LANDMARCLANDMARCIndoor Location Sensing Indoor Location Sensing

Using Active RFIDUsing Active RFID

Abhishek P. PatilAbhishek P. PatilLionel M. NiLionel M. NiYunhao LiuYunhao LiuYiu Cho LauYiu Cho Lau

Proceedings of the First IEEE Conference on Proceedings of the First IEEE Conference on Pervasive Computing and Communications Pervasive Computing and Communications ( PerCom’03)( PerCom’03)

OverviewOverview

• IntroductionIntroduction• Technologies And Some Related Technologies And Some Related

WorkWork• RFID TechnologyRFID Technology• Description of LANDMARC Description of LANDMARC • Experimental ResultsExperimental Results• ConclusionConclusion• Future ResearchFuture Research

IntroductionIntroduction

• Proliferation of wireless Proliferation of wireless technologies, mobile computing technologies, mobile computing devices, and the Internet has devices, and the Internet has fostered a new growing interest in fostered a new growing interest in location-aware systems and serviceslocation-aware systems and services

ObjectiveObjective

• To develop an indoor location-To develop an indoor location-sensing system for various mobile sensing system for various mobile commerce applications.commerce applications.

Principle Techniques of Principle Techniques of Automatic Location SensingAutomatic Location Sensing• TriangulationTriangulation• Scene AnalysisScene Analysis• ProximityProximity

Technologies and Technologies and Related WorkRelated Work

• Infrared – Active Badge Infrared – Active Badge • IEEE 802.11 – RADARIEEE 802.11 – RADAR• Ultrasonic – Cricket Location Ultrasonic – Cricket Location

Support SystemSupport System

Active Bat Location Active Bat Location SystemSystem

• RFID - SpotONRFID - SpotON

RFID TechnologyRFID Technology

• It is a means of storing and It is a means of storing and retrieving data through retrieving data through electromagnetic transmission to an electromagnetic transmission to an RF compatible integrated circuit.RF compatible integrated circuit.

Components Of RFID Components Of RFID SystemSystem

• RFID readersRFID readers• RFID TagsRFID Tags

Basic OperationBasic Operation

• The antenna emits radio signals to The antenna emits radio signals to activate the tag and read and write activate the tag and read and write data to it. Antennas are the conduits data to it. Antennas are the conduits between the tag and the transceiver, between the tag and the transceiver, which controls the system’s data which controls the system’s data acquisition and communication acquisition and communication

Active RFID TagActive RFID Tag

• Active RFID tags are powered by an Active RFID tags are powered by an internal battery and are typically internal battery and are typically read/write.read/write.

• An active tag’s memory size varies An active tag’s memory size varies according to application requirements; according to application requirements; some systems operate with up to 1MB of some systems operate with up to 1MB of memory. memory.

• The battery-supplied power of an active The battery-supplied power of an active tag generally gives it a longer read tag generally gives it a longer read range. range.

TradeoffTradeoff

• Greater size, Greater cost, and a Greater size, Greater cost, and a limited operational life (which may limited operational life (which may yield a maximum of 10 years, yield a maximum of 10 years, depending upon operating depending upon operating temperatures and battery type).temperatures and battery type).

Passive RFID TagPassive RFID Tag

• Passive RFID tags operate without a Passive RFID tags operate without a separate external power source and separate external power source and obtain operating power generated obtain operating power generated from the reader. from the reader.

• Are consequently much lighter than Are consequently much lighter than active tags, less expensive, and offer active tags, less expensive, and offer a virtually unlimited operational a virtually unlimited operational lifetime.lifetime.

Trade OffTrade Off

• Shorter read ranges than active tags Shorter read ranges than active tags • Require a higher-powered reader.Require a higher-powered reader.• Read-only tags are typically passive Read-only tags are typically passive

and are programmed with a unique and are programmed with a unique set of data (usually 32 to 128 bits) set of data (usually 32 to 128 bits) that cannot be modified.that cannot be modified.

Frequency RangesFrequency Ranges

• Low-frequency - 30 KHz to 500 KHz Low-frequency - 30 KHz to 500 KHz systems have short reading ranges systems have short reading ranges and lower system costs. and lower system costs.

• High-frequency- 850 MHz to 950 MHz High-frequency- 850 MHz to 950 MHz

2.4 GHz to 2.5 GHz2.4 GHz to 2.5 GHz

offering long read ranges greater offering long read ranges greater than 90 feet and high reading than 90 feet and high reading speeds.speeds.

RFID ApplicationsRFID Applications

• Security access, Asset tracking, and Security access, Asset tracking, and Animal identification applications Animal identification applications

• Railroad Car Tracking and Railroad Car Tracking and Automated Toll Collection Automated Toll Collection

AdvantagesAdvantages

• Non-line-of-sight nature.Non-line-of-sight nature.• RF tags can be read despite the RF tags can be read despite the

extreme environmental factors like extreme environmental factors like snow, fog, ice, paint.snow, fog, ice, paint.

• Can be read in less than 100 Can be read in less than 100 milliseconds. milliseconds.

• Cost-effectiveness Cost-effectiveness

EquipmentEquipment

Spider System by RF CodeSpider System by RF Code• RF ReaderRF Reader

– Range up to 150 feetRange up to 150 feet– Identify 500 tags in 7.5 seconds with the collision Identify 500 tags in 7.5 seconds with the collision

avoidanceavoidance– Support 8 power levels (function of distance) Support 8 power levels (function of distance) – Operate at the frequency of 303.8 MHzOperate at the frequency of 303.8 MHz

• Active Tag systemActive Tag system– Emit signal, which consists of a unique 7-Emit signal, which consists of a unique 7-

character ID, every 7.5 seconds for identification character ID, every 7.5 seconds for identification by the readersby the readers

– Button-cell battery (2-5 years life)Button-cell battery (2-5 years life)

Basic SetupBasic Setup

• The Basic system is setup as shown The Basic system is setup as shown in Fig 1.in Fig 1.

LANDMARCLANDMARC

ApproachApproach

• Increase accuracy without placing Increase accuracy without placing more readers.more readers.

• Employs idea of having extra fixed Employs idea of having extra fixed location reference tags to help location reference tags to help location calibration.location calibration.

AdvantagesAdvantages

• No need for large number of No need for large number of expensive RFID readers.expensive RFID readers.

• Environmental dynamics can easily Environmental dynamics can easily be accommodated.be accommodated.

• Location information more reliable Location information more reliable and accurate.and accurate.

IssuesIssues

• Current RFID system does not Current RFID system does not provide the signal strength of tags provide the signal strength of tags directly to readers.directly to readers.

• Power level distribution is dynamic Power level distribution is dynamic in a complicated indoor in a complicated indoor environment.environment.

System SetupSystem Setup

• Prototype environment consists of a Prototype environment consists of a sensing network [ RF readers and RF sensing network [ RF readers and RF tags ] and a wireless network that tags ] and a wireless network that enables the communication between enables the communication between mobile devices and the internet.mobile devices and the internet.

• Also consists of a Tag Tracker Also consists of a Tag Tracker Concentrator LI Concentrator LI

[ API provided by RF Code ] which acts a [ API provided by RF Code ] which acts a central configuration interface for RF central configuration interface for RF readers.readers.

MethodologyMethodology

• We have ‘n’ RF readers along with We have ‘n’ RF readers along with ‘m’ tags as reference tags and ‘u’ ‘m’ tags as reference tags and ‘u’ tracking tags as objects being tracking tags as objects being tracked.tracked.

• Readers configured with continuous Readers configured with continuous mode and detection range of 1-8 mode and detection range of 1-8 which cycle at a rate of 30secs per which cycle at a rate of 30secs per range.range.

DefinitionsDefinitions

• Signal Strength Vector of a tracking/moving tag is given as S=(S1,

S2,…, Sn) , where Si denotes the signal strength of the tracking tag perceived on reader i, where i € ( 1,n ).

• For the reference tags, we denote the corresponding Signal Strength vector as

θ =(θ1, θ2,…, θn) where θi denotes the signal strength.

Definitions [ Continued ]Definitions [ Continued ]

• Euclidian distance in signal strengths between a tracking tag and a reference tag .

For each individual tracking tag p where p € (1,u) we define:

where j € (1,m)

Definitions [ Continued ]Definitions [ Continued ]

• Let E denote the location relationship between the reference tags and the tracking tag i.e. the nearer reference tag to the tracking tag is supposed to have a smaller E value.

• A tracking tag has the vector È= A tracking tag has the vector È= (E(E11,E,E22,..,E,..,Enn).).

Issues in Locating the Issues in Locating the unknown Tagunknown Tag

• Placement of reference tags.Placement of reference tags.• Number of reference tags in a Number of reference tags in a

reference cell.reference cell.• Determine the weights associated Determine the weights associated

with different neighbors.with different neighbors.

FormulaeFormulae

• The unknown tracking tag coordinate (x, y) is obtained by:

• where wi is the weighting factor to the i-th neighboring reference tag.

Formulae [Continued]Formulae [Continued]

• wi is a function of the E values of k-nearest neighbors. Empirically, in LANDMARC, weight is given by:

Experimental ResultsExperimental Results

• Standard Setup: Standard Setup:

WeWe place 4 RF readers (n=4) in our lab and 16 tags (m=16) as reference tags while the other 8 tags (u=8) as objects being tracked. [ Fig 2a ].

Basis For AccuracyBasis For Accuracy

• To quantify how well the LANDMARC system performs, the error distance is used as the basis for the accuracy of the system. We define the location estimation error, e, to be the linear distance between the tracking tag’s real coordinates (x0,y0) and the computed coordinates (x,y) given by :

Placement Configuration Placement Configuration

Effect of the number of Effect of the number of nearest neighborsnearest neighbors

Influence of the Influence of the Environmental FactorsEnvironmental Factors

Comparison between the Comparison between the two placement two placement configurationsconfigurations

Effect of the Number Of Effect of the Number Of ReadersReaders

Effect Of Placement Of Effect Of Placement Of Reference TagsReference Tags

Possible SolutionPossible Solution

Setup for Higher Density Setup for Higher Density placements of Reference placements of Reference

TagsTags

Results for Higher Results for Higher Reference Tag densityReference Tag density

Setup for Lower Density Setup for Lower Density placements of Reference placements of Reference

TagsTags

Results for Low Reference Results for Low Reference Tag densityTag density

ConclusionConclusion

• Using 4 RF readers in the lab, with Using 4 RF readers in the lab, with one reference tag per square meter, one reference tag per square meter, it can accurately locate the objects it can accurately locate the objects within error distance such that within error distance such that the the largest error is 2 meterslargest error is 2 meters and the and the average is about 1 meter. average is about 1 meter.

Issues to OvercomeIssues to Overcome

• None of the currently available RFID products provides the signal strength of tags directly.

• Long latency between a tracking tag being physically placed to its location being computed by the location server.

• The variation of the behavior of tags.

Future WorkFuture Work

• Investigating the use of Bluetooth for location sensing based on the same methodology.

• Influence of having other shapes of reference tags to the selection of the number of nearest neighbors needs to be investigated.

Thank youThank you

Questions Questions Anyone ?Anyone ?