Realization of high performance satellite onboard clock is vital for various positioning, navigation, and timing applications. For further improvement of the synchronization-based satellite time and frequency referenc...Realization of high performance satellite onboard clock is vital for various positioning, navigation, and timing applications. For further improvement of the synchronization-based satellite time and frequency references, we propose a geosynchronous(GEO) satellite virtual clock concept based on ground–satellite synchronization and present a beacon transponder structure for its implementation(scheduled for launch in 2025), which does not require atomic clocks to be mounted on the satellite. Its high performance relies only on minor modifications to the existing transponder structure of GEO satellites. We carefully model the carrier phase link and analyze the factors causing link asymmetry within the special relativity. Considering that performance of such synchronization-based satellite clocks is primarily limited by the link's random phase noise, which cannot be adequately modeled, we design a closed-loop experiment based on commercial GEO satellites for pre-evaluation. This experiment aims at extracting the zero-means random part of the ground-satellite Ku-band carrier phase via a feedback loop. Ultimately, we obtain a 1σ value of 0.633 ps(two-way link), following the Gaussian distribution. From this result, we conclude that the proposed real-time Einstein-synchronization-defined satellite virtual clock can achieve picosecond-level replication of onboard time and frequency.展开更多
Virtual time Ethemet is a multiple access protocol proposed to provide FCFS transmission service over the predominant Ethemet bus. It incorporates a novel message-rescheduling algorithm based on the virtual clock mech...Virtual time Ethemet is a multiple access protocol proposed to provide FCFS transmission service over the predominant Ethemet bus. It incorporates a novel message-rescheduling algorithm based on the virtual clock mechanism. By manipulating virtual clocks back up over a common virtual time axis and performing timely collision resolution, the algorithm guarantees the system＇s queuing strictness. The protocol is particularly modeled as a finite state machine and implemented using OPNET tools. Simulation studies prove its correctness and effectiveness.展开更多
为避免在AFDX(Avionics Full Duplex Switched Ethernet)的复杂网络结构下发生同一优先级的数据由于路径的不同而使数据到达节点的延迟时间差过大,整个网络负载不平衡,引入分组交换网络中的虚拟时钟这一概念,减小延时差,保证AFDX通信的...为避免在AFDX(Avionics Full Duplex Switched Ethernet)的复杂网络结构下发生同一优先级的数据由于路径的不同而使数据到达节点的延迟时间差过大,整个网络负载不平衡,引入分组交换网络中的虚拟时钟这一概念,减小延时差,保证AFDX通信的确定性。利用轨迹方法计算在该调度方式下的延迟时间上限,减少不必要的悲观因素,使结果更加接近真实情况,并与常用的调度方法比较,通过仿真说明其优越性。展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2021YFA1402100)。
文摘Realization of high performance satellite onboard clock is vital for various positioning, navigation, and timing applications. For further improvement of the synchronization-based satellite time and frequency references, we propose a geosynchronous(GEO) satellite virtual clock concept based on ground–satellite synchronization and present a beacon transponder structure for its implementation(scheduled for launch in 2025), which does not require atomic clocks to be mounted on the satellite. Its high performance relies only on minor modifications to the existing transponder structure of GEO satellites. We carefully model the carrier phase link and analyze the factors causing link asymmetry within the special relativity. Considering that performance of such synchronization-based satellite clocks is primarily limited by the link's random phase noise, which cannot be adequately modeled, we design a closed-loop experiment based on commercial GEO satellites for pre-evaluation. This experiment aims at extracting the zero-means random part of the ground-satellite Ku-band carrier phase via a feedback loop. Ultimately, we obtain a 1σ value of 0.633 ps(two-way link), following the Gaussian distribution. From this result, we conclude that the proposed real-time Einstein-synchronization-defined satellite virtual clock can achieve picosecond-level replication of onboard time and frequency.
基金Supported by the National Natural Science Foundation of China （No. 69984003）, 863/CIMS High Technology Foundation （No. 511-845-008） and Science and Technology Phosphor Program of Shanghai （No. 990D14012）.
文摘Virtual time Ethemet is a multiple access protocol proposed to provide FCFS transmission service over the predominant Ethemet bus. It incorporates a novel message-rescheduling algorithm based on the virtual clock mechanism. By manipulating virtual clocks back up over a common virtual time axis and performing timely collision resolution, the algorithm guarantees the system＇s queuing strictness. The protocol is particularly modeled as a finite state machine and implemented using OPNET tools. Simulation studies prove its correctness and effectiveness.
文摘为避免在AFDX(Avionics Full Duplex Switched Ethernet)的复杂网络结构下发生同一优先级的数据由于路径的不同而使数据到达节点的延迟时间差过大,整个网络负载不平衡,引入分组交换网络中的虚拟时钟这一概念,减小延时差,保证AFDX通信的确定性。利用轨迹方法计算在该调度方式下的延迟时间上限,减少不必要的悲观因素,使结果更加接近真实情况,并与常用的调度方法比较,通过仿真说明其优越性。
