LANDMARC Indoor Location Sensing Using Active RFID

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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 (
  PerCom03)

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Overview

• Introduction
• Technologies And Some Related Work
• RFID Technology
• Description of LANDMARC
• Experimental Results
• Conclusion
• Future Research

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Introduction

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

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Objective

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

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Principle Techniques of Automatic Location Sensing

• Triangulation
• Scene Analysis
• Proximity

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Technologies and Related Work

• Infrared Active Badge
• IEEE 802.11 RADAR
• Ultrasonic Cricket Location Support System
• Active Bat Location System
• RFID - SpotON

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RFID Technology

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

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Components Of RFID System

• RFID readers
• RFID Tags

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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 systems data acquisition and
  communication

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Active RFID Tag

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

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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).

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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.

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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.

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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.

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RFID Applications

• Security access, Asset tracking, and Animal
  identification applications
• Railroad Car Tracking and Automated Toll
  Collection

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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

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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)

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Basic Setup

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

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LANDMARC
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Approach

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

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Advantages

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

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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.

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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.

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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.

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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
• ? (?1, ?2,, ?n) where ?i denotes the signal
  strength.

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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)

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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).

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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.

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Formulae

• The unknown tracking tag coordinate (x, y) is
  obtained by
• where wi is the weighting factor to the i-th
  neighboring reference tag.

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Formulae Continued

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

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Experimental Results

• Standard Setup
• We place 4 RF readers (n4) in our lab and 16
  tags (m16) as reference tags while the other 8
  tags (u8) as objects being tracked. Fig 2a .

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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 tags real
  coordinates (x0,y0) and the computed coordinates
  (x,y) given by

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Placement Configuration
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Effect of the number of nearest neighbors
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Influence of the Environmental Factors
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Comparison between the two placement
configurations
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Effect of the Number Of Readers
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Effect Of Placement Of Reference Tags
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Possible Solution
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Setup for Higher Density placements of Reference
Tags
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Results for Higher Reference Tag density
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Setup for Lower Density placements of Reference
Tags
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Results for Low Reference Tag density
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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.

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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.

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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.

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Thank you

• Questions Anyone ?