Research On Optimization Of UAV-assisted Communication System Based On Vehicle Path Prediction

As aerial flight platforms,unmanned aerial vehicles(UAVs)bear the characteristics of strong mobility,high flexibility and low price,which have been widely employed in various fields.In wireless communication systems,UAVs also have broad application prospects.As compared with traditional terrestrial communication systems,UAV-aided communication systems can be deployed more quickly can be configured more conveniently.Moreover,because there is a line-of-sight link which is high-reliability and short-distance,UAV-aided communication systems can provide low-cost communication service according to specific requirements of users and actual communication scenarios.However,the employment of UAVs in wireless communications also brings some new challenges.For example,the high mobility of UAVs and the movement of ground users will inevitably lead to huge changes in the quality of communication services,and this may cause the user’s communication quality to decline.In addition,the amount of energy in the batteries that are carried by UAVs is limited,which is consumed for the load on the UAVs,communication,and mobile flight,and thus the energy efficiency at UAVs is an issue that cannot be ignored.In this thesis,taking into account the scene of a moving vehicle on the ground,the involved UAV-aided communication system,energy efficiency and the path prediction of the moving vehicle will be studied.The thesis includes the following aspects.(1)The scheme of UAV-aided communication system based on single carrier is studied.Firstly,assuming that the position information of the moving vehicle is fully known,the flight trajectory of UAV is optimized to maximize the energy efficiency of UAV-aided communication in bits/joule.Secondly,it is difficult to obtain the channel state information from UAV to moving vehicle in advance due to the changing position of moving vehicle in the actual scene,which makes the optimization design of UAV assisted vehicle communication system a great challenge.In order to solve this problem,this thesis proposes a moving vehicle path prediction scheme combining short-term accurate trajectory prediction and long-term coarse trajectory prediction,which can predict the position information of subsequent time in advance during the vehicle moving process.According to the position prediction information of moving vehicles,an online UAV-aided communication scheme based on the path prediction of moving vehicles is proposed.Then,in order to solve the problem of high computational complexity of on-line solution,this thesis decomposes the energy efficiency optimization problem of UAV-aided communication system into a series of receding horizon optimization subproblems,each of which can be solved by quasi convex optimization and successive convex approximation,Thus,the UAV trajectory in each short-term accurate trajectory prediction time period in the vehicle journey can be obtained.(2)The corresponding optimization scheme of broadband UAV-aided communication based on multi carrier transmission is studied.The goal is still to maximize the energy efficiency of UAV-aided communication in bits/joule.Different from the first research work,in the UAV-aided communication system composed of UAV and moving vehicle,the broadband communication between UAV and moving vehicle is completed by multi carrier modulation.In addition to optimizing the flight trajectory of UAV,power allocation is also carried out for the subcarriers of multi carrier modulation.The simulation results of the above two parts show that the proposed scheme can significantly improve the system energy efficiency compared with the simple benchmark scheme,and the maximum gain is 27.30% and 42.68% respectively.At the same time,the energy efficiency performance obtained is very close to the upper bound of the system energy efficiency.