RFIDcover: A Coverage Planning Tool for RFID Networks with Mobile Readers

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RFIDcoverA Coverage Planning Toolfor RFID
Networks withMobile Readers
MTP Thesis Presentation by S. Anusha Guide
Prof. Sridhar Iyer
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RFID System

• Basics
• Radio Frequency IDentification use of radio
  waves
• RF Tag a low functionality microchip with an
  antenna
• Passive derives power from readers
  transmission, computationally thin, limits
  interrogation range.
• Active has its own battery power
• Reader a device that can read/write information
  from tags
• Applications
• Identification and Tracking of objects, Access
  Control

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Problem Statement

• Completely Covering an Area
• At all time Eg. intrusion detection
• Placing sufficient number of fixed readers
• High deployment costs
• Periodically, within every T seconds Eg.
  inventory check
• Can use mobile readers
• Cost-effective
• Challenge to determine the number of readers,
  their movement, their velocity etc.

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The Coverage ProblemUsing Fixed Readers

• Fixed size circles covering rectangle
• Non-overlapping cover
• Optimal coverage - 90.69
• Overlapping cover
• Optimal density - 1.209
• Fopt 2v3XY/9r2
• where
• X, Y dimensions of area
• r interrogation range
• Example
• 10mx10m and r2m, Fopt 10
• 50mx50m and r2m, Fopt 241

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The Coverage ProblemUsing Mobile Readers

• Ellipse-like shape covering rectangle
• Non-overlapping cover
• Coverage (2rvTpr2)/(vT2r)2r
• where
• r interrogation range
• v velocity
• T period T
• Overlapping cover
• Density 1(pr2/2rvT)
• Msufficient-bound XY/2rvT
• where
• X, Y dimensions of area

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RFIDcover

• Purpose
• Given an application scenario and reader
  specifications, RFIDcover automatically
  determines the number of readers required, their
  placement and movement pattern to guarantee
  complete coverage of an area within the specified
  period T.
• Features
• Has an extendible architecture
• Permits user to tune additional constraints
  online
• Use
• Supermarkets, Warehouse, Libraries ... any place
  where periodic inventory is needed.

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RFIDcover Architecture
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RFIDcover Operation

• Three Phased Operation
• Selection Phase
• The mobility model, the MAC mechanism and an
  appropriate heuristic for layout generation is
  selected.
• Generation Phase
• A set of possible layouts, each conforming to the
  input constraints and completely covering the
  given area is generated. Cost of deployment (as a
  function of the number of readers), and the TRT
  (total time taken to read all the tags in the
  entire area) are computed for each layout.
• Optimization Phase
• An appropriate objective function for
  optimization is chosen and applied to the set of
  layouts generated and the best layout amongst
  them is selected and recommended to the user.

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RFIDcover Inputs

• Application Scenario parameters say
  Supermarket with aisle length and inter aisle
  distance
• Reader Specification - interrogation range,
  interference range, tag reading speed (TRS), unit
  cost, maximum speed (if mobile)
• Topology Specification dimensions of the
  min-area bounding rectangle, tag distribution
  with parameters
• Constraints number of fixed readers, number of
  mobile readers, maximum tag reading time (TRT),
  maximum cost, maximum number of slots

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RFIDcover Outputs

• Graphs
• Summarizing all layouts conforming to the
  constraints TRT variation, NMR variation, TRT
  Vs NMR, Optimizing Objective Function
• Best Layout
• The details of the best layout - Number of
  readers, Placement of readers, Mobility pattern
  of mobile readers, Velocity of mobile readers,
  Tag Reading Time (TRT), Cost, Number of slots

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RFIDcover Implementation

• Application Scenario
• Retail Inventory - Supermarket
• Mobility Model
• Zig-Zag Mobility Model
• Layout Generating Heuristic
• LGH1 Heuristic
• MAC Mechanism
• Static Coloring MAC Mechanism
• Optimizing Objective Function
• Least Square Sum Optimizing Function

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RFIDcover Design
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Zig-Zag Mobility Model
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LGH1 Heuristic

• Definition
• l length of the aisle d inter aisle
  distance X, Y dimensions of the area to
  be covered.
• Assumption The length of the aisle is along X.
• generateLayout Function
• for ( d1 ld d1 lt X d1 d1ld )
• for ( d2 d d2 lt Y d2 d2d )
• Form a column of readers by placing them d2
  distance apart, along Y.
• Place a copy of the column formed d1 distance
  apart, along X.
• Within each d1xd2 rectangle, place as many mobile
  readers as needed for completely covering the
  area within specified time.
• This forms one layout.

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Static Coloring MAC Mechanism

• A TDMA mechanism
• Models the reader network as a graph G(R)
  (V,E), with the set of vertices V representing
  the readers, and the set of edges E representing
  interference between readers.
• Assignment of slots to readers equivalent to the
  problem of coloring this graph.
• Considers all possible scenarios, assigns and
  operates with as many colors as needed in the
  worst case.
• Simple and easy to implement for specific
  mobility models and layouts of readers.
• May be inefficient.

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Least Square Sum OOF

• Requirement
• To use minimum number of readers
• Read as often as possible i.e., TRT be as small
  as possible
• Hence
• Least Square Sum is used
• Applied on TRT and NMR

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Screen Shots Input
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Demonstration

• Demo of RFIDcover

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Screen Shots Output Layout1
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Screen Shots Output Layout2
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Screen Shots Output Graphs
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RFIDcover Evaluation

• The Primary Example

Reader Specification Topology Specification Application
Interrogation Range 2m Dimension X 24m Supermarket
Interference Range 2.5m Dimension Y 15m Scenario
Tag Reading Speed (TRS) 70tags/s Tag Distribution Uniform Aisle Length 5m
Unit Cost 1 Tag Density 5/m2 Inter Aisle Distance 3m
Maximum Speed 5m/s Aisle Length Along X
The Other Example - Same as above except
Dimension X 48m Aisle Length 10m
Dimension Y 30m Inter Aisle Distance 6m
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Mobile Vs Fixed Readers
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Zig-zag Mobility Model
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RFIDcover Extensions

• Retail Inventory Tracking Application Variant
• To-and-Fro Mobility Model, LGH2 Layout Generating
  Heuristic, Static Coloring MAC Mechanism

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RFIDcover Extensions

• Dynamic Coloring MAC Mechanism
• Starts with Min-Color-Mode and goes into
  General-Color-Mode when collisions occurs
• Number of slots given by 1P1 2P2 ... mPm
  where Pi Pr(i-Color-Mode)
  m total readers
• Considerable overhead

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RFIDcover Extensions

• Covering 3-Dimensional Space
• To-and-Fro Mobility Model, LGH2 Layout Generating
  Heuristic, Static Coloring MAC Mechanism
• Limitations due to Assumptions
• No Environmental Effects
• Circular Range
• Homogeneous System

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Conclusions

• Providing complete coverage of an area is an
  important requirement in an RFID system.
• Using mobile readers is cost-effective for
  providing complete coverage periodically, within
  every T seconds, even for small values of T.
• Deriving sufficient bound for number of mobile
  readers is theoretically useful.
• The Zig-Zag mobility model and LGH1 layout
  generating heuristic result in layouts with
  number of readers close to the sufficient bound.
• RFIDcover architecture and design is easily
  extendible, making it a useful RFID deployment
  tool.

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References

• 1 Klaus Finkenzeller. RFID Handbook
  Fundamentals and Applications in Contactless
  Smart Cards and Identification. Chichester John
  Wiley, Leipzig, dritte edition, 2003.
• 2 Radio Frequency Identification - A Basic
  Primer. White Paper, AIM Inc WP-98/002R2, August
  2001 http//www.aimglobal.org/
• 3 http//mathworld.wolfram.com/CirclePacking.htm
  l
• 4 Richard Kershner. The Number of Circles
  Covering a Set. In American Journal of
  Mathematics, volume 61, page 665, July 1939.
• 5 Yi Guo and Zhihua Qu. Coverage Control for a
  Mobile Robot Patrolling a Dynamic and Uncertain
  Environment. Proceedings of World Congress on
  Intelligent Control and Automation, June 2004.
• 6 Daniel W. Engels. The Reader Collision
  Problem. Technical report, EPC Global, 2002.
  http//www.epcglobal.org/
• 7 J. Waldrop, D. W. Engels, and S. E. Sarma.
  Colorwave An anticollison algorithm for the
  reader collision problem. In IEEE Wireless
  Communications and Networking Conference (WCNC),
  2003.
• 8 Draft paper on Characteristics of
  RFID-systems. White Paper, AIM Inc WP-98/002R2,
  July 2000.
• 9 A Basic Introduction to RFID Technology and
  its use in Supply Chain. Technical report, Laran
  Technologies, January 2004.

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Acknowledgement
My sincere thanks to

• Prof. Sridhar Iyer
• Research Scholars and members of the Mobile
  Computing Research Group at KReSIT
• My batchmates B. Nagaprabhanjan, Charu Tiwari and
  Shailesh M. Birari

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Questions?