Design of Clock Synchronization Algorithm in Networked Control Systems

With the publication of version 2.0 of the IEEE1588 Standard for accurate time transfer over packet networks in 2008, the Precision Time Protocol (PTP) quickly became the only viable clock synchronization technology for all application domains relying on Ethernet as a transport medium. PTP was deliberately defined in highly generic terms allowing it to be tailored to applicationspecific requirements via PTP profiles. The SMPTE ST 2059-2 standard is the PTP profile for the broadcasting industry and a crucial element for any All-IP Studio deployment. In 2019 the IEEE published a new version of the IEEE1588 standard (PTP v2.1), where PTP was enhanced with several interesting optional features aimed primarily at improving the overall reliability of PTP, especially for larger deployments. — In this paper, we will explain all major new features of PTP v2.1 and investigate to what extent broadcasting applications may benefit from adopting them as part of a new version of the ST 2059-2 PTP profile. Specific focus will be put on possible implications with respect to implementation efforts and operating requirements. We will analyze whether the overall reliability of PTP can be improved by adding new features such as PTP security or extended monitoring. The high accuracy extensions to PTP v2.1 will be described together with a rough effort estimate required to develop and deploy products supporting sub-nanosecond accuracy. — The paper will conclude with a list of recommendations summarizing the benefits of these new features for deploying broadcasting networks at scale.

In order to reduce accumulation errors in the time synchronization for higher required systems,in this paper,the source of residual in clock synchronization and the working principle of transparent clock were in-depth analyzed.Combined with the delay request-response mechanism and the peer delay mechanism of IEEE 1588v2,a precise clock synchronization protocol applied to networked measurement and control systems,a set of high precision simultaneous algorithm based on transparent clock was summarized in detail.According to the test results,synchronization accuracy and precision in the sub-microsecond range can be perfectly reached by drift adjustment and offset adjustment,which can fully comply with the required precision requirments.

Clock synchronization is a mechanism for providing a standard time to various devices across a network. This monograph provides a comprehensive overview of recent developments for clock synchronization protocols built on two-way message exchanges. Several clock synchronization protocols are available in the literature for distributing time from high-cost, high-stability clocks (termed masters) to low-cost, low-stability clocks (termed slaves) via an interconnecting network. A number of clock synchronization protocols are built on two-way message exchanges. These include the timing protocol for sensor networks (TPSN), lightweight time synchronization (LTS) protocol, tiny-sync and mini-sync, network time protocol (NTP) and the IEEE 1588 precision time protocol (PTP). The messages traveling between the master and slave nodes can encounter several intermediate switches and routers, accumulating delays at each node. The main factors contributing to the overall delay are the fixed propagation and processing delays at the intermediate nodes along the network path between the master and slave, as well as the stochastic queuing delays at each such node. Popular probability density function (pdf) models for modeling the stochastic delays include Gaussian, exponential, gamma, Weibull, and log-normal. Although these pdf models for the stochastic queuing delays apply to several scenarios, they might not be suitable in specific scenarios such as cellular base station synchronization using mobile backhaul networks and IEEE 1588 in 4G Long Term Evolution (LTE) networks. Further, there could be possibly unknown asymmetries between the fixed path delays in the forward master-to-slave path and the reverse slave-to-master path. These unknown asymmetries could arise from various sources, including delay attacks or incorrect modeling. In this monograph, we present recent developments for clock synchronization protocols built on the two-way message exchange. After an introduction to the basic concepts and mathematical models, the optimum estimators are presented for estimating the clock skew and offset that are applicable for any pdf model of the stochastic delays. Robust algorithms that can also handle unknown path asymmetries are presented next. The focus is on techniques that consider practical, relevant measurement models in order to guide the reader from physical observations to the actual synchronization of the clocks at the slave and master.

Base stations in mobile networks have very strict frequency synchronisation (also referred to as syntonisation) requirements. As backhaul networks are migrated to asynchronous packet-switching technology, timing over packet using the IEEE 1588 Precision Time Protocol (PTP) replaces current synchronisation methods that rely on the synchronous bit clock of the network. With PTP, base-station clocks derive their frequency from the inter-packet delays of Sync messages sent by a high-quality time source at regular time intervals. Packet-delay variation (PDV) thus has a major impact on the achievable synchronisation quality, and the amount of PDV of a backhaul network determines whether the network can support frequency synchronisation of base stations. We present a simulation and an analytical approach to assessing the suitability of backhaul networks for clock synchronisation using PTP and derive two methods for reducing PDV.KeywordsPrecision Time ProtocolFrequency SynchronisationMobile Backhaul Networks

Clock synchronization is an essential problem faced by packet transport network. PTP (precise time protocol) can be used to solve this problem.Its feasibility has been verified by related literatures. In this paper, we use the OPNET simulation platform to further study the key factors affect the clocks' accuracy of packet-based synchronization schemes, e.g., queuing disciplines, network traffic load, whether low-pass filter is used or not, and deployment of the PTP enabled router. We intend to answer the question how much influence can each factor make to the clocks' synchronization performance.

Time synchronization has played an important role in modern measurement and control systems which require high time accuracy to maintain optimal performance in sample acquisition, signal control and safety protection. The Ethernet/IP based IEEE 1588 precise time protocol (PTP) provides us a prospective solution. By means of taking hardware timestamps, the time synchronization accuracy can be kept in the range of sub-microsecond with minimal network load and low demand on computing resources. Based on the OMNeT++ simulator, we build the PTP ordinary clock model and simulate the typical process of the PTP clock synchronization. The complete clock synchronization process and its performance are both analyzed and evaluated.

This work explores clock synchronization algorithms used to process timestamps from the IEEE 1588 precision time protocol (PTP). It focuses on the PTP-unaware network scenario, where the network nodes do not actively contribute to PTP’s operation. This scenario typically imposes a harsh environment for accurate clock distribution, primarily due to the packet delay variation experienced by PTP packets. In this context, it is essential to process the noisy PTP measurements using algorithms and strategies that consider the underlying clock and packet delay models. This work surveys some attractive algorithms and introduces an open-source analysis library that combines several of them for better performance. It also provides an unprecedented comparison of the algorithms based on datasets acquired from a sophisticated testbed composed of field-programmable gate arrays (FPGAs). The investigation provides insights regarding the synchronization performance under various scenarios of background traffic and oscillator stability.

Recent advances in the industrial internet of things (IIoT) and cyber–physical systems drive Industry 4.0 and have led to remote monitoring and control applications that require factories to be connected to remote sites over wide area networks (WAN). The adequate performance of remote applications depends on the use of a clock synchronization scheme. Packet delay variations adversely impact the clock synchronization performance. This impact is significant in WAN as it comprises wired and wireless segments belonging to public and private networks, and such heterogeneity results in inconsistent delays. Highly accurate, hardware–based time synchronization solutions, global positioning system (GPS), and precision time protocol (PTP) are not preferred in WAN due to cost, environmental effects, hardware failure modes, and reliability issues. As a software–based network time protocol (NTP) overcomes these challenges but lacks accuracy, the authors propose a software–based clock synchronization method, called CoSiWiNeT, based on the random sample consensus (RANSAC) algorithm that uses an iterative technique to estimate a correct offset from observed noisy data. To evaluate the algorithm’s performance, measurements captured in a WAN deployed within two cities were used in the simulation. The results show that the performance of the new algorithm matches well with NTP and state–of–the–art methods in good network conditions; however, it outperforms them in degrading network scenarios.

Network performance relies on the design of control algorithm and network information scheduling in a networked control system (NCS). The effect of the network scheduling is to allocate rationally network resources and improve network utilization. A scheduling approach is presented to implement the scheduling of a set of periodic tasks in this paper. And an immune-genetic algorithm (IGA) is proposed to realize the network scheduling optimization. We take the transmission error of control systems as an object function. The simulation results show that the approach can optimize the scheduling of NCS and improve the network resource utilization.

After distributed generation accessed in the power distribution network, the traditional type of distribution network will be no longer a radial network any more. This will bring many uncertain factors and make some difficulty to protection configuration and setting. First, this paper reviews the proposed protection principles. But so far, a variety of improvement schemes have some shortcomings, but also a need for deeply and extensively research. In this paper, basing on the existing intelligent protection scheme an IEEE 1588 intelligent protection is proposed. IEEE 1588 defines a precision time protocol (PTP) for networked measurement and control systems, it can well meet the needs of the requirements of data synchronization after distributed generation accessed. In addition, with the introduction of the multi-agent system (MAS), it can make full use of computer intelligence and the inherent distribution of power system to build a protection system. So the computer protection device can be regarded as a combination of multi-agent, each agent has its own goals, tasks and communication with other agents and methods of cooperation, every agent into full play their intelligence to coordinate the work to improve the performance of the whole protection device, it is suitable for distribution network protection scheme Containing distributed generation.

Design, Analysis and Real-time Implementation of Networked Predictive Control Systems

In this chapter is introduced the issues involved in the Wind Farms Sensorial Data Acquisition and Processing. This chapter is organized in five sub chapters summarized afterwards. The first sub chapter is the introduction. The second sub chapter makes an overview of a wind maintenance system, describing in detail the software related to the acquisition system, the information system and other software. This sub chapter explains also the operation of the acquisition system, including algorithms, hardware and firmware details. The third sub chapter deals with algorithms that manage the results of a methodology presented in the second sub chapter, with the objective to illustrate the operation of the system. The penultimate sub chapter will present results including simulation and real operation of the system, data details for clock synchronization protocols with improved changes, acquisition time and a SVM (Support Vector Machines) classifier applied to sensorial wind data. Finally we will make the chapter conclusions and present the references used in this chapter. The contribution of this chapter is in the design of the architecture proposed with emphasis for synchronous data acquisition in different geographic points. An improvement for PTP (Precision Time Protocol) is included to achieve fast time convergence in the initial phase of a clock synchronization setup. The control and setup of acquisition timings also play an important role in the system behaviour. This chapter also includes different alternatives for this subject. Given the current energy framework and global climate change, the emphasis on renewable energy has grown a lot. One of the most important renewable energies is from wind that has given great contribution for this new paradigm. There are, however, many aspects that must be considered and are related to its framework as an energy environmentally friendly. This growth in wind farms has the effect of the increase in diversity of the type of equipment in wind turbines. Moreover, the average life of each wind generator and readiness of this kind of technology means that there is a legacy of equipments for different ages and maintenance needs. An information system for maintenance, called SMIT (Terology Integrated Modular System) is used as a general base to manage the assets and for the strategic lines to the evolution of

Algorithms following the peer-to-peer Precision Time Protocol (PTP) specified by the IEEE 1588 standard achieve synchronization of distributed clocks by propagating the timing information of a preselected master clock throughout the entire network. Based on this noisy timing information, each slave clock tries to follow as closely as possible the master time. In this work we formulate clock synchronization as a stochastic estimation-control problem. A two dimensional LQG controller is derived which produces an optimal reconstruction of the master time at each slave in the sense of minimizing the mean square error of the estimated master counter and frequency. Owing to its specific structure, the LQG controller does not violate the transparent clock concept. The performance of the proposed controller is verified by simulations.

If all clocks within a distributed system share the same notion of time, the application domain can gain several advantages. Among those is the possibility to implement real-time behavior, accurate time stamping, and event detection. However, with the wide spread application of clock synchronization another topic has to be taken into consideration: the fault tolerance. The well known clock synchronization protocol IEEE1588 (precision time protocol, PTP), is based on a master/slave principle, which has one severe disadvantage. This disadvantage is the fact that the failure of a master automatically requires the re-election of a new master. The start of a master election based on timeout and thus takes a certain time span during which the clocks are not synchronized and thus running freely. Moreover the usage of a new master also requires new delay measurements, which prolong the time of uncertainty as well. This paper analyzes the results of such a master failure and proposes democratic master groups instead of hot-stand-by masters to overcome this problem by. It is shown by means of simulation that the proposed solution will not deteriorate the accuracy of the slave clocks in case of a master failure.

To support system-wide synchronization accuracy and precision in the sub-microsecond range without using GPS technique, the Precise Time Protocol (PTP) standard IEEE-1588V2 is introduced. Various factors affect the clock synchronization precision, such as the location of timestamp point, frequency difference between Master and Slave, delay asymmetry and error accumulation. In this paper, we analyze these factors and propose an implementation of 1588v2 over UDP in Ethernet. This implement method efficiently reduces the effect of the above factors and guarantees the time and frequency synchronization precision supported by PTP.