EBAS: An Energy-Efficient Event Boundary Approximated Suppression Algorithm in Wireless Sensor Networks Longjiang Guo Heilongjiang University

Outline Introduction EBAS Algorithm Experiment And Result Analysis Conclusion

Introduction Event Boundary Approximated

Example Forest fire alarm system

Challenge Sink has to collect information from all the nodes that lie in field boundaries. Therefore:  A lot of the number of sending messages  Much more energy consuming  The higher the message packets collision rate

Resolving Based on the above challenge, we propose a novel energy-efficient algorithm (EBAS).  In EBAS, sink do not need all the information from the nodes in field boundaries.  EBAS supports a suppression scheme that conservers energy by reducing the number of sending message.

Outline Introduction EBAS Algorithm Experiment And Result Analysis Conclusion

EBAS algorithm EBAS is composed of three parts  Key node automatically selection in-network  Transportation  Event boundary rebuilt

Key node selection Definition 1 :[Slope] We define the slope of a sensor node i which lies in an event boundary as following: Given the coordination of sensor node i as (X i, Y i ) and the coordination of the neighbor j of sensor node i as (X j, Y j ), we calculate the slope of sensor node i with its neighbor j as following:

Key node selection Definition 2. [Verge Node] A node is called verge node if it has only one neighbor on an event boundary. Definition 3. [Key Node] A sensor node m is called Key node if and only if it satisfies one of the following 2 conditions: (1) Difference of slopes with its two neighbor nodes i and j outrages the predefined threshold, ε. i.e. (2) It is a verge node in an event boundary.

Slope: K 23, 24 =-2, K 23, 22 =0.5. Node 1 and node 27 is Verge Node. When ε=0.5, | K 23, 24 -K 23, 22 |>0.5,so node 23 is a Key Node

Key node selection Initialization Phase: Individual behavior :Each node lies in an event boundary broadcasts its node ID and coordination (ID, X, Y) to its neighbors.  If a node just gets one message. Definition 2  If a node just gets two messages. Definition 3  if a node receives more than 2 messages, for each received node id, calculate the distance between the two nodes using Euclidean distance, then sort these distances, pick out the 2 nodes with least distances. Then apply Definition 3.

EBAS algorithm EBAS is composed of three parts  Key node automatically selection in-network  Transportation  Event boundary rebuilt

Transportation Building aggregation tree Transportation key node information Suppression Strategy

Building aggregation tree There are two types of message package in building aggregation tree: one is Tree-building package:  (PackageType=1, NodeID, level)  (PackageType=2, ParentNode, NodeID). Initialization sink node broadcasts the Tree-building package (1, sink’s NodeID, 0) and set the local level with 0. Individual Behavior Each node in senor networks maintains three variables: parent, child and level which are initialized with null, null, and. parent, child and level indicate the parent, children and level of sensor node in aggregation tree respectively.

Example

Transportation key node information Given a set of key nodes M i ={d i1, d i2, d i3, …} located on sensor node i. Sensor node i will send M i to his parent node. Suppose j is a parent node in aggregation tree. i 1, i 2 …i k are j’s children. When sensor node j receives M i1, M i2 …M ik, sensor node j will unite M i1, M i2 …M ik as following operation: (1) M j  M i1  M i2  …  M ik.. (2) Sensor node j sends M j to his parent.

Suppression Strategy Given a set of key nodes M= {d i1, d i2, d i3 …}, the FM sketch of M, denoted S (M), is a bitmap of length k. The entries of S (M), denoted S (M) [0… k-1], are initialized to zero and are set to one using a random binary hash function h applied to the elements of M. Formally,

EBAS algorithm EBAS is composed of three parts  Key node automatically selection in-network  Transportation  Event boundary rebuilt

Event Boundary Rebuilt Transportation over,Since we know exactly all key node ID, we can put event boundary rebuilt easy.

Outline Introduction EBAS Algorithm Experiment And Result Analysis Conclusion

Experiment and result analysis We have completed EBAS implementation in the TinyOS2.x TOSSIM simulator. The accuracy error is defined as follows: This Figure shows that the accuracy of EBAS mainly depends on the predefined threshold, ε. The smaller the predefined threshold is, the smaller the accuracy error of the recovered event boundaries is.

Message quantity with slope threshold varying

Outline Introduction EBAS Algorithm Experiment And Result Analysis Conclusion

In this paper, we present a novel energy-efficient algorithm EBAS to solve event boundaries transportation problems. The entire idea can be divided into 4 parts:  Key node generation;  Key nodes set suppression;  Transportation;  Decompression. Our experiment results confirmed the correctness and effectiveness of our algorithm.

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