Transcript RSSI Based Tracking Algorithms for Wireless Sensor
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 Group http://dgt.dei.unipd.it Special Interest Group on NEtworking & Telecommunications Department of Information Engineering, University of Padova, Italy
Outline
motivation experimental setup wireless channel characterization multi-channel analysis communication protocol conclusion
Motivation
RSSI: Received Signal Strength Indicator
Supported by most commercial RF transceivers Largely used to assess channel quality and/or used in many localization algos for ranging High variability
Goals:
Experimental characterization of RSSI Reducing RSSI variability by multi-channel samples harvesting
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) 5 MHz 3 MHz f m = 2405 + 5(m-11) Mhz m = 11, …, 26 2405 MHz 2480 MHz
Experimental setup
indoor & outdoor • N fixed nodes • 1 mobile node for each position for each couple of nodes for each channel 10 RSSI samples collected over time
Outline
motivation experimental setup wireless channel characterization multi-channel analysis communication protocol conclusion
P rx
rx power (in [dBm])
P tx
Classical path loss model with Gaussian shadowing
path loss coefficient actual distance slow fading (shadowing)
K
10 log 10
d
/
d
0 fast fading (
t
) tx power (in [dBm]) free space + shadowing constant (free space atten., antenna gain,…) reference distance
K
2 20 log 10 ( / 4
d
0 )
N
( 0 , 2 ) Least Mean Square criterion to estimate K and η
Parameter estimation
K dB η σ Ψ dB
Ch 11
-21.7 -21.6 -21.7 -22 2.03
4.8
Ch 12
2.03
4.4
Ch 13
2 4.5
Ch 14
1.98
4.4
···
··· ··· ···
Ch 23
-22.1 -22 2.01
4.1
Ch 24
1.96
4.3
Ch 25
-22 2 4.4
Ch 26
-21.9
1.98
4.2
For each couple of nodes and channel →10 RSSI samples collected over time
Ψ: fitting the normal pdf
indoor → σ Ψ = 4.6 dB outdoor → σ Ψ = 3.5 dB
Rx signal statistic
z
(
t
)
|
r
(
t
) |
Weibull distributed [1]
P rx
P tx
K
20log
10
(
z
(
t
))
20log
10
(
d P tx
K
/
d
0
) 20log
10
(
d
/
d
0
)
Extreme Value distributed EV(θ location , θ scale ) [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)
Ψ: fitting the Extreme Value pdf
Indoor (Kullback-Leibler divergence) KL(emp,norm) = 0,0824 KL(emp,ev) = 0,0169 Outdoor (Kullback-Leibler divergence) KL(emp,norm) = 0,1371 KL(emp,ev) = 0,0146 Extreme Value distribution fits better the empirical data than the Normal distribution
Outline
motivation experimental setup wireless channel characterization multi-channel analysis communication protocol conclusion
Narrowband fading
T ds
B
1
u
(
t
n
)
u
(
t
) T ds B → → delay spread tx signal bandwidth u(t) → baseband signal τ n → delay associated with the n-th component
r
(
t
)
u
(
t
) τ 1 τ 2
e j
τ 3 2
f m t
n N
0
a n e
j
n
,
m
t
Example: two rays
n
,
m
(
t
) 2
f m
n
phase associated with n-th component d TX @ 2405[MHz] (m=11) TX @ 2455[MHz] (m=21) d 1 ' if δ 1 then and = ( d 1 ' + d 1 '' ) – d = 3[m] τ 1 = δ Δϕ = |ϕ 1 /v p 1,11 = 10[ns] – ϕ 1,21 | = π d 1 ''
# ch
1 4 8 16
Multichannel
Averaging RSSI samples over frequencies
σ Ψ dB
4.6
3.15
3.05
3
Outline
motivation experimental setup wireless channel characterization multi-channel analysis communication protocol conclusion
Communication protocol
I’m in CH1! (Next CH2) Anybody in CH1? (Next CH2) I’m in CH1! (Next CH2) Everybody’s switching on CH2. Let’s follow them!
Inquirer
scheduled channels: default, NC(1), ..., NC(end) next channel = NC(1) start REQ T.O.
TX REQUEST next channel = NC(i) start REQ T.O.
TX REQUEST no REQ T.O.
elapsed no RX REPLY yes i>end yes no reply restart REQ T.O.
channel = next channel i = i+1 yes no END RX REPLY REQ T.O.
elapsed
Replier
IDLE channel = default IDLE channel = next channel no RX REPLY yes no RX REQUEST yes TX REPLY
Conclusion
RSSI characterization parametric and statistical statistic model validation RSSI variability mitigation RSSI averaged over time RSSI averaged over frequency Communication protocol Indoor & Outdoor 802.15.4 RSSI and LQI measurements http://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