Roaming HART_A Collaborative Localization System on WirelessHART

RoamingHART:ACollaborativeLocalizationSystemonWirelessHART
XiumingZhu,Pei-ChiHuang,SongHan,AloysiusK.MokUniversityofTexasatAustin{xmzhu,peggy,shan,mok}@cs.utexas.eduDejiChen,MarkNixon
EmersonProcessManagement
{deji.chen,mark.nixon}@emerson.com

Abstract—Localizationinwirelesssensornetworksisanimportant
functionalitythatisrequiredfortrackingpersonnelandassetsin
industrialenvironments,especiallyforemergencyresponse.Current
commerciallocalizationsystemssuchasGPSsufferfromthelim-
itationsofeitherhighcostorlowavailabilityinmanysituations
(e.g.,in-doorenvironmentsthatexcludedirectline-of-sightsignal
reception).Thedevelopmentofindustrialwirelesssensornetworks
suchasWirelessHARTprovidesanalternative.Inthispaper,
wepresentthedesignandimplementationofRoamingHART:a
collaborativelocalizationsystemonWirelessHARTasanindustrially
viablesolution.Thissolutionisbuiltuponseveraltechnological
advances.First,RoamingHARTaddstheroamingfunctionalityto
WirelessHARTandthusprovidesameansforkeepingmobileWire-
lessHARTdevicesconnectedtothenetwork.Second,RoamingHART
employsacollaborativeframeworktointegratedifferenttypesof
distancemeasurementsintothelocationestimationalgorithmby
weighingthemaccordingtotheirprecisionlevels.RoamingHART
adoptsseveralnoveltechniquestoimprovedistanceestimation
accuracyanddecreasestheRSSIpre-surveycost.Thesetechniques
includeintroducingdistanceerrorrangeconstraintstothemeasure-
ments,judiciouslyselectingtheinitialpointinlocationestimation
andonlineupdatingthesignalpropagationmodelsintheanchor
nodes.OurimplementationofRoamingHARTcanbeappliedto
anyWirelessHART-conformingnetworkbecausenomodificationis
neededontheWirelessHARTfielddevices.Wehaveimplemented
acompleteRoamingHARTsystemtovalidateboththedesignand
theeffectivenessofourlocalizationalgorithm.Ourexperimentsshow
thatthemobiledeviceneverdropsoutoftheWirelessHARTnetwork
whilemovingaround;withthehelpofevenonedependableanchor,
usingRSSIcanyieldatleast75%ofdistanceerrorsbelow5meters,
whichisquiteacceptableformanytypicalindustrialautomation
applications.

Keywords-WirelessHART,Real-timeembeddedsystem,Localiza-
tion,Roaming,UWBlocalization,CollaborativeTOA/RSSIlocaliza-
tion

I.INTRODUCTION
Locationdeterminationisanimportantfunctionalityinmany
industrialenvironments.WhileGPSisusedwidelyforthis
purpose,itistoocostlyandmoreimportantly,doesnotwork
wellinmanysituationsbecauseitrequiresline-of-sightsignal
coverage.Inrecentyears,thereisarisingneedforpersonneland
assettrackinginindustryduetothehazardousenvironment.In
particular,itiscriticalforthecontrolcentertoknowhowmany
peoplearebeingexposedtodangerandwheretheyarelocatedin
theplantduringemergencies.Asolutionisnowpossiblewiththe
widedeploymentofWirelessHARTnetworksinrecentyearssuch
thatlow-costandaccuratelocationtrackingbecomespossible.
Figure1showsapilotplantlocatedintheJameRFairProcess
ScienceandTechnologyCenter(PSTC)[1]attheUniversity

TheworkispartiallysupportedbyNSFaward1014146andONRgrantnumber
N000141010359

Fig.1:ApilotplantinPSTC.ThewhitesymbolswithindicesaretheWire-
lessHARTfielddevices.Thecontrolcenterisinthebuildingbehind

ofTexasatAustin.Themainfacilityisa5-floorbuildingfull
ofpipesandvalves.Thecontrolcenterisinsidethebuilding
behindtheplant.Inthisenvironment,GPSonlyworksina
limitedareabecauseofsignalshieldingproblems.However,the
facilitycanbefullycoveredbytheWirelessHARTsignal.Thus,
thereisanopportunitytobuildalocalizationapplicationupona
WirelessHARTnetworkinfrastructure.
Thereareseveralchallengesinusingwirelesssensornetworks
forlocationdeterminationinthisapplicationenvironment.First,
thereisnotyetaroamingfunctionalityspecifiedinWirelessHART
andaWirelessHARTnetworkisnotrequiredtosupportany
mobiledevice.Asaresult,amovingdevicemayloseconnection
soonafteritjoinsthenetwork.Second,whileitispossibleto
useonlyRSSI(ReceivedSignalStrengthIndication)forlocation
estimation,theresultisnotsatisfactorybecauseRSSIisingeneral
notaccurateenough.Whileitispossibletoimprovetheaccuracy
bydeployingmoreWirelessHARTdevicesintheenvironment,
itisnotpracticalbecausethenumberofWirelessHARTdevices
hasbeendeterminedbyprocesscontrolneeds,notforlocalization.
Finally,trilaterationbasedonTOA(TimeOfArrival)measure-
mentsisveryexpensiveifhighcoverageisneeded.Asshownin
Figure1,inordertogetatleastthreedirectdistancemeasurements
atanylocation,manyanchorsmustbedeployedtoenableline-
of-sightcommunication.
Inordertoprovidebothacost-effectiveandaccurateenough
localizationserviceintheabovescenarios,wehavedesignedand
developedRoamingHART:acollaborativelocalizationsystemon
WirelessHART.Thetechnicalcontributionsareasfollows:

•
RoamingHARTaddstheroamingfunctionalityonWire-
lessHARTtoprovidethenecessaryplatformforlocalizing
mobilenodes.WhileWirelessHARTisbasedonwireless
communication,thecurrentstandardsupposesthatalldevices
arekeptatthesamelocationforalongtime;thereislittle

2012 IEEE 18th Real Time and Embedded Technology and Applications Symposium
1080-1812/12 $26.00 © 2012 IEEEDOI 10.1109/RTAS.2012.37241