Mesh topology based clock synchronization technique for pseudolite systems

Time consistency of each node and each core is one of the kernel problems that must be addressed to promote the development of many-core cluster system that keeps the distributed system in step, and it is the basis of performance evaluation. In this study, a new model of hybrid time synchronization architecture was established to improve the precision of internal clock synchronization of a many-core cluster and the accuracy of time. First, some clock synchronization method was compared for clock synchronization model decision. Second, a high precision time acquire method based on was explored. Third, a hybrid clock synchronization and time acquire architecture on cluster system was designed to enhance the time precision and internal clock consistency. Finally, the architecture was implemented on a Zynq SoC and Epiphany many-core processor combined platform. An experiment was conducted to evaluate the precision and accuracy of this architecture. The result shows that the hybrid architecture achieved a higher level time precision and internal clock consistency than common clock synchronization method like NTP. And result demonstrates the promising application of the proposed architecture in study many-core cluster system and in supplying reliable time reference for the evaluation of distributed system performance.

The global clock synchronization problem in distributed multi-hop wireless networks is studied in this paper. A fully distributed synchronization solution based on mean field is proposed. A neighbor system and a label problem are defined to describe clock synchronization problem. The clock offset and skew are mapped to clique potential, and an energy function is established based on clique potential. Then the clock synchronization is transformed to finding the minimum of the energy function. By minimizing the energy function, clock synchronization is reached. A distributed energy minimization algorithm is also proposed. The simulation results show the proposed solution achieves high precise global clock synchronization and has the virtue of low overhead, robustness and scalability.

Clock synchronization is essential not only for precise data integration and sensor reading fusion in wireless sensor networks which consists of distributed sensors but for packet-switched networks. Over past years, clock synchronization techniques have been proposed for different environments and applications. In this paper, we propose a novel clock synchronization protocol which does not require timestamp exchanges. This proposed protocol focuses on enhancing energy efficiency and communication bandwidth efficiency, and can be realized without any additional message transmissions. This paper shows maximum likelihood estimator of clock skew and clock offset and the corresponding Cramer-Rao lower bounds under Gaussian delay model. Moreover, it is demonstrated that this protocol has the same performance to traditional timestamping techniques through simulations.

IP networks allow constructing versatile device configurations for multimedia streaming. However, the stochastic nature of the packet-switched data transmission may complicate IP-based implementations of some conventional applications such as analog wired transmission of synchronized multi-channel audio. This paper introduces a multimedia streaming system based on the synchronization of multiple playback clients as a ‘swarm’. The proposed ‘swarm synchronization’ mechanism is based on precise clock synchronization with the PTP protocol and adjusting the client-specific sampling rates according to the true playback rates of other clients. A streamlined version of the RTP protocol is employed to minimize playout delay. The proposed system is empirically evaluated in wired Ethernet LAN and in wireless IEEE 802.11g LAN. The experimental results show that in the Ethernet network the proposed streaming system is able to achieve very precise synchronization.

Existing response time analysis and optimization techniques for real-time distributed systems show that EDF schedulers feature better scheduling capabilities when a global clock reference can be used; this form of scheduling is known as global-clock EDF. In this context, precise clock synchronization is an enabling technology for future distributed real-time systems that want to leverage EDF scheduling. The IEEE 802.1AS protocol can be considered a stable technology for this purpose, as it is part of the Time-Sensitive Networking (TSN) family of standards to provide real-time communication over Ethernet. This paper presents a system architecture for applying global-clock EDF scheduling in distributed systems with soft real-time requirements. It also presents experiments to (1) assess the synchronization capabilities of the clock synchronization mechanism in the proposed architecture, (2) evaluate the performance of different scheduling deadline assignment techniques, and (3) contrast the theoretical results obtained by the schedulability analysis against those obtained through the execution of these experiments.

Execution of a task in a synchronized manner in a distributed setting, one needs the common idea of time. To accomplish this task, clock synchronization is conceptualized. Clock drifting is an intrinsic property of a clock, which necessitates the synchronization and resynchronization. A network consists of nodes, which may behave appropriately or behave badly. The mischievous node may pose difficulty in clock synchronization. We require a method to overcome the effect of mischievous nodes. Synchronization can be achieved in two ways namely accuracy and precision. In this paper, we present an accurate weighted average clock synchronization algorithm to execute a coordinated activity in a fault-tolerant manner. We use trusted clock value from GPS/GLONASS/IRNSS as a reference clock to achieve better accuracy. We also use behavior of the node to compute normalized weight in a localized manner, which lies between unit intervals. This weight assignment enables us to contain the effect of misbehavior up to some extent. This algorithm offers better accuracy and precision while tolerating mischievous nodes. The upper bound of tolerance boundary is one-third of the network size.

Execution of a task in a synchronized manner in a distributed setting, one needs the common idea of time. To accomplish this task, clock synchronization is conceptualized. Clock drifting is an intrinsic property of a clock, which necessitates the synchronization and resynchronization. A network consists of nodes, which may behave appropriately or behave badly. The mischievous node may pose difficulty in clock synchronization. We require a method to overcome the effect of mischievous nodes. Synchronization can be achieved in two ways namely accuracy and precision. In this paper, we present an accurate weighted average clock synchronization algorithm to execute a coordinated activity in a fault-tolerant manner. We use trusted clock value from GPS/GLONASS/IRNSS as a reference clock to achieve better accuracy. We also use behavior of the node to compute normalized weight in a localized manner, which lies between unit intervals. This weight assignment enables us to contain the effect of misbehavior up to some extent. This algorithm offers better accuracy and precision while tolerating mischievous nodes. The upper bound of tolerance boundary is one-third of the network size.

In order to solve the problem about the clock synchronization and high precision in the TDOA location system, a clock synchronization scheme was designed. In the article, the GPS+TCXO clock module was used as the front end of the reference clock source, and the PLL + clock buffer solution was used in the back end. The effect of the clock and ADC was analyzed on the TDOA location system; the system hardware designs were analyzed, such as the selection principle of the reference clock source and the PLL clock hardware circuit design and the parameter selection basis; the synchronous sampling method of the system clock and the register allocation process through the FPGA logic were introduced. The experimental result showed that the proposed scheme can reduce the clock jitter and improve the accuracy and stability of the input clock.

The high popularity of ultra-wideband technology for accurate indoor positioning in industrial and public spaces has led to a large amount of research in recent years. The focus has mostly been on localization accuracy in small-scale setups with a single localization zone. However, solutions designed for line-of-sight environments are not suitable for many large-scale applications. To overcome this lack of research, we propose novel concepts for precise wireless multi-hop clock synchronization and localization zone selection. By integration into a time-difference-of-arrival-based ultra-wideband localization scheme, continuous cross-spatial positioning in large-scale scenarios is enabled. Validation is carried out in an unprecedented testbed with multiple rooms. We could show that positioning accuracy in multi-room scenarios is up to three times higher when exploiting the proposed concepts compared to the initial accuracy achieved with existing approaches. In addition, we provide an open-source implementation of our real-time localization system.

Since GPS has been an effective and convenient means to transfer precise time, clock synchronization technique based on GPS is more popular and important than ever before in many auto-control fields. The theory of clock synchronization between GPS and high-precision clock built in computers is introduced in this paper; then the first-order and second-order mathematical model of clock synchronization are proposed. The results of the test with real raw data show that the first-order model has advantage over the second-order model in terms of precision and stabilization. Also, several condition parameters correlated with the clock synchronization results are analyzed with tests. An algorithm used to correct the spikes of the time-stamp data was implemented, which had been proved to be able to find and correct the spikes effectively, so it can improve the synchronization in terms of precision to some extent. In order to mitigate the errors accumulating with time, a weighted average method with the results generated by early-processed parameters and later-processed ones is given, which can obtain obvious improvement to a large extent in terms of precision.

SpaceWire fiber-optic Bus is a development of the SpaceWire ECSS-E-50-12C standard. Its transmission rate can reach 2 Gbps. However, it suffers from the problems of imprecise clock synchronization and link blocking in networks. Therefore, we analysis the problems and propose following methods. Firstly, we design clock synchronization algorithms to guarantee the precision of clock synchronization. Furthermore, we design static time distribution scheduling table which takes time-triggered traffic for real-time messages. Through simulation verification, the time precision can be within 58 ns while using clock synchronization algorithm. The use of scheduling table can effectively avoid network conflicts and reduce the delay of data transmission. The improved scheduling method can meet the real-time requirements of SpaceWire fiber-optic Bus systems, and will effectively promote the space application of fiber-optic technology.

The high-precision clock synchronization is pursued with the consideration of the balance for time-domain resource utilization, when 5G technologies are expected to carry the timing services. Firstly, a clock synchronization model is established in the case that the system exists the observed value loss. The probability distribution of the loss of the observed value is evaluated by a newly proposed delay deterministic confidence method. Then, the error boundness of the clock synchronization is investigated by the Kalman filter algorithm, and the optimization problem for 5G time-domain resource configuration is formulated with guaranteeing the precision of clock synchronization; Finally, the proposed optimization problem is solved by dueling double deep Q-learning-based Lyapunov optimization. The experimental results verify the effectiveness and superiority of the proposed method in terms of the joint optimization of clock synchronization error covariance and throughput.

Scheduling multicasts on unit-capacity trees and meshes

Clock synchronization is a critical technology in wireless sensor networks (WSNs), providing an essential foundation for data fusion, event scheduling, and collaborative operations among network nodes. However, existing clock synchronization methods face challenge of random delay in practical applications. To address these issues, this paper first proposes a pulse‐based physical layer clock synchronization method, which can achieve the synchronization directly at the physical layer, thereby avoiding the random delays introduced by the upper‐layer network. Specifically, the high‐precision phase offset estimation between the reference node and the slave nodes is first accomplished under the one‐way dissemination mechanism by leveraging the correlation property of pulse sequences. On this basis, the estimated clock information is quantized and encoded into pulse signals for transmission using pulse position modulation (PPM) technology, thereby enabling synchronization and communication between any two slave nodes at the physical layer. Simulation results demonstrate that our proposed pulse‐based method significantly improves estimation accuracy, achieving the mean square error (MSE) of approximately −45 dB in synchronization precision. Compared to the benchmark schemes, the proposed pulse‐based physical layer scheme exhibits notable advantages in system performance: it can reduce the MSE by approximately 16 dB compared to Benchmark Scheme 1 and by approximately 10 dB compared to Benchmark Scheme 2.

High speed IP communication is a killer application for 3rd generation (3G) mobile systems. Thus 3G network operators should perform extensive tests to check whether expected end-to-end performances are provided to customers under various environments. An important objective of such tests is to check whether network nodes fulfill requirements to durations of processing packets because a long duration of such processing causes performance degradation. This requires testers (persons who do tests) to precisely know how long a packet is hold by various network nodes. Without any tool's help, this task is time-consuming and error prone. Thus we propose a multi-point packet header analysis tool which extracts and records packet headers with synchronized timestamps at multiple observation points. Such recorded packet headers enable testers to calculate such holding durations. The notable feature of this tool is that it is implemented on off-the shelf hardware platforms, i.e., lap-top personal computers. The key challenges of the implementation are precise clock synchronization without any special hardware and a sophisticated header extraction algorithm without any drop.