1 indoor location sensing using active rfid lionel m. ni, hkust yunhao liu, hkust yiu cho lau, ibm...
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1
Indoor Location Sensing Using Active RFID
Lionel M. Ni, HKUSTYunhao Liu, HKUST
Yiu Cho Lau, IBMAbhishek P. Patil, MSU
Indoor Location Sensing Using Active RFID
Lionel M. Ni, HKUSTYunhao Liu, HKUST
Yiu Cho Lau, IBMAbhishek P. Patil, MSU
2
MotivationMotivation
Overview of RFIDOverview of RFID
Performance EvaluationPerformance Evaluation
LANDMARC Approach LANDMARC Approach
ConclusionConclusion
4
Location-aware Computing
• The location is an important context that changes whenever the object moves
• Location-aware services allow to offer value-added service to the user, depending on their current geographic position and will be a key feature of many future mobile applications
• Sensing the location: explicit and implicit cooperation; outdoor or indoor
5
Location Sensing Techniques
• Triangulation: use geometric properties of triangle to compute object locations– Signal strength: signal attenuation is a
function of distance to the signal source
• Scene analysis: use features of a scene observed from a certain reference point
• Proximity: determine if an object is near a known location
7
Existing Technologies and SystemsInfrared Example: Active Badge Location
System
• Low power requirements• Low circuitry costs: $2-$5
for the entire coding/decoding circuitry
• Simple circuitry• Higher security• Portable • High noise immunity
• Line-of-sight • Coarse resolution• Short range• Blocked by common
materials• Light, weather sensitive
• Pollution can affect
transmission
8
IEEE 802.11Example: RADAR
• It is using a standard 802.11 network adapter to measure signal strengths at multiple base stations positioned to provide overlapping coverage in a given area
9
• Strength– Easy to set up– Requires few base
stations– Uses the same
infrastructure that provides general wireless networking in the building
• Weakness– Poor overall accuracy:
• scene-analysis: within 3 meters with 50 percent probability
• signal strength: 4.3 meters at the same probability
– Support Wave LAN NIC
Microsoft RADAR
10
Ultrasonic
• Active Bat (AT&T)– ultrasound time-
of-flight measurement
– can locate Bats to within 9cm of their true position for 95 percent of the measurements
11
Cricket Location Support System (M.I.T)
• Ultrasonic time-of-flight and a radio frequency control signal
• Lateration and proximity techniques
• Decentralized scalability
• 4x4 square-foot regions
12
RFID: SpotON
• Objects are located by homogenous sensor nodes without central control
• SpotOn tags use received radio signal strength information as a sensor measurement for estimating inter-tag distance
• No complete system yet
13
LANDMARC Prototype
•Selection criteria–Use commodity products or off-the-shelf components–Low cost–Resolution: no more than 2-3 meters
•Decision: RFID technology
14
What is RFID (Radio Frequency Identification) ?
• RFID is a means of storing and retrieving data through electromagnetic transmission to a RF compatible integrated circuit
• 3 basic components
Card Reader Antenna
Reader/ Programmer
TagAntenna
Ai rI nterface
Transponderor Tag
16
Active RFID
• RF Reader– Range up to 150 feet– Identify 500 tags in 7.5 seconds with the collision
avoidance– Support 8 power levels (function of distance)
• Active Tag system– Emit signal, which consists of a unique 7-character
ID, every 7.5 seconds for identification by the readers– Button-cell battery (2-5 years life)– Operate at the frequency of 303.8 MHz
17
Active RFID AdvantagesLocat i on
Sever
RFTags
RFReadersWi rel ess
Network
• Non-line-of-sight nature
• RF tags can be read despite the extreme environmental factors : snow, fog, ice, paint …
• be read in less than 100 milliseconds
• promising transmission range
• cost-effectiveness
18
Using RFID: First Attempt
• How many readers are needed?– Build an array of
readers: too expensive
• How reliable is the tag detection?– Not very reliable
due to signal attenuation
• Placement of RF readers
• Cannot measure distance directly
RR
R
R
R
R R
R R
21
LANDMARC Approach
• The LANDMARC system mainly consists of two physical components, the RF readers and RF tags
22
The Concept of Reference Tags
1m
1m
Ref erence Tag
Tracki ng Tag
RF Reader
(0, 0)
1 m2 m3 m4 m
1 m
2 m
4 m
3 m
5 m
6 m
7 m
8 m
9 m
23
a b c
d e f
g h i
g k l
RFReader1
RFReader2
FourNearest
tracki ngtag
• Distance estimation• Placement of
reference tags• Selection of k
neighboring reference tags
• Weight of each selected reference tags
Known Reference Tags
24
the placement of the reference tags •
•
Three Key IssuesThree Key Issues
the value of k in this algorithm •
• the formula of the weight•
•
25
Distance Estimation: Signal Strength
• Signal Strength Vector of an unknown tag
• Signal Strength Vector of a reference tag
• Euclidian distance
28
Effect of the Value k
0%
25%
50%
75%
100%
0 1 2 3
e (meters)
cu
mu
lati
ve
%
k=2,Av e=1.47,Worst=2.68
k=3, Av e=1.13,Worst=1.98
k=4, Av e=1.09,Worst=1.81
k=5, Av e=1.13,Worst=1.99
Cumulative Percentile Of Error Distance When K Value Is 2, 3, 4, 5
29
Influence of The Environmental Factors
Cumulative Percentile Of Error Distance in Daytime & Night
0%
25%
50%
75%
100%
0 0.5 1 1.5 2 2.5 3
e(meters)
cum
ula
tive
%
Daytime,Worst=1.956
Night,Worst=1.783
30
Influence of The Environmental Factors (cont’d)
Change The Placements Of Tracking Tags
1m
1m
Reference Tag
Tracki ng Tag
RF Reader
(0, 0)
1 m2 m3 m4 m
1 m
2 m
4 m
3 m
5 m
6 m
7 m
8 m
9 m
31
Influence of The Environmental Factors (cont’d)
Cumulative Percentile Of Error Distance When Changing The Placement Of Tracking Tags
0%
25%
50%
75%
100%
0 0.5 1 1.5 2 2.5 3
e(meters)
cum
ula
tive
%
original setup,Worst=1.81
changeTrkTag,Worst=1.82
32
Effect of The Number of Readers
Cumulative Percentile Of Error Distance With 3 or 4 Readers Data
0%
25%
50%
75%
100%
0 0.5 1 1.5 2 2.5 3
e (meters)
cum
ulat
ive
%
4 readers data, Worst=1.81
3 readers data, Worst=2.59
33
The Effect of Placement of Reference Tags
Without Partition
a b c
d e f
g h i
g k l
RFReader1
RFReader2
FourNearest
tracki ngtag
34
Effect of Placement of Reference Tags (cont’d)
With Partition
a b c
d e f
g h i
g k l
RFReader1
RFReader2
Fournearest
Part i t i on P
realposi t i on
computedposi t i on
35
Effect of Placement of Reference Tags (cont’d)
With Partition
a b c
d e f
g h i
g k l
RFReader1
RFReader2
m n
o
Ori gi nal Reference Tags
New Reference Tags
Tracki ng Tag
36
Placement of Reference Tags
Replacements of the Reference Tags with a Higher Density
1m
1m
Ref erence Tag
Tracki ng Tag
RF Reader
1m
1m
near 1 near 2
37
Effect of Higher Density Reference Tags
Cumulative Percentile Of Error Distance With Higher Reference Tag Density
0%
25%
50%
75%
100%
0 0.4 0.8 1.2 1.6 2
e(meters)
cum
ula
tive
%
Original, Worst=1.81
near1, Worst=1.76
near 2, Worst=1.69
38
Lower Density of Reference Tags
Replacements of the Reference Tags with a Lower Density
1m
1m
Ref erence Tag
Tracki ng Tag
RF Reader
1m
1m
f ar 1 far 2
39
Effect of Lower Density Reference Tags
Cumulative Percentile Of Error Distance With lower Reference Tag Density
0%
25%
50%
75%
100%
0 0.5 1 1.5 2 2.5 3 3.5e (meters)
cum
ula
tive
%
Original, Worst=1.81
far 1,Worst=2.59
far 2,Worst=3.17
40
• Using 4 RF readers in the lab, with one reference tag per square meter, accurately locate the objects within error distance such that the largest error is 2 meters and the average is about 1 meter.
41
Conclusions
• RFID can be a good candidate for building location-sensing systems
• Able to handle dynamic environments• Suffer some problems
– Difference of Tags’ Behavior– RFID does not provide the signal strength of
tags directly – Unable to adjust emitting interval– Standardization
44
DeskRefrigerator
Desk
Desk SofaRefrigerator
2. Tracking
movement
3. Notify where you are (Location sensing)4. Notify your eating schedule
7. Time sensing8. immobility sensing
11. Proximity sensing
16. Notify
“ok to eat”
1.walk
5.Stop eating
6.Back to desk
10. Walk around
9. Notify to move
12. Walk away from sofa
13. Distance& Time
sensing
14. Notify to stop
15. Go back to desk
17. Go to kitchen
18. Refer
Healthy food
19. Eat matched food
46
(2) Scene Analysis• use features of a scene observed from a
certain reference point
(3) Proximity• determine if an object is near a known
location
47
Project Motivation
• GPS’s inability for accurate indoor location sensing
• Develop a cost-effective indoor location sensing infrastructure
• Enables location-based Web services for mobile-commerce (m-commerce) environment
• Plenty of other application scenarios, depending on your imagination and creativity
48
Passive RFID vs. Active RFID
Reader
Ai rI nterface
RF Si gnal toTag
Tag DataAntenna
Transponder
or Tag
Active tag System
50
I nternetweb/ database
serversl ocati onservers
A B C D E F G H
S EL E CT E D
O N -L IN E
A B C D E F G H
S EL E CT E D
O N -L IN E
A B C D E F G H
S EL E CT E D
O N -L IN E
A B C D E F G H
S EL E CT E D
O N -L IN E
Wi red Network Connecti onWi
red
Netw
ork
Conn
ecti
on
Wire
d Ne
twor
k Co
nnec
tion
WAP
WAPWAP
WAP
Ad Hoc PDARouter
802. 11b
802. 11b
802. 11b
802. 11b
802. 11b
802. 11b
RF Communi cat i on
RF Communi cat i on
PDA/RF Tag
PDA
PDA/RF Tag
regi strati onservers
Ref erenceTag
802. 11b
RF Communi cat i on
802. 11b
RF Communi cat i on
802. 11b
RFReader
RFReader
RFReader
RFReader
51
Active RFID
• RF Reader– Range up to 150 feet– Identify 500 tags in 7.5 seconds with the collision
avoidance– Support 8 power levels (function of distance)
• Active Tag system– Emit signal, which consists of a unique 7-character
ID, every 7.5 seconds for identification by the readers
– Button-cell battery (2-5 years life)– Operate at the frequency of 303.8 MHz
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