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Andrea Bardella, Nicola Bui, Andrea Zanella and Michele Zorzi {bardella,bui,zanella,zorzi}@dei.unipd.it Signet Research Group http://dgt.dei.unipd.it Department of Information Engineering, University of Padova, Italy. SIGNET. Special Interest Group on NEtworking & Telecommunications. - PowerPoint PPT Presentation
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An Experimental Study on IEEE 802.15.4 Multichannel Transmission
to Improve RSSI-Based Service Performance
Andrea Bardella, Nicola Bui, Andrea Zanella and Michele Zorzi{bardella,bui,zanella,zorzi}@dei.unipd.it
Signet Research Grouphttp://dgt.dei.unipd.it
Department of Information Engineering, University of Padova, Italy
Special Interest Group on
NEtworking & Telecommunications
Outline
motivation experimental setup wireless channel characterization multi-channel analysis communication protocol conclusion
Motivation
Goals: Experimental characterization of RSSI Reducing RSSI variability by multi-channel samples harvesting
RSSI: Received Signal Strength IndicatorSupported by most commercial RF transceiversLargely used to assess channel quality and/or used in many localization algos for rangingHigh variability
Outline
motivation experimental setup wireless channel characterization multi-channel analysis communication protocol conclusion
Tmote Sky platform
CC2420 transceiver 250 kbps @ 2.4 Ghz external isotropic antenna (5 dBi)
2405 MHz
2480 MHz
5 MHz 3 MHz
fm = 2405 + 5(m-11) Mhzm = 11, …, 26
Experimental setup
indoor & outdoor
• N fixed nodes• 1 mobile node
for each positionfor each couple of nodesfor each channel
10 RSSI samplescollected over time
Outline
motivation experimental setup wireless channel characterization multi-channel analysis communication protocol conclusion
Classical path loss model with Gaussian shadowing
)(/log10 010 tddKPP txrx
rx power (in [dBm])
tx power (in [dBm]) reference
distance
actual distance slow fading
(shadowing)
constant (free space atten., antenna gain,…)
path loss coefficient
free space +
shadowing ),0(
2)4/(log20
2
010
N
dK
fast fading
Least Mean Square criterion to estimate K and η
Parameter estimationCh 11 Ch 12 Ch 13 Ch 14 ··· Ch 23 Ch 24 Ch 25 Ch 26
K dB -21.7 -21.6 -21.7 -22 ··· -22.1 -22 -22 -21.9η 2.03 2.03 2 1.98 ··· 2.01 1.96 2 1.98σΨ dB 4.8 4.4 4.5 4.4 ··· 4.1 4.3 4.4 4.2For each couple of nodes and channel →10 RSSI samples collected over time
Ψ: fitting the normal pdf
indoor → σΨ = 4.6 dB outdoor → σΨ = 3.5 dB
Rx signal statistic
Extreme Value distributedEV(θlocation, θscale)
Weibull distributed [1]
[1] Sagias, N.C., Karagiannidis, G.K.: “Gaussian Class Multivariate Weibull Distribution: Theory and Applications in Fading Channels”, IEEE Trans. on Information Theory (Oct 2005)
z(t)| r(t) | Prx Ptx K 20log10(d /d0)20log10(z(t)) Ptx K 20log10(d /d0)
Ψ: fitting the Extreme Value pdf
Extreme Value distribution fits better the empirical data than the Normal distribution
Indoor (Kullback-Leibler divergence)
KL(emp,norm) = 0,0824KL(emp,ev) = 0,0169
Outdoor (Kullback-Leibler divergence)
KL(emp,norm) = 0,1371KL(emp,ev) = 0,0146
Outline
motivation experimental setup wireless channel characterization multi-channel analysis communication protocol conclusion
Narrowband fading
tam
plitu
deτ1
τ2 τ3
N
n
jn
tfj mnm eaetutr0
2 ,)()(
Tds → delay spread B → tx signal bandwidth u(t) → baseband signal τn → delay associated with the n-th component
1 BTds )()( tutu n
Example: two rays
d
d1' d1''
if δ1 = (d1' +d1'') – d = 3[m] then τ1 = δ1/vp = 10[ns]and Δϕ = |ϕ1,11 – ϕ1,21| = π
TX @ 2405[MHz] (m=11)TX @ 2455[MHz] (m=21)
nmmn ft 2)(, phase associated with n-th component
Multichannel
Averaging RSSI samples over frequencies
# ch σΨ dB1 4.6
4 3.15
8 3.05
16 3
Outline
motivation experimental setup wireless channel characterization multi-channel analysis communication protocol conclusion
Communication protocol
Anybody in CH1? (Next CH2)
I’m in CH1! (Next CH2)
I’m in CH1! (Next CH2)
Everybody’s switching on CH2. Let’s follow
them!
Inquirer
next channel = NC(1)start REQ T.O.TX REQUEST
RX REPLY
no reply restart REQ T.O.
next channel = NC(i)start REQ T.O.TX REQUEST
channel = next channeli = i+1
scheduled channels: default, NC(1), ..., NC(end)
i>endno yes
yes
yes
REQ T.O.elapsed
noRX REPLYEND
no
REQ T.O.elapsed
Replier
IDLEchannel = default
TX REPLY
IDLEchannel = next channel
yes
noRX REQUESTRX REPLY
yes
no
Conclusion RSSI characterization parametric and statistical statistic model validation RSSI variability mitigation RSSI averaged over time RSSI averaged over frequency Communication protocol
simulationtools
Indoor & Outdoor 802.15.4 RSSI and LQI measurementshttp://telecom.dei.unipd.it/pages/read/59/
Questions?
THANK YOU FOR YOUR ATTENTION!An Experimental Study on IEEE 802.15.4
Multichannel Transmission to Improve RSSI-Based Service Performance
Andrea Bardella, Nicola Bui, Andrea Zanella and Michele Zorzi
{bardella,bui,zanella,zorzi}@dei.unipd.it