wireless sensor networks

Wireless Sensor Networks

Introduction:-

A wireless sensor network [wsn] is a wireless network consisting of spatially distributed autonomous devices that use sensors to monitor physical or environmental conditions. These autonomous devices, or nodes. Combine with routers and a gateway to create a typical WSN system. The distributed measurement nodes communicate wirelessly to a central gate way, which provides a connection to the wired world where you can collect, process, analyse, present your measurement data. To extend distance and reliability in a wireless sensor network, you can use routers to gain an additional communication link between and nodes and the gateway.
National instruments wireless sensor networks offers reliable, low-pressure measurements nodes that operate for up to three years on 4AA batteries and can be deployed for long-team, remote operation. The NI WSN protocol based on IEEE 802.15.4 and ZIGBEE technology provides a low-power communication standard that offers mesh routing capability to extend network distance and reliability. The wireless protocol we select for a network depends on the applications requirement.
WSN Application:-
Embedded monitoring covers a large range of application areas, including those in which power or infrastructure limitations make a wired solutions costly, challenging or even impossible. You can position wireless sensor networks alongside wired systems to create a complete wired and wireless measurement and control system.
A WSN system is ideal for an application like environmental monitoring in which the requirement mandate a long term deployed solution of acquire water Soil or climate measurements. For utilities such as the electricity grid, street lights and water municipals wireless sensor offer a lower cost method for collecting system health data to reduce energy usage. And better manage resource. In structural health monitoring, you can use wireless sensors to effectively monitor high ways, bridges and tunnels. You can also deploy these systems to continually monitor office buildings, hospitals, airports, factories, power plants or productions facilities.
WSN System Architecture:-
In a common WSN architecture, the measurement nodes are deployed to acquire measurements such as temperature, voltage, or even dissolved oxygen. The nodes are part of wireless network administrated by the gateway, which governs network Aspects such as client authentication and data security. The gateway collects the measurement data from each nodes and send it over a wired connection, typically ETHERNET, to host controlled. These, software such as the NI Lab view graphical development environment can perform advanced processing and analysis and present your data in a fashion that meets your needs.
The NI wireless sensor network advantage:-
With the NI WSN platform, we can customize and enhance a typical WSN architecture to create a complete wired and wireless measurement system for our flexibility to choose a windows-based host controller for our WSN systems or a real-time controllers such as NI complete RIO, giving you the ability to integrate. Reconfigurable input-output with our wireless measurement. With either host controller, we can use lab view and NI-WSN software with lab view project integration and drag and drop programming to easily configure our WSN systems. Exact high quality measurement data, perform analysis and present our data.
Working of wireless sensor network:-
The development of network technologies has prompted sensor folks to consider alternatives that reduces cost and complexity and improve reliability early sensor networks used simple twisted shielded pair [TSP] implementations for each sensor earlier the industry adopted multi drop buses [eg:- ETHERNET] now we are starting to true web-based networks [eg:- the world wide web] implemented on factory floor.
As wireless sensor become real commodities on the markets, new options or new arguments for old options are causing professional to consider network strategies once ruled out. Lets look at how the rules have changed now that wireless systems are coming online.
In addition to build functional sensor networks, we will probably have to integrate hardware and software from multiple vendors. So along with every thing else, we have to come to terms with standards and protocols – those that exists, that are emerging and those needed to ensure inter operability on the factory floor.
Wireless sensor network topologies:-
Point to point networks:-
Theoretically, these systems are the most reliable because these is only one single point of failure in the topology, the host itself. We can improve the system by adding redundant host but writing two hosts can be a problem. The 4-20 ma standard allows multiple read-out circuits. If the standard loads are used at each read out. Problems can arise if read out device load the circuit beyond its capability but most designers are familiar with the limitations and are sufficiently care full.
Multiple networks:-
Multi drop [networks] busses began the appear in the late 70’s and early 80’s. one of these mod bus from modicon [Schneider automation, north and over, massa chussets] leads the way into the industrial sphere, followed by several proprietary and open busses.
The emergence of intelligent sensors and micro computer cable of operating in industrial environments irrevocable changed the sensor networks land scape. Multi drop networks reduced the number of wires required to connect field devices to the host, but they also introduced another single point of failure the cable.
Web networks:-
The promise of the web topology had to wait until vendour developed a way to inter connect nodes without the required wiring connections. A network of any applicable size becomes infisible if all wires must connected specially for the networks. Early star topology was successful as long as star was not too large. The WWW illustrate what is available connectivity in most parts of the country, although at less than suitable speeds in many locations.
The advantages of web connectivity for sensor networks become clear as the level of intelligence in each sensor increases. Co-operating sensors can form a temporary configuration that provides sufficient capacity to replace the host self-hosting networks then became self configuring and finally, years from now, perhaps even self-aware. But several problems remaining and are the topic of significant research, such as size and power consumption reduction, through put and performance during transmission and algorithms from allocating priorities and authority.
Characteristics of wireless sensor networks:-
 Ability to with stand harsh environment
 Conditions limited power they can store
 Ability to cope with node failure
 Mobility of nodes
 Dynamic network topology
 Communication failures
 Heterogeneity nodes
 Large scale of deployment
 Unattended operation
 Node capability in scalable
Advantages of wireless sensor networks:-
 Flexibility if there is ad-hoc situation when additional work station was required.
 Implementation cost is cheaper than wired networks
 Ideal for the non-reachable places
 Ideal for temperary network setup
Disadvantages of wireless sensor networks:-
 Lower speed compared to wired network
 Less secure because hackers laptop can act as access point
 More complex to configure than wired networks
 Effected by surroundings