the practicality of multi-tag rfid systems
DESCRIPTION
The Practicality of Multi-Tag RFID Systems. Leonid Bolotnyy Scott Krize Gabriel Robins. Department of Computer Science University of Virginia. passive. semi-passive. active. Introduction. RFID. Tags types:. Frequencies: Low (125KHz), High (13.56MHz), UHF (915MHz). Coupling methods:. - PowerPoint PPT PresentationTRANSCRIPT
Department of Computer Science
University of Virginia
The Practicality of Multi-Tag RFID Systems
Leonid BolotnyyScott Krize
Gabriel Robins
Introduction• RFID
passive semi-passive active
• Tags types:
• Frequencies: Low (125KHz), High (13.56MHz), UHF (915MHz)
• Coupling methods:
readerantenna
signal signal
Inductive coupling Backscatter coupling
History
• Auto-ID Center formed - 1999
• EPCglobal formed - 2004
• Radar invented - 1935
• EAS invented - early 1960’s
• First RFID book published - 1999
• First RFID patent filed - 1973
• First RFID game marketed - 2006
Object Identification
• Bar-codes vs. RFID– line-of-sight– scanning rate
• Unreliability of object detection– radio noise is ubiquitous– temperature and humidity– objects/readers moving speed– liquids and metals are opaque to RF
• milk, water, juice• metal-foil wrappers
– object occlusion– number of objects grouped together– tag variability and receptivity– tag aging
Case Studies
• Defense Logistics Agency trials (2001)– 3% of moving objects did not reach destination– 20% of tags recorded at every checkpoint– 2% of a tag type detected at 1 checkpoint– some tags registered on arrival but not departure
• Wal-Mart experiments (2005)– 90% tag detection at case level– 95% detection on conveyor belts– 66% detection inside fully loaded pallets
Multi-Tag RFID
Use Multiple tags per object to increase reliability of object detection/identification
The Power of an Angle• Inductive coupling: voltage ~ sin(β), distance ~ (power)1/6
• Far-field propagation: voltage ~ sin2(β), distance ~ (power)1/2
32.7
58.11
47.98
61.86
30
35
40
45
50
55
60
65
1 2 3 4Number of Tags
Ex
pe
cte
d a
ng
le (
in D
eg
ree
s)
4 2
40[ (2 cos ) ( )(2 cos ) ] /
2
x x dx x x dx
2
0[ (2 cos ) ] /(2 )
x x dx
B-field
β
• Optimal Tag Placement:
1
4
32
Equipment and Setup• Equipment
• Setup– empty room– 20 solid non-metallic & 20 metallic and liquid objects– tags positioned perpendicular to each other– tags spaced apart– software drivers
– 4 linear antennas by Alien Technology– 4 circular antennas by Alien Technology– 4 circular antennas by ThingMagic
Experiments• Read all tags in reader’s field• Randomly shuffle objects• Compute average detection rates
• Variables– reader type– antenna type– tag type– antenna power– object type– number of objects– number of tags per object– tags’ orientation– tags’ receptivity
Linear Antennas
Antenna Pair #1, Power = 31.6dBm
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Object Number
Det
ecti
on
Pro
bab
ilit
y
1Tag: 58%
2Tags: 79%
3Tags: 89%
4Tags: 93%
Circular Antennas
Antenna Pair #1, Power = 31.6dBm
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Object Number
Det
ecti
on
Pro
bab
ilit
y
1Tag: 75%
2Tags: 94% 3Tags: 98%
4Tags: 100%
Linear Antennas vs. Multi-tags
Power = 31.6dBm
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Object Number
De
tec
tio
n P
rob
ab
ilit
y
1 Reader, 1 Tag 58.0%
2 Readers, 1 Tag 64.9%
1 Reader, 2 Tags 79.3%
2 Readers, 2 Tags 84.5%
Δ=21.3%
Δ=19.8%Δ= 5.2%
Δ=14.4%
Δ= 6.9%
Circular Antennas vs. Multi-Tags
Power = 31.6dBm
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Object Number
Det
ecti
on
Pro
bab
ility
1 Reader, 1 Tag 75.9%
2 Readers, 1 Tag 91.0%
1 Reader, 2 Tags 94.2%
2 Readers, 2 Tags 99.4%
Δ=18.3%
Δ=8.4%Δ= 5.2%
Δ=3.2%
Δ= 15.1%
Linear Antennas
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
31.6 30.6 29.6 28.6 27.6 26.6 25.6
Power (dBm)
Det
ectio
n P
rob
abili
ty
Circular Antennas
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
31.6 30.6 29.6 28.6 27.6 26.6 25.6
Power (dBm)D
etec
tion
Pro
bab
ility
1 Tag 2 Tags 3 Tags 4 Tags
Power
• Decrease in detection with decrease in power• More rapid decrease in detection for circular antennas
Importance of Tag Orientation
Uni-polar tags
1 Tag 2 Tags 1 Tag 2 Tags180-same 0.55 0.37180-diff 0.74 0.5290-same 0.67 0.5290-diff 0.80 0.63
Circular Linear
0.47 0.33
Bi-polar tags
1 Tag 2 Tags 3 Tags 1 Tag 2 Tags 3 Tags180 1 1 0.57 0.790 0.93 1 0.97 1
Circular Linear
0.75 0.53
Controlling Variables1. Radio noise
2. Tag variability
3. Reader variability
4. Reader power level
5. Distance to objects &type, # of antennas
Detection in Presence of Metals & Liquids
Power=31.6dBm, No Liquids/Metals Power=31.6dBm, With Liquids/Metals
Power=27.6dBm, No Liquids/Metals Power=27.6dBm, With Liquids/Metals
Circular Antenna
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1 2 3 4
Number of Tags
Det
ecti
on
Pro
bab
ilit
y
• Decrease in solid/non-liquid object detection• Significant at low power• Similar results for linear antennas
• Low detection probabilities• Drop in detection at low power
• Linear antennas outperform circular• Multi-tags better than multiple readers
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1 Tag 2 Tags 3 Tags 1 Tag 2 Tags 3 Tags 1 Tag 2 Tags 3 Tags
Antenna #1 Antenna #2 Antenna #1 and #2
Number of Tags
De
tec
tio
n P
rob
ab
ilit
y
Power=31.6dBm, Circular AntennasPower=31.6dBm, Linear AntennasPower=27.6dBm, Circular AntennasPower=27.6dBm, Linear Antennas
Multi-Tags on Metals and Liquids
Varying Number of Objects
Experiment 1: 15 solid non-metallic & 15 liquids and metals
Experiment 2: 20 solid non-metallic & 20 liquids and metals
Effect of the Number of Objects on Detection Probability
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1 Tag 2 Tags 3 Tags 1 Tag 2 Tags 3 Tags 1 Tag 2 Tags 3 Tags 1 Tag 2 Tags 3 Tags
1 Antenna 2 Antennas 3 Antennas 4 Antennas
Det
ecti
on
Pro
bab
ilit
y
15/15 experiment
20/20 experiment
15/15 experiment
20/20 experiment
Metals & Liquids∆ : 3%-13%
Detection Delta
Change in Detection Based on # of Antennas and Tags
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
1 Antenna 2 Antennas 3 Antennas 4 Antennas
Ch
ang
e in
Det
ecti
on
Pro
bab
ilit
y
1 Tag
2 Tags
3 Tags
Anti-Collision Algorithms
Binary No Effect No Effect
Binary Variant No Effect No Effect
Randomized Linear Increase** No Effect*
STAC Causes DoS No Effect*
Slotted Aloha Linear Increase** No Effect*
Algorithm Redundant Tags Connected-Tags
* Assuming tags communicate to form a single response** If all tags are detected
Applications of Multi-TagsReliability Availability
Safety
Localization
More Applications
Tagging Bulk MaterialsPackaging
Theft PreventionSecurity
Economics of Multi-TagsPassive Tag Cost Trend
$0.00$0.20$0.40$0.60$0.80$1.00
2001 2002 2003 2004 2005 2006 2007 2008 2011
Year
Ta
g C
os
t
Historical Cost Prediction Cost
2001 $1.042002 $0.812003 $0.452004 $0.192005 $0.132006 $0.082007 $0.062008 $0.052011 $0.01
Year Cost
• Rapid decrease in passive tag cost• 5 cent tag expected in 2008• 1 penny tag in a few years
Cost Trends
Time
Business Case for RFID
• Costs & benefits (business case)– Moore’s law– higher employee productivity– reduction in workforce– automated business processes– workforce reduction
• Tag manufacturing yield and testing– 30% of chips damaged during manufacturing– 15% damaged during printing [U.S. GAO]– 20% tag failure rate in field [RFIDJournal]– 5% of tags purchased marked defective
RFID Tag Demand
• Demand drivers– tag cost– desire to stay competitive
• Cost effective tag design techniques– memory design (self-adaptive silicon)– assembly technology (fluidic self assembly)– antenna design (antenna material)
Increase in RFID tag demand
Decrease in RFID tag cost
Conclusion• Unreliability of object detection
– radio noise is ubiquitous– temperature and humidity– objects/readers moving speed– liquids and metals are opaque to RF
• milk, water, juice• metal-foil wrappers
– object occlusion– number of objects grouped together– tag variability and receptivity– tag aging
• Many useful applications
Passive Tag Cost Trend
$0.00$0.20$0.40$0.60$0.80$1.00
2001 2002 2003 2004 2005 2006 2007 2008 2011
Year
Ta
g C
os
t
Historical Cost Prediction Cost
• Favorable economics
Our ResearchGeneralized “Yoking Proofs”
3
Multi-Tags
PUF Inter-Tag Communication
RFID
Thank You
Questions?