Q 1> what is WSN
A wireless sensor network (WSN) (sometimes called a wireless sensor and actor network (WSAN)) are spatially distributed autonomous sensors to monitor physical or environmental conditions, such as temperature, sound, pressure, etc. and to cooperatively pass their data through the network to a main location.
Q 2> Comparison of Wireless network and wireless sensor n/w
1) A wireless network is any type of computer network that uses wireless data connections for connecting network nodes.
A wireless sensor network (WSN) (sometimes called a wireless sensor and actor network (WSAN)) are spatially distributed autonomous sensors to monitor physical or environmental conditions, such as temperature, sound, pressure, etc. and to cooperatively pass their data through the network to a main location.
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What is sensors ?
A sensor is a device that detects and responds to some type of input from the physical environment. The specific input could be light, heat, motion, moisture, pressure, or any one of a great number of other environmental phenomena. The output is generally a signal that is converted to human-readable display at the sensor location or transmitted electronically over a network for reading or further processing.
In a mercury-based glass thermometer, the input is temperature. The liquid contained expands and contracts in response, causing the level to be higher or lower on the marked gauge, which is human-readable.
An oxygen sensor in a car’s emission control system detects the gasoline/oxygen ratio, usually through a chemical reaction that generates a voltage. A computer in the engine reads the voltage and, if the mixture is not optimal, readjusts the balance.
Motion sensors in various systems including home security lights, automatic doors and bathroom fixtures typically send out some type of energy, such as microwaves, ultrasonic waves or light beams and detect when the flow of energy is interrupted by something entering its path.
A photosensor detects the presence of visible light, infrared transmission (IR), and/or ultraviolet (UV) energy.
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applicationsof Wireless sensor network :
Sensors: Infrared, Sunlight, Radiation, Ultraviolet, color
• Optical sensors to detect human presence through the IR spectrum
are the most voted sensors in this area.
• Agriculture applications where the sun light, radiation and ultraviolet
sensors are required in order to measure the total amount of energy
and light which is absorbed by the plants.
Smart Parking: An Application of Optical Wireless Sensor Network
It is realized that this simple invention could be applied to monitor vehicles in a parking garage. The system can then inform drivers of the number of available parking spaces and in which area should they be directed to. This kind of system should avoid driver’s frustration in trying endlessly to find a parking space in a crowded parking garage.
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Arch . of WSN
1. Sensor network architecture
Most common architecture for WSN follows the OSI Model. Basically in sensor network we need
five layers: application layer, transport layer, network layer, data link layer and physical layer. Added to
the five layers are the three cross layers planes as shown in Fig. 1 [1].
CROSS LAYERS
The three cross planes or layers are; power management plane, mobility management plane and task
management plane. These layers are used to manage the network and make the sensors work together in
order to increase the overall efficiency of the network
1 ) Mobility management plane: detect sensor nodes movement. Node can keep track of neighbours
and power levels (for power balancing).
2) Task management plane: schedule the sensing tasks to a given area. Determine which nodes are
off and which ones are on.
WSN OSI layers
I. Transport layer:
⦁ The function of this layer is to provide reliability and congestion avoidance
where a lot of protocols designed to provide this function are either applied on the upstream
(user to sink, ex: ESRT, STCP and DSTN), or downstream (sink to user, ex: PSFQ and
GARUDA). These protocols use different mechanisms for loss detection ((ACK, NACK, and
Sequence number)) and loss recovery ((End to End or Hop by Hop)) [4, 5].
⦁ This layer is
specifically needed when a system is organised to access other networks.
The following are some popular protocols in this layer with brief description:
• STCP (Sensor Transmission Control Protocol)reliability, congestion detection and congestion avoidance. STCP function is applied on
the base station. The node sends a session initiation packet to the sink which contains
information about transmission rate, required reliability, data flow.
• PORT (Price-Oriented Reliable Transport Protocol) [4, 7]: downstream protocol; assure
that the sink receives enough information from the physical phenomena.
II. Network layer:
The major function of this layer is routing. This layer has a lot of challenges
depending on the application but apparently, the major challenges are in the power saving,
limited memory and buffers, sensor does not have a global ID and have to be self organized.
This is unlike computer networks with IP address and central device for controlling [1, 11].
The basic idea of the routing protocol is to define a reliable path and redundant paths according
to a certain scale called metric, which differs from protocol to protocol.
III. Data link layer:
Responsible for multiplexing data streams, data frame detection, MAC,
and error control, ensure reliability of point–point or point– multipoint. Errors or unreliability
comes from.
IV. Physical Layer [5]: Can provide an interface to transmit a stream of bits over physical
medium. Responsible for frequency selection, carrier frequency generation, signal detection,
Modulation and data encryption.
IEEE 802.15.4: proposed as standard for low rate personal area and WSN with low: cost,
complexity, power consumption, range of communication to maximize battery life. Use
CSMA/CA, support star and peer to peer topology. There are many versions of IEEE 802.15.4.
V. Application layer:
Responsible for traffic management and provide software for different
applications that translate the data in an understandable form or send queries to obtain certain
information. Sensor networks deployed in various applications in different fields, for example;
military, medical, environment, agriculture fields .
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Tools used For WSN
1 NS-2
NS-2 is the abbreviation of Network simulator version two, which first been developed by 1989 using as the REAL network simulator. Now, NS-2 is supported by Defense Advanced Research Projects Agency and National Science Foundation. NS-2 is a discrete event network simulator built in Object-Oriented extension of Tool Command Language and C++ [C++]. People can run NS-2 simulator on Linux Operating Systems or on Cygwin, shown in Figure 3, which is a Unix-like environment and command-line interface running on Windows. NS-2 is a popular non-specific network simulator can used in both wire and wireless area. This simulator is open source and provides online document.
2 . TOSSIM
It is an emulator specifically designed for WSN running on TinyOS, which is an open source operating system targeting embedded operating system. In 2003, TOSSIM was first developed by UC Berkeley’s TinyOS project team. TOSSIM is a bit-level discrete event network emulator built in Python[Python], a high-level programming language emphasizing code readability, and C++. People can run TOSSIM on Linux Operating Systems or on Cygwin on Windows. TOSSIM also provides open sources and online documents.
3 . EmStar
It is an emulator specifically designed for WSN built in C, and it was first developed by University of California, Los Angeles. EmStar is a trace-driven emulator [Girod04] running in real-time. People can run this emulator on Linux operating system. This emulator supports to develop WSN application on better hardware sensors. Besides libraries, tools and services, an extension of Linux microkernel is included in EmStar emulator.
4. OMNeT++
It is a discrete event network simulator built in C++. OMNeT++ provides both a noncommercial license, used at academic institutions or non-profit research organizations, and a commercial license, used at “for-profit” environments. This simulator supports module programming model. Users can run OMNeT++ simulator on Linux Operating Systems, Unix-like system and Windows. OMNeT++ is a popular non-specific network simulator, which can be used in both wire and wireless area. Most of frameworks and simulation models in OMNeT++ are open sources.
5 .J-Sim
IT is a discrete event network simulator built in Java. This simulator provides GUI library, which facilities users to model or compile the Mathematical Modeling Language, a “text-based language” written to J-Sim models. J-Sim provides open source models and online documents. This simulator is commonly used in physiology and biomedicine areas, but it also can be used in WSN simulation. In addition, J-Sim can simulate real-time processes.
6.ATEMU
is an emulator of an AVR processor for WSN built in C; AVR is a single chip microcontroller commonly used in the MICA platform. ATEMU provides GUI, Xatdb; people can use this GUI to run codes on sensor nodes, debug codes and monitor program executions. People can run ATEMU on Solaris and Linux operating system. ATEMU is a specific emulator for WSNs; it can support users to run TinyOS on MICA2 hardware. ATEMU can emulate not only the communication among the sensors, but also every instruction implemented in each sensor. This emulator provides open sources and online documents.
7. Avrora
Avrora is a simulator specifically designed for WSNs built in Java. Similar to ATEMU, Avrora can also simulate AVR-based microcontroller MICA2 sensor nodes. This simulator was developed by University of California, Los Angeles Compilers Group. Avrora provides a wide range of tools that can be used in simulating WSNs. This simulator combines the merits of TOSSIM and ATEMU, and limits their drawbacks. Avrora does not provide GUI. Avrora also supports energy consumption simulation. This simulator provides open sources and online documents. However, this simulator has some drawbacks. It does not have GUI. In addition, Avrora can not simulate network management algorithms because it does not provide network communication tools
Tolologies of WSN
A. Bus Topology
In this topology, there is a node send message to another node on
the network sends a broadcast message onto the network that all
other nodes see, but only the intended recipient actually accepts
and processes the message. Bus topology is easy to install but
congestion of traffic and single path communication. However,
bus networks work best with a limited number of nodes. If more
than a few dozen nodes are added to a network bus, performance
problems will likely result.
B. Tree Topology
The network use a central hub called a root node as the main
communication router. In the hierarchy, central hub is one level
below from the root node. This lower level forms a star network.
The tree network can be considered a hybrid of both the Star and
Peer to Peer networking topologies as shown in Fig
C. Star Topology
Star networks are connected to a centralized communication hub
(sink) and the nodes cannot communicate directly with each other.
The entire communication must be routed through the centralized
hub. Each node is then a “client” while the central hub is the
“server or sink” as shown in Fig. 2.3. But there is disadvantage
of single path communication.
Yang et al.[10] proposed Turb
D. Ring Topology
In a ring network, every node has exactly two neighbors for
communication purposes. All messages travel through a ring in
the same direction (either “clockwise” or “counterclockwise”). A
failure in node breaks the loop and can take down the entire network.
but congestion of traffic and double path communication.
E. Mesh Topology
Mesh topologies involve message can take any of several paths
from source to destination. (Recall that even in a ring, although
two paths exist, messages can only travel in one direction.) A mesh
network in which every node connects to every other is called a
full mesh and there is partial mesh networks also exist in which
some devices (nodes) connect only indirectly to others
F. Circular Topology
In this topology, there is a circular sensing area and that the sensing
area has a sink (at center). The sensor nodes sense the event of
interest and transmit these data to the sink. The nodes are randomly
deployed with uniform density all around the sink as shown in
Fig.2.6. Depending on the distance of a node from the sink and
the transmission range of the nodes, data have to traverse single
or multiple hops before being received by the sink. The circular
web topology is easy to establish, easy to maintain, and more
efficient [16].
G. Grid Topology
The sensor network field dividing into grids as shown in Fig 2.7.
The network area is partitioned into non-overlapping square grid
with same size. There should be at least one and only one node
in working state in each grid at any time.
In order to extend the network life time, the nodes in a grid should
work in turn. Inside each grid, one node is selected as a grid
head which is responsible for forwarding routing information and
transmitting data packets. Routing is performed in a grid-by- grid
manner. Grid-based multi-path routing protocol intended to route
packets fast, utilize and extend sensor nodes energy in addition
to avoiding and handling network congestion when happens in
the network
Different routing protocols in WSN:
Routing Protocols can be classified
Based on Mode of functioning and type of target applications into Proactive, Reactive and Hybrid.
Based on Participation style of the nodes into as Direct Communication, Flat and Clustering Protocols .
Depending on the Network Structure as Hierarchical, Data Centric and Location based
Proactive, Reactive and Hybrid
In a Proactive Protocol the nodes switch on their sensors and transmitters, sense the environment and transmit the data to a BS through the predefined route.
The Low Energy Adaptive Clustering hierarchy protocol (LEACH) utilizes this type of protocol.
In Reactive Protocol if there are sudden changes in the sensed attribute beyond some pre-determined threshold value, the nodes immediately react. This type of protocol is used in time critical applications
The Threshold sensitive Energy Efficient sensor Network(TEEN) is an example of a reactive protocol.
Hybrid Protocols Incorporate both Proactive and Reactive concepts.
They first compute all routes and then improve the routes at the time of routing.
Adaptive Periodic TEEN(APTEEN) is an example of Hybrid Protocols.
Direct Communication, Flat and Clustering Protocols
In Direct Communication Protocols, any node can send information to the BS directly.
When this is applied in a very large network, the energy of sensor nodes may be drained quickly.
Its scalability is very small.
SPIN is an example of this type of protocol.
In the case of Flat Protocols, if any node needs to transmit data, it first searches for a valid route to the BS and then transmits the data.
Nodes around the base station may drain their energy quickly.
Its scalability is average.
Rumor Routing is an example of this type of protocol.
According to the clustering protocol, the total area is divided into numbers of clusters.
Each and every cluster has a cluster head (CH) and this cluster head directly communicates with the BS.
All nodes in a cluster send their data to their corresponding Cluster Head.
The Threshold sensitive Energy Efficient sensor Network(TEEN) is an example of a clustering protocol.
Data Centric, Hierarchical and Location based
Data centric protocols
are query based and they depend on the naming of the desired data, thus it eliminates much redundant transmissions.
The BS sends queries to a certain area for information and waits for reply from the nodes of that particular region.
Depending on the query, sensors collect a particular data from the area of interest.
This particular information is only required to transmit to the BS and thus reducing the number of transmissions
SPIN was the first data centric protocol
Hierarchical routing
is used to perform energy efficient routing.
Higher energy nodes can be used to process and send the information and low energy nodes are used to perform the sensing in the area of interest
examples: LEACH, TEEN, APTEEN
Location based routing protocols
need some location information of the sensor nodes.
Location information can be obtained from GPS signals, received radio signal strength, ETC.
Using location information, an optimal path can be formed without using flooding techniques.
GEAR is an example of a location based routing protocol.
Infrastructure of WSN
⦁ The WSN is built of “nodes” – from a few to several hundreds or even thousands, where each node is connected to one (or sometimes several) sensors.
⦁ Each such sensor network node has typically several parts: a radio transceiver with an internal antenna or connection to an external antenna, a microcontroller, an electronic circuit for interfacing with the sensors and an energy source, usually a battery or an embedded form of energy harvesting. A sensor node might vary in size from that of a shoebox down to the size of a grain of dust, although functioning “motes” of genuine microscopic dimensions have yet to be created. The cost of The WSN is built of “nodes” – from a few to several hundreds or even thousands, where each node is connected to one (or sometimes several) sensors. Each such sensor network node has typically several parts: a radio transceiver with an internal antenna or connection to an external antenna, a microcontroller, an electronic circuit for interfacing with the sensors and an energy source, usually a battery or an embedded form of energy harvesting. A sensor node might vary in size from that of a shoebox down to the size of a grain of dust, although functioning “motes” of genuine microscopic dimensions have yet to be created. The cost of sensor nodes is similarly variable, ranging from a few to hundreds of dollars, depending on the complexity of the individual sensor nodes. Size and cost constraints on sensor nodes result in corresponding constraints on resources such as energy, memory, computational speed and communications bandwidth. The topology of the WSNs can vary from a simple star network to an advanced multi-hop wireless mesh network. The propagation technique between the hops of the network can be routing or flooding.[2][3]sensor nodes is similarly variable, ranging from a few to hundreds of dollars, depending on the complexity of the individual sensor nodes.
⦁ Size and cost constraints on sensor nodes result in corresponding constraints on resources such as energy, memory, computational speed and communications bandwidth. The topology of the WSNs can vary from a simple star network to an advanced multi-hop wireless mesh network. The propagation technique between the hops of the network can be routing or flooding.
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