Sunday, October 07, 2007

Development of Sensor networks


It can be seen rapid advances in micro-electro-mechanical systems (MEMS) technology,
wireless communications, and digital electronics recently. It has enabled the
development of low-cost, low-power, multifunctional sensor nodes. They are small
in size and communicate in short distances. These tiny sensor nodes are capable of
sensing, data processing, and communicating components. The idea of sensor networks
is based on collaborative effort of a large number of nodes. Sensor networks
represent a significant improvement over traditional sensors.


Type of sensors
Sensor networks may consist of many different types of sensors such as seismic, low
sampling rate magnetic, thermal, visual, infrared, and acoustic and radar. They are
able to monitor a wide variety of conditions that include the following:
ˆ Temperature
ˆ Humidity
ˆ Vehical movement
ˆ Lightning condition
ˆ Pressure
ˆ Soil makeup
ˆ Noise levels
ˆ The presence or absence of certain kinds of objects
ˆ Mechanical stress levels on attached objects
ˆ Current characteristics such as speed, direction, and size of an object


Application areas
Sensor nodes can be used for continuous sensing, event detection, event ID and
location sensing. The concepts of micro-sensing and sensor networks open many new
application areas. It can be categorize the applications into agriculture, military,
environment, health, home and other commercial areas. It is possible to expand this
classification with more categories such as space exploration, chemical processing
and disaster relief.
For example, the physiological data about a patient can be monitored remotely
by a doctor[5, 6]. Sensor networks can also be used to detect foreign chemical agents
in the air and the water. They can help to identify the type, concentration, and
location of pollutants. If it say directly, sensor networks will provide the end user
with intelligence and a better understanding of the environment.
Sensor networks and ad hoc networks
Sensor network applications require wireless ad hoc networking techniques. Although
many protocols and algorithms have been proposed for traditional wireless
ad hoc networks, they are not well suited for the unique features and application
requirements of sensor networks. To illustrate this point, the differences between
sensor networks and ad hoc networks are outlined below :

ˆ The number of sensor nodes in a sensor network can be several orders of
magnitude higher than the nodes in an ad hoc network.
ˆ Sensor nodes are thickly deployed.
ˆ Sensor nodes are prone to failures.
ˆ The topology of a sensor network changes very frequently
ˆ Sensor nodes mainly use broadcast communication paradigm whereas most ad
hoc networks are based on point-to-point communications.
ˆ Sensor nodes are limited in power, computational capacities, and memory.
ˆ Sensor nodes may not have global identification (ID) because of the large
amount of overhead and large number of sensors.

Sensor network deploying ways

Sensor networks are deployed in the following two ways .
ˆ Sensors can be positioned far from the actual phenomenon, i.e., something
known by sense awareness. In this approach, large sensors that use some
complex techniques to distinguish the targets from environmental noise are
required.

ˆ Several sensors that perform only sensing can be deployed. The positions
of the sensors and communications topology are carefully engineered. They
transmit time series of the sensed phenomenon to the central nodes. These
central nodes are the place that computations are performed and data are
combined. A sensor network is composed of a large number of sensor nodes,
which are tightly deployed either inside the phenomenon or very close to it.
The position of sensor nodes need not be engineered or pre-determined. This allows
random deployment in inaccessible places or disaster relief operations. Another
unique feature of sensor networks is the cooperative effort of sensor nodes. Sensor
nodes are fitted with an on-board processor. Instead of sending the raw data to the
nodes responsible for locally carry out simple computations and transmit only the
required and partially processed data. The above described features ensure a wide
range of applications for sensor networks.

Reliability consideration in WSN

The reliability of the wireless sensor network is of great importance as it wants to
prevent the loss of data and statistics. Several mechanisms has been implemented
to make sure that all data and statistics are eventually delivered to the gateway.
They are,
ˆ Each node is logging both data and statistics in EEPROM and overwrites it
only once acknowledged.
ˆ The gateway is checking once a day that all the expected data and statistics
packets were received correctly. It uses a network wide acknowledgment to
signal the nodes which portion of their log can be safely reused.

Technological Options

Deployment of wireless sensor networks in agriculture is at its beginning. Currently
three main wireless standards are used. They are: WiFi Bluetooth and
ZigBee. Of these, ZigBee is the most promising standard owing to its low power
consumption and simple networking configuration. However ZigBee standardisation
is not yet complete.

limitations
Some of the main Barriers to implement WSNs are:
ˆ The limitations to power supply in a wireless sensor network
ˆ The significant overhaul of existing IT infrastructure required if wireless sensor
networks are to achieve their full potential
ˆ The potential for the bulk of data generated by thousands of sensor nodes to
overcome the system while providing limited value

ˆ The reliability of wireless sensors in agriculture is unproven and is considered
risky.
Actually, no unique solution that solves all of these problems. However the application
of wireless sensors in land management can raise awareness of the effectiveness
of new technologies in the agricultural field.