1-4244-1506-3/08/$25.00 ©2008 IEEEWhen HART Goes Wireless: Understanding and Implementing theWirelessHART StandardAnna N. Kim‡Fredrik Hekland†Stig Petersen§Paula Doyle‡Centre for Quantifiable Quality of Service in Communication Systems (Q2S)∗Norwegian University of Science and Technology, Trondheim, Norway†ABB Corporate Research Centre (CRC),§Sintef ICT Trondheim, Norway‡ABB Strategic R&D for Oil and Gas, Oslo NorwayAbstractAs a newly released industrial communication stan-dard, WirelessHART complements the ever so successfulHART field devices by providing the possible means forcommunicating via wireless channels. The WirelessHARTstandard is d esigned to offer simple configuration, flexibleinstallation and easy access of instrument data, and at thesame time, ensure robust and reliable communications. Inthis paper, we first look closely into the specifications andpresent a comprehensive overview of the standard by sum-marizing the main functions of the various protocol lay-ers. We then survey the literature and identify amongstthe existing methods and algorithms, which ones can beeffectively adopted in implementing the standard. Morespecifically, we set our fo cus on issues relating to realiza-tion of the medium access layer and the network manager,which are essential in creating a successful WirelessHARTnetwork for specific applications.1. IntroductionThe adoption of wireless technology has been slow inthe process automation and manufacturing industries. Amajor reason for this has been the lack of an open stan-dard which both fulfills the industrial requirements as wellas ensures that the customers are not locked to one singlesupplier. This is about to change, at least for the processautomation industries. Owing to the HART Communica-tion Foundation and its member companies’ efforts to cre-ate a wireless interface for the HART standard, the bene-fits of wireless access to field instruments might finallyoutweigh th e risks and uncertainties of rolling out a wire-less network to the field devices.∗Centre for Quantifiable QoS in Communication Systems, Centre ofExcellence is appointed by the Research Council of Norway (NFR) andfunded by NFR, NTNU and Uninett.The author(s) wish to acknowledge the support of NFR and the TAILIO project for their continued funding and support for this research. TheTAIL IO project is an international cooperative research project led byStatoilHydro and an R&D consortium consisting of ABB, IBM, AkerKvaerner and SKFThe HART field communication protocol h as morethan 20 years on its back and is still going strong. Withan estimated 24 million devices in operation, the standardhas proven its worth and shows no sign reduction is saleseither. Although part of the explanation of HART’s popu-larity is the failure to create a single standard for a digitalfieldbus, the major motivation for customers to still chooseHART in 2008 is its inherent simplicity and robustness.The combination of the analog 4-20mA control loop witha superimposed digital signal for configuration and diag-nostics simply works, and requires much less training thanthe competing digital fieldbuses. Another drawback of thedigital fieldbuses is the higher power consumption due tohigher complexity.With the release of Version 7 of the HART protocol inSeptember 2007, the process automation industry now hasaccess to an open standard which offered a wireless inter-face to field devices, referred to as WirelessHART. Wire-lessHART p romises to bring the heritage o f simplicity androbustness the customers know from the earlier revision ofthe HART standard. Little or no training is necessary forthe plant workers to start using the wireless products as thewireless mesh network is self-organizing. Robust com-munication is expected through the application of modula-tion techniques like both direct-sequence spread-spectrum(DSSS) and frequency-hopping spread-spectrum (FHSS),as well as by retranmission mechanisms and spatial pathdiversity through the mesh network. Proper data secu-rity is also covered in the standard; a multi-layered ap-proach for authentication, integrity and encryption usingwell-tested encryption algorithms ensures the user can se-lect the level of security necessary for the plant.Communication standards th at are similar to Wire-lessHART include Zigbee [3] and ISA 100 [4]. The Zig-Bee specification is a low rate, low power wireless meshnetworking standard developed by the Zig Bee Alliance,primarily targeting home automation and consumer elec-tronics applications. Initially released in 2004 and up-dated in 2006, the specification provides a network andapplication layer on top of the PHY and MAC layers ofthe IEEE 802.15.4 specification.899Authorized licensed use limited to: Univ of Calif Berkeley. Downloaded on January 17, 2010 at 20:22 from IEEE Xplore. Restrictions apply.Unlike WirelessHART, ZigBee does not support fre-quency hopping. A ZigBee network operates on the samestatic channel throughout its entire lifetime. The use of astatic channel makes the ZigBee networks more suscep-tible to noise and interference, and because of this, Zig-Bee has not been regarded as robust enough for harsh ra-dio frequency environments often encountered in indus-trial applications. To counter this, and to gain more mo-mentum as a viable option for industrial instrumentation,the ZigBee Alliance released the ZigBee PRO specifica-tion in October 2007. The ZigBee PRO is specificallyaimed at the industrial market, employing, among otherthings, enhanced security features as well as a new ”fre-quency a gility” concep t which allows fo r an en tire net-work to change its operative channel when faced with re-duced link q ualities caused by noise and/or interference.Frequency hopping, which is a more flexible solution thatthe frequency agility, requires modifications to the IEEE802.15.4 MAC layer, and as the ZigBee Alliance want tofully adopt the IEEE 802.15.4 specification, this is not aviable option for ZigBee PRO.ISA100 on the other hand, is more of a closer con-testant for industrial communications. The goal of theISA100 standards committee is to create a family of wire-less standards for industrial automation. The first standardto emerge will be the ISA100.11a Release 1, which is ex-pected to be ratified by the fourth quarter of 2008. Theaim of the ISA100.11a is to provide secure and reliablewireless communication for fixed, portable and movingdevices