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Journal ArticleDOI

Clock Synchronization Over IEEE 802.11—A Survey of Methodologies and Protocols

TL;DR: This survey looks into the details of synchronization over IEEE 802.11 with a particular focus on the infrastructure mode which is most relevant for industrial use cases and highlights the different parameters which affect the performance of clock synchronization over WLAN and compares the performances of existing synchronization methods to analyze their shortcomings.
Abstract: Just like Ethernet before, IEEE 802.11 is now transcending the borders of its usage from the office environment toward real-time communication on the factory floor. However, similar to Ethernet, the availability of synchronized clocks to coordinate and control communication and distributed real-time services is not a built-in feature in WLAN. Over the years, this has led to the design and use of a wide variety of customized protocols with varying complexity and precision, both for wired and wireless networks, in accordance with the increasingly demanding requirements from real-time applications. This survey looks into the details of synchronization over IEEE 802.11 with a particular focus on the infrastructure mode which is most relevant for industrial use cases. It highlights the different parameters which affect the performance of clock synchronization over WLAN and compares the performance of existing synchronization methods to analyze their shortcomings. Finally, it identifies new trends and directions for future research as well as features for wireless clock synchronization which will be required by the applications in the near future.
Citations
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Journal ArticleDOI
TL;DR: R-Sync is presented, a robust time synchronization scheme for IIoT that makes all the nodes get synchronized and gets the better performance in terms of accuracy and energy consumption, compared with three existing time synchronization algorithms TPSN, GPA, STETS.
Abstract: Energy-efficient and robust-time synchronization is crucial for industrial Internet of things (IIoT). Some energy-efficient time synchronization schemes that achieve high accuracy have been proposed recently. However, some unsynchronized nodes namely isolated nodes exist in the schemes. To deal with the problem, this paper presents R-Sync, a robust time synchronization scheme for IIoT. We use a pulling timer to pull isolated nodes into synchronized networks whose initial value is set according to level of spanning tree. Then, another timer is set up to select backbone node and its initial value is related to the distance to parent node. Moreover, we do experiments based on simulation tool NS-2 and testbed based on wireless hardware nodes. The experimental results show that our approach makes all the nodes get synchronized and gets the better performance in terms of accuracy and energy consumption, compared with three existing time synchronization algorithms TPSN, GPA, STETS.

124 citations


Cites background from "Clock Synchronization Over IEEE 802..."

  • ...Therefore, many existing time synchronization protocols have been proposed for sensor networks [13]....

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Journal ArticleDOI
05 Mar 2019
TL;DR: An innovative approach for high-performance industrial wireless networks [wireless high performance (WirelessHP)] is presented, based on a substantial redesign of the lower layers of the industrial wireless protocol stack, with the aim of supporting the requirements of critical industrial control applications.
Abstract: Wireless networks are ever more deployed in the industrial control scenario, thanks to the numerous benefits they can bring, especially in terms of costs and flexibility. However, some critical fields of application, such as motion control, power systems automation, or power electronics control, to mention some, have extremely tight requirements in terms of timeliness, reliability, and determinism, which nowadays can only be satisfied by wired communication networks. Indeed, the available industrial wireless solutions are far from offering adequate performance levels, especially in the timing budget, due to the native limitations of their physical (PHY) layers. In this paper, an innovative approach for high-performance industrial wireless networks [wireless high performance (WirelessHP)] is presented, based on a substantial redesign of the lower layers of the industrial wireless protocol stack, with the aim of supporting the requirements of critical industrial control applications. The required levels of timeliness, reliability, and determinism are first derived through a comprehensive survey that looks at real-world application scenarios as well as at the performance of wired networks for industrial control, such as real-time Ethernet networks. The design of a new solution, which is able to satisfy these targets, is then discussed in detail, introducing a low-latency PHY layer that aims at reducing the transmission time of short packets to $1~\mu \text{s}$ , or even less. The feasibility of the proposed solution is presented through an experimental demonstrator based on software-defined radios, while its performance bounds are computed through theoretical analyses. Finally, future activities in the context of WirelessHP are widely discussed, providing an overview of the directions that will have to be addressed, particularly in the design of the upper layers.

87 citations


Cites background from "Clock Synchronization Over IEEE 802..."

  • ...This is a reasonable value, since the TDMA MAC should be able to provide submicrosecond synchronization accuracy to support ultracritical industrial applications and this looks feasible to some extent [63]....

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  • ...The problem of maintaining synchronization in wireless networks has been tackled by many researchers [27], [63], [64], and achieving microsecondlevel synchronization accuracy in TDMA networks looks possible....

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  • ...4, and it has been studied widely in the scientific literature [27], [63], [64]....

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Journal ArticleDOI
21 Mar 2019
TL;DR: An overview of the potential applications, requirements, and unique research challenges to extend time-synchronized networking capabilities over wireless and a classification of wireless applications and a reference architecture for enabling the integration of wired and wireless TSN capabilities in future industrial automation systems are provided.
Abstract: Many industrial automation systems rely on time-synchronized (and timely) communication among sensing, computing, and actuating devices. Advances in Ethernet enabled by time-sensitive networking (TSN) standards, being developed by the IEEE 802.1 TSN Task Group, are significantly improving time synchronization as well as worst case latencies. Next-generation industrial systems are expected to leverage advances in distributed time coordinated computing and wireless communications to enable greater levels of automation, efficiency, and flexibility. Significant progress has been made in extending accurate time synchronization over the air (e.g., 802.1AS profile for IEEE 802.11/Wi-Fi). Given the inherently unreliable, varying capacity and latency prone characteristics associated with wireless communications, proving the feasibility of worst case latency performance over the wireless medium is a major research challenge. More specifically, understanding what levels of capacity, reliability, and latency could be guaranteed over wireless links with high reliability are important research questions to guide the development of new radios, protocols, and time coordinated applications. This paper provides an overview of the potential applications, requirements, and unique research challenges to extend TSN capabilities over wireless. The paper also describes advances in wireless technologies (e.g., next-generation 802.11 and 5G standards) toward achieving reliable and accurate time distribution and timeliness capabilities. It also provides a classification of wireless applications and a reference architecture for enabling the integration of wired and wireless TSN capabilities in future industrial automation systems.

79 citations

Journal ArticleDOI
01 Apr 2020-Heliyon
TL;DR: The purpose of this research is to show a systematic review of the most recent studies about the architecture, security, latency, and energy consumption that FC presents at industrial level and thus provide an overview of the current characteristics and challenges of this new technology.

71 citations

Posted Content
TL;DR: The key features of IEEE 802.11be are introduced and the benefits and requirements of the most representative Internet of Things low-latency use cases for WiFi 7 are reviewed: multimedia, healthcare, industrial, and transport.
Abstract: Short time after the official launch of WiFi 6, IEEE 802.11 working groups are already designing its successor in the wireless local area network (WLAN) ecosystem: WiFi 7. With the IEEE 802.11be amendment as one of its main constituent parts, future WiFi 7 aims to include time-sensitive networking (TSN) capabilities to support low latency and ultra reliability in license-exempt spectrum bands. This article first introduces the key features of IEEE 802.11be, which are then used as the basis to discuss how TSN functionalities could be implemented in WiFi 7. Finally, benefits and requirements of the most representative low-latency use cases for WiFi 7 are reviewed.

49 citations


Cites background from "Clock Synchronization Over IEEE 802..."

  • ...10 ns) and some other minor changes that do not hamper backwards compatibility [38]....

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References
More filters
Proceedings ArticleDOI
Matt Bishop1
03 Dec 1990
TL;DR: The author examines the security requirements of such a service, analyzes version 2 of the NTP protocol to determine how well it meets these requirements, and suggests improvements where appropriate.
Abstract: The network time protocol (NTP) is being used throughout the Internet to provide an accurate time service. The author examines the security requirements of such a service, analyzes version 2 of the NTP protocol to determine how well it meets these requirements, and suggests improvements where appropriate. Five types of security attacks on a time service are possible. An attacker could cause a nontime server to impersonate a time server (masquerade), an attacker could modify some (or all) time messages sent by a time server (modification), an attacker could resend a time server's time messages (replay), an attacker could intercept a time server's time messages and delete them (denial of service), and an attacker could delay the time messages by, for example, deliberately flooding the network, thereby introducing large transmission delays (delay). >

38 citations

Journal ArticleDOI
TL;DR: A careful analysis of timestamp mechanism and time management in a PC platform is carried out and a method for the experimental evaluation of uncertainty contributions is proposed, highlighting that the main uncertainty source of a software-only synchronization approach is the timestamp method.
Abstract: Over the past few decades, centralized computing systems have been replaced by decentralized systems, consisting of simple nodes interconnected by a communication network. The time reference of the distributed nodes must be synchronized in order to be able to coordinate the operation or compare the data collected by the different nodes. Several synchronization protocols have been developed to be used instead of global positioning system or dedicated synchronization systems. For example, the network time protocol (NTP) is a very popular synchronization protocol used to synchronize computers over wide area networks, like the Internet. In addition, IEEE 1588, a synchronization protocol dedicated to high-performance synchronization in local networks, was recently established. However, submicroseconds synchronization can be obtained only using dedicated hardware devices, thereby increasing the cost of each node. For these reasons, PTP software-only implementations are quite common in real systems, with a resulting synchronization uncertainty varying from a few to hundreds of microseconds and quite burdensome to estimate or measure. The work presented in this paper focuses on the analysis of the major uncertainty contributions in a software-only implementation. Particularly, a careful analysis of timestamp mechanism and time management in a PC platform is carried out. In addition, a method for the experimental evaluation of uncertainty contributions is proposed. A test case based on a software implementation of the IEEE 1588 (the so-called PTPd) is presented. The experimental tests presented in the paper highlight that the main uncertainty source of a software-only synchronization approach is the timestamp method. Timestamping accuracy can be affected by the computational load of the node itself: in normal conditions, the maximum uncertainty introduced by the timestamp mechanism is in the order of 10 , but in case of high computational load, it can raise up to 224 μs.

36 citations


"Clock Synchronization Over IEEE 802..." refers background in this paper

  • ...Moreover, choosing a smaller value for kp and ki results in poles with large magnitudes in (11) which lead to larger loop settling times....

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Journal ArticleDOI
TL;DR: This work proposes an enhanced synchronization algorithm for IEEE 1588 in order to compensate the offset error due to the dynamically changing data rate of the wireless link and to enhance the accuracy of time.
Abstract: IEEE 1588 is the clock synchronization protocol for networked measurement and control system, and widely used for both wire-line and wireless network environments. IEEE 1588 was initially considered for wire-line networks, but its application is extended to wireless network especially for indoor wireless networks which can not use Global Positioning System (GPS) technology. However, the conventional IEEE 1588 assumes symmetric/asymmetric fixed data rate links, and time accuracy errors are caused for dynamically changing wireless links. We propose an enhanced synchronization algorithm for IEEE 1588 in order to compensate the offset error due to the dynamically changing data rate of the wireless link and to enhance the accuracy of time.

35 citations


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Book ChapterDOI
01 Aug 2004
TL;DR: The design and implementation of an IEEE 1588 PC software prototype for Wireless LANs (WLAN) is presented and accuracy is improved using two new developed methods for outbound latency estimation.
Abstract: IEEE 1588 is a new standard for precise clock synchronization for networked measurement and control systems in LAN environment. This paper presents the design and implementation of an IEEE 1588 PC software prototype for Wireless LANs (WLAN). Accuracy is improved using two new developed methods for outbound latency estimation. In addition, an algorithm for adjusting the local clock is presented. The achieved accuracy is measured and compared between WLAN and fixed LAN environments. The results show that 2.8 μs average clock offset can be reached on WLAN, while wired Ethernet connection enables 2.5 μs.

34 citations

Journal ArticleDOI
TL;DR: Analyzes various asymmetry mitigation measures for software timestamping and proposes a timestamp correction-based asymmetry compensation scheme that can almost mitigate the link asymmetry without requiring any changes in PTP or additional messages.
Abstract: The IEEE 1588 standard defines the Precision Time Protocol (PTP) which provides mechanisms for synchronizing distributed clocks in packet-based networks. The accuracy of PTP synchronization depends on a number of factors such as the quality of the timestamps, packet delay variation, clock stability, and the asymmetry. In the latest update of the standard, IEEE 1588 version 2008, compensations for asymmetric delays have been introduced into the protocol. However, specific procedures for determining the asymmetry have not been specified. This paper analyzes various asymmetry mitigation measures for software timestamping and proposes a timestamp correction-based asymmetry compensation scheme. Measurements using WLAN synchronization hardware show that the proposed scheme can almost mitigate the link asymmetry without requiring any changes in PTP or additional messages.

34 citations


Additional excerpts

  • ...5)....

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