RFID Reader Networks: Channel allocation algorithms, performance evaluation and simulator
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Transcript of RFID Reader Networks: Channel allocation algorithms, performance evaluation and simulator
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RFID Reader Networks: Channel allocation algorithms, performance evaluation and simulator
John Sum, National Chung Hsing University
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John Sum, Kevin Ho RFID Reader Networks 2
OUTLINE
RFID Reader Network Reader Collision Problem Algorithms
Non Progressive Progressive Hybrid
Simulation Results Conclusions Simulator design
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I. RFID Reader Network
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I. RFID Reader Network
Reader Host Computer 802.11bgn
Reader Tags ETSI EN 302 208 (European regulation)
15 sub-bands (channels) in the ISM band, 10 channels are available and 5 guard bands
Readers access the medium by Carrier Sense Multiple Access (CSMA) mechanism (Listen Before Talk). If the sub-band is free, the readers start to transmit into. Then, the sub-band is used for up to 4 s, after which it must be free for at least 100 ms.
EPC global Class-1 Gen-2 UHF Protocol 50 different sub-bands. Readers randomly alternate (every 0.4 s) between bands,
following the Frequency Hopping Spread Spectrum (FHSS) Readers do not listen to the channel before accessing to it. The reader
transmissions are restricted to operate in even-numbered sub-bands and tag backscatter in odd-numbered sub-bands.
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I. RFID Reader Network
Readers are powered by batteries, with much powerful computational and memory capacities.
Tags (passive) are powered by the radio signal transmitted by the readers. Memory is small. Backscattered signal is weak.
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John Sum, Kevin Ho RFID Reader Networks 6
I. RFID Reader Network
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I. RFID Reader Network
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I. RFID Reader Network
Tag collision problem Single reader multiple tags Multiple tags receive signal from the same reader.
The backscattered signals interfere. As a result, reader could not read from anyone of them.
This problem can be alleviated by TDMA like methods.
One tag responses at a time, by something like tag address.
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I. RFID Reader Network
Reader collision problem Multiple readers single (or multiple) tags Neighbor readers send the same frequency signal
to the air. At the same time, these two signals interfere each other. Tags are unable to backscatter signal.
This problem can be alleviated by TDMA (CSMA) or FDMA (frequency hopping) like methods.
Time slot allocation and channel allocation
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I. RFID Reader Network
EPC Class 1 Gen 2 UHF Air Interface Protocol (2004)
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II. READER COLLISION PROBLEM Operation Environment
Any two readers will have collision if their distance apart d(i,j) is within a range r and they are collecting data in the same time slot.
Readers are not able to select their frequency bands. The readers are deployed uniformly random within an area
of 100m × 100m, and are not moveable. Each reader can only assigned with one channel τ (for i = 1,
2, · · · ,N ) in each cycle of interrogation. No mobile reader is allowed within the area of deployment.
rjidif
rjidifije),(1
.),(0
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II. READER COLLISION PROBLEM Operation Mechanism
Channel allocation is done by the control computer. Once the solution has obtained, the control computer will send
message informing the readers the channels being assigned. The readers will thus record their channels being assigned and
wait for the synchronization signal from the control computer. Once the syn. signal has been received, each reader will then
operate at the dedicated channel to read the tags’ data. Communication between the control computer and the readers
are implemented by wireless LAN.
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II. READER COLLISION PROBLEM The collision matrix: For i, j = 1, 2, • • • , N an
d i≠j,
The number of collision pairs (CP) in a reader network can be defined as follows:
}{}1{1
.0jiij andeif
otherwiseijc
.2
1
1 1
N
i
N
jijcCP
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III. ALGORITHMS (Non Progressive) The maximum number of channels available
is predefined.
Non progressive algorithms Heuristics Simulated Annealing (CT, KIRK, GG) Distributed Color Selection
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III. ALGORITHMS (Non Progressive) Heuristics
S1 Generate random numbers in {1, 2, • • • , T} for τ1, τ2, • • • , τN as their initial random channels allocation.
S2 Random select a reader, say i. S3 If reader’s channel assignment has no collision to its nei
ghbor readers, then goto S2. S4 If reader’s channel assignment has collision to its neigh
bors, select a new {1, 2, • • • , T} such that the number of collision pairs between the reader and its neighbors is the minimum.
S5 Repeat steps S2 to S4 until no more improvement can be made.
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III. ALGORITHMS (Non Progressive) Simulated Annealing
S1 Generate random numbers in {1, 2, · · · , T} for τ1, τ2, · · · , τN as their initial random channels allocation. k = 0.
S2 Random select a reader, say i. Then, k = k + 1. S3 If reader’s channel assignment has no collision to its neig
hbor readers, then goto S2. S4 If reader’s channel assignment has collision to its neighb
ors, random generate a new {1, 2, · · · , T}. S5 If the number of collision pairs between the reader and it
s neighbors reduces.
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III. ALGORITHMS (Non Progressive) Simulated Annealing
S6 If the number of collision pairs between the reader and its neighbors increases by ∆, generate a random number u from a uniform distribution in [0, 1]. Then,
S7 Repeat steps S2 to S6 for k ≤ MaxRun.
)),(/exp(*
)).(/exp(
kuifi
i
kuifi
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III. ALGORITHMS (Non Progressive) a) Constant Temperature: For all k ≥ 0 and a << 1 is a small c
onstant,
b) Geman-Geman Rule: For all k ≥ 0 and b is a constant,
c) Kirkpatrick et al Rule: For all k ≥ 0 and 0 < α < 1. i.e.
λ(k) = αλ(k − 1).
.)( ak
.)1log(
)(
k
bk
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III. ALGORITHMS (Progressive) The maximum number of channels required f
or allocation is determined automatically by the algorithms.
Progressive algorithms Progressive Heuristics Progressive SA (CT, KIRK, GG) Colorwave
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III. ALGORITHMS (Progressive)
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IV. SIMULATION RESULTS
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IV. SIMULATION RESULTS
250 readers in random locations within an area of 100m×100m.
Readers at the end of an edge are neighbors. The number of edges in the experimental net
work is 3830. In average, each reader has 15.32 neighbors. The constants a, d, c, and α in the simulated
annealing algorithms are 0.01, 1, 2 and 0.99 respectively.
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IV. SIMULATION RESULTS (NP) Comparison
Average number of collision pairs Convergence properties Channel distributions (Entropies) Fault tolerance
Labels RAND: Initial Random Allocation HEU: Heuristic Algorithm CT: Constant Temperature SA GG: Geman-Geman Rule KP: Kirkpatrick et al Rule.
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IV. SIMULATION RESULTS (NP)
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IV. SIMULATION RESULTS (NP)
Convergence – Collision Pairs VS Number of Steps
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IV. SIMULATION RESULTS (NP)
Algo. –Σt Pt log(Pt)
Random 2.7721
Heuristic 2.5249
SA CT 2.7605
SA GE 2.7633
SA KP 2.7622
Slots Distributions
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IV. SIMULATION RESULTS (P)
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IV. SIMULATION RESULTS (P)
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IV. SIMULATION RESULTS (Hybrid)
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IV. SIMULATION RESULTS(Fault tolerance) Experimental setup
20 random reader networks are generated Channel allocation for each of these reader networks is don
e by the 5 algorithms (heuristics, SA-CT, SA-GG, SA-KP, and Colorwave) separately.
For heuristics, SA-CT, SA-GG, SA-KP algorithms, the number of available channels is fixed to 16.
For Colorwave, the initial channel number is set to 16. Once the channel allocations have been finished, all reader
s are set randomly to fault with fault rate 0.05. This step is repeated 20 times.
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IV. SIMULATION RESULTS
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IV. SIMULATION RESULTS
Colorwave algorithm
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V. CONCLUSIONS
Towards a framework for the RFID developer to investigate the performance of an RFID system
Simulate the environment in which the RFID readers are not perfect.
Algorithms for solving RCP are introduced, including
HEUR, SA-CT, SA-KIRK, SA-GEM, DCS P-HEUR, PSA-CT, PSA-KIRK, PSA-GEM, CW HYBRID
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V. CONCLUSIONS
Computational Speed (for NP type): HEUR > DCS > SA
Channel Distribution (for NP type): SA > DCS > HEUR
DCS is unable to solve the problem
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V. CONCLUSIONS
Channel Distribution (Progressive) PSA > P.HEUR > CW
Fault tolerance Similar behaviors
Overall (Comp. Speed + Distribution) HYBRID > Progressive > Non-Progressive
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V. CONCLUSIONS
Even slot distributions Demand on high bandwidth communication between readers and control computer can be reduced.
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VI. Simulator System Design
管理系統與 RFID網路架構
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VI. Simulator System Design
管理系統程式設計
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VI. Simulator System Design
模擬器程式設計
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VI. Simulator System Design
MATLAB M-file, MATLAB FIG-file。 User is able to set the following parameters for si
mulation Number of Readers Transmission Range Number of Channel Number of Steps Reader Fault Rate Channel Allocation Algorithm
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VI. Simulator System Design
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VI. Simulator System Design
即時監控故障讀取器•250個讀取器隨機部署在 100m×100m內•讀取器故障率為 0.05 •通道配置之方法為啟發式演算法•紅色的方框代表讀取器為故障
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VII What’s Next
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VII What’s Next
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VII What’s Next
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VII What’s Next
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VII What’s Next
Hai Liu, Miodrag Bolic, Amiya Nayak and Ivan Stojmenovi, Integration of RFID and wireless sensor networks, Encyclopedia on Ad Hoc and Ubiquitous Computing, Dharma P. Agrawal, Bin Xie (eds.), World Scientific Press, Singapore, 2009.
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VII What’s Next
Cyber-digital Ecosystem: Systems merge. Telecom networks
Connecting people Each person is identified by a mobile phone number (or multiple phon
e numbers) Facebook
Connecting people Each person is identified by an account name (or multiple account na
mes) Internet
Connecting networks Each network is uniquely identified by a domain ID
Computer network Connecting computing machines Each machine is uniquely identified by a unique local IP address
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VII What’s Next
Cyber-digital Ecosystem: Systems merge. Sensor networks
Connecting sensors for environmental information Each information is uniquely identified by a unique sensor ID
RFID systems Connecting physical stuffs Each stuff is uniquely identified by a tag ID
Vehicle networks Connecting Moving compartments Each compartment is a LAN which is identified by an ID
Personal area networks Connecting body sensors, wireless headset Each device is uniquely identified by a unique ID
Finally ……
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VII What’s Next
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