Distributed Event Detection in Sensor Networks

1. Distributed Event Detection in Sensor Networks by Fernando Martincic, Loren Schwiebert March 25, 2008 Presented by Chinh Vu

2. Introduction • Sensors periodically send data to BS. • Sensors send data to BS when threshold is exceeded. (reactive method) • Sensors collaboratively detect object • How: appl. defines event signature and disseminates to network.

3. Problem • How nodes match their sensor readings against these event signatures.

4. SYSTEM MODEL • Nodes are assumed to be stationary and location-aware. • Node distribution is uniform and the network is 1-connected. • Communication links between nodes are assumed to be relatively stable.

5. Partition • Trade-off of the size of the cell

6. Cell-membership • Nodes know which cell they belong to. • Nodes know neighboring nodes which are within the same cell. • Periodically update cell membership • Each cell elects a leader node • Cell leadership is rotated between nodes

7. Sensing value • Each cell member publishes a timestamped cell value. • Leader calculates a weighted average (e.g., majority vote) of all cell members. • Disseminate to all members • Disseminate to adjacent cells

8. WSN Cell matrix • m × n matrix

9. Local cell sub-matrix • Sensors store pxq matrix of itself and its neighbor cells. • p≤n, q≤m

10. Matching signatures • An event signature is an r×s matrix (r≤p, s≤q) • To detect an event • Anode “overlays” an event signature over its cell sub-matrix • performs a cell by cell comparison.

11. Matching • Exact matching • Threshold: • a signature may represent minimal threshold values

12. Simulation • Using TinyOS • A lossless communication model was employed • Sensing value (payload) is 8-bit. • Message header is negligible • Area is clustered into 4×4-unit cells

13. Total traffic

14. Byte Transmission Distribution