topology management -- power efficient spatial query
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Topology ManagementTopology Management----Power Efficient Spatial QueryPower Efficient Spatial Query
Presented byPresented by Weihang jiangWeihang jiang
Today’s planToday’s plan
Introduction: 10-15 minsIntroduction: 10-15 mins Details : Details :
• heuristic algorithm 15 minsheuristic algorithm 15 mins• GreedyGreedy
Centralized 10minsCentralized 10mins Decentralized 5minsDecentralized 5mins
Questions Questions
Problem definitionProblem definition
Select a Select a smallsmall number of sensors number of sensors that are sufficient to answer the that are sufficient to answer the query accurately. Also these selected query accurately. Also these selected sensors should form a sensors should form a connectedconnected communication path, so that they communication path, so that they form a logical routing topologyform a logical routing topology
Context of researchContext of researchSensor 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
Sensor databaseSensor 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 acti
vity• 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 in
volved (usually geographical conditions).
Back
Art Gallery Problem
DEMO:DEMO: http://valis.cs.uiuc.edu/~sariel/http://valis.cs.uiuc.edu/~sariel/
research/CG/applets/art_gallery/research/CG/applets/art_gallery/artgal.htmlartgal.html
http://www.cs.mcgill.ca/~thierry/http://www.cs.mcgill.ca/~thierry/507applet/triangulize.html507applet/triangulize.html
Back
Art Gallery Problem
Broadcast -- MDCS
The idea is to suppress redundant The idea is to suppress redundant broadcast by using only a small broadcast by using only a small number of nodes to broadcast, but number of nodes to broadcast, but ensuring that ensuring that all the nodesall the nodes in the in the network receive the broadcast network receive the broadcast messagemessage
Coverage: all the areaCoverage: all the area
Back
Back
Power efficient organization
Power Efficient Organization of Wireless Sensor NetworksSasa Slijepcevic, Miodrag Potkonjak
Choose nodes rather than deploy nChoose nodes rather than deploy nodesodes
Divide sensors into mutually exclusiDivide sensors into mutually exclusive sets, each of those sets completeve sets, each of those sets completely covers query arealy covers query area•Power savingPower saving
Divide to as many groups as possibleDivide to as many groups as possible
AlgorithmAlgorithm Definition of fieldDefinition of field
• A set of points. Two points belong to A set of points. Two points belong to the same field iff they are covered by the same field iff they are covered by the same set of sensors the same set of sensors
Critical ElementCritical Element• A field covered by the minimal number of sensors A 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 setsFind 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 cri2) Then use objective function to choose one sensor which covers this cri
tical elementtical 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 Else
• Goto 1)Goto 1)
objective functionobjective 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
The heuristicThe heuristic
Power efficient organization(cont)
DrawbacksDrawbacks•CentralizedCentralized•Communication costCommunication cost
Back
Connected sensor Cover
Back
Compared with breath first flooding D+2qm VS 2qn (n>>m)
Important definitionsImportant definitions
Subelement; Valid SubelementSubelement; Valid Subelement• = Field ; a field in query area= Field ; a field in query area
Candidate Sensor; Candidate pathCandidate Sensor; Candidate path• A sensor contains a Subelement which has not beeA sensor contains a Subelement which has not bee
n chosenn chosen• A path connects a candidate sensor with previously A path connects a candidate sensor with previously
chosen sensorschosen sensors Uncovered Valid Subelement; Benefit of a CanUncovered Valid Subelement; Benefit of a Can
didate pathdidate path• Benefit = # of uncovered Valid Subelement / # of seBenefit = # of uncovered Valid Subelement / # of se
nsor on the path but not chosennsor on the path but not chosen
Greedy algorithm (centralized)Greedy algorithm (centralized)
Start with chosen sensor set M (the origiStart with chosen sensor set M (the original sensor)nal sensor)
Find out SC (set of candidate sensors)Find out SC (set of candidate sensors) Basing on Benefit of a Candidate path, cBasing on Benefit of a Candidate path, c
hoose one candidate sensor, add it and thoose one candidate sensor, add it and the path into Mhe path into M
Goto beginningGoto beginning
DecentralizedDecentralized
Instead send Candidate Path Search to tInstead send Candidate Path Search to the SC (set of candidate sensors, which is he SC (set of candidate sensors, which is hard to find out locally), send CPS to the hard to find out locally), send CPS to the Candidate sensors around newest addeCandidate sensors around newest added sensord sensor
Seems no much impact on # of selected Seems no much impact on # of selected sesorssesors
END!!!END!!!
Question???Question???
MotivationMotivation
Sensor DatabaseSensor Database
Limited Battery PowerLimited Battery Power
OverviewOverview
MotivationMotivation
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