Fast and Reliable Estimation Schemes in RFID Systems MobiCom 2006 Presented by Yiyang Zhao
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Fast and Reliable Estimation Schemes in RFID Systems
MobiCom 2006Presented by Yiyang Zhao
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Outline
MotivationBackgroundRelated Work
Basic IdeaProposed AlgorithmConclusionDiscussion
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Motivation
RFID systems have been widely used in many areasTwo major problems arise in any RFID deployment
IdentificationEstimation
Some applications need to estimate the number of tags as fast as possible for a given accuracy Existing protocols are not fast enough
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Background I—RFID system
An RFID system
Three types of tagsPassiveSemi-passiveActive
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Background II—ALOHA protocols
Slotted ALOHA—DeterministicTree based algorithm
Framed ALOHA—Probabilistic
frame
time
slottag
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Related Work
Many existing protocols just focus on the identification Few of them proposed a simple algorithm for estimating the number of tags
Identification timeN N1+2Nc
The estimation time is too long≥
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Outline
MotivationBackgroundRelated Work
Basic IdeaProposed AlgorithmConclusionDiscussion
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Basic Idea
Authors use the numbers of empty slots and collision slots to calculate the cardinality of a tag set in a very short time compared to the time needed for identification
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Contributions
Proposing two estimation algorithms (estimators) for a static set of RFID tagsIntroducing an Unified Simple Estimation Algorithm (USEA)Using a probabilistic framed-ALOHAmodel to estimate magnitude numbers of tags (UPEA)
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Outline
MotivationBackgroundRelated Work
Basic IdeaProposed AlgorithmConclusionDiscussion
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Basic Estimation Algorithms
Three types of slotsEmpty –n0
Singleton—n1
Collision—nc
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Estimators
Load FactorZero Estimator (ZE)ρ<1, many empty slots and few singleton and collision slots
Collision Estimator (CE)
ρ>1, many collision slots and singleton slots decrease
Singleton Estimator (SE) ρ=1
tfρ =
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Operating Range for the Estimators
Operating range is the upper bound of t for an estimatorRange of CE is greater than that of ZE
CE
ZE
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Simulation Results
With increasing frame size, the operation range for CE is bigger than for ZE
CE works well for greater range of load factors than ZE
CE
ZE
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Accuracy of the Estimators
ρ<1 ZE gets more accurate results than CECE performs better when ρ greater than a threshold
CE
ZE
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Comparison
CE compares with the Vogt methodFar superior and higher confidence
Vogt
CE
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Unified Simple Estimation Algorithm
USEA computes the estimate simply combined the two estimatorsAccording to the total number of slots for estimators, USEA chooses ZE or CE as the estimator for each repetition
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Simulation Results of USEA
Large number of slots needed for the desired accuracyThe estimation time is faster than the identification time within an accuracy
16s vs. 100s
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Unified Probabilistic Estimation Algorithm
UPEA introduces the probabilistic framed ALOHA protocolAn additional contention probability—p PZE and PCE estimator
Combined estimators using same approach of USEA
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Simulation Results of UPEA
The number of slots needed is nearlyindependent of the tag sizeThe estimation slots needed is significantly smaller than USEA
0.25s vs. 16s
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Outline
MotivationBackgroundRelated Work
Basic IdeaProposed AlgorithmConclusionDiscussion
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Conclusion
Presenting three estimation algorithms to estimate the number of a set of RFID tags at a given accuracy in a very short timeUSEA and UPEA have complementary propertiesUPEA is faster than any known algorithm for estimation of the huge number of tags in a desired accuracy
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Outline
MotivationBackgroundRelated Work
Basic IdeaProposed AlgorithmConclusionDiscussion
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Discussion
AdvantagesDifferent point of view in identification Good looking mathematicsExciting simulation results
PitfallsA theoretical work (simulation)The analysis of the estimation time is not very clear (different size of a frame)
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Thanks!
Q & A
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