Friday, July 25, 2008

A sensor network which covers 2 Km x 2 Km to measure a temperature, humidity and CO2 levels every 10 seconds.


We design a sensor network that collects data monitoring temperature, humidity and CO2 levels. The sensors in 2x2 Km2 area relays collected data to its neighboring sensors and then to a base node. Base node is connected with computer that processes and analyzes data. We selected following factors to design the network

Sensor Nodes (Motes): Crossbow Berkeley Motes may be the most versatile wireless sensor network devices in the market commercially available. MICAz is the latest generation of Motes from Crossbow Technology. MICAz motes come with several sensors installed - Temperature, Humidity, Gas, Light, Acceleration/Seismic, Vibration etc. Different sensors can be installed if desired. The MPR2400 (2400 MHz to 2483.5 MHz band) uses the Chipcon CC2420, IEEE 802.15.4 compliant, ZigBee ready radio frequency transceiver integrated with an Atmega128L micro-controller. 51 pin I/O connector, and serial flash memory is used. Alternatively, USS 2400 marketed by a Korean Company HUINS (Human Intelligent System) can be used. USS 2400 is compatible with Berkeley Motes. 
These motes are low power and small physical size enable placement virtually anywhere. Since all sensor nodes in a network can act as base stations, the network can self configure and has multi-hop routing capabilities. 

Number of Nodes required: We can apply a grid structure to uniformly deploy sensors. MICAz’s maximum transmission range is 100m in open air. However it is always safe to use  N= Gx × Gy = X/r × Y/r

=(2000 m)/(50 m)×(2000 m)/(50 m)=1600

Where, Gx and Gy are the total number of grids in X and Y respectively. r is a transmission range of the node (transmission range is given as 50 m). Above calculation shows total number of nodes required is 1600. 


Base Stations: A base station allows the aggregation of sensor network data onto a PC or other computer platform. According to our network plan at least one Base Station is required. Any MICAz Mote can function as a base station by plugging the MPR2400CA Processor/Radio Board into an MIB510CA serial interface board. The MIB510CA provides an RS-232 serial interface for both programming and data communications. 

Computer (PC): We need at least one computer for data aggregation, processing and analysis. Any latest version of readily available computer can be used for this purpose. Better and dedicated server can be considered according to the significance of the data.

Routers: As we implement AODV (Ad Hoc on Demand Distance Vector) routing protocol we do not need dedicated router. It is an ad hoc structure i.e. any normal sensor node (MICAz mote) in the network can be a router. 

Battery Power : MICAz form factor is designed to match up with two AA batteries; however any battery combination (AAA, C, D, etc., cells) can be used provided that the output is between 2.7 VDC to 3.6 VDC.

Softwares: 
OS: Freely available and open source, TinyOS has become the de facto industry-standard operating system for sensor network research and applications. A researcher’s group from UC Berkeley designed this sophisticated operating system to manage mote hardware. TinyOS is written in nesC. nesC supports the event-driven processing that is typical of motes, which remain "asleep" until sensors acquire data or receive messages. 

Protocols: 
MAC: We use S-MAC as a MAC layer protocol. S-MAC protocol is designed for wireless sensor networks. S-MAC uses three novel techniques to reduce energy consumption and support self-configuration. To reduce energy consumption in listening to an idle channel, nodes periodically sleep. Neighboring nodes form virtual clusters to auto-synchronize on sleep schedules. S-MAC applies message passing to reduce contention latency for sensor-network applications that require store-and-forward processing as data move through the network. 

Routing: Our network design is static or barely dynamic in nature. AODV (Ad Hoc on Demand Distance Vector) routing protocol can be used. AODV routing algorithm is an on demand algorithm, it is loop-free, self-starting, and scales to large numbers of nodes. AODV builds routes using a route request / route reply query cycle. If any link is broken in the link it repairs using route error message.



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