1. Wireless Sensor Network 2014
A wireless sensor network (WSN) is a wireless network consisting of spatially
dispersed and dedicated autonomous devices that use sensors to monitor
physical or environmental conditions. A usual WSN system is formed by
combining these autonomous devices, or nodes with routers and a gateway.
The dispersed measurement nodes communicate wirelessly to a central
gateway, which provides a connection to the wired world where you can collect,
process, analyse, and present your measurement data. You can use routers to
gain an additional communication link between end nodes and the gateway for
extend distance and reliability in a wireless sensor network.
The wireless sensor is networked and scalable, require very little power. It is
also smart and software programmable, and also capable of fast data
acquisition, reliable and accurate over the long term, but costs little to purchase
and install, and requires nearly zero maintenance.
Wireless Sensor Network
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2. Wireless Sensor Network 2014
A Wireless Sensor Network (WSN) is a wireless network consisting of spatially
distributed autonomous devices using sensors to cooperatively monitor physical
or environmental conditions, such as temperature, sound, vibration, pressure,
motion or pollutants, at different locations. The development of wireless sensor
networks was originally motivated by military applications such as battlefield
surveillance. However, wireless sensor networks are now used in many civilian
application areas, including environment and habitat monitoring, healthcare
applications, home automation, and traffic control.
In addition to one or more sensors, each node in a sensor network is typically
equipped with a radio transceiver or other wireless communications device, a
small microcontroller, and an energy source, usually a battery. The size of a
single sensor node can vary from shoebox-sized nodes down to devices the size
of grain of dust. The cost of sensor nodes is similarly variable, ranging from
hundreds of dollars to a few cents, depending on the size of the sensor network
and the complexity required of individual sensor nodes. Size and cost constraints
on sensor nodes result in corresponding constraints on resources such as
energy, memory, computational speed and bandwidth.
In computer science and telecommunications, wireless sensor networks are
an active research area with numerous workshops and conferences arranged
WSN are used to collect data from the environment. They consists of large
number of sensor nodes and one or more Base Stations.
The nodes in the network are connected via Wireless communication channels.
Each node has capability to sense data, process the data and send it to rest
of the nodes or to Base Station.
These networks are limited by the node battery lifetime.
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3. Wireless Sensor Network 2014
Block Diagram of Wireless Sensor Networks
Wireless Sensor Network is different from traditional network.
• Wireless Sensor Network is a Single-purpose design means serving one
specific application where as traditional network general-purpose design means
serving many applications.
• Energy is the main constraint in the design of all node and network
components in wireless sensor network where as in traditional network typical
primary design concerns are network performance and latencies, energy is not
a primary concern.
• Sensor networks often operate in environments with harsh conditions where
as in traditional network devices and networks operate in controlled and mild
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1.1 HOW WIRELESS SENSOR NETWORKS WORK??
Wireless Sensor Network mechanism is quite simple and applicable
to a variety of fields. It is based on smaller nodes, controller, radio
transceiver, and battery. The key to stimulate the sensor networking is
the algorithm sponsor multi-router phenomenon. The system is totally
dependent on the nodes and the harmony established between them
through proper frequency. These nodes are of different sizes according
to the function they perform.
To activate the monitoring / tracking function of these nodes a radio
transmitter is attached to forward the information in the form of waves.
They are controlled by the microcontroller according to the function
and device in which they are used. All the system remains in working
condition with the help of energy supply which is in the form of
battery. The Wireless Sensor Networks perform function concurrently
where nodes are autonomous bodies incorporated in the field spatially
for the accurate results. The information transmits through proper
channel taking the information collecting it in the form of data and send
to the base.
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5. Wireless Sensor Network 2014
In the year of 1978, the Defence Advanced Research Projects Agency
(DARPA) organized the Distributed Sensor Nets Workshop (DAR 1978), focusing
on sensor network research challenges such as networking technologies, signal
processing techniques, and distributed algorithms. That is the reason that the
military has been a driving force behind the development of wireless sensor
In the early 1980’s DARPA also operated the Distributed Sensor Networks
(DSN) program which was then followed by the Sensor Information Technology
(SensIT) program, which provided the present sensor networks with new
capabilities such as ad hoc networking, dynamic querying and tasking,
reprogramming and multitasking.
The University of California at Los Angeles along with the Rockwell Science
Centre proposed the concept of Wireless Integrated Network Sensors or WINS.
One outcome of the WINS project was the Low Power Wireless Integrated Micro
sensor (LWIM), produced in 1996 (Bultetal. 1996). This smart sensing system
was based on a CMOS chip, integrating multiple sensors, interface circuits,
digital signal processing circuits, wireless radio, and microcontroller onto a
In the year 1999 the University of California at Berkeley focused on the
design of extremely small sensor nodes called motes in the Smart Dust Project
(Khanetal. 1999).The main aim of this project was to demonstrate that a
complete sensor system can be integrated into tiny devices, possibly the size of
a grain of sand or even a dust particle.
In the year 2000 the Berkeley Wireless Research Centre (BWRC) focuses on
the development of low-power sensor devices in the PicoRadio project
(Rabaeyetal. 2000), whose power consumption is so small that they can power
themselves from energy sources of the operating environment, such as solar or
The MIT μAMPS (micro-Adaptive Multi-domain Power-aware Sensors) project
focuses on low power hardware and software components for sensor nodes,
which includes the use of microcontrollers capable of dynamic voltage scaling
and techniques to restructure data processing algorithms to reduce power
requirements at the software level (Calhounetal, 2005).
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Characteristics of WSN
The general structure of Wireless sensor network consists of a base station
or “gateway” which can communicate with a number of wireless sensors via a
radio link. Data is captured at the wireless sensor node, then compressed, and
transmitted to the gateway directly or, if required, uses other wireless sensor
nodes to forward data to the gateway.
The transmitted data is then passed to the system through the gateway
connection. Sensor nodes are likely 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, a
communication device, and a power source usually in the form of a battery.
The base stations act as a gateway between sensor nodes and the end user
and they normally forward data from the WSN on to a server. Other special
components are routers, designed to compute, calculate and distribute the
On the basis of functionality of sensor nodes and other element, the major
characteristics of WSN are as following:-
Power consumption constrains for nodes using batteries or energy
Ability to cope with node failures
Mobility of nodes
Dynamic network topology
Heterogeneity of nodes
Scalability to large scale of deployment
Ability to withstand harsh environmental conditions
Ease of use
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A Wireless Sensor Network (WSN) consists of spatially distributed sensor
nodes and each sensor node can perform some processing and sensing tasks
independently. In addition, sensor nodes communicate with each other in order
to forward their sensed information to a central processing unit or conduct
some local coordination such as data fusion. The sensor node consists of several
hardware components that include an embedded processor, a radio transceiver,
internal and external memories, and one or more sensors, a Geo-Positioning
system, a power source.
Architecture of Sensor Node
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8. Wireless Sensor Network 2014
Hardware Components of WSN:-
4.1 Embedded Processor
The functionality of an embedded processor in a sensor node is to schedule
tasks, process data and control the functionality of other hardware components.
There are several types of embedded processors available that can be used in a
sensor node include Microcontroller, Digital Signal Processor (DSP), Field
Programmable Gate Array (FPGA) and Application Specific Integrated Circuit
(ASIC) been the most used embedded processor for sensor nodes is the
Microcontroller because of its flexibility to connect to other devices and its
cheap price. For example, the most recent CC2531 development board
provided by Chipcon (acquired by Texas Instruments) uses 8051 microcontroller,
and the Mica2 Mote platform provided by Crossbow uses ATMega128L
The responsibility of a transceiver is for the wireless communication of a
sensor node. There are different types of wireless transmission media, which
includes Radio Frequency (RF), Laser and Infrared. The most used transmission
media to fits to most of WSN applications is the RF based communication. The
different operational states of a transceiver are Transmit, Receive, Idle and
Sleep. Mica2 Mote uses two kinds of RF radios one is RFM TR1000 and other one
is Chipcon CC1000. The Mica2 Mote’s outdoor transmission range of is about
Memories in the sensor nodes includes both program memory (from which
instructions are executed by the processor), and data memory (for storing raw
and processed sensor measurements and other local information). The
quantities of memory and storage on board a WSN device are often limited. It
include in-chip flash memory and RAM of a microcontroller and external flash
memory. For example, the ATMega128L microcontroller running on Mica2 Mote
has 128-Kbyte flash program memory and 4-Kbyte static RAM. Further, a 4 Mbit
Atemel AT45DB041B serial flash chip can provide external memories for Mica
and Mica2Motes (Hill 2003).
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Due to limited bandwidth and power, Wireless Sensor Network devices
primarily support only low-data-rate sensing. There are various applications call
for multi-modal sensing, as a result each device may have several sensors on
board. The specific sensors are used according to the requirement of the
application. For example, they may include temperature sensors, light sensors,
humidity sensors, pressure sensors, accelerometers, magnetometers, chemical
sensors, acoustic sensors, or even low-resolution imagers.
4.5 Geo-Positioning System(GPS)
It is important for all sensor measurements to be location stamped in
numerous WSN applications. To obtain positioning you need to pre-configure
sensor locations at deployment, but this may only be possible in limited
deployments. Mainly for outdoor operations, when the network is deployed in
an ad hoc manner, such information is most easily obtained via satellite based
GPS. The Global Positioning System (GPS) is a space-based Global Navigation
Satellite System (GNSS) which provides location and time information in all
weather, anywhere on or near the Earth, where there is a clear line of sight to
four or more GPS satellites.
4.6 Power Source
In deployment of the WSN device is likely to be battery powered. Power is
consumed by sensing, communication and data processing by a sensor node. .
Batteries are the main source of power supply for sensor nodes. For example,
Mica2 Mote runs on 2 AA batteries. While some of the nodes may be wired to a
continuous power source in some applications, and energy harvesting
techniques may provide a degree of energy renewal in some cases, the finite
battery energy is probable to be the most critical resource bottleneck in most
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10. Wireless Sensor Network 2014
The software component plays major role in the development of wireless
sensor network. The development of wireless sensor network composed of
three custom software components, such as:-
The Web program
5.1 The Web Program
Web program was written in PHP and make use of the Chart-Director
charting software. The web application queried MySQL database for the data,
then we use a Chart-Director to generate a graph of that data.
WiseDB is the custom software component that interfaced with the gateway
via a serial link to and with the SQL database via a TCP/IP link. WiseDB was
written in C++ and utilized two open-source API’s (application programming
WiseDB collects the data captured by sensor nodes of sensor mots network
and passed through gateway and accessed by using SQL server applications. This
is the way that, the WiseDB interacted with the rest of the system in the wireless
The one of the most important custom software component is the TinyOS. It
is an operating system specifically designed to address the needs of wireless
sensor networks. It is based on an event driven execution engine that
simultaneously provides efficiency and fine-grained concurrency.
As you know, TinyOS is a real-time operating system designed for use in
sensor network applications where low-power, limited resources and hard real-time
constraints are critical parameters.
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Architecture of WSN
The entire system can be described as consist as two subsystems depending
upon the operation performed by the entire system, such as:-
Data Analysis subsystem is software-only. It relied on existing Internet and web
(HTTP) infrastructure to ensure communications between the Client and Server
components. The main use of this subsystem was to selectively present the
gathered environmental data to the end user in a graphical manner.
Data Acquisition subsystem is used to collect and store environmental data for
later processing by the Data Analysis subsystem. This subsystem is consists of
PC, embedded system software and also embedded system hardware. In the
other word you can say, it is composed of both the Server and Sensor Mote
Wireless Sensor Network Architecture
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The Client component is external to the development of wireless sensor
network. That means, any computer with a web browser and Internet access
could be a Client. It served only as a user interface to the Data Analysis
The Server plays a significant role between the Data Acquisition and Data
Analysis subsystems. In case of Data Analysis, in this side, a web (HTTP) server
hosting a web application. When a page request came in, the web server
executes the web application, which retrieved data from the database,
processes it, and returns a web page that is transmitted to the Client through
the web server. In case of Data Acquisition system, there is a daemon (WiseDB)
running to provide the facility to establish the communication with the Sensor
This daemon collects raw data packets from the Sensor Mote Network. Then
these packets are then processed and then convert the raw data into meaningful
environmental data. Then this processed data is then inserted into the database.
Thus the database is the link between the Data Analysis and Data Acquisition
The main focus of wireless sensor network is the development of the Sensor
Mote Network component. Wireless Sensor Networks are collections of motes.
Motes are the individual computers that work together to form networks. It is
the component responsible for collecting and transmitting raw environmental
data to the Server. The requirements for motes are extensive.
They must be small, energy efficient, multifunctional, and wireless.
The component consists of two parts. Such as:-
The sensor mote
The gateway mote
The sensor mote is developed to collect and transmit raw environmental data.
When not doing this, it went into a low-power idle mode to conserve energy. It
also have some other feature involved ad-hoc networking and may be for multi-hop
The second part of the Sensor Mote Network is the gateway mote .The gateway
mote is responsible for serving as the liaison between the Server and the Sensor
Mote Network and transport all the data packets to WiseDB. It is possible to
implement both sensor and gateway motes on the same hardware PCB and with
the same software.
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Networking Topologies of WSN
You need to coordinate the WSN gateway, end nodes, and router nodes. For
which you can use several network topologies. You can use Router nodes in two
different ways, one way Router nodes are similar to end nodes as they can
acquire measurement data, in other way you also can use them to pass along
measurement data from other nodes.
Cluster or Tree Topology
Ring Topology, etc.
The most basic topology is the star topology, in which each node is directly connected with
the gateway. This topology is simple but restricts the overall distance that your network can
Cluster or Tree Topology:
You can implement a cluster, or tree, topology to increase the distance a network can
cover. This is a more complex structure and in this each node still maintains a single
communication path to the gateway but can use other nodes to route its data along that path.
This topology suffers from a problem that if a router node goes down, all the nodes that
depend on that router node also lose their communication paths to the gateway.
Mesh Network Topology:
The mesh network topology eliminates the issue evolved during the Cluster / Tree Topology
by using redundant communication paths to increase system reliability. In a mesh network,
nodes maintain multiple communication paths back to the gateway, hence if one router node
goes down, the network automatically reroutes the data through a different path. The mesh
topology is very reliable but from an increase in network latency as data must make multiple
hops before arriving at the gateway.
In a ring topology, each device has a dedicated point-to-point connection with only the two
devices on either side of it. A signal is passed along the ring in one direction, from device to
device, until it reaches its destination. Each device in the ring incorporates a repeater. When
a device receives a signal intended for another device, its repeater regenerates the bits and
passes them along.
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Star Topology Cluster / Tree Topology
Fully Connected Mesh Topology
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Applications of WSN
The applications for WSNs are many and varied. They are used in commercial
and industrial applications to monitor data that would be difficult or expensive
to monitor using wired sensors. They could be deployed in wilderness areas,
where they would remain for many years (monitoring some environmental
variable) without the need to recharge/replace their power supplies. They could
form a perimeter about a property and monitor the progression of intruders
(passing information from one node to the next). There are a many uses for
Typical applications of WSNs include monitoring, tracking, and controlling. Some
of the specific applications are habitat monitoring, object tracking, nuclear
reactor controlling, fire detection, traffic monitoring, etc. In a typical application,
a WSN is scattered in a region where it is meant to collect data through its sensor
Wireless Sensor Networks are applied for:-
Process Monitoring, etc.
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Military application was the original motivation behind the research into WSNs
.At the later period of time costs for sensor nodes and communication networks
have been reduced and thus the application area has also increased.
Military surveillance and target tracking:
Wireless sensor networks originated mainly in military-related research in the
Unattended sensor networks can be rapidly deployed for surveillance and used
to provide battlefield intelligence regarding the location, numbers, movement,
and identity of troops and vehicles, and for detection of chemical, biological, and
nuclear weapons. Faster development of wireless sensor networks has been
provided though several programs funded by the US Defence Advanced
Research Projects Agency (DARPA), through a program known as Sensor
Information Technology (SensIT) which provides the present sensor networks
with new capabilities such as ad hoc networking, dynamic querying and tasking,
reprogramming and multitasking.
Environmental monitoring can be used for animal tracking, forest surveillance,
flood detection, and weather forecasting. It is a natural candidate for applying
WSNs because the variables that is considered to be temperature, are usually
distributed over a large region.
Wireless sensor network is a major application in health sector. WSNs can be
embedded into a hospital building to track and monitor patients and all medical
resources. There are various kinds of sensors which can measure blood pressure,
body temperature and electrocardiograph
(ECG). A special kind of sensor network called a body sensor network (BSN)
formed When the sensors are worn or implanted for healthcare purposes. BSN
is a rich interdisciplinary area which reforms the healthcare system by allowing
inexpensive, continuous and ambulatory health monitoring with real-time
updates of medical records via the Internet. Now a days a specialized BSN sensor
node and BSN Development Kit are available for use in health monitoring
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Traffic control is another area where wireless sensor network plays a major role.
Wireless sensor networks have been used for vehicle traffic monitoring and
control for some time. There are either overhead or buried sensors used to
detect vehicles and to control the traffic lights. WSNs will completely change the
landscape of traffic monitoring and control by installing cheap sensor nodes in
the car, at the parking lots, along the roadside. Streetline, Inc. is a company
which uses sensor network technology to help drivers find unoccupied parking
places and avoid traffic jams.
Sensor nodes can be deeply embedded into machines and there is no
infrastructure, WSNs make it economically feasible to monitor the “health” of
machines and to ensure safe operation. Aging pipelines and tanks have become
a major problem in the oil and gas industry. Monitoring corrosion using manual
processes is extremely costly, time consuming, and unreliable. A network of
wireless corrosion sensors can be economically deployed to reliably identify
issues before they become catastrophic failures.
WSNs can be used for infrastructure security and counterterrorism applications.
Security is the major aspect of wireless sensor network. Critical buildings and
facilities such as power plants, airports, and military bases have to be protected
from attacks. Networks of video, acoustic, and other sensors can be deployed
around these facilities.
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Pros and Cons of WSN’s
There are several advantages of wireless sensor networking as they can store
a limited source of energy, they have no hassle of cables and have mobility. The
major advantage is that it can work efficiently under the harsh conditions, and
it has deployment up to large scale etc. Same time it also has some
disadvantages which really take the moral of this technology down as they have
very insufficient speed of communication, it is to disturb the propagation of
waves and hack your networking and the major disadvantage of wireless sensor
networking is it is too costly to use.
• It avoid lot of wiring.
• It can accommodate new devices at any time.
• It’s flexible to go through physical partitions.
• It can be accessed through a centralized monitor.
• WSN’s can be applied on large scale and in various fields.
• It is very easy for hackers to hack it as we can’t control
propagation of waves.
• Comparatively low speed of communications.
• Gets distracted by various elements like Blue-tooth.
• Still costly at large.
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As the wireless sensor network is under research, there are a number of
improvements we can think of.
We can think of expanding the sensor mote network by adding
more motes. This would allow the development and testing of
advanced network-layer functions, such as multi-hop routing.
We can think of alternative energy sources to extend mote
battery life. Which may include solar cells and rechargeable
batteries, these systems could provide a long term, maintenance
free, wireless monitoring solution.
Wireless sensor network has the potential to trigger the next
revolution in computing. While its applications and potential
benefits can spread far and beyond, and could finally break the
barrier between physical and digital worlds to allow
disappearance of computation.
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Wireless sensor networks must be designed to meet a number of
challenging requirements including extended lifetime in the face of
energy constraints, robustness, scalability, and autonomous operation.
Wireless sensor networks are getting smaller and faster, increasing their
potential applications in commercial, industrial, and residential
However, the limit of applications depends only upon the sensors
used and the interpretation of the data obtained. As the technology
improves and new low-power digital sensors become more readily
available, motes will increase functionality without increasing power
consumption and will expand the wireless sensing market.
The flexibility, fault tolerance, high sensing fidelity, low-cost and
rapid deployment characteristics of sensor networks create many new
and exciting application areas for remote sensing. In the future, this
wide range of application areas will make sensor networks an integral
part of our lives. However, realization of sensor networks needs to
satisfy the constraints introduced by factors such as fault tolerance,
scalability, cost, hardware, topology change, environment and power
Since these constraints are highly stringent and specific for sensor
networks, new wireless ad hoc networking techniques are required.
Many researchers are currently engaged in developing the technologies
needed for different layers of the sensor networks protocol stack.
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