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Adaptive Fuzzy Controlled Sliding Backoff Scheme

for Optimal Fair Access Wireless Networks

Authors: M. R. M. Rizk et al

Present by: Chien-Chia Chen2008. Nov.05

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Agenda

BEB Recap BEB Fairness Issues Related Work: MACAW Fuzzy Controlled Sliding Backoff Load Estimation Fuzzy membership functions Simulation Results

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BEB Recap

Binary Exponential Backoff When collision occurs, one picks up a random numb

er T from [1, ], and retransmit after T time slots How to determine

After each collision After each success

BEB

0B

0B

0_ 0_new inc oldB F B 0_ 0_new dec oldB F B

0_ 0_ maxmin 2 ,inc old oldF B B B 0_ 0_ mindec oldF B B

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BEB Fairness Issues

BEB tends to favor the node that last succeeds

Losers are likely to lose again and again

data

wait

B0 = 5

B0 = 12

B0 = 2

B0 = 7

data

wait

……Node 1

Node 2

B0 = 7

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MACAW

Use MILD (Multiplicative Increase Linear Decrease) instead of BEB

Extend header to carry Every node shares the same

(copy whatever values it heard)

0B

0B

0_ 0_ maxmin 1.5 ,inc old oldF B B B

0_ 0_ minmax 1,dec old oldF B B B

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off

Use the load estimation as an input to adjust contention window dynamically

Increasing when collision occurs:

Decreasing when tx succeeds:

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Load Estimation Pempty_slot = Pr[no access in T] Model the system as a Poisson process

where λ=PATL*g PATL=probability to be permitted to access (assume as 1) g=avg. number of users who want to access per second

(All the above explanations are from Random-Access Control Mechanisms Using Adaptive Traffic Load in ALOHA and CSMA Strategies for EDGE by Mario E. Rivero-Angeles et al. on IEEE Trans on Vehicular Tech., Vol. 54, No. 3, May 2005.)

_

#

#empty slot

Total of Empty SlotsP

Total of Slots

0( )Pr[ ] Pr(0, )

0!

TTT e

noaccess inT T e

_ _

1ln( )ATLP gTT

empty slot empty slotP e e g PT

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Fuzzy Membership Functions

g

FSFIncreasement

BSFIncreasement

Small 20% 80%

Medium 40% 60%

High 60% 40%

Very Hign 80% 20%

For example, if g=0.75

Small=0.5Medium=0.5High=0Very High=0

FSF=20%*0.5+40%*0.5=30%

BSF=80%*0.5+60%*0.5=70%

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Simulation Results On MATLAB Using slotted system (for the convenience to calcula

te Pempty_slot) Don’t know what kind of random access scheme the

y use Every node in the system always has a packet to tra

nsmit Each run contains a fixed number of nodes All nodes are in the same collision domain Bmax=1024 (255 in 802.11b) Bmin=2, 4, 8, 16 (7 in 802.11b)

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Bmax Unlimited (1/3)

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Bmax Unlimited (2/3)

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Bmax Unlimited (3/3)

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Bmax=1024 (1/4)

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Bmax=1024 (2/4)

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Bmax=1024 (3/4)

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Bmax=1024 (4/4)

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THANK YOU