Unit -2

Introduction To Wireless Networking, Various Generations of Wireless

Networks, Wireless LANs, Advantages and Disadvantages of WLANs,
Fixed Network Transmission Hierarchy, Traffic Routing in Wireless
Networks, WAN Link Connection Technologies, CellularNetworks.

1. Introduction To Wireless Networking

Computer networks that are not connected by cables are called wireless
networks. They generally use radio waves for communication between the
network nodes. They allow devices to be connected to the network while
roaming around within the network coverage.

Types of Wireless Networks

 Wireless LANs − Connects two or more network devices using wireless

distribution techniques.
 Wireless MANs − Connects two or more wireless LANs spreading over a
metropolitan area.
 Wireless WANs − Connects large areas comprising LANs, MANs and
personal networks.

Advantages of Wireless Networks

 It provides clutter-free desks due to the absence of wires and cables.

 It increases the mobility of network devices connected to the system
since the devices need not be connected to each other.
 Accessing network devices from any location within the network
coverage or Wi-Fi hotspot becomes convenient since laying out cables is
not needed.
  Installation and setup of wireless networks are easier.
 New devices can be easily connected to the existing setup since they
needn’t be wired to the present equipment. Also, the number of
equipment that can be added or removed to the system can vary
considerably since they are not limited by the cable capacity. This makes
wireless networks very scalable.
 Wireless networks require very limited or no wires. Thus, it reduces the
equipment and setup costs.

Examples of wireless networks

 Mobile phone networks

 Wireless sensor networks
 Satellite communication networks
 Terrestrial microwave networks
 Here is an outline of the five generations of mobile networks:

2.various generations of wireless

networks
Wireless networks have evolved significantly over the years, with each
generation bringing improvements in speed, capacity, and functionality. Here
is an overview of the various generations of wireless networks:

2.EXAMPLES OF GENERATIONS
1G (First Generation)

 Timeframe: Early 1980s

 Technology: Analog
 Speed: Up to 2.4 kbps
 Features: Basic voice communication
 Limitations: Poor voice quality, limited capacity, no data services

2G (Second Generation)

 Timeframe: Early 1990s

 Technology: Digital (GSM, CDMA)
  Speed: Up to 64 kbps
 Features: Improved voice quality, SMS (Short Message Service), limited
data services (e.g., MMS - Multimedia Messaging Service)
 Benefits: Enhanced security, better voice clarity, introduction of text
messaging

2.5G

 Timeframe: Late 1990s

 Technology: GPRS (General Packet Radio Service), EDGE (Enhanced Data
Rates for GSM Evolution)
 Speed: Up to 144 kbps (GPRS), up to 384 kbps (EDGE)
 Features: Improved data services, mobile internet access

3G (Third Generation)

 Timeframe: Early 2000s

 Technology: UMTS (Universal Mobile Telecommunications System),
CDMA2000
 Speed: Up to 2 Mbps
 Features: Enhanced mobile internet, video calling, mobile TV, improved
voice quality
 Benefits: Higher data rates, better connectivity, multimedia services

3.5G

 Timeframe: Mid-2000s
 Technology: HSPA (High-Speed Packet Access), HSPA+
 Speed: Up to 21 Mbps (HSPA), up to 42 Mbps (HSPA+)
 Features: Faster mobile internet, improved multimedia services

4G (Fourth Generation)

 Timeframe: Late 2000s

 Technology: LTE (Long-Term Evolution), WiMAX
 Speed: Up to 100 Mbps (mobile) and 1 Gbps (stationary)
 Features: High-definition mobile TV, video conferencing, enhanced
gaming, VoIP (Voice over IP)
 Benefits: Significant increase in data speeds, better quality of service,
support for a wide range of applications
4.5G

 Timeframe: Mid-2010s
 Technology: LTE-Advanced
 Speed: Up to 1 Gbps
 Features: Carrier aggregation, higher-order MIMO (Multiple Input
Multiple Output), improved spectral efficiency
 Benefits: Even faster data speeds, better performance in densely
populated areas

5G (Fifth Generation)

 Timeframe: Late 2010s to early 2020s

 Technology: NR (New Radio)
 Speed: Up to 10 Gbps
 Features: Enhanced mobile broadband, ultra-reliable low-latency
communication, massive machine-type communications
 Benefits: Extremely high speeds, very low latency, support for IoT
(Internet of Things), improved capacity and efficiency, enables new
applications like autonomous vehicles and smart cities

6G (Sixth Generation) [Future]

 Expected Timeframe: 2030s

 Technology: Still under research and development
 Speed: Expected to be up to 100 Gbps
 Features: Further enhanced speeds, extremely low latency, integration
with advanced AI, seamless global connectivity
 Potential Benefits: Even more advanced IoT applications, ubiquitous
connectivity, advancements in virtual and augmented reality, new types
of communication and interactioN

ANSWER OF GENERATION
1.First Generation (1G)
 First-generation mobile networks relied on analogue radio systems,
which meant that users could only make phone calls and not send or
receive text messages. The 1G network was first introduced in Japan in
1979 before being rolled out in other countries, such as the USA, in
1980.
 Cell towers were built around the country to make it work, meaning that
signal coverage could be obtained from greater distances. However, the
network was unreliable and had some security issues. For instance, cell
coverage would often drop, it would experience interference by other
radio signals, and it could easily be hacked due to a lack of encryption.
 This means that conversations can be heard and recorded with a few
tools.
2.Second Generation (2G)
 THe 1G network was not perfect, but it remained until 1991, when it was
replaced with 2G. This new mobile network ran on digital signal, not
analogue, vastly improving its security and capacity. On 2G, users could
send SMS and MMS messages (although slowly and often without
success), and when GPRS was introduced in 1997, users could receive
and send emails on the move.
3. Third Generation (3G)
 Third-generation mobile networks are still in use, but normally, when
the superior 4G signal fails. 3G revolutionized mobile connectivity and
the capabilities of cell phones. Compared to 2G, 3G was much faster and
could transmit greater amounts of data. This means that users could
video call, share files, surf the internet, watch TV online, and play games
on their mobiles for the first time.
 Under 3G, cell phones were no longer just about calling and texting; they
were the hub of social connectivity.
4. Fourth Generation (4G)
 The introduction of 4G went one step further than the revolutionary 3G.
 It is five times faster than the 3G network – and can theoretically provide
speeds of up to 100Mbps. All mobile models released from 2013
onwards should support this network, which can offer connectivity for
tablets, laptops, and smartphones.
 Under 4G, users can experience better latency (less buffering), higher
voice quality, easy access to instant messaging services and social media,
quality streaming, and faster downloads.
5.Fifth Generation (5G)


 The network has arrived and has been largely welcomed by the mobile
industry. The network has changed more than our mobile use and
affects how we connect our devices to the internet. The improved speed
 and the massive network capacity have developed new IoT trends, such
as smart cities, healthcare, IoT in the home or office and connected cars.
 5G can theoretically have a download speed 20x faster than 4G and
boasts a very low latency compared to its predecessor. This means the
time delay for online gaming, video calls, and critical mission
applications will be significantly lower.
 With almost a decade of 5G development left, the technology’s full
potential is yet to come. The 5G network will revolutionize how people
live and work worldwide, so expect to see exciting changes in the
coming years.

6. Looking Beyond 5G: The Dawn of 6G

 As we continue to embrace the wonders of 5G, the tech world is already

buzzing about 6G.
 Expected to launch around 2030, 6G will take wireless communication to
new heights, offering speeds up to 100 times faster than 5G.
 It promises to usher in advanced applications like high-fidelity
holographic communication, AI-driven networks, and ultra-precise
location sensing. The leap from 5G to 6G will mark a significant
advancement in technology, further connecting the world in ways we're
just beginning to imagine.

3.WIRELESS LANS
WLAN stands for Wireless Local Area Network. WLAN is a local area network
that uses radio communication to provide mobility to the network users
while maintaining the connectivity to the wired network. A WLAN basically,
extends a wired local area network. WLAN’s are built by attaching a device
called the access point(AP) to the edge of the wired network. Clients
communicate with the AP using a wireless network adapter which is similar in
function to an ethernet adapter. It is also called a LAWN is a Local area
wireless network.
The performance of WLAN is high compared to other wireless networks. The
coverage of WLAN is within a campus or building or that tech park. It is used
in the mobile propagation of wired networks. The standards of WLAN are
HiperLAN, Wi-Fi, and IEEE 802.11. It offers service to the desktop laptop,
mobile application, and all the devices that work on the Internet. WLAN is an
affordable method and can be set up in 24 hours. WLAN gives users the
mobility to move around within a local coverage area and still be connected
to the network. Most latest brands are based on IEE 802.11 standards, which
are the WI-FI brand name.
History
A professor at the University of Hawaii who’s name was Norman Abramson,
developed the world’s first wireless computer communication network. In
1979, Gfeller and u. Bapst published a paper in the IEE proceedings reporting
an experimental wireless local area network using diffused infrared
communications. The first of the IEEE workshops on Wireless LAN was held in
1991.

1.WLAN Architecture
Components in Wireless LAN architecture as per IEEE standards are as
follows:
1. Stations: Stations consist of all the equipment that is used to
connect all wireless LANs. Each station has a wireless network
controller.
2. Base Service Set(BSS): It is a group of stations communicating at the
physical layer.
3. Extended Service Set(ESS): It is a group of connected Base Service
Set(BSS).
4. Distribution Service (DS): It connects all Extended Service Set(ESS).

WLAN Architecture

2.Types of WLANs
As per IEEE standard WLAN is categorized into two basic modes, which are as
follows:
1. Infrastructure: In Infrastructure mode, all the endpoints are
connected to a base station and communicate through that; and this
can also enable internet access. A WLAN infrastructure can be set
 up with: a wireless router (base station) and an endpoint (computer,
mobile phone, etc). An office or home WiFi connection is an
example of Infrastructure mode.
2. Ad Hoc: In Ad Hoc mode WLAN connects devices without a base
station, like a computer workstation. An Ad Hoc WLAN is easy to set
up it provides peer-to-peer communication. It requires two or more
endpoints with built-in radio transmission.
3.Working of WLAN
WLAN transmits data over radio signals and the data is sent in the form of a
packet. Each packet consists of layers, labels, and instructions with
unique MAC addresses assigned to endpoints. This enables routing data
packets to correct locations.
4.How is a WLAN Created ?
A WLAN is a collection of nodes interconnected with each other for the
purpose of data sharing, transmitting messages over the internet, connecting
for peer-2-peer connectiob etc. As discussed above in types, it can be created
in following 2 ways :-
1. Connecting through one base station and that could be the router
that acts as a doorway to the internet, and every other nodes
(devices like computer, smartphones) can connect to the internet
and to each other through it.
2. Peer-2-Peer connection using the wifi direct technology. This is
more suitable for situations when we require to connect two or
more devices without internet and only for purpose of data
exchange, connecting over a same local network.
5.Is a WLAN Secure ?
Whether or not WLAN is secure depends on multiple factors of
implementation configured by the network administrator. However, by
default it has multiple security vulnerabilities. So the security team should
consider all the factor and configure accordingly.
Following are 3 ways to ensure best security practices :-
1. Encryption: Ensure that the network is using highest level of
encryption
2. Authentication: There are multiple authentication mechanism, its
good to use protocols that rely on 802.1x standards like WPA-EAP
(Wireless Protected Acess-Extensible Authentication Protocol) for
organisation as this method ONLY gives access when correct
username and passwords are inputed. And usernames and
passwords are not shared and are individual specific only.
 3. Monitor Rougue APs: The Rougue APs (Access Points) are similar set
of networks that user can unknowingly connect to where all the
activities of the user will be tracked and monitored by the bad actor
who set up the network. Hence the security team can be on the
lookout for such configured networks occasionally.
6.Characteristics of WLAN
1. Seamless operation.
2. Low power for battery use.
3. Simple management, easy to use for everyone.
4. Protection of investment in wired networks.
5. Robust transmission technology.
7.Advantages of WLAN
1. Installation speed and simplicity.
2. Installation flexibility.
3. Reduced cost of ownership.
4. Reliability.
5. Mobility.
6. Robustness.
8.Disadvantages of WLAN
1. Slower bandwidth.
2. Security for wireless LANs is the prime concern.
3. Less capacity.
4. Wireless networks cost four times more than wired network cards.
5. Wireless devices emit low levels of RF which can be harmful to our
health.
Conclusion
In conclusion, WLAN is a quickly configurable type of network that doesn’t
require physical equipment just to connect multiple devices with each other
or over the internet. But just like every other type of network setup it has its
own set of disadvantages.

3.A fixed network transmission hierarchy

fixed network transmission hierarchy refers to the layered structure of a wired
telecommunications network. This structure is designed to ensure efficient,
reliable, and scalable data transmission across different segments of the
network. Below is a typical representation of this hierarchy:
1. End-User Layer

 Components: Customer Premises Equipment (CPE) such as modems,

routers, telephones, set-top boxes.
 Function: Interfaces between the end-user and the access network. This
is where data transmission begins and ends for users.

2. Access Network Layer

 Technologies: DSL (Digital Subscriber Line), FTTH/B (Fiber to the

Home/Building), PON (Passive Optical Network), coaxial cables.
 Components: Local access lines, distribution points, street cabinets.
 Function: Connects end-user devices to the local exchange or central
office. It handles the first mile of data transmission.

3. Local Exchange (Central Office) Layer

 Components: DSLAMs (Digital Subscriber Line Access Multiplexers), OLTs

(Optical Line Terminals), switches, and routers.
 Function: Aggregates data traffic from multiple access networks and
routes it to higher network layers. It serves as the local hub for data
transmission.

4. Aggregation/Distribution Network Layer

 Technologies: Metro Ethernet, fiber-optic rings, microwave links.

 Components: Aggregation switches, distribution switches, regional data
centers.
 Function: Connects local exchanges to regional or metropolitan nodes. It
consolidates traffic from multiple local exchanges and routes it
efficiently to the core network.

5. Core Network Layer

 Technologies: IP/MPLS (Multiprotocol Label Switching), SONET/SDH

(Synchronous Optical Networking/Synchronous Digital Hierarchy), high-
capacity fiber-optic cables.
 Components: Core routers, backbone switches, high-capacity
transmission lines.
  Function: Provides high-speed, long-distance data transport between
regional nodes, ensuring data can travel across large geographical areas
with minimal latency and high reliability.

6. Backbone Network Layer

 Technologies: Ultra-high-capacity fiber-optic cables, submarine cables,

satellite links.
 Components: Backbone routers, international gateways, major data
centers.
 Function: Forms the main data routes across countries and continents. It
handles the bulk of global data traffic and connects national networks to
the global internet.

7. Peering and Interconnection Points

 Components: Internet Exchange Points (IXPs), peering routers,

interconnection switches.
 Function: Facilitates data exchange between different network
providers. Peering points allow different ISPs and networks to exchange
traffic, enhancing the efficiency and speed of data transmission.

Key Concepts:

 Bandwidth and Latency: Higher layers in the hierarchy offer greater

bandwidth and lower latency to support efficient data transmission over
long distances.
 Redundancy and Reliability: Implementing redundant paths and backup
systems at various layers to enhance network reliability and minimize
downtime.
 Quality of Service (QoS): Mechanisms to prioritize certain types of
traffic, ensuring critical data gets delivered promptly and efficiently.
 Network Management and Security: Monitoring, managing, and
securing network operations to protect against outages, cyber threats,
and data breaches.

This hierarchical structure helps in managing the complexity of modern

telecommunications networks, ensuring scalability, reliability, and efficient
data transfer from end-users to global data centers and back

OR
A fixed network transmission hierarchy,
also known as the telecommunications hierarchy or network hierarchy, refers
to the structured layers of network components and technologies used to
facilitate data transmission in a fixed (wired) telecommunications network.
This hierarchy ensures efficient and reliable data transfer across various parts
of the network. Here's an overview of the main components and layers
typically found in such a hierarchy:

1. Customer Premises Equipment (CPE)

 Devices: Modems, routers, set-top boxes, telephones.

 Function: Interfaces between the end-user and the service provider's
network.

2. Access Network

 Technologies: DSL, fiber-optic cables (FTTH/B), coaxial cables, PON

(Passive Optical Network).
 Function: Connects the CPE to the service provider's central office or
local exchange.

3. Local Exchange (Central Office)

 Equipment: DSLAMs (Digital Subscriber Line Access Multiplexers), OLTs

(Optical Line Terminals), switches.
 Function: Aggregates and manages data traffic from multiple access
networks.

4. Distribution Network

 Technologies: Metro Ethernet, fiber-optic rings, microwave links.

 Function: Connects local exchanges to regional or metropolitan nodes,
often using higher capacity links.

5. Core Network

 Technologies: High-capacity fiber-optic cables, IP/MPLS (Multiprotocol

Label Switching) networks, SONET/SDH (Synchronous Optical
Networking/Synchronous Digital Hierarchy).
  Function: Provides high-speed, long-distance data transport, connecting
regional nodes to national or international backbone networks.

6. Backbone Network

 Technologies: Ultra-high-capacity fiber-optic cables, submarine cables,

satellite links.
 Function: Forms the main data routes across countries and continents,
handling vast amounts of data traffic between major data centers and
service providers.

7. Data Centers and Peering Points

 Equipment: Servers, switches, routers, storage systems.

 Function: Hosts and manages content, services, and applications.
Peering points facilitate data exchange between different network
providers.

Key Concepts and Technologies:

 Bandwidth and Latency: Higher layers in the hierarchy typically offer

greater bandwidth and lower latency to ensure efficient data
transmission over long distances.
 Redundancy and Reliability: Implementing redundant paths and backup
systems at various layers to enhance network reliability and minimize
downtime.
 Quality of Service (QoS): Mechanisms to prioritize certain types of
traffic, ensuring critical data gets delivered promptly and efficiently.
 Network Management and Security: Monitoring, managing, and
securing network operations to protect against outages, cyber threats,
and data breaches.

This hierarchical structure helps in managing the complexity of modern

telecommunications networks, ensuring scalability, reliability, and efficient
data transfer from end-users to global data centers and back.

4.Traffic Routing in Wireless Networks

Traffic routing in wireless networks refers to the process of directing data
packets from a source node to a destination node in a wireless network. It
involves determining the optimal path for data transmission to ensure efficient
and reliable communication. There are several routing protocols and
algorithms used in wireless networks, including:

Ad-hoc On-demand Distance Vector (AODV): A reactive routing protocol that

establishes routes on-demand. It uses route discovery and route maintenance
mechanisms to find and maintain routes between nodes.

Dynamic Source Routing (DSR): Another reactive routing protocol that allows
nodes to dynamically discover and maintain routes. It uses source routing,
where the entire route is included in the packet header.

Destination-Sequenced Distance Vector (DSDV): A proactive routing protocol

that maintains routing tables at each node. It uses sequence numbers to
ensure the freshness of routing information and avoid routing loops.

Optimized Link State Routing (OLSR): A proactive routing protocol that uses
multipoint relays (MPRs) to reduce the overhead of flooding control messages.
It creates a topology map of the network and calculates the shortest paths.

Wireless Mesh Routing Protocol (WMRP): A hybrid routing protocol that

combines proactive and reactive approaches. It uses a proactive approach for
intra-mesh routing and a reactive approach for inter-mesh routing. These
protocols and algorithms consider factors such as network topology, link
quality, congestion, and energy efficiency to determine the best path for data
transmission. They aim to minimize packet loss, delay, and energy
consumption while maximizing network throughput and reliability. It is
important to note that the choice of routing protocol depends on the specific
requirements and characteristics of the wireless network, such as network size,
mobility, and application type.
5.WAN Link Connection Technologies
WAN (Wide Area Network) link connection technologies refer to the
various methods used to connect geographically dispersed networks
or locations over large distances. These technologies provide the
backbone for connecting multiple local area networks (LANs) and
enable communication over long distances, often across cities,
countries, or even globally. Here’s an overview of the primary WAN
link connection technologies:

1. Leased Lines

 Description: Leased lines are dedicated point-to-point

connections between two locations, providing a fixed amount of
bandwidth. They are often used for connecting corporate offices
or data centers.
 Examples: T1, T3, E1, E3 lines.
 Advantages: High reliability, consistent performance, secure as
the line is not shared.
 Disadvantages: Expensive, limited scalability.

2. Frame Relay

 Description: Frame Relay is a packet-switched technology that

routes data across virtual circuits in a WAN. It is cost-effective
and was commonly used in the 1990s for connecting LANs and
providing telecommunication services.
 Advantages: Cost-efficient for medium-to-large networks,
flexible bandwidth allocation.
 Disadvantages: Decreased popularity with the advent of newer
technologies, shared bandwidth can lead to congestion.

3. Asynchronous Transfer Mode (ATM)

 Description: ATM is a high-speed, cell-based switching

technique that uses fixed-sized cells (53 bytes) for data
transmission. It supports multiple types of traffic, including
voice, video, and data.
 Advantages: High performance, supports QoS (Quality of
Service), scalable.
 Disadvantages: Complexity, higher costs, largely obsolete.

4. Multiprotocol Label Switching (MPLS)

 Description: MPLS is a versatile, high-performance technology

that directs and manages data traffic across a WAN by labeling
 data packets and making forwarding decisions based on these
labels.
 Advantages: High reliability, supports QoS, scalable, can carry
multiple types of traffic (e.g., IP, ATM, Frame Relay).
 Disadvantages: Can be expensive, complex configuration and
management.

5. Digital Subscriber Line (DSL)

 Description: DSL is a technology that provides high-speed

internet access over standard telephone lines. It is widely used
for connecting small businesses and residential users to the
internet.
 Advantages: Cost-effective, uses existing telephone
infrastructure, relatively fast.
 Disadvantages: Limited range, speed decreases with distance
from the DSLAM (Digital Subscriber Line Access Multiplexer).

6. Cable Broadband

 Description: Cable broadband uses coaxial cables to provide

high-speed internet access, typically through the same
infrastructure as cable television.
 Advantages: High-speed internet, widely available in urban
areas, relatively cost-effective.
 Disadvantages: Shared bandwidth with other users in the area
can lead to reduced speeds during peak times.

7. Fiber Optic

 Description: Fiber optic technology uses light signals to

transmit data at extremely high speeds over glass or plastic
fibers. It is increasingly used for high-speed internet connections
and backbone networks.
 Advantages: Extremely high bandwidth, low latency, long-
distance transmission without loss of signal quality.
 Disadvantages: Expensive to install and maintain, requires
specialized equipment.
8. Satellite

 Description: Satellite communication provides internet and

network connectivity via geostationary or low-earth orbit
satellites. It is especially useful in remote or rural areas where
other forms of connectivity are not feasible.
 Advantages: Wide coverage, can reach remote locations, quick
deployment.
 Disadvantages: High latency, weather can affect performance,
expensive.

9. Cellular (3G/4G/5G)

 Description: Cellular networks use mobile phone infrastructure

to provide wireless internet and data services over large
geographic areas. 5G is the latest generation, offering
significantly higher speeds and lower latency.
 Advantages: Mobility, wide coverage, relatively easy
deployment.
 Disadvantages: Variable performance depending on location
and network congestion, data caps may apply.

10. Wireless Microwave

 Description: Microwave links use high-frequency radio waves

to transmit data between two locations. It’s often used for point-
to-point communication, especially in areas where laying cables
is impractical.
 Advantages: High bandwidth, long-distance communication,
quick deployment.
 Disadvantages: Line-of-sight requirement, weather can affect
performance, potential for interference.

11. Virtual Private Network (VPN) over Internet

 Description: VPNs allow secure, encrypted communication

over the internet, making it possible to create a private network
over a public one.
 Advantages: Cost-effective, flexible, secure remote access.
  Disadvantages: Dependent on internet quality, potential
performance issues due to encryption overhead.

Considerations for Choosing WAN Technologies

 Bandwidth Requirements: The amount of data that needs to be

transmitted.
 Cost: Budget constraints, including both initial setup and
ongoing operational costs.
 Latency and Speed: Requirements for real-time applications
like VoIP or video conferencing.
 Geographic Coverage: The locations that need to be connected
and the distance between them.
 Reliability and Redundancy: The need for consistent uptime
and backup connections in case of failure.
 Scalability: The ability to scale bandwidth and connections as
the network grows.

The choice of WAN link technology depends on the specific needs of

the organization, including factors such as the required bandwidth,
budget, and geographical considerations.

6. CELLULAR NETWORKS
A Cellular Network is formed of some cells. The cell covers a
geographical region and has a base station analogous to 802.11
AP which helps mobile users attach to the network and there is
an air interface of physical and data link layer protocol between
mobile and base station. All these base stations are connected to
the Mobile Switching Center which connects cells to a wide-
area net, manages call setup, and handles mobility.

There is a certain radio spectrum that is allocated to the base

station and to a particular region and that now needs to be
shared. There are two techniques for sharing mobile-to-base
station radio spectrum:
 Combined FDMA/TDMA: It divides the spectrum into
frequency channels and divides each channel into time slots.

 Code Division Multiple Access (CDMA): It allows the reuse of

the same spectrum over all cells. Net capacity improvement.
Two frequency bands are used one of which is for the
forwarding channel (cell-site to subscriber) and one for the
reverse channel (sub to cell-site).

Cell Fundamentals

In practice, cells are of arbitrary shape(close to a circle) because

it has the same power on all sides and has same sensitivity on all
sides, but putting up two-three circles together may result in
interleaving gaps or may intersect each other so order to solve
this problem we can use equilateral triangle, square or a regular
hexagon in which hexagonal cell is close to a circle used for a
system design. Co-channel reuse ratio is given by:

DL/RL = Square root of (3N)

Where,

DL = Distance between co-channel cells

RL = Cell Radius

N = Cluster Size

The number of cells in cluster N determines the amount of co-

channel interference and also the number of frequency channels
available per cell.

Cell Splitting

When the number of subscribers in a given area increases

allocation of more channels covered by that channel is
necessary, which is done by cell splitting. A single small cell
midway between two co-channel cells is introduced.
 Cell Splitting

Need for Cellular Hierarchy

Extending the coverage to the areas that are difficult to cover by

a large cell. Increasing the capacity of the network for those
areas that have a higher density of users. An increasing number
of wireless devices and the communication between them.

Cellular Hierarchy

 Femtocells: The smallest unit of the hierarchy, these cells need

to cover only a few meters where all devices are in the physical
range of the uses.

 Picocells: The size of these networks is in the range of a few

tens of meters, e.g., WLANs.

 Microcells: Cover a range of hundreds of meters e.g. in urban

areas to support PCS which is another kind of mobile
technology.

 Macrocells: Cover areas in the order of several kilometers, e.g.,

cover metropolitan areas.
 Mega cells: Cover nationwide areas with ranges of hundreds of
kilometers, e.g., used with satellites.

Fixed Channel Allocation

For a particular channel, the frequency band which is associated

is fixed. The total number of channels is given by

Nc = W/B

Where,

W = Bandwidth of the available spectrum,

B = Bandwidth needed by each channels per cell,

Cc = Nc/N where N is the cluster size

Adjacent radio frequency bands are assigned to different cells.

In analog, each channel corresponds to one user while in digital
each RF channel carries several time slots or codes
(TDMA/CDMA). Simple to implement as traffic is uniform.

Global System for Mobile (GSM) Communications

GSM uses 124 frequency channels, each of which uses an 8-slot

Time Division Multiplexing (TDM) system. There is a
frequency band that is also fixed. Transmitting and receiving do
not happen in the same time slot because the GSM radios cannot
transmit and receive at the same time and it takes time to switch
from one to the other. A data frame is transmitted in 547
microseconds, but a transmitter is only allowed to send one data
frame every 4.615 microseconds since it is sharing the channel
with seven other stations. The gross rate of each channel is 270,
833 bps divided among eight users, which gives 33.854 kbps
gross.

Control Channel (CC)

 Apart from user channels, there are some control channels
which is used to manage the system.

1. The broadcast control channel (BCC): It is a continuous stream

of output from the base station’s identity and the channel status.
All mobile stations monitor their signal strength to see when
they move into a new cell.

2. The dedicated control channel (DCC): It is used for location

updating, registration, and call setup. In particular, each base
station maintains a database of mobile stations. Information
needed to maintain this database is sent to the dedicated control
channel.

Common Control Channel

Three logical sub-channels are:

1. Is the paging channel, that the base station uses to announce

incoming calls. Each mobile station monitors it continuously to
watch for calls it should answer.

2. Is the random access channel that allows the users to request a

slot on the dedicated control channel. If two requests collide,
they are garbled and have to be retried later.

3. Is the access grant channel which is the announced assigned

slot.

Advantages of Cellular Networks

 Mobile and fixed users can connect using it. Voice and data
services also provided.

 Has increased capacity & easy to maintain.

 Easy to upgrade the equipment & has consumes less power.

 It is used in place where cables can not be laid out because of its
wireless existence.
 To use the features & functions of mainly all private and public
networks.

 Can be distributed to the larger coverage of areas.

Disadvantages of Cellular Networks

 It provides a lower data rate than wired networks like fiber

optics and DSL. The data rate changes depending on wireless
technologies like GSM, CDMA, LTE, etc.

 Macrophage cells are impacted by multipath signal loss.

 To service customers, there is a limited capacity that depends on

the channels and different access techniques.

 Due to the wireless nature of the connection, security issues

exist.

 For the construction of antennas for cellular networks, a

foundation tower and space are required. It takes a lot of time
and labor to do this.