Distributed Time Synchronization Research Articles

A Novel Consensus-Based Distributed Time Synchronization Algorithm in High-Dynamic Multi-UAV Networks

A Novel Consensus-Based Distributed Time Synchronization Algorithm in High-Dynamic Multi-UAV Networks

Parameter-Sharing-Based Average-Consensus Time Synchronization in IoT Networks

Average-consensus protocol is one of the ways to develop distributed time-synchronization algorithms in Internet of Things (IoT) networks. However, the large number of iteration leads to a common time notion issue in nodes. This poses a critical challenge in the convergence of the time-synchronization algorithm and resulting asymptotic convergence in the average consensus protocol. In this paper, a parameter-sharing-based average-consensus time-synchronization (PACTS) algorithm is proposed. For fast convergence, the proposed PACTS quickly forwards the time information to multi-hop nodes and employs multi-hop average-consensus instead of single-hop average-consensus. Specifically, a node asynchronously and periodically broadcasts the relative clock offset estimation of neighbors with its local time information. Meanwhile, the relative clock offset estimation of the multi-hop node is calculated and used to estimate the average value. Consequently, an average-consensus among local multi-hop nodes is obtained. As a result, the iteration number and convergence time are significantly reduced over the network. Finally, the experimental results indicate that the proposed PACTS algorithm has low complexity, high accuracy, and quick convergence.

Neighborhood Selection Synchronization Mechanism-Based Moving Source Localization Using UAV Swarm

To obtain the accurate time difference of arrival (TDOA) and frequency difference of arrival (FDOA) for passive localization in an unmanned aerial vehicle (UAV) swarm, UAV swarm network synchronization is necessary. However, most of the traditional distributed time synchronization protocols are based on iteration, which hinders efficiency improvement. High communication costs and long convergence times are often required in large-scale UAV swarm networks. This paper presents a neighborhood selection-all selection (NS-AS) synchronization mechanism-based moving source localization method for UAV swarms. First, the NS-AS synchronization mechanism is introduced, to model the UAV swarm network synchronization process. Specifically, the UAV neighbors are first grouped by sector, and the most representative neighbors are selected from each sector for the state update calculation. When the UAV swarm network reaches a fully connected state, the synchronization mechanism is switched to select all neighbors, to improve the convergence speed. Then, the TDOA-FDOA joint localization algorithm is employed to locate the moving radiation source. Through simulation, the effectiveness of the proposed method is verified by the system convergence and localization performance under different parameters. Experimental results show that the synchronization mechanism based on NS-AS effectively improves the convergence speed of the system while ensuring the accuracy of moving radiation source localization.

Design and Implementation of Precision Phase Measurement Module Base on Digital Dual Mixer Time Difference

Precise phase difference measurement is critical for distributed time synchronization systems. Aiming at the problem of how to realize the sub-nanosecond phase difference measurement of the time signal, the digital dual mixer time difference (DDMTD) measurement technology is used to measure the fine transmission delay and the two digital clock phase difference. Given the problem that it is difficult to generate a common clock source with fine frequency changes inside the FPGA chip, the Si5338 chip is used to generate 4 differential clocks, and the communication with the FPGA is completed through the I2C protocol, and the differential signal is converted into a single-ended clock source inside the FPGA as two The common standard frequency of clock signals with the same frequency and different phases, realize the amplification of the phase difference measurement range, making the measurement accuracy reach sub-nanosecond level.

Distributed event-triggered multi-timer synchronization scheme for secondary control in islanded microgrids

Consensus-based distributed control has been widely applied in the secondary control for microgrids (MGs) with the assumption that the control actions of each distributed generations (DGs) are triggered at the same time as others in the state-of-art literature. However, in the absence of centralized timer synchronization, the asynchrony resulting from the independent timer localized in each DG would inevitably undermine the system performance or even cause instability. This paper proposes a distributed time synchronization strategy to guarantee the update actions of individual DGs to be triggered at the same discrete instants. First, the asynchrony problem in the distributed secondary control due to the essential distributed characteristic is elaborated and the resultant convergence deviation is deduced. Then, the distributed time synchronization strategy based on pinning consensus is described, with the optimal pinning timer selected to achieve superior propagation performance. Further, the event-triggered mechanism is introduced, which reduces the communication burden significantly compared to the time-driven mode and maintains the global clock synchronization efficiently. The selection of event triggering threshold is formulated for the tradeoff between the trigger frequency and convergence accuracy. The effectiveness as well as flexibility of the proposed control strategy is demonstrated by simulations.

Distributed time synchronization algorithm based on sequential belief propagation in wireless sensor networks

In the context of the non-Gaussian delay model, the fully distributed time synchronization approach based on Gaussian belief propagation will lead to the decline of synchronization accuracy. This paper proposes a distributed time synchronization algorithm based on sequential belief propagation (SBP-DTS), which assumes that the network delay is unknown. SBP-DTS first establishes a factor graph (FG) model for the time synchronization problem of wireless sensor networks (WSNs), and then uses sequential belief propagation (BP) algorithms to estimate node clock parameters under an unknown random delay model. At the same time, in order to reduce the amount of data exchanged between nodes during the execution of sequential belief propagation algorithm, the weighted expectation–maximization (EM) algorithm is used to reduce the number of Gaussian mixture components in the message. At last, the performance of SBP-DTS is evaluated under asymmetric Gaussian and exponential delay models.

Distributed Network Time Synchronization: Social Learning Versus Consensus

The objective of this paper is to investigate a social learning-based distributed network time synchronization (SLDNTS) and compare it to a classic approach: consensus-based distributed network time synchronization (CDNTS). An observation random variable (ORV), which is a conditional likelihood (e.g., Gaussian) given a synchronized true time hypothesis, is used to generate clock times at each node and each iteration. A time offset and time quality of each node clock are represented, respectively, by a mean shift from the true time and variance of a Gaussian random variable (RV) to consider a practical environment. Then, this paper proposes a simple method to construct an observation matrix that satisfies both the identifiability condition (IC) and the prevailing observation signal existence condition (POSEC) required for the social learning (SL). Each node quantizes its ORV into a heads and tails Bernoulli RV with $(1-\varepsilon)$ and $\varepsilon$ probability, respectively, where $\varepsilon$ is a control parameter for the SLDNTS convergence speed. Using this proposed observation matrix, each node computes its intermediate belief on each possible time hypothesis, shares the information with its connected neighbor nodes, and updates its belief probabilities. Then, this paper verifies, through simulation, that the proposed SLDNTS shows superior performance compared to the classic CDNTS including average time synchronization (ATS) algorithm, maximum time synchronization (MTS) algorithm, and least square time synchronization (LSTS) algorithm under the same observation environment.

A Convergence-Accelerated Distributed Time Synchronization Algorithm for Energy-Harvesting Wireless Sensor Networks

Time synchronization is an essential problem for energy-harvesting wireless sensor networks (EH-WSNs), which is closely related to efficient resource schedules, energy harvesting, data fusion, location, etc. With the advantage of being more robust than master controlling synchronization, distributed time synchronization algorithms are usually used to EH-WSNs for cooperating sleeping nodes. This paper proposes a novel accelerated time co-synchronization algorithm based on the storage-and-prediction method to improve the convergence rate. In this algorithm, each node in the network first predicts the estimated current time state value according to previous time state values stored in the local node, and then adjusts the time state value according to the estimated time state value deviations between all its adjacent nodes. Theoretical analysis in a more general case shows that the proposed algorithm can improve the convergence rate of distributed time synchronization when selecting the appropriate parameter, and the closed-form solution of the optimal parameter is also given. Finally, the simulation of comparing the classical algorithm with the proposed algorithm based on different scenarios is completed.

Analysis of BDS-3 distributed autonomous navigation based on BeiDou system simulation platform

Satellite autonomous navigation is an important function of the BeiDou-3 navigation System (BDS-3). Satellite autonomous navigation means that the navigation satellite uses long-term forecast ephemeris and Inter-Satellite Link (ISL) measurements to determinate its own spatial position and time reference without the support of the ground Operation and Control System (OCS) for a long time to ensure that the navigation system can normally maintain the time and space reference. This paper aims to analyze the feasibility of distributed autonomous navigation algorithms. For the first time, a ground parallel autonomous navigation test system (GPANTS) is built. The performance of distributed autonomous navigation is then analyzed using the two-way ISL ranging of BDS-3 satellites. First, the BDS simulation platform and the GPANTS are introduced. Then, the basic principles of distributed satellite autonomous orbit determination and time synchronization based on ISL measurements are summarized. Preliminary evaluation of the performance of the BDS-3 constellation autonomous navigation service under ideal conditions through simulation data. Then the performance of autonomous navigation for 22 BeiDou-3 satellites using ISL measurements is evaluated. The results show that when satellites operate autonomously for 50 days without the support of any ground station, the User Range Error (URE) of autonomous orbit determination is better than 3 m, and the time synchronization accuracy is better than 4 ns.

An enhanced distributed control-theoretic time synchronization protocol using sliding mode control for wireless sensor and actuator network

<span>Time synchronization is very important in a wireless sensor and actuator network (WSAN) as it provides a common time notation to the WSAN. To handle the time synchronization issue, this paper presented an enhanced distributed control-theoretic time synchronization protocol for wireless sensor and actuator networks, named Time Synchronization using Distributed Observer algorithm with Sliding mode control element (TSDOS). In this protocol, an augmented sliding mode control element is used for robustification purpose. From the theoretical convergence analysis and simulation results presented in this paper, it proved that the proposed TSDOS is the best if compared to another two algorithms from the literature in terms of cumulative integral absolute error.</span>

High-Reliability Sub-Nanosecond Network Time Synchronization Method Enabled by Double-Frequency Distributed Time Synchronization

Time synchronization is a long-standing challenge in distributed systems like indoor/outdoor positioning, coordinated multi-point in 4G/5G mobile communication, etc., which require nanosecond-level high-reliable time sync networks. At present, a widely adopted solution for time sync networks is the precision time protocol specified in IEEE 1588v2, which can provide sub-microsecond sync accuracy. In addition, a novel network time sync method called distributed time synchronization has also been proposed recently, which can achieve 50-ns-level accuracy and stronger survivability in metro, regional, and backbone networks. However, both of the above methods encounter difficulties in achieving nanosecond sync accuracy and network reliability simultaneously. In this paper, by analyzing the main factors influencing the degradation of time sync accuracy, we reveal that the finite clock resolution is a major barrier to achieving nanosecond-level time synchronization. In order to establish a low-cost, high-reliability, and sub-nanosecond-level time sync network, we propose a novel network time sync method called double-frequency distributed time synchronization (DF- DTS). By selecting two specific and distinct frequencies for the sending and receiving clocks of the nodes/devices being synchronized, the time sync errors induced by the finite clock resolution can be reduced by a statistical approach. We set up a theoretical model for the DF-DTS and analyze the time sync accuracy through both mathematical derivations and network simulations. Furthermore, we propose a failure-restoration mechanism to enhance the reliability of DF-DTS networks by improving the time sync accuracy under failures and reducing the failure recovery time. Finally, we conduct both point- to-point and network time sync experiments to validate the proposed DF-DTS method. The results demonstrate that DF-DTS can achieve sub-nanosecond-level sync accuracy that is 1-2 orders of magnitude higher than the clock resolution in a prototype four-node DF-DTS network. Moreover, a network simulation under failure cases is conducted, and the results show that our method has significant advantages in both time sync accuracy and recovery time in the failure-restoration process compared to IEEE 1588v2.

An anomaly node detection method for distributed time synchronization algorithm in cognitive radio sensor networks

In wireless sensor networks, time synchronization is an important issue for all nodes to have a unified time. The wireless sensor network nodes should cooperatively adjust their local time according to certain distributed synchronization algorithms to achieve global time synchronization. Conventionally, it is assumed that all nodes in the network are cooperative and well-functioned in the synchronization process. However, in cognitive radio wireless sensor networks, the global time synchronization process among secondary users is prone to fail because the communication process for exchanging synchronization reference may be frequently interrupted by the primary users. The anomaly nodes that failed to synchronize will significantly affect the global convergence performance of the synchronization algorithm. This article proposes an anomaly node detection method for distributed time synchronization algorithm in cognitive radio sensor networks. The proposed method adopts the statistical linear correlation analysis approach to detect anomaly nodes through the historical time synchronization information stored in local nodes. Simulation results show that the proposed method can effectively improve the robustness of the synchronization algorithm in distributed cognitive radio sensor networks.

Distributed time synchronization for networks with random delays and measurement noise

In this paper a new distributed asynchronous algorithm is proposed for time synchronization in networks with random communication delays, measurement noise and communication dropouts. Three different types of the drift correction algorithm are introduced, based on different kinds of local time increments. Under nonrestrictive conditions concerning network properties, it is proved that all the algorithm types provide convergence in the mean square sense and with probability one (w.p.1) of the corrected drifts of all the nodes to the same value (consensus). An estimate of the convergence rate of these algorithms is derived. For offset correction, a new algorithm is proposed containing a compensation parameter coping with the influence of random delays and special terms taking care of the influence of both linearly increasing time and drift correction. It is proved that the corrected offsets of all the nodes converge in the mean square sense and w.p.1. An efficient offset correction algorithm based on consensus on local compensation parameters is also proposed. It is shown that the overall time synchronization algorithm can also be implemented as a flooding algorithm with one reference node. It is proved that it is possible to achieve bounded error between local corrected clocks in the mean square sense and w.p.1. Simulation results provide an additional practical insight into the algorithm properties and show its advantage over the existing methods.

Distributed Time Synchronization Algorithms and Opinion Dynamics

We propose new deterministic and stochastic models for synchronization of clocks in nodes of distributed networks. An external accurate time server is used to ensure convergence of the node clocks to the exact time. These systems have much in common with mathematical models of opinion formation in multiagent systems. There is a direct analogy between the time server/node clocks pair in asynchronous networks and the leader/follower pair in the context of social network models.

An Algorithm for Accurate Distributed Time Synchronization in Mobile Wireless Sensor Networks from Noisy Difference Measurements

AbstractWe propose a distributed algorithm for time synchronization in mobile wireless sensor networks. The problem of time synchronization is formulated as nodes estimating their skews and offsets from noisy difference measurements of offsets and logarithm of skews; the measurements acquired by time‐stamped message exchanges between neighbors. The algorithm ensures that the estimation error is mean square convergent (variance converging to 0) under certain conditions. A sequence of scheduled update instants is used to meet the requirement of decreasing time‐varying gains that need to be synchronized across nodes with unsynchronized clocks. Moreover, a modification on the algorithm is also presented to improve the initial convergence speed. Simulations indicate that highly accurate global time estimates can be achieved with the proposed algorithm for long time durations, while the errors in competing algorithms increase over time.

Distributed time synchronization in wireless sensor networks via second-order consensus algorithms

This paper proposes a distributed second-order consensus time synchronization, which incorporates the second-order consensus algorithm into wireless sensor networks. Since local clocks may have different skews and offsets, the algorithm is designed to include offset compensation and skew compensation. The local clocks are not directly modified, thus the virtual clocks are built according to the local clocks via the compensation parameters. Each node achieves a virtual consensus clock by periodically updated compensation parameters. Finally, the effectiveness of the proposed algorithm is verified through a number of simulations in a mesh network. It is proved that the proposed algorithm has the advantage of being distributed, asymptotic convergence, and robust to new node joining.

Estimation and Compensation of Non-deterministic Delays for Time Synchronization in Wireless Sensor Networks

New research opportunities are emerging as Wireless Sensor Networks (WSNs) are penetrating into the industrial domain; one such prospect is within time synchronization. For the operation of WSNs, partial or full time synchronization is needed. Time synchronization is very important in a distributed WSN for the purpose of data fusion, time interval calculation, context-free access to radio channel, coordination, event ordering and power management. This paper proposes a novel distributed time synchronization protocol for WSNs, which compensates for the nondeterministic delays by estimating the uncertainties in the synchronization packet delays. The main idea is to minimize the uncertainties in the synchronization packet delays to achieve a synchronization scheme that is accurate, efficient and has a low communication overhead. An average per hop synchronization accuracy of 2.4µs has been achieved.

생체모방 알고리즘을 이용한 OFDMA 무선 메쉬 통신시스템의 분산 시간 동기화 기법 연구

본 논문에서는 최근 차세대 무선 통신네트워크 기술로 주목받고 있는 OFDMA 무선 메쉬통신시스템에서의 분산 시간동기화 기법을 제안한다. 제안방식은 물리계층 기반에서 이루어지는 생체모방 알고리즘을 활용한 자가 분산 시간동기화 기법으로, 인접 이웃노드로부터 수신된 신호의 TDoA(Time Difference of Arrival) 정보를 이용하여 다음 주기의 전송주기와 FFT 시작점을 업데이트한다. 분산처리가 가능한 생체모방 알고리즘의 장점이 반영되어, 제안된 동기화 기법에서도 중앙제어 없이 주위 정보(local Information)와 각 노드에 의한 분산처리만으로 빠르고 간단하게 노드 간 시간 동기 획득이 가능하다. 제안된 분산 시간 동기화 기법은 모의실험을 통하여 시간동기화 수렴 확률 및 정확도 등의 측면에서 성능을 분석한다. In this paper, we propose a distributed time synchronization technique for OFDMA- based wireless mesh communication systems. The proposed technique employs the bio-inspired algorithm for self-time synchronization in the physical layer. To achieve the network synchronicity, the proposed technique updates the transmission time and the FFT window using the TDoA information of received signals from the neighbor nodes. The proposed technique can achieve fast self-synchronization among nodes with a simple algorithm, without the need of a centralized controller. The performance of the proposed time synchronization technique is evaluated by simulation in terms of convergence speed and convergence probability.

Timestamping of IEEE 802.15.4a CSS Signals for Wireless Ranging and Time Synchronization

Accurate positioning and distributed time synchronization for short-range personal area networks (PAN) are expected to boost the impact of mobile wireless systems in a variety of applications. At the moment, wireless ranging and time synchronization are often addressed independently. The two main underlying reasons are: 1) the different accuracy requirements for time-of-arrival measurements and local clock correction and 2) the intrinsic difficulty to timestamp the received radio frames with uncertainty lower than some nanoseconds due to the joint effect of clock resolution, wideband noise, clock frequency offsets, and multipath propagation. Of course, if the influence of such phenomena were minimized, time synchronization could benefit from accurate one-way ranging and vice versa. One of the most recent and promising communication schemes to reach this goal is chirp spread spectrum (CSS) modulation. Indeed, this is also one of the alternative physical (PHY) layers for PANs recommended in the amendment IEEE 802.15.4a-2007, recently included in the standard IEEE 802.15.4-2011. In this paper, the features of IEEE 802.15.4a CSS signals for low-level timestamping are analyzed both theoretically and through simulations under the effect of various uncertainty contributions. Accordingly, an effective solution for frame timestamping at the symbol level is proposed. Some experimental results based on a software defined radio implementation of the IEEE 802.15.4a PHY layer confirm that CSS can be successfully adopted both for time synchronization and ranging.

A Distributed Time Synchronization Solution without Satellite Time Reference for Mobile Communication

Synchronization is one of the most important issues for telecommunication. Some 3G and LTE mobile communication systems require high-accuracy time synchronization between neighboring base stations. Existing synchronization solutions rely heavily on the satellite time service system, such as GPS, as the common time reference. In the event that satellite systems become unavailable, time synchronization in a wide area would be lost. In this paper, a distributed time synchronization solution is proposed without relying on satellite time reference. Simulation and experimental results show that the proposed solution converges fast and can realize high-accuracy time synchronization for large-scale networks.