1. 1 Localization in Wireless Sensor Networks: Strategies to reduce energy consumption Sadaf Tanvir Benoît Ponsard {sadaf.tanvir, benoit.ponsard}@imag.fr EMSoC 23-24 October 2008 Drakkar Group

2. 2 Introduction 23-24 October 2008EMSoC

3. 3 23-24 October 2008EMSoC 17-10-07 Sadaf Tanvir-INP 20073 WSNs  Numerous  Tiny & cheap nodes  Spatially distributed  Autonomous  Communicate wirelessly  Power constrained

4. 4 Need for Localization in WSNs 23-24 October 2008EMSoC Coordinate System -Relative -Absolute Environment/ Forest monitoring Inventory monitoring Machine surveillance

5. 5 Our focus: localization with trilateration 23-24 October 2008EMSoC -Coarse Grained Localization -Fine Grained Localization

6. 6 Implementations 23-24 October 2008EMSoC

7. 7 23-24 October 2008EMSoC Basic Lateration t 1 et t 4 measured by node UN t 2 et t 3 measured by node AN t 3 -t 2 : response time Ranging process carried out at the physical layer Ref : L. de Nardis, M. Gabriella Di Benedetto (Univ. Rome), 2005 AN t t2t2 t3t3 UN t1t1 t4t4 X y d

8. 8 23-24 October 2008EMSoC Intuitive way to implement Tri-lateration 23-24 October 2008 Hello msg : sent by UNs (1 st step of two-way ranging) Reply msg : sent by ANs (2 nd step of two-way ranging) AN 1 t AN 2 AN 3 UN EMSoC y x t O

9. 9 23-24 October 2008EMSoC Propagation of localization wave d3d3 d2d2 d1d1 AN1 AN2 AN3 d1d1 d2d2 d3d3 d1d1 d2d2 d3d3 d1d1 d2d2 d3d3

10. 10 23-24 October 2008EMSoC So, when does it work? -Protocol simulated in OPNET -LxL network with “AN nucleus” in the centre -Random uniform distribution of UNs -Unit disk graph model -Need to have node degree above “threshold”

11. 11 23-24 October 2008EMSoC Consumption of energy Intuitive process – easy to implement Network wide useless emission of “Hello” messages Radio communication –most energy consuming operation Communication to be limited The “Beacon” based process

12. 12 23-24 October 2008EMSoC Beacon : sent by ANs to inform their presence Query : sent by UNs (1 st step of two- way ranging) Response : sent by ANs (2 nd step of two-way ranging) LN transmits beacon msgs AN 1 t AN 2 AN 3 UN Tri-lateration with Beacon mode Implementation y x t O

13. 13 23-24 October 2008EMSoC Propagation of localization wave d3d3 d2d2 d1d1 AN1 AN2 AN3 d1d1 d2d2 d3d3 d1d1 d2d2 d3d3 d1d1 d2d2 d3d3

14. 14 Simulation Results 23-24 October 2008EMSoC

15. 15 Energy Consumption: Radio communication 23-24 October 2008EMSoC Tx msg: msg tx by a node to get localized Rx ul msg: useful msg rcvd by node to get localized Rx disc msg: msg rcvd by a node but are useless for it

16. 16 On going work: Optimized protocol 23-24 October 2008EMSoC

17. 17 Idea of an optimized protocol 23-24 October 2008EMSoC Shortcomings of the two previously proposed approaches: 1.No limit on the emission of messages 2.Starting messages incur significant protocol overhead 3.Inefficient usage of wireless medium

18. 18 Let the sink node start the process 23-24 October 2008EMSoC Sink AN UN

19. 19 UNs overhear other UN’s QM to start their own QM emission 23-24 October 2008EMSoC -A UN hears a Query Message from its neighboring UN -it starts an internal counter to wait for a certain time during which the neighboring UN is sure to become LN -upon expiration of this timer, it broadcasts it Query Message Limit the emission of messages by LNs/UNs through counters

20. 20 Initial Results 23-24 October 2008EMSoC

21. 21 Future work 23-24 October 2008EMSoC -Consider packet loss -Use of additional Anchor nodes  limit error propagation -Comparison with existing localization approaches: energy consumption vs. the achieved localization accuracy

22. 22 23-24 October 2008EMSoC