In this paper, a four-dimensional coordinated path planning algorithm for multiple UAVs is proposed, in which time variable is taken into account for each UAV as well as collision free and obstacle avoidance. A Spatia...In this paper, a four-dimensional coordinated path planning algorithm for multiple UAVs is proposed, in which time variable is taken into account for each UAV as well as collision free and obstacle avoidance. A Spatial Refined Voting Mechanism(SRVM) is designed for standard Particle Swarm Optimization(PSO) to overcome the defects of local optimal and slow convergence.For each generation candidate particle positions are recorded and an adaptive cube is formed with own adaptive side length to indicate occupied regions. Then space voting begins and is sorted based on voting results, whose centers with bigger voting counts are seen as sub-optimal positions. The average of all particles of corresponding dimensions are calculated as the refined solutions. A time coordination method is developed by generating specified candidate paths for every UAV, making them arrive the same destination with the same time consumption. A spatial-temporal collision avoidance technique is introduced to make collision free. Distance to destination is constructed to improve the searching accuracy and velocity of particles. In addition, the objective function is redesigned by considering the obstacle and threat avoidance, Estimated Time of Arrival(ETA), separation maintenance and UAV self-constraints. Experimental results prove the effectiveness and efficiency of the algorithm.展开更多
为研究自由飞行条件下给定间距的飞机碰撞风险评估问题,通过分析自由飞行下的飞机碰撞过程,分解碰撞事故发生过程,将与碰撞密切相关的风险因素或过程事件视为节点,并确定节点之间的关系,建立自由飞行状态下基于贝叶斯网络的碰撞风险模型...为研究自由飞行条件下给定间距的飞机碰撞风险评估问题,通过分析自由飞行下的飞机碰撞过程,分解碰撞事故发生过程,将与碰撞密切相关的风险因素或过程事件视为节点,并确定节点之间的关系,建立自由飞行状态下基于贝叶斯网络的碰撞风险模型;利用传统的位置误差模型,以及最大期望(EM)算法,求解节点事件的先验概率,导入贝叶斯网络模型,求得2架飞机碰撞风险。算例结果表明,用该模型计算出的碰撞风险与实际情况相符,算例中飞机之间保持8 n mile的间距是安全的;利用该模型可在满足安全目标水平条件下缩小最小安全间距,提高空域利用率。展开更多
In this paper,a contention-based connection-free transmission scheme is proposed to meet the stringent requirements of ultra-reliability and low-latency for critical machine-type communication(cMTC).To improve reliabi...In this paper,a contention-based connection-free transmission scheme is proposed to meet the stringent requirements of ultra-reliability and low-latency for critical machine-type communication(cMTC).To improve reliability,we design multiple independent sparse orthogonal pilots(MISOP)to significantly reduce the probability of pilot collision to the order of 10^(−5).Besides,the advancements of massive MIMO(mMIMO)are exploited to further enhance the reliability.To achieve low latency,connection-free slot-based one-shot transmission without retransmissions is adopted.On the receiver side,single round of multi-user detection(MUD)without interference cancellation(IC)can reduce the processing delay.The imprecise synchronization between cMTC device and the gNB in connection-free transmission,e.g.,time and frequency offsets,are also considered.The simulation results shows that the proposed scheme can well satisfy the ambitious requirements of cMTC,and has the potential applications in supporting massive cMTC devices in 6G.展开更多
Disturbance-Free Payload(DFP)spacecraft can meet the requirements of ultra-high attitude pointing accuracy and stability for future space missions.However,as the main control actuators of DFP spacecraft,Linear Non-Con...Disturbance-Free Payload(DFP)spacecraft can meet the requirements of ultra-high attitude pointing accuracy and stability for future space missions.However,as the main control actuators of DFP spacecraft,Linear Non-Contact Lorentz Actuators(LNCLAs)have control output problems with six-degree-of-freedom coupling and nonlinear effects,which will affect the attitude control performance of DFP spacecraft.To solve this problem,a novel concept for Non-Contact Annular Electromagnetic Stabilized Satellite Platform(NCAESSP)is proposed in this study.The concept is centered on replacing the LNCLAs with a non-contact annular electromagnetic actuator to solve the two problems mentioned above.Furthermore,for the different control requirements of the payload module and the support module of the NCAESSP,a high-precision attitude controller based on the robust model matching method and a dual quaternion-based adaptive sliding mode controller are proposed.Additionally,the simulation results verify the feasibility and effectiveness of the proposed approach.展开更多
The low earth orbit(LEO) satellite system provides a promising solution for the global coverage of Internet of Things(IoT) services.Confronted with the sporadic uplink transmission from massive IoT terminals, this wor...The low earth orbit(LEO) satellite system provides a promising solution for the global coverage of Internet of Things(IoT) services.Confronted with the sporadic uplink transmission from massive IoT terminals, this work investigates the grant-free access scheme and resource allocation algorithm for the beam-hopping(BH) based LEO satellite systems.To improve the packet success rate, the time slots are pre-allocated to each cell according to the number of terrestrial terminals and the probability of packet arrival.When the packets arrive, the terrestrial terminals perform contention-free or contention-based grant-free access with packet repetition in the time slots allocated to their cells.The analytical expression of the packet collision probability for the grant-free access scheme is derived to provide reference for the resource allocation.To reduce the computational complexity, a heuristic resource allocation algorithm is proposed to minimize the maximum cell packet collision probability in the system.Simulation results show that the proposed resource allocation scheme achieves lower packet collision probability and higher resource utilization ratio when compared with the uniform resource allocation scheme.展开更多
基金co-supported by China Scholarship Council (No. 201604000003)the National Natural Science Foundation of China (Nos. U1433203, U1533119 and L142200032)the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (No. 61221061)
文摘In this paper, a four-dimensional coordinated path planning algorithm for multiple UAVs is proposed, in which time variable is taken into account for each UAV as well as collision free and obstacle avoidance. A Spatial Refined Voting Mechanism(SRVM) is designed for standard Particle Swarm Optimization(PSO) to overcome the defects of local optimal and slow convergence.For each generation candidate particle positions are recorded and an adaptive cube is formed with own adaptive side length to indicate occupied regions. Then space voting begins and is sorted based on voting results, whose centers with bigger voting counts are seen as sub-optimal positions. The average of all particles of corresponding dimensions are calculated as the refined solutions. A time coordination method is developed by generating specified candidate paths for every UAV, making them arrive the same destination with the same time consumption. A spatial-temporal collision avoidance technique is introduced to make collision free. Distance to destination is constructed to improve the searching accuracy and velocity of particles. In addition, the objective function is redesigned by considering the obstacle and threat avoidance, Estimated Time of Arrival(ETA), separation maintenance and UAV self-constraints. Experimental results prove the effectiveness and efficiency of the algorithm.
文摘为研究自由飞行条件下给定间距的飞机碰撞风险评估问题,通过分析自由飞行下的飞机碰撞过程,分解碰撞事故发生过程,将与碰撞密切相关的风险因素或过程事件视为节点,并确定节点之间的关系,建立自由飞行状态下基于贝叶斯网络的碰撞风险模型;利用传统的位置误差模型,以及最大期望(EM)算法,求解节点事件的先验概率,导入贝叶斯网络模型,求得2架飞机碰撞风险。算例结果表明,用该模型计算出的碰撞风险与实际情况相符,算例中飞机之间保持8 n mile的间距是安全的;利用该模型可在满足安全目标水平条件下缩小最小安全间距,提高空域利用率。
基金supported by the Key-Area Research and Development Program of Guangdong Province under Grant 2019B010157002the National Key Research and Development Program of China under grant 2020YFB1807202.
文摘In this paper,a contention-based connection-free transmission scheme is proposed to meet the stringent requirements of ultra-reliability and low-latency for critical machine-type communication(cMTC).To improve reliability,we design multiple independent sparse orthogonal pilots(MISOP)to significantly reduce the probability of pilot collision to the order of 10^(−5).Besides,the advancements of massive MIMO(mMIMO)are exploited to further enhance the reliability.To achieve low latency,connection-free slot-based one-shot transmission without retransmissions is adopted.On the receiver side,single round of multi-user detection(MUD)without interference cancellation(IC)can reduce the processing delay.The imprecise synchronization between cMTC device and the gNB in connection-free transmission,e.g.,time and frequency offsets,are also considered.The simulation results shows that the proposed scheme can well satisfy the ambitious requirements of cMTC,and has the potential applications in supporting massive cMTC devices in 6G.
基金co-supported by the National Natural Science Foundation of China(No.12172168)。
文摘Disturbance-Free Payload(DFP)spacecraft can meet the requirements of ultra-high attitude pointing accuracy and stability for future space missions.However,as the main control actuators of DFP spacecraft,Linear Non-Contact Lorentz Actuators(LNCLAs)have control output problems with six-degree-of-freedom coupling and nonlinear effects,which will affect the attitude control performance of DFP spacecraft.To solve this problem,a novel concept for Non-Contact Annular Electromagnetic Stabilized Satellite Platform(NCAESSP)is proposed in this study.The concept is centered on replacing the LNCLAs with a non-contact annular electromagnetic actuator to solve the two problems mentioned above.Furthermore,for the different control requirements of the payload module and the support module of the NCAESSP,a high-precision attitude controller based on the robust model matching method and a dual quaternion-based adaptive sliding mode controller are proposed.Additionally,the simulation results verify the feasibility and effectiveness of the proposed approach.
基金Supported by the Science and Technology Innovation Action Plan of Shanghai (No. 21DZ2200200)the Science and Technology Cooperation Funding of Chengdu and CASthe National Key Research and Development Program of China (No. 2019YFB1803101)。
文摘The low earth orbit(LEO) satellite system provides a promising solution for the global coverage of Internet of Things(IoT) services.Confronted with the sporadic uplink transmission from massive IoT terminals, this work investigates the grant-free access scheme and resource allocation algorithm for the beam-hopping(BH) based LEO satellite systems.To improve the packet success rate, the time slots are pre-allocated to each cell according to the number of terrestrial terminals and the probability of packet arrival.When the packets arrive, the terrestrial terminals perform contention-free or contention-based grant-free access with packet repetition in the time slots allocated to their cells.The analytical expression of the packet collision probability for the grant-free access scheme is derived to provide reference for the resource allocation.To reduce the computational complexity, a heuristic resource allocation algorithm is proposed to minimize the maximum cell packet collision probability in the system.Simulation results show that the proposed resource allocation scheme achieves lower packet collision probability and higher resource utilization ratio when compared with the uniform resource allocation scheme.
