dominates.Based on the above research background,this dissertation studies the UAV-assisted communication network as a countermeasure for the communication needs of hotspots,and discusses non-orthogonal multiple access(NOMA)as the improvement of spectrum efficiency for the system.This dissertation proposes an UAV-assisted communication system to guarantee needs of users in special scenarios.In this scenario,users have the equivalent requirements for uplink and downlink rates,rather than the traditional downlink dominant;in addition,users also have diversified traffic demands for diversified services,such as instantaneous rate requirements and average rate requirements.In order to solve user’s requirements in such scenario,a dual-mode multiple access(DMMA)strategy is proposed in this paper to meet the heterogeneous service requirements of all users,where the orthogonal multiple access method is used to meet the instantaneous rates requirement of each user,and the NOMA providing high spectrum efficiency gain is used to meet the average rates requirement,realizing communication guarantee for all users.In the joint uplink and downlink optimization,the two-dimensional trajectory of UAV,user scheduling,NOMA decoding order,and resource allocation are considered to meet the scenario requirements.In order to make better use of space resources,this dissertation further studies the optimization of the vertical trajectory of UAV,and proposes a NOMA-based three-dimensional UAV trajectory design method to further improve the UAVassisted wireless network rate performance.In this dissertation,the angle-dependent fading channel model is used to design the UAV 3-dimension trajectory,which makes the design more practical.In addition,the existing content is extended to solve the problem that the system provides users unbalanced uplink and downlink rates due to the limitations of NOMA,and also proposes the strategy meeting the user rate guarantee in the single NOMA mode,so that users not only get the guarantee of instantaneous and average rates,but also realize the characteristics of their uplink and downlink rates balance.