Time synchronization(TS)is crucial for ensuring the secure and reliable functioning of the distribution power Internet of Things(IoT).Multi-clock source time synchronization(MTS)has significant advantages of high reli...Time synchronization(TS)is crucial for ensuring the secure and reliable functioning of the distribution power Internet of Things(IoT).Multi-clock source time synchronization(MTS)has significant advantages of high reliability and accuracy but still faces challenges such as optimization of the multi-clock source selection and the clock source weight calculation at different timescales,and the coupling of synchronization latency jitter and pulse phase difference.In this paper,the multi-timescale MTS model is conducted,and the reinforcement learning(RL)and analytic hierarchy process(AHP)-based multi-timescale MTS algorithm is designed to improve the weighted summation of synchronization latency jitter standard deviation and average pulse phase difference.Specifically,the multi-clock source selection is optimized based on Softmax in the large timescale,and the clock source weight calculation is optimized based on lower confidence bound-assisted AHP in the small timescale.Simulation shows that the proposed algorithm can effectively reduce time synchronization delay standard deviation and average pulse phase difference.展开更多
Time synchronization is one of the base techniques in wireless sensor networks(WSNs).This paper proposes a novel time synchronization protocol which is a robust consensusbased algorithm in the existence of transmissio...Time synchronization is one of the base techniques in wireless sensor networks(WSNs).This paper proposes a novel time synchronization protocol which is a robust consensusbased algorithm in the existence of transmission delay and packet loss.It compensates for transmission delay and packet loss firstly,and then,estimates clock skew and clock offset in two steps.Simulation and experiment results show that the proposed protocol can keep synchronization error below 2μs in the grid network of 10 nodes or the random network of 90 nodes.Moreover,the synchronization accuracy in the proposed protocol can keep constant when the WSN works up to a month.展开更多
A Beidou 3(BD3)system-based power reference station can provide high-precision time synchronization for power distribution systems by sending synchronization data packets to devices in a multi-hop routing fashion.Howe...A Beidou 3(BD3)system-based power reference station can provide high-precision time synchronization for power distribution systems by sending synchronization data packets to devices in a multi-hop routing fashion.However,optimizing route selection to reduce both time synchronization error and delay is a challenging problem.In this paper,we establish a software-defined network-enabled power reference station time synchronization framework based on BD3.Then,we formulate the joint problem to minimize cumulative synchronization error and delay through multi-hop route selection optimization.A back propagation(BP)neural network-improved intelligent time synchronization route selection algorithm named BP-RS is proposed to learn the optimal route selection,which uses a BP neural network to dynamically adjust the exploration factor to achieve rapid convergence.Simulation results show the superior performance of BP-RS in synchronization delay,synchronization error,and adaptability with changing routing topologies.展开更多
Purpose–As the strategy of 5G new infrastructure is deployed and advanced,5G-R becomes the primary technical system for future mobile communication of China’s railway.V2V communication is also an important applicati...Purpose–As the strategy of 5G new infrastructure is deployed and advanced,5G-R becomes the primary technical system for future mobile communication of China’s railway.V2V communication is also an important application scenario of 5G communication systems on high-speed railways,so time synchronization between vehicles is critical for train control systems to be real-time and safe.How to improve the time synchronization performance in V2V communication is crucial to ensure the operational safety and efficiency of high-speed railways.Design/methodology/approach–This paper proposed a time synchronization method based on model predictive control(MPC)for V2V communication.Firstly,a synchronous clock for V2V communication was modeled based on the fifth generation mobile communication-railway(5G-R)system.Secondly,an observation equation was introduced according to the phase and frequency offsets between synchronous clocks of two adjacent vehicles to construct an MPC-based space model of clock states of the adjacent vehicles.Finally,the optimal clock offset was solved through multistep prediction,rolling optimization and other control methods,and time synchronization in different V2V communication scenarios based on the 5G-R system was realized through negative feedback correction.Findings–The results of simulation tests conducted with and without a repeater,respectively,show that the proposed method can realize time synchronization of V2V communication in both scenarios.Compared with other methods,the proposed method has faster convergence speed and higher synchronization precision regardless of whether there is a repeater or not.Originality/value–This paper proposed an MPC-based time synchronization method for V2V communication under 5G-R.Through the construction of MPC controllers for clocks of adjacent vehicles,time synchronization was realized for V2V communication under 5G-R by using control means such as multistep prediction,rolling optimization,and feedback correction.In view of the problems of low synchronization precision and slow convergence speed caused by packet loss with existing synchronization methods,the observer equation was introduced to estimate the clock state of the adjacent vehicles in case of packet loss,which reduces the impact of clock error caused by packet loss in the synchronization process and improves the synchronization precision of V2V communication.The research results provide some theoretical references for V2V synchronous wireless communication under 5G-R technology.展开更多
Time synchronization is a critical middleware service of wireless sensor networks. Researchers have already proposed some time synchronization algorithms. However, due to the demands for various synchronization precis...Time synchronization is a critical middleware service of wireless sensor networks. Researchers have already proposed some time synchronization algorithms. However, due to the demands for various synchronization precision, existing time synchronization algorithms often need to be adapted. So it is necessary to evaluate these adapted algorithms before use. Software simulation is a valid and quick way to do it. In this paper, we present a time synchronization simulator, Simsync, for wireless sensor networks. We decompose the packet delay into 6 delay components and model them separately. The frequency of crystal oscillator is modeled as Gaussian. To testify its effectiveness, we simulate the reference broadcast synchronization algorithm (RBS) and the timing-sync synchronization algorithm (TPSN) on Simsync. Simulated results are also presented and analyzed.展开更多
Micro-satellite cluster enables a whole new class of missions for communications, remote sensing, and scientific research for both civilian and military purposes. Synchronizing the time of the satellites in a cluster ...Micro-satellite cluster enables a whole new class of missions for communications, remote sensing, and scientific research for both civilian and military purposes. Synchronizing the time of the satellites in a cluster is important for both cluster sensing capabilities and its autonomous operating. However, the existing time synchronization methods are not suitable for microsatellite cluster, because it requires too many human interventions and occupies too much ground control resource. Although, data post-process may realize the equivalent time synchronization, it requires processing time and powerful computing ability on the ground, which cannot be implemented by cluster itself. In order to autonomously establish and maintain the time benchmark in a cluster, we propose a compact time difference compensation system（TDCS）, which is a kind of time control loop that dynamically adjusts the satellite reference frequency according to the time difference. Consequently, the time synchronization in the cluster can be autonomously achieved on-orbit by synchronizing the clock of other satellites to a chosen one＇s. The experimental result shows that the standard deviation of time synchronization is about 102 ps when the carrier to noise ratio（CNR） is 95 d BHz, and the standard deviation of corresponding frequency difference is approximately0.36 Hz.展开更多
To cope with the arbitrariness of the network delays,a novel method,referred to as the composite particle filter approach based on variational Bayesian(VB-CPF),is proposed herein to estimate the clock skew and clock o...To cope with the arbitrariness of the network delays,a novel method,referred to as the composite particle filter approach based on variational Bayesian(VB-CPF),is proposed herein to estimate the clock skew and clock offset in wireless sensor networks.VB-CPF is an improvement of the Gaussian mixture kalman particle filter(GMKPF)algorithm.In GMKPF,Expectation-Maximization(EM)algorithm needs to determine the number of mixture components in advance,and it is easy to generate overfitting and underfitting.Variational Bayesian EM(VB-EM)algorithm is introduced in this paper to determine the number of mixture components adaptively according to the observations.Moreover,to solve the problem of data packet loss caused by unreliable links,we propose a robust time synchronization(RTS)method in this paper.RTS establishes an autoregressive model for clock skew,and calculates the clock parameters based on the established autoregressive model in case of packet loss.The final simulation results illustrate that VB-CPF yields much more accurate results relative to GMKPF when the network delays are modeled in terms of an asymmetric Gaussian distribution.Moreover,RTS shows good robustness to the continuous and random dropout of time messages.展开更多
As the popularization of dual ring fieldbus, the optimized dual ring synchronization methods are still in short. The current synchronization methods are generally established in traditional industrial fieldbus, in whi...As the popularization of dual ring fieldbus, the optimized dual ring synchronization methods are still in short. The current synchronization methods are generally established in traditional industrial fieldbus, in which transmission is commonly considered in single track, the two-way transmitting cannot take full effect, and would result in unwanted idle load on equipment lines. In stamp-transferring part, the synchronizing algorithm is not properly processed to diminish the latency, so the real-time performance of entire system cannot be ensured. To support the synchronization control of stations in the CNC system, a real-time time synchronization method for dual ring fieldbus in the CNC system is designed in this paper. In this method a synchronizing message transmission scheme based on dual ring architecture and the synchronization algorithm between master and secondary stations are integrated. In the scheme, the clock models of both master and secondary stations are optimized with corresponding modules and the stamp data transmission based on the dual ring fieldbus is devised exclusively, so the transmitting efficiency improves with less idle work. In the algorithm, all the secondary stations can accomplish the consistent state with master station by updating clock discrepancy information in one communication cycle, and it takes the advantage of two-way transmitting and makes the best use of dual ring structure, so the real-time performance of the system can be promoted while retaining the precision of synchronization. To evaluate the performance, the costs of the method and errors during synchronizing are noted and analyzed based on the actual running environment in the industrial fieldbus. The results show that it reduces communication cost and ensures the smoothness of the system with low lag effects under heavy load. The proposed time synchronization method optimizes the architecture of sync message transmission in dual ring fieldbus, and improves the efficiency of time synchronization in the stations of CNC system.展开更多
In the conventional chaos synchronization methods, the time at which two chaotic systems are synchronized, is usually unknown and depends on initial conditions. In this work based on Lyapunov stability theory a slidin...In the conventional chaos synchronization methods, the time at which two chaotic systems are synchronized, is usually unknown and depends on initial conditions. In this work based on Lyapunov stability theory a sliding mode controller with time-varying switching surfaces is proposed to achieve chaos synchronization at a pre-specified time for the first time. The proposed controller is able to synchronize chaotic systems precisely at any time when we want. Moreover, by choosing the time-varying switching surfaces in a way that the reaching phase is eliminated, the synchronization becomes robust to uncertainties and exogenous disturbances. Simulation results are presented to show the effectiveness of the proposed method of stabilizing and synchronizing chaotic systems with complete robustness to uncertainty and disturbances exactly at a pre-specified time.展开更多
For the high precision time synchronization demand of ships, advantages and disadvantages of the present time transfer methods are analyzed, the two-way microwave time transfer （TWMTT） method is adopted to resolve t...For the high precision time synchronization demand of ships, advantages and disadvantages of the present time transfer methods are analyzed, the two-way microwave time transfer （TWMTT） method is adopted to resolve the time synchronization problem in the Naval Ship Formation. After expounding the principle and system composition of TWMTT method, the various factors influencing the synchronous precision are analyzed, such as time-interval measurement error, TWMTT equipment delay error, signal propagation error in air, and signal delay error caused by shipping. To improve the time synchronization precision, all the error sources above are deduced with mathematical measures to definite the critical one, and the signal processing measures such as Pseudo code spread spectrum time comparison signal generation technology, FFT fast acquisition technology and precise tracking technology are used into the modem which is the core equipment of the TWMTT. And, calibration method of TWMTT equipment delay are developed. Through theoretical a- nalysis and simulation verification, the precision of shipboard two-way microwave time synchroniza- tion can reach 1 ns.展开更多
In this paper,we present a maximum likelihood(ML) based time synchronization algorithm for Wireless Body Area Networks(WBAN).The proposed technique takes advantage of soft information retrieved from the soft demapper ...In this paper,we present a maximum likelihood(ML) based time synchronization algorithm for Wireless Body Area Networks(WBAN).The proposed technique takes advantage of soft information retrieved from the soft demapper for the time delay estimation.This algorithm has a low complexity and is adapted to the frame structure specified by the IEEE 802.15.6standard[1]for the narrowband systems.Simulation results have shown good performance which approach the theoretical mean square error limit bound represented by the Cramer Rao Bound(CRB).展开更多
Recent advances in wireless sensor technology have enabled simultaneous exploitation of multiple channels in wireless sensor systems. In this paper, a novel time synchronization algorithm is proposed for multi- channe...Recent advances in wireless sensor technology have enabled simultaneous exploitation of multiple channels in wireless sensor systems. In this paper, a novel time synchronization algorithm is proposed for multi- channel Wireless Sensor Networks (WSNs) called Multi-Channel Time Synchronization (MCTS) protocol. Time synchronization is critical for many WSN applications and enables efficient communications between sensor nodes along with intelligent spectrum access. Contrary to many existing protocols that do not exploit multi-channel communications, the protocol takes advantage of potential multiple channels and distributes the synchronization of different nodes to distinct channels and thus, reduces the convergence time of synchronization processes significantly.展开更多
Underwater optical wireless communication (UOWC) technology facilitates high-speed data transmission among multiple nodes in underwater networks. Nevertheless, the absence of a common clock poses a challenge to achiev...Underwater optical wireless communication (UOWC) technology facilitates high-speed data transmission among multiple nodes in underwater networks. Nevertheless, the absence of a common clock poses a challenge to achieving systematic and reliable access for multiple nodes within these networks. This paper presents a time synchronization method for UOWC networks to ensure the successful execution of the media access control (MAC) protocol. In this method, the node obtains timestamps by exchanging messages with the optical access point (OAP). Subsequently, the node calculates the clock drift relative to the OAP and the propagation time,ensuring that transmitted data packets can arrive approximately at the time specified by the OAP. To validate the effect of the proposed method, an experimental UOWC prototype, including the OAP and nodes, is implemented using field programmable gate array (FPGA). The experimental results demonstrate that the maximum difference between the actual arrival times of two data packets that are expected to reach the OAP simultaneously according to the MAC protocol meets the requirements of the quasi-synchronous code division multiple access (QS-CDMA) system, thereby substantiating the effectiveness of this synchronization method.展开更多
This study aims to evaluate the effect of serum concentration, synchronization time, and confluence degree on the synchronisation efficiency of goat fibroblast cycle. The results indicated that there was no difference...This study aims to evaluate the effect of serum concentration, synchronization time, and confluence degree on the synchronisation efficiency of goat fibroblast cycle. The results indicated that there was no difference in the percentage of nucleated fibroblasts in the G0/G1 stage between serum concentrations of 0.3% and 0.4% (83.89% and 82.69%, respectively, P > 0.05) as well as between serum concentrations of 0.2% and 0.5% (76.95% and 75.46%, respectively, P > 0.05). The percentage of nucleated fibroblasts in the G0/G1 stage was highest at the concentration of 0.3% and lowest in the control group (83.89% vs. 62.67%, P 0.05). The beneficial effect of high confluence was confirmed by the large percentage of nucleated fibroblasts at the G0/G1 stage. The 60% confluency was significantly lower than the 80% and 100% confluency (73.44%, 86.63%, and 87.17%, respectively, P < 0.05). The results indicate that the goat fibroblast cycle synchronization is the most effective at the serum concentration of 0.3%, 72 hours of synchronization and 100% confluency.展开更多
Aiming at regional services,the space segment of COMPASS (Phase I) satellite navigation system is a constellation of Geostationary Earth Orbit (GEO),Inclined Geostationary Earth Orbit (IGSO) and Medium Earth Orbit (ME...Aiming at regional services,the space segment of COMPASS (Phase I) satellite navigation system is a constellation of Geostationary Earth Orbit (GEO),Inclined Geostationary Earth Orbit (IGSO) and Medium Earth Orbit (MEO) satellites.Precise orbit determination (POD) for the satellites is limited by the geographic distribution of regional tracking stations.Independent time synchronization (TS) system is developed to supplement the regional tracking network,and satellite clock errors and orbit data may be obtained by simultaneously processing both tracking data and TS data.Consequently,inconsistency between tracking system and TS system caused by remaining instrumental errors not calibrated may decrease navigation accuracy.On the other hand,POD for the mixed constellation of GEO/IGSO/MEO with the regional tracking network leads to parameter estimations that are highly correlated.Notorious example of correlation is found between GEO's orbital elements and its clock errors.We estimate orbital elements and clock errors for a 3GEO+2IGSO constellation in this study using a multi-satellite precise orbit determination (MPOD) strategy,with which clock error elimination algorithm is applied to separate orbital and clock estimates to improve numerical efficiency.Satellite Laser Ranging (SLR) data are used to evaluate User Ranging Error (URE),which is the orbital error projected on a receiver's line-of-sight direction.Two-way radio-wave time transfer measurements are used to evaluate clock errors.Experimenting with data from the regional tracking network,we conclude that the fitting of code data is better than 1 m in terms of Root-Mean-Square (RMS),and fitting of carrier phase is better than 1 cm.For orbital evaluation,difference between computed receiver-satellite ranging based on estimated orbits and SLR measurements is better than 1 m (RMS).For clock estimates evaluation,2-hour linear-fitting shows that the satellite clock rates are about 1.E-10 s/s,while receiver clock rates are about 1×10 13-1×10 12 s/s.For the 72-hour POD experiment,the average differences between POD satellite clock rates estimates and clock measurements based on TS system are about 1×10 13 s/s,and for receiver clock rates,the differences are about 1×10 15 s/s.展开更多
In this paper we investigate methods to achieve highly accurate time synchronization among the satellites of the COMPASS global navigation satellite system(GNSS).Owing to the special design of COMPASS which implements...In this paper we investigate methods to achieve highly accurate time synchronization among the satellites of the COMPASS global navigation satellite system(GNSS).Owing to the special design of COMPASS which implements several geo-stationary satellites(GEO),time synchronization can be highly accurate via microwave links between ground stations to the GEO satellites.Serving as space-borne relay stations,the GEO satellites can further disseminate time and frequency signals to other satellites such as the inclined geo-synchronous(IGSO)and mid-earth orbit(MEO)satellites within the system.It is shown that,because of the accuracy in clock synchronization,the theoretical accuracy of COMPASS positioning and navigation will surpass that of the GPS.In addition,the COMPASS system can function with its entire positioning,navigation,and time-dissemination services even without the ground link,thus making it much more robust and secure.We further show that time dissemination using the COMPASS-GEO satellites to earth-fixed stations can achieve very high accuracy,to reach 100 ps in time dissemination and 3 cm in positioning accuracy,respectively.In this paper,we also analyze two feasible synchronization plans.All special and general relativistic effects related to COMPASS clocks frequency and time shifts are given.We conclude that COMPASS can reach centimeter-level positioning accuracy and discuss potential applications.展开更多
Time synchronization systems that utilize the global navigation satellite systems(GNSS)are widely used in the monitoring,control,and protection of transmission networks.They ensure that phasor measurement units(PMUs)c...Time synchronization systems that utilize the global navigation satellite systems(GNSS)are widely used in the monitoring,control,and protection of transmission networks.They ensure that phasor measurement units(PMUs)can accurately monitor voltage phase angles,increase the accuracy of fault locators,enhance the capabilities of disturbance recorders,and allow differential feeder protection to use re-routable communication networks.However,concern about the reliability of GNSS receivers used in intelligent electronic devices(IEDs)have been reported;problems include mal-operations of differential protection,erroneous satellite timing/location messages,inappropriate installations,and blocking of satellite signals due to illegal use of GNSS jammers in vehicles.Utilities now require a timing system less dependent on the use of low cost GNSS receivers integrated into IEDs,but one that uses Grandmaster clocks,slave and transparent clocks,and an Ethernet communication network.The IEEE 1588-2008 synchronization protocol uses the Ethernet to disseminate a global time reference around a substation.A future substation will probably include duplicate 1588 grandmasters,each incorporating stable oscillators with GNSS and terrestrial receivers,in conjunction with a 1588 compliant Ethernet data network with slave and transparent clocks,and redundancy boxes for interfacing with IEDs.Although IEEE 1588 protocol is promising for future substation automation systems,its performance and impact has to be fully evaluated before it can be used in real substations.This paper describes how an IEEE 1588 time synchronization testbed is designed,constructed,and tested.Testing involves measuring the time offset when the Ethernet is heavily loaded with other traffic and the holdover capability of 1588 clocks.Additional delay introduced by IEEE 1588 traffic is also measured.As there is limited testing on GPS receivers within the power industry,this paper also uses the testbed to evaluate the steady state and transient behavior of GPS receivers.The results show a 1588 time synchronization system is accurate,secure,and ideally suited for protection and control applications,compared to a timing system merely based on GPS receivers.The information described in this paper should increase a utility’s confidence in applying IEEE 1588 timing in a real substation.展开更多
A complete method of synchronization technology of bistatic radar using global position system （GPS） is presented. The pulse per second signal （1PPS） is elaborately modified to increase the time synchronization pr...A complete method of synchronization technology of bistatic radar using global position system （GPS） is presented. The pulse per second signal （1PPS） is elaborately modified to increase the time synchronization precision and keep loop locking. A very high time synchronization precision is achieved. Using the modified 1PPS to discipline the local OCXO, the reference frequency signal achieves both high long term stability （LTS） and short term stability （STS） properties. An algorithm, named phase abrupt change CFAR is presented to restrain the 1PPS phase abrupt change and keep loop locking. The experimental results indicate that this time and frequency synchronization method is effective and the time synchronization precision of the synchronization system can be improved from ±100 ns to ±25 ns. In addition, the phase noise is improved to 20 dB.展开更多
Satellite-station two-way time comparison is a typical design in Beidou System(BDS)which is significantly different from other satellite navigation systems.As a type of two-way time comparison method,BDS time synchron...Satellite-station two-way time comparison is a typical design in Beidou System(BDS)which is significantly different from other satellite navigation systems.As a type of two-way time comparison method,BDS time synchronization is hardly influenced by satellite orbit error,atmosphere delay,tracking station coordinate error and measurement model error.Meanwhile,single-way time comparison can be realized through the method of Multi-satellite Precision Orbit Determination(MPOD)with pseudo-range and carrier phase of monitor receiver.It is proved in the constellation of 3GEO/2IGSO that the radial orbit error can be reflected in the difference between two-way time comparison and single-way time comparison,and that may lead to a substitute for orbit evaluation by SLR.In this article,the relation between orbit error and difference of two-way and single-way time comparison is illustrated based on the whole constellation of BDS.Considering the all-weather and real-time operation mode of two-way time comparison,the orbit error could be quantifiably monitored in a real-time mode through comparing two-way and single-way time synchronization.In addition,the orbit error can be predicted and corrected in a short time based on its periodic characteristic.It is described in the experiments of GEO and IGSO that the prediction accuracy of space signal can be obviously improved when the prediction orbit error is sent to the users through navigation message,and then the UERE including terminal error can be reduced from 0.1 m to 0.4 m while the average accuracy can be improved more than 27%.Though it is still hard to make accuracy improvement for Precision Orbit Determination(POD)and orbit prediction because of the confined tracking net and the difficulties in dynamic model optimization,in this paper,a practical method for orbit accuracy improvement is proposed based on two-way time comparison which can result in the reflection of orbit error.展开更多
An IEEE 1588 based application scheme was proposed to achieve accurate time synchronization for a deep seafloor observatory network based on the communication topological structure of the Zhejiang University Experimen...An IEEE 1588 based application scheme was proposed to achieve accurate time synchronization for a deep seafloor observatory network based on the communication topological structure of the Zhejiang University Experimental and Research Observatory.The principles of the network time protocol(NTP)and precision time protocol(PTP)were analyzed.The framework for time synchronization of the shore station,undersea junction box layer,and submarine science instrument layer was designed.NTP and PTP network signals were decoded by a PTP master clock on a shore station that receives signals from the Global Positioning System and the BeiDou Navigation Satellite System as reference time sources.These signals were remotely transmitted by a subsea optical–electrical composite cable through an Ethernet passive optical network.Accurate time was determined by time synchronization devices in each layer.Synchronization monitoring experiments performed within a laboratory environment indicated that the proposed system is valid and has the potential to realize microsecond accuracy to satisfy the time synchronization requirements of a high-precision seafloor observatory network.展开更多
基金supported by Science and Technology Project of China Southern Power Grid Company Limited under Grant Number 036000KK52200058(GDKJXM20202001).
文摘Time synchronization(TS)is crucial for ensuring the secure and reliable functioning of the distribution power Internet of Things(IoT).Multi-clock source time synchronization(MTS)has significant advantages of high reliability and accuracy but still faces challenges such as optimization of the multi-clock source selection and the clock source weight calculation at different timescales,and the coupling of synchronization latency jitter and pulse phase difference.In this paper,the multi-timescale MTS model is conducted,and the reinforcement learning(RL)and analytic hierarchy process(AHP)-based multi-timescale MTS algorithm is designed to improve the weighted summation of synchronization latency jitter standard deviation and average pulse phase difference.Specifically,the multi-clock source selection is optimized based on Softmax in the large timescale,and the clock source weight calculation is optimized based on lower confidence bound-assisted AHP in the small timescale.Simulation shows that the proposed algorithm can effectively reduce time synchronization delay standard deviation and average pulse phase difference.
文摘Time synchronization is one of the base techniques in wireless sensor networks(WSNs).This paper proposes a novel time synchronization protocol which is a robust consensusbased algorithm in the existence of transmission delay and packet loss.It compensates for transmission delay and packet loss firstly,and then,estimates clock skew and clock offset in two steps.Simulation and experiment results show that the proposed protocol can keep synchronization error below 2μs in the grid network of 10 nodes or the random network of 90 nodes.Moreover,the synchronization accuracy in the proposed protocol can keep constant when the WSN works up to a month.
基金supported by the Science and Technology Project of the China Southern Power Grid Company Limited under grant number GDKJXM20202032。
文摘A Beidou 3(BD3)system-based power reference station can provide high-precision time synchronization for power distribution systems by sending synchronization data packets to devices in a multi-hop routing fashion.However,optimizing route selection to reduce both time synchronization error and delay is a challenging problem.In this paper,we establish a software-defined network-enabled power reference station time synchronization framework based on BD3.Then,we formulate the joint problem to minimize cumulative synchronization error and delay through multi-hop route selection optimization.A back propagation(BP)neural network-improved intelligent time synchronization route selection algorithm named BP-RS is proposed to learn the optimal route selection,which uses a BP neural network to dynamically adjust the exploration factor to achieve rapid convergence.Simulation results show the superior performance of BP-RS in synchronization delay,synchronization error,and adaptability with changing routing topologies.
基金supported by the National Natural Science Foundation of China(Grant Nos.61963023&61841303)the Tianyou Innovation Team Science Foundation of Lanzhou Jiaotong University(Grant No.TY202003).
文摘Purpose–As the strategy of 5G new infrastructure is deployed and advanced,5G-R becomes the primary technical system for future mobile communication of China’s railway.V2V communication is also an important application scenario of 5G communication systems on high-speed railways,so time synchronization between vehicles is critical for train control systems to be real-time and safe.How to improve the time synchronization performance in V2V communication is crucial to ensure the operational safety and efficiency of high-speed railways.Design/methodology/approach–This paper proposed a time synchronization method based on model predictive control(MPC)for V2V communication.Firstly,a synchronous clock for V2V communication was modeled based on the fifth generation mobile communication-railway(5G-R)system.Secondly,an observation equation was introduced according to the phase and frequency offsets between synchronous clocks of two adjacent vehicles to construct an MPC-based space model of clock states of the adjacent vehicles.Finally,the optimal clock offset was solved through multistep prediction,rolling optimization and other control methods,and time synchronization in different V2V communication scenarios based on the 5G-R system was realized through negative feedback correction.Findings–The results of simulation tests conducted with and without a repeater,respectively,show that the proposed method can realize time synchronization of V2V communication in both scenarios.Compared with other methods,the proposed method has faster convergence speed and higher synchronization precision regardless of whether there is a repeater or not.Originality/value–This paper proposed an MPC-based time synchronization method for V2V communication under 5G-R.Through the construction of MPC controllers for clocks of adjacent vehicles,time synchronization was realized for V2V communication under 5G-R by using control means such as multistep prediction,rolling optimization,and feedback correction.In view of the problems of low synchronization precision and slow convergence speed caused by packet loss with existing synchronization methods,the observer equation was introduced to estimate the clock state of the adjacent vehicles in case of packet loss,which reduces the impact of clock error caused by packet loss in the synchronization process and improves the synchronization precision of V2V communication.The research results provide some theoretical references for V2V synchronous wireless communication under 5G-R technology.
基金Supported in part by National Basic Research Program of P. R. China(2005CB321604) in part by National Natural Science Foundation of P. R. China (90207002)
文摘Time synchronization is a critical middleware service of wireless sensor networks. Researchers have already proposed some time synchronization algorithms. However, due to the demands for various synchronization precision, existing time synchronization algorithms often need to be adapted. So it is necessary to evaluate these adapted algorithms before use. Software simulation is a valid and quick way to do it. In this paper, we present a time synchronization simulator, Simsync, for wireless sensor networks. We decompose the packet delay into 6 delay components and model them separately. The frequency of crystal oscillator is modeled as Gaussian. To testify its effectiveness, we simulate the reference broadcast synchronization algorithm (RBS) and the timing-sync synchronization algorithm (TPSN) on Simsync. Simulated results are also presented and analyzed.
基金supported by the National Natural Science Foundation of China(61401389)the Joint Fund of the Ministry of Education of China(6141A02033310)
文摘Micro-satellite cluster enables a whole new class of missions for communications, remote sensing, and scientific research for both civilian and military purposes. Synchronizing the time of the satellites in a cluster is important for both cluster sensing capabilities and its autonomous operating. However, the existing time synchronization methods are not suitable for microsatellite cluster, because it requires too many human interventions and occupies too much ground control resource. Although, data post-process may realize the equivalent time synchronization, it requires processing time and powerful computing ability on the ground, which cannot be implemented by cluster itself. In order to autonomously establish and maintain the time benchmark in a cluster, we propose a compact time difference compensation system（TDCS）, which is a kind of time control loop that dynamically adjusts the satellite reference frequency according to the time difference. Consequently, the time synchronization in the cluster can be autonomously achieved on-orbit by synchronizing the clock of other satellites to a chosen one＇s. The experimental result shows that the standard deviation of time synchronization is about 102 ps when the carrier to noise ratio（CNR） is 95 d BHz, and the standard deviation of corresponding frequency difference is approximately0.36 Hz.
基金This work was supported by the National Natural Science Foundation of China(No.61672299)the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province of China(No.18KJB520035)+2 种基金the Youth Foundation of Nanjing University of Finance and Economics(No.L-JXL18002)the Youth Foundation of Nanjing University of Posts and Telecommunications(No.NY218142)the Natural Science Foundation of Jiangsu Province(No.BK20160913).
文摘To cope with the arbitrariness of the network delays,a novel method,referred to as the composite particle filter approach based on variational Bayesian(VB-CPF),is proposed herein to estimate the clock skew and clock offset in wireless sensor networks.VB-CPF is an improvement of the Gaussian mixture kalman particle filter(GMKPF)algorithm.In GMKPF,Expectation-Maximization(EM)algorithm needs to determine the number of mixture components in advance,and it is easy to generate overfitting and underfitting.Variational Bayesian EM(VB-EM)algorithm is introduced in this paper to determine the number of mixture components adaptively according to the observations.Moreover,to solve the problem of data packet loss caused by unreliable links,we propose a robust time synchronization(RTS)method in this paper.RTS establishes an autoregressive model for clock skew,and calculates the clock parameters based on the established autoregressive model in case of packet loss.The final simulation results illustrate that VB-CPF yields much more accurate results relative to GMKPF when the network delays are modeled in terms of an asymmetric Gaussian distribution.Moreover,RTS shows good robustness to the continuous and random dropout of time messages.
基金supported by National Projects for Science and Technology Development of China(Grant No.2011ZX04016-071)National Basic Research Program of China(973 Program,Grant No.2011CB302400-G,the mathematical mechanization method and its application in digital design and manufacturing)
文摘As the popularization of dual ring fieldbus, the optimized dual ring synchronization methods are still in short. The current synchronization methods are generally established in traditional industrial fieldbus, in which transmission is commonly considered in single track, the two-way transmitting cannot take full effect, and would result in unwanted idle load on equipment lines. In stamp-transferring part, the synchronizing algorithm is not properly processed to diminish the latency, so the real-time performance of entire system cannot be ensured. To support the synchronization control of stations in the CNC system, a real-time time synchronization method for dual ring fieldbus in the CNC system is designed in this paper. In this method a synchronizing message transmission scheme based on dual ring architecture and the synchronization algorithm between master and secondary stations are integrated. In the scheme, the clock models of both master and secondary stations are optimized with corresponding modules and the stamp data transmission based on the dual ring fieldbus is devised exclusively, so the transmitting efficiency improves with less idle work. In the algorithm, all the secondary stations can accomplish the consistent state with master station by updating clock discrepancy information in one communication cycle, and it takes the advantage of two-way transmitting and makes the best use of dual ring structure, so the real-time performance of the system can be promoted while retaining the precision of synchronization. To evaluate the performance, the costs of the method and errors during synchronizing are noted and analyzed based on the actual running environment in the industrial fieldbus. The results show that it reduces communication cost and ensures the smoothness of the system with low lag effects under heavy load. The proposed time synchronization method optimizes the architecture of sync message transmission in dual ring fieldbus, and improves the efficiency of time synchronization in the stations of CNC system.
文摘In the conventional chaos synchronization methods, the time at which two chaotic systems are synchronized, is usually unknown and depends on initial conditions. In this work based on Lyapunov stability theory a sliding mode controller with time-varying switching surfaces is proposed to achieve chaos synchronization at a pre-specified time for the first time. The proposed controller is able to synchronize chaotic systems precisely at any time when we want. Moreover, by choosing the time-varying switching surfaces in a way that the reaching phase is eliminated, the synchronization becomes robust to uncertainties and exogenous disturbances. Simulation results are presented to show the effectiveness of the proposed method of stabilizing and synchronizing chaotic systems with complete robustness to uncertainty and disturbances exactly at a pre-specified time.
基金Supported by the Ministerial Level Foundation(2102812)
文摘For the high precision time synchronization demand of ships, advantages and disadvantages of the present time transfer methods are analyzed, the two-way microwave time transfer （TWMTT） method is adopted to resolve the time synchronization problem in the Naval Ship Formation. After expounding the principle and system composition of TWMTT method, the various factors influencing the synchronous precision are analyzed, such as time-interval measurement error, TWMTT equipment delay error, signal propagation error in air, and signal delay error caused by shipping. To improve the time synchronization precision, all the error sources above are deduced with mathematical measures to definite the critical one, and the signal processing measures such as Pseudo code spread spectrum time comparison signal generation technology, FFT fast acquisition technology and precise tracking technology are used into the modem which is the core equipment of the TWMTT. And, calibration method of TWMTT equipment delay are developed. Through theoretical a- nalysis and simulation verification, the precision of shipboard two-way microwave time synchroniza- tion can reach 1 ns.
基金supported by the franco-chinese NSFC-ANR program under the Greencocom Project
文摘In this paper,we present a maximum likelihood(ML) based time synchronization algorithm for Wireless Body Area Networks(WBAN).The proposed technique takes advantage of soft information retrieved from the soft demapper for the time delay estimation.This algorithm has a low complexity and is adapted to the frame structure specified by the IEEE 802.15.6standard[1]for the narrowband systems.Simulation results have shown good performance which approach the theoretical mean square error limit bound represented by the Cramer Rao Bound(CRB).
基金supported in part by TEKES(Finnish Funding Agency for Technology and Innovation)as part of the Wireless Sensor and Actuator Networks for Measurement and Control(WiSA-II)programby the U.S.Army Research Office under Cooperative Agreement W911NF-04-2-0054.
文摘Recent advances in wireless sensor technology have enabled simultaneous exploitation of multiple channels in wireless sensor systems. In this paper, a novel time synchronization algorithm is proposed for multi- channel Wireless Sensor Networks (WSNs) called Multi-Channel Time Synchronization (MCTS) protocol. Time synchronization is critical for many WSN applications and enables efficient communications between sensor nodes along with intelligent spectrum access. Contrary to many existing protocols that do not exploit multi-channel communications, the protocol takes advantage of potential multiple channels and distributes the synchronization of different nodes to distinct channels and thus, reduces the convergence time of synchronization processes significantly.
基金supported in part by the National Key Research and Development Program of China under Grant 2022YFB2903400in part by the Strategic Priority Research Program of CAS under Grant XDA22000000in part by the National Natural Science Foundation of China under Grants 62301525 and 62101526.
文摘Underwater optical wireless communication (UOWC) technology facilitates high-speed data transmission among multiple nodes in underwater networks. Nevertheless, the absence of a common clock poses a challenge to achieving systematic and reliable access for multiple nodes within these networks. This paper presents a time synchronization method for UOWC networks to ensure the successful execution of the media access control (MAC) protocol. In this method, the node obtains timestamps by exchanging messages with the optical access point (OAP). Subsequently, the node calculates the clock drift relative to the OAP and the propagation time,ensuring that transmitted data packets can arrive approximately at the time specified by the OAP. To validate the effect of the proposed method, an experimental UOWC prototype, including the OAP and nodes, is implemented using field programmable gate array (FPGA). The experimental results demonstrate that the maximum difference between the actual arrival times of two data packets that are expected to reach the OAP simultaneously according to the MAC protocol meets the requirements of the quasi-synchronous code division multiple access (QS-CDMA) system, thereby substantiating the effectiveness of this synchronization method.
文摘This study aims to evaluate the effect of serum concentration, synchronization time, and confluence degree on the synchronisation efficiency of goat fibroblast cycle. The results indicated that there was no difference in the percentage of nucleated fibroblasts in the G0/G1 stage between serum concentrations of 0.3% and 0.4% (83.89% and 82.69%, respectively, P > 0.05) as well as between serum concentrations of 0.2% and 0.5% (76.95% and 75.46%, respectively, P > 0.05). The percentage of nucleated fibroblasts in the G0/G1 stage was highest at the concentration of 0.3% and lowest in the control group (83.89% vs. 62.67%, P 0.05). The beneficial effect of high confluence was confirmed by the large percentage of nucleated fibroblasts at the G0/G1 stage. The 60% confluency was significantly lower than the 80% and 100% confluency (73.44%, 86.63%, and 87.17%, respectively, P < 0.05). The results indicate that the goat fibroblast cycle synchronization is the most effective at the serum concentration of 0.3%, 72 hours of synchronization and 100% confluency.
基金supported by the Shanghai Committee of Science and Technology,China (Grant No.11ZR1443500)the National Natural Science Foundation of China (Grant No.11033004)
文摘Aiming at regional services,the space segment of COMPASS (Phase I) satellite navigation system is a constellation of Geostationary Earth Orbit (GEO),Inclined Geostationary Earth Orbit (IGSO) and Medium Earth Orbit (MEO) satellites.Precise orbit determination (POD) for the satellites is limited by the geographic distribution of regional tracking stations.Independent time synchronization (TS) system is developed to supplement the regional tracking network,and satellite clock errors and orbit data may be obtained by simultaneously processing both tracking data and TS data.Consequently,inconsistency between tracking system and TS system caused by remaining instrumental errors not calibrated may decrease navigation accuracy.On the other hand,POD for the mixed constellation of GEO/IGSO/MEO with the regional tracking network leads to parameter estimations that are highly correlated.Notorious example of correlation is found between GEO's orbital elements and its clock errors.We estimate orbital elements and clock errors for a 3GEO+2IGSO constellation in this study using a multi-satellite precise orbit determination (MPOD) strategy,with which clock error elimination algorithm is applied to separate orbital and clock estimates to improve numerical efficiency.Satellite Laser Ranging (SLR) data are used to evaluate User Ranging Error (URE),which is the orbital error projected on a receiver's line-of-sight direction.Two-way radio-wave time transfer measurements are used to evaluate clock errors.Experimenting with data from the regional tracking network,we conclude that the fitting of code data is better than 1 m in terms of Root-Mean-Square (RMS),and fitting of carrier phase is better than 1 cm.For orbital evaluation,difference between computed receiver-satellite ranging based on estimated orbits and SLR measurements is better than 1 m (RMS).For clock estimates evaluation,2-hour linear-fitting shows that the satellite clock rates are about 1.E-10 s/s,while receiver clock rates are about 1×10 13-1×10 12 s/s.For the 72-hour POD experiment,the average differences between POD satellite clock rates estimates and clock measurements based on TS system are about 1×10 13 s/s,and for receiver clock rates,the differences are about 1×10 15 s/s.
基金supported by the Ministry of Science and Technology of China(Grant No.2010CB922901)Tsinghua University under its Scientific Research Initiative Program(Grant No.20091081474)a special research fund from the National Institute of Metrology of China(NIM)
文摘In this paper we investigate methods to achieve highly accurate time synchronization among the satellites of the COMPASS global navigation satellite system(GNSS).Owing to the special design of COMPASS which implements several geo-stationary satellites(GEO),time synchronization can be highly accurate via microwave links between ground stations to the GEO satellites.Serving as space-borne relay stations,the GEO satellites can further disseminate time and frequency signals to other satellites such as the inclined geo-synchronous(IGSO)and mid-earth orbit(MEO)satellites within the system.It is shown that,because of the accuracy in clock synchronization,the theoretical accuracy of COMPASS positioning and navigation will surpass that of the GPS.In addition,the COMPASS system can function with its entire positioning,navigation,and time-dissemination services even without the ground link,thus making it much more robust and secure.We further show that time dissemination using the COMPASS-GEO satellites to earth-fixed stations can achieve very high accuracy,to reach 100 ps in time dissemination and 3 cm in positioning accuracy,respectively.In this paper,we also analyze two feasible synchronization plans.All special and general relativistic effects related to COMPASS clocks frequency and time shifts are given.We conclude that COMPASS can reach centimeter-level positioning accuracy and discuss potential applications.
文摘Time synchronization systems that utilize the global navigation satellite systems(GNSS)are widely used in the monitoring,control,and protection of transmission networks.They ensure that phasor measurement units(PMUs)can accurately monitor voltage phase angles,increase the accuracy of fault locators,enhance the capabilities of disturbance recorders,and allow differential feeder protection to use re-routable communication networks.However,concern about the reliability of GNSS receivers used in intelligent electronic devices(IEDs)have been reported;problems include mal-operations of differential protection,erroneous satellite timing/location messages,inappropriate installations,and blocking of satellite signals due to illegal use of GNSS jammers in vehicles.Utilities now require a timing system less dependent on the use of low cost GNSS receivers integrated into IEDs,but one that uses Grandmaster clocks,slave and transparent clocks,and an Ethernet communication network.The IEEE 1588-2008 synchronization protocol uses the Ethernet to disseminate a global time reference around a substation.A future substation will probably include duplicate 1588 grandmasters,each incorporating stable oscillators with GNSS and terrestrial receivers,in conjunction with a 1588 compliant Ethernet data network with slave and transparent clocks,and redundancy boxes for interfacing with IEDs.Although IEEE 1588 protocol is promising for future substation automation systems,its performance and impact has to be fully evaluated before it can be used in real substations.This paper describes how an IEEE 1588 time synchronization testbed is designed,constructed,and tested.Testing involves measuring the time offset when the Ethernet is heavily loaded with other traffic and the holdover capability of 1588 clocks.Additional delay introduced by IEEE 1588 traffic is also measured.As there is limited testing on GPS receivers within the power industry,this paper also uses the testbed to evaluate the steady state and transient behavior of GPS receivers.The results show a 1588 time synchronization system is accurate,secure,and ideally suited for protection and control applications,compared to a timing system merely based on GPS receivers.The information described in this paper should increase a utility’s confidence in applying IEEE 1588 timing in a real substation.
基金the National Ministry Innovation Foundation (7130302)
文摘A complete method of synchronization technology of bistatic radar using global position system （GPS） is presented. The pulse per second signal （1PPS） is elaborately modified to increase the time synchronization precision and keep loop locking. A very high time synchronization precision is achieved. Using the modified 1PPS to discipline the local OCXO, the reference frequency signal achieves both high long term stability （LTS） and short term stability （STS） properties. An algorithm, named phase abrupt change CFAR is presented to restrain the 1PPS phase abrupt change and keep loop locking. The experimental results indicate that this time and frequency synchronization method is effective and the time synchronization precision of the synchronization system can be improved from ±100 ns to ±25 ns. In addition, the phase noise is improved to 20 dB.
基金supported by the National Natural Science Foundation of China(Grant No.11103064)the Basic Research Foundation Program of Education Ministry Key Laboratory for Earth Space Environment and Geodetic survey,China(Grant No.11-01-06)
文摘Satellite-station two-way time comparison is a typical design in Beidou System(BDS)which is significantly different from other satellite navigation systems.As a type of two-way time comparison method,BDS time synchronization is hardly influenced by satellite orbit error,atmosphere delay,tracking station coordinate error and measurement model error.Meanwhile,single-way time comparison can be realized through the method of Multi-satellite Precision Orbit Determination(MPOD)with pseudo-range and carrier phase of monitor receiver.It is proved in the constellation of 3GEO/2IGSO that the radial orbit error can be reflected in the difference between two-way time comparison and single-way time comparison,and that may lead to a substitute for orbit evaluation by SLR.In this article,the relation between orbit error and difference of two-way and single-way time comparison is illustrated based on the whole constellation of BDS.Considering the all-weather and real-time operation mode of two-way time comparison,the orbit error could be quantifiably monitored in a real-time mode through comparing two-way and single-way time synchronization.In addition,the orbit error can be predicted and corrected in a short time based on its periodic characteristic.It is described in the experiments of GEO and IGSO that the prediction accuracy of space signal can be obviously improved when the prediction orbit error is sent to the users through navigation message,and then the UERE including terminal error can be reduced from 0.1 m to 0.4 m while the average accuracy can be improved more than 27%.Though it is still hard to make accuracy improvement for Precision Orbit Determination(POD)and orbit prediction because of the confined tracking net and the difficulties in dynamic model optimization,in this paper,a practical method for orbit accuracy improvement is proposed based on two-way time comparison which can result in the reflection of orbit error.
基金Project supported by the National High-Tech R&D(863)Program ofChina(No.2012AA09A408)the National Natural ScienceFoundation of China(No.51221004)
文摘An IEEE 1588 based application scheme was proposed to achieve accurate time synchronization for a deep seafloor observatory network based on the communication topological structure of the Zhejiang University Experimental and Research Observatory.The principles of the network time protocol(NTP)and precision time protocol(PTP)were analyzed.The framework for time synchronization of the shore station,undersea junction box layer,and submarine science instrument layer was designed.NTP and PTP network signals were decoded by a PTP master clock on a shore station that receives signals from the Global Positioning System and the BeiDou Navigation Satellite System as reference time sources.These signals were remotely transmitted by a subsea optical–electrical composite cable through an Ethernet passive optical network.Accurate time was determined by time synchronization devices in each layer.Synchronization monitoring experiments performed within a laboratory environment indicated that the proposed system is valid and has the potential to realize microsecond accuracy to satisfy the time synchronization requirements of a high-precision seafloor observatory network.
