Localization by RFID

1
Localization by RFID

• LANDMARC Indoor Location Sensing Using Active
  RFID, PerCom03

2
RFID Background

• The current (2003) RFID system does not provide
  the transmission strength of tags to readers.
• Readers only report the power level of the tag
  being detected.

3
Goal

• LANDMARC LocAtioN iDentification based on
  dynaMic Active Rfid Calibration
• A location sensing prototype system that uses
  RFID technology for in-building use.
• Improves localization accuracy by utilizing the
  concept of reference tags.

4
(No Transcript)
5
LANDMARC Approach (I)

• In the sensing field
• n readers
• m fixed tags (i.e., reference tags)
• u tracking tags (i.e., moving objects)
• Readers are all configured with continuous mode
  and a detection-range of 1-8 level.
• Signal Strength Vector of a tracking tag
• Signal Strength Vector of a fixed tag

6
LANDMARC Approach (II)

• Definition Euclidian distance between a tracking
  tag and a reference tag j
• Definition The location relationship vector
  between the m reference tags and the tracking tag

7
LANDMARC Approach (III)

• The placement of the unknown tag is surrounded by
  k most likely reference tags.
• Weighted location (x, y) of the unknown tag
• where weights are defined as

8
Experimental Environment

• Spider System
• Reader 308MHz, has an 802.11b interface to
  communicate, detection range of 150 feet, detect
  up to 500 tags in 7.5 seconds, 8 different power
  levels
• Active tag read range of 150 feet and can be
  increased to 1000 feet with the addition of a
  special antenna, send signal in random with an
  average of 7.5 seconds
• Performance metric
• Location estimation error

9
Experiment Environment
10
Effect of k (Number of Nearest Neighbors)
11
Environmental Factors Daytime vs. Night
12
Effect of n (Number of Readers)
13
Effect of Placement of Reference Tags
14

• The accuracy is improved with a higher reference
  tag density. However, it is not as great as
  expected.

15
Conclusions

• A new RFID-based location system.
• Major advantages
• No need for a large number of expensive RFID
  readers
• The environmental dynamics can easily be
  accommodated.
• The accuracy can be greatly improved if RFID
  vendors can make some design changes
• The error due to the dynamics of the environment
  can hardly be alleviated.