This document discusses principles of cellular communication systems. It describes how cellular systems overcome limitations of conventional systems by dividing geographic areas into small cells served by low-power base stations, and reusing frequencies in different cells. This allows for higher capacity within limited spectrum. Key aspects covered include cell structure, frequency reuse patterns, cluster size and its impact on capacity, methods for locating co-channel cells, and factors like interference that influence network design.

1. Principles of
Cellular
Communication

2. • 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

3. Conventional Mobile Communication
• Large coverage area.
• Single high powered transmitter on tall tower
• Had very limited capacity since frequencies could not be
reused due to interference.
 High power consumption
 Low capacity
 Large size of the mobile

4. 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

5. Mobile Radio systems
• Replace single, high power transmitter
(large cell) with many low power
transmitters (small cells), each providing
coverage to only a small portion of
coverage area.

6. Cellular Telephone System

7. Characteristic
• Limited number of users
• Large Geographic area
• Limited frequency spectrum
• High capacity is achieved by limiting
coverage of each BS into small
geographical region called “cell’’.

8. Cellular Systems

9. Cellular concept
• High capacity is achieved by limiting coverage of
each BS into small geographical region called “cell’’.
• Each cellular base station is allocated a group of
radio channels within a small geographic area called
a cell.
• A cell is the basic geographic unit of a cellular
system.
• It is also called a footprint.
• Neighboring cells are assigned different channel
groups.

10. Cell Structure (Cell Shape)
 Determined by the desired received signal level
by the mobile subscribers from its base station
transmitter in its operating area.
o Ideal, actual and fictitious cell models

11. Cell with BS and MS

12. Cell Structure (Cell Shape)
 Determined by the desired received signal level
by the mobile subscribers from its base station
transmitter in its operating area.
o Ideal, actual and fictitious cell models

13. Geometric Cellular Structures

14. Hexagonal cells 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.
• Approximating a circular radiation pattern for an
omni-directional base station antenna and free space
propagation
• Simplifies the planning and design of a cellular
system
o

15. A Cellular Cluster
• A group of cells that use a different set of frequencies in
each cell
• The N cells which use the complete set of channels is
called cluster.
• 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 N
o

16. Hexagonal Cluster Patterns

17. System Capacity & Spectrum Utilization?

18. 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

19. Frequency Reuse
 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 or
frequency planning.
Two main factors to consider during frequency
planning:
–Interference b/w co-channels
–Capacity

20. Frequency Reuse
For Cluster size (N)=7

21. Frequency Reuse
For Cluster size (N)=7

22. 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

23. Cluster Size and Cell Capacity
Consider a cellular system which has a total
of S duplex channels.
Each cell is allocated a group of k channels,
k<S.
The S channels are divided among N cells.
 The total number of available radio
channels
S=kN
The N number of cells in a cluster
(cluster size) use the complete set of
available frequency channels,S.

24. Cluster Size and Cell Capacity
• The cluster can be repeated M times
within the system. The total number of
channels, C, is used as a measure of
capacity.
C=MkN=MS (S=kN)

25. Cluster Size and Cell Capacity
Cluster size: N is typically 4, 7 or 12 for
hexagonal cell shape.
If N=4 and cellular system has total 660
channels available, so total number of
channels available per cell=660/4=165
channels.
For the same cell size at a given area.
If “N” is reduced while the cell size is kept
constant, more clusters are required to
cover a given area, and hence more

26. Method to Locate Co-channel Cells
• To locate the nearest co-channel cell of a
particular cell, one must do the following
operation:
 Step 1: Move i cells along any side of
a hexagon.
 Step 2: Turn 60 degrees anticlockwise.
 Step 3: Move j cells
• where i and j are shift parameters and can
have integer value 0, 1, 2, 3, and so on …

27. Co-channel Cells for i =3, j = 2

28. Re-use Distance

29. Re-use Distance
• The distance between the co-channel cell
in adjacent cluster is given by:
• The geometry of hexagons is such that the
number of cells per cluster, N, can only
have values which satisfy the following eqn
:
where i and j are non-negative integers.

30. Co-channel Re-use Factor (Q)
• The frequency reuse ratio, Q is also referred as
 Co-channel reuse ratio
 Co-channel reuse factor
 Co-channel interference reduction
factor
• For Hexagonal cells the re-use distance(D) is
given by