Wireless sensor network

A wireless sensor network (WSN) is a network made of many small computers, which are employed in the processing of sensor data. These small computers are extremely basic in terms of their interfaces and their components. They usually only consist of sensors (including specific conditioning circuitry), a communication device (radio transceivers), and a power supply. Other possible inclusions are energy harvesting modules, secondary ASICs, and possibly secondary communication devices (RS232, USB...).

Uses for WSNs

The uses for WSNs are many and varied. They could be used in industry to monitor dangerous/hermitically-sealed environments. They could be deployed in wilderness areas, where they would remain for many years (monitoring some environmental variable) without the need to recharge/replace their power supplies. They could form a perimeter about a property and monitor the progression of intruders (using advanced application transfer techniques?). There are simply a near infinite amount of uses for WSNs!!

Challenges

There are many challenges in implementing a WSN ranging from hardware, software, mechanical and even human-related. Keeping the power usage sufficiently low so that they operate for enough time involves careful power management and in some cases managing charging. Radio communication hardware has to be small enough while using a suitable network algorithm. A high bit-rate saves power by reducing communication time but in order to obtain a good range, especially in wet environments high-power hardware is often needed. These two tasks illustrate the careful balance and compromises that are needed in WSN designs.

Hardware

The main challenge is to produce low cost and tiny sensor nodes. With respect to these objectives, current sensor nodes are mainly prototypes. Miniaturization and low cost are understood to follow from recent and future progress in the fields of MEMS and NEMS.

Software

Energy is the most scarce resource of WSN nodes, and it determines the lifetime of WSN's. WSN are meant to be deployed in large numbers, in an ad-hoc way, in remote, hostile, etc... regions. For this reason, the algorithms and protocols need to adress the following isues:

• Lifetime maximization
• Robustness and fault tolerancy
• Self-configuration

Amongst the hot topics in WSN software, the following can also be pointed out:

• Security
• Mobility (when sensor nodes or base stations are moving)
• Middleware: the design of middle-level primitives between the Software and the Hardware

Algorithms

WSN's are composed of a large number of sensor nodes, therefore, an algorithm for a WSN is implicitely a distributed algorithm. In WSN's the scarcest resource is energy, and one of the most energy-expensive operation is data transmision. For this reason, algorithmic research in WSN mostly focuses on the study and design of energy aware algorithms for data transmission from the sensor nodes to the bases stations. Data transmission is usually multi-hop (from node to node, towards the base stations), due to the polynomial growth in the energy-cost of radio tranmission with respect to the tranmission distance.

The algorithmic approach to WSN differentiates itself from the protocol approach by the fact that the mathematical models used are more abstract, more general, but sometimes less realistic than the models used for protocol design.

Protocols

Protocols for WSN need to address the specificities of the WSN nodes hardware.

Middleware

There is a need and considerable research efforts currently invested in the design of middleware for WSN's.

Visualization of Wireless Sensor Networks Data

The data gathered from wireless sensor networks is usually saved in the form of numerical data in a central base station. There are many programs, like TosGUI and MonSense, that facilitate the viewing of these large amounts of data. Additionally, the Open Geospatial Consortium (OGC) is specifying standards for interoperability interfaces and metadata encodings that enable real time integration of heterogeneous sensor webs into the Internet, allowing any individual to monitor or control Wireless Sensor Networks through a Web Browser.

WSN Research Centers

Examples of major academic centers for research in wireless sensor networks are CITRIS at Berkeley and CENS at UCLA, in the USA and the NCCR MICS at EPFL, in Switzerland.

Center for Embedded Networked Sensing (CENS)

The Center for Embedded Networked Systems (CENS) at the University of California, Los Angeles, directed by Deborah Estrin, is also a leading research center with $40 million in core funding from the National Science Foundation [1].

Center for Information Technology Research in the Interest of Society (CITRIS)

The Center for Information Technology Research (CITRIS) in the Interest of Society at the University of California, Berkeley, currently directed by S. Shankar Sastry, is a $300 million multicampus research center that includes research and development of wireless sensor networks, and has used them to study microclimate variations in individual redwood trees [2].

National Center of Competence in Research on Mobile Information and Communication Systems (NCCR MICS)

The NCCR MICS was launched in 2001 at EPFL. It is performing research in mobile information and communication systems, with a strong emphasis on wireless sensor networks and novel self-organizing networks and information systems.

See also

• TinyOS
• Smartdust
• Mesh networking
• Sensor network
• BTnodes
• Mobile ad-hoc network (MANETS)
• ZigBee
• TinyMaCLaS

External links

• Overview of wireless sensor networks from the IEEE Computer Society.
• EnOcean EnOcean enables a wireless community of batteryless sensors to connect to just a few transceivers that need to be powered for continuous operation.
• Software Infrastructure for Wireless Sensor Networks.
• Sun: Small Programmable Object Technology.
• TECO Particle Web Site.