| Wireless Sensor Network |
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Sensor nodes are small computers, extremely basic in terms of their interfaces and their components. They usually only consist of a ''processing unit'' with limited computational power and limited memory, ''sensors'' (including specific conditioning circuitry), a ''communication device'' (usually radio transceivers or alternativelly Optical ), and a power supply. Other possible inclusions are energy harvesting modules, secondary ASIC s, and possibly secondary communication devices ( RS232 , USB ...). The base stations are one or more distinguished components of the WSN with much more computational, energy and communication resources. They act as a gateway between sensor nodes and the end user. USES FOR WSNS The uses for ''WSNs'' are many and varied. They could be used in industry to monitor dangerous/hermetically-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!! TYPICAL APPLICATIONS In a typical application, a wireless sensor network is scattered in a region where it is meant to collect data throug its sensor nodes. Area Monitoring Area monitoring is a typical application of WSN's. In area monitoring, the WSN is deployed over a region where some phenomenon is to be monitored. As an example, a large quantity of tiny sensor nodes could be deployed over a battlefield to detect enemy intrusion instead of using '' Landmines ''. When the sensors detect the event being monitored (heat, pressure, sound, light, elctro-magnetic field, vibration, etc...), the event needs to be reported to one of the base stations, which can take appropriate action (e.g., send a message on the internet, to a satellite, etc...). Depending, on the exact application, different objective functions will require different data-propagation strategies, depending on things such as need for ''real-time'' response, ''redundancy'' of the data (which can be tackled via ''data aggregation'' techniques), need for ''security'', etc... 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 scarcest 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 address the following isues:
Amongst the hot topics in WSN software, the following can also be pointed out:
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 transmission. 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. They are usually more "down to earth", compared to the algorithmic approach, and more directly implementable in real world WSN's. 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 , 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 {Link without Title} . 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 {Link without Title} . 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. Tyndall National Institute (formerly NMRC) The Microelectronic Applications Integration (MAI), sector of the Tyndall National Institute in Cork, Ireland , headed by Dr. Cian O'Mathuna, is currently involved in developing microsensing and microactuation devices for use in miniaturised wireless sensor networks. In particular the Ambient Technology Group is developing modular interchangeable hardware layers for use in many sensor network applications. SENSOR DEVICES The following lists some of the sensor nodes on the market.
WIRELESS SENSOR NETWORK SIMULATORS There exists platforms specifically designed to simulate Wireless Sensor Networks, like TOSSIM which is a part of TinyOS . Traditional network simulations like NS-2 have also been used. SEE ALSO EXTERNAL LINKS
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