Department of Electronics And Communication Engineering
UNIT-I
THE CELLULAR CONCEPT-SYSTEM DESIGN FUNDAMENTALS
Introduction – Frequency Reuse - Channel Assignment Strategies - Handoff Strategies: Prioritizing
Handoffs, Practical Handoff Considerations. Interference And System Capacity: Co-Channel
Interference And System Capacity-Channel Planning For Wireless Systems, Adjacent Channel
Interference, Power Control For Reducing Interference, Trunking And Grade Of Service. Improving
Coverage And Capacity In Cellular Systems: Cell Splitting, Sectoring.
1.1 The Cellular Concept - Introduction
1. Explain the concept of cellular topology and cell fundamentals. [Dec 2015, May 2023]
For a given set of frequencies or radio channels can be reused without increasing the
interference, the large geographical area covered by a single high power transmitter can be
divided into a number of small areas, each allocated power transmitters with lower antennas can
be used.
The Hexagon shape was used for cell because it provides the most effective transmission.
Each cellular base station is allocated a group of radio channels to be used with a small
geographic area called a cell.
A group of cells that use a different set of frequencies in each cell is called a cell cluster.
Types of cell
The physical size of a cell varies, depending on user density and calling patterns.
1. Macro cells:
They are large cells.
They have a radius between 1 mile and 15 miles.
Base station transmits power between 1W and 6W.
2. Microcells:
They are the smallest cells.
They have a radius between of 1500 feet or less.
Base station transmit powers between 0.1W and 1W.
They are used in high-density areas such as in large cities and inside the buildings.
Location of base station
For location of the base station, designing a system using hexagonal-shaped cells.
1. Center-excited cell- Base station transmitters:
They can be located in the center of the cell.
They use Omni directional antennas which radiate and receive signals equally well in all
directions.
Edge- excited cell- Base station transmitters:
They can be located in the edge of the cell.
They use sectored antennas which radiate for a particular direction.
2. Corner- excited cell- Base station transmitters:
, Department of Electronics And Communication Engineering
They can be located in the corner of the cell.
They use sectored directional antennas.
Cellular system
Figure shows a basic cellular system.
It consists of mobile stations, base stations and a mobile switching center (MSC).
Figure: Cellular system
Mobile station:
The mobile station contains a transceiver, an antenna, and control circuitry.
It may be mounted in a vehicle or used as a portable hand-held unit.
Each mobile communicates via radio with one of the base stations
It may be handed off to any number of base stations throughout the duration of a call.
Base station:
The base station consists of several transmitters and receivers which simultaneously handle
full duplex communications.
It has towers which support several transmitting and receiving antennas.
It serves as a bridge between all mobile users in the cell.
It connects the simultaneous mobile calls via telephone lines or microwave links to the MSC.
The channels used for voice transmission from the base station to mobiles are called forward
voice channels (FVC).
The channels used for voice transmission from mobiles to the base station are called reverse
voice channels (RVC).
The two channels responsible for initiating mobile calls are the forward control channels
(FCC) and reverse control channels (RCC).
Mobile Switching Center:
The Mobile Switching Center is sometimes called a mobile telephone switching office
(MTSO).
It is responsible for connecting all mobiles to the PSTN in a cellular system.
The MSC coordinates the activities of all of the base stations.
It connects the entire cellular system to the PSTN.
A typical MSC handles 100,000 cellular subscribers’ and 5,000 simultaneous conversations at
a time.
It accommodates all billing and system maintenance functions.
, Department of Electronics And Communication Engineering
1.2 Frequency Reuse
2. Discuss in detail about frequency reuse. [8m] [Dec 2014] (or)
Given a foot print by the service provider, prepare and illustrate the frequency planning
addressing all practical limitations that can be envisaged. [Dec 2021]
Frequency reuse is the process in which the same set of frequencies can be allocated to more
than one cell and the cells are separated by sufficient distance.
It is also known as frequency planning.
The ability to reuse the frequencies to expand the total system capacity without the need to
employ high power transmitters.
Figure shows a geographic cellular radio coverage area.
It contains three groups of cell called clusters.
A cell cluster is outlined in bold and replicate over the coverage area.
Each cluster has seven cells in it and all cells are assigned the same number of full duplex
cellular telephone channels.
Cells with the same letter use the same set of frequencies.
The letters A, B, C, D, E, F and G denote the seven sets of frequencies.
The actual radio coverage of a cell is known as the foot print. It is determined from field
measurement or propagation prediction models.
Figure: Illustration of the cellular frequency reuse concept.
Capacity expansion by frequency reuse
Consider a cellular system which has a total of S duplex channels available for use.
Let N be the cluster size in terms of the number of cells within it.
Each cells is allocated a group of K channels (K<S).
The N cells which collectively use the complete set of available frequencies is called cluster.
The cluster can be replicated many times to form the entire cellular communication systems.
The N cells in the cluster would utilize all K available channels.
For the total number of Channels C, the total number of available radio channels can be
expressed as
S = KN
, Department of Electronics And Communication Engineering
where,
S Number of full duplex cellular channels available in the cluster
K Number of channels in a cell
N Number of cells in the cluster
Let M be the number of times the cluster is replicated and C be the total number of channels
used in the entire cellular system with frequency reuse.
C is then the system capacity and is given by
C=MKN
C=MS
where,
C Total channel capacity in a given area
M Number of clusters in a given area
The capacity of a cellular system is directly proportional to the number of times a cluster is
replicated in a fixed service area.
The cluster size factor N = 4, 7, or 12.
If the cluster size N is reduced while the cell size is kept constant.
More clusters are required to cover a given area and hence more capacity is achieved.
The number of subscribers who can use the same set of frequencies in non-adjacent cells at
the same area is dependent on the total number of cells in the area.
The number of users use the same set of frequencies is called the Frequency Reuse Factor
(FRF) and is defined as
N
FRF
C
where,
N Cluster size
C Total number of full duplex channels in an a cell.
Rules for determining the nearest co-channel neighbors
To find the nearest co-channel neighbors of a particular cell:
Step 1: Move I cells along any chain of hexagons.
Step 2: Turn 60 degrees counter clockwise and more j cells.
Figure: Method of locating co-channel cells in a cellular system.
In this example, N = 19 (i.e., i = 3, j = 2).
UNIT-I
THE CELLULAR CONCEPT-SYSTEM DESIGN FUNDAMENTALS
Introduction – Frequency Reuse - Channel Assignment Strategies - Handoff Strategies: Prioritizing
Handoffs, Practical Handoff Considerations. Interference And System Capacity: Co-Channel
Interference And System Capacity-Channel Planning For Wireless Systems, Adjacent Channel
Interference, Power Control For Reducing Interference, Trunking And Grade Of Service. Improving
Coverage And Capacity In Cellular Systems: Cell Splitting, Sectoring.
1.1 The Cellular Concept - Introduction
1. Explain the concept of cellular topology and cell fundamentals. [Dec 2015, May 2023]
For a given set of frequencies or radio channels can be reused without increasing the
interference, the large geographical area covered by a single high power transmitter can be
divided into a number of small areas, each allocated power transmitters with lower antennas can
be used.
The Hexagon shape was used for cell because it provides the most effective transmission.
Each cellular base station is allocated a group of radio channels to be used with a small
geographic area called a cell.
A group of cells that use a different set of frequencies in each cell is called a cell cluster.
Types of cell
The physical size of a cell varies, depending on user density and calling patterns.
1. Macro cells:
They are large cells.
They have a radius between 1 mile and 15 miles.
Base station transmits power between 1W and 6W.
2. Microcells:
They are the smallest cells.
They have a radius between of 1500 feet or less.
Base station transmit powers between 0.1W and 1W.
They are used in high-density areas such as in large cities and inside the buildings.
Location of base station
For location of the base station, designing a system using hexagonal-shaped cells.
1. Center-excited cell- Base station transmitters:
They can be located in the center of the cell.
They use Omni directional antennas which radiate and receive signals equally well in all
directions.
Edge- excited cell- Base station transmitters:
They can be located in the edge of the cell.
They use sectored antennas which radiate for a particular direction.
2. Corner- excited cell- Base station transmitters:
, Department of Electronics And Communication Engineering
They can be located in the corner of the cell.
They use sectored directional antennas.
Cellular system
Figure shows a basic cellular system.
It consists of mobile stations, base stations and a mobile switching center (MSC).
Figure: Cellular system
Mobile station:
The mobile station contains a transceiver, an antenna, and control circuitry.
It may be mounted in a vehicle or used as a portable hand-held unit.
Each mobile communicates via radio with one of the base stations
It may be handed off to any number of base stations throughout the duration of a call.
Base station:
The base station consists of several transmitters and receivers which simultaneously handle
full duplex communications.
It has towers which support several transmitting and receiving antennas.
It serves as a bridge between all mobile users in the cell.
It connects the simultaneous mobile calls via telephone lines or microwave links to the MSC.
The channels used for voice transmission from the base station to mobiles are called forward
voice channels (FVC).
The channels used for voice transmission from mobiles to the base station are called reverse
voice channels (RVC).
The two channels responsible for initiating mobile calls are the forward control channels
(FCC) and reverse control channels (RCC).
Mobile Switching Center:
The Mobile Switching Center is sometimes called a mobile telephone switching office
(MTSO).
It is responsible for connecting all mobiles to the PSTN in a cellular system.
The MSC coordinates the activities of all of the base stations.
It connects the entire cellular system to the PSTN.
A typical MSC handles 100,000 cellular subscribers’ and 5,000 simultaneous conversations at
a time.
It accommodates all billing and system maintenance functions.
, Department of Electronics And Communication Engineering
1.2 Frequency Reuse
2. Discuss in detail about frequency reuse. [8m] [Dec 2014] (or)
Given a foot print by the service provider, prepare and illustrate the frequency planning
addressing all practical limitations that can be envisaged. [Dec 2021]
Frequency reuse is the process in which the same set of frequencies can be allocated to more
than one cell and the cells are separated by sufficient distance.
It is also known as frequency planning.
The ability to reuse the frequencies to expand the total system capacity without the need to
employ high power transmitters.
Figure shows a geographic cellular radio coverage area.
It contains three groups of cell called clusters.
A cell cluster is outlined in bold and replicate over the coverage area.
Each cluster has seven cells in it and all cells are assigned the same number of full duplex
cellular telephone channels.
Cells with the same letter use the same set of frequencies.
The letters A, B, C, D, E, F and G denote the seven sets of frequencies.
The actual radio coverage of a cell is known as the foot print. It is determined from field
measurement or propagation prediction models.
Figure: Illustration of the cellular frequency reuse concept.
Capacity expansion by frequency reuse
Consider a cellular system which has a total of S duplex channels available for use.
Let N be the cluster size in terms of the number of cells within it.
Each cells is allocated a group of K channels (K<S).
The N cells which collectively use the complete set of available frequencies is called cluster.
The cluster can be replicated many times to form the entire cellular communication systems.
The N cells in the cluster would utilize all K available channels.
For the total number of Channels C, the total number of available radio channels can be
expressed as
S = KN
, Department of Electronics And Communication Engineering
where,
S Number of full duplex cellular channels available in the cluster
K Number of channels in a cell
N Number of cells in the cluster
Let M be the number of times the cluster is replicated and C be the total number of channels
used in the entire cellular system with frequency reuse.
C is then the system capacity and is given by
C=MKN
C=MS
where,
C Total channel capacity in a given area
M Number of clusters in a given area
The capacity of a cellular system is directly proportional to the number of times a cluster is
replicated in a fixed service area.
The cluster size factor N = 4, 7, or 12.
If the cluster size N is reduced while the cell size is kept constant.
More clusters are required to cover a given area and hence more capacity is achieved.
The number of subscribers who can use the same set of frequencies in non-adjacent cells at
the same area is dependent on the total number of cells in the area.
The number of users use the same set of frequencies is called the Frequency Reuse Factor
(FRF) and is defined as
N
FRF
C
where,
N Cluster size
C Total number of full duplex channels in an a cell.
Rules for determining the nearest co-channel neighbors
To find the nearest co-channel neighbors of a particular cell:
Step 1: Move I cells along any chain of hexagons.
Step 2: Turn 60 degrees counter clockwise and more j cells.
Figure: Method of locating co-channel cells in a cellular system.
In this example, N = 19 (i.e., i = 3, j = 2).
