The wireless communication systems based on Unmanned Aerial Vehicles(UAVs) have found a wide range of applications recently. In this paper, we propose a new three-dimensional(3 D) non-stationary multiple-input multipl...The wireless communication systems based on Unmanned Aerial Vehicles(UAVs) have found a wide range of applications recently. In this paper, we propose a new three-dimensional(3 D) non-stationary multiple-input multiple-output(MIMO) channel model for the communication links between the UAV and mobile terminal(MT). The new model originates the traditional geometry-based stochastic models(GBSMs) but considers the non-stationary propagation environment due to the rapid movements of the UAV, MT, and clusters. Meanwhile, the upgrade time evolving algorithms of time-variant channel parameters, i.e., the path number based on birth-death processes of clusters, path delays, path powers, and angles of arrival and departure, are developed and optimized. In addition, the statistical properties of proposed GBSM including autocorrelation function(ACF), cross-correlation function(CCF), and Doppler power spectrum density(DPSD) are investigated and analyzed. Simulation results demonstrate that our proposed model provides a good agreement on the statistical properties with the corresponding derived theoretical ones, which indicates its usefulness for the performance evaluation and validation of the UAV based communication systems.展开更多
随着无人机硬件成本的降低和深度学习算法的发展,部署在无人机终端的实时目标检测算法在诸多领域展现出广泛的应用前景。然而,嵌入式设备有限的能耗和算力,以及普适性目标检测算法对于小目标特征提取不够充分等问题,制约了此类算法速度...随着无人机硬件成本的降低和深度学习算法的发展,部署在无人机终端的实时目标检测算法在诸多领域展现出广泛的应用前景。然而,嵌入式设备有限的能耗和算力,以及普适性目标检测算法对于小目标特征提取不够充分等问题,制约了此类算法速度和精度的提升。文中提出了一种部署在无人机终端上的小目标实时检测算法DS⁃YOLO(Dense⁃SPP YOLO),算法基于密集连接的思想设计了全新的主干网络,并改进了空间金字塔池化模块以增强小目标的特征提取和多尺度特征复用,最后基于批归一化层(Batch⁃Normalization)的缩放因子修剪网络中不重要的通道,修剪瘦身后的算法更加适合部署在移动端。在Visdrone2019⁃DET数据集上的测试结果表明,DS⁃YOLO算法mAP(mean Average Precision)指标比SlimYOLOv3算法提升约3%,检测速度达到89 FPS(Frames Per Second),高于SlimYOLOv3的67 FPS。展开更多
This paper proposes a new distributed formation flight protocol for unmanned aerial vehicles(UAVs)to perform coordinated circular tracking around a set of circles on a target sphere.Different from the previous results...This paper proposes a new distributed formation flight protocol for unmanned aerial vehicles(UAVs)to perform coordinated circular tracking around a set of circles on a target sphere.Different from the previous results limited in bidirectional networks and disturbance-free motions,this paper handles the circular formation flight control problem with both directed network and spatiotemporal disturbance with the knowledge of its upper bound.Distinguishing from the design of a common Lyapunov fiunction for bidirectional cases,we separately design the control for the circular tracking subsystem and the formation keeping subsystem with the circular tracking error as input.Then the whole control system is regarded as a cascade connection of these two subsystems,which is proved to be stable by input-tostate stability(ISS)theory.For the purpose of encountering the external disturbance,the backstepping technology is introduced to design the control inputs of each UAV pointing to North and Down along the special sphere(say,the circular tracking control algorithm)with the help of the switching function.Meanwhile,the distributed linear consensus protocol integrated with anther switching anti-interference item is developed to construct the control input of each UAV pointing to east along the special sphere(say,the formation keeping control law)for formation keeping.The validity of the proposed control law is proved both in the rigorous theory and through numerical simulations.展开更多
随着无人机软硬件技术的发展,多无人机集群自组织形成的无人机自组网(Flying Ad-Hoc networks,FANETs)受到了越来越多的来自学术界和工业界的关注,其灵活的部署和快速的反应能力使其能高效地完成多种多样的任务。而无人机自组网路由协...随着无人机软硬件技术的发展,多无人机集群自组织形成的无人机自组网(Flying Ad-Hoc networks,FANETs)受到了越来越多的来自学术界和工业界的关注,其灵活的部署和快速的反应能力使其能高效地完成多种多样的任务。而无人机自组网路由协议是提高服务质量(Quality of service,QoS)最重要的方法之一,但无人机自组网的移动性和动态性给路由协议的设计带来了严峻的挑战。传统的移动路由协议不能很好地满足无人机自组网的路由需求,因此研究者们从基于拓扑、地理和分层的角度提出了各式各样的无人机自组网路由协议,旨在克服移动性和提高网络的服务质量,并指出未来无人机自组网的路由协议可以考虑机会路由、软件定义网络(Software defined network,SDN)决策和预测驱动决策等综合提高QoS。本文主要针对无人机自组网网络特征,从不同的路由方法出发,SDN对路由协议进行总结和归纳,并对未来的研究方向进行了展望。展开更多
基于快速扩展随机树(rapidly exploring random tree,RRT)的运动规划算法,通过随机采样的方式探索未知任务空间,具有概率完备性和较高的计算效率.该类算法在应用于无人机运动规划时必须对飞行距离、过程安全性和航路平滑度进一步优化....基于快速扩展随机树(rapidly exploring random tree,RRT)的运动规划算法,通过随机采样的方式探索未知任务空间,具有概率完备性和较高的计算效率.该类算法在应用于无人机运动规划时必须对飞行距离、过程安全性和航路平滑度进一步优化.针对这一问题,首先对威胁环境、无人机运动学性能和探测能力建模,然后根据飞行特征设计了随机采样、威胁规避、路径可跟踪性以及全局与局部平滑性等优化策略,并构建快速平滑收敛RRT(quick and smooth convergence RRT,QS-RRT),最后以此为基础分别提出了面向已知和未知任务空间的无人机运动规划算法.仿真结果表明,该算法能够在保证飞行路径收敛性、安全性及其规划效率的基础上,有效缩短飞行距离,改善航路的可跟踪性和平滑度,增强在实际飞行过程中的可操作性.此外,该算法还易于在航路优化效果和规划效率之间权衡,增强了对不同规划任务需求的适应性.展开更多
基金supported by the National Key Scientific Instrument and Equipment Development Project(Grant No.2013YQ200607)China NSF Grants(Grant No.61631020)+1 种基金Aeronautical Science Foundation of China(Grant No.2017ZC52021)Open Foundation for Graduate Innovation of NUAA(Grant No.kfjj20170405 and kfjj20180408)
文摘The wireless communication systems based on Unmanned Aerial Vehicles(UAVs) have found a wide range of applications recently. In this paper, we propose a new three-dimensional(3 D) non-stationary multiple-input multiple-output(MIMO) channel model for the communication links between the UAV and mobile terminal(MT). The new model originates the traditional geometry-based stochastic models(GBSMs) but considers the non-stationary propagation environment due to the rapid movements of the UAV, MT, and clusters. Meanwhile, the upgrade time evolving algorithms of time-variant channel parameters, i.e., the path number based on birth-death processes of clusters, path delays, path powers, and angles of arrival and departure, are developed and optimized. In addition, the statistical properties of proposed GBSM including autocorrelation function(ACF), cross-correlation function(CCF), and Doppler power spectrum density(DPSD) are investigated and analyzed. Simulation results demonstrate that our proposed model provides a good agreement on the statistical properties with the corresponding derived theoretical ones, which indicates its usefulness for the performance evaluation and validation of the UAV based communication systems.
文摘随着无人机硬件成本的降低和深度学习算法的发展,部署在无人机终端的实时目标检测算法在诸多领域展现出广泛的应用前景。然而,嵌入式设备有限的能耗和算力,以及普适性目标检测算法对于小目标特征提取不够充分等问题,制约了此类算法速度和精度的提升。文中提出了一种部署在无人机终端上的小目标实时检测算法DS⁃YOLO(Dense⁃SPP YOLO),算法基于密集连接的思想设计了全新的主干网络,并改进了空间金字塔池化模块以增强小目标的特征提取和多尺度特征复用,最后基于批归一化层(Batch⁃Normalization)的缩放因子修剪网络中不重要的通道,修剪瘦身后的算法更加适合部署在移动端。在Visdrone2019⁃DET数据集上的测试结果表明,DS⁃YOLO算法mAP(mean Average Precision)指标比SlimYOLOv3算法提升约3%,检测速度达到89 FPS(Frames Per Second),高于SlimYOLOv3的67 FPS。
基金supported in part by the National Natural Science Foundation of China(61673106)the Natural Science Foundation of Jiangsu Province(BK20171362)the Fundamental Research Funds for the Central Universities(2242019K40024)
文摘This paper proposes a new distributed formation flight protocol for unmanned aerial vehicles(UAVs)to perform coordinated circular tracking around a set of circles on a target sphere.Different from the previous results limited in bidirectional networks and disturbance-free motions,this paper handles the circular formation flight control problem with both directed network and spatiotemporal disturbance with the knowledge of its upper bound.Distinguishing from the design of a common Lyapunov fiunction for bidirectional cases,we separately design the control for the circular tracking subsystem and the formation keeping subsystem with the circular tracking error as input.Then the whole control system is regarded as a cascade connection of these two subsystems,which is proved to be stable by input-tostate stability(ISS)theory.For the purpose of encountering the external disturbance,the backstepping technology is introduced to design the control inputs of each UAV pointing to North and Down along the special sphere(say,the circular tracking control algorithm)with the help of the switching function.Meanwhile,the distributed linear consensus protocol integrated with anther switching anti-interference item is developed to construct the control input of each UAV pointing to east along the special sphere(say,the formation keeping control law)for formation keeping.The validity of the proposed control law is proved both in the rigorous theory and through numerical simulations.
文摘随着无人机软硬件技术的发展,多无人机集群自组织形成的无人机自组网(Flying Ad-Hoc networks,FANETs)受到了越来越多的来自学术界和工业界的关注,其灵活的部署和快速的反应能力使其能高效地完成多种多样的任务。而无人机自组网路由协议是提高服务质量(Quality of service,QoS)最重要的方法之一,但无人机自组网的移动性和动态性给路由协议的设计带来了严峻的挑战。传统的移动路由协议不能很好地满足无人机自组网的路由需求,因此研究者们从基于拓扑、地理和分层的角度提出了各式各样的无人机自组网路由协议,旨在克服移动性和提高网络的服务质量,并指出未来无人机自组网的路由协议可以考虑机会路由、软件定义网络(Software defined network,SDN)决策和预测驱动决策等综合提高QoS。本文主要针对无人机自组网网络特征,从不同的路由方法出发,SDN对路由协议进行总结和归纳,并对未来的研究方向进行了展望。
文摘基于快速扩展随机树(rapidly exploring random tree,RRT)的运动规划算法,通过随机采样的方式探索未知任务空间,具有概率完备性和较高的计算效率.该类算法在应用于无人机运动规划时必须对飞行距离、过程安全性和航路平滑度进一步优化.针对这一问题,首先对威胁环境、无人机运动学性能和探测能力建模,然后根据飞行特征设计了随机采样、威胁规避、路径可跟踪性以及全局与局部平滑性等优化策略,并构建快速平滑收敛RRT(quick and smooth convergence RRT,QS-RRT),最后以此为基础分别提出了面向已知和未知任务空间的无人机运动规划算法.仿真结果表明,该算法能够在保证飞行路径收敛性、安全性及其规划效率的基础上,有效缩短飞行距离,改善航路的可跟踪性和平滑度,增强在实际飞行过程中的可操作性.此外,该算法还易于在航路优化效果和规划效率之间权衡,增强了对不同规划任务需求的适应性.
