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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
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Proceedings ArticleDOI
24 Oct 2013
TL;DR: This paper shows how to capture and calculate the impairments relevant for the servo clocks, in particular the oscillator wander, and shows that proper parametrization of the PI controller is the key for minimizing the clock offset to the grandmaster.
Abstract: Slave servo clocks are of essential importance to maintain synchronization between the grandmaster and its associated slaves. The servo structure and parametrization should ideally achieve fast settling times, minimize the clock jitter, and keep the clock offset below a predefined boundary. Commonly used solutions for this challenge are adder-based clocks or voltage controlled oscillators together with proportional-integral (PI) controllers. This paper shows how to capture and calculate the impairments relevant for the servo clocks, in particular the oscillator wander. Based on these data we show that proper parametrization of the PI controller is the key for minimizing the clock offset to the grandmaster.

30 citations


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

  • ...Nevertheless, performance requirements for TSF in IEEE 802.11 are not particularly high; accuracy and precision in the range of a few microseconds are sufficient, which is still achievable with hardware timestamps from TSF timers even if no propagation delay compensation is performed....

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  • ...In the RR paradigm, the receivers do not synchronize to the sender time, but use a broadcast message from the sender as a timing signal....

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Journal ArticleDOI
TL;DR: A survey and classification of IEEE 802.11 wireless parameters and open source tools available to collect or estimate these parameters and the combination of tools that best suit the needs of the wireless experiments are proposed.
Abstract: The analysis and evaluation of new wireless network protocols is a long process that requires mathematical analysis, simulations, and increasingly experimentations under real conditions. Measurements are essential to analyze the performance of wireless protocols such as IEEE 802.11 networks in real environments, but experimentations are complex to perform and analyze. Usually, network researchers develop their own tools, sometimes from scratch, to fit the requirements of their experimentations, and these tools are then abandoned when the paper is published. In this study, we emphasize the importance, for the network research community, to use and contribute to the development of open source measurement tools. In this regard, we propose a survey and classification of IEEE 802.11 wireless parameters and open source tools available to collect or estimate these parameters. We highlight the parameters that can be extracted from wireless traffic probes and those that are available through the driver of wireless cards. Then, we introduce and compare open source tools that can be used to make the measurements, with special attention to the flexibility of the tools and their application scope. Finally, we discuss with several case studies the combination of tools that best suit the needs of the wireless experiments and provide a list of common pitfalls to avoid.

27 citations

Proceedings ArticleDOI
19 Nov 2007
TL;DR: A behavioral simulation of PTP synchronization, based on the OMNeT++ simulator, which allows to focus on fundamental aspects of analysis and can be useful to assess the suitability of P TP synchronization in relation to network architecture and operating conditions, as well as for the optimization of clock servo design.
Abstract: In the paper we present a behavioral simulation of PTP synchronization, based on the OMNeT++ simulator. Node, link and traffic source behavior are represented by statistical source and flow models. This approach, which differs from most approaches to PTP analysis, allows to focus on fundamental aspects of analysis and can be useful to assess the suitability of PTP synchronization in relation to network architecture and operating conditions, as well as for the optimization of clock servo design.

26 citations


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

  • ...In the master–slave design, the master or the reference clock is chiefly responsible for synchronizing the slaves in the network via unicast or multicast messages....

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Journal ArticleDOI
J. Aweya1
TL;DR: This paper describes the architecture, servo algorithm, and phase-locked loop (PLL) of a method for implementing differential clock recovery over packet networks that is general enough to be applied in a wide variety of packet networks such IP, MPLS, Ethernet, etc.
Abstract: Accurate timing transfer and recovery over packet networks (IP, Ethernet, MPLS, etc.) has become an important requirement for delivering many telecommunication services. This requirement stems from the fact that current networks are migrating from time-division multiplexing (TDM) technologies to packet based ones, and also the need to synchronize the many timing-dependent devices like TDM access devices and wireless base stations. Unlike TDM, packet networks are asynchronous by design and do not have embedded timing transfer capabilities. Differential clocking is used when there is a network interface with its own reference source clock (the service clock) and there is the need to transfer this clock over a core packet network (with its own independent reference network clock) to another interface. The network clock serves as a sampling clock for the service clock. Timing transfer and recovery over a packet network is a networked control problem given the difficulty in making the recovered clock at the remote location compliant with strict telecom standards. In this paper, we describe the architecture, servo algorithm, and phase-locked loop (PLL) of a method for implementing differential clock recovery over packet networks. The technique involves a clock source or transmitter sending counter values to a receiver from a counter that is clocked and reset, respectively, by the service clock and network clock. It is general enough to be applied in a wide variety of packet networks such IP, MPLS, Ethernet, etc.

26 citations

Proceedings ArticleDOI
05 May 2014
TL;DR: This work addresses the synchronization means provided by the IEEE802.11 standard, including the ones mentioned by IEEE 802.11v, and analyses the impact of both software and hardware timestamps on the synchronization performance through test-bed implementations.
Abstract: The possibility of equipping devices on the factory floor with wireless communication has brought up new applications and challenges. Among one of these challenges is clock synchronization which is required for easy network management and monitoring. The IEEE 802.11v amendment to IEEE 802.11 has opened the doors for establishing clock synchronization in industrial applications by providing mechanisms and guidelines for synchronization. This work addresses the synchronization means provided by the IEEE 802.11 standard, including the ones mentioned by IEEE 802.11v, and analyses the impact of both software and hardware timestamps on the synchronization performance through test-bed implementations. The results indicate that there are several elements which can affect the quality of both software and hardware time-stamps, which in turn affect the synchronization performance. Moreover, it is also shown that the timestamping accuracy itself is only one factor, and other factors such as control loop settings and synchronization interval also affect the final synchronization performance over WLAN.

26 citations


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

  • ...In addition to Beacons, Probe Response frames are also used to perform TSF timer synchronization....

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  • ...This method is a part of IEEE 802.1AS-2011 [7], which is the standard to provide CS guidelines for time-sensitive applications in wired-wireless audio–video bridging (AVB) networks....

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