Research On Multi-Relay Offshore Broadband Communication Technology Based On UAV-Terrestrial Network

Various services in maritime communication network are gradually modernized and intelligent.The continuous development of marine activities has also led to a rapid increase in the demand for maritime broadband communications.Unmanned Air Vehicle(UAV),with its flexibility and lightness,has already demonstrated considerable power in relay communication networks.The industry has reason to believe that its application to maritime scenes will also play a huge role.This thesis focuses on the cooperative auxiliary communication capability of multi-UAV and Terrestrial Base Station(TBS),proposes a multi-UAV relay communication system and network architecture to provide stable network service for maritime users.On this basis,this thesis carries out research on the following two aspects.One is to improve the link quality by dynamically adjusting the flight trajectory and posture of the UAV.With the movement of ships and UAVs,the network state among TBS,ships and UAVs changes accordingly.The fluctuating network conditions would make the network quality of service worse.This requires the UAV to dynamically adjust its flight trajectory and posture to ensure the stability of the wireless link.The other is the service migration problem in multi-UAV relay communication system and network architecture.When a ship travels from one TBS-covered area to another,the relay communication link provided by UAV deteriorates in quality,and the service of the ship in TBS may be interrupted.Therefore,this scenario is facing the problem of base station switching,whitch services from the original TBS to the new TBS.In this process,rational design of migration strategy is the key to maintain network continuity,ensure service efficiency and save UAV energy.To solve the problem of UAV dynamic position and flight trajectory adjustment,the research objective of this thesis is to minimize the change in data rate of the network caused by the UAV adjustments.This thesis first introduces a multi-UAV relay communication system and network architecture.Then the space model is discretized,the offshore channel and UAV energy consumption are analyzed,and the reward function is finally designed.On these bases,a UTAA-DQ algorithm is designed,which combines a two-stage Q-learning algorithm framework.The semi-physical simulation results show that the algorithm has good performance in data transfer rate and task completion rate.For the service migration problem in the multi-UAV relay communication system and network architecture,this thesis has two parts of the research.Firstly,this thesis uses and improves a transmission strategy based on buffer and network coding,which improves the task transmission efficiency in the network.The mathematical analysis of this strategy also provides a certain mathematical basis for the study of service migration problem.Subsequently,the premigration judgment model,the migration model between TBS and the UAV deployment model are designed in combination with the architecture of multi-UAV relay communication system and network architecture and the movement characteristics of ships.On these bases,a USRICMA algorithm is proposed.The semi-physical simulation results show that compared with a series of comparison algorithms,this algorithm can reduce the waiting time of user service and reduce the extra energy consumption of UAV by coordinating the waiting time between migrating subtasks.This thesis studies UAV dynamic trajectory adjustment and service migration problem under the architecture of multiple UAV relay-assisted communication system for OBCN.The UTAA-DQ algorithm and USRI-CMA algorithm are proposed through the research and analysis of the related mathematical models.The feasibility and effectiveness of the algorithm proposed in this thesis are verified through embedded semi-physical simulation experiments.