Composite Event Detection in Wireless Sensor Networks

Transcription

1 Composite Event Detection in Wireless Sensor Networks Chinh T. Vu, Raheem A. Beyah and Yingshu Li Georgia State University

2 Outline Why? Motivation What? Preliminaries How? Scheme Conclusion 2

3 Motivation 3

4 Event detection 4

5 User interest Applications: Emergency alarming systems Tasks: Event detection = Event occurrence decision + Warning delivery Users may not be interested in the sensors or the raw data from the sensors, but more interested in the events. To guarantee accuracy and reliability for emergency alarming applications, a conclusion indicating the happening of an event should not be decided only based on one property of the event. 5

6 Existing methods Data collection: all the sensors periodically send their data to an information processing center, a conclusion is then made to decide whether a pre-defined event has happened based on the reported data. Data aggregation: data is processed at some nodes innetwork before being forwarded. Realtime requirement not considered. Further analyzing received data delays the alarm to be timely announced. Large amount of exchanged data causes large energy consumption. 6

7 Considered issues Composite events Timely warning delivery Routing and topology control Energy efficiency Fault tolerance 7

8 Preliminaries 8

9 Composite / Atomic events Generally: E =F(σ 1,.., σ r ) E is a composite event. σ l (l=1..r) are atomic events. F is a Boolean algebra involving AND, OR, NOT. Fire = F(temperature, smoke, humidity) = (temperature > 100 o C) AND (smoke >100mg/L) AND (humidity < 20%) 9

10 Assumptions More than one sensing components of different types on each sensor Numbers and types of sensing components may be different among sensors. All of a sensor s sensing components turn on or off simultaneously. Event definitions are diffused to all the sensors in deployment phase. 10

11 TEKWED problem Detection set: A subset of sensors which jointly accomplish the event detection and alarming task. k-watched event: An event that can be detected by at least k sensors in a detection set. TEKWED (Timely Energy-efficient k-watching Event Detection): Partition sensors into a number of detection sets and decide their activation durations such that The event is continuously k-watched. Network lifetime is maximized. Warning delivery time is minimized. 11

12 Scheme 12

13 Event Occurrence Decision fire=(temp=1)and(smk=1)and(hmd=1)= Temp>100 o C Smk>100mg/L Hmd<20% 13

14 Detection Set Construction Parameters: Counter c l : for each atomic event σ l, initially, c l = k. Sensing component q l : on each sensor, q l can detect event σ l and counted by counter c l. If c l >0 c l is a correlated counter. q l is a useful component. For a sensor, at a point of time: Contributi on = Residual lifetime Number of helpful components Total number of components 14

15 Constructing One Detection Set Choose a sensor gw close to BS as gateway node. Build a BFS tree rooted at gw. Traverse through the tree layer by layer. For each layer : Sort nodes in increasing order of contribution, color a node RED if its contribution is 0. Greedily add a node having biggest contribution to detection set and color it BLACK if its parent is BLACK, color it GREEN otherwise. Update all correlated counters of that sensor. Stop when all the counters become 0. Add RED nodes to detection set to connect GREEN nodes with their parents. 15

16 Constructing One Detection Set (cont.) 1 1 [3] k=3 Build BFS tree [3] 2 3 [1,3] [1,2,3] [1] [1,3] [1] 7 8 [2] [1] [1,3] [2] [1] The original network 2 3 [1,3] [1,2,3] [1] [1,3] [1] 7 8 [2] [1] [1,3] [2] [1] The BFS tree : Network and BFS tree link 16 : Network but not BFS tree link

17 Constructing One Detection Set (cont.) 1 [3] 2 3 [1,3] [1,2,3] [1] [1,3] [1] 7 8 [2] [1] k=3 Discover detection set Counter: C 1 = C 2 = C3 C 3 = [1,3] [2] [1] 17

18 Constructing One Detection Set (cont.) k=3 Connectivity 1 [3] 1 [3] 2 3 [1,3] [1,2,3] 2 3 [1,3] [1,2,3] [1] [1,3] [1] 7 8 [2] [1] [1] [1,3] [1] 7 8 [2] [1] [1,3] [2] [1] [1,3] [2] [1] The final detection set 18

19 Working Schedule for All Detection Sets Detection Set 1 Detection Set 2 Detection Set 3 19

20 Q&A THANK YOU 20

21 Simulation Monitored area: 100 m x100 m. Communication range: 15 m. Maximum number of sensing components on a sensor: 4. Initial energy: 20 J 30 J. Conduct simulations for different number of sensors and different values of k. 21

22 Simulation (cont.) 22

23 Simulation (cont.) 23

24 Simulation (cont.) 24