RL and AHP-Based Multi-Timescale Multi-Clock Source Time Synchronization for Distribution Power Internet of Things

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.

A consensus time synchronization protocol in wireless sensor network

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.

Accurate time synchronization of power reference station based on BD3 system

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.

MPC-based time synchronizationmethod for V2V (vehicle-tovehicle)communication

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.

Simsync: A Time Synchronization Simulator for Sensor Networks

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.

Approach to inter-satellite time synchronization for micro-satellite 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.

Research on Time Synchronization Method Under Arbitrary Network Delay in Wireless Sensor Networks

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.

Real-time Synchronization Method Based on Dual Ring Fieldbus in CNC System

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.

Robust pre-specified time synchronization of chaotic systems by employing time-varying switching surfaces in the sliding mode control scheme

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.

Technology of shipboard two-way microwave time synchronization

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.

Network-Wide Time Synchronization in Multi-Channel Wireless Sensor Networks

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.

Design and Implementation of a Time Synchronization Method for UOWC Networks

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.

Effects of Serum Concentration, Synchronization Time and Confluence on the Cell-Cycle Synchronization Efficiency of Goat Fibroblasts

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.

Time Synchronization for Transmission Substations Using GPS and IEEE 1588

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.

Precise time frequency synchronization technology for bistatic radar

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.

IEEE 1588 based time synchronization system for a seafloor observatory network

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.

Algorithm of simulation time synchronization over large-scale nodes

In distributed simulation, there is no uniform physical clock. And delay cannot be estimated because of jitter. So simulation time synchronization is essential for the event consistency among nodes. This paper investigates time synchronization algorithms over large-scale distributed nodes, analyzes LBTS （lower bound time stamp） computation model described in IEEE HLA standard, and then presents a grouped LBTS model. In fact, there is a default premise for existing algorithms that controi packets must be delivered via reliable transportation. Although, a theorem of time synchronization message＇s reliability is proposed, which proves that only those control messages that constrain time advance need reliability. It breaks out the default premise for reliability. Then multicast is introduced into the transmis- sion of control messages, and algorithm MCTS （multi-node coordination time synchronization） is proposed based on multicast. MCTS not only promotes the time advance efficiency, but also reduces the occupied network bandwidth. Experiment results demonstrate that the algorithm is better than others in both time advance speed and occupied network bandwidth. Its time advance speed is about 50 times per second when there are 1000 nodes, approximately equal to that of similar systems when there are 100 nodes.

Efficient Time Synchronization Approach for Wireless Communication Systems on GPP-Based Software-Defined Radio Platform

General purpose processer （GPP） based software-defined radio （SDR） platforms provide wireless communication system engineers with maximal architecture flexibility and versatility to construct a wideband wireless communication system. Nevertheless, the lack of hardware real-time timing control makes it difficult to achieve time synchronization between the base station and the terminals. In this paper, a software-based time synchronization （STS） method is proposed to realize the time synchronization of time division multiple access （TDMA） based wireless communication systems. A high precision software clock source is firstly constructed to measure the elapse of processing time. The Round-Trip Delay （RTD） algorithm is then presented to calculate timing advance values and achieve time synchronization. An example TDMA system is implemented on Microsoft Sora platforms to evaluate is effective to enable time synchronization for wideband the performance. Experiments show that the proposed mechanism wireless communication systems on GPP-based SDR platforms.

Orbit determination and time synchronization for BDS-3 satellites with raw inter-satellite link ranging observations

To provide competitive global positioning and timing services under the condition that monitoring stations are confined to Chinese territory,inter-satellite link(ISL)technology is used by the third-generation BeiDou Navigation Satellite System(BDS-3).The ISL,together with the dual one-way links between satellites and anchor stations,may enable autonomous navigation for BDS-3.In this paper,we propose a general observation model for orbit determination(OD)and time synchronization(TS)directly using non-simultaneous observations,such as raw ISL pseudoranges.With the proposed model,satellite orbits,clocks,and hardware delay biases of ISL equipment can be determined simultaneously by jointly processing inter-satellite one-way pseudorange data and observation data from ground monitoring stations.Moreover,autonomous OD and TS are also achievable with one-way pseudorange data from anchor stations and satellites.Data from eight BDS-3 satellites,two anchor stations,and seven monitoring stations located in China were collected to validate the proposed method.It is shown that by jointly processing data from the ISL and seven monitoring stations,the RMS of overlap orbit differences in radial direction is 0.019 m,the overlap clock difference(95%)is 0.185 ns,and the stability of the estimated hardware delay biases for each satellite is greater than 0.5 ns.Compared with the results obtained with the seven stations,the improvements of orbits in radial direction and clocks are 95.7%and 90.5%,respectively.When the hardware delay biases are fixed to predetermined values,the accuracies of orbits and clocks are further improved.By jointly processing pseudoranges from the satellites and the two anchor stations,the RMS of overlap orbit differences is 0.017 m in the radial direction,and the overlap clock difference(95%)is 0.037 ns.It has also been demonstrated that under the condition of one-way ranging links,the accuracies of orbits and clocks obtained by the above two modes are still significantly better than those obtained by using the data from the monitoring stations alone.

Joint transfer of time and frequency signals and multi-point synchronization via fiber network

A system of jointly transferring time signals with a rate of 1 pulse per second （PPS） and frequency signals of 10 MHz via a dense wavelength division multiplex-based （DWDM） fiber is demonstrated in this paper. The noises of the fiber links are suppressed and compensated for by a controlled fiber delay line. A method of calibrating and characterizing time is described. The 1PPS is synchronized by feed-forward calibrating the fiber delays precisely. The system is experimen- tally examined via a 110 km spooled fiber in laboratory. The frequency stabilities of the user end with compensation are 1.8x 10-14 at 1 s and 2.0x 10-17 at 104 s average time. The calculated uncertainty of time synchronization is 13.1 ps, whereas the direct measurement of the uncertainty is 12 ps. Next, the frequency and 1PPS are transferred via a metropoli- tan area optical fiber network from one central site to two remote sites with distances of 14 km and 110 km. The frequency stabilities of 14 km link reach 3.0x 10-14 averaged in 1 s and 1.4x 10-17 in 104 s respectively; and the stabilities of 110 km link are 8.3 x 10-14 and 1.7 x 10-17, respectively. The accuracies of synchronization are estimated to be 12.3 ps for the 14 km link and 13.1 ps for the 110 km link, respectively.