design, deployment and analysis - winlab · 1. asset tracking with roll-call. tm: design,...
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Asset Tracking with Roll-CallTM: Design, Deployment and Analysis
Yanyong Zhang, Ben Firner, Rich Howard, Wade Trappe
WINLAB, Rutgers University
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RFID: Technology of the Future RFID: Technology of the Future We envision that an efficient asset tracking application should:•
Continuously track the position of each item•
Detect the missing of an item in real time•
E.g., jewelry tracking
MooreMoore’’s Law (Techie View)s Law (Techie View)
Year
1010
10 9
10 8
10 7
10 6
10 5
10 41970 1980 1990 2000 2010
Encyclopedia2 hrs CD Audio30 sec HDTV
Book1 min CD Audio1/4 sec HDTV
Page
No.
of B
its/C
hip
0.15μm
0.15-0.2μm
0.25-0.3μm
0.35-0.4μm
1.0-1.2μm
0.5-0.6μm
0. 7-0.8μm
0.6-2.4μm
4Gb
1Gb
256Mb
64Mb
16Mb
4Mb
1Mb
256Kb
64Kb
MooreMoore’’s Law (Business View)s Law (Business View)
Year
No.
of M
Bits
/Chi
p
0500
1,0001,5002,0002,5003,0003,5004,000
1982
1985
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Dumb Idea !
Start Study
Out of business
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Limitations with Existing RFIDLimitations with Existing RFIDPassive RFID Tags
+ Inexpensive+ Long Lifetime-
Poor Range
Active RFID Tags+ Good Range- More Expensive-
Short Lifetime
- Larger
Passive Tag Reader
Passive Tag Reader
Anyone there?
Active Tag Receiver
Active Tag Receiver
I’m still here!
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Our Solution: Our Solution: Roll-CallTM
Active Tag:•
Tag periodically announces its ID.•
Receiver disabled.•
Life time: 1 year (3 V,220 mA-hr coin battery).
Basestation:•
Receives and timestamps the packets, then transfer them to the processing station
•
Multiple receives used to provide overlapping coverage.Central Processing Unit:•
Tracks the tags using data from multiple receivers.
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Challenges: Packet LossesChallenges: Packet LossesPacket losses can lead to false alarms.There are three types of losses:•
Ambient losses due to radio environment
Tag 7 had a loss ratio over 80%
Solution: better placement of basestations
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Challenges: Packet LossesChallenges: Packet LossesPacket losses can lead to false alarms.There are three types of losses:•
Ambient losses due to radio environment•
Collision lossesRandom transmissions lead to collisionsOur model shows that in a 100-tag system with each tag transmitting a 100 bit packet in 100ms epochs, the collision probability is 5%
Soln II: Varying Transmission Periods
A tag varies its transmission period
it won’t collide with the same set of tags repeatedly.
Soln I: Software Collision Prediction
Roll-call can predict the times for tag transmissions and collisions
If a corrupted packet is received, we know it is a collision!
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Challenges: Packet LossesChallenges: Packet LossesPacket losses can lead to false alarms.There are three types of losses:•
Ambient losses due to radio environment•
Collision losses•
Dead-time losses due to unavailability of the basestationProcessing timeTransfer time
Solution: Reduce the processing at the basestation, and buffering the packets for a batch transfer
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Throughput Limit TestThroughput Limit TestExperiment setup: a tag transmits 20,000 packets at different packet intervals
Combining buffering and use of multiple basestations achieves the best performance
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Raw Packet Loss RatioRaw Packet Loss Ratio
Number of basestations
Pack
et los
s (%
)
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Presence DetectionPresence DetectionRaw packet loss ratio information is not fed into applications; instead, we need to detect whether a tag is missingDeclare miss ratio (DMR)•
how resilient a detection scheme is against packet losses•
n packet losses, out of which we detect m tag misses, then the DMR is m/n
Report Latency (RL) •
The interval between the last when a tag was heard and the time it was declared missing given that it is actually lost
Detection Heuristicsmethod DMR (%) RL (rounds)Single Miss 100 1
Single Ambient Miss 1.47 1.33
5 ambient misses 0.0122 12.5
Max misses 0.0393 5.10
Max misses + 5 0.0034 23.3
Presence DetectionPresence Detection
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Conclusions and Future DirectionsConclusions and Future DirectionsThe initial Roll-CallTM design is promisingPacket losses can be further reduced•
More enhancements are on the wayExtracting information from collided packetsEmploying basestations with multiple processors
More sophisticated detection algorithms are neededWill extensively study the performance in different environments
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Questions & AnswersQuestions & Answers