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Marine controlled source electromagnetic (MCSEM) method is widely used to reveal the electrical structure of shallow media below the seafloor. It is an indispensable geophysical means in the exploration of marine oil and gas exploration, natural gas hydrates and seafloor geological structures. The transmitter and receiver in electromagnetic detection equipment need to maintain a high temporal consistency, usually using high-stability pulse-per-second (PPS) generated by GPS or BeiDou navigation modules as a synchronization signal. Coaxial cable is a widely used tow cable, so it is necessary to design a clock synchronization method of marine controlled source electromagnetic transmitter using coaxial cable. This paper proposes a method for synchronizing the internal clocks of the transmitter with PPS using ship-borne power supply when coaxial cable is used as tow cable. In this method, the ship-borne high-power supply outputs a high-voltage AC signal that is synchronized with the 400 Hz signal output from GPS; the coaxial cable transmits AC high power electrical energy and control commands; the AC signal transmitted via the coaxial cable is converted into a stable and continuous 1 Hz signal by step-down, waveform shaping and frequency division for synchronizing the internal time pulses of the transmitter. The test result shows that the 1 Hz signal obtained by this method has a deviation of about 504 ns relative to the PPS. This deviation meets the need of MCSEM transmitter for clock synchronization. [ABSTRACT FROM AUTHOR]

Clock synchronization is critically important in positioning, navigation and timing systems. While its performance has been intensively studied in a wide range of disciplines, much less is known for the fundamental thermodynamics of clock synchronization‒what limits the precision and how to optimize the energy cost for clock synchronization. Here, we report the first experimental investigation of two stochastic autonomous clocks synchronization, unveiling the thermodynamic relation between the entropy cost and clock synchronization in an open cavity optomechanical system. Two interacting clocks are synchronized spontaneously owing to the disparate decay rates of hybrid modes by engineering the controllable cavity-mediated dissipative coupling. The measured dependence of the degree of synchronization on the overall entropy cost exhibits an unexpected non-monotonic characteristic, while the relation between the degree of synchronization and the entropy cost for the synchronization is monotonically decreasing. The investigation of transient dynamics of clock synchronization exposes a trade-off between energy and time consumption. Our results demonstrate the possibility of clock synchronization in an effective linear system, reveal the fundamental relation between clock synchronization and thermodynamics, and have a great potential for precision measurements, distributed quantum networks, and biological science. [ABSTRACT FROM AUTHOR]

Clock synchronization is one of the popular research topics in Distributed Measurement and Control Systems (DMCSs). In most industrial fields, such as Smart Grid and Flight Test, the highest requirement for synchronization accuracy is 1 μs. IEEE 1588 Precision Time Protocol-2008 (PTPv2) can theoretically achieve sub-microsecond accuracy, but it relies on the assumption that the forward and backward delays of PTP packets are symmetrical. In practice, PTP packets will experience random queue delays in switches, making the above assumption challenging to satisfy and causing poor synchronization accuracy. Although using switches supporting the Transparent Clock (TC) can improve synchronization accuracy, these dedicated switches are generally expensive. This paper designs a PTP clock servo for compensating Queue-Induced Delay Asymmetry (QIDA), which can be implemented based on ordinary switches. Its main algorithm comprises a minimum window filter with drift compensation and a fuzzy proportional–integral (PI) controller. We construct a low-cost hardware platform (the cost of each node is within USD 10) to test the performance of the clock servo. In a 100 Mbps network with background (BG) traffic of less than 70 Mbps, the maximum absolute time error (max |TE|) does not exceed 0.35 μs, and the convergence time is about half a minute. The accuracy is improved hundreds of times compared with other existing clock servos. [ABSTRACT FROM AUTHOR]

The Mössbauer rotor effect recently gained a renewed interest due to the discovery and explanation of an additional effect of clock synchronization which has been missed for about 50 years, i.e. starting from a famous book of Pauli, till some more recent experimental analyses. The theoretical explanation of such an additional effect is due to some recent papers in the general relativistic framework. Here, we show that the additional effect of clock synchronization can be calculated in another way via the third postulate of relativity. [ABSTRACT FROM AUTHOR]

The Lorentz transformations transform the coordinates in a frame at rest and those in a frame moving with a constant velocity with respect to the rest frame. We analyze the Lorentz transformations using a world line diagram and simple algebra, obtaining some astonishing results. We use two examples to demonstrate that the Lorentz transformations contradict reality and are invalid. Employing the proper definition of simultaneity, we formulate the coordinate transformations between the two frames and obtain the Galileo transformations. Additionally, we suppose A, M, and B are points on the x-axis moving in the x direction and the distances AM = MB. Source S rests on the x-axis and emits signals when S and M coincide. The emitted signal reaches A earlier than it reaches B. In other words, A, which is approaching the signal source, receives the signal earlier than B, which is moving away from the signal source. [ABSTRACT FROM AUTHOR]

In order to improve clock synchronization precision of the power distribution field network, a power distribution field network with high‐speed power line broadband carrier communication is designed, and a step‐by‐step precision clock synchronization strategy is developed based on modified timing‐sync protocol for sensor networks. In the strategy, the clock of the central node is calibrated in real‐time as the master clock of the field network by the communication master station through the long‐distance communication network, the time and frequency deviations of the clocks of each node in the network are accurately monitored using the broadcast mechanism and the network time base of the carrier communication, and the clock frequency is gradually amended by re‐calibrating the clock temperature compensation coefficient of the node so that the clock of the node is synchronized step‐by‐step within a clock synchronization cycle. The clock synchronization performances of the field network are tested in the laboratory and jobsite, and test results show that the clock synchronization accuracy of the field network is within ± 0.23 s/24 h, which is 28% higher than that of the power distribution field network based on narrowband power line carrier, and these phenomena of time gap or time repetition are avoided in the clock synchronization process. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

The importance of synchronization of spatially separated clocks in observing event coordinates cannot be overemphasized. We illustrate this with a real-world example. The results show the dependence of both length contraction and time dilation on the adopted synchronization convention. It is illustrated that a change in synchronization convention completely alters the appearance of the physical world. This is to be viewed in the context of the stated position in physics that synchronization of spatially separated clocks in any inertial frame depended on the adoption of a convention for its resolution. The preferred method of synchronization of spatially separated clocks is the standard convention recommended by the theory of relativity; however, it still remains a convention. [ABSTRACT FROM AUTHOR]

The rapid development of multi-satellite formations requires inter-satellite radio frequency (RF) measurement to be both precise and scalable. The navigation estimation of multi-satellite formations using a unified time reference demands the simultaneous RF measurement of the inter-satellite range and time difference. However, high-precision inter-satellite RF ranging and time difference measurements are investigated separately in existing studies. Different from the conventional two-way ranging (TWR) method, which is limited by its reliance on a high-performance atomic clock and navigation ephemeris, asymmetric double-sided two-way ranging (ADS-TWR)-based inter-satellite measurement schemes can eliminate such reliance while ensuring measurement precision and scalability. However, ADS-TWR was originally proposed for ranging-only applications. In this study, by fully exploiting the time-division non-coherent measurement characteristic of ADS-TWR, a joint RF measurement method is proposed to obtain the inter-satellite range and time difference simultaneously. Moreover, a multi-satellite clock synchronization scheme is proposed based on the joint measurement method. The experimental results show that when inter-satellite ranges are hundreds of kilometers, the joint measurement system has a centimeter-level accuracy for ranging and a hundred-picosecond-level accuracy for time difference measurement, and the maximum clock synchronization error was only about 1 ns. [ABSTRACT FROM AUTHOR]

In view of the problem of clock Byzantine failure and node communication link loss failure in the non-master clock synchronization in the distributed real-time system, a fault-tolerant clock synchronization algorithm based on gray prediction is proposed in this study. The proposed algorithm is based on the LL model of the broadcast communication network, and uses the gray prediction method of GM（1,1） to analyze the correction deviation value of the previous round, so as to predict the correction deviation value of the node in the failure order, and then obtain the correction value through calculation. The experimental results show that the gray prediction algorithm proposed in this study can tolerate Byzantine faults, and at the same time, it can overcome the problems caused by the failure of node communication link loss, and improve the universality of the FTA algorithm. The data comparison analysis results show that the clock synchronization precision of this algorithm is improved by 24.3% when compared with Original algorithm. At the same time, the algorithm complexity has certain advantages when compared with other algorithms. [ABSTRACT FROM AUTHOR]

The information theoretically secure Kirchhoff-law-Johnson-noise (KLJN) key exchange scheme, similarly to quantum key distribution (QKD), is also potentially vulnerable against clock attacks, where Eve takes over the control of clock synchronization in the channel. This short note aims to introduce a time synchronization protocol scheme for Alice and Bob, which is resistant against arbitrary time delay attacks, both symmetric and asymmetric ones. We propose and explore various ways of clock synchronization for the KLJN system and propose an ultimate protocol that preserves time and hardware integrity under arbitrary attacks. [ABSTRACT FROM AUTHOR]

Clock synchronization provides fundamental timing reference for various services in the Internet of Things. Unlike centralized synchronization algorithm, which relies heavily on the synchronization routing and brings about error accumulation consequently, the distributed synchronization algorithm achieves clock synchronization through time message exchange and calculation among adjacent nodes, hence the error accumulation can be greatly eliminated. However, the convergence speed of existing distributed synchronization algorithms is generally slow, and network topology information is seldom utilized to improve the convergence speed, which may cause additional energy consumption, especially in resource-constrained scenarios. To improve the convergence speed of distributed clock synchronization, a consensus tracking-based clock synchronization (CTCS) algorithm is proposed in this paper. By analyzing the synchronization process in the state space framework, the convergence acceleration term is designed to optimize the eigenvalue distribution of synchronization error matrix, hence the convergence speed can be greatly improved. To be suitable for clock synchronization in the dynamic network, a reference clock input term is designed in the clock update formula, which eliminates the oscillation of synchronized clocks triggered by synchronization of newly joined nodes. To prove the convergence of CTCS, an in-depth analysis of the algorithm is conducted. Both simulation and experimental results validate the effectiveness of CTCS in comparison with other solutions. [ABSTRACT FROM AUTHOR]

Time triggered communication provides fault tolerance and determinism in a distributed dependable real time systems. These systems crucially depend on fault tolerant clock synchronization. The article presents simulation of fault tolerant averaging algorithm for clock synchronization and it's modification for improved convergence. We present the simulation results of synchronization algorithm to verify fault tolerance and convergence to a single time base. By modification, we show how a two node system can also be synchronized eliminating the criteria of minimum three nodes. This article also reports a custom time triggered protocol named as deterministic fault tolerant communication protocol particularly suitable for mission critical applications or safety-critical control applications such as in automotive “by-wire” and aerospace systems. The article also presents a different approach for membership service which is based on majority voting and can be used in systems based on time triggered architecture. [ABSTRACT FROM AUTHOR]

TADA is a unique toolkit designed to foster the use and implementation of approximate distributed agreement primitives. Developed in Java, TADA provides ready-to-use implementations of several approximate agreement algorithms, as well as the tools to enable programmers/researchers to easily implement further protocols: A template that enables new protocol implementations to be created by simply changing specific functions; and high-level abstractions for communication and concurrency control. As an example, the toolkit includes a ready-to-use implementation for clock synchronisation between distributed processes. Further use cases can include sensor input stabilisation and distributed machine learning, or other instances of distributed agreement where network synchrony cannot be assumed, byzantine fault tolerance may be required and a bounded divergence in decision values can be tolerated. [ABSTRACT FROM AUTHOR]

This work proposes a distributed gradient descent estimator for clock synchronization in wireless sensor networks and provides an analysis of its convergence behavior under practical assumptions. Based on the clock rigidity theory proposed in our previous work, we first establish the exponential convergence of the estimator and characterize its convergence rate. We then study a non-generic configuration with a commonly adopted broadcast communication scheme and show that practical inter-node distances and a broadcast scheme in a wireless sensor network cause very slow convergence in network clock synchronization. A simple modification of the broadcast scheme is proposed and proved to be able to improve the estimator's convergence rate. Simulation examples are provided to support the analysis. [ABSTRACT FROM AUTHOR]

The Mössbauer rotor effect recently gained a renewed interest due to the discovery and explanation of an additional effect of clock synchronization which has been missed for about 50 years, i.e. starting from a famous book of Pauli, till some recent experimental analyses. The theoretical explanation of such an additional effect is due to some recent papers in both the general relativistic and the special relativistic frameworks. In the first case (general relativistic framework) the key point of the approach is the Einstein’s equivalence principle (EEP), which, in the words of the same Einstein, enables “the point of view to interpret the rotating system K’ as at rest, and the centrifugal field as a gravitational field”. In this paper, we analyse both the history of the Mössbauer rotor effect and its interpretation from the point of view of Einstein’s general theory of relativity (GTR) by adding some new insight. In particular, it will be shown that, if on one hand the “traditional” effect of redshift has a strong analogy with the gravitational redshift, on the other hand the additional effect of clock synchronization has an intriguing analogy with the cosmological redshift. Finally, we show that a recent claim in the literature that the second effect of clock synchronization does not exist is not correct. [ABSTRACT FROM AUTHOR]

Inspired by excellent precision of carrier phase positioning, this paper presents a new carrier phase positioning technique for 5G new radio cellular networks with a focus on clock synchronization and integer ambiguity resolution. A carrier-phase based clock offset estimation method is first proposed to achieve precise clock synchronization among base stations, and proved to achieve the Cramér–Rao Lower Bound (CRLB) asymptotically. A fusion method is developed to fuse the estimated positions of a mobile station (MS) based on time-difference-of-arrival, with the estimated position changes based on the temporal changes of carrier phase measurements. While circumventing the integer ambiguities of the carrier phase measurements, the fusion method provides quality interim estimates of the MS positions, at which the measurements can be linearized to resolve the integer ambiguities. As a result, precise MS positions can be obtained based on the disambiguated carrier phase measurements. Numerical simulations show that the proposed carrier phase positioning can achieve a centimeter-level accuracy in wireless cellular networks. [ABSTRACT FROM AUTHOR]

Clock synchronization is crucial for applications in wireless sensor networks, such as event scheduling and data fusion. In practical wireless networks, environmental changes cause the oscillator to be imperfect. Thus, it is necessary to track the nonlinear varying clock dynamically. In this paper, we propose a timestamp-free clock skew (frequency difference) and offset (time difference) joint tracking algorithm based on extended Kalman filter (EKF), which can be embedded into the general network data flow to achieve long-term synchronization without additional communication overhead. To further improve energy efficiency of clock synchronization, this paper develops an EKF clock skew tracking algorithm for silent nodes in receiver-only synchronization. For the situation that silent node overhears synchronization information from multiple active nodes, we present multi-information timestamp-free synchronization and multi-observation clock skew fusion scheme for silent nodes. Simulation results show the effectiveness of the proposed tracking algorithms. [ABSTRACT FROM AUTHOR]

The quantum positioning system (QPS) takes advantage of the entanglement property of the quantum system itself, and it is possible to breakthrough the limitation of the positioning accuracy due to signal bandwidth and power limitation in classical radio-based global positioning system (GPS), and improve the positioning performance. In this paper, a comprehensive survey of the research status of QPS and its several key components are presented, including the quantum entanglement states preparation, the quantum satellite technique, the optical signal acquisition, tracking and pointing (ATP) system, and the quantum positioning and clock synchronization technique. We also discuss the current challenges and future research directions at the end of the paper. [ABSTRACT FROM AUTHOR]

The EDF (Earliest Deadline First) scheduling policy can take advantage of the existence of a synchronization clock mechanism to reach higher utilizations in distributed real-time systems, as indicated by theoretical research. In this work, we give the first steps to enable the usage of EDF and a global clock in a distributed system. To this end, our proposal relies on Linux to provide the global clock and on a Real-Time Operating System (RTOS) to provide the global EDF policy. The objective is the evaluation of global EDF to verify to what extent the theoretical results are met. [ABSTRACT FROM AUTHOR]

The time resolution of active pixel sensors whose timestamp mechanism is based on time-to-digital converters is critically linked to the accuracy in the distribution of the master clock signal that latches the timestamp values across the detector. The clock distribution network (CDN) that delivers the master clock signal must compensate process–voltage–temperature variations to reduce static time errors (skew) and minimize the power supply bounce to prevent dynamic time errors (jitter). To achieve sub-100-ps time resolution within pixel detectors and thus enable a step forward in multiple imaging applications, the network latencies must be adjusted in steps well below that value. Power consumption must be kept as low as possible. In this work, a self-regulated CDN that fulfills these requirements is presented for the FastICpix single-photon detector aiming at a 65-nm process. A 40-MHz master clock is distributed to 64 × 64 pixels over an area of 2.4 × 2.4 cm2 using digital delay-locked loops, achieving clock leaf skew below 20 ps with a power consumption of 26 mW. Guidelines are provided to adapt the system to arbitrary chip area and pixel pitch values, yielding a versatile design with very fine time resolution. [ABSTRACT FROM AUTHOR]

The clock synchronization is considered as a key technology in the time-sensitive networking (TSN) of 5G fronthaul. This paper proposes a clock synchronization enhancement method to optimize the link delays, in order to improve synchronization accuracy. First, all the synchronization dates are filtered twice to get the good calculation results in the processor, and then FPGA adjust the timer on the slave side to complete clock synchronization. This method is implemented by Xilinx Zynq UltraScale+ MPSoC (multiprocessor system-on-chip), using FPGA+ARM software and hardware co-design platform. The master and slave output Pulse Per-Second signals (PPS). The synchronization accuracy was evaluated by measuring the time offset between PPS signals. Contraposing the TSN, this paper compares the performance of the proposed scheme with some previous methods to show the efficacy of the proposed work. The results show that the slave clock of proposed method is synchronized with the master clock, leading to better robustness and significant improvement in accuracy, with time offset within the range of 40 nanoseconds. This method can be applied to the time synchronization of the 5G open fronthaul network and meets some special service needs in 5G communication. [ABSTRACT FROM AUTHOR]

This paper proposes a novel three-dimensional guidance method based on clock synchronization algorithms, creatively solving the problems of randomized change, non-connection and even communication outage caused by packet loss and delay in the co-guidance of loitering munitions. The proposed method is characterized by fast convergence of the aspect angle rate in the longitudinal plane, and the attack time constrains in the lateral plane. Normal accelerations on the two sub-planes are thereby calculated, so as to control the munitions' co-attack. Simulation experiments show that the proposed method can ensure reliable and stable asymptotic agreement of attack time expectation for the cooperative multiple munitions under the switching and noisy networks. [ABSTRACT FROM AUTHOR]

Spatiotemporal information plays crucial roles in a multiagent system (MAS). However, for a highly dynamic and dense MAS in unknown environments, estimating its spatiotemporal states is a difficult problem. In this article, we present BLAS—a wireless broadcast relative localization and clock synchronization system to address these challenges. Our BLAS system exploits a broadcast architecture, under which a MAS is categorized into parent agents that broadcast wireless packets and child agents that are passive receivers, to reduce the number of required packets among agents for relative localization and clock synchronization. We first propose an asynchronous broadcasting and passively receiving protocol. The protocol schedules the broadcast of parent agents using a distributed time division multiple access scheme and delivers interagent information used for joint relative localization and clock synchronization. We then present distributed state estimation approaches in parent and child agents that utilize the broadcast interagent information for joint estimation of spatiotemporal states. The simulations and real-world experiments based on ultra-wideband illustrate that our proposed BLAS can not only enable accurate, high-frequency, and real-time estimation of relative position and clock parameters but also support theoretically an unlimited number of agents. [ABSTRACT FROM AUTHOR]

Clock synchronization is critical for synchronous pseudolite systems. Wireless synchronization methods are desirable for their flexibility in system deployment, and most of them build a tree topology of time information flow based on master‐slave synchronization between pseudolites. A slave pseudolite can receive signals broadcast by multiple pseudolites; however, existing methods usually utilize one signal and ignore others in which the time information could improve synchronization precision and reliability. We present a mesh topology based clock synchronization (MTCS) technique by utilizing all received signals. MTCS builds a mesh topology of time information flow, which can keep synchronization in case of link interruption or pseudolite failure. The coupling relationship of slave clocks is derived, and the influence of measurement biases is analyzed. As shown by both analysis and simulations, MTCS has better clock synchronization precision. When link interruption or pseudolite failures occur, MTCS is more robust than tree topology based methods. [ABSTRACT FROM AUTHOR]

IEEE 1588, built on the classical two-way message exchange scheme, is a popular clock synchronization protocol for packet-switched networks. Due to the presence of random queuing delays in a packet-switched network, the joint recovery of the clock skew and offset from the timestamps of the exchanged synchronization packets can be treated as a statistical estimation problem. In this paper, we address the problem of clock skew and offset estimation for IEEE 1588 in the presence of possible unknown asymmetries between the deterministic path delays of the forward master-to-slave path and reverse slave-to-master path, which can result from incorrect modeling or cyber-attacks. First, we develop lower bounds on the mean square estimation error for a clock skew and offset estimation scheme for IEEE 1588 assuming the availability of multiple master-slave communication paths and complete knowledge of the probability density functions (pdf) describing the random queuing delays. Approximating the pdf of the random queuing delays by a mixture of Gaussian random variables, we then present a robust iterative clock skew and offset estimation scheme that employs the space alternating generalized expectation-maximization (SAGE) algorithm for learning all the unknown parameters. Numerical results indicate that the developed robust scheme exhibits a mean square estimation error close to the lower bounds. [ABSTRACT FROM AUTHOR]

Precise distributed clock synchronization is important for Time-Triggered Ethernet (TTEthernet) in which fail-arbitrary synchronization failure cannot be treated by existed protocols unless every synchronization node is equipped with a dedicated clock monitoring. A novel method was presented to detect arbitrary synchronization failure by some application-level routines which make distributed decisions mainly by monitoring the protocol control frames (PCFs). An arbitrary failure node can be exactly detected and located by the routine resided on each of the Compression Masters based on the concerned accusation messages sent from Synchronization Masters or Synchronization Clients. The proposed method can make up the weak points on the detection of the arbitrary failure node of the existed fault-tolerant synchronization mechanism and enhance the synchronization node to resist the arbitrary failure for TTEthernet. By our SAL-based model checking, this method had been formally verified to have a fail-arbitrary detection capacity even in a standard integration configuration. Simulations imply that the quality of the whole clock synchronization is effectively improved after the failure node has been isolated. [ABSTRACT FROM AUTHOR]

In this paper, we present an explanation of several fundamental tests of special relativity from the perspective of the frame co-moving with a rotating observer. The solution is of great interest for real-time applications because Earth-bound laboratories are inertial only in approximation. We present the derivation of the Sagnac, Michelson–Morley, Kennedy–Thorndike and the Hammar experiments as viewed from the Earth-bound uniformly rotating frame or, as in the case of the Mossbauer rotor experiments, from the perspective of the rotating device. An entire section is dedicated to length/time measurement and to clock synchronization and another one to the Doppler effect and aberration on uniformly rotating platforms. This paper brings new information in the following areas: – new approach for clock synchronization on a rotating platform – new approach for length measurement in rotating frames – new explanation of the Doppler effect and of the Mossbauer rotor experiment – new explanation of the Kennedy–Thorndike experiment. The main thrust of this paper is to give a consistent explanation of various tests of special relativity as judged from the perspective of the rotating frame of the experimental setup. In addition, we correct certain misconceptions relative to clock synchronization and length measurement that have survived a long time in the specialty literature. A special chapter is dedicated to the derivation of the Doppler effect and of aberration in rotating frames. It is shown that such derivation is far from being trivial. [ABSTRACT FROM AUTHOR]

The packet transmission among sensor nodes mainly focuses on clock synchronization. This paper proposes a protocol for efficient clock synchronization in energy based approaches to overcome the clock synchronization invariances and communication overheads. Clustering technique helps to design the sensor network architectures and broadcast the sensor nodes. The existing Mobility Zonal Based Stable Election Protocol (Mob-ZSEP) protocol identifies best path using clustering approach. The selected best path using Mob-ZSEP routing protocol will be utilized by proposed clock synchronization protocols. This research paper proposes two novel protocols: Energy based Proportional Integral and Least Common Multiple (EPILCM) and Weighted based Least Common Multiple (WLCM). EPILCM protocol hybrids two methods such as Energy based Proportional Integral (EPI) and Energy based Least Common Multiple (ELCM). The proposed EPILCM protocol is used for clock synchronization using energy based approach which reduces energy consumption, synchronization error, propagation delay, clock inaccuracy and communication overhead. WLCM protocol performs transmission based on the weight of the packet in sensor networks. The EPILCM, WLCM protocols are compared and the simulation results shows that EPILCM protocol outperforms WLCM protocol. [ABSTRACT FROM AUTHOR]

The modular multilevel matrix converter (M3C) is a direct ac/ac topology and is promising in the medium-voltage high-power application. However, the current M3C prototypes mainly adopt the centralized control structure that may hinder its modularity and flexibility. Based on the new distributed control architecture, the corresponding design principles for the M3C are proposed to realize both the distribution of control tasks and improve the expandability. And in order to reduce the dependence of a real-time communication network, a time-dimension decoupling strategy based on a voltage decoupling and current coupling control algorithm is employed, in which the voltage loop is divided into the input side, output side, and inner circulating decoupling models that are executed in the system controller, while the real-time current loop is established on the coupling abc coordinate frame in each local controller. In order to reduce the influence of communication delay, a novel scheme to replace the direct ac current reference with dc power value and double synchronization phase information is adopted. The controller parameters of the current loop are also designed carefully after frequency decomposition. Finally, an experimental prototype is constructed to verify the feasibility of the proposed control scheme after a series of tests in steady-state and dynamic operations. [ABSTRACT FROM AUTHOR]

Laser frequency coupling noise due to unbalanced arm lengths is the dominant noise source for space-based gravitational wave detection. Time-delay interferometry is a proposed technique to eliminate the coupling noise by constructing a virtual equal-arm-length interferometer, where the real-time information of both absolute inter-satellite distance and clock synchronization is required. Inter-satellite laser ranging based on pseudo-random noise (PRN) sequence modulation has become the main technical means for extraction of the inter-satellite distance and clock difference information. This paper shows a bi-directional laser ranging scheme based on PRN code modulation and experimentally demonstrates its function by using an optical fiber of 10 km long. The measured results of the transmission time duration and the clock difference are compared with independent methods of pulse laser ranging and 1PPS signal measurement, respectively, both of which coincide well. It is also evaluated that the laser ranging accuracy is 1.2 m, and the clock synchronization accuracy reaches 6.7 ns, applicable to TianQin with the preliminarily determined requirement of 3 m and 10 ns. This laser ranging scheme can be applied to satellite navigation and space-based gravitational wave detection. [ABSTRACT FROM AUTHOR]

• Proposes a novel partial timestamp synchronization (PTS) scheme. • Achieves the joint estimation of skew and offset when observation is limited. • Derives the joint MLE under Gaussian distribution, achieving improved accuracy. • Derives joint BLUE under exponential distribution, proving the effectiveness of PTS. Most existing clock synchronization algorithms in wireless sensor networks require full timestamp information to estimate clock skew and offset so as to maintain the same time scale between nodes. However, in many scenarios, with the purpose of decreasing energy consumption, reducing communication overhead, or improving security, timestamps are not exchanged in synchronization process, resulting in insufficient access to all time information by nodes to be synchronized. Hence, how to jointly estimate clock skew and offset with limited observation is a significant challenge. In order to solve this issue, this paper proposes a partial timestamp synchronization (PTS) scheme, which can implement complete synchronization function only according to the local timestamps and the timestamp relationships obtained by the basic synchronization protocol. Then, based on PTS, a joint Maximum Likelihood Estimator is developed to estimate clock skew and offset when stochastic delays follow Gaussian distribution. In addition, a Best Linear Unbiased Estimator for PTS with exponential random delays is presented, which can also estimate clock skew and offset simultaneously. Finally, simulations are conducted to illustrate the effectiveness of the proposed algorithms. [ABSTRACT FROM AUTHOR]

Shanghai Synchrotron Radiation Facility (SSRF) is a 3.5 GeV storage ring with a bunch rate of 499.654 MHz, harmonic number of 720, and circumference of 432 meters. SSRF injection works at 3.5 GeV, where the multi-bunch instabilities limit the maximum stored current. In order to suppress multi-bunch instabilities caused by transverse impedance, a bunch-by-bunch transverse feedback system is indispensable for SSRF. The key component of that system is the bunch-by-bunch transverse feedback electronics. An important task in the electronics is precise time synchronization. In this paper, a novel clock synchronization and precise delay adjustment method based on the PLLs and delay lines are proposed. Test results indicate that the ENOB (Effective Number Of Bits) of the analog-to-digital conversion circuit is better than 9 bits in the input signal frequency range from 100 kHz to 700 MHz, and the closed loop attenuation at the critical frequency points is better than 40 dB. The initial commissioning tests with the beam in SSRF are also conducted, and the results are consistent with the expectations. [ABSTRACT FROM AUTHOR]

The quality of the links between the different space geodetic techniques (VLBI, SLR, GNSS and DORIS) is still one of the major limiting factors for the realization of a unique global terrestrial reference frame that is accurate enough to allow the monitoring of the Earth system, i.e., of processes like sea level change, postglacial rebound and silent earthquakes. According to the specifications of the global geodetic observing system of the International Association of Geodesy, such a reference frame should be accurate to 1 mm over decades, with rates of change stable at the level of 0.1 mm/year. The deficiencies arise from inaccurate or incomplete local ties at many fundamental sites as well as from systematic instrumental biases in the individual space geodetic techniques. Frequently repeated surveys, the continuous monitoring of antenna heights and the geometrical mount stability (Lösler et al. in J Geod 90:467-486, 2016. 10.1007/s00190-016-0887-8) have not provided evidence for insufficient antenna stability. Therefore, we have investigated variations in the respective system delays caused by electronic circuits, which is not adequately captured by the calibration process, either because of subtle differences in the circuitry between geodetic measurement and calibration, high temporal variability or because of lacking resolving bandwidth. The measured system delay variations in the electric chain of both VLBI- and SLR systems reach the order of 100 ps, which is equivalent to 3 cm of path length. Most of this variability is usually removed by the calibrations but by far not all. This paper focuses on the development of new technologies and procedures for co-located geodetic instrumentation in order to identify and remove systematic measurement biases within and between the individual measurement techniques. A closed-loop optical time and frequency distribution system and a common inter-technique reference target provide the possibility to remove variable system delays. The main motivation for the newly established central reference target, locked to the station clock, is the combination of all space geodetic instruments at a single reference point at the observatory. On top of that it provides the unique capability to perform a closure measurement based on the observation of time. [ABSTRACT FROM AUTHOR]

In digital circuits, metastability can cause deteriorated signals that neither are logical 0 nor logical 1, breaking the abstraction of Boolean logic. Synchronizers, the only traditional countermeasure, exponentially decrease the odds of maintained metastability over time. We propose a fundamentally different approach: It is possible to deterministically contain metastability by fine-grained logical masking so that it cannot infect the entire circuit. At the heart of our approach lies a time- and value-discrete model for metastability in synchronous clocked digital circuits, in which metastability is propagated in a worst-case fashion. The proposed model permits positive results and passes the test of reproducing Marino's impossibility results. We fully classify which functions can be computed by circuits with standard registers. Regarding masking registers, we show that more functions become computable with each clock cycle, and that masking registers permit exponentially smaller circuits for some tasks. Demonstrating the applicability of our approach, we present the first fault-tolerant distributed clock synchronization algorithm that deterministically guarantees correct behavior in the presence of metastability. As a consequence, clock domains can be synchronized without using synchronizers, enabling metastability-free communication between them. [ABSTRACT FROM AUTHOR]

A model is presented which explains the forces between charges in uniform motion in a novel way, without reference to magnetism or special relativity. Building on Coulomb's law of electrostatics, the model explains the magnitude and the direction of such forces in terms of changes in the flow of information from one charge to the other resulting from their acceleration histories. The model enables a deeper understanding of the forces between moving charges than classical electromagnetism, which notably leaves the origin of the magnetic field unexplained. It also offers fresh insights into the foundations of special relativity. In particular, the model provides a simple and direct explanation of how the forces between charges in uniform motion are transformed in a way that is consistent with length contraction. The model also implies that, in the framework of special relativity, events with equal time coordinates are in general not simultaneous. Some implications of this finding for causality, the "block universe" idea and the Andromeda paradox are briefly discussed. [ABSTRACT FROM AUTHOR]

This paper proposes a novel clock synchronization algorithm for wireless sensor networks (WSNs). The algorithm is derived using a fast finite-time average consensus idea, and is fully distributed , meaning that each node relies only on its local clock readings and reading announcements from its neighbours. For networks with an acyclic graph, the algorithm converges in only d iterations for clock rate synchronization and another d iterations for clock offset synchronization, where d is the graph diameter. The algorithm enjoys low computational and communicational complexities and robustness against transmission adversaries. Each node can execute the algorithm asynchronously without the need for global coordination. Due to its fast convergence, the algorithm is most suitable for large-scale WSNs. For WSNs with a cyclic graph, a fast distributed depth-first-search (DFS) algorithm can be applied first to form a spanning tree before applying the proposed synchronization algorithm. [ABSTRACT FROM AUTHOR]

In inverter-based microgrids, individual inverters operate usually with their own digital processor. The clocks used to generate the time signals of these processors differ from each other due to clock drifts. This paper analyzes the impact that the drifts of the processors clocks produce on the operation of inverter-based islanded microgrids. Several communication-free secondary control schemes, which avoid well-known problems caused by digital communication networks, are considered. Active power sharing and frequency regulation are the metrics used to evaluate the performance of the control schemes. The study reveals advantages, drawbacks, and practical limitations of the control schemes caused by the clocks drifts. Therefore, it facilitates the selection of the most suitable control scheme for the practical deployment of microgrids. The theoretical results are validated by experimental tests in a laboratory microgrid equipped with three inverters and three digital signal processors driven by autonomous internal clocks. [ABSTRACT FROM PUBLISHER]

How to narrow the gap of security between theory and practice has been a notoriously urgent problem in quantum cryptography. Here, we analyze and provide experimental evidence of the clock jitter effect on the practical continuous-variable quantum key distribution (CV-QKD) system. The clock jitter is a random noise which exists permanently in the clock synchronization in the practical CV-QKD system, it may compromise the system security because of its impact on data sampling and parameters estimation. In particular, the practical security of CV-QKD with different clock jitter against collective attack is analyzed theoretically based on different repetition frequencies, the numerical simulations indicate that the clock jitter has more impact on a high-speed scenario. Furthermore, a simplified experiment is designed to investigate the influence of the clock jitter. [ABSTRACT FROM AUTHOR]

Global Mobile Network provides global roaming service to the users moving from one network to another. It is essential to authenticate and protect the privacy of roaming users. Recently, Marimuthu and Saravanan proposed a secure authentication scheme for roaming service in mobile networks. This scheme can protect user anonymity, untraceability, and is believed to have many abilities to resist a range of attacks in global mobile networks. In this paper, we analyse the security strength of their scheme and show that the authentication protocol is in fact insecure against insider attack, stolen-verifier attack, impersonation attack, denial-of-service attack, synchronization problem, lack of user anonymity and operational inefficiencies. Hence, we propose a secure and lightweight authentication scheme for Global Mobile Networks. In addition, the proposed scheme requires few message exchanges between the entities such as MU (Mobile User), FA (Foreign Agent) and HA (Home Agent). The scheme ensures both communication and computation efficiency as compared to the well-known authentication schemes. The performance analysis shows that the proposed authentication scheme is well suited for resource limited wireless and mobile environments. [ABSTRACT FROM AUTHOR]

In a system on a chip (SoC), there are several long global wires that typically limit the maximum SoC clock speed. Therefore, through-silicon via (TSV) technology has been proposed to shorten the length of the global wires. However, the TSV delay variation phenomenon created during the manufacturing process may prevent SoC systems from working properly. This TSV delay variation problem affects data transmission between dies. In this paper, we present an all-digital delay-locked loop (ADDLL) architecture to synchronize clock signals between two dies. We implement the proposed ADDLL in TSMC 90-nm CMOS process with standard cells, which can tolerate process, voltage, and temperature (PVT) variations. In addition, the ADDLL architecture can overcome the TSV delay variation problem using only a single TSV channel. The proposed ADDLL can operate in an input frequency range of 195–960 MHz with a maximum phase error of less than 40.6 ps. [ABSTRACT FROM AUTHOR]

In this research, we propose the Clock Synchronization by Least Common Multiple (CSLCM) method to remove the clock offset and clock skew among the sensor nodes. The proposed CSLCM enables the nodes to reach a network synchronization time by calculating the least common multiple of their Clock Time Period (CTP). The network is organized into clusters and every node reaches the network synchronization time using its own CTP. Simulation results show that, the CSLCM algorithm is more efficient compared to the Average Time Synchronization with Pairwise messages (ATSP) in terms of accuracy, communication overhead, and computation overhead. [ABSTRACT FROM AUTHOR]

Distributed real-time systems often rely on clock synchronization. However, the achievement of precise synchronization in Wireless Sensor Networks (WSNs) is hampered by competing design challenges, which finally causes many WSN hardware platforms to rely on low frequency clock crystal for local timebase provision. Although this solution is inexpensive and with a remarkably low energy consumption, it limits the resolution at which time can be measured. The FLOPSYNC synchronization scheme was then introduced to compensate for possible quartz crystal imperfections. The main limitation of FLOPSYNC is that it does not account for the effects of quantization. In this paper we propose a switched control variant of the base FLOPSYNC scheme to address quantization explicitly in the compensator design, providing clock synchronization in cost-sensitive WSN node platforms with a minimal additional overhead. Experimental evidence is given that the approach reaches a synchronization error of at most 1 clock tick in a real WSN. [ABSTRACT FROM AUTHOR]

It is important and challenging to achieve accurate clock synchronization in wireless sensor networks. Various noises, e.g., communication delay, clock fluctuation and measurement errors, are inevitable and difficult to be estimated accurately, which is the main challenge for achieving accurate clock synchronization. In this paper, we focus on how to achieve accurate clock synchronization by considering a practical noise model, bounded noise, which may not satisfy any known distributions. The principle that a bounded monotonic sequence must possess a limit and the concept of maximum consensus are exploited to design a novel clock synchronization algorithm for the network to achieve accurate and fast synchronization. The proposed algorithm is fully distributed, with high synchronization accuracy and fast convergence speed, and is able to compensate both clock skew and offset simultaneously. Meanwhile, we prove that the algorithm converges with probability one, which means that an accurate clock synchronization is achieved. We further prove that the probability of the complete synchronization converges exponentially fast. Experiments and simulations are conducted to verify the noise model and demonstrate the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

This paper develops an offset-based response-time analysis technique for analyzing complex distributed real-time systems where processing and communication resources use the time-partitioning strategy to isolate the operation of separate software components. Time partitioning may be provided in the processors by an ARINC 653 compliant operating system, and in the networks via the TTP communication protocol. The software components executed by the system may themselves be distributed and complex, composed of many concurrent tasks and with one or more end-to-end flows that may have end-to-end timing requirements. The developed analysis supports hierarchical scheduling where a primary scheduler performs time partitioning into separate partitions, and secondary fixed-priority schedulers dispatch the different concurrent tasks inside each partition. It also supports end-to-end flows that are either synchronized with the partition schedule or not. This is the first time that this kind of analysis is developed. An evaluation of an improvement introduced in the analysis is discussed. Two representative case studies are described. [ABSTRACT FROM PUBLISHER]

• An architecture to use the IEEE 802.1AS clock for EDF scheduling in distributed systems with soft real-time requirements has been proposed. • Different scheduling deadline assignment techniques that can be applied to distributed real-time systems have been evaluated. • The experimental results obtained for EDF scheduling in distributed systems do not follow the same behaviour as the theoretical results obtained by state-of-the-art schedulability analysis techniques. • In general, the theoretical dominance of global-clock EDF (GC-EDF) over local-clock EDF(LC-EDF) has not been observed in the experimental results. 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. [ABSTRACT FROM AUTHOR]

Numerous experiments have been carried out to validate the Lorentz transformation or to find possible violations of Lorentz invariance, based on test theories to test special relativity. The test theory of Mansouri and Sexl (MS) provides a general framework for the transformation of inertial frames, presuming a preferred system of reference. Based on the MS framework, this paper systematically approaches the relativistic Doppler effect such that its dependency on transformation coefficients and parameters can be investigated. The Doppler effect is formulated in a complex Euclidean space where time is represented with imaginary numbers. Two formulae of the Doppler effect, which have been derived in an arbitrary transformation within the MS framework, are presented: one between an inertial frame and the preferred one and the other between arbitrary inertial frames. It is shown from the former formulation that the Doppler effect is independent of the synchronization of clocks, which implies that the Doppler-shifted frequency in the absolute synchronization is the same as that in the standard synchronization. The latter formula can allow us to find Doppler shifts without information on the velocities of inertial frames relative to the preferred frame. Exploiting these theoretical results, we examine the transverse and the longitudinal Doppler effects in detail. [ABSTRACT FROM AUTHOR]

EtherCAT has been widely applied in the motion control domain due to its advantages of the fast response speed, low CPU usage and good synchronization performance. Although the built-in distributed clock (DC) synchronization mechanism exhibits strong performance between slaves, the method of clock synchronization between the master and the reference clock is left open for selection by users and there are very few studies in this area. This paper introduces three synchronization modes for EtherCAT and analyzes the reasons for packet loss in free run mode and DC mode. This paper presents a novel method to realize the master clock synchronization with the reference clock. The proposed method can eliminate the settling time which is unusual in other synchronization mechanisms. The method is implemented on Windows with real-time extension and experimental results prove its feasibility. [ABSTRACT FROM AUTHOR]

ABSTRACT Light is the major stimulus for the synchronization of circadian clocks with day-night cycles. The light-driven entrainment of the clock that controls rest-activity rhythms in Drosophila relies on different photoreceptive molecules. Cryptochrome (CRY) is expressed in most brain clock neurons, whereas six different rhodopsins (RH) are present in the light-sensing organs. The compound eye includes outer photoreceptors that express RH1 and inner photoreceptors that each express one of the four rhodopsins RH3-RH6. RH6 is also expressed in the extraretinal Hofbauer-Buchner eyelet, whereas RH2 is only found in the ocelli. In low light, the synchronization of behavioral rhythms relies on either CRY or the canonical rhodopsin phototransduction pathway, which requires the phospholipase C-β encoded by norpA (no receptor potential A). We used norpAP24 cry02 double mutants that are circadianly blind in low light and restored NORPA function in each of the six types of photoreceptors, defined as expressing a particular rhodopsin. We first show that the NORPA pathway is less efficient than CRY for synchronizing rest-activity rhythms with delayed light-dark cycles but is important for proper phasing, whereas the two light-sensing pathways can mediate efficient adjustments to phase advances. Four of the six rhodopsin-expressing photoreceptors can mediate circadian entrainment, and all are more efficient for advancing than for delaying the behavioral clock. In contrast, neither RH5-expressing retinal photoreceptors nor RH2-expressing ocellar photoreceptors are sufficient to mediate synchronization through the NORPA pathway. Our results thus reveal different contributions of rhodopsin-expressing photoreceptors and suggest the existence of several circuits for rhodopsin-dependent circadian entrainment. J. Comp. Neurol. 524:2828-2844, 2016. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]