Today the researchers want to collect as much data as possible from different locations for monitoring reasons. In this context large-scale wireless sensor networks are becoming an active topic of research (Kahn1999). Because of the different locations and environments in which these sensor networks can be used, specific requirements for the hardware apply. The hardware of the sensor nodes must be robust, provide sufficient storage and communication capabilities, and get along with limited power resources. Sensor nodes such as the Berkeley-Mote Family (Polastre2006, Schmitt2006) are capable of meeting these requirements. These sensor nodes are small and light devices with radio communication and the capability for collecting sensor data. In this chapter the authors review the key elements for sensor networks and give an overview on possible applications in the field of monitoring.
In this section the corresponding keywords in the field of wireless sensor networks are mentioned which will be characterized in more detail in section two.
Today the industrial production is able to produce very small mobile devices (Warneke2001). Two sorts can be distinguished: very small, specialized nodes, and larger nodes with commercial off-the-shelf (COTS) components.
An embedded system is a specialized computer which is used for device control (e.g. cars, mobiles, hand-held-units, washing machine). Typically, the end user has no control over it because the device is hidden.
Embedded systems and highly embedded systems can be differentiated. Highly embedded systems would be particularly small, resulting in highly limited resources. This implies the use of sophisticated hardware, in combination with the use of suitable, special operating systems. Data can be collected by a variety of sensors. After collection, this data has to be transmitted to other nodes. Thus, wireless sensor systems have to support highly developed communication.
Wireless sensor nodes have their own energy supply provided by batteries or solar cells. Some sensor nodes have processors that allow to process data before passing it on. Different technologies for wireless transmission are used such as infrared or radio frequency technology. A sensor node consists of several components which are illustrated in figure 2 in section two.
Components of a sensor node
Wireless sensor networks (WSNs) (Röm04, Haenselmann2006) have a decentralized structure in which messages cannot be addressed directly to their destination. Instead messages are sent to neighboring nodes (e.g. using a local broadcast). Nodes that receive messages have to decide whether to further forward the received data. Due to the absence of planned connectivity between specific nodes, these networks are called ad-hoc networks. Another problem of these networks is their limitations concerning security and anonymity.
Like the short description of WSNs above implicit special software (e.g. TinyOS for Berkeley Motes) must be developed to optimize the quality of the established network. Therefore the developers have to look at the requirements of the environment where to use the network and also at the participating components and their limitations. On important aspect is the realization of energy saving procedures and memory saving methods for data acquiring and transmission within the network.
Key Terms in this Chapter
Ad-Hoc Network: A self-configuring network of routers which are connected by links.
Two-Level Scheduling: Describes a method to more efficiently perform process scheduling.
Sensors: Devices that measure data from the environment and which they can pass on.
Se nsor Network: A network which consists of different sensor nodes that can communicate with each other. If the network consists of wireless component it is a so called wireless sensor network (WSN).
Sensor Nodes: Represent the basis for the sensor networks and consist of a great number of single components like the data recording unit, computation unit, radio unit, external data source, actors for mobility and an antenna.
Embedded System: A specialized computer that is used for device control where the user has no control of it because it is hidden from him.
Structural Health Monitoring (SHM): Deals with the observation of structural health in different research fields like building health or animal observation.
Multihop Communication: Means that the message needs to hop over several subsystems until it reaches the final destination.