localization algorithms for wireless sensor networks m.srbinovska, c.gavrovski ss.cyril and...
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Localization algorithms for wireless sensor networks
M.Srbinovska, C.GavrovskiSs.Cyril and Methodius University,
SkopjeFaculty of Electrical Engineering and IT-
Skopje, R. Macedonia
NIS, 2010 210/04/23
OUTLINE
Introduction Propagation models Measurement uncertainty for position
estimation Experimental results Conclusion
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Introduction
Wireless sensor networks monitor large areas, monitoring the environment, air, water
and soil. GPS (global positioning system) does not
work indoors. Define the coordinates during the
instalation.
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Wireless channel model
Three propagation models are used: Free space propagation model
Two – Ray ground model
Log-distance model
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Received Signal Strength Indicator (RSSI)
RSSI – power of the signal at the receiver Direct path
n- path loss exponent
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Received Signal Strength Indicator (RSSI)
The RSSI can be used to characterize the channel status.
Friis’ free space transmission equation is:
10RSSI 10 n(log d) A RSSI dBm
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Multilateration
2n
21n
2n
21n
2n
21n
2n
21
2n
21
2n
21
1nn1nn
1n1n
yyxxd~
d~
yyxxd~
d~
y
x
yyxx
yyxx
2
iii dd~
Minimizing the mean square error:
BAxAA TT
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Measured vs. calculated RSSI with different n
-110
-100
-90
-80
-70
-60
-50
-40
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
RSS
I (d
Bm
)
distance (m)
RSSI as a function of distance
n=1 n=2 n=2.25 n=3 n=4 measured
Measured vs. calculated RSSI with different n
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Root mean square error between theoretical and measured RSSI with different n
0
2
4
6
8
10
12
14
1 2 2.15 2.25 2.375 2.5 2.625 2.75 2.875 3 4
dB
m
n
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Received Signal Strength Indicator
Sensor node
• It works at the 2.4 GHz ISM Band.
• Each board features :
• Silicon laboratories C8051F121 microcontroller
• Chipcon CC2420 2.4 GHz 802.15.4 transceiver.
Position of sensor nodes
X3
X1X2
A4
A5A6
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Measurement uncertainty for position estimation
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2n
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1
n
ss)x(u
)x,....,x,....,x,x(fy ni21
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Experimental results
Distance uncertainties of the sensor nodes
0
0.2
0.4
0.6
0.8
1
1.2
15.9 16.4 18.7 19 23.6 24.2 28.7 29.5
Loca
lizati
on e
rror
(m)
Distance (m)
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Conclusion
The relationship between RSSI and distance was determined through practical experiments.
Distance uncertainties of the sensor nodes through experimental measurements
were presented.
Wireless sensor networks are widely applicable to many practical
applications including environmental monitoring, military applicationsetc. in which sensors may need
to know their geographical locations
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Thank You for your attention!