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

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MTP Thesis Presentation by

S. Anusha

Guide: Prof. Sridhar Iyer

Basics

RadioFrequencyIDentification: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

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.

Fixed size circles covering rectangle

Non-overlapping cover

Optimal coverage - 90.69%

Overlapping cover

Optimal density - 1.209

Fopt = 2√3XY/9r2

where

X, Y : dimensions of area

r : interrogation range

Example

10mx10m and r=2m, Fopt = 10

50mx50m and r=2m, Fopt = 241

- Ellipse-like shape covering rectangle
- Non-overlapping cover
- Coverage =(2rvT+πr2)/(vT+2r)2r
where

r : interrogation range

v : velocity

T : period T

- Coverage =(2rvT+πr2)/(vT+2r)2r
- Overlapping cover
- Density = 1+(πr2/2rvT)
- Msufficient-bound = XY/2rvT
where

X, Y : dimensions of area

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.

- 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.

- Selection Phase

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

- 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

- Application Scenario
- Retail Inventory - Supermarket

- Mobility Model
- Zig-Zag Mobility Model

- Layout Generating Heuristic
- LGH1Heuristic

- MAC Mechanism
- Static Coloring MAC Mechanism

- Optimizing Objective Function
- Least Square Sum Optimizing Function

- 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 = l+d; d1 <= X; d1 = d1+l+d ) {
- for ( d2 = d; d2 <= Y; d2 = d2+d ) {
- 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.

- 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.

- 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

Demo of RFIDcover

The Primary Example

The Other Example - Same as above except:

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

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

- 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

- 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.

[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.html

[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.

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

My sincere thanks to