rfid reader networks: channel allocation algorithms, performance evaluation and simulator john sum,...

RFID Reader Networks: Channel allocation algorithms, performance evaluation and simulator

John Sum, National Chung Hsing University

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


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.



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.



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.



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



EPC Class 1 Gen 2 UHF Air Interface Protocol (2004)


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


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.


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


III. ALGORITHMS (Non Progressive) The maximum number of channels available

is predefined.

Non progressive algorithms Heuristics Simulated Annealing (CT, KIRK, GG) Distributed Color Selection


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.


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.


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


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


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


III. ALGORITHMS (Progressive)


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.


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.


IV. SIMULATION RESULTS (NP)



Convergence – Collision Pairs VS Number of Steps



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


IV. SIMULATION RESULTS (P)


IV. SIMULATION RESULTS (Hybrid)


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.



Colorwave algorithm


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


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


V. CONCLUSIONS

Channel Distribution (Progressive) PSA > P.HEUR > CW

Fault tolerance Similar behaviors

Overall (Comp. Speed + Distribution) HYBRID > Progressive > Non-Progressive


V. CONCLUSIONS

Even slot distributions Demand on high bandwidth communication between readers and control computer can be reduced.


VI. Simulator System Design

管理系統與 RFID網路架構



管理系統程式設計



模擬器程式設計



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



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


VII What’s Next


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.


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


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 ……


VII What’s Next

rfid reader networks: channel allocation algorithms, performance evaluation and simulator john sum,...

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