| UAV systems have been widely employed in various fields due to their flexibility and scalability.Among them,the UAV’s formation plays an important role in various scenarios,such as disaster environment,large-scale live broadcast,facility inspection,and military operations.The cooperation between nodes in multi-UAVs system can effectively eliminate the limitation of propagation distance and overcome the problems caused by obstacles.Due to the complexity of UAV’s formation mission scenarios,in large-scale or harsh communication environments,links between nodes in the system will be frequently disconnected,which brings challenges to the communication stability of UAVs systems.While UAVs execute tasks cooperatively,the internal nodes of the cluster formation frequently exchange information,and the instability of communication will reduce the efficiency of the cooperative task.Therefore,how to solve the problem of intermittent communication links caused by obstacles,channel fading and other factors needs to be studied urgently.From the perspective of solving the instability of the communication links between UAV nodes in a complex environment,a relay implementation mechanism to ensure communication stability is systematically designed.Moreover,the trajectory should be carried out in accordance with the restrictions of the UAV’s real flight scene smooth tracking verifies the stability and effectiveness of the design system.The specific research process includes: in the low-altitude scene where obstacles and interference exist,considering the problem of disconnection of the source UAV and the target UAV communication,consider using an intermediate UAV as a relay node as the target UAV provide conditions for inter-communication.In this process,considering the high dynamics of the UAV system and the real-time nature of the mission,the real-time trajectory planning of the relay UAV has become one of the main challenges of the relay system.To solve the above problems,a relay optimization scheme based on the Extended Kalman Filter(EKF)prediction and the penalty function Particle Swarm Algorithm(PSO)is proposed.This scheme adopts the EKF-based source UAV and destination UAV position prediction algorithm,and predicts the location of the UAV in real time and transmits the location information to the relay UAV.The relay UAV makes timely decisions and calculates the location to fly.The PSO algorithm with penalty function is applied to obtain the optimal trajectory points of the relay UAV aiming at maximizing the transmission rate target.Based on the basis mentioned above,taking into account the flight characteristics of the UAV,in order to solve the actual dynamic constraints of the UAV system that were not considered in the previous research work,and to verify the feasibility and effectiveness of the scheme,a method for generating the Minimum Snap method for the smooth continuous trajectory of the relay UAV and a proportional derivative(PD)control algorithm used to control the relay UAV to track and plan a smooth trajectory.By continuing the calculated discrete trajectory points of the optimal relay UAV,adjusting the control parameter values to control the UAV to track the designed optimal trajectory,and obtain the difference between the actual flight trajectory and the ideal optimal trajectory.This reflects the performance of system communication.The simulation results show that the difference between the actual flight state of the relay UAV and the ideal optimal trajectory is small,which proves that the mechanism has better performance in the communication stability and trajectory tracking of the UAV at high velocity. |
