indoor location sensing using active rfids

LANDMARCLANDMARCIndoor Location Sensing Using Indoor Location Sensing Using

Active RFIDActive RFID

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

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

OverviewOverview

• IntroductionIntroduction• Technologies And Some Related WorkTechnologies And Some Related Work• RFID TechnologyRFID Technology• Description of LANDMARC Description of LANDMARC • Experimental ResultsExperimental Results• ConclusionConclusion• Future ResearchFuture Research

IntroductionIntroduction

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

ObjectiveObjective

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

Principle Techniques of Automatic Principle Techniques of Automatic Location SensingLocation Sensing

• TriangulationTriangulation• Scene AnalysisScene Analysis• ProximityProximity

Technologies and Related WorkTechnologies and Related Work

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

Active Bat Location SystemActive Bat Location System• RFID - SpotONRFID - SpotON

RFID TechnologyRFID Technology

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

Components Of RFID SystemComponents Of RFID System

• RFID readersRFID readers• RFID TagsRFID Tags

Basic OperationBasic Operation

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

Active RFID TagActive RFID Tag

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

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

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

TradeoffTradeoff

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

Passive RFID TagPassive RFID Tag

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

• Are consequently much lighter than active tags, Are consequently much lighter than active tags, less expensive, and offer a virtually unlimited less expensive, and offer a virtually unlimited operational lifetime.operational 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 and are Read-only tags are typically passive and are

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

Frequency RangesFrequency Ranges

• Low-frequency - 30 KHz to 500 KHz systems Low-frequency - 30 KHz to 500 KHz systems have short reading ranges and lower system have short reading ranges and lower system costs. 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 than 90 feet offering long read ranges greater than 90 feet and high reading speeds.and high reading speeds.

RFID ApplicationsRFID Applications

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

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

AdvantagesAdvantages

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

environmental factors like snow, fog, ice, paint.environmental factors like snow, fog, ice, paint.• Can be read in less than 100 milliseconds. Can be read in less than 100 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 avoidanceIdentify 500 tags in 7.5 seconds with the collision avoidance– 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-character ID, every Emit signal, which consists of a unique 7-character ID, every

7.5 seconds for identification by the readers7.5 seconds for identification by 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 in Fig 1.The Basic system is setup as shown in Fig 1.

LANDMARCLANDMARC

ApproachApproach

• Increase accuracy without placing more readers.Increase accuracy without placing more readers.• Employs idea of having extra fixed location Employs idea of having extra fixed location

reference tags to help location calibration.reference tags to help location calibration.

AdvantagesAdvantages

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

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

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

IssuesIssues

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

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

System SetupSystem Setup

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

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

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

MethodologyMethodology

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

• Readers configured with continuous mode and Readers configured with continuous mode and detection range of 1-8 which cycle at a rate of detection range of 1-8 which cycle at a rate of 30secs per range.30secs per 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= (EA tracking tag has the vector È= (E11,E,E22,..,E,..,Enn).).

Issues in Locating the unknown TagIssues in Locating the unknown Tag

• Placement of reference tags.Placement of reference tags.• Number of reference tags in a reference cell.Number of reference tags in a reference cell.• Determine the weights associated with different Determine the weights associated with different

neighbors.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 nearest Effect of the number of nearest neighborsneighbors

Influence of the Environmental Influence of the Environmental FactorsFactors

Comparison between the two Comparison between the two placement configurationsplacement configurations

Effect of the Number Of ReadersEffect of the Number Of Readers

Effect Of Placement Of Reference Effect Of Placement Of Reference TagsTags

Possible SolutionPossible Solution

Setup for Higher Density placements Setup for Higher Density placements of Reference Tagsof Reference Tags

Results for Higher Reference Tag Results for Higher Reference Tag densitydensity

Setup for Lower Density placements Setup for Lower Density placements of Reference Tagsof Reference Tags

Results for Low Reference Tag Results for Low Reference Tag densitydensity

ConclusionConclusion

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