WSNs are used in many different areas of applications, e.g. area monitoring, envi- ronmental monitoring, industrial monitoring, etc. Different WSNs applications are presented further:
1. Military applications – one of the primary uses for WSNs in this area would be remote sensing. A survey of WSN military applications is made in [7]. An example of a battle field can be considered where the enemy intrusion needs to be monitored Figure 1.3 . For this a first step will be to deploy wireless sensor nodes across the monitored area using different techniques (by air using airplanes or by land using specially built robots) [8], [9]. These sensors will form a WSN that will cover the entire battlefield and that can monitor different parameters like heat, pressure, sound, light, electromagnetic field, vibrations, etc.. The U.S. Army’s Disposable Sensor Program is an initiative by the U.S. Army to deploy nodes with seismic, acoustic, RF, magnetic, chemical, biological, and infrared sensors [10]. Through these sensor nodes, the army will obtain a complete picture of almost any environment. These sensors would have to be disposable and inexpensive. Urban warfare is another application in which WSN can be used. Nodes could be deployed in a urban environment with the purpose to detect enemy intrusion, movement or chemical attacks [11]. The collected information from the WSN area can be sent to a static base or
1.2 WSN applications
mobile military unit which moves on the WSN periphery. This information can be vital in saving lives or to reduce material loses so it needs to reach the destination fast.
Figure 1.3: WSN military application scenario
[12]
2. Building monitoring - it is expected that in the near future each building will be monitored through the use of a WSN as a standard functionality. The sensors will monitor heat and smoke which allows detection, localization and tracking of fires. The information gathered from the building can help occupants by guiding them to the nearest exit and also fireman’s to decide which will be the best approach to avoid a disaster [13]. Smart Buildings are envisioned to have smart nodes which could allow distributed monitoring and control to improve the living conditions and reduce to minimum the energy consumption [11].
Examples from literature on how the energy consumption can be reduced in smart buildings through the use of WSN are [14], [15], [16], [17]:
• Lights, chairs and tables automatically adjust as soon as the family gath- ers in the living room to watch TV.
• Phones only ring in rooms where someone is present. • Music in a room adapts automatically to people within. • Support elderly people in their daily life routines.
• Security systems like emergency alarms for burglars, fire with complete awareness of home owners wherever they are.
• Natural interface of devices through speech and gesture.
Through the use of WSN, the headquarters building of the New York Times consumes 30% less energy than traditional office buildings [18]. This building system relies on a large-scale sensor network which gathers information from the offices and uses air conditioning, heating, etc. only when needed. In an event of fire, firefighters outside the building can receive real time information which can help them minimize the loss of lives and material. So, receiving this information fast is crucial in these type of situations.
3. Habitat monitoring - the deployment of sensor nodes provides a non- invasive approach for environments which are rather sensitive to human pres- ence [11], [19]. For example, through the use of sensors, environmental data (air temperature, light, wind, relative humidity and rainfall) is gathered in the South-West Rift Zone, in Volcanoes National Park on the Big Island of Hawaii for the Pods project at the University of Hawaii at Manoa [20]. An- other example is the PermaSense Project [21] which was designed to gather reliable data of physical parameters in natural and diverse slope areas in Swiss Alps Figure 1.4. With this data they aim to develop theoretical models for temperature simulation and for hazard assessment.
1.2 WSN applications
Figure 1.4: WSN PermaSense project
[21]
In Princeton’s Zebranet Project [22], sensor nodes are used to monitor zebras movement and behavior. It is crucial not to have human presence for wildlife monitoring in order to obtain accurate data which represents animals behavior in natural conditions. These areas are usually large so data collection can be made with the help of mobile units which move outside the WSN area, on the boundary. In [18] a plane deploys 30 airborne sensors in the arctic for analysis and assessment of global warming. The collected information can be sent to a boat or a plane which surpasses at a low altitude the monitored area.
4. Industrial applications - these can require networks to function in both in-door and outdoor environment. Possible applications refer to monitoring and control of industrial equipment, processes and personnel. Few examples of WSN industrial applications are given by Banner Engineering [23] as follows:
• Wireless perimeter guard - by using a solar powered wireless alert system they can alert the security personnel when a security breach was detected Figure 1.5.
• Monitoring in a bottling facility - a bottling plant monitors the level, pressure and temperature inside each rotary filler to accurately determine when to activate the inflow into the tank. WSNs offer a viable solution to eliminate the wires on moving assemblies (Figure 1.6).
• Day tank level monitoring - for tank locations not wired for power or data transfer, a wireless sensor network can gather the tank data and transmit it to a central control location for analysis and logging. Day tank fill levels are monitored continuously so that materials are maintained at a specific quantity. Because these tanks are slowly filled or depleted, ultrasonic sensors can be used to measure the tank levels without false readings or tank wall interference (Figure 1.7).
WSN specifications and constrains are presented further in order to understand the challenges that these impose.