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Exploiting Constructive Interference for Scalable Flooding in Wireless Networks

InfoCom 2012Yin Wang, Yuan He, Xufei Mao, Yunhao Liu, Zhiyu Huang, Xiangyang Li

NSLab study group 2013/1/21Presented by: Yu-Ting

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Outline

• Theoretical Analysis• Scalability Problem• Lower Bound of PRR• SCIF

Modulation & Demodulation• Symbol (4bits) period: 16us (4bit/250kbps)• Chip period Ts: 16(us/symbol) ÷ 32(chip/symbol) = 0.5us

bits(MSB)…0101…(LSB)

bit → symbol

symbol…5…

symbol→PN series

O-QPSK Mod.

PN series (LSB)…00110101001000101110110110011100…(MSB)

modulating wave

noise

O-QPSK Demod.

PN series→symbol(find the highest correlation)

PN series (with 1 bit error) (LSB)…10110101001000101110110110011100…(MSB)

symbol…5…

(correctly Demod.)

symbol → bit

bits(MSB)…0101…(LSB)

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Modulation of QPSK & O-QPSK(from Wiki)

• QPSK

• O-QPSK

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Threshold ofMaximum Temporal Displacement ∆

• Tc = 0.5us

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Theoretical Analysis

Interference Gain Factor (IGF)

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Simulation of Theoretical Analysis

• Amplitudes: [1 , 1 , 0.5 , 1.5 ]• Phase offsets: [0 , 0.25 , 0.5 , 0.75]

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Outline

• Theoretical Analysis• Scalability Problem• Lower Bound of PRR• SCIF

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Scalability Problem

• To be simple, there's time uncertainty τe during transmission in each hop

• For a path of h hops, the PMF of accumulated τe is:

• For m independent paths, each of which consists h hops originated at the sink node:∆ = max( τh

e) − min(τhe)

• ∆ increases as m & h increase• PRR decreases as ∆ increases

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• m = 5

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Outline

• Theoretical Analysis• Scalability Problem• Lower Bound of PRR• SCIF

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Lower Bound of PRR

• Assume in grid networks• Γh

m(∆ ≤ t): CDF of ∆ of a common ancestor node propagates a packet

• CDF of ∆ ≤ 0.5µs between nodeN8 and N9:

N5 → {N8,N9}N2 → {N4,N5} → {N8,N9}N0 → {N1,N2} → {N4,N5} → {N8,N9}

• (Skip proof)For 32 bytes packet length,Γh

m(∆ ≤ 0.5) between parent and childs >= 95.4%

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Outline

• Theoretical Analysis• Scalability Problem• Lower Bound of PRR• SCIF

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SCIF

• Spine Constructive Interference based Flooding

• Key:– Decrease the # of m– Length of a grid cell=0.5

of communication range=> guarantee connection

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Simulation Result

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Comments

• Decent mathematical analysis• Good introduction to related work• No implementation• With capture effect (strong capture), Glossy is

actually not so vulnerable• With noise, SCIF is probably not so good

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Q&A

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BACKUP SLIDES

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Scalability Problem

• Time uncertainty τe during transmission in each hop

• In Glossy: τe = τsw + τd + τtx + τp

τsw: software delayτd: radio processingτtx: clock uncertainty due to clock frequency driftsτp: propagation delay