Wireless Sensor Networks UNIT-2 Find More Materials at: https://www.slideshare.net/Easyn/edit_my_uploads https://easyninspire.blogspot.com/ YouTube link: https://www.youtube.com/channel/UC_fItK7wBO6zdWHVPIYV8dQ?view_as=subscriber

1. WIRELESS SENSORWIRELESS SENSOR
NETWORKS
UNIT 2
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WIRELESS SENSOR
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2. UNIT-2
Networking Technologies
 Physical layer and transceiver design considerations in WSNs:
Physical layer: The functions and components of a sensor node that mediate between the transmission and
reception of wireless signals and processing of data, including the higher – level protocol processing.
 The physical (PHY) layer is responsible for the conversion of bit streams into signals that are best
suited for communication across the wireless channel.
 It provides an overview of RF communication, which is most frequently used in WSNs.
 The main concern of the physical layer is modulation and demodulation of digital data, i.e.
transmission and reception of the data.
 The physical layer in wireless networked sensors has to be designed with sensor networking
requirements in mind.
 In particular, The Communication device must be containable in a small size, since the sensor
nodes are small.
 So cheaper, slightly larger antennas may be acceptable in those cases. The Communication devices
must be cheap, since the sensors will be used in large numbers in redundant fashion
For all the above reasons, the physical layer cannot be too complex. Therefore, the nature and complexity
of the physical layer processing is an important consideration in selecting a physical layer technology for
wireless networked sensors
Important parameters which are to be considered while designing Physical layer in wireless sensor
networks are (i.e. Design considerations)
1. Low Power Consumption
2. Error free transmission
3. Low Transmission and Reception range
4. Interference from other systems, working in the same band.
5. Low complexity.
6. Low duty cycle, i.e. most of the time sensor nodes are switched off.
7. Low data rates most of the time and high data rate only for a short period of time.
8. Routing between nodes
9. Modulation schemes (The most common form of modulation is the band pass modulation)
The physical layer is mostly concerned with modulation and demodulation of digital data; this task is
carried out by so-called transceivers. In sensor networks, the challenge is to find modulation schemes and
transceiver architectures that are simple, low cost, but still robust enough to provide the desired service. In
this section, we discuss some of the implications of these requirements
1. Energy usage profile
2. Choice of modulation scheme
3. Antenna considerations

3. 1. Energy usage profile:
 The choices of a small transmit power leads to an energy consumption profile different from other
wireless devices like cell phones.
 If the radiated energy is small, transceiver consumes much more energy than is actually radiated.
 It is even possible that reception requires more power than transmission depending on the
transceiver architecture
 The idle mode’s power consumption can be less or in the same range as the receive power.
 To reduce average power consumption in a low-traffic wireless sensor network, keeping the
transceiver in idle mode all the time would consume significant amounts of energy.
2. Choice of modulation scheme:
 A crucial point is the choice of modulation scheme. Several factors have to be balanced here.
 They are required and desirable data rate, symbol rate, the implementation complexity, the
relationship between radiated power and target BER
 A second important observation is that the power consumption of a modulation scheme depends
much more on the symbol rate than on the data rate
 Obviously, the desire for “high” data rates at “low” symbol rates calls for m-ary modulation scheme
3. Antenna considerations:
 The desired small form factor of the overall sensor nodes restricts the size and the number of
antennas
 If the antenna is much smaller than the carrier’s wavelength, it is hard to achieve good antenna
efficiency so one must spend more transmit energy to obtain the same radiated energy.
 Secondly, with small sensor node cases, it will be hard to place two antennas with suitable distance
to achieve receive diversity.
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 PAN (PERSONAL AREA NETWORK):
o The communication network established for the purpose of connecting computer devices of
personal use is known as the personal area network PAN.
o When a network is established by connecting phone lines to PDAs (Personal Digital Assistants),
this communication is known as PAN
o PANs can be wired (USB or FireWire) or wireless
o Wireless Personal Area Network (WPAN) can perform really efficient operations if we connect
them with specialized devices.
o The range of a PAN typically is a few meters. PAN often covers an area of 30 feet.
o Examples of wireless PAN, or WPAN, devices include
* cell phone headsets, * wireless keyboards,
* wireless mic, * printers,
* bar code scanners and * game consoles.

4. o The basic purpose of establishing PAN (Personal Area Network) is providing a communication
channel to the individuals, who want to carry their own digital devices.
o However at the same time they want to stay in contact with the network.
o Personal computer devices may include palm tops mobile phones, potable media players,
play stations and net books.
o There are many wireless technologies which are helpful in developing wireless personal area
network.
 Blue tooth wireless PAN
 ZigBee
 Ultra-Wide Band(UWB)
 Wi-Fi or WiMAX
Wired PAN
Wireless digital devices work twenty four hours a day and seven days a week. This enables you to
stay in communication circle always.
PAN (Personal Area Network) network has enabled the transfer of data within the small geographical
areas with the help of many small and portable carrying devices.
Wireless PAN
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5.  PAN Topologies:
The arrangement of a network which comprises of nodes and connecting lines via sender and receiver
is referred as network topology.
The various network topologies are:
1. Bus topology
2. Star topology
3. Ring topology
4. Tree topology
5. Mesh topology
1. Bus topology:
Bus topology is a network type in which every computer and network device is connected to single
cable. When it has exactly two endpoints, then it is called Linear Bus topology.
Advantages of this topology:
 If N devices are connected to each other in bus topology, then the number of cables required to
connect them is 1 which is known as backbone cable and N drop lines are required.
 Cost of the cable is less as compared to other topology, but it is used to build small networks.
Problems with this topology:
 If the common cable fails, then the whole system will crash down.
 If the network traffic is heavy, it increases collisions in the network. To avoid this, various protocols
are used
2. Star topology:
All the devices are connected to a single hub through a cable. This hub is the central node and all
others nodes are connected to the central node.
Advantages of this topology:
 If N devices are connected to each other in star topology, then the number of cables required to
connect them is N. So, it is easy to set up.

6.  Each device requires only 1 port i.e. to connect to the hub.
Problems with this topology:
 If the concentrator (hub) on which the whole topology relies fails, the whole system will crash down.
 Cost of installation is high.
 Performance is based on the single concentrator i.e. hub.
3. Ring topology:
 In this topology, it forms a ring connecting devices with its exactly two neighbouring devices.
 A number of repeaters are used for Ring topology with large number of nodes, because if someone
wants to send some data to the last node in the ring topology with 10 nodes, then the data will have to
pass through 9 nodes to reach the 10th node.
 Hence to prevent data loss repeaters are used in the network
 The transmission is unidirectional, but it can be made bidirectional by having 2 connections between
each Network Node, it is called Dual Ring Topology
Advantages of this topology:
 The possibility of collision is minimum in this type of topology.
 Cheap to install and expand.
Problems with this topology:
 Troubleshooting is difficult in this topology.
 Addition of stations in between or removal of stations can disturb the whole topology.
4. Tree topology:
It has a root node and all other nodes are connected to it forming a hierarchy. It is also called
hierarchical topology. It should at least have three levels to the hierarchy.

7. Advantages of Tree Topology:
 Expansion of nodes is possible and easy.
 Easily managed and maintained.
 Error detection is easily done.
Disadvantages of Tree Topology:
 Heavily cabled.
 If more nodes are added maintenance is difficult.
 Central hub fails, network fails.
5. Mesh Topology:
In mesh topology, every device is connected to another device via particular channel.
It is also called as complete topology
If suppose, N number of devices are connected with each other in mesh topology, then total
number of ports that is required by each device is N-1.
Advantages of Mesh Topology:
 Each connection can carry its own data load.
 It is robust.
 Fault is diagnosed easily
 Provides security and privacy
Disadvantages of Mesh Topology:
 Installation and configuration is difficult.
 Cabling cost is more.
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 Hidden node and Exposed node Problem:
In WSN, to exchange data two exchange control frames are used before transmitting data
1. Request to Send(RTS)
2. Clear to Send(CTS)
These control frames duty includes
 If sender sees CTS, transmits data.
 If other node sees CTS, will idle for specified period.
 If other node sees RTS but not CTS, free to send

8. Hidden node problem:
In wireless networking, the hidden node problem or hidden terminal problem occurs when a node is visible
to a wireless access point (AP) or hub, but not to other nodes while communicating with that hub. This
leads to difficulties in media access control sub layer. (or)
The hidden terminal problem is a transmission problem that arises when two or more stations who are out
of range of each other transmit simultaneously to a common recipient.
Consider, a node A is from the access point range and another node C from outside of the range want to
send the data to a same node B. There occur collision between A and C
Because the transmission range of A reaches B but not C. Similarly, the range of C reaches B but not A.
Also the range of B reaches both A and C.
To solve the hidden node problem, the 802.11 MAC protocol includes an optional channel reservation
scheme to help avoid collisions. This scheme is implemented through a technique using the four-way
handshake.
Another way to solve hidden node problem is by using RTS/CTS signals
We can observe that transmitters T1 and T2 can’t see each other, both send to receiver R.
Then RTS/CTS can help
 Both T1 and T2 would send RTS that R would see first.
 R only responds with one CTS (say, for T1’s RTS).
 T2 detects that CTS doesn’t match and won’t send.
 Because, the T2 node postpones the transmission to R until it detects the medium to be free.
 Then only one transmission (from T1 to R) occurs without any collision.

9. Exposed node Problem:
In wireless networks, the exposed node problem occurs when a node is prevented from sending packets to
other nodes because of a neighbouring transmitter. The exposed node problem is not an issue in cellular
networks as the power and distance between cells is controlled to avoid it.
 Consider the below wireless network having four nodes labelled A, B, C, and D, where the two
receivers (A, D) are out of range of each other
 But the two transmitters (B, C) in the middle are in the same range of each other.
 Here, if a transmission between A and B is taking place, then node C is prevented from transmitting
to D because it is effected by the transmission of B. (both B and C share same media to transmit the
data)
 However note that node D could still receive the transmission of C without interference because it is
out of range from B.
 This problem is solved by,
We can observe that T1 sending to R1, T2 wants to send to R2. Then RTS/CTS signals can help
 T2 hears RTS from T1, but not CTS from R1 ( i.e. R1 is not ready to receive)
 Now T2 knows that its transmission will not interfere at T1’s receiver then it can transmit the data to
R2 node.
 T2 is safe to transmit to R2.
Similarly
If T1 hears CTS from R1 then it sends data to R1 only after checking T2 transmission.
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10.  WANET:
Wireless ad hoc network (WANET) is a decentralized technology designed for the establishment of a
network anywhere and anytime without any fixed infrastructure to support the mobility of the users in the
network.
The network is ad-hoc because each node is willing to forward data for other nodes.
Wireless ad-hoc networks can be further classified by their application:
1. Mobile ad hoc networks (MANETs): MANET is a continuously self-configuring, infrastructure-less
network of mobile devices connected without wires.
2. Vehicular ad hoc networks (VANETs): VANETs are used for communication between vehicles and
roadside equipment.
3. Intelligent vehicular ad hoc networks: Intelligent VANETs are a kind of artificial intelligence networks
that helps vehicles to behave in intelligent manners during vehicle-to-vehicle collisions, accidents. Vehicles
are using radio waves to communicate with each other.
4. Smart-Phone Ad-hoc networks (SPANs): SPANs influence the existing hardware (primarily Bluetooth
and Wi-Fi) in commercially available smart phones to create networks without depending on cellular
carrier networks, wireless access points, or traditional network infrastructure.
5. Internet-based Mobile Ad-hoc networks (iMANETs): iMANETs are ad hoc networks that link mobile
nodes and fixed Internet-gateway nodes
In computer networking, an ad hoc network refers to a network connection established for a single session
and does not require a router or a wireless base station.
For example, if you need to transfer a file to your friend's laptop, you might create an ad hoc network
between your computer and his laptop to transfer the file.
.
Here are the key features:
 Infrastructure-less, self-configuring, self-forming, self-healing network
 Nodes are static, network is connected (exist end-to-end path)
 Transmission through multiple hops
 The decentralized nature improves the scalability.

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 MANET:
MANET stands for Mobile adhoc Network also called as wireless adhoc network or adhoc wireless
network that usually has a routable networking environment on top of a Link Layer ad hoc network. They
consist of set of mobile nodes connected wirelessly in a self configured, self healing network without
having a fixed infrastructure.
MANET nodes are free to move randomly as the network topology changes frequently.
Each node behaves as a router as they forward traffic to other specified node in the network.
Here are the key features:
 A highly dynamic, autonomous topology
 The primary challenge in building a MANET is equipping each device to continuously maintain the
information required to properly route traffic.
The ad hoc routing protocol for MANET can be classified as:
 Table-driven (proactive) routing
 On-demand (reactive) routing
 Hybrid (both proactive and reactive) routing
Characteristics of MANET:
 Dynamic Topologies: Network topology which is typically multichip may change randomly and
rapidly with time, it can form unidirectional or bi-directional links.
 Bandwidth constrained, variable capacity links: Wireless links usually have lower reliability,
efficiency, stability and capacity as compared to wired network. The throughput of wireless
communication is even less than a radio’s maximum transmission rate after dealing with the
constraints like multiple access, noise, interference conditions, etc.
 Autonomous Behaviour: Each node can act as a host and router, which shows its autonomous
behaviour.

12.  Energy Constrained Operation: As some or all the nodes rely on batteries or other exhaustible means
for their energy. Mobile nodes are characterized with less memory, power and light weight features.
 Limited Security: Wireless network are more prone to security threats. A centralized firewall is
absent due to its distributed nature of operation for security, routing and host configuration.
 Less Human Intervention: They require minimum human intervention to configure the network;
therefore they are dynamically autonomous in nature.
Pros and Cons of MANET –
Pros:
1. Seperation from central network administration.
2. Each nodes can play both the roles i.e. if router and host showing autonomous nature.
3. Self configuring and self healing nodes, does not require human intervention.
Cons:
1. Resources are limited due to various constraints like noise, interference conditions, etc.
2. Lack of authorization facilities.
3. More prone to attacks due to limited physical security.
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13. Easy n Inspire…..
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