**2. Preliminaries**

Wireless sensor networks are composed of small, inexpensive devices that are designed to sense some phenomena, perform light computations and communicate with one another. These devices are usually scattered over some area. This technology has seen a wide range of applications ranging from military use to personal security. In the following, we discuss the history of WSNs and some of their most pertinent applications.

Wireless sensor networks evolved form the Smartdust project, which was developed and funded by DARPA in the late 1990s. The Smartdust project was designed to show that "a complete sensor/communication system can be integrated into a cubic millimeter package" (Pister, 2001). The Smartdust motes were engineered to be power efficient. This and other similar projects have led to the explosion of research in the area of wireless Ad Hoc and sensor networks, which was and still is heavily supported by US government agencies including the National Science Foundation. While working on the Smartdust project, the researchers recognized the variety of applications for their work both in the military field and elsewhere.

Some of the applications for the Smartdust projects are virtual keyboard, inventory control, product quality monitoring and smart office spaces among others (Pister, 2001). In the virtual keyboard application, dust motes would be glued into fingernails to sense the orientation and motion of the fingertips and communicate with a computer. This could be used in sign language translations, piano play, etc... In the inventory and quality control applications, a system of communication could be implemented and deployed in all aspects of the production process in order to monitor the location of the product and control and monitor its quality (from temperature, to humidity exposure etc...). In the smart office spaces application, the person's preferred temperature, humidity settings could be directly communicated to the environment they walk into. Some of the military applications that the Smartdust project was developed for include battlefield surveillance, transportation monitoring and missile monitoring.

In the past few year, Wireless Sensor Networks made the transition from the Berkeley research centers to the production arena with the creation of companies, such as Crossbow Technologies (Crossbow Technologies, n.d.) that started manufacturing them. The appeal of Wireless Sensor Networks stems from the fact that you can deploy them and just leave. We discuss in the remainder of this section the main classes of applications for the general WSNs.

WSN applications can be categorized into habitat and environmental monitoring, heath applications, commercial applications, military applications among others.

One of the most prevalent uses of WSNs is in habitat and environmental monitoring. It has been shown that direct human contact with some plant or animal colonies can result in disastrous consequences. For example, (Mainwaring et al., 2002) describe the use of a sensor network to monitor Seabird colonies because of their sensitivity to human disturbance. In fact, a 15 minute visit to the colony could result in up to 20% rate of mortality among eggs. Not only are WSNs useful in monitoring colonies without causing any disturbances but they also represent a more economic method of monitoring for long periods of time.

Another example of the environmental use of WSNs is in forecasting systems. WSNs are now scattered around large areas to forecast pollution, flooding and seismic activity. The Automated Local Evaluation in Real Time (ALERT) was developed in the 70s by the National Weather Service. It has been used by several government and state agencies and international 2 Will-be-set-by-IN-TECH

Wireless sensor networks are composed of small, inexpensive devices that are designed to sense some phenomena, perform light computations and communicate with one another. These devices are usually scattered over some area. This technology has seen a wide range of applications ranging from military use to personal security. In the following, we discuss the

Wireless sensor networks evolved form the Smartdust project, which was developed and funded by DARPA in the late 1990s. The Smartdust project was designed to show that "a complete sensor/communication system can be integrated into a cubic millimeter package" (Pister, 2001). The Smartdust motes were engineered to be power efficient. This and other similar projects have led to the explosion of research in the area of wireless Ad Hoc and sensor networks, which was and still is heavily supported by US government agencies including the National Science Foundation. While working on the Smartdust project, the researchers recognized the variety of applications for their work both in the military field and elsewhere. Some of the applications for the Smartdust projects are virtual keyboard, inventory control, product quality monitoring and smart office spaces among others (Pister, 2001). In the virtual keyboard application, dust motes would be glued into fingernails to sense the orientation and motion of the fingertips and communicate with a computer. This could be used in sign language translations, piano play, etc... In the inventory and quality control applications, a system of communication could be implemented and deployed in all aspects of the production process in order to monitor the location of the product and control and monitor its quality (from temperature, to humidity exposure etc...). In the smart office spaces application, the person's preferred temperature, humidity settings could be directly communicated to the environment they walk into. Some of the military applications that the Smartdust project was developed for include battlefield surveillance, transportation monitoring and missile

In the past few year, Wireless Sensor Networks made the transition from the Berkeley research centers to the production arena with the creation of companies, such as Crossbow Technologies (Crossbow Technologies, n.d.) that started manufacturing them. The appeal of Wireless Sensor Networks stems from the fact that you can deploy them and just leave. We discuss in the remainder of this section the main classes of applications for the general WSNs. WSN applications can be categorized into habitat and environmental monitoring, heath

One of the most prevalent uses of WSNs is in habitat and environmental monitoring. It has been shown that direct human contact with some plant or animal colonies can result in disastrous consequences. For example, (Mainwaring et al., 2002) describe the use of a sensor network to monitor Seabird colonies because of their sensitivity to human disturbance. In fact, a 15 minute visit to the colony could result in up to 20% rate of mortality among eggs. Not only are WSNs useful in monitoring colonies without causing any disturbances but they

Another example of the environmental use of WSNs is in forecasting systems. WSNs are now scattered around large areas to forecast pollution, flooding and seismic activity. The Automated Local Evaluation in Real Time (ALERT) was developed in the 70s by the National Weather Service. It has been used by several government and state agencies and international

applications, commercial applications, military applications among others.

also represent a more economic method of monitoring for long periods of time.

history of WSNs and some of their most pertinent applications.

**2. Preliminaries**

monitoring.

organizations to provide a real time data collection system that can forecast floods (ALERT, n.d.).

Another use for WSNs is in intelligent building management. In fact, they have been used in HVAC, lighting, climate control, fire protection, energy monitoring and security applications among others. In Canada for example, the National Research Council launched a three-year project to develop wireless sensor networks to do just that. The project started in 2008 and is anticipated to continue through 2011.

A very important application of WSNs is in the healthcare field. WSNs can be used to provide continuous, remote, inexpensive, instantaneous and non-invasive monitoring of a patient's vital signs. This technology can be used to allow the elderly to remain in their own residences but still be able to continuously check their vitals.

All these WSN applications consist of deploying the network for an extended period of time on a single battery charge. It is therefore imperative that the motes be power efficient and that the lifetime of the network as a whole be as long as possible.
