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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
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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Simulation of Theoretical Analysis
• Amplitudes: [1 , 1 , 0.5 , 1.5 ]• Phase offsets: [0 , 0.25 , 0.5 , 0.75]
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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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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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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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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