1. Experimental comparison of RSSI-based localization algorithms for indoor wireless sensor networks*
Giovanni Zanca, Francesco Zorzi, Andrea Zanella and Michele Zorzi
Signet research Group
Department of Information Engineering, University of Padova, Italy
RealWSN08 Workshop
ACM Eurosys 2008
April 1st 2008
Glasgow - UK
*This work was partially supported by “Fondazione Cassa di Risparmio Padova e Rovigo” under the project ``A large scale wireless sensor network for pervasive city-wide ambient intelligence.”

2. RealWSN08 Workshop - Glasgow
Outline
Problem statement
Possible approaches
Wireless channel characterization
SOA review
Experimental setup
Results
Conclusions
RealWSN08 Workshop - Glasgow
April 1st 2008

3. RealWSN08 Workshop - Glasgow
Problem Statement
Position knowledge required by many WSN applications
Two main approaches
Nodes position hard written:
High deployment cost/time
Not always feasible
Very accurate
Motes capable of self-localizing:
Easy deployment
Need dedicated hardware to achieve high precision
RealWSN08 Workshop - Glasgow
April 1st 2008

4. Localization Approaches
Three main ranging approaches:
Angle of Arrival
Time of Arrival
Received Signal Strength Indicator (RSSI)
Focus on RSSI:
No specific Hardware required 
Poor outdoor ranging performance 
Very poor indoor ranging performance   
RealWSN08 Workshop - Glasgow
April 1st 2008

5. Indoor Radio Channel Characterization
Highly affected by log-normal shadowing
Moderate path loss
RealWSN08 Workshop - Glasgow
April 1st 2008

6. Channel Model Path loss channel model: received power Pi @ distance di
real transmitter-receiver distance
environmental constant
Shadowing
Received power
Transmitted power
Path loss coefficient
reference distance
fast fading
RealWSN08 Workshop - Glasgow
April 1st 2008

7. Localization Algorithms
RSSI samples
Anchor positions
Range free approach
Avoid ranging by direct comparison of RSSI samples
Independent of channel parameters
Imperfect localization even with ideal channel
Range based approach
Localization based on RSSI ranging
Depend on channel parameters
“Potential” perfect localization with ideal channel
Localization Algorithm
Mote position
RealWSN08 Workshop - Glasgow
April 1st 2008

8. Selected Localization Algorithms
Range based:
Min-Max
Extremely simple
Limited performance
Multilateration
Simple and scalable
Highly affected by noisy samples
Maximum Likelihood
Complex
Asymptotically optimum
Range free:
ROCRSSI
Computationally demanding
RealWSN08 Workshop - Glasgow
April 1st 2008

9. Mote Platform: EyesIFX V2
MSP430 MCU 4 MHz
10 KB RAM
48 KB ROM
USB interface
Infineon TDA5250 transceiver
900 MHz narrowband FSK
External omni-directional antenna
RealWSN08 Workshop - Glasgow
April 1st 2008

10. Experimental Testbeds
h=1.64
sy=6.82 dB
h=1.51
sy=6.34 dB
RealWSN08 Workshop - Glasgow
April 1st 2008

11. RealWSN08 Workshop - Glasgow
Results – Mean Error
Localization error remains quite high
ML benefits from increasing the number of beacons, unlikely Min-Max, ROCRSSI, Multilateration
Better performance in testbed 2 due to smaller distance to the closest beacon
RealWSN08 Workshop - Glasgow
April 1st 2008

12. RealWSN08 Workshop - Glasgow
Results – Error CDF
Min-Max performance does not improve by adding beacons
Localization error is confined within a rather narrow range around 4 meters
ML improves performance, though errors are distributed over a wide range
RealWSN08 Workshop - Glasgow
April 1st 2008

13. RealWSN08 Workshop - Glasgow
Conclusions
ML yields better performance than the others with more than 6-7 beacons
Multilateration is much simpler but shows very low performance
ROCRSSI also achieves low performance but it is independent of channel parameters
Min-Max is extremely simple but tends to localize nodes in the center of the area
RSSI ranging is very unreliable and does not appear suitable for indoor localization
RealWSN08 Workshop - Glasgow
April 1st 2008

14. Experimental comparison of RSSI-based localization algorithms for indoor wireless sensor networks*
Giovanni Zanca, Francesco Zorzi, Andrea Zanella and Michele Zorzi
Signet research Group
Department of Information Engineering, University of Padova, Italy
RealWSN08 Workshop
ACM Eurosys 2008
April 1st 2008
Glasgow - UK
*This work was partially supported by “Fondazione Cassa di Risparmio Padova e Rovigo” under the project ``A large scale wireless sensor network for pervasive city-wide ambient intelligence.”