RFIDcover: A Coverage Planning Tool for RFID Networks with Mobile Readers MTP Thesis Presentation by S. Anusha Guide: Prof. Sridhar Iyer.

RFIDcover:A Coverage Planning Tool

for RFID Networks withMobile Readers

MTP Thesis Presentation byS. Anusha

Guide: Prof. Sridhar Iyer

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

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.

The Coverage Problem:Using Fixed Readers

● 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

The Coverage Problem:Using Mobile Readers

● Ellipse-like shape covering rectangle

● Non-overlapping cover● Coverage =(2rvT+πr2)/(vT+2r)2r

wherer : interrogation rangev : velocityT : period T

● Overlapping cover● Density = 1+(πr2/2rvT)● Msufficient-bound = XY/2rvT

where X, Y : dimensions of area

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.

RFIDcover Architecture

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.

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

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

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

Zig-Zag Mobility Model

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 = 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.}

}

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.

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

Example

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0 5 10 15NMR

TRT

Screen Shots: Input

Demonstration

Demo of RFIDcover

Screen Shots: Output Graphs

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

Mobile Vs Fixed Readers

Zig-zag Mobility Model

RFIDcover Extensions

● Retail Inventory Tracking Application Variant● To-and-Fro Mobility Model, LGH2 Layout Generating

Heuristic, Static Coloring MAC Mechanism

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 1*P1 + 2*P2 + ... + m*Pm where

Pi = Pr(i-Color-Mode)& m = total readers

● Considerable overhead

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

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.

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.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.

Acknowledgement

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

Questions?