WIRELESS SENSOR NETWORKS
A wireless sensor network is a collection of nodes organized into a corporate
network. Each node consists of processing capability (one or more
microcontrollers, CPUs or DSP chips), may contain multiple types of memory
(program, data and flash memories), have a RF transreceiver (usually with a
single Omni directional antenna), have a power source (e.g., batteries and solar
cells), and accommodate various sensors and actuators. The nodes
communicate wirelessly and even self organize after being deployed in an ad
hoc fashion. Systems of 1000s or even 10000s nodes are anticipated. Such
systems can revolutionize our live and work.
Currently wireless networks are beginning to be deployed at an accelerated
pace. It is not un reasonable to expect that in 10-15 years that the world will be
covered with wireless sensor networks with access to them via the Internet.
This can be considered as the Internet becoming physical network. This new
technology is exciting with unlimited potential for numerous application areas
including environmental, medical, military, transportation, entertainment, crisis
management homeland defense, and smart spaces.
In computer science and telecommunications, wireless sensor networks are an active
research area with numerous workshops and conferences arranged each year. The
topology of the wireless sensor networks can vary from a simple star network to an
advanced multi-hop wireless mesh network.
The main characteristics of a WSN include:
Power consumption constrains for nodes using batteries or energy harvesting
Ability to cope with node failures
Mobility of nodes
Heterogeneity of nodes
Scalability to large scale of deployment
Ability to withstand harsh environmental conditions
Ease of use
HARDWARE AND SOFTWARE:
One of the major challenge in a Wireless Sensor Network is to produce low cost and
tiny sensor nodes. Now a days, many companies are producing WSN and the
commercial situation can be compared to home computing in 1970s. Most of the
nodes are still in the research and development stage particularly their software.
To determine the lifetime of Wireless Sensor Networks, energy is the scarcest
resource for the Wireless Sensor nodes. The key component for the software of a
Wireless Sensor Network is ad-hoc communications.
The algorithms and protocols need to address the following issues:
Life time Maximization
Robustness and fault tolerance
The lifetime of a Wireless Sensor Network is based upon the limited energy resource.
In order to conserve power the node should shut off the radio power supply when
not in use.
Air Quality monitoring includes Interior monitoring and Exterior monitoring
Air pollution monitoring
Forest fire detection
Water quality monitoring
Industrial monitoring which includes machine health monitoring
Simulation of Wireless Sensor Networks:
At present, agent-based modeling and simulation is the only paradigm which allows
the simulation of complex behavior in the environments of wireless sensors
(such as flocking). Agent-based simulation of wireless sensor and ad-hoc networks
is a relatively new paradigm. Agent-based modeling was originally based on social
Network simulators like OPNET, NetSim and NS2 can be used to simulate a wireless
The prominent standards of Wireless Sensor networks include:
The IEEE focuses on the physical and MAC layers and the Internet Engineering task
force works on the layer 3. Standards are not used much i.e. used very less in the case
of Wireless Sensor Networks.
A medium access control (MAC) protocol coordinates actions over a shared channel.
The most commonly used solutions are contention-based. One general contention-
based strategy is for a node which has a message to transmit to test the channel to
see if it is busy, if not busy then it transmits, else if busy it waits and tries again later.
After colliding, nodes wait random amounts of time trying to avoid re-colliding. If two
or more nodes transmit at the same time there is a collision and all the nodes
colliding try again later. Many wireless MAC protocols also have a doze mode where
nodes not involved with sending or receiving a packet in a given timeframe go into
sleep mode to save energy. Many variations exist on this basic scheme.
MAC protocol for wireless sensor networks must consume little power, avoid
collisions, be implemented with a small code size and memory requirements, be
eﬃcient for a single application, and be tolerant to changing radio frequency and
One example of a good MAC protocol for wireless sensor networks is B-MAC.
B-MAC is highly conﬁgurable and can be implemented with a small code and
memory size. It has an interface that allows choosing various functionality and only
that functionality as needed by a particular application.
B-MAC contains four main parts :
Clear Channel Assessment (CCA)
Link layer acks
Low power listening.
For CCA, B-MAC uses a weighted moving average of samples when the channel is idle
in order to assess the background noise and better be able to detect valid packets
The packet backoﬀ time is conﬁgurable and is chosen from a linear range as opposed
to an exponential backoﬀ scheme typically used in other distributed systems. This
reduces delay and works because of the typical communication patterns found in a
wireless sensor network. B-MAC also supports a packet by packet link layer
acknowledgement. In this way only important packets need pay the extra cost.
A low power listening scheme is employed where a node cycles between awake and
sleep cycles. While awake it listens for a long enough preamble to assess if it needs to
stay awake or can return to sleep mode. This scheme saves signiﬁcant amounts of
TYPES OF WIRELESS SENSOR NETWORKS:
1.Unstructured Wireless Sensor Network 2.Structured Wireless Network
Dense collection of nodes Few and scarcely distributed nodes
Ad-hoc deployment Pre planned deployment
Difficulty in network maintenance Lower network maintenance
Diagramatically a Wireless sensor Network can be represented as
The Wireless sensor networks helps the present technology to Blend and
interconnect individual smart devices, Enable access to information about the real
world and also interact and influence the real world. Also this Wireless Sensor
Network receives live information from the road authority about the state of the
Roads including traffic jams, road accident and weather. The capability and
accessibility of the networks can also be increased to a large extent with the help of
this Wireless Sensor Networks.
Jennifer Yick, Biswanath Mukherjee, Dipak Ghosal, Wireless Sensor networks Survey,