LANDMARCIndoor 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 • Introduction • Technologies And Some Related Work • RFID Technology • Description of LANDMARC • Experimental Results • Conclusion • Future Research
Introduction • Proliferation 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.
Principle Techniques of Automatic Location Sensing • Triangulation • Scene Analysis • Proximity
Technologies and Related Work • Infrared – Active Badge • IEEE 802.11 – RADAR • Ultrasonic – Cricket Location Support System Active Bat Location System • RFID - SpotON
RFID Technology • It is a means of storing and retrieving data through electromagnetic transmission to an RF compatible integrated circuit.
Components Of RFID System • RFID readers • RFID 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 communication
Active RFID Tag • 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. • 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).
Passive RFID Tag • 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.
Trade Off • Shorter read ranges than active tags • 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.
Frequency Ranges • Low-frequency - 30 KHz to 500 KHz systems have short reading ranges and lower system costs. • High-frequency- 850 MHz to 950 MHz 2.4 GHz to 2.5 GHz offering long read ranges greater than 90 feet and high reading speeds.
RFID Applications • Security access, Asset tracking, and Animal identification applications • Railroad Car Tracking and Automated Toll Collection
Advantages • Non-line-of-sight nature. • RF tags can be read despite the extreme environmental factors like snow, fog, ice, paint. • Can be read in less than 100 milliseconds. • Cost-effectiveness
Equipment Spider System by RF Code • RF 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 303.8 MHz • Active 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.
Approach • Increase accuracy without placing more readers. • Employs idea of having extra fixed location reference tags to help location calibration.
Advantages • No need for large number of expensive RFID readers. • Environmental dynamics can easily be accommodated. • Location information more reliable and accurate.
Issues • Current RFID system does not provide the signal strength of tags directly to readers. • 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. • Also consists of a Tag Tracker Concentrator LI [ 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. • 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=(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 ] • 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= (E1,E2,..,En).
Issues in Locating the unknown Tag • Placement of reference tags. • Number of reference tags in a reference cell. • 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: 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 (x0,y0) and the computed coordinates (x,y) given by :
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.
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 ?