Real Time Data Acquisition in Wireless Sensor Networks

Implementation of low cost sensor nodes in recent years allow sensor nodes to be applicable in many different areas e.g. environment monitoring, homeland security and disaster relief operations. One major contribution is their high demand on data acquisition. Real-time data acquisition is more challenging and promising issue in these application areas. There are many approaches and solutions proposed for real-time data acquisition in the literature. In this chapter, we focus on real-time data acquisition in wireless sensor networks. Wireless Sensor Networks (WSNs) consist of many tiny wireless sensors which operate in an environment in order to collect data for a specific mission. In most type of WSNs, once sensor nodes are deployed, thereafter no additional actions are employed. In a typical WSN, data is gathered from the environment by sensor nodes, aggregated in intermediate nodes and then transmitted to a base station. Because all these operations are executed by sensor nodes with limited power in a wireless media; reliable communication, power efficiency and network survivability issues are among critical concerns. WSNs are different from traditional networks because of their inherent characteristics. The specific properties of these networks pose various challenges such as energy consumption, limited bandwidth, and low storage. In the following sections we will introduce these constraints in detail. WSNs can be used in a wide range of application areas. Networks e.g. composed of video and audio sensors can be used to provide monitoring and surveillance systems or can be used to enhance the existing ones. Some critical areas for homeland security, such as borders, gulfs, strait entrances and port approach waters, are subject to enemy infiltration in crisis and in wartime. Using an instantly deployable network composed of sensor nodes in these operation areas would be a good solution to increase the probability of detecting a penetration in a cost effective and efficient way than the conventional ones. Some applications, e.g. military operations, introduce additional requirements on sensor and ad-hoc networks such as reliability and operating in real-time. Limited battery life of the nodes requires efficient energy consumption techniques which challenge real-time and reliability requirements. There are many routing approaches to provide either or both of the objectives of reducing the end-to-end delay and providing the reliability. However, most of these routing approaches challenge with other aspects such as energy-efficiency, long-lifetime and low-cost expect of the system. Energy aware protocols in the literature generally use multi-hop paths to use energy more efficiently. However, increase in number of hops between the source and the destination