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.
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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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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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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
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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24 Oct 2008
TL;DR: The implementation of a grandmaster clock with two separate network ports, one operating as a V1 and one as aV2 compliant grandmaster is described and the test setup used at the LXI Plug-fest in Toronto, Canada is described.
Abstract: Since the release of the first version of IEEE 1588 in 2002 a significant number of vendors released V1 compliant devices to the market. Since V1 compliant devices can be negatively affected by V2 compliant devices when they are operating in the same network segment, a scheme for synchronizing both V1 and V2 devices based on the same time source is required in order to allow end users to smoothly migrate to V2 while maintaining a common timebase among all their devices. The LXI Consortium, maintainer of the LXI (LAN eXtensions for Instrumentation) Standard for Test & Measurement designed a possible solution which requires a grandmaster clock with two separate network ports, one operating as a V1 and one as a V2 compliant grandmaster. This paper describes the implementation of such a device and the test setup that was used at the LXI Plug-fest in Toronto, Canada. The plug-fest was part of the LXI General Meeting which was hosted by Testforce Systems from May 20th to May 23rd, 2008.
5 citations
"Clock Synchronization Over IEEE 802..." refers background in this paper
...…a de facto standard for CS in various applications domains such as industrial automation, telecommunication, and entertainment [5]–[7], owing to its simple structure and ability to achieve high CS performance in nanosecond range using hardware timestamping and dedicated networking elements [8]....
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12 Nov 2015
TL;DR: This paper introduces a concept, how the clocks of low-complexity stationary receivers can be adjusted to the same frequency with the help of a television broadcast signal.
Abstract: Synchronization of a Wireless Sensor Network is a crucial task and is based on a precise syntonization of all clocks within the network. The synchronization precision is usually closely connected to the positioning accuracy in networks for the purpose of localization. This paper introduces a concept, how the clocks of low-complexity stationary receivers can be adjusted to the same frequency with the help of a television broadcast signal. Only parts of the signal information are used to achieve a manageable data rate for the embedded low-power processor. With a new algorithm the performance of the frequency estimation can be kept high compared to the use of the total signal energy, while the processing load can be reduced dramatically.
4 citations
TL;DR: This approach combines network coverage planning on the physical layer, bandwidth management on the link layer and live network monitoring to improve the reliability, availability and maintainability of a WMN.
Abstract: Wireless Mesh Networks (WMNs) are replacing wireless Infrastructure networks in many areas because of their lower cost and higher flexibility. However, applications in the Process Industry and Telerobotics field require not only flexible but also dependable service, which is not provided by existing solutions. To make a WMN dependable, many problems have to be solved on different layers. With this paper, we describe our ongoing work to provide an integrated solution to increase the dependability of WMNs. Our approach combines network coverage planning on the physical layer, bandwidth management on the link layer and live network monitoring to improve the reliability, availability and maintainability of a WMN. We provide fine-grained means to improve the predictability of the network components, thus making the WMN more dependable. In this paper, we present first results of our ongoing work, and describe how they are interleaved.
4 citations
Patent•
28 Apr 2009TL;DR: In this article, a time stamp counter (TSC) register of the CPUs in a multiprocessor computer system is used to detect the clock skew between the various CPUs in the system.
Abstract: Systems and methods (“utility”) for providing more accurate clock skew measurements between multiple CPUs in a multiprocessor computer system by utilizing the cache control or management protocols of the CPUs in the multiprocessor system. The utility may utilize a time stamp counter (TSC) register of the CPUs in the multiprocessor computer system to detect the clock skew between the various CPUs in the system. Further, the delay between measurements of the TSC registers of the CPUs may be minimized by utilizing the features of the hardware cache control or management protocols of the computer system, thereby providing more accurate clock skew measurements.
4 citations
01 Jan 2007
TL;DR: Simulation results indicate that this approach can tolerate the message loss and achieve a continuously clock synchronization and can release the burden of computing overhead compared to the software-only solution.
Abstract: Keeping distributed clocks closely synchronized is one of the basic requirements in wireless real-time embedded applications. This paper presents a hardware-assisted clock synchronization scheme for wireless real-time application based on the IEEE 802.11 standard. The implementation algorithm is designed based on the principle of feedback control systems which tracking the value of timestamps in an IEEE 802.11 AP, this approach can release the burden of computing overhead compared to the software-only solution. Simulation results indicate that this approach can tolerate the message loss and achieve a continuously clock synchronization.
4 citations