Abstract—Wireless sensor networks have been attracting increasing research interest given the recent advances in microelectronics, array processing, and wireless networking. Consisting of a large collection of small, wireless, low-cost, integrated sensing, computing, and communicating nodes capable of performing various demanding collaborative space-time processing tasks, wireless sensor network technology poses various unique design challenges, particularly for real-time operation. In this paper, we review the Approximate Maximum-Likelihood (AML) method for source localization and direction-of-arrival (DOA) estimations. Then, we consider the use of least-squares (LS) method applied to DOA bearing crossings to perform source localization. A novel virtual array model applicable to the AML-DOA estimation method is proposed for reverberant scenarios. Details on the wireless acoustical testbed are given. We consider the use of Compaq iPAQ 3760s, which are handheld, battery-powered device normally meant to be used as personal organizers (PDAs), as sensor nodes. The iPAQ provide a reasonable balance of cost, availability, and functionality. It has a build-in StrongARM processor, microphone, codec for acoustic acquisition and processing, and a PCMCIA bus for external IEEE 802.11b wireless cards for radio communication. The iPAQs form a distributed sensor network to perform real-time acoustical beamforming. Computational times and associated real-time processing tasks are described. Field measured results for linear, triangular, and square subarrays in free-space and reverberant scenarios are presented. These results show the effective and robust operation of the proposed algorithms and their implementations on a real-time acoustical wireless testbed. Index Terms—Beamforming, source localization, distributed sensor network, wireless network, microphone array, time synchronization, reverberance.

In this paper, we explore the information dissemination problem in ad-hoc wireless networks. First, we analyze the probability of successful broadcast, assuming: the nodes are uniformly distributed, the available area has a lower bound relative to the total number of nodes, and there is zero knowledge of the overall topology of the network. By showing that the probability of successful broadcast within a bounded number of transmissions is small, we are motivated to extract good graph topologies to minimize the overall transmissions. Three algorithms are used to generate topologies of the network with guaranteed connectivity. These are the minimum radius graph, the relative neighborhood graph and the minimum spanning tree. Our simulation shows that the relative neighborhood graph has certain good graph properties, which makes it suitable for efficient information dissemination.

Sensor networks are becoming increasingly important as tools for monitoring remote environments. As sensors are typically batteryoperated, it is important to efficiently use the limited energy of the nodes to extend the lifetime of the sensor network. Two factors can greatly influence the performance of protocols for these networks– the data delivery model, which describes how the end user wants to access the data, and the network dynamics, which include sensor mobility as well as changes in sensor data rates throughout the lifetime of the network. In this paper, we look at several media access control protocols for sending data from sensors to a local data collector. Comparing these protocols shows that there is an inherent tradeoff in energy efficiency with adaptability of the protocol. 1.

Abstract—One of the most compelling technological advances of this decade has been the advent of deploying wireless networks of heterogeneous smart sensor nodes for complex information gathering tasks. A wireless distributed sensor network (DSN) is a self-organizing, ad-hoc network of a large number of cooperative intelligent sensor nodes. Due to the limited power of sensor nodes, energy-efficient DSN are essentially multi-hop networks. The self-organizing capabilities, and the cooperative operation of DSN allow for forming reliable clusters of sensors deployed near, or at, the sites of target phenomena. Reliable monitoring of a phenomenon (or event detection) depends on the collective data provided by the target cluster of sensors, and not on any individual node. The failure of one or more nodes may not cause the operational data sources to be disconnected from the data sinks (command nodes or end user stations). However, it may increase

In space exploration, cooperative modulation techniques have been proposed for prolonging the life-time of sensor nodes within a multihop network. The desire to efficiently reduce the overall energy-per-bit of a node motivated this study on the hop diameter (synonomous to the number of hops in a path) of sensor networks. In this study, we analysed and found that when the number of transmissions are bounded by constants 20, the likelihood of successful broadcast is small. Using simulations, we observed that the diameter decreases very fast as the transmission radius increases. Another observation is that the largest connected component emerges when the transmission radius reaches 0.3 # A, where A is the area containing the nodes. This may be used to determine the ideal amplification, although further simulations on larger networks could be helpful. We also found a large gap between the number of nodes required to populate the area, when all the nodes must be connected, or when only 90% of the nodes are connected.

A network is k-connected if it remains connected after the removal of any k − 1 of its nodes. Assume that n sensors, modeled here as (omni)directional antennas, are dropped randomly and independently with the uniform distribution on the interior of a unit length segment or a unit square. We derive sufficient conditions on the beam width of directional antennas so that the energy consumption required to maintain k-connectivity of the resulting network of sensors is lower when using directional than when using omnidirectional antennas. Our theoretical bounds are shown by experiment to be accurate under most circumstances. For the case of directional antennae, we provide simple algorithms for setting up a k-connected network requiring low energy. 1

Abstract — Sensor networks consist of a large number of sensor nodes performing distributed sensing and event detection. As sensor nodes are energy-constrained, energy-efficient routing is essential for increasing the lifetime of a sensor network. In [15] we proposed an ILP-based method for routing in sensor networks with multiple mobile base stations. The ILP-based method does not guarantee integral routes and bounds on running time. In this paper, we consider static base stations and propose an algorithmic approach to obtain integral energy-efficient routes. We propose to split the lifetime of a sensor network into equal periods of time referred to as rounds and model the energy constrained routing during a round as polynomial-time solvable flow problems. The flow information from an optimum solution to a flow problem is then used as a basis for an energy-efficient routing protocol. Through simulations, we demonstrate that our routing algorithm performs significantly better than the shortest path based algorithms and consumes less energy than the ILPbased method. In addition, we present an algorithm to determine, a priori, lower bound on the lifetime of the sensor network. Keywords: Wireless Sensor Networks, Routing. I.

In this paper, we consider the use of Compaq iPAQ 3760s, equipped with a built-in microphone and an external wireless card, for acoustic acquisition and processing to perform a distributed acoustical beamforming. Time synchronization among the microphones is achieved by the ReferenceBroadcast Synchronization method. Two beamforming algorithms, based on the time difference of arrivals (TDOAs) among the microphones followed by a least-squares estimation, and the maximum-likelihood (ML) parameter estimation method, are used to perform source detection, enhancement, localization, delay-steered beamforming, and direction-of-arrival estimation. Experimental beamforming results using the iPAQs and the wireless network are reported. 1.

This paper motivates, from historical, philosophical, and industrial points of view, the adoption of a novel scheme for developing complex measuring systems as perceptive agencies. The general concept of agency, a cooperative multiagent system defined within distributed artificial intelligence and robotics, is discussed together with its particular application to the field of intelligent instruments. An embryonic example of perceptive agency applied to the field of environmental monitoring is reported.

In sensor networks, where power and bandwidth are at a premium, there is a clear need to use compression to limit the amount of information exchanged by the sensors. In this paper we study the signal compression problem in situations where signals are being processed for the purpose of source localization. In these scenarios compression should be optimized for the accuracy of source localization, rather than to provide a reproduction of the signals with some desired fidelity. We show how this leads to novel design techniques that have clear advantages over standard quantizer design approaches.