Efficient On-Demand Image Transmission in Visual Sensor Networks
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Research Article Efficient On-Demand Image Transmission in Visual Sensor Networks Kit-Yee Chow, King-Shan Lui, and Edmund Y. Lam Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong Received 30 November 2005; Revised 13 September 2006; Accepted 14 September 2006 Recommended by Chun-Shien Lu In a tracking system, an object of interest is monitored continuously in a sensor network. Information about the object is kept in the sensors and sensors transmit the information upon request. In this paper, we consider the scenario where all sensors around a targeted object capture images of it and these pictures will be sent to a mobile agent upon request. Due to the size and energy limitations in sensors, images kept in sensors are often small and highly compressed. We describe a framework to facilitate a mobile agent in the sensor network to request images of the object of interest. As sensors are limited in energy, it is desirable to reduce the energy used in transmitting the images. We observe that, in a sensor network that is sufficiently dense, images from neighbor cameras would likely overlap, and therefore intermediate sensors can process and combine overlapping portions so as to reduce the energy spent on image transmission. We develop a protocol for involved sensors to determine how to transmit the images they have kept to the mobile agent in an energy efficient manner. Our protocol is truly distributed and does not require any global information. We evaluate our protocol through extensive simulations. Copyright © 2007 Hindawi Publishing Corporation. All rights reserved.
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INTRODUCTION
A wireless sensor network consists of thousands of sensors that span a large geographical region. Research and development in wireless sensor networks are becoming increasingly widespread due to their low cost and low maintenance in deployment [1]. These sensors are able to communicate with each other to collaboratively detect objects, collect information, and transmit messages. Sensor networks have become an important technology especially for environmental monitoring, target tracking, military applications, disaster management, and so forth [2, 3]. A sensor is a very small device and the battery inside is not likely to be rechargeable. This limitation in energy puts extra constraints in the operations of a sensor. In order to prolong its lifetime, a sensor should carefully utilize its energy. Message transmission has been shown to be the major source of energy dissipation. To save energy used in transmission, the size of the messages and the number of messages to be transmitted should be minimized. In this paper, we study how images can be processed and transmitted efficiently in terms of energy in a visual sensor network. We consider a tracking system where objects of interest are traced. All sensors are equipped with cameras and they
can take images of a target while it moves inside the sensor network. The images captured are kept in the local memory of the sensors. As sensors a
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