WC Paper IMP

Seat No.:

Enrolment No.

GUJARAT TECHNOLOGICAL UNIVERSITY

BE - SEMESTER–VII (NEW) EXAMINATION – WINTER 2021

Subject Code:3171608

Date:10/12/2021

Subject Name: Wireless Communication

Time: 10:30 AM TO 01:00 PM

Instructions:

Total Marks: 70

1. Attempt all questions.

2. Make suitable assumptions wherever necessary.

3. Figures to the right indicate full marks.

4. Simple and non-programmable scientific calculators are allowed.

MARKS

03

What is Wireless Communication? Also Explain the Types of Wireless

Communication.

Q.1 (a)

Wireless communication refers to the exchange of data or information

between devices or machines without the use of physical connections such

as cables or wires. Instead, wireless communication relies on

electromagnetic waves or signals to transmit data over the air.

There are several types of wireless communication technologies, including:

1. Radio frequency (RF) communication

2. Infrared (IR) communication

3. Bluetooth

4. Wi-Fi

5. Satellite communication

6. Cellular communication

7. Near field communication (NFC)

Explain the Difference between Wired and Wireless

Communication.

(b)

04

Wired Communication

Wireless Communication

Physical

connection

Requires a physical

connection such as a cable connection

Does not require a physical

or wire

Range

Limited by the length of

the physical connection

Can transmit data over

longer distances using

electromagnetic waves or

signals

Speed

Generally faster than

wireless communication

May be slower than wired

communication, depending

on the technology used

May be less secure as data

is transmitted over the air

and can potentially be

intercepted

Security

Generally more secure as

data is transmitted over a

physical connection

Flexibility

Limited in terms of

placement and movement in terms of placement and

Allows for greater flexibility

of devices

movement of devices

Interference

Less likely to be affected

May be more prone to

by interference from other interference from other

devices or sources

May be cheaper to install

and maintain

devices or sources

May be more expensive to

install and maintain

Cost

Explain the Evolution of Mobile Communication.

(c)

07

The evolution of mobile communication has occurred in several stages over

the past several decades:

1. First generation (1G): The first generation of mobile communication,

also known as analog cellular, was introduced in the 1980s. 1G

networks used analog signals to transmit voice and basic data services

such as text messaging.

2. Second generation (2G): The second generation of mobile

communication, also known as digital cellular, was introduced in the

1990s. 2G networks used digital signals to transmit voice and data

services, including the ability to send and receive text messages,

access the Internet, and make phone calls over the Internet (VoIP).

3. Third generation (3G): The third generation of mobile communication,

also known as broadband cellular, was introduced in the early 2000s.

3G networks provided faster data speeds and the ability to access more

advanced data services such as streaming video and audio.

4. Fourth generation (4G): The fourth generation of mobile

communication, also known as LTE (Long-Term Evolution), was

introduced in the late 2000s. 4G networks provided even faster data

speeds and the ability to access high-definition video and other

advanced data services.

5. Fifth generation (5G): The fifth generation of mobile communication,

also known as 5G, was introduced in the 2010s. 5G networks provide

ultra-high data speeds and low latency, making it possible to access

even more advanced data services such as virtual and augmented

reality.

Each new generation of mobile communication has brought significant

improvements in terms of data speeds and the types of services that can be

accessed, enabling the proliferation of mobile devices and the widespread

use of mobile communication for both personal and business purposes.

Q.2 (a) What is Wi-Fi?

Wi-Fi (Wireless Fidelity) is a wireless networking technology that allows

03

devices to connect to the Internet or to other devices through a wireless

network. It operates in the 2.4 GHz and 5 GHz frequency bands and uses

radio waves to transmit data over short distances. Wi-Fi enables devices

such as computers, smartphones, and tablets to connect to the Internet and

exchange data without the need for physical cables or wires. Wi-Fi is

commonly used in home and office networks, as well as in public places

such as cafes, airports, and hotels. It has become an essential part of modern

communication and has greatly facilitated the use of the Internet and other

online services.

(b) Explain the CSMA Protocols in Detail.

04

CSMA (Carrier Sense Multiple Access) is a type of protocol used in

wireless and Ethernet networks to enable multiple devices to share the same

communication channel and access the network efficiently. CSMA protocols

allow devices to detect when the channel is in use and to avoid transmitting

data at the same time, reducing the risk of data collision and improving the

overall performance of the network.

There are several different types of CSMA protocols, including:

1. CSMA/CD (Collision Detection): This is the most common type of

CSMA protocol and is used in Ethernet networks. When a device

wants to transmit data, it first listens to the channel to see if it is in

use. If the channel is free, the device begins transmitting. If another

device starts transmitting at the same time, a collision occurs and both

devices stop transmitting. The devices then wait a random amount of

time before trying to transmit again.

2. CSMA/CA (Collision Avoidance): This type of CSMA protocol is

used in wireless networks. Like CSMA/CD, CSMA/CA allows

devices to listen to the channel before transmitting. However, instead

of simply waiting a random amount of time before retrying, the device

sends a request to transmit (RTS) message to the receiving device,

which responds with a clear to send (CTS) message. This allows the

devices to coordinate their transmissions and avoid collisions.

3. CSMA/CA with ACK (Acknowledgment): This is a variant of

CSMA/CA that includes an additional step to ensure that the data was

received successfully. After transmitting the data, the transmitting

device waits for an acknowledgement (ACK) message from the

receiving device before ending the transmission. If the ACK message

is not received, the transmitting device assumes that the transmission

was not successful and retries the transmission.

CSMA protocols help to improve the efficiency and reliability of wireless

and Ethernet networks by enabling multiple devices to share the same

communication channel without interfering with each other.

(c) Write a Short notes.1) TDMA 2) CDMA

07

TDMA (Time Division Multiple Access) is a multiplexing technique used in

digital communication systems to allow multiple devices to share the same

frequency spectrum. It works by dividing the channel into different time

slots and assigning each device a specific time slot in which it can transmit

data. This allows multiple devices to transmit simultaneously without

interfering with each other. TDMA is commonly used in 2G and 3G mobile

communication systems. It is an efficient way to increase the capacity of a

communication system by allowing multiple devices to share the same

frequency band. TDMA works by dividing the channel into time slots, with

each device assigned a specific time slot in which it can transmit data. This

allows multiple devices to transmit simultaneously without interfering with

each other. TDMA is a popular choice for mobile communication systems

because it is relatively simple to implement and can provide good

performance in a variety of environments.

CDMA (Code Division Multiple Access) is a multiplexing technique used in

digital communication systems to allow multiple devices to share the same

frequency spectrum. It works by assigning each device a unique code that is

used to spread the data signal over a wide frequency band. This allows

multiple devices to transmit simultaneously without interfering with each

other. CDMA is commonly used in 3G and 4G mobile communication

systems, as well as in some types of wireless networking. It is an efficient

way to increase the capacity of a communication system by allowing

multiple devices to share the same frequency band. CDMA works by

assigning each device a unique code that is used to spread the data signal

over a wide frequency band. This allows multiple devices to transmit

simultaneously without interfering with each other. CDMA is a popular

choice for mobile communication systems because it can provide good

performance in a variety of environments and has the ability to support a

large number of users in a single frequency band.

OR

(c) Write a Short notes.1) FDMA 2) OFDM

07

1. FDMA (Frequency Division Multiple Access): FDMA is a

multiplexing technique used in digital communication systems to

allow multiple devices to share the same frequency spectrum by

dividing the frequency band into different channels and assigning each

device a specific channel. This allows multiple devices to transmit

simultaneously without interfering with each other. FDMA is

commonly used in analog communication systems, such as AM and

FM radio, as well as in some types of digital communication systems.

2. OFDM (Orthogonal Frequency Division Multiplexing): OFDM is a

multiplexing technique used in digital communication systems to

allow multiple devices to share the same frequency spectrum by

dividing the frequency band into multiple subcarriers and assigning

each device a specific subcarrier. OFDM is commonly used in

wireless networking and broadband communication systems, such as

Wi-Fi and digital TV. It is an efficient way to increase the capacity of

a communication system by allowing multiple devices to transmit

simultaneously without interfering with each other. OFDM is

particularly useful in environments with high levels of interference, as

it is less susceptible to interference than other multiplexing

techniques.

Q.3 (a) Explain the Wireless Protocol.

03

A wireless protocol is a set of rules and standards that govern how devices

communicate with each other over a wireless network. Wireless protocols

specify the technical details of how devices transmit and receive data,

including the type of wireless technology used, the frequency bands and

channels used for communication, and the data rates and transmission

ranges supported.

There are several different types of wireless protocols, including:

1. IEEE 802.11: This is a family of wireless networking protocols that is

commonly used for Wi-Fi networks. It includes several different

versions, such as 802.11b, 802.11g, and 802.11n, which define the

technical details of how the Wi-Fi network operates and the features

and capabilities of the network.

2. Bluetooth: This is a wireless protocol that is commonly used for short-

range communication between devices such as headphones, speakers,

and personal devices. Bluetooth uses a low-power radio frequency to

transmit data over short distances and can be used to connect devices

without the need for physical cables or wires.

3. Zigbee: This is a wireless protocol that is commonly used for low-

power, low-data-rate communication between devices such as sensors,

smart home devices, and industrial automation systems. Zigbee uses a

low-power radio frequency to transmit data over short distances and is

designed to be energy-efficient.

4. Cellular: This is a wireless protocol that is used for mobile

communication and data transfer over long distances. Cellular

communication uses a network of cell towers and antennas to transmit

data and is commonly used for mobile phone communication and

mobile data transfer.

(b) What is Soft Handoff in Wireless Systems?

04

Soft handoff is a process used in wireless communication systems to

improve the continuity of service and the quality of communication when a

mobile device moves between cells or coverage areas. In a soft handoff, the

mobile device maintains a connection to multiple cells or base stations at the

same time, allowing it to seamlessly switch between them as it moves

around.

The process of soft handoff involves several steps:

1. The mobile device establishes a connection with a base station or cell

and begins transmitting and receiving data.

2. As the mobile device moves out of the coverage area of the initial cell,

it begins to establish a connection with a new base station or cell.

3. The mobile device maintains both connections simultaneously,

allowing it to continue transmitting and receiving data without

interruption.

4. As the mobile device moves closer to the new cell, the connection

with the initial cell is gradually phased out, and the connection with

the new cell becomes stronger.

5. When the connection with the initial cell is completely terminated, the

mobile device is fully connected to the new cell and continues to

transmit and receive data.

Soft handoff helps to improve the continuity of service and the quality of

communication for mobile devices, as it allows them to maintain a

connection even when they are moving between cells or coverage areas. It is

an important feature of modern wireless communication systems and is used

to provide reliable and seamless communication for users.

Explain the GSM Architecture.

GSM (Global System for Mobile Communications) is a widely-used mobile

communication system that provides voice and data services to mobile

devices. The GSM architecture consists of several different components,

including:

1. Mobile station (MS): This is the mobile device that is used by the user

to access the GSM network. It includes a SIM (Subscriber Identity

Module) card, which stores the user's subscription information and

enables the device to connect to the GSM network.

2. Base station subsystem (BSS): This includes the base transceiver

stations (BTS) and the base station controllers (BSC) that are used to

transmit and receive signals between the mobile devices and the

network. The BTS is

(c) Explain the GSM Architecture.

07

GSM (Global System for Mobile Communications) is a widely-used mobile

communication system that provides voice and data services to mobile

devices. The GSM architecture consists of several different components,

including:

1. Mobile station (MS): This is the mobile device that is used by the user

to access the GSM network. It includes a SIM (Subscriber Identity

Module) card, which stores the user's subscription information and

enables the device to connect to the GSM network.

2. Base station subsystem (BSS): This includes the base transceiver

stations (BTS) and the base station controllers (BSC) that are used to

transmit and receive signals between the mobile devices and the

network. The BTS is responsible for transmitting and receiving signals

to and from the mobile devices within its coverage area, while the

BSC is responsible for managing the BTS and coordinating

communication between the mobile devices and the network.

3. Network and Switching Subsystem (NSS): This includes the mobile

switching center (MSC) and the home location register (HLR), which

are responsible for switching calls and providing services to the

mobile devices. The MSC is responsible for routing calls and

messages between the mobile devices and the rest of the network,

while the HLR stores the subscription and location information for

each mobile device.

4. Operation and Support Subsystem (OSS): This includes the various

systems and processes that are used to support and maintain the GSM

network, including the authentication center (AUC), the equipment

identity register (EIR), and the billing systems. The AUC is

responsible for verifying the authenticity of the SIM card and the

mobile device, while the EIR is used to track and manage the

equipment used in the network. The billing systems are used to track

and charge for the use of the network and the services provided by the

network.

Overall, the GSM architecture is designed to provide reliable and efficient

communication services to mobile devices and to support the various

functions and processes required to operate the network. It has become the

dominant mobile communication system in many parts of the world and has

been the foundation for the development of many other mobile

communication systems.

OR

Q.3 (a) Explain the Difference LAN and WLAN.

03

Feature

LAN

WLAN

A wireless version of a LAN,

which connects devices in a

local area using wireless

technology

A network that connects

devices in a local area, such

as an office or home

Definition

Connection type

Coverage area

Maximum

distance

Data transfer

rate

Physical cables

Limited to the local area

Wireless

Limited to the local area

Typically up to 100 meters

Faster than WLAN

Typically up to 100 meters

Slower than LAN

Generally more secure than Generally, less secure than

Security

Cost

WLAN

LAN

Generally cheaper than

WLAN

Generally, more expensive

than LAN

Computers, printers,

routers,

Computers, smartphones,

tablets,

Examples of

devices

printers, routers, switches,

hubs

switches, hubs

(b) Explain the Indoor and outdoor propagation models.

04

Propagation models are mathematical models that are used to predict the

behavior of electromagnetic waves as they propagate through different

environments. They are used to understand how the signal strength and

quality of a wireless communication system may be affected by the

characteristics of the environment, including the type of materials and

objects present, the distance between the transmitter and receiver, and the

presence of any obstacles or reflections.

There are two main types of propagation models: indoor and outdoor.

Indoor propagation models are used to predict the behavior of

electromagnetic waves as they propagate through indoor environments, such

as buildings and homes. These models take into account the characteristics

of the materials and objects present in the indoor environment, such as

walls, floors, and furniture, as well as the presence of any obstacles or

reflections. Indoor propagation models are useful for understanding how the

signal strength and quality of a wireless communication system may be

affected by the layout and materials of the indoor environment.

Outdoor propagation models are used to predict the behavior of

electromagnetic waves as they propagate through outdoor environments,

such as streets, fields, and forests. These models take into account the

characteristics of the terrain and the atmosphere, as well as the presence of

any obstacles or reflections. Outdoor propagation models are useful for

understanding how the signal strength and quality of a wireless

communication system may be affected by the terrain and atmospheric

conditions of the outdoor environment.

(c) Explain the GPRS Architecture.

07

GPRS (General Packet Radio Service) is a wireless communication system

that provides data transfer and internet access for mobile devices. It is an

evolution of the GSM (Global System for Mobile Communications) system

and is designed to support higher data rates and more efficient data transfer.

The GPRS architecture consists of several different components, including:

1. Mobile station (MS): This is the mobile device that is used by the user

to access the GPRS network. It includes a SIM (Subscriber Identity

Module) card, which stores the user's subscription information and

enables the device to connect to the GPRS network.

2. Base station subsystem (BSS): This includes the base transceiver

stations (BTS) and the base station controllers (BSC) that are used to

transmit and receive signals between the mobile devices and the

network. The BTS is responsible for transmitting and receiving signals

to and from the mobile devices within its coverage area, while the

BSC is responsible for managing the BTS and coordinating

communication between the mobile devices and the network.

3. Network and Switching Subsystem (NSS): This includes the mobile

switching center (MSC) and the home location register (HLR), which

are responsible for switching calls and providing services to the

mobile devices. The MSC is responsible for routing calls and

messages between the mobile devices and the rest of the network,

while the HLR stores the subscription and location information for

each mobile device.

4. Gateway GPRS Support Node (GGSN): This is a network element

that connects the GPRS network to other networks, such as the

internet. It is responsible for routing data packets between the GPRS

network and the other networks and for translating between different

protocols.

5. Serving GPRS Support Node (SGSN): This is a network element that

is responsible for managing the connection between the mobile

devices and the GPRS network. It is responsible for tracking the

location of the mobile devices, maintaining the connection with the

mobile devices, and routing data packets between the mobile devices

and the GPRS network.

Explain the CDMA features. (Any Four)

Q.4 (a)

03

1. Multiple Access: CDMA (Code Division Multiple Access) is a

multiple access technique that allows multiple devices to share the

same frequency spectrum by assigning each device a unique code.

This allows multiple devices to transmit simultaneously without

interfering with each other.

2. Spread Spectrum: CDMA uses spread spectrum technology to spread

the data signal over a wide frequency band. This helps to reduce

interference and improve the capacity of the communication system.

3. Interference Rejection: CDMA uses advanced algorithms to reject

interference and noise, which helps to improve the quality and

reliability of the communication system.

4. Multiple User Detection: CDMA is able to detect and separate

multiple users transmitting on the same frequency, allowing them to

communicate simultaneously without interference.

5. Power Control: CDMA uses power control algorithms to adjust the

power of the transmitted signal in order to optimize the use of the

available frequency spectrum and reduce interference.

6. Handoff: CDMA supports seamless handoff between cells, allowing

mobile devices to move between coverage areas without interrupting

their communication.

(b) Write Short Note: ZigBee Networks

04

ZigBee is a wireless communication protocol that is designed for low-

power, low-data-rate communication between devices such as sensors, smart

home devices, and industrial automation systems. It uses a low-power radio

frequency to transmit data over short distances and is designed to be energy-

efficient.

ZigBee networks are self-organizing and self-healing, which means that

they can automatically adjust to changes in the network environment and

recover from disruptions. They are also highly scalable, allowing them to

support a large number of devices on a single network.

ZigBee supports a variety of networking topologies, including star, tree, and

mesh, which allows it to be used in a variety of different applications and

environments. It is also interoperable with other wireless technologies, such

as Wi-Fi and Bluetooth, which allows it to be used in conjunction with these

technologies in a variety of different applications.

Overall, ZigBee is a widely-used wireless communication protocol that is

known for its low power consumption, low data rates, and reliability. It is an

important technology in the Internet of Things (IoT) and is used in a variety

of applications, including smart home systems, industrial automation, and

environmental monitoring.

(c) Explain the Authentication and security in GSM

07

Authentication and security are important aspects of the GSM (Global

System for Mobile Communications) mobile communication system. GSM

uses several different mechanisms to authenticate users and protect the

confidentiality and integrity of communication over the network.

Authentication:

1. SIM (Subscriber Identity Module) card: The SIM card is a small smart

card that is inserted into the mobile device and stores the user's

subscription information. It is used to authenticate the user and

authorize access to the network.

2. Authentication center (AUC): The AUC is a network element that is

responsible for verifying the authenticity of the SIM card and the

mobile device. It uses a secret key that is stored on the SIM card and

shared between the mobile device and the AUC to authenticate the

user.

Security:

1. Encryption: GSM uses encryption to protect the confidentiality of

communication over the network. It uses a variety of encryption

algorithms, such as A5/1 and A5/3, to encode the data transmitted

over the network.

2. Integrity protection: GSM uses integrity protection mechanisms to

ensure the integrity of the data transmitted over the network. It uses a

variety of techniques, such as message authentication codes (MACs)

and cyclic redundancy checks (CRCs), to detect and prevent the

tampering of data.

3. Access control: GSM uses access control mechanisms to restrict

access to the network and to prevent unauthorized use. It uses a

variety of techniques, such as subscription-based access and network-

based access control, to ensure that only authorized users can access

the network.

OR

Q.4 (a) Write Short Note: Hand Over

03

Handover, also known as handoff, is a process that is used in wireless

communication systems to transfer a connection from one cell or base

station to another as a mobile device moves around. It is an important

feature of modern wireless communication systems, as it allows mobile

devices to maintain a connection even when they are moving between cells

or coverage areas.

There are two main types of handover:

1. Hard handover: This is a process in which the connection with the

current cell or base station is terminated before a connection is

established with a new cell or base station. Hard handover is generally

used in systems with low mobility, as it requires a strong and stable

connection to be established with the new cell before the connection

with the old cell is terminated.

2. Soft handover: This is a process in which the connection with the

current cell or base station is maintained while a connection is

established with a new cell or base station. Soft handover allows the

mobile device to maintain a connection with both cells or base stations

simultaneously, allowing it to seamlessly switch between them as it

moves around. Soft handover is generally used in systems with high

mobility, as it allows the mobile device to maintain a connection even

when it is moving between cells or coverage areas.

(b) Explain the Security issues and challenges in a Wireless network.

04

Wireless networks present a number of security issues and challenges that

must be addressed in order to protect against unauthorized access and ensure

the confidentiality and integrity of the communication. Some of the main

security issues and challenges in a wireless network include:

1. Unauthorized access: Wireless networks are vulnerable to

unauthorized access, as they use wireless signals that can be

intercepted and accessed by anyone with a wireless device within

range. This can lead to unauthorized users gaining access to the

network and potentially compromising its security.

2. Eavesdropping: Wireless networks are vulnerable to eavesdropping, as

the wireless signals can be intercepted and monitored by anyone with

the right equipment. This can lead to the confidentiality of

communication being compromised, as the intercepted data may be

sensitive or confidential.

3. Man-in-the-middle attacks: Wireless networks are vulnerable to man-

in-the-middle attacks, in which an attacker intercepts and alters the

communication between two parties. This can lead to the integrity of

the communication being compromised and the parties being misled

or deceived.

4. Denial-of-service attacks: Wireless networks are vulnerable to denial-

of-service attacks, in which an attacker floods the network with traffic

in an attempt to overwhelm it and prevent legitimate users from

accessing it.

5. Weak encryption: Wireless networks may use weak encryption

algorithms or keys, which can make them vulnerable to being hacked

and the data transmitted over the network being compromised.

Overall, wireless networks present a number of security issues and

challenges that must be addressed in order to protect against unauthorized

access and ensure the confidentiality and integrity of the communication. It

is important for organizations to implement robust security measures and to

regularly update and maintain them in order to protect against these threats.

(c) What is UWB Radio? Explain in Detail.

07

UWB (Ultra-Wideband) radio is a wireless communication technology that

uses very low-power, high-frequency signals to transmit data over short

distances. It is characterized by its wide bandwidth, which allows it to

transmit large amounts of data with low power consumption and low

interference.

UWB radio operates in the unlicensed frequency bands, typically between

3.1 GHz and 10.6 GHz, and uses a pulse-based modulation scheme to

transmit data. The pulse-based modulation allows UWB radio to transmit

data at a very high rate, with data rates of up to several gigabits per second

being possible.

UWB radio is well-suited for a variety of applications, including short-range

wireless data transfer, location tracking, and high-precision ranging. It is

used in a variety of different industries, including consumer electronics,

healthcare, and industrial automation.

UWB radio has several advantages over other wireless communication

technologies, including:

1. High data rates: UWB radio is capable of transmitting data at very

high rates, making it suitable for applications that require fast data

transfer.

2. Low power consumption: UWB radio uses very low-power signals,

making it an energy-efficient choice for applications that require long

battery life.

3. Low interference: UWB radio uses a wide bandwidth and a pulse-

based modulation scheme, which helps to reduce interference with

other wireless systems.

4. High-precision ranging: UWB radio is capable of providing high-

precision ranging and location information, making it suitable for

applications such as indoor positioning and asset tracking.

Write a short Note : Bluetooth

Q.5 (a)

03

Bluetooth is a wireless communication technology that is used to connect

devices over short distances. It uses a low-power radio frequency to transmit

data and is designed to be energy-efficient. Bluetooth is widely used in a

variety of devices, including smartphones, tablets, laptops, and smart home

devices, and is known for its ease of use and compatibility with a wide range

of devices.

Bluetooth is based on the IEEE 802.15.1 standard and operates in the

unlicensed 2.4 GHz frequency band. It uses a variety of protocols and

techniques to transmit data, including frequency-hopping spread spectrum

and time-division multiplexing.

Bluetooth supports a variety of networking topologies, including point-to-

point, point-to-multipoint, and mesh, and is able to support a large number

of devices on a single network. It is also interoperable with other wireless

technologies, such as Wi-Fi and ZigBee, which allows it to be used in

conjunction with these technologies in a variety of different applications.

(b) Write a short Note : Personal Area Network

04

A personal area network (PAN) is a type of computer network that is used to

connect devices in close proximity to each other, typically within a range of

a few meters. PANs are used to connect devices such as laptops,

smartphones, tablets, and smart home devices, and are often used to

exchange data and enable device control.

There are several technologies that can be used to create a PAN, including

Bluetooth, infrared, and NFC (Near Field Communication). These

technologies use a variety of protocols and techniques to transmit data and

enable device communication.

PANs are often used to connect devices that are used by a single person,

such as a laptop and a smartphone, and are designed to be easy to set up and

use. They are an important part of the Internet of Things (IoT) and are used

in a variety of applications, including wireless audio, data transfer, and

device control.

(c) Explain the Wireless Ad Hoc Network and Mobile Portability.

07

A wireless ad hoc network is a type of wireless network that is formed

spontaneously and does not require a central infrastructure or access point.

In an ad hoc network, the devices communicate directly with each other and

form a network on the fly, without the need for a central coordinating device

or access point.

Ad hoc networks are often used in situations where a traditional network

infrastructure is not available, such as in disaster recovery situations or in

remote or rural areas. They are also used in applications where mobility is a

requirement, such as in military operations or in emergency response

situations.

Mobile portability, also known as mobility management, is the ability of a

wireless communication system to support the movement of mobile devices

within and between cells or coverage areas. Mobile portability allows

mobile devices to maintain a connection and access services as they move

around, even if they are outside of the coverage area of their home network.

There are several different techniques that can be used to support mobile

portability, including:

1. Handover: This is a process in which the connection with the current

cell or base station is transferred to a new cell or base station as the

mobile device moves around. Handover allows the mobile device to

maintain a connection and access services as it moves between cells or

coverage areas.

2. Roaming: This is the ability of a mobile device to access services and

communicate with other devices outside of its home network.

Roaming allows mobile devices to access services and communicate

with other devices in other countries or regions.

OR

Q.5 (a) Explain the Small scale multipath propagation.

03

Small-scale multipath propagation refers to the phenomenon of a wireless

signal being reflected, refracted, and scattered as it travels through a

wireless communication environment. This can result in multiple copies of

the signal arriving at the receiver at different times and with different

amplitudes, which can cause interference and degradation of the signal.

Small-scale multipath propagation is a common problem in wireless

communication systems and is caused by a variety of factors, including

reflections from objects and surfaces, refraction through layers of different

materials, and scattering from small irregularities in the environment.

Small-scale multipath propagation can have a significant impact on the

performance of a wireless communication system, as it can cause

interference, fading, and reduced signal-to-noise ratio. It can also make it

difficult to accurately determine the location of a device, as the multipath

signals can cause errors in the position estimate.

There are several techniques that can be used to mitigate the effects of

small-scale multipath propagation, including:

1. Diversity techniques: These techniques use multiple antennas or

multiple paths to transmit and receive the signal, which can help to

reduce the impact of fading and interference caused by multipath

propagation.

2. Channel estimation: This involves using algorithms to estimate the

characteristics of the channel, such as the delay, phase, and amplitude

of the multipath signals. This information can be used to cancel or

mitigate the effects of the multipath signals.

3. Multipath fading compensation: This involves using algorithms to

estimate the multipath fading and compensate for it, which can help to

improve the performance of the communication system.

(b) Explain the cell Splitting and cell sectorization.

04

ell splitting and cell sectorization are techniques that are used to improve the

coverage and capacity of a wireless communication system. They are used

to divide a cell or coverage area into smaller areas, which can help to reduce

interference, increase capacity, and improve the quality of service for users.

Cell splitting involves dividing a single cell into two or more smaller cells,

each with its own base station. This can help to reduce interference and

increase capacity, as more users can be served by the network.

Cell sectorization involves dividing a cell into smaller sectors, each with its

own base station and antenna. This can help to reduce interference and

increase capacity, as the base station can transmit and receive signals from

different directions and serve multiple users simultaneously.

Both cell splitting and cell sectorization can help to improve the

performance and capacity of a wireless communication system, but they also

have some drawbacks. They can be expensive to implement and may require

the deployment of additional base stations and antennas. They may also

require the allocation of additional frequency bands, which can be a limited

resource.

(c) Explain Hexagonal geometry cell and concept of frequency reuse,

07

Hexagonal geometry cells are a common arrangement used in cellular

wireless communication systems to divide a coverage area into smaller cells

or sectors. In this arrangement, the coverage area is divided into a grid of

hexagonal cells, each with its own base station. The base stations are

typically located at the center of the cells and use antennas to transmit and

receive signals within the cell.

The concept of frequency reuse refers to the use of the same frequency band

in multiple cells or sectors within a wireless communication system. In

order to increase capacity and improve the performance of the system, the

same frequency band can be used in multiple cells or sectors, provided that

the cells are spaced far enough apart to avoid interference.

The hexagonal geometry of the cells and the concept of frequency reuse are

closely related, as the hexagonal shape of the cells allows for a more

efficient use of the available frequencies. By using a hexagonal cell

arrangement and carefully controlling the spacing between cells, it is

possible to reuse the same frequency band in multiple cells while

minimizing interference.

To optimize the use of the available frequencies and minimize interference,

the spacing between cells is carefully controlled in a cellular wireless

communication system. This is typically done using a frequency reuse

factor, which determines how many cells can reuse the same frequency

band. A frequency reuse factor of 1 means that the same frequency band is

used in every cell, while a higher frequency reuse factor means that the

same frequency band is used in fewer cells.

Overall, the hexagonal geometry of the cells and the concept of frequency

reuse are important considerations in the design and operation of a cellular

wireless communication system. They are used to optimize the use of the

available frequencies and improve the performance and capacity of the

system.

*************

1

Seat No.: XXXXXXX

Enrolment No. XXXXXXX

GUJARAT TECHNOLOGICAL UNIVERSITY

BE - SEMESTER–VII (NEW) EXAMINATION – SUMMER 2022

Subject Code:3171608

Date:01/06/2022

Subject Name: Wireless Communication

Time: 02:30 PM TO 05:00 PM

Instructions:

Total Marks: 70

1. Attempt all questions.

2. Make suitable assumptions wherever necessary.

3. Figures to the right indicate full marks.

4. Simple and non-programmable scientific calculators are allowed.

Q.1

(a) Why hexagonal cell shape is preferred in cellular architecture?

03

There are several reasons why hexagonal cell shapes are often

preferred in cellular architecture:

1. Efficiency: Hexagonal cell shapes provide a more efficient use

of space compared to other shapes like square or triangular

cells. This is because hexagons can pack together more tightly

without any gaps, resulting in a higher density of cells in a

given area.

2. Symmetry: Hexagonal cells have rotational symmetry, which

means that they look the same no matter how they are rotated.

This property makes it easier to design and build networks

using hexagonal cells.

3. Strength: Hexagonal cells are also stronger and more stable

than other shapes because their sides are evenly distributed

around a central point. This makes them less prone to

deformation or collapse under load.

4. Communication: In cellular communication networks,

hexagonal cell shapes are often used to create a regular pattern

of coverage that can be easily predicted and planned for. This

allows for more efficient use of resources and better overall

coverage.

(b) Explain the concept of frequency reuse in cellular system

04

Frequency Reuse is the scheme in which allocation and reuse of

channels throughout a coverage region is done. Each cellular base

station is allocated a group of radio channels or Frequency sub-bands

to be used within a small geographic area known as a cell. The shape

of the cell is Hexagonal. The process of selecting and allocating the

frequency sub-bands for all of the cellular base station within a

system is called Frequency reuse or Frequency Planning.

Salient features of using Frequency Reuse:

•

Frequency reuse improve the spectral efficiency and signal

Quality (QoS).

Frequency reuse classical scheme proposed for GSM systems

offers a protection against interference.

The number of times a frequency can be reused is depend on

the tolerance capacity of the radio channel from the nearby

transmitter that is using the same frequencies.

In Frequency Reuse scheme, total bandwidth is divided into

•

different sub-bands that are used by cells.

Frequency reuse scheme allow WiMax system operators to

reuse the same frequencies at different cell sites.

•

(c)

Draw and Explain GSM system architecture.

07

The Global System for Mobile Communications (GSM) is a standard

for mobile telephony that was developed to replace the analog

cellular networks that were in use in the 1980s. The GSM system

architecture is made up of several different components, including

the following:

1. Mobile Station (MS): This is the device that the user carries,

such as a mobile phone or a wireless device. The MS is

responsible for transmitting and receiving voice and data

signals over the network.

2. Base Station Subsystem (BSS): This is the infrastructure that

connects the MS to the network. It consists of two main

components: the Base Transceiver Station (BTS) and the Base

Station Controller (BSC). The BTS is responsible for

managing the radio frequency (RF) communication between

the MS and the network, while the BSC is responsible for

managing the communication between the BTS and the

network core.

3. Network Switching Subsystem (NSS): This is the central

component of the GSM network, responsible for switching and

routing calls and data between different MSs and other

networks. It consists of a Mobile Switching Center (MSC) and

a Home Location Register (HLR). The MSC is responsible for

switching calls and data between the BSS and other networks,

while the HLR is a database that stores information about each

MS, including its location and capabilities.

4. Operation Support Subsystem (OSS): This component of the

GSM network is responsible for maintaining and managing the

network, including tasks such as provisioning, billing, and

fault management. It consists of various subsystems, such as

the Equipment Identity Register (EIR), the Authentication

Center (AuC), and the Visitor Location Register (VLR).

In summary, the GSM system architecture consists of the following

components: mobile stations (MSs), base station subsystems (BSSs)

that include base transceiver stations (BTSs) and base station

controllers (BSCs), a network switching subsystem (NSS) that

includes a mobile switching center (MSC) and a home location

register (HLR), and an operation support subsystem (OSS) that

includes various subsystems such as the equipment identity register

(EIR), the authentication center (AuC), and the visitor location

register (VLR). These components work together to provide mobile

telephony services to users.

Q.2

(a) Explain the concept of umbrella cell.

03

An umbrella cell is a type of cell in a mobile communication

network that covers a large geographic area and provides coverage to

a large number of mobile devices. It is called an "umbrella" cell

because it is typically used to provide coverage over a wide area, like

an umbrella providing shelter from the rain.

In a cellular network, the coverage area of each cell is determined by

the location and power of the base station that serves the cell.

Umbrella cells are typically used in areas where the demand for

mobile services is high, such as in urban areas or along major

transportation corridors. They are also used to provide coverage in

areas where it is not practical or cost-effective to install a large

number of smaller cells, such as in rural or remote areas.

(b) Compare Wi-Fi and Wi-max technology.

04

Here is a comparison of Wi-Fi and WiMAX technology in table

form:

Feature

Wi-Fi

WiMAX

Definition

A wireless

networking

technology that

A wireless networking

technology that uses radio

waves to provide high-speed

uses radio waves to Internet access over a wide

provide Internet

access to devices

within a limited

range

area, such as a city or a region

Range

Typically covers a Can cover a range of up to 50

range of about 100 kilometers (31 miles)

meters (328 feet)

Bandwidth Typically provides Can provide bandwidth of up

bandwidth of up to to 75 Mbps

54 megabits per

second (Mbps)

Frequency Operates at a

Operates at a frequency of 2.5

GHz, 3.5 GHz, or 5.8 GHz

frequency of 2.4

GHz or 5 GHz

Mobility

Security

Provides limited

mobility, as

devices must

remain within

range of the Wi-Fi

access point

Provides security

through the use of use of encryption protocols

Provides high mobility, as

devices can move freely within

the coverage area

Provides security through the

encryption

protocols such as

WPA2

such as WPA2 and IEEE

802.16e

(c) With the help of a neat sketch, describe GPRS architecture.

07

GPRS architecture works on the same procedure like GSM network, but, has

additional entities that allow packet data transmission. This data network

overlaps a second-generation GSM network providing packet data transport

at the rates from 9.6 to 171 kbps. Along with the packet data transport the

GSM network accommodates multiple users to share the same air interface

resources concurrently.

GPRS Mobile Stations

New Mobile Stations (MS) are required to use GPRS services because

existing GSM phones do not handle the enhanced air interface or packet

data. A variety of MS can exist, including a high-speed version of current

phones to support high-speed data access, a new PDA device with an

embedded GSM phone, and PC cards for laptop computers. These mobile

stations are backward compatible for making voice calls using GSM.

GPRS Base Station Subsystem

Each BSC requires the installation of one or more Packet Control Units

(PCUs) and a software upgrade. The PCU provides a physical and logical

data interface to the Base Station Subsystem (BSS) for packet data traffic.

The BTS can also require a software upgrade but typically does not require

hardware enhancements.

When either voice or data traffic is originated at the subscriber mobile, it is

transported over the air interface to the BTS, and from the BTS to the BSC

in the same way as a standard GSM call. However, at the output of the BSC,

the traffic is separated; voice is sent to the Mobile Switching Center (MSC)

per standard GSM, and data is sent to a new device called the SGSN via the

PCU over a Frame Relay interface.

GPRS Support Nodes

Following two new components, called Gateway GPRS Support Nodes

(GSNs) and, Serving GPRS Support Node (SGSN) are added:

Gateway GPRS Support Node (GGSN)

The Gateway GPRS Support Node acts as an interface and a router to

external networks. It contains routing information for GPRS mobiles, which

is used to tunnel packets through the IP based internal backbone to the

correct Serving GPRS Support Node. The GGSN also collects charging

information connected to the use of the external data networks and can act as

a packet filter for incoming traffic.

Serving GPRS Support Node (SGSN)

The Serving GPRS Support Node is responsible for authentication of GPRS

mobiles, registration of mobiles in the network, mobility management, and

collecting information on charging for the use of the air interface.

OR

(c) Briefly explain knife-edge diffraction model.

07

The knife-edge diffraction model is a mathematical model used to

predict the behavior of electromagnetic waves as they pass through

or around obstacles. It is based on the principle of diffraction, which

describes how waves bend and spread as they pass through small

openings or around obstacles.

The knife-edge diffraction model is often used to predict the strength

and pattern of the electromagnetic field at a point on the far side of

an obstacle, such as a building or a hill. The model assumes that the

obstacle is a sharp edge or a thin strip, and it calculates the

diffraction of the wave as it passes over or around the obstacle.

The knife-edge diffraction model is useful for predicting the

behavior of radio waves in urban environments, where there are

many obstacles that can affect the strength and coverage of the

signal. It is also used in the design of wireless communication

systems, such as cellular networks, to ensure that the signal can reach

all areas of the coverage area.

Q.3

(a) Define: (1) Control Channel

(2) Dwell time

03

(3) Full Duplex Systems

(1) Control Channel: In a communication system, a control channel is

a dedicated channel that is used for transmitting control signals and

information. It is separate from the channels that are used for

transmitting data or voice signals. Control channels are used to

establish and maintain communication between devices, and they can

be used for tasks such as signaling, handshaking, and synchronization.

(2) Dwell time: In a communication system, the dwell time is the

amount of time that a device spends receiving or transmitting on a

particular frequency or channel. In a mobile communication system,

the dwell time is an important factor that can affect the performance

and efficiency of the system. For example, a device with a long dwell

time may be less efficient at transmitting and receiving data, as it

spends more time on a single frequency or channel.

(3) Full Duplex Systems: A full duplex system is a communication

system that allows devices to transmit and receive signals

simultaneously over the same channel. This means that the devices

can communicate with each other at the same time, in both directions.

Full duplex systems are often used in telephony and other two-way

communication systems, as they allow for real-time, interactive

communication between devices.

In summary:

•A control channel is a dedicated channel used for transmitting

control signals and information in a communication system.

•The dwell time is the amount of time that a device spends

receiving or transmitting on a particular frequency or channel.

•A full duplex system is a communication system that allows

devices to transmit and receive signals simultaneously over the

same channel.

(b) Write short note on: Bluetooth.

04

Bluetooth is a wireless technology that allows devices to

communicate with each other over short distances using radio waves.

It was developed in the late 1990s as a way for devices to

communicate with each other without the need for cables or other

physical connections.

Bluetooth operates in the 2.4 GHz frequency band and uses a

technique called frequency-hopping spread spectrum to transmit

data. It is designed to be low-power and low-cost, and it is

commonly used in devices such as mobile phones, laptops, and

headsets.

Bluetooth devices communicate with each other using a wireless

connection called a piconet, which consists of a master device and up

to seven slave devices. The master device controls the connection

and determines which slave devices are allowed to transmit data.

Bluetooth has a number of different applications, including file

transfer, wireless networking, and wireless audio. It is also used in a

variety of consumer and industrial products, such as smart watches,

fitness trackers, and industrial automation systems.

In summary, Bluetooth is a wireless technology that allows devices

to communicate with each other over short distances using radio

waves. It is low-power, low-cost, and commonly used in a wide

range of consumer and industrial products.

(c) Discuss the fixed channel allocation, Channel borrowing and

07

dynamic channel allocation techniques in cellular systems.

In a cellular communication system, the available frequency

spectrum is divided into a number of channels, which are used to

transmit data and voice signals between the mobile devices and the

network. There are several different techniques that can be used to

allocate these channels to the cells in the network. These techniques

include fixed channel allocation, channel borrowing, and dynamic

channel allocation.

1. Fixed channel allocation: In fixed channel allocation, each cell

in the network is assigned a fixed set of channels that it can

use to communicate with mobile devices. These channels are

typically chosen based on the expected traffic demand in the

cell and the available frequency spectrum. The advantage of

fixed channel allocation is that it is simple and easy to

implement, as the channels are assigned to the cells in advance

and do not need to be reallocated. However, it can be

inflexible and may not be able to adapt to changing traffic

conditions.

2. Channel borrowing: In channel borrowing, cells can borrow

channels from neighboring cells when they need additional

capacity. This allows cells with low traffic demand to share

their unused channels with cells that are experiencing high

traffic demand. The advantage of channel borrowing is that it

can increase the overall capacity of the network and make

better use of the available frequency spectrum. However, it can

also lead to interference between cells and may require

additional signaling between cells to coordinate the borrowing

of channels.

3. Dynamic channel allocation: In dynamic channel allocation,

the channels are assigned to the cells on an as-needed basis,

based on the current traffic demand in each cell. This allows

the network to adjust to changing traffic conditions and

allocate resources more efficiently. The advantage of dynamic

channel allocation is that it can improve the capacity and

efficiency of the network, but it can also be more complex and

require more sophisticated signaling and control mechanisms.

OR

Q.3

(a) Briefly describe Hand-off strategies in cellular system.

03

In cellular telecommunications, the

terms handover or handoff refers to the process of transferring

ongoing call or data connectivity from one Base Station to other

Base Station. When a mobile moves into the different cell while the

conversation is in progress then the MSC (Mobile Switching Center)

transfer the call to a new channel belonging to the new Base Station.

When a mobile user A moves from one cell to another cell then BSC

1 signal strength loses for the mobile User A and the signal strength

of BSC 2 increases and thus ongoing calls or data connectivity for

mobile user goes on without interrupting.

Types of Handoffs:

Hard Handoff:

When there is an actual break in the connectivity while switching

from one Base Station to another Base Station. There is no burden on

the Base Station and MSC because the switching takes place so

quickly that it can hardly be noticed by the users. The connection

quality is not that good. Hard Handoff adopted the ‘break before

make’ policy.

Soft Handoff:

In Soft Handoff, at least one of the links is kept when radio signals

are added or removed to the Base Station. Soft Handoff adopted the

‘make before break’ policy. Soft Handoff is more costly than Hard

Handoff.

(b) Compare TDMA, FDMA and CDMA techniques.

04

FDMA

TDMA

CDMA

FDMA stands for

Frequency Division Time Division

TDMA stands for

CDMA stands for

Code Division

Multiple Access.

In this, only the

sharing of time of

satellite

transponder takes

place.

Multiple Access.

In this, there is

sharing of both i.e.

bandwidth and time

among different

stations takes place.

In this, sharing of

bandwidth among

different stations

takes place.

There is no need of

any codeword.

There is no need of Codeword is

any codeword. necessary.

In this, there is only

need of guard bands In this, guard time In this, both guard

between the

of the adjacent

bands and guard time

adjacent channels

are necessary.

Synchronization is

not required.

The rate of data is

low.

slots are necessary. are necessary.

Synchronization is Synchronization is

required.

The rate of data is

medium.

not required.

The rate of data is

high.

Mode of data

transfer is

continuous signal.

Mode of data

transfer is signal in

bursts.

Mode of data transfer

is digital signal.

It is moderate

flexible.

It is little flexible.

It is highly flexible.

(c) Explain the hidden-node problem and exposed-node problem in

07

context of mobile ad-hoc networks.

In a mobile ad-hoc network (MANET), a hidden-node problem

occurs when two nodes are able to communicate with a third node,

but they are unable to communicate directly with each other because

they are out of range or obstructed by an obstacle. This can cause

problems in the network because the two nodes may transmit data

simultaneously, resulting in a collision that can cause errors and

reduce the efficiency of the network.

The hidden-node problem can be particularly challenging in a

MANET because the nodes are constantly moving and changing

their positions, which can make it difficult to predict and avoid

collisions. One solution to the hidden-node problem is to use a

protocol that allows nodes to coordinate their transmissions and

avoid colliding with each other, such as the Carrier Sense Multiple

Access with Collision Avoidance (CSMA/CA) protocol.

The exposed-node problem is a related issue that occurs when a node

is able to communicate with another node, but it is not able to

communicate with the rest of the network because it is too far away

or obstructed by an obstacle. This can create a "black hole" in the

network, as the node is able to receive data but is not able to transmit

it to other nodes.

The exposed-node problem can be solved by using relay nodes or

mesh routing protocols that allow data to be forwarded from one

node to another. These techniques can help to extend the range and

coverage of the network and ensure that all nodes are able to

communicate with each other.

Q.4

(a) Explain channel assignment strategies.

03

Channel Allocation means to allocate the available channels to the

cells in a cellular system. When a user wants to make a call request

then by using channel allocation strategies their requests are fulfilled.

Channel Allocation Strategies are designed in such a way that there

is efficient use of frequencies, time slots and bandwidth.

Types of Channel Allocation Strategies:

These are Fixed, Dynamic, and Hybrid Channel Allocation as

explained as following below.

•

Fixed Channel Allocation (FCA):

Fixed Channel Allocation is a strategy in which fixed number

of channels or voice channels are allocated to the cells. Once

the channels are allocated to the specific cells then they cannot

be changed. In FCA channels are allocated in a manner that

maximize Frequency reuse.

•

Dynamic Channel Allocation (DCA):

Dynamic Channel allocation is a strategy in which channels

are not permanently allocated to the cells. When a User makes

a call request then Base Station (BS) send that request to the

Mobile Station Center (MSC) for the allocation of channels or

voice channels. This way the likelihood of blocking calls is

reduced. As traffic increases more channels are assigned and

vice-versa.

•

Hybrid Channel Allocation (HCA):

Hybrid Channel Allocation is a combination of both Fixed

Channel Allocation (FCA) and Dynamic Channel Allocation

(DCA). The total number of channels or voice channels are

divided into fixed and dynamic set.

(b) Discuss the concept of spread spectrum.

04

Spread spectrum is a technique used to transmit data over a

communication channel in a way that spreads the data over a wider

frequency band. It is used in a variety of communication systems,

including wireless networks, satellite systems, and radar systems.

There are several different types of spread spectrum, including

frequency-hopping spread spectrum (FHSS), direct-sequence spread

spectrum (DSSS), and chirp spread spectrum (CSS). In FHSS, the

data is transmitted by rapidly switching between different

frequencies within the frequency band. In DSSS, the data is

transmitted by modulating it with a spread spectrum code, which is a

sequence of pseudorandom binary digits (bits). In CSS, the data is

transmitted by modulating the frequency of the signal over a wide

range.

Spread spectrum has several advantages over other techniques,

including the following:

1. Resistance to interference: Because the data is spread over a

wide frequency band, it is less vulnerable to interference from

other sources.

2. Security: Spread spectrum techniques can be used to encode

the data, which makes it more difficult for unauthorized users

to intercept and decode the transmission.

3. Capacity: Spread spectrum techniques can increase the

capacity of a communication system by allowing multiple

users or devices to share the same frequency band.

4. Robustness: Spread spectrum techniques can improve the

robustness of a communication system by allowing it to

recover from errors or interference.

(c) Explain the working of UWB radio. Discuss the features,

07

advantages and disadvantages of UWB technology.

Ultra-wideband (UWB) radio is a type of wireless communication

technology that uses very short pulses of radio frequency (RF)

energy to transmit data over a wide frequency band. UWB

technology is characterized by its very wide bandwidth, which can

be hundreds of megahertz or even gigahertz in some cases.

UWB radio works by transmitting extremely short pulses of RF

energy, which can be as short as a few nanoseconds in duration.

These pulses are spread over a very wide frequency band, which

allows them to carry a large amount of data. UWB radio is able to

transmit data over a wide frequency range because it uses a special

type of modulation called pulse-position modulation (PPM), which

encodes the data by varying the timing of the pulses rather than their

amplitude or frequency.

UWB technology has several features and characteristics that

distinguish it from other wireless communication technologies:

•

Very wide bandwidth: UWB technology uses a very wide

bandwidth, which allows it to transmit a large amount of data

in a short period of time.

Low power: UWB technology uses very low power levels,

which makes it suitable for use in devices with limited battery

life.

Short range: UWB technology has a relatively short range,

typically a few meters or less, which makes it suitable for use

in close proximity applications.

High resolution: UWB technology can provide high spatial and

temporal resolution, which makes it useful for applications

such as radar and location tracking.

Some advantages of UWB technology include:

•

High data rates: UWB technology can achieve very high data

rates, making it suitable for applications that require a lot of

bandwidth.

Low interference: Because UWB signals have such a wide

bandwidth, they are less likely to interfere with other signals in

the same frequency band.

High security: UWB signals are difficult to detect and

intercept, which makes them suitable for use in secure

communication systems.

Some disadvantages of UWB technology include:

•

Short range: The short range of UWB signals limits their use

to applications that require communication over a small area.

Complexity: UWB technology can be complex to implement,

as it requires specialized hardware and software.

Limited availability: UWB technology is not as widely

available as other wireless technologies, and it may not be

supported by all devices.

OR

Explain: I-persistent CSMA, non-persistent CSMA,

P-persistent CSMA.

Q.4

(a)

03

1. I-persistent CSMA: In I-persistent CSMA, a

node waits for a fixed interval of time before

attempting to transmit data. If the channel is

still idle after the interval has elapsed, the

node transmits its data. If the channel is

busy, the node continues to wait until it

becomes idle.

2. Non-persistent CSMA: In non-persistent

CSMA, a node waits for a random interval of

time before attempting to transmit data. If the

channel is still idle after the interval has

elapsed, the node transmits its data. If the

channel is busy, the node defers its

transmission and tries again later.

3. P-persistent CSMA: In P-persistent CSMA, a

node waits for a random interval of time

before attempting to transmit data. If the

channel is idle, the node transmits its data

with a probability of p. If the channel is busy,

the node defers its transmission and tries

again later.

(b) Explain wireless Ad-Hoc network.

04

A wireless ad-hoc network (WANET) is a type of wireless network

that does not require a fixed infrastructure or central coordinating

device. Instead, the nodes in the network communicate directly with

each other and form a temporary network on the fly.

WANETs are self-organizing and self-configuring, which means that

they can automatically detect and connect to nearby nodes and form

a network without the need for any central control. This makes them

highly flexible and resilient, as they can adapt to changing conditions

and continue to operate even if some of the nodes fail or are removed

from the network.

WANETs have several characteristics that distinguish them from

other types of wireless networks:

•

Decentralized: WANETs do not have a central coordinating

device or fixed infrastructure, which makes them decentralized

and self-organizing.

•

Dynamic: WANETs are dynamic, as the nodes can move

freely and the network can change in size and configuration.

Ad-hoc: WANETs are ad-hoc, as they are formed on the fly

and do not require any pre-planning or coordination.

Peer-to-peer: WANETs are peer-to-peer, as the nodes

communicate directly with each other and do not rely on a

central server or hub.

WANETs have several advantages, including:

•

Flexibility: WANETs are highly flexible, as they can be

deployed quickly and easily in any location.

Resilience: WANETs are resilient, as they can continue to

operate even if some of the nodes fail or are removed from

(c) Describe the various outdoor propagation models.

07

Outdoor propagation models are mathematical models that are used

to predict the behavior of electromagnetic waves as they propagate

through the environment. These models are used to design and

analyze communication systems, such as wireless networks and

satellite systems, and to understand the impact of the environment on

the performance of the system.

There are several different outdoor propagation models that are used

to predict the behavior of electromagnetic waves in different

situations, including:

1. Free-space propagation model: The free-space propagation

model assumes that the electromagnetic waves propagate

through a vacuum or a homogeneous medium with no

obstacles or reflections. It is often used to predict the behavior

of electromagnetic waves over long distances or in situations

where the environment is relatively simple.

2. Two-ray ground reflection model: The two-ray ground

reflection model assumes that the electromagnetic waves

propagate through the air and are reflected off the ground. It is

often used to predict the behavior of electromagnetic waves at

low frequencies or over short distances, where the ground

reflection is significant.

3. Log-distance path loss model: The log-distance path loss

model assumes that the power of the electromagnetic waves

decreases with distance according to a logarithmic function. It

is often used to predict the behavior of electromagnetic waves

over moderate distances, where the environment is relatively

homogeneous.

4. Okumura-Hata model: The Okumura-Hata model is a more

complex model that takes into account the effect of obstacles

and reflections on the propagation of electromagnetic waves. It

is often used to predict the behavior of electromagnetic waves

in urban or suburban environments, where there are many

buildings and other obstacles.

5. Longley-Rice model: The Longley-Rice model is a highly

detailed model that takes into account the effect of the

environment, including terrain, vegetation, and weather, on the

propagation of electromagnetic waves. It is often used to

predict the behavior of electromagnetic waves over long

distances or in complex environments.

Explain briefly how a RAKE receiver improves the received signal

strength.

Q.5

(a)

03

A RAKE receiver is a type of receiver that is used in communication

systems to improve the performance of the system in the presence of

multipath interference. A RAKE receiver works by combining

multiple copies of the same signal that have arrived at the receiver

via different paths, in order to improve the signal-to-noise ratio

(SNR) and increase the received signal strength.

In a communication system, the signal can arrive at the receiver via

multiple paths due to reflections, scattering, and other effects. This

can result in multipath interference, which can cause errors and

reduce the quality of the received signal.

A RAKE receiver addresses this problem by using multiple "fingers"

to independently receive and demodulate the different copies of the

signal. The fingers are then combined using a RAKE combiner,

which combines the signals based on their relative timing and

amplitudes. This process can improve the SNR and increase the

received signal strength by effectively canceling out the multipath

interference.

RAKE receivers are used in a variety of communication systems,

including mobile phones, satellite systems, and wireless networks.

They are particularly useful in environments where there is a high

level of multipath interference, such as in urban or suburban areas or

in the presence of moving objects.

Mention the techniques to improve the capacity in cellular system

and explain any one.

(b)

04

There are several techniques that can be used to improve the capacity

of a cellular system, which refers to the ability of the system to

handle more users or devices simultaneously. These techniques

include:

1. Frequency reuse: Frequency reuse is a technique that allows

the same set of frequencies to be used by multiple cells in the

system. By carefully arranging the cells in a pattern known as

a reuse pattern, the system can ensure that the frequencies are

used efficiently and avoid interference between cells.

2. Cell splitting: Cell splitting is a technique that involves

dividing a large cell into smaller cells, which increases the

number of cells in the system and allows more users or devices

to be served.

3. Sectorization: Sectorization is a technique that involves

dividing a cell into sectors, which are smaller areas that are

served by separate antennas. This allows the system to increase

capacity by serving more users or devices within a given

frequency band.

4. Cell breathing: Cell breathing is a technique that involves

adjusting the size of the cells in a cellular system based on the

traffic demand. By dynamically adjusting the cell size, the

system can increase capacity in areas with high traffic demand

and reduce capacity in areas with low traffic demand.

5. Coordinated multipoint (CoMP): Coordinated multipoint

(CoMP) is a technique that involves using multiple base

stations to serve a single user or device. By using multiple base

stations, the system can increase capacity and improve

coverage.

One example of a technique to improve capacity in a cellular system

is frequency reuse. Frequency reuse involves using the same set of

frequencies in multiple cells in the system, but arranging the cells in

a pattern to avoid interference between cells. This allows the system

to increase capacity by efficiently using the available frequencies and

avoiding interference.

(c) Write a short note on OFDM.

07

Orthogonal Frequency Division Multiplexing (OFDM) is a type of

digital modulation technique that is used to transmit data over a

communication channel. It works by dividing the available frequency

band into a number of narrow subcarriers, and modulating each

subcarrier with a different data stream.

The following diagram illustrates the basic structure of an OFDM

system:

In the transmitter, the data is divided into a number of parallel data

streams and encoded using a forward error correction (FEC) code.

Each data stream is then modulated onto a different subcarrier using

a technique such as quadrature amplitude modulation (QAM). The

modulated subcarriers are then combined using an inverse fast

Fourier transform (IFFT) to create the OFDM symbol, which is

transmitted over the communication channel.

In the receiver, the OFDM symbol is demodulated using a fast

Fourier transform (FFT) to separate the subcarriers. The data streams

are then decoded using the FEC code and recovered.

OFDM has several advantages, including:

•

High spectral efficiency: OFDM allows a large amount of data

to be transmitted in a narrow frequency band, making it highly

spectrally efficient.

•

Robustness to frequency-selective fading: OFDM is robust to

frequency-selective fading, which is a type of interference that

affects only certain frequencies. This makes it suitable for use

in environments where the channel conditions are variable.

Low complexity: OFDM requires relatively simple hardware

and algorithms, which makes it suitable for use in low-cost

devices.

OFDM is used in the following area −

•

Wi-Fi

DSL internet access

4G wireless communications

digital television

radio broadcast services

OR

Q.5

(a) List the security issues of wireless networks.

03

Wireless networks are vulnerable to a number of security threats and

issues, which can compromise the confidentiality, integrity, and

availability of the data transmitted over the network. Some of the

security issues of wireless networks include:

1. Unauthorized access: Wireless networks are vulnerable to

unauthorized access, as attackers can potentially gain access to

the network by intercepting the wireless signals or cracking the

encryption used to secure the network.

2. Eavesdropping: Wireless networks are vulnerable to

eavesdropping, as attackers can potentially intercept and listen

to the data transmitted over the network.

3. Man-in-the-middle attacks: Wireless networks are vulnerable

to man-in-the-middle attacks, in which an attacker intercepts

and modifies the data transmitted between two parties.

4. Denial of service (DoS) attacks: Wireless networks are

vulnerable to DoS attacks, in which an attacker overloads the

network with traffic or sends malicious data to disrupt the

network's operation.

5. Rogue access points: Wireless networks are vulnerable to

rogue access points, which are unauthorized access points that

are set up by attackers to gain access to the network.

6. Unsecured data: Wireless networks are vulnerable to

unsecured data, as data transmitted over the network may not

be encrypted or may be encrypted using weak or outdated

algorithms.

(b) Write a short note on software defined radio.

04

Software defined radio (SDR) is a type of radio system that uses

software to define the radio's function and characteristics. SDRs are

flexible and programmable, as the software can be easily modified to

support different communication standards, protocols, and frequencies.

In an SDR system, the radio functions are implemented in software

rather than in hardware. This allows the radio to be reconfigured and

reprogrammed easily, without the need to replace any hardware

components. SDRs are often implemented using general-purpose

processors and digital signal processing (DSP) algorithms, which allows

them to be highly flexible and adaptable.

SDRs have several advantages, including:

•

Flexibility: SDRs are highly flexible, as they can be easily

reconfigured and reprogrammed to support different

communication standards, protocols, and frequencies.

Cost-effectiveness: SDRs can be implemented using low-cost,

general-purpose hardware and software, which makes them cost-

effective compared to traditional radio systems that require

specialized hardware.

•

Scalability: SDRs are scalable, as they can be easily modified and

expanded to support new features and capabilities.

SDRs are used in a variety of applications, including wireless

communication, military systems, and emergency response systems.

They are also used in research and development, as they provide a

platform for testing and evaluating new communication technologies.

(c) Explain Frequency Division Multiple Access (FDMA) in wireless

07

communication with figure.

Frequency Division Multiple Access (FDMA) is one of the most

common analogue multiple access methods. The frequency band is

divided into channels of equal bandwidth so that each conversation is

carried on a different frequency (as shown in the figure below).

In FDMA method, guard bands are used between the adjacent signal

spectra to minimize crosstalk between the channels. A specific

frequency band is given to one person, and it will received by

identifying each of the frequency on the receiving end. It is often used

in the first generation of analog mobile phone.

Advantages of FDMA

As FDMA systems use low bit rates (large symbol time) compared to

average delay spread, it offers the following advantages −

•

Reduces the bit rate information and the use of efficient

numerical codes increases the capacity.

•

It reduces the cost and lowers the inter symbol interference (ISI)

Equalization is not necessary.

•

An FDMA system can be easily implemented. A system can be

configured so that the improvements in terms of speech encoder

and bit rate reduction may be easily incorporated.

Since the transmission is continuous, less number of bits are

required for synchronization and framing.

Disadvantages of FDMA

Although FDMA offers several advantages, it has a few drawbacks as

well, which are listed below −

•

It does not differ significantly from analog systems; improving

the capacity depends on the signal-to-interference reduction, or

a signal-to-noise ratio (SNR).

•

The maximum flow rate per channel is fixed and small.

Guard bands lead to a waste of capacity.

Hardware implies narrowband filters, which cannot be realized

in VLSI and therefore increases the cost.

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