UNIT II:
WIRELESS WANS
THE CELLULAR CONCEPT
The cellular concept divides the mobile network into the small areas called cells.
Each cell has a base station that communicates with mobile devices within that cell.
The same radio frequencies can be reused in different cells far apart. As you move,
your device automatically switches to the new cell’s base station in a process called
handoff. This allows efficient use of limited frequencies to provide wide coverage and
better service.
The cellular concept refers to the way mobile communication networks are designed
and organized. Instead of having the big powerful transmitter covering the large area
the network is divided into the smaller areas called cells. Each cell has its own small
transmitter called a cell site or the base station.
A cellular network is a wireless communication network which provides services to
mobile users covered by a region consisting of multiple cells. Frequency reuse is a
fundamental concept in cellular networks.
This base station can communicate with mobile devices like phones or tablets within
that cell. The idea behind this cellular setup is to allow the same radio frequencies to
be reused in different cells that are far apart. This way more people can use the
network without the interference.
Frequencies used in one cell area will be reused at the same time in a different cell
that is far away. For example The typical seven cell pattern can be used.
The total available frequency resources are divided into seven parts, with each part
having a number of radio channels. One part is allocated to each cell site. In the
group of 7 cells the available frequency spectrum is fully used. The same seven sets
of the frequency can be reused after the certain distance.
The group of cells where the available frequency spectrum is totally used up is called
a cluster of cells.
,THE CELLULAR PRINCIPLE ENABLES THE FOLLOWING :
1. More efficient use of limited radio frequency resources.
2. Manufacturing of all subscriber devices in a region with the same set of
channels, so any mobile can be used anywhere within that region.
HISTORICAL BACKGROUND
Prior to the invention of cellular technologies, there were few mobile telephone
systems in the late 1940s in the USA and in the early 1950s in Europe, such as
car-based telephone systems. The push-to-talk technique was used in these
systems, and communication was performed over a single channel.
With a single channel and a single antenna at each device, the transmission and
reception of signals were performed in a half-duplex manner. Due to low capacity,
restricted mobility support, and poor service quality, those systems were not efficient.
Later on, mobile telephone system (MTS) and improved MTS (IMTS) were
introduced in order to support a larger number of mobile stations.
CELLULAR ARCHITECTURE
Cellular architecture is constituted of the following −
A network of cells each with a base station.
A packet switched network for communication between the base stations and
mobile switching centers.
The public switched telephone network to connect subscribers to the wider
telephony network
CELLULAR CONFIGURATION
In all cellular systems, land area is divided into a number of cells each with its
radio service. In AMPS the area is large which in digital services, the area is
much smaller. Conventionally cells are hexagonal in shape. Each cell uses a
frequency range that is not used by its adjacent cells. However frequencies
may be reused in non-adjacent cells.
At the centre of each cell is a base station through which mobile phones and
other mobile devices transmit data and voice.
The following diagram represents the configuration
, MOBILE SWITCHING CENTRES
A mobile switching centre (MSC) is a network switching subsystem of a cellular
phone system. It is also called mobile telephone switching office (MTSO). All base
stations are connected to an MSC.
The functions of MSC are −
Call set-up and release.
Routing of calls and messages sent via SMS.
Managing conference calls and calls on hold.
Fax services.
Billing
Interfacing with other networks like public switched telephone network (PSTN)
and Internet.
WIRELESS WANS
THE CELLULAR CONCEPT
The cellular concept divides the mobile network into the small areas called cells.
Each cell has a base station that communicates with mobile devices within that cell.
The same radio frequencies can be reused in different cells far apart. As you move,
your device automatically switches to the new cell’s base station in a process called
handoff. This allows efficient use of limited frequencies to provide wide coverage and
better service.
The cellular concept refers to the way mobile communication networks are designed
and organized. Instead of having the big powerful transmitter covering the large area
the network is divided into the smaller areas called cells. Each cell has its own small
transmitter called a cell site or the base station.
A cellular network is a wireless communication network which provides services to
mobile users covered by a region consisting of multiple cells. Frequency reuse is a
fundamental concept in cellular networks.
This base station can communicate with mobile devices like phones or tablets within
that cell. The idea behind this cellular setup is to allow the same radio frequencies to
be reused in different cells that are far apart. This way more people can use the
network without the interference.
Frequencies used in one cell area will be reused at the same time in a different cell
that is far away. For example The typical seven cell pattern can be used.
The total available frequency resources are divided into seven parts, with each part
having a number of radio channels. One part is allocated to each cell site. In the
group of 7 cells the available frequency spectrum is fully used. The same seven sets
of the frequency can be reused after the certain distance.
The group of cells where the available frequency spectrum is totally used up is called
a cluster of cells.
,THE CELLULAR PRINCIPLE ENABLES THE FOLLOWING :
1. More efficient use of limited radio frequency resources.
2. Manufacturing of all subscriber devices in a region with the same set of
channels, so any mobile can be used anywhere within that region.
HISTORICAL BACKGROUND
Prior to the invention of cellular technologies, there were few mobile telephone
systems in the late 1940s in the USA and in the early 1950s in Europe, such as
car-based telephone systems. The push-to-talk technique was used in these
systems, and communication was performed over a single channel.
With a single channel and a single antenna at each device, the transmission and
reception of signals were performed in a half-duplex manner. Due to low capacity,
restricted mobility support, and poor service quality, those systems were not efficient.
Later on, mobile telephone system (MTS) and improved MTS (IMTS) were
introduced in order to support a larger number of mobile stations.
CELLULAR ARCHITECTURE
Cellular architecture is constituted of the following −
A network of cells each with a base station.
A packet switched network for communication between the base stations and
mobile switching centers.
The public switched telephone network to connect subscribers to the wider
telephony network
CELLULAR CONFIGURATION
In all cellular systems, land area is divided into a number of cells each with its
radio service. In AMPS the area is large which in digital services, the area is
much smaller. Conventionally cells are hexagonal in shape. Each cell uses a
frequency range that is not used by its adjacent cells. However frequencies
may be reused in non-adjacent cells.
At the centre of each cell is a base station through which mobile phones and
other mobile devices transmit data and voice.
The following diagram represents the configuration
, MOBILE SWITCHING CENTRES
A mobile switching centre (MSC) is a network switching subsystem of a cellular
phone system. It is also called mobile telephone switching office (MTSO). All base
stations are connected to an MSC.
The functions of MSC are −
Call set-up and release.
Routing of calls and messages sent via SMS.
Managing conference calls and calls on hold.
Fax services.
Billing
Interfacing with other networks like public switched telephone network (PSTN)
and Internet.
