Wireless sensor network -2

Wireless sensor network -2

Applications

The applications for WSNs are many and varied, but typically involve some kind of monitoring, tracking, and controlling. Specific applications for WSNs include habitat monitoring, object tracking, nuclear reactor control, fire detection, and traffic monitoring. In a typical application, a WSN is scattered in a region where it is meant to collect data through its sensor nodes.

Area monitoring

Area monitoring is a common application of WSNs. In area monitoring, the WSN is deployed over a region where some phenomenon is to be monitored. As an example, a large quantity of sensor nodes could be deployed over a battlefield to detect enemy intrusion instead of using landmines[1]. When the sensors detect the event being monitored (heat, pressure, sound, light, electro-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 or to a satellite). 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.

Characteristics This article does not cite any references or sources.

Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed. (August 2006)

Unique characteristics of a WSN include:

Limited power they can harvest or store

Ability to withstand harsh environmental conditions

Ability to cope with node failures

Mobility of nodes

Dynamic network topology

Communication failures

Heterogeneity of nodes

Large scale of deployment

Unattended operation

Sensor nodes can be imagined as small computers, extremely basic in terms of their interfaces and their components. They usually consist of a processing unit with limited computational power and limited memory, sensors (including specific conditioning circuitry), a communication device (usually radio transceivers or alternatively optical), and a power source usually in the form of a battery. Other possible inclusions are energy harvesting modules, secondary ASICs, and possibly secondary communication devices (e.g. RS-232 or 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.

Platforms

Standards

Several standards are currently either ratified or under development for wireless sensor networks. ZigBee is a mesh-networking standard intended for uses such as industrial control, embedded sensing, medical data collection, building automation. Zigbee is promoted by a large consortium of industry players. WirelessHART is an extension of the HART Protocol and is pecifically designed for Process Monitoring and Control. WirelessHART was added to the overall HART protocol suite as part of the HART 7 Specification, which was approved by the HART Communication Foundation in June 2007[4]. 6lowpan [5] is a proposed standard for the Network Layer, but it has not been adopted yet. ISA100 is a new standard under development that includes WSN[citation needed]. ISA100 is scheduled for completion by year-end 2008. WirelessHART, ISA100, and ZigBee all are based on the same standard: IEEE 802.15.4 - 2005.

Hardware

Main article: sensor node

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. Some of the existing sensor nodes are given below. Some of the nodes are still in research stage.

An overview of commonly used sensor network platforms, components, technology and related topics is available in the SNM - Sensor Network Museumtm.

Software

Energy is the scarcest resource of WSN nodes, and it determines the lifetime of WSNs. WSNs are meant to be deployed in large numbers in various environments, including remote and hostile regions, with ad-hoc communications as key. For this reason, algorithms and protocols need to address the following issues:

Lifetime maximization

Robustness and fault tolerance

Self-configuration

Some of the "hot" topics in WSN software research are:

Security

Mobility (when sensor nodes or base stations are moving)

Middleware: the design of middle-level primitives between the software and the hardware