For more details, visit www.mhhe.com/singal/wc

1. National-Level Faculty Development Workshop
“Challenges for Research in Wireless Communication
Technologies”
Presented by
Prof. T. L. Singal
May 21-23, 2012
Chitkara University, Punjab
1

2. Principles of
Cellular
Communications
Cell structure and
Cellular Terminology
cluster
Cluster Size and
Frequency Reuse Concept
System Capacity
Method of Locating Co- Frequency Reuse
channel Cells Distance
Co-channel Interference Co-channel Interference
and Signal Quality Reduction Methods
2

3.  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
3

4. Determined by the desired
R
received signal level by the
mobile subscribers from
(a) Ideal Cell
its base station transmitter
in its operating area
Ideal, actual and
fictitious cell models
(b) Actual Cell
R
R
R
R
(c) Fictitious Cell
4

5. 5

6. 6

7. 7

8.  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
8

9.  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
9

10. 10

11. One very powerful transmitter located at the
highest spot in an area would broadcast in a
radius of up to 50 kilometers.
Limitations:
 High power
consumption
 Low capacity
 Large size of the
mobile
11

12. 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
12

13. System capacity at required QoS The need:
with conventional frequency plan • Optimum
Out of spectrum usage
Capacity!!! • More capacity
• High quality of
Subscriber
growth service (QoS)
Time • Low cost
How to increase capacity & Spectrum utilization
?
13

14.  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
14

15.  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
15

16. 16

17.  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
17

18. Suppose the system has RF
spectrum for 100 voice
2 3 channels
Scenario 1: A high power
1
7
4
base station covering entire
6
area – system capacity = 100
5 channels
Scenario 2: Divide spectrum
HPT – High Power Transmitter
into 4 groups of 25 channels
each; cells (1, 7), (2, 4), (3, 5),
LPT – Low Power Transmitter
6 are assigned distinct
channel groups – system
capacity = 175 channels 18

19. 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
19

20.  In a cellular system, the whole
geographical service area is divided into a
number of clusters having finite number
of cells.
 The K number of cells in a cluster (cluster
size) use the complete set of available
frequency channels, N.
 Each cell in the cluster contains J = (N/K)
number of channels only
Therefore, N = J x K; where J ≤ N
20

21.  The cluster can be replicated many times to
cover the desired geographical area by a
cellular communication system
 Let M be the number of clusters in the
system, then overall system capacity, C is
given as
C=MxN→C=MxJxK (N = J x K)
 When K is reduced, J is proportionally
increased since N = J x K is constant.
 To increase C, M is increased. But reducing K
will increase co-channel interference!
21

22. 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.
22

23. The shift parameters i
and j are separated by
60 degrees in a
hexagonal geometry
It can have any
integer value 0, 1, 2,
….
These can be used to
determine the location
of cochannel cells
23

24. Rules for determining the nearest cochannel cell
using “Shift parameters” (i, j) to lay out a
cellular system is:
 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 …
24

25. 25

26. Distance between
two adjacent cells,
d = √3 R
Let D be the distance
between two
co-channel cells.
D = √{3R2(i2+j2+ixj)}
D2/(3R2) = i2+j2+i x j
26

27. By joining the
centers of the six
nearest cochannel
cells, a large
hexagon is formed
with radius equal
to D, which is also
the cochannel cell
separation.
27

28. Asmall hex = (3√3/2)xR2
Alarge hex = (3√3/2)xD2
Number of cells in large
hexagon, L = D2∕R2
Number of cells enclosed
by large hexagon,
L = K+6x[(1 ∕3)x K] = 3 x
K
K = D2∕ (3 x R2)
K = i 2 + j2 + i x j
28

29. 29

30. 30

31. 9 9
8 10 8 10
2 11 2
7 11
3 7 3
1 12 1
6 12
4 6 4
9 5 9
8 5
10 8 10
2 11 2
7 11
3 7
1 3
12 1 12
6 4 6 4
5 5
31

32.  Reusing an identical frequency channel in
different cells is limited by co-channel
interference between cells.
 The co-channel interference can become a
major problem in cellular communication.
 It is desirable to find the minimum frequency
reuse distance D in order to reduce this co-
channel interference.
32

33.  The number of co-channel cells in the vicinity
of the center cell
 The type of geographic terrain contour
 The antenna height
 The transmitted power at each cell site
NOTE: As long as the cell size is fixed, co-
channel interference is independent of
transmitter power of each cell.
33

34. C1 C1
D
R R
q=D ∕R
The frequency reuse ratio, q is also referred as
 the co-channel reuse ratio
 the co-channel reuse factor
 co-channel interference reduction factor
34

35. • The real power
of the cellular
concept is that
 Interference is
D not related to
the absolute
distance
between cells
6  but related to
6 5 1 the ratio of the
R distance
5 1 7 between co-
7 4 2 channel (same
frequency) cells
4 2 3 to the cell
radius
3
35

36.  The frequency reuse factor, q can be
determined from the cluster size K as
q = D / R = (3K)
 The frequency reuse factor determines the
minimum distance for repeating a set of
frequencies
 The spectrum efficiency is most significantly
influenced by the frequency reuse factor
36

37. 37

38.  Theoretically, a large value of D is desired to
reduce co-channel interference. Large D can
be obtained by choosing large cluster size K.
 However, when K is too large, the number of
channels assigned to each of K cells becomes
small since N is fixed.
 As K increases, system capacity per cell and
hence spectrum efficiency reduces
significantly.
38

39.  Now the challenge is to obtain the smallest K
which can still meet the desired system
performance requirements in terms of
capacity per cell, spectrum utilization
efficiency and received signal quality
(minimum co-channel interference).
 This involves estimating co-channel
interference and selecting the minimum
frequency reuse distance D to reduce co
channel interference (and hence small K).
39

40. Advantage: The Disadvantage: If the
frequency reuse system is not
system can properly designed,
drastically increase co-channel
the spectrum interference may
efficiency, thereby, occur due to the
increasing the simultaneous use of
system capacity. the same channel.
Co-channel Interference is the major
concern in the concept of frequency reuse.
40

41. Sources of Interference
 Another mobile in the same cell
 A call in progress in a neighboring cell
 Other base stations operating in the same frequency
band or
 Any non cellular system which inadvertently leaks
energy into the cellular frequency band
41

42. On Control Channels On Voice Channels
Interference leads to Causes cross talk
missed calls and where the
blocked calls due to subscriber hears
error in the digital
signaling interference in the
background due to
an undesirable
transmission.
 Interference is more pronounced in urban
areas due to greater RF noise floor and
the large number of base stations and
mobiles.
 Capacity cannot be increased.
42

43. 43

44. A channel scanning mobile receiver records
three received signals while moving in any one
co-channel cell, under following conditions:
 When only serving cell transmits (signal
recorded is termed as C)
 Cell-sites of all six co-channel cells only
transmit (signal recorded is termed as I)
 No transmission by any cell site (signal
recorded is termed as N)
44

45.  If C/I > 18 dB in most of the area being served
by a cell, the system is said to be properly
designed.
 If C/I < 18 dB and C/N > 18 dB in some areas,
the system is said to have co-channel
interference problem.
 If both C/I and C/N < 18 dB and C/I is
approximately same as C/N in a given area,
the system is said to have radio coverage
problem.
 If both C/I and C/N are < 18 dB and C/I <
C/N in a given area, the system is said to have
both co-channel interference as well as radio
coverage problem. 45

46. 46

47.  When only the mobile unit in the serving cell
transmits (signal recorded is termed as C)
 Up to six interference levels are obtained at
the serving cell site from six mobile units
transmitting in six co-channel interfering
cells. (the statistical average signal recorded is
termed as I)
 No transmission by any mobile unit (signal
recorded is termed as N)
47

48. Increasing the Using directional
separation antennas at the
between two co- cell site
channel cells (D)
Lowering the Use of diversity
antenna heights scheme at
at the cell site receiver
48

49.  The essential principles of cellular
communication include frequency reuse, co-
channel cells, and co-channel interference
 Various cell parameters based on regular
hexagonal cellular pattern include cluster,
frequency reuse distance, reuse factor
 Co-channel interference reduction methods
aim at maintaining desired signal quality
and cell capacity
49

50. T. L. Singal graduated from National Institute of Technology,
Kurukshetra in 1981 . He began his illustrious career with Avionics
Design Bureau at HAL, Hyderabad and worked on design and
development of Air-Route Surveillance Radar Communication
System. Then he led R&D group in a Telecom company and
successfully developed Multi-Access Wireless Communication
Systems.
He executed international assignment as Senior Network
Consultant with Flextronics International Inc. USA during 2000-
02. He was associated with Nokia, AT&T, Cingular Wireless and
Nortel Networks, for optimization of 2G/3G Cellular Networks in
USA. Since 2003, he is in teaching profession in engineering
colleges in India. He has number of technical research papers
published in the IEEE Proceedings, Journals, and
International/National Conferences. He has authored two text-
books `Wireless Communications’ and `Analog & Digital
Communications’, published by renowned publisher Tata
McGraw-Hill.
50

51. T L Singal, Wireless Communications,
ISBN: 978-0-07-068178-1,
Tata McGraw-Hill, First Edition, 2010.
www.mhhe.com/singal/wc
51

52. tl.singal@chitkara.edu.in
Contact No: +91-98145-42041
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