LANDMARC Indoor Location Sensing Using Active RFID Abhishek P. Patil Lionel M. Ni Yunhao Liu Yiu Cho Lau Proceedings of the First IEEE Conference on Pervasive Computing and Communications ( PerCom’03)

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

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

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

Principle Techniques of Automatic Location Sensing TriangulationTriangulation Scene AnalysisScene Analysis ProximityProximity

Technologies and Related Work Infrared – Active BadgeInfrared – Active Badge IEEE – RADARIEEE – RADAR Ultrasonic – Cricket Location Support SystemUltrasonic – Cricket Location Support System Active Bat Location System Active Bat Location System RFID - SpotONRFID - SpotON

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

Components Of RFID System RFID readersRFID readers RFID TagsRFID Tags

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

Active RFID Tag Active RFID tags are powered by an internal battery and are typically read/write.Active RFID tags are powered by an internal battery and are typically read/write. An active tag’s memory size varies according to application requirements; some systems operate with up to 1MB of memory.An active tag’s memory size varies according to application requirements; some systems operate with up to 1MB of memory. The battery-supplied power of an active tag generally gives it a longer read range.The battery-supplied power of an active tag generally gives it a longer read range.

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

Passive RFID Tag Passive RFID tags operate without a separate external power source and obtain operating power generated from the reader.Passive RFID tags operate without a separate external power source and obtain operating power generated from the reader. Are consequently much lighter than active tags, less expensive, and offer a virtually unlimited operational lifetime.Are consequently much lighter than active tags, less expensive, and offer a virtually unlimited operational lifetime.

Trade Off Shorter read ranges than active tagsShorter read ranges than active tags Require a higher-powered reader.Require a higher-powered reader. Read-only tags are typically passive and are programmed with a unique set of data (usually 32 to 128 bits) that cannot be modified.Read-only tags are typically passive and are programmed with a unique set of data (usually 32 to 128 bits) that cannot be modified.

Frequency Ranges Low-frequency - 30 KHz to 500 KHz systems have short reading ranges and lower system costs.Low-frequency - 30 KHz to 500 KHz systems have short reading ranges and lower system costs. High-frequency- 850 MHz to 950 MHzHigh-frequency- 850 MHz to 950 MHz 2.4 GHz to 2.5 GHz 2.4 GHz to 2.5 GHz offering long read ranges greater than 90 feet and high reading speeds. offering long read ranges greater than 90 feet and high reading speeds.

RFID Applications Security access, Asset tracking, and Animal identification applicationsSecurity access, Asset tracking, and Animal identification applications Railroad Car Tracking and Automated Toll CollectionRailroad Car Tracking and Automated Toll Collection

Advantages Non-line-of-sight nature.Non-line-of-sight nature. RF tags can be read despite the extreme environmental factors like snow, fog, ice, paint.RF tags can be read despite the extreme environmental factors like snow, fog, ice, paint. Can be read in less than 100 milliseconds.Can be read in less than 100 milliseconds. Cost-effectivenessCost-effectiveness

Equipment Spider System by RF Code RF ReaderRF Reader –Range up to 150 feet –Identify 500 tags in 7.5 seconds with the collision avoidance –Support 8 power levels (function of distance) –Operate at the frequency of MHz Active Tag systemActive Tag system –Emit signal, which consists of a unique 7-character ID, every 7.5 seconds for identification by the readers –Button-cell battery (2-5 years life)

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

LANDMARC

Approach Increase accuracy without placing more readers.Increase accuracy without placing more readers. Employs idea of having extra fixed location reference tags to help location calibration.Employs idea of having extra fixed location reference tags to help location calibration.

Advantages No need for large number of expensive RFID readers.No need for large number of expensive RFID readers. Environmental dynamics can easily be accommodated.Environmental dynamics can easily be accommodated. Location information more reliable and accurate.Location information more reliable and accurate.

Issues Current RFID system does not provide the signal strength of tags directly to readers.Current RFID system does not provide the signal strength of tags directly to readers. Power level distribution is dynamic in a complicated indoor environment.Power level distribution is dynamic in a complicated indoor environment.

System Setup Prototype environment consists of a sensing network [ RF readers and RF tags ] and a wireless network that enables the communication between mobile devices and the internet.Prototype environment consists of a sensing network [ RF readers and RF tags ] and a wireless network that enables the communication between mobile devices and the internet. Also consists of a Tag Tracker Concentrator LIAlso consists of a Tag Tracker Concentrator LI [ API provided by RF Code ] which acts a central configuration interface for RF readers. [ API provided by RF Code ] which acts a central configuration interface for RF readers.

Methodology We have ‘n’ RF readers along with ‘m’ tags as reference tags and ‘u’ tracking tags as objects being tracked.We have ‘n’ RF readers along with ‘m’ tags as reference tags and ‘u’ tracking tags as objects being tracked. Readers configured with continuous mode and detection range of 1-8 which cycle at a rate of 30secs per range.Readers configured with continuous mode and detection range of 1-8 which cycle at a rate of 30secs per range.

Definitions Signal Strength Vector of a tracking/moving tag is given as S=(S 1, S 2,…, S n ), 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 =(θ 1, θ 2,…, θ n ) where θ i denotes the signal strength.

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 ] 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= (E 1,E 2,..,E n ).A tracking tag has the vector È= (E 1,E 2,..,E n ).

Issues 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 neighbors.Determine the weights associated with different neighbors.

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

Experimental Results Standard Setup:Standard Setup: We We 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 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 (x 0,y 0 ) and the computed coordinates (x,y) given by :

Placement Configuration

Effect of the number of nearest neighbors

Influence of the Environmental Factors

Comparison between the two placement configurations

Effect of the Number Of Readers

Effect Of Placement Of Reference Tags

Possible Solution

Setup for Higher Density placements of Reference Tags

Results for Higher Reference Tag density

Setup for Lower Density placements of Reference Tags

Results for Low Reference Tag density

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

Issues 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 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 you Questions Anyone ? Questions Anyone ?