1

Position Estimationfor Goods Tracking System

using Mobile Detectors

Hiroshi Mineno, Kazuo Hida, Miho Mizutani, Naoto Miyauchi,Kazuhiro Kusunoki, Akira Fukuda, Tadanori Mizuno

Shizuoka University, JapanMitsubishi Electric Corporation

Kyushu University, Japan

Hiroshi Mineno, Kazuo Hida, Miho Mizutani, Naoto Miyauchi,Kazuhiro Kusunoki, Akira Fukuda, Tadanori Mizuno

Shizuoka University, JapanMitsubishi Electric Corporation

Kyushu University, Japan

†

‡†

†‡

2

Outline

Introduction – location awareness -Related workMobiTra overviewHierarchical trackingPosition estimationPrototype testbedExperimental resultSimulation resultConclustion

3

Introduction

Location awareness is useful to applicationsLibraries: guide readers to books they chooseHospitals: keep track of patients or nursesMolls: guide parents to their lost childHome: guide us to something looking for

Context aware ubiquitous service

Pervasive Sentient Invisible

Accurate positioning, tracking systemAccurate positioning, tracking system

4

Related workActive badge:

Infrared signal, room level granularity

Active bat, cricket:TDoA between RF and ultrasound

RADAR:RSSI of 802.11 RF, several meters

RF based proximity:The location is given as a centroid.

Requiring special devices to track the objectTrade-off between position accuracy and the number of sensing devices

Reader

Tag

Large Expensive Hard to install

5

Solution is RFID tags

Categorized by existence of battery

Active RFID tags Passive RFID tagsMerit Long read range No battery, small, lightweight

Demerit Need battery exchange, expensive

Short read range

Tag readers will be commonly mobileSmall and lightweight have been developed

Ubiquitous Communicator byYRP Ubiquitous Networking Lab.

2004.9.15 2005.3.2Trial model

Compact Flash type Cell phone with tag reader by KDDI

6

MobiTra overview

UserUser

ObjectsObjects

Mobile tag readers (MTRs)Mobile tag readers (MTRs)

MobiTra Server

Internet

PassiveRFID tags

Hierarchicaltracking

Sensing EnvironmentSensing Environment Traditionalresearch

7

Position estimation

204738C10:15

204020C10:15

204532A10:13

203030A10:18

202512A10:13

203433B10:09

205050C10:15

205050C10:15

201525A10:17

204040B10:16

201010A10:18

……………

Read range

MTR’s y-coordinate

MTR’s x-coordinateObject IDTime

MTRs’ Detection histories (i)

(ii)

(iii)

(iv)

Estimated area

8

Position estimation methods

AA

B

B

(a) Sensing constraint (b) Connectivityconstraint

(c) Negative constraint

9

Prototype testbed

Target object

Mobile active RFID tag reader

(MTR)

Tracking environment

for MTRs

Passive RFID tag reader

Passive RFID tag reader

Passive RFID tags(at 20cm intervals)Passive RFID tags(at 20cm intervals)

Active RFID tagActive RFID tag

Active RFID tag reader

Active RFID tag reader

10

Experimental result

The number of applied detection histories

1.0

0.8

0.6

0.4

0.2

00 1 2 3 4 5 6 7 8

◆

◆

◆

◆ ◆

◆ ◆ ◆ ◆

Ext

inct

ion

ratio

of e

stim

ated

are

a

11

Simulation result

0

0.5

1

1.5

2

2.5

3

3.5

4

0 80 160

240

320

400

Elapsed time (sec)

0

0.5

1

1.5

2

2.5

3

3.5

4

0 80 160

240

320

400

(a) Tags at four corners

Estim

ated

are

a (m

^2)

Estim

ated

are

a (m

^2)

(b) Other tags

Using negative constraintsNot using negative constraints

Elapsed time (sec) Elapsed time (sec)

12

Detailed analysis

(a) Tags not at four corners( Connectivity constraints)

(b) Tags at four corners(Connectivity constraints)

Target object

MTR

Estimated area

(c) Tags at four corners(Negative constraints)

13

Conclusion

This presentation showed:Hierarchical goods tracking system using RFID tags and mobile detectorsEffect of position estimation is evaluated through prototype testbedand simulation

Future work:Developing MobiTra v.2 (TDoA, Web I/F)

Evaluate estimated location accuracyNew position estimation method

B

14

15

MobiTra v.2

User

Beacon

MTR

Wireless LANAccess Point

MobiTra server

Tag reader

Listener

PDATDoA

Web browser

Objects

Position estimation

16

Interval v.s. Num of MTR

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

3 4 5 6 7 8 9 10

Square on a side (m)

Elapsed time to detect all targets (s) Num of MTR: 1

Num of MTR: 2

Num of MTR: 3

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

3 4 5 6 7 8 9 10

Square on a side (m)

Elapsed time to detect all targets (s) Num of MTR: 1

Num of MTR: 2

Num of MTR: 3

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

3 4 5 6 7 8 9 10

Square on a side (m)

Elapsed time to detect all targets (s) Num of MTR: 1

Num of MTR: 2

Num of MTR: 3

Interval: 10sec

Interval: 20sec

Interval: 5sec

Num of MTR: 1

Interval: 20sec

Interval: 10sec

Interval: 5sec

MTR × 1

MTR × 2

MTR × 3

MTR × 1

MTR × 2MTR × 3

MTR × 1MTR × 2MTR × 3

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

3 4 5 6 7 8 9 10

Square on a side (m)

Elapsed time to detect all targets (s) Interval: 1sec

Interval: 3sec

Interval: 5sec

Interval: 10sec

Interval: 20sec

17

Effect of Negative Constraint

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50 100 150 200 250

Applied detection histories

Decrease of estimated area (%) Square on a side: 3m

Square on a side: 4m

Square on a side: 5m

Square on a side: 6m

Square on a side: 7m

Square on a side: 8m

Square on a side: 9m

Square on a side: 10m

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50 100 150 200 250

Applied detection histories

Decrease of estimated area (%) Square on a side: 3m

Square on a side: 4m

Square on a side: 5m

Square on a side: 6m

Square on a side: 7m

Square on a side: 8m

Square on a side: 9m

Square on a side: 10m

18

Detailed analysis

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50 100 150 200 250

Applied detection histories

Decrease of estimated area (%)

Square on a sede: 3m Square on a side: 4m

Square on a side: 5m Square on a side: 6m

Square on a side: 7m Square on a side: 8m

Square on a side: 9m Square on a side: 10m

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50 100 150 200 250

Applied detection histories

Decrease of estimated area (%) Square on a side: 3m

Square on a side: 4mSquare on a side: 5mSquare on a side: 6m

Square on a side: 7mSquare on a side: 8mSquare on a side: 9mSquare on a side: 10m

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50 100 150 200 250

Applied detection histories

Decrease of estimated area (%)

Square on a side: 3mSquare on a side: 4mSquare on a side: 5mSquare on a side: 6mSquare on a side: 7mSquare on a side: 8mSquare on a side: 9mSquare on a side: 10m

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50 100 150 200 250

Applied detection histories

Decrease of estimated area (%) Square on a side: 3m

Square on a side: 4m

Square on a side: 5m

Square on a side: 6m

Square on a side: 7m

Square on a side: 8m

Square on a side: 9m

Square on a side: 10m

Connectivity constraints (others)

Negative constraints (at 4 corners)

Negative constraints (others)

Connectivity constraints (at 4 corners)

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Solution is RFID tags

Active type Passive typeMerit Long read range No battery, small, lightweight

Demerit Need battery exchange, expensive

Short read range

~135kHz 13.56MHz 860～930MHz 2.45GHz

Communication method

Electromagnetic induction Electromagnetic wave propagation

Read range ～10cm ～30cm ～3m ～1.5mDirectivity ○ ○ ◎ ◎

Water resistance

◎ ○ △ ×

Metal resistance

◎ ○ △ ×

(LF) (HF) (UHF)

Categorized by existence of battery

Categorized by radio frequency

20

Hierarchical tracking

ObjectsObjects

Mobile DetectorsMobile Detectors

MobiTra Server

21

A)無線ICタグとの交信距離と指向性２

読取り可能なタグ方向（電磁誘導方式）

無指向性アンテナ 指向性アンテナ（低周波）

標準的なゲートアンテナ

×

○○

○○

○○

○

２つのゲートアンテナ

アンテナ交信範囲と指向性 距離

幅

指向性アンテナ（高周波）

距離

幅

交信可能時間

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A)無線ICタグとの交信距離と指向性３

ある程度の検知率を得るためには，指向性が弱く，交信距離が１ｍ程度の検知器が望ましい？

RF Code社 Spider Reader IIIAタグリーダ & タグアクティブタグ（約20g），303.825MHz帯電波（UHF）2本のヘリカルアンテナを用いて指向性の調整可能10cm～10mで8段階に交信距離を調整可能複数同時読み取り（最大1,000個）バッテリ内臓（約4時間），約450gタグ内のコイン型電池交換可能

タグID送信間隔7秒（△）

23

Triangulation

Proximity- Cell-ID方式など

Lateration- RSS，TOA，TDOA方式など

Angulation- AOA方式など