(Georgia Institute of Technology, 2006)
Ould-Ahmed-Vall, ElMoustapha; Riley, George F.; Ferri, Bonnie H.
Distributed event detection using wireless sensor networks has received growing interest in recent years. In such applications, a large number of inexpensive and unreliable sensor nodes are distributed in a geographical region to make firm and accurate local decisions about the presence or absence of specific events based on their sensor readings. However, sensor readings can be unreliable, due to either noise in the sensor readings or hardware failures in the devices, and may cause nodes to make erroneous local decisions. We present a general fault-tolerant event detection scheme that allows nodes to detect erroneous local decisions based on the local decisions reported by their neighbors. This detection scheme does not assume homogeneity of sensor nodes and can handle cases where nodes have different accuracy levels. We prove analytically that the derived fault-tolerant estimator is optimal under the maximum a posteriori (MAP) criterion. An equivalent weighted voting scheme is also derived. Further, we describe two new error models that take into account the neighbor distance and the geographical distributions of the two decision quorums. These models are particularly suitable for detection applications where the event under consideration is highly localized. Our fault-tolerant estimator is simulated using a network of 1024 nodes deployed randomly in a square region and assigned random probability of failures.
(Georgia Institute of Technology, 2005)
Ould-Ahmed-Vall, ElMoustapha; Blough, Douglas M.; Ferri, Bonnie H.; Riley, George F.
A sensor network consists of a set of battery-powered nodes, which collaborate to perform sensing tasks in a given environment. It may contain one or more base stations to collect sensed data and possibly relay it to a central processing and storage system. These networks are characterized by scarcity of resources, in particular the available energy.
We present a distributed algorithm to solve the unique ID assignment problem. The proposed solution starts by assigning long unique IDs and organizing nodes in a tree structure. This tree structure is used to compute the size of the network. Then, unique IDs are assigned using the minimum number of bytes. Globally unique IDs are useful in providing many network functions, e.g. configuration, monitoring of individual nodes, and various security mechanisms.
Theoretical and simulation analysis of the proposed solution have been preformed. The results demonstrate that a high percentage of nodes (more than 99%) are assigned globally unique IDs at the termination of the algorithm when the algorithm parameters are set properly. Furthermore, the algorithm terminates in a relatively short time that scales well with the network size. For example, the algorithm terminates in about 5 minutes for a network of 1,000 nodes.