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Principles of
Cellular
Communication

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Principles of Cellular Communication
 Cellular Terminology
 Cell Structure and Cluster
 Frequency Reuse Concept
 Cluster Size and System Capacity
 Method of Locating Co-channel Cells
 Frequency Reuse Distance
 Co-channel Interference and Signal Quality
 Co-channel Interference Reduction Methods

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Cellular Terminology – A Cell
 A cell is the basic geographic unit of a
cellular system.
 It is also called a footprint.
 A cell is the radio area covered by a cell-
site that is located at its center
 A large geographical area is divided into
a number of contiguous smaller
geographical coverage areas called cells

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Cell Structure (Cell Shape)
Determined by the desired received signal level
by the mobile subscribers from its base station
transmitter in its operating area
Ideal, actual and fictitious cell models
R
R
R
R
R
(a) Ideal cell(b) Actual cell (c) Fictitious cell models

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A Cell with a CS and Mobile

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Cell Structure

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Geometric Cellular Structures

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Hexagonal Cellular Geometry

Offers best possible non-overlapped cell
radio coverage
 Multiple hexagons can be arranged next
to each other
 For a given radius (largest possible
distance between the polygon center and its
edge), the hexagon has the largest area
 Simplifies the planning and design of a
cellular system

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A Cellular Cluster
 A group of cells that use a different set of
frequencies in each cell
 Only selected number of cells can form
a cluster
 Can be repeated any number of times in a
systematic manner
 The cluster size is the number of cells
within it, and designated by K

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Hexagonal Cluster Patterns

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Conventional Mobile Communication
Limitations:
High power consumption
Low capacity
Large size of the mobile
Conventional mobile communication service was
structured in a fashion similar to television
broadcasting: One very powerful transmitter located
at the highest spot in an area would broadcast in a
radius of up to 50 kilometers.

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System Design Problem?
Main limitation of a conventional mobile
wireless communication system is:
Limited availability of FREQUENCY
SPECTRUM !!!
So the big challenge is …
to serve large number of mobile users ..
 within limited allocated frequency
spectrum
 with a specified system quality

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System Capacity & Spectrum Utilization?
System capacity at required QoS
with conventional frequency plan
Subscriber
growth
Time
Out of
Capacity!!!
The need:
•Optimum
spectrum usage
•More capacity
•High quality of
service (QoS)
•Low cost
How to increase capacity & Spectrum utilization
?

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Possible Solution – Frequency Reuse
Reuse allocated RF spectrum or a given
set of frequencies (frequency channels)
in a given large geographical service
area without increasing the interference
Divide the service area into a number of
small areas called cells
Allocate a subset of frequencies to each cell
Use low-power transmitters with lower
height antennas at the base stations

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Frequency Reuse Concept
Large coverage area, efficient spectrum
utilization and enhanced system capacity are
the major attributes of cellular communication
Frequency reuse is the core concept
of cellular communications
The design process of selecting and allocating
channel groups for all the cellular base
stations within a system is called frequency
reuse

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Illustration of Frequency Reuse

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Co-channel and Adjacent Channel
Cells
Cells, which use the same set of frequencies,
are referred to as cochannel cells
Co-channel cells are located sufficiently
physically apart so as not to cause
cochannel interference
The space between adjacent cochannel cells
is filled with other cells that use different
frequencies to provide frequency isolation

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Frequency Reuse & Spectrum Efficiency
Suppose the system has RF
spectrum for 100 voice channels
Scenario 1: A high power
base station covering entire
area – system capacity = 100
channels
Scenario 2: Divide spectrum
into 4 groups of 25 channels
each; cells (1, 7), (2, 4), (3, 5),
6 are assigned distinct channel
groups – system capacity =
175 channels
1
2
6
3
4
5
7
HPT – High Power Transmitter
LPT – Low Power Transmitter
Total no. of channels allocated to all cells is equal to no. of channels per channel
group multiplied by the Number of distinct cells i.e.
Total no. of channels allocated to all cells is equal to no. of channels per channel
group multiplied by the Number of distinct cells i.e.

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Technical Issues
Technical issues for proper design and
planning of a cellular network:
Selection of a suitable frequency reuse pattern
Physical deployment and radio coverage modeling
Plans to account for the expansion of the
cellular network
Analysis of the relationship between the
capacity, cell size, and the cost of the
infrastructure

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Cluster Size and Cell Capacity

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Cluster Size and System Capacity

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Co-channel Cells
Cells which use the same set of
frequencies are referred to as
cochannel cells.
The interference between
cochannel cells is referred to as
cochannel interference.
The space between adjacent
cochannel cells are filled with cells
using different frequencies.

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Shift Parameters i and j in a
Hexagonal Geometry

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Method to Locate Co-channel Cells

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Cochannel Cells for i =3, j = 2

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Co-channel Hexagonal Geometry

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A Larger Hexagon in First Tier

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Cluster Size, K = i
2
+ j
2
+ i x j

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Reuse Pattern and Cluster Size

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Cell Structure for K = 4 and K = 7

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The Cellular Structure for K = 12
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Frequency Reuse Distance, D

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Factors which Influence `D’

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R
C
1
R
C
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D

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q = D/R Ratio
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5 7
6
1
2
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R
D

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Frequency Reuse Factor, q and
Cluster Size, K

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Frequency Reuse Ratio and
Cluster Size

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What is Optimum Cluster Size?

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How to estimate D and K?

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Frequency Reuse – Pros & Cons

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Interference in Cellular System

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Effects of Interference

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Cochannel Interference and
Signal Quality (Test 1)

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Interference Measurement at Mobile

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Interference Measurement Analysis

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Cochannel Interference and
Signal Quality (Test 2)

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Interference Measurement at Cell-site

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Cochannel Interference Reduction

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Summary
 The essential principles of cellular
communication include frequency reuse,
cochannel cells, and cochannel interference
 Various cell parameters based on regular
hexagonal cellular pattern include cluster,
frequency reuse distance, reuse factor
 Cochannel interference reduction methods
aim at maintaining desired signal quality and
cell capacity

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