By Fernando Martincic, Loren Schwiebert. Sensors periodically send data to BS. Sensors send data to BS when threshold is exceeded. (reactive method)

Distributed Event Detection in Sensor Networks

March 25, 2008

Presented by Chinh Vu

by Fernando Martincic, Loren Schwiebert

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.

Problem

How nodes match their sensor readings against these event signatures.

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.

Partition

Trade-off of the size of the cell

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

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

WSN Cell matrix

m × n matrix

Local cell sub-matrix Sensors store pxq matrix of

itself and its neighbor cells. p≤n, q≤m

Matching signatures An event signature is an r×s matrix (r≤p, s≤q) To detect an event

A node “overlays” an event signature over its cell sub-matrix

performs a cell by cell comparison.

Matching

Exact matching Threshold:

a signature may represent minimal threshold values

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

Total traffic

Byte Transmission Distribution