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RFID-Syste ch 2010 Ciudad Real, June 2010 A nalysis of the identification process in active RFID systems with the Capture Effect assumption M.V. Bueno-Delgado , J. Vales-Alonso Technical University of Cartagena

RFID Systech2010

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RFID-Systech 2010

Ciudad Real, June 2010

Analysis of the identification process

in active RFID systems with the

Capture Effect assumption

M.V. Bueno-Delgado, J. Vales-Alonso

Technical University of Cartagena

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Index

` Introduction

` ISO 18000-7

` Capture effect phenomenon in RFID

` Markovian analysis

` Analytical and Simulation results

` Conclusions and future issues

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Introduction (I)

` Active RFID used in scenarios where passive technologylimits implementation, e.g. product traceability with control of external factors.

` Active RFID systems implement an anti-collision protocolfor avoiding/handling collisions, ensuring fast and reliablereader-tag communication.

` Frame Slotted Aloha (FSA) is the d e facto procedure foractive RFID anti-collision protocols

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Introduction (II)

N tags enter coverage area

No new tags enter until previous one have identified

ISO 18000-7 (K static value configurable: 7, 14, 21,«)

NN

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Introduction (III) I

SO 18000-7:Identification/anti-collision protocol based on

Frame SlottedAloha (FSA)

Collection

Command

(K slots)

...

SleepTag

ID#1

ID #1

ID #N

ID #2

ID #3

Reader

Tag #1

Tag #2

Tag #3

Tag #N

...

³Collection round´ (divided into K slots)

Wake upSleepTag

ID#N

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Introduction (IV)

` K  slots in a collection round andN tags` Theoretical throughput of FSA (tags identified per time unit)

`

FSA

Max. throughput whenN=K 

,

=e

-1

§0.36` Collection rounds are fixed (K  static)

` We cannot maximize throughput per collection round but we can configureRFID system for minimizing total identification delay

1

11

¹ º

 ¸©ª

¨ !; N 

 K  K 

 N 

N1=K1=256

Collection

round 1«.

.

Collection

round S 

N2=164

K2=256

N3=121

K3=256

92 tags sent data

sucessfully

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43 tags sent data

sucessfully

Collection

round 2

Collection

round 3

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N tags enter coverage area

No new tags enter until previous one have identified

ISO 18000-7 (K static value configurable: 7, 14, 21,«)

Goal: to minimize the total identification delay{N, K, T}

NN

No tag

signals

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Introduction (V)

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Capture Effect (I)

Signals of two or more tags arrive at the reader simultaneously

Stronger signal is decoded To model CE in RFID Signal-to-Interference-Ratio (SIR) SIR > Threshold (Cr) Readers in the market, Cr=6 dB Cr SIR "

COLLISION!

NNN

8 RFID Systech 2010

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 z 

r  z 

v y y y

vr  q z C 

 Pw

 PwC SIR z  !

¹¹¹¹

 º

 ¸

©©©©

ª

¨"!"!

§{!

)(Pr )Pr()(

,1

H H  Capture Probability

Cr=6dB q=0.5

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Capture Effect (II)

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Why do we consider Capture Effect? Real phenomenon in readers on the market It has a direct influence on the identification performance

¹

 º

 ¸©

ª

¨ !Cr 

 K  N 

10

11

 K  N dBC r  25.16 !p!

46.0};

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Capture Effect (III)

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Goals

Analytical characterization of the identificationprocess in active RFID Systems Focused on standard ISO 18000-7 (fixed collection round procedure)

Considering Capture Effect (not considered in previous works)

From the analysis« Optimal configuration parameters to minimize total identification delay

Optimal criteria depends on the scenario studied: in this work, staticscenario

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Analysis of the identification process

in static scenarios with CE (I)

For every configuration {N,K }: mean number of collection rounds(identification delay) to identify N

Markovian Analysis (Discrete Time Markov Chain, DTMC) Homogeneous markov process { Xs}

State : { Xs} number of tags unidentified in collection round s

Goal: average number of steps until absorbing state

Initial state

X0=NAbsorbing state

Xs=0

Transitory states

{X1, X2, X3,,«, Xs-1 } 

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Analysis of the identification

process in static scenarios with CE (II)

State {Xs}: number of tags unidentified in collection round s

Transition probabilities

From transitionMatrix P«

Canonical form Fundamental Matrix

Mean number of collection rounds

Mean number of slots K  s L !!

!1

0

,0

 N 

 y y D s

1

)(,

01

!¹¹

 º

 ¸

©©ª

¨

! F  I  D F Q P 

±±°

±±¯

®

!!

e

!

other ise

i j K ii y yi

 p

i j K  jcr id i K 

 ji p

,,0

,1 ,

1

2,),(,r 

,

§ §

§

* =

*

!

!!

 F E

 F

 F FE

 F F

)(r )|r(

)(r )|,(r ),(r 

,

,,,

i K 

i K i K i K  cr id cr id 

)())(1()()r(

K  QK K H H 

 Q QK K 

¹

¹

 º

 ¸

©

©

ª

¨!! t t t 

t t t 

t r t 

v y y y

vr  qt C 

 Pw

 PwC SIRt  !

¹¹¹¹

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§{!

)(Pr )Pr()(

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H H 

13 RFID Systech 2010

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 K Tags in coverage

( N )7 N  24

14 24   N < 42

21 42 N < 63

28 63  N < 74

35 74  N < 97

42 97  N < 112

49 112  N < 128

56 128  N < 134

63 134  N < 163

70 163  N < 184

77 184  N < 205

84 205  N < 226

91 226

 

N <254

« «.

Identification process in static

scenarios with CE: Analytical results

50 tags per pallet:

K=21, T=140 slots

K=7, T=320 slots, 228% more time

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e.g. N=120

Without CE K=63, T=430 slots

With CE K=49, T=350 slotsSaving 19.4% time

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Conclusions and Future Issues

` Analytical characterization of the identification process in activeRFID systems under ISO 18000-7` Capture effect is a real phenomenon in readers` Considering CE improving analytical results (close to real behaviour)` Results:

` Optimal configuration parameters {N, K,T} to minimize total identificationdelay in static scenarios

` Future issues` To add channel model in the analysis` Measurements with a commercial active RFID system

` To consider other scenarios` To consider variable number of slots per collection round (open issue in

ISO 18000-7)

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Thank you!!

[email protected]

http://www.ait.upct.es

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