1. Topology Management -- Power Efficient Spatial Query Presented by Weihang jiang

2. Today’s plan Introduction: 10-15 mins Introduction: 10-15 mins Details : Details : heuristic algorithm 15 minsheuristic algorithm 15 mins GreedyGreedy Centralized 10mins Centralized 10mins Decentralized 5mins Decentralized 5mins Questions Questions

3. Problem definition Select a small number of sensors that are sufficient to answer the query accurately. Also these selected sensors should form a connected communication path, so that they form a logical routing topology Select a small number of sensors that are sufficient to answer the query accurately. Also these selected sensors should form a connected communication path, so that they form a logical routing topology

4. Context of research Sensor Database [4] Query operation Power efficient organization[25] Decentralized, cost of communication Connected sensor Cover Broadcast MDCS [14] [9,18,26,1, 17] Nodes cover VS area cover Art Gallery Problem [20,10] Optimal placement VS Optimal selections Geometric set cover problems [16,17,5] Notion of connectivity

5. Sensor database P. Bonnet, J. Gehrke, and P. Seshadri. Towards sensor database systems. In Proc. of Intl. Conf. on Mobile Data Management, 2001. Example Factory Warehouse Sensor Database stored data: the set of sensors and environment sensor data: produced by signal processing functions. Query Monitoring queries are long running. The desired result of a query is typically a series of notifications of system activity Queries need to correlate data produced simultaneously by different sensors. Queries need to aggregate sensor data over time windows. Most queries contain some condition restricting the set of sensors that are involved (usually geographical conditions). Back

6. Art Gallery Problem DEMO: DEMO: http://valis.cs.uiuc.edu/~sariel/resea rch/CG/applets/art_gallery/artgal.ht ml http://valis.cs.uiuc.edu/~sariel/resea rch/CG/applets/art_gallery/artgal.ht ml http://valis.cs.uiuc.edu/~sariel/resea rch/CG/applets/art_gallery/artgal.ht ml http://valis.cs.uiuc.edu/~sariel/resea rch/CG/applets/art_gallery/artgal.ht ml http://www.cs.mcgill.ca/~thierry/50 7applet/triangulize.html http://www.cs.mcgill.ca/~thierry/50 7applet/triangulize.html Back

7. Art Gallery Problem

8. Broadcast -- MDCS The idea is to suppress redundant broadcast by using only a small number of nodes to broadcast, but ensuring that all the nodes in the network receive the broadcast message The idea is to suppress redundant broadcast by using only a small number of nodes to broadcast, but ensuring that all the nodes in the network receive the broadcast message Coverage: all the area Coverage: all the area Back

10. Power efficient organization Power Efficient Organization of Wireless Sensor NetworksSasa Slijepcevic, Miodrag Potkonjak Choose nodes rather than deploy nodes Choose nodes rather than deploy nodes Divide sensors into mutually exclusive sets, each of those sets completely covers query area Divide sensors into mutually exclusive sets, each of those sets completely covers query area Power savingPower saving Divide to as many groups as possible Divide to as many groups as possible

11. Algorithm Definition of field Definition of field A set of points. Two points belong toA set of points. Two points belong to the same field iff they are covered by the same set of sensors Critical Element Critical Element A field covered by the minimal number of sensorsA field covered by the minimal number of sensors 2,3,6,8 are critical elements2,3,6,8 are critical elements Find as many as possible exclusive covering sets Find as many as possible exclusive covering sets 1) Start with a critical element1) Start with a critical element 2) Then use objective function to choose one sensor which covers this critical element2) Then use objective function to choose one sensor which covers this critical element 3) If now all the chosen sensor cover the query area3) If now all the chosen sensor cover the query area we got one exclusive covering set Goto 1)we got one exclusive covering set Goto 1)Else Goto 1)Goto 1)

12. objective function (1) favor sets that cover a high number of uncovered elements (less sensors) (2) favor sets that cover more sparsely covered elements (3) favor sets that do not cover the area redundantly (more exclusive sets) (4) favor sets that redundantly cover the elements that do not belong to sparsely covered areas

13. The heuristic

14. Power efficient organization(cont) Drawbacks Drawbacks CentralizedCentralized Communication costCommunication cost Back

15. Connected sensor Cover Back Compared with breath first flooding D+2qm VS 2qn (n>>m)

16. Important definitions Subelement; Valid Subelement Subelement; Valid Subelement = Field ; a field in query area= Field ; a field in query area Candidate Sensor; Candidate path Candidate Sensor; Candidate path A sensor contains a Subelement which has not been chosenA sensor contains a Subelement which has not been chosen A path connects a candidate sensor with previously chosen sensorsA path connects a candidate sensor with previously chosen sensors Uncovered Valid Subelement; Benefit of a Candidate path Uncovered Valid Subelement; Benefit of a Candidate path Benefit = # of uncovered Valid Subelement / # of sensor on the path but not chosenBenefit = # of uncovered Valid Subelement / # of sensor on the path but not chosen

17. Greedy algorithm (centralized) Start with chosen sensor set M (the original sensor) Start with chosen sensor set M (the original sensor) Find out SC (set of candidate sensors) Find out SC (set of candidate sensors) Basing on Benefit of a Candidate path, choose one candidate sensor, add it and the path into M Basing on Benefit of a Candidate path, choose one candidate sensor, add it and the path into M Goto beginning Goto beginning

19. Decentralized Instead send Candidate Path Search to the SC (set of candidate sensors, which is hard to find out locally), send CPS to the Candidate sensors around newest added sensor Instead send Candidate Path Search to the SC (set of candidate sensors, which is hard to find out locally), send CPS to the Candidate sensors around newest added sensor Seems no much impact on # of selected sesors Seems no much impact on # of selected sesors

20. END!!! Question???

21. Motivation Sensor Database Sensor Database Limited Battery Power Limited Battery Power

22. Overview Motivation Motivation