Elsevier

Computer Networks

Volume 67, 4 July 2014, Pages 1-13
Computer Networks

Adding accurate timestamping capability to wireless networks for smart grids

https://doi.org/10.1016/j.comnet.2014.03.005Get rights and content

Abstract

Smart grids rely on bi-directional communications between energy production sites and utilization sites. Usually, different approaches are used for implementing the required Wide, Field, and Home Area Networks (WAN, FAN and HAN, respectively). These networks are realized using very different (hybrid) technologies, for instance wired for WAN and wireless for FAN and HAN. However, an accurate common sense of time must be guaranteed among all smart grid participants, as it happens in any other distributed systems. Satisfying this need is challenging for wireless networks, while mature time distribution technologies are available for wired networks. The major issue for wireless devices is to provide accurate timestamping of network events, the key element of any time synchronization protocol. The objective of this paper is to propose low-cost and low-complexity timestamping techniques that also maintain full compatibility with already existing (unlicensed) communication standard for wireless nodes used in smart grids. In addition, a suitable platform exploiting the Software Defined Radio paradigm for comparative evaluation of these techniques is also discussed. Simulation and experimental results confirm the feasibility of the proposed approach, with the standard deviation of the timestamping error scalable down to 5 ns.

Introduction

The advantages offered by smart grids are widely known: improved safety and efficiency, better use of existing assets, enhanced reliability, and power quality. Several governments are pushing the transformation of the legacy power grid into a newer smart grid in order to satisfy efficiency, sustainability, resilience and global warming issues [1], [2].

From the architectural point of view [3], a smart (power) grid can be divided into three different tiers: the physical power tier (including generation and distribution), the communication networking tier, and the application tier (including advanced services as smart remote metering and load management).

The communication tier allows devices to exchange information on power demand, thus maximizing the overall efficiency. An ensemble of very heterogeneous solutions is adopted in order to cover different requirements ranging from power plants interconnection by means of high-speed geographical networks to local networks of home appliances, as confirmed by several survey works [4], [5].

Despite the hybrid approach previously described, an accurate common sense of time must be guaranteed among all smart grid participants. Sharing the time reference is crucial for merging/elaborating the information collected through the entire network, as it happens in many other distributed systems [6]. Time distribution on wired networks is widely investigated [7] and may be applied, for instance, to Wide Area Networks (WAN) for smart grids. Conversely, if certain sections of the network are implemented using wireless communication, some issues may arise. Even if a high number of wireless time synchronization protocols have been proposed [8], the major problem for wireless devices is to provide accurate timestamping of network events due to intrinsic characteristics of the communication medium (noise, interferences, etc.).

The aim of this paper is to propose new accurate timestamping techniques that can be used, potentially, with any existing solution for wireless networking maintaining low-cost and low-complexity. The proposed methods are designed to have the following characteristics:

  • full compatibility (at data level) with unlicensed wireless standard communications systems used in smart grid networks;

  • full interoperability between devices with (enhanced) timestamping and devices without timestamping (i.e. using today commercially-available transceivers).

In particular, this work suggests two possible solutions: received signal thresholding, and adding chirp preamble to frames. The feasibility of the proposal is proved by means of a flexible transceiver based on a Software Defined Radio (SDR), as done in [9].

The paper is structured as follows. A brief overview of the smart grid network architectures, focusing of wireless technology and time synchronization, is given in Section 2. In Section 3 some timestamping methodologies are introduced. In Section 4, the proposed approach for timestamping evaluation is described, and in Section 5 a case study is analyzed, showing the effectiveness of the proposed solutions. Finally, conclusions are drawn.

Section snippets

Smart grids networks

The communication networks used by smart grids must cope with very dissimilar requirements: high availability and reliability; large coverage area; interconnection of different objects. The smart grid network may be divided into three different segments [3], [10]:

  • 1.

    The home area networks (HANs), connecting appliances with smart meters.

  • 2.

    The advanced metering infrastructure or field area networks (AMI/FANs), moving information from premises towards an aggregation point.

  • 3.

    The wide area network (WAN)

Timestamping techniques

A wireless receiver already performs time synchronization in order to track the transmitter; there is a natural progression from carrier frequency locking, through clock recovering (i.e. symbol timing estimation) and finally to frame synchronization (i.e. locating words and other structures in the symbol stream). The timestamping mechanism is based on the precise marking of a time instant corresponding to a particular field within data packets, e.g. the frame delimiter. Working on the base band

The proposed approach

According to the goals of this work stated in the introduction, two timestamping techniques have been implemented and evaluated. They are compatible (and tested) with standard communication protocol for smart grid wireless HAN devices operating in the 2.4 GHz region (e.g. IEEE802.15.4-2006). Moreover, they can be ported in the TVWS band, i.e. in a single TV channel (6 MHz wide), thus allowing to cover FAN requirements.

The evaluation process is focused on threshold and chirp based timestamping

Experimental evaluation

The aim of experimental tests is to evaluate the feasibility of the proposed approach. Some considerations about capabilities of commercial IEEE802.15.4-2006 devices are preliminary discussed for sake of completeness. It should be noted that the timestamping performance determined by simulations and experiments is independent of the synchronization protocol, hence the results are significant both for sender/receiver and receiver/receiver strategies. In the following, the test signal transmitted

Conclusions

Smart grids are becoming a reality, whose advantages and benefits are well known. The smart grids rely on hybrid communication networks in order to satisfy the heterogeneous requirements of WAN, FAN and HAN. The very different implementation of these networks (wired, wireless) may impair the distribution of a common time reference across the smart grid. Whatever the time synchronization protocol is adopted, the performance depends on timestamping of network events; FANs and HANs are usually

Paolo Ferrari was born in Brescia, Italy, in 1974. In 1999 he graduated with honors in Electronic Engineering at the University of Brescia, Italy, where, in 2003, he received the Ph.D. degree in Electronic Instrumentation. He is employed as Assistant Professor with the Department of Electronics and Automation, University of Brescia. His main research activities are signal conditioning and processing for embedded measurement instrumentation, smart sensors, sensor networking, smart grids,

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    Paolo Ferrari was born in Brescia, Italy, in 1974. In 1999 he graduated with honors in Electronic Engineering at the University of Brescia, Italy, where, in 2003, he received the Ph.D. degree in Electronic Instrumentation. He is employed as Assistant Professor with the Department of Electronics and Automation, University of Brescia. His main research activities are signal conditioning and processing for embedded measurement instrumentation, smart sensors, sensor networking, smart grids, Real-time Ethernet, and fieldbus applications. He is member of IEC TC65C MT9. He has authored and co-authored more than 80 international papers.

    Emiliano Sisinni was born in 1975 in Lauria (PZ), Italy. In 2000 he graduated in Electronics Engineering at the University of Brescia. He obtained his Ph.D. degree in Elettronic Instrumentation in 2004. Since 2005 he has become Assistant Professor. His research activity focuses on numerical signal analysis and on industrial communication systems, mainly implemented by wireless sensor networks. He has been involved in the development of new wireless communication solutions, including instruments for wireless sensor networks testing. Recently, he has been involved in the foundation of the department wireless sensor networking laboratory. He actively seats in national and international standardization bodies, including WG16 and WG17 of the IEC TC65C regarding industrial communications. He has authored and co-authored more than 70 international papers.

    Alessandra Flammini graduated with honors with a Laurea degree in Physics at the University of Rome in 1985. From 1985 to 1995, she was involved with industrial research and development on digital drive control. She is currently with the University of Brescia, Italy, where she was a Researcher from 1995 to 2002 and has been an Associate Professor since 2002. She is the responsible of the Electronics Laboratory and since 2004 she realized the National Competence Centre of PNI (Profibus Network Italia) for PROFIBUS and PROFINET. Her main research activity includes: electronic instrumentation; digital processing of sensor signals; smart sensors; wired and wireless sensor networks with a special attention to synchronization. She has authored and co-authored more than 150 international papers.

    Alessandro Depari was born in Italy, in 1976. He received the Laurea degree in electronics engineering and the Ph.D. degree in electronic instrumentation from the University of Brescia, Brescia, Italy, in 2002 and 2006, respectively. Since 2007, he has been an Assistant Professor (Researcher) with the Department of Information Engineering, University of Brescia. He is a coauthor of more than 50 scientific papers published on international journals and conference proceedings. His research interests are in the areas of signal conditioning and processing for chemical sensors, particularly resonant and resistive sensors for artificial olfactory systems, the development of sensor networks for distributed measurement, and the design of methods and digital electronic circuits for numeric measurement instrumentation.

    This work was supported in part by the Italian research grants MIUR PRIN 2009 “New generation hybrid networks in measurement and industrial automation applications – Characterization and wired/wireless performance measurement” N. 2009ZTT5N4_002.

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