by Fernando Martincic, Loren Schwiebert

 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.

 How nodes match their sensor readings against these event signatures.

 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.

 Trade-off of the size of the cell

 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

 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

 m × n matrix

 Sensors store pxq matrix of itself and its neighbor cells.  p≤n, q≤m

 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.

 Exact matching  Threshold:  a signature may represent minimal threshold values

 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