u-blox’ Dead Reckoning for Automotive Applications

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Intelligent solutions for modern urban navigation

Dr. Etienne FaveyVP Software Development, u-blox

Dr. Alexander SomieskiSoftware Design Engineer, u-blox

Dr. Christine HollensteinSoftware Design Engineer, u-blox

Michael AmmannVP Application Engineering, u-blox

Carl FengerProduct Communications Manager, u-blox

August 2010

Whitepaper by:

Table of contents Executive Summary 3

Intelligent solutions for modern urban navigation 4

Challenges to urban navigation 4

A solution: GPS enhanced with Dead Reckoning 5

Distance Sensing 5

Sensing distance travelled 6

Sensing direction 6

Map matching 6

The u-blox ADR solution 7

u-blox Automotive DR solution: drive test in Chicago 7

Solution for Automotive Tier-1 suppliers 8

Solution for After-market devices 9

Additional reading 9

About the Authors 10

About u-blox 11

u-blox’ Dead Reckoning for Automotive Applications / Whitepaper Published by u-blox AG | 2

Executive Summary Increasinglydenseurbanenvironmentsposeasignificantproblemtonaviga-tionsystemsbasedonthereceptionofextremelyweakGPSsatellitesignals.Asevermoresystems(e.g.roadpricing,fleetmanagement,emergencyservices,etc.)dependonreliable,uninterruptednavigation,“DeadReckoning”GPSisbecomingincreasinglyimportant.

DeadReckoningaidstraditionalGPSnavigationviaintelligentalgorithmsbasedonavehicle’sdistanceanddirectionalchangesduringGPSsignalinterruption.u-bloxprovidestwosolutionsforDeadReckoningGPSbasedonindividualwheelspeedand/orgyroscopicinformation:

1) For first-mount navigation and emergency call systems: u-blox’AutomotiveDeadReckoning(ADR)GPSreceiverchipsarede-

signedforin-carnavigationandtelematicssystemsusinggyroand/orwheeltickinformationtakendirectlyfromthevehicledatabus.

2) For After-Market add-on devices: Independentofthevehicledatabus,u-blox’LEA-6Rstand-aloneGPS

receivermoduleinterfacesdirectlytothevehicleodometerandgyro.Itisthereforesuitableforafter-marketdevicessuchasfleetandassetmanagement,road-pricingandinsurancesystemsaswellasAutomaticVehicleLocators(AVL).

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Dead Reckoning u-blox’ Dead Reckoning for Automotive Applications

An intelligent solution for modern urban navigation

Asmillionsofpeoplemigratetocitiesacrosstheglobe,higheranddenserbuildingconstructionhasbecometheonlywaytoaccommodatetheincreasingpopulation.Addtothattherequirementtoaccommodatemorecarsandincreasedundergroundtrafficroutes,andyouhaveasignificantchallengetoGPSnavigationinmoderncities.

BecauseGPSsatellitestransmittheirsignalswiththeequivalentpowerofa30wattlightbulbfromadistanceof20,000km,theyarrivewithtypi-calsignalstrength,inthebestcase,of–120dBm(1x10–15Watts).ThisismillionsoftimesweakerthanatypicalhomeWiFisignal!Thesesignalscaneasilybedegradedbyanadditional20-30dBincityconditions,orblockedcompletely,furtherimpactingtheaccuracyofGPSnavigation.

Challenges to urban navigation

Forcarnavigationdevices,atleast4GPSsatellitesmustbeidentifiedandtheirsignalsreceivedanddecodedbeforeapositioncanbedetermined.Withoutthis,GPSnavigationisimpossible.

NumerousbarrierstoalreadyweakGPSsignalsinclude:

• Tunnelsandparkinggarages,theworstcasescenariowhereGPSsignalsarecompletelyblocked

• Multi-levelroads,overpassesandbridgeswhichcanconfuseGPSreceiver(whichroadamIon?)

• TallbuildingswhichcanreflectGPSsignals(multipathpropagation),fool-ingaGPSreceiverintothinkingitissomewhereelse

Theendresultoftheseobstructionsrangefromminorirritationtomajorproblem:

• Fordriversunfamiliarwiththearea,navigationcanbeintermittentorfailaltogether,especiallywhenexitingtunnelsandparkgarages,resultinginirritation,wastedtimeandfuel

• Forcommuterswhomayalreadyknowtheirway,traffic-jamavoidanceservicescanberendereduseless

• Forpublictransportationsystemssuchasbusesandtrams,thelossof expectedarrivaltimesposesaninconveniencetothousandsofcommuters

• Forcommercialtransportationservicessuchastaxis,freightandlogisticscompanies,thelossofpositionaloverviewandsecurityoftransportedgoodscanhavemajorfinancialramifications

• Emergencyvehiclessuchaspolice,fireandambulanceservicesarepre-ventedfromreachingthelocationofanincidentquickly

• Systemsusedforautomaticroad-pricingorpay-as-you-driveinsurancehaveinsufficientdatatochargeforroadusage

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Dead Reckoning GPS extends cover-age to areas without GPS reception, while boosting accuracy in areas with adverse signal conditions such as urban areas with heavy multipath effects.

Dead Reckoning A solution: GPS enhanced with Dead Reckoning

Toaddressthisgrowingproblem,u-bloxhasintegratedDeadReckoningfunctionalityintoitsGPSreceiverchiptechnology.DeadReckoningisactu-allyacenturiesoldconceptoriginallyusedbysailorstoextrapolatetheirpositionbasedonhowfarandinwhatdirectiontheyhavetravelledfromalastknownlocation,typicallythelastharbor.

Basedonproprietary“SensorFusionDeadReckoning”technology,u-bloxADRaccomplishesthesametaskwhentravellingthroughregionsofpoorGPSreception.Basedonthelastknownposition,vehiclesensorsfeedinfor-mationtotheu-bloxGPSreceiverindicatinghowfarandinwhatdirectionthevehiclehastravelled.TheGPSreceiverprocessesthesensordataandblendsitwithGPSpositionalreadings.Inthisway,abetterapproximationofwherethevehicleactuallyiscanbeextrapolated,regardlessofGPSsatel-litevisibility.

DeadReckoninghasonedrawback:thedisplacementandheadingerrorsaccumulateovertime.Theerrorsdependontheaccuracyofthesensors,dataquantizationerrors,andtimegranularity.ItisthejobofDeadReckon-inghardwareandsoftwaretominimizetheerrorsforaslongaspossibletoprovideaccuratelocationinformationduringshortsignalinterruptionsaswellaslongdrivesthroughtunnels.

ThefigurebelowillustratesaccumulatedDeadReckoningerror.

u-blox’ Dead Reckoning for Automotive Applications / Whitepaper Published by u-blox AG | 5

AccumulatedDeadReckoningerror

ThefollowinglistshowstypicalsensorandinformationsourcesusedbyDeadReckoningtechnologytocalculateaposition:

Distance Sensing:

• Odometerpulses(absolutedistancetravelled,thisismosttypical)

• Distanceinformationfromwheelticks

• Digitalspeedinformation(distanceisreconstructedfromasingle

integration)

• Linearaccelerometers(distancereconstructedfromdouble-integrating

acceleration)

• Radar,optical,andacousticsensors

Direction Sensing:

• Turnratesensor(gyroscopes,mosttypical)

• Linearaccelerometers

• Steeringlinkageangularsensor

• Differentialwheelspeedinformation(betweenleftandrightwheels)

• Magneticcompass

LEA-6Ru-blox GPS module withintegrated Dead Reckoning

u-blox’ Dead Reckoning for Automotive Applications / Whitepaper Published by u-blox AG | 6

Dead Reckoning Sensing distance travelled

Thereareavarietyofsensortechniquesfordetectingdistancetravelled.Typicallyadirectconnectiontothevehicle’sodometerisenough.Ifthisisnotavailable,forexampleforafter-marketinstallations,wheelsensorscanprovidetherawinformationfordistancetravelled.ThevariablereluctancesensorandHallEffectpositionsensoraretwocommontypesofelectro-magneticsensorsforthispurpose.

Sensing direction

Besidesdistance,directionorturn-rateinformation(measured,forexample,indegreespersecond)isalsoneededtoextrapolatethetravelledroute.Theeasiestapproachistouseasmallturn-ratesensor,alsocalledagyroscope.Severaltypesofgyroscopesexist:mechanical(arotatingmasssuspendedingimbals),optical,andmicro-electromechanicalsystem(MEMS)vibratingstructures.

Thefirsttwotypesprovideexcellentaccuracybutarelargeandexpensive.MEMSgyroscopesexcelintheirsmallsize,goodperformance,anduser-friendlinessandarerelativelyinexpensive.Theyarealsoavailableassurface-mountdeviceseasilyinstalledonaprintedcircuitboard.

Map matching

Inaddition,atechniqueknownasmapmatchingcanbeused.Basedonanactualmap,applicationsoftwareknowstoalwaysreportapositionlocatedonanactualroad,eveniftheextrapolationcalculatedbytheGPSreceiverisslightlyoffduetoaccumulatedpositionandheadingerror.

Ultimately,anapproachofusingtheDeadReckoningsolutionbasedonbothGPSandsensormeasurementssimultaneouslytogetherwithmapmatchingdeliversthebestresultincityenvironmentswhereawiderangeofsignalconditionscanbeexpected:partial,reflected,andblockedGPSsignals.

u-blox’ Dead Reckoning for Automotive Applications / Whitepaper Published by u-blox AG | 7

Dead Reckoning The u-blox ADR solution

u-blox’ADRsolutionisbasedontheKalmanFilter,amathematicalconceptfirstpublishedin1960byHungarian-Americanmathematician,RudolfE.Kalman.Theconceptiswidelyusedincontrolsystems,avionics,andspacevehicles.Thefilterisverypowerfulandabletoestimatepresentandfuturestatesofasystem,evenwhentheprecisenatureofthesystemisunknown.

Inthecaseofu-bloxADR,atightly-coupledKalmanfilteralgorithmispro-grammedintheGPSchiptodeterminevehiclelocationbasedonweightedaveragesofmultiplesensordatainputprovidedbytheGPSreceiver,wheel-tickand(optional)gyroscopesensors.Theresultisanestimatedpositionthatliesin-betweenthepredictedandmeasuredlocationthatisfarmoreaccuratethanifeithermethodswereusedalone.Thisprocessisrepeatediteratively,withthenewestimateusedinthefollowingcalculation.

DuringtimesofgoodGPSsignalreception,themeasurementsfromthevehiclesensorsareconstantlycalibrated.IflaterasituationwithbadornoGPSsignals(i.e.urbancanyons,tunnels)isencountered,theubloxADRsolutioncontinuestoprovideahighlyaccuratelocationbasedonthevehiclesensors’inputs.

Theu-bloxADRsolutionhasbeenextensivelytestedinreal-worldenviron-ments,includingcitydrivetestsinDetroit,Chicago,SanFrancisco,NewYorkCity,andZurichwithexcellentresults.Thefigurebelowshowstheperformanceofu-blox’ADRsolutionduringadrivetestinChicagoversusGPSalone.

u-blox Automotive DR solution: drive test in Chicago

Thisdrivetestwasdonethroughdenseurbancanyons,includingsomeoftheworld’stallestskyscrapers,aswellasthroughundergroundtunnels.Ascanbeseenbythepositionaltraces,theu-bloxADRsolution(right)deliv-eredamuchhigherdegreeofaccuracythanasystemrelyingonGPSsatel-litesignalsalone(left).

u-bloxAutomotiveDRsolutionGPSonly

u-blox’ Dead Reckoning for Automotive Applications / Whitepaper Published by u-blox AG | 8

Dead Reckoning Solution for Automotive Tier-1 suppliers

Idealforfirst-mountnavigationsystems,u-blox’AutomotiveDeadReckoningSolution(ADR)blendsdatafromGPSsatelliteswithwheeltickand(op-tional)gyroscopeinformationtakendirectlyfromthevehicledata(i.e.CAN)bus.Makinguseofthedataavailablefromthevehicledatabusbringscostsavings;noadditionalsensorsarerequiredtoimplementDeadReckoning.Thesolutionrunsonublox’GPSreceiverchipandisahighly-accuratesolu-tionforin-carnavigationandvehicletelematicssystems.

u-blox’proprietaryADRsolutionisrevolutionaryinthatitrunscompletelyontheGPSchip.Differencesinindividualwheelspeeds(usedtodeterminethevehicle’sspeedandheadingrate)areblendedwithGPSpositionaldataandoptionalgyroscopereadings.Thesolutionrequiresminimumpre-con-figuration,andafterinitialset-upremainspermanentlycalibrated.DesignedspecificallyforautomotiveDeadReckoningapplications,ublox’ADRchipsareAEC-Q100qualifiedandmanufacturedaccordingtoTS-16949standards.

Benefitsofu-blox’ADRsolutionforfirst-mountapplications:

• Requiresminimumhostintegrationandcustomization=lowerrisk,lower

cost,andfastertime-to-market

• Self-calibrating

• ProvensolutionwithTier-1referencecustomers

• Compatiblewithvirtuallyanymodelcarordrivetraintype(i.e.front-

wheel,rear-wheel,all-wheeldrive)

• Suitablenotonlyforcarnavigation,butformanyothercartelematics

applicationssuchaseCall,pay-as-you-driveinsurance,road-pricing,and

stolenvehicletracking

• Supportsmultiplesensorconfigurations,butdoesnotrequireagyroto

work

• ADRrunsonu-blox’automotive-grade,industry-certifiedGPSreceiver

chips

u-blox’ Automotive DR solution is compatible with virtually any car model

u-blox’ Automotive DR chip connects directly do the vehicle data bus, and requires no pre-configuration

u-blox’ Dead Reckoning for Automotive Applications / Whitepaper Published by u-blox AG | 9

Dead Reckoning LEA-6R: u-blox’ solution for after-market devices

Using gyroscope and odometer pulses from a tachometer, the u-blox LEA-6R GPS receiver module solution is independent of the vehicle data bus and thus ideal for after-market add-on systems requiring uninterrupted navi-gation such as fleet and asset management, road-pricing and insurance systems as well as Automatic Vehicle Locators (AVL).

The LEA-6R supplements satellite GPS information via direct connection to a vehicle-mounted gyroscope (turn rate sensor) and the vehicle’s odometer to execute dead reckoning navigation through periods of poor GPS reception.

Depending on the quality of the available GPS signals, the LEA-6R uses a proprietary algorithm specially developed by u-blox to extrapolate future positions accurately by using a combination GPS receiver and sensor inputs. The LEA-6R is a stand-alone solution requiring no host integration.

u-blox‘ Dead Reckoning technology can be evaluated with u-blox Dead Reckoning evaluation kit EVK-6R which can be ordered via u-blox’ Online Shop at:

http://www.u-blox.com/en/online-shop.html

Additional reading:

• Technical paper: “Performance of low-cost real-time navigation system using single frequency GNSS measurements combined with wheel-tick data”

• LEA-6R Application Note• u-blox DR article published in GPS World: “Continuous Navigation: Combining GPS with Sensor-Based Dead Reck-

oning.”

u-bloxDeadReckoningevaluationkit

LEA-6R u-blox GPS receiver modulewith Dead Reckoning interfaces directly to the vehicle odometer and gyroscope

LEA-6RTIMEPULSE

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UART

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Gyro

DigitalTemp.

AntennaSupervisor

RF_IN

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Odometer

SPI

Using gyroscope and odometer data, the u-blox LEA-6R GPS receiver module is independent of the vehicle data bus and thus ideal for after-market applications

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About the Authors

Dr. Etienne Favey

Etienne Favey is Vice-President Navigation Software Development at u-blox AG, Thalwil, Switzerland. He obtained his Ph.D-degree in Geodesy and Geomatics in 2001 from the Swiss Federal Institute of Technology (ETH), Zurich, Switzerland. His research interests include innovative positioning techniques, and combination of GPS with other methods and sensors.

Dr. Alexander Somieski

Alexander Somieski is Project Engineer for GNSS software at u-blox AG, Thalwil, Switzerland. He holds a diploma of Geodesy from the Technical University of Dresden and has received a Ph.D-degree from the Swiss FederalInstitute of Technology (ETH) Zurich in 2005. Since 1999, his research has been focused on GNSS systems, with special focus on atmospheric mitiga-tion methods, Precise Point Positioning and Sensor Fusion Dead Reckoning.

Dr. Christine Hollenstein

Christine Hollenstein is Project Engineer for GNSS navigation software at u-blox AG, Thalwil, Switzerland. She received her diploma of Surveying Engineering in 2000 and obtained her Ph.D-degree in Geodesy and Geomatics in 2006, both from the Swiss Federal Institute of Technology (ETH), Zurich, Switzerland. Since 1999, her research has been focused on GPS, with special emphases on high-precision geodesy for geodynamics and on multisensor navigation.

Michael Ammann

Michael Ammann is Vice-President of Application Engineering at u-blox AG, Thalwil, Switzerland. He obtained his Master’s Degree in Electrical Engineer-ing in 1998 from the Swiss Federal Institute of Technology (ETH) Zurich. He is a member of the Institute of Navigation (ION). His research interestsinclude Global Navigation Satellite System (GNSS) receiver architectures andtechnologies.

Carl Fenger

Carl has 25 years of international experience working in the semiconductor, software, telecoms, and GPS industries based in the USA and Switzerland. Carl is a published author of numerous technical articles and conference papers in the areas of embedded computing, telecom services billing, and broadband multimedia distribution. Carl holds a Bachelors of Science in Electrical and Computer Engineering from the University of California. Carl is a classical pianist and avid chess player.

Michael Ammann

Carl Fenger

Etienne Favey

Alexander Somieski

Christine Hollenstein

About u-blox u-blox is a leading fabless semiconductor provider of embedded position-ing and wireless communication solutions for the consumer, industrial and automotive markets. Our solutions enable people, devices, vehicles and ma-chines to locate their exact position and wirelessly communicate via voice, text or video.

With a broad portfolio of GPS modules, cards, chips, and software solutions together with wireless modules and solutions, u-blox is uniquely positioned to enable OEMs to develop innovative solutions quickly and cost-effectively. Headquartered in Switzerland and with global presence in Europe, Asia and the Americas, u-blox employs 200 people. Founded in 1997, u-blox is listed on the SIX Swiss Exchange.

Copyright © 2010 u-blox AG

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior per-mission of the copyright owners.

Published by u-blox AG, August 2010

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u-blox AG Zuercherstrasse 68 8800 Thalwil Switzerland info@u-blox.com