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



Index

` Introduction

` ISO 18000-7

` Capture effect phenomenon in RFID

` Markovian analysis

` Analytical and Simulation results

` Conclusions and future issues

2 RFID Systech 2010



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

3 RFID Systech 2010



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

4 RFID Systech 2010



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

5 RFID Systech 2010



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

6 RFID Systech 2010

43 tags sent data

sucessfully

Collection

round 2

Collection

round 3



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

7 RFID Systech 2010

Introduction (V)



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



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

9 RFID Systech 2010

Capture Effect (II)



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};

10 RFID Systech 2010

Capture Effect (III)



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




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 }




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

K

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

º

¸

©©©©

ª

¨

"!"!

§{!

)(Pr )Pr()(

,1

H H




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


e.g. N=120

Without CE K=63, T=430 slots

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



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)




Thank you!!

[email protected]

http://www.ait.upct.es


Documents

RFID Systech2010