Sensors_**2011**, _11_, 10048-10062; doi:10.3390/s1111110048  
OPEN ACCESS  
_Sensors_  
**ISSN 1424-8220**  
www.mdpi.com/journal/sensors  
_Article_  
**A Grid-Based Distributed Event Detection Scheme for Wireless Sensor Networks**  
**[PERSON] and [PERSON] \({}^{\star}\)**  
Department of Computer Engineering, Hongik University, Seoul 121-791, Korea;  
E-Mail: [EMAIL_ADDRESS]  
\({}^{\star}\) Author to whom correspondence should be addressed; E-Mail: [EMAIL_ADDRESS];  
Tel. : +82-2-320-1688. _Received: 18 August 2011; in revised form: 11 October 2011 / Accepted: 19 October 2011 / Published: 25 October 2011_  
**Abstract:** This paper presents a grid-based distributed event detection scheme for wireless sensor networks. The network is divided into square-shaped grids of predefined grid size, where sensor nodes in each grid form a cluster with a cluster head. Event detection at each grid alone based on the readings of its member nodes is limited in event detection performance, especially for a small event region compared to the grid size. To improve the performance, each grid is further divided into 2 \(\times\) 2 sub-grids of equal size. The decision on an event is made by finding a square region of 2 \(\times\) 2 sub-grids, not necessarily in the same grid, that passed a predefined threshold. This process is conducted at each cluster head in a distributed manner by inter-cluster communications. Event detection is initiated when a cluster head receives an alarm from its member nodes. The cluster-head communicates with its neighboring cluster heads to exchange the number of nodes reporting an alarm. The threshold for event detection can be dynamically adjusted to reflect the number of sensor nodes in a grid and event size, if known. High event detection accuracy is achieved with a relatively low threshold without sacrificing false alarm rate by filtering most errors due to transient faults and isolating nodes with permanent faults. Experimental results show that the proposed scheme can achieve high detection accuracy, while maintaining low false alarm rate. **Keywords:** grid-based sensor networks; fault detection; event detection Introduction  
Wireless sensor networks, composed of a large number of small sensor nodes with sensing, computing, and wireless communication capabilities, often operate in an unattended mode to monitor various environments and detect events of interest [1]. Due to large-scale deployment of inexpensive sensor nodes, it is common for sensor nodes to exhibit faulty behavior. Hence it is important for a fault-prone sensor network to detect events in the face of fault-induced errors. Several fault-tolerant event detection schemes have been proposed in [2, 3, 4]. [PERSON] and [PERSON] presented Bayesian algorithms to detect events in the presence of faulty sensor nodes [2]. They exploited the notion that measurement errors due to faults are likely to be uncorrelated, while measurements in a target region are spatially correlated. A fault-tolerant energy-efficient event detection scheme was proposed in [3]. For a given detection error bound, the number of neighboring nodes is determined to minimize the communication cost. [PERSON] _et al_. [4] proposed a localized event boundary detection algorithm. Random bisection and trisection methods are employed to detect event boundary nodes. In [5] a secure event boundary detection scheme was presented to correctly identify event boundaries in adversarial environments. More recently, event detection using decision tree classifiers running on individual sensor nodes and applying a voting scheme to reach consensus among detections made by various sensor nodes has been proposed for disaster management [6]. Meanwhile, energy efficient data aggregation and routing in grid-based sensor networks have been investigated in [7, 8, 9]. In [7], a grid-based directed diffusion is presented. The network is divided into virtual grids and only one node in a grid-cluster participates in communication to reduce energy consumption.