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8/8/2019 3. Cellular Technology
1/31
HKIVE (ST)
Dept. of Electronic and Information Engg. Page 1 Comm. Products / Cellular Technology
CELLULAR MOBILE DESIGN PRINCIPLES
1 A General Trunking
In order to utilize the switching network moreeffectively, the low-usage local loops (subscribers
lines) are grouped into high-usage trunk-groups before
switching.
Router
ConcentratorSubscribers'lines
Expander
Incoming Outgoing
Central control
trunk-groups
2 Traffic Theory
Traffic theory is used to perform cost-effectivedimensioning of switching and transmission equipment.
2.1 Traffic Unit
Traffic unit is a measure of traffic intensity. The
international unit of traffic intensity is the erlang. Itrepresents the proportion of time within an hour that a
circuit is occupied.
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Trunk-group traffic is the product of the number of calls
and the mean duration of calls handled by the trunk-
group.
A = M Tc (2.1)
where A = Offered traffic in erlangs
M = Number of calls during the busy hour
Tc = Mean call-holding time in hours
2.2 Busy Hour
It is the given period within a day that bears the highest
traffic intensity. The 'busy hour' traffic is used to work
out the equipment quantities of the network. The
reason to use busy hour traffic is that this period usuallyhas the highest amount of blocked or lost calls. If the
dimensioning of equipment at this period is correct and
blocked calls can be minimized, all other non-busy hour
traffic should then be handled satisfactorily.
2.3 Congestion
If all the trunks in a group are busy, it can accept no
further calls. This state is known as congestion (Fig.
2.1).
Traffic carried = traffic offered - traffic lost (2.2)
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traffic
offered
Call
Set-up ConversationCall
Attempt
Call
Cleared
no channel
with channel
traffic
lost
traffic
carried
Figure 2.1 Lost traffic
To specify the performance of a network, the term
grade of service (GOS) is used. It is defined as
B = traffic lost / traffic offered
= proportion of time for which congestion
exists
= probability of congestion or blocking
probability
= probability that a call will be lost due tocongestion (2.3)
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2.4 Erlang-B Distribution
The Erlang-B formula is used in block-call-clear
condition and is given in Eq. 2.4:
B =
=
N
0k
k
N
!k
A
!N
A
(2.4)
where B = Erlang-B loss probability
A = offered traffic intensity
N = available number of circuits
2.4.1 Erlang-B Traffic Table
Erlang-B traffic table (Table 2.1) is used to determine
the maximum amount of offered traffic to a group of N
trunks under a specified grade of service.
2.5 Trunking Efficiency
It is a measure of channel utilization and is defined as
Carried trunk-group traffic / number of channel in the
trunk-group (2.5)
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Number 1 lost call in Number 1 lost call inof 50 100 200 1000 of 50 100 200 1000
trunks (0.02) (0.01) (0.005) (0.001) trunks (0.02) (0.01) (0.005) (0.001)
E E E E E E E E
1 0.02 0.01 0.005 0.001 51 41.2 38.8 36.8 33.4
2 0.22 0.15 0.105 0.046 52 42.1 39.7 37.6 34.2
3 0.6 0.45 0.35 0.19 53 43.1 40.6 38.5 35.0
4 1.1 0.9 0.7 0.44 54 44.0 41.5 39.4 35.85 1.7 1.4 1.1 0.8 55 45.0 42.4 40.3 36.7
6 2.3 1.9 1.6 1.1 56 45.9 43.3 41.2 37.5
7 2.9 2.5 2.2 1.6 57 46.9 44.2 42.1 38.3
8 3.6 3.2 2.7 2.1 58 47.8 45.1 43.0 39.1
9 4.3 3.8 3.3 2.6 59 48.7 46.0 43.9 40.0
10 5.1 4.5 4.0 3.1 60 49.7 46.9 44.7 40.8
11 5.8 5.2 4.6 3.6 61 50.6 47.9 45.6 41.6
12 6.6 5.9 5.3 4.2 62 51.6 48.8 46.5 42.5
13 7.4 6.6 6.0 4.8 63 52.5 49.7 47.4 43.4
14 8.2 7.4 6.6 5.4 64 53.4 50.6 48.3 44.1
15 9.0 8.1 7.4 6.1 65 54.4 51.5 49.2 45.016 9.8 8.9 8.1 6.7 66 55.3 52.4 50.1 45.8
17 10.7 9.6 8.8 7.4 67 56.3 53.3 51.0 46.6
18 11.5 10.4 9.6 8.0 68 57.2 54.2 51.9 47.5
19 12.3 11.2 10.3 8.7 69 58.2 55.1 52.8 48.3
20 13.2 12.0 11.1 9.4 70 59.1 56.0 53.7 49.2
21 14.0 12.8 11.9 10.1 71 60.1 57.0 54.6 50.1
22 14.9 13.7 12.6 10.8 72 61.0 58.0 55.5 50.9
23 15.7 14.5 13.4 11.5 73 62.0 58.9 56.4 51.8
24 16.6 15.3 14.2 12.2 74 62.9 59.8 57.3 52.6
25 17.5 16.1 15.0 13.0 75 63.9 60.7 58.2 53.5
26 18.4 16.9 15.8 13.7 76 64.8 61.7 59.1 54.327 19.3 17.7 16.6 14.4 77 65.8 62.6 60.0 55.2
28 20.2 18.6 17.4 15.2 78 66.7 63.6 60.9 56.1
29 21.1 19.5 18.2 15.9 79 67.7 64.5 61.8 56.9
30 22.0 20.4 19.0 16.7 80 68.6 65.4 62.7 58.7
31 22.9 21.2 19.8 17.4 81 69.6 66.3 63.6 58.7
32 23.8 22.1 20.6 18.2 82 70.5 67.2 64.5 59.5
33 24.7 23.0 21.4 18.9 83 71.5 68.1 65.4 60.4
34 25.6 23.8 22.3 19.7 84 72.4 69.1 66.3 61.3
35 26.5 24.6 23.1 20.5 85 73.4 70.1 67.2 62.1
36 27.4 25.5 23.9 21.3 86 74.4 71.0 68.1 63.0
37 28.3 26.4 24.8 22.1 87 75.4 71.9 69.0 63.9
38 29.3 27.3 25.6 22.9 88 76.3 72.8 69.9 64.8
39 30.1 28.2 26.5 23.7 89 77.2 73.7 70.8 65.6
40 31.0 29.0 27.3 24.5 90 78.2 74.7 71.8 66.6
41 32.0 29.9 28.2 25.3 91 79.2 75.6 72.7 67.4
42 32.9 30.8 29.0 26.1 92 80.1 76.6 73.6 68.3
43 33.8 31.7 29.9 26.9 93 81.0 77.5 74.3 69.1
44 34.7 32.6 30.8 27.7 94 81.9 78.4 75.4 70.0
45 35.6 33.4 31.6 28.5 95 82.9 79.3 76.3 70.9
46 36.6 34.3 32.5 29.3 96 83.8 80.3 77.2 71.8
47 37.5 35.2 33.3 30.1 97 84.8 81.2 78.2 72.6
48 38.4 36.1 34.2 30.9 98 85.7 82.2 79.1 73.5
49 39.4 37.0 35.1 31.7 99 86.7 83.2 80.0 74.4
50 40.3 37.9 35.9 32.5 100 87.6 84.0 80.9 75.3
Table 2.1 Traffic table
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3 Limitation of Radio Telephone
Limited coverage. Poor service performance. Inefficient spectrum utilization.4 Background of Cellular Mobile System
4.1 Network Configuration
In a cellular system (Fig. 4.1), the area to be covered is
divided into a number of small areas called cells. A
base station is used in the center of the cell to serve the
mobiles within its coverage. Each base station is
connected by a fixed data link to a MSC. The MSCs
are interconnected to each other and to the publicswitched telephone network (PSTN).
BS
MSCBS BS
BSMSC
PSTN
BSMScell
Figure 4.1 Cellular Network Infrastructure
Abbreviation: MS ----- Mobile station
BS ----- Base station
MSC -- Mobile switching centre
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4.2 Radio Cells
Hexagonal-shaped cell layouts are used in initial design
to partition coverage areas. They provide seamlesscoverage.
In flat terrain, circular cell layouts are used. They
provide sufficient overlapping regions for call
handovers in addition to seamless coverage.
In most urban area, irregular layouts are used. Noticethat overlapping regions and seamless coverage still
maintained.
Fictitious Ideal Real
Figure 4.2 Cell coverage
4.3 Cluster and Frequency Re-use
Each cellular network has assigned two bands of radio
spectrum for duplex operation. The duplex bands are
divided into a number of carrier pairs and are then
assigned to a defined number N of cells. The N cellsform a group known as the cluster. The cluster repeats
itself over the whole coverage area and therefore
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frequencies are re-used as many times as possible
depending upon the number of clusters. The pattern of
the cells within a cluster is fixed (Fig. 5.1) as it is
optimized for minimizing interference and therefore N
is also known as reuse pattern.
4.4 Frequency Channels
There are two groups of channel operate in forwardor
down (BS to MS) direction and reverse or up (MS to
BS) direction.
Traffic channels are for speech or data
communication.
Control channels are for management purposes.
BS MS
FCCH
RCCH
FTCH
RTCH
FCCH - Forward control channeRCCH - Reverse control channe
FTCH - Forward traffic channelRTCH - Reverse traffic channel
Figure 4.3 Communication between mobile and base
station
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4.5 Location Registration
When a mobile is not engaged in a call, it tunes to the
control channel of the situated cell and monitors theforward signaling information. As the mobile moves
across the network, it will scan all control channels and
lock onto the strongest one which is usually the situated
cells control channel.
The mobile checks the broadcasted location information
and if this differs from the previous cell, the mobileautomatically updates with the network of its location.
Therefore, the network continues to maintain an
updated location database of all mobiles.
4.6 Handoff / Handover
It is a process of transferring a call to another base
station. Handoff occurs when the mobile is at the cell
boundary or in signal-strength holes within a cell.
Handoff decision is based on one or more of the
following conditions:
Received power is below certain threshold (e.g.-95 dBm).
Received Carrier-to-Interference power ratio, C/I isbelow certain threshold (e.g. 18 dB).
A better channel is available from adjacent cell. The local cell is too congested while the adjacent
cell is not (forced handoff).
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4.7 Soft Handoff
The handoff described above belongs to the break-
before-make type. It has higher probability of call dropdue to unsuccessful handover.
In CDMA system the mobile station can use one
frequency but with different codes to communicate with
two base stations at the same time. Handover can be
carried out in a make-before-break condition. It
guarantees higher successful rate of handover.
5 Frequency Reuse Pattern Selection
Because of the frequency re-use, nearby mobiles may
use the same frequency and cause co-channelinterference. The key objective of planning a cellular
radio system is to design the reuse pattern N and
frequency allocation in order to maximize the capacity
of the network whilst controlling co-channel
interference and other interference to within acceptable
limits.
Typical values of N are 3, 4, 7 and 12 (Fig. 5.1).
Reducing N will increase the trunking efficiency.
However, as N decreases, the distance between cocells
(cells with same channels) also reduces, which
increases the co-channel interference.
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AB
DC
A
BC
DE
F
G
4-cell cluster 7-cell cluster
A
GB
CD
E
F
12-cell cluster
HI
J
K
L
BA
C
3-cell cluster
Figure 5.1 Cell reuse patterns
The minimum distance which allows the same
frequency to be reused is called reuse distance D. D isrelated to the cell radius Ras shown in Fig. 5.2 and the
ratio of D to R, called the reuse ratio, is a function of N,
namely
N3R
D= (5.1)
DR
Figure 5.2 D and R of a cluster
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5.1 Co-channel Interference
During a call, the mobile receives wanted carrier signal
C from the base station in which it is located, and alsointerfering signal I from other cells. The carrier-to-
interference ratio C/I ratio is related to the D/R ratio.
For the 3-cell, 4-cell and 7-cell cluster there could be up
to six immediate interferes, as shown in Fig. 5.3.
4-cell clusters 7-cell clusters3-cell clusters
Figure 5.3 The geometry associated with interfering
cells using 3-cell 4-cell and 7-cell clusters
Assuming the fourth power propagation law, an
approximate value of C/I ratio is
C/I =4
4
D6
R
I6
C
I
C
==
(5.2)
Using the D/R ratio,
C/I = 22 N5.1)N3(6
1
I
C== (5.3)
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This shows that the C/I ratio is a function of the reuse
pattern N. For example, suppose N = 7, then C/I 73,
or 18 dB.
Cellular radio systems are designed to tolerate a certain
amount of C/I ratio. Beyond this level, speech quality
will be severely degraded. This lower limit on C/I ratio
effectively sets the minimum D/R ratio that can be used.
The C/I ratio requirement has two other factors may
need to be taken into account:
Adjacent channel interference from near channelsin neighbouring cells.
Multipath fading which may weaken C ascompared to I.
The C/I ratio requirement for analogue cellular systems
varies from 18 to 21 dB. The C/I ratio requirement for
GSM is 9 dB in theory and is 15 dB in practice to
provide quality services.
5.2 Frequency Reuse Pattern of CDMASystem
In CDMA system, because of spread spectrum
technique, much high C/I ratio can be acceptable.
Therefore, all frequencies are re-used in every sector of
cell.
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1
11
1
1
1
111
Figure 5.4 CDMA reuse pattern
5.3 Power Control
Both the base station and the mobile transmission
power needed to be controlled. This has multiple
effects of
(i) Reducing power consumption of the mobile.
(ii) Reducing the co-channel and adjacent channel
interference.
(iii) Reducing the generation of intermodulation
product.
(iv) Conforming the coverage of cell.
5.4 Cell Size
Cell size need not be the same. The cells are
subdivided into smaller cells (microcells) towards the
middle of the city to permit management of a higher
density of users. The peripheral is served by large cells
(macrocells). The underlying principle is if each cell
(whether large or small) has the same amount of
frequency channels, a small cell in size can carry moretraffic per unit area than a large cell.
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5.5 Sectorization
Sectorization is a standard practice in most cellular
systems. In a regular cellular layout, co-channelinterference will be received from six surrounding cells.
One way of cutting the interference is to use several
directional antennas at the base stations, with each
antenna illuminating a sector of the cell and with a
separate channel set allocated to each sector.
60o and 120o cell sectorization are commonly employed(Fig. 5.5). It reduces the number of prime interference
sources to one and two respectively (Fig. 5.6).
120o
60o 120
o
Figure 5.5 60o and 120o sectors
D
Mobile
D+0.7R
Mobile
D+0.7R
R
Figure 5.6 Interference in 7-cell cluster with sectors
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From Fig. 5.6 and Eq. 5.2, worst case C/I ratio:
(7-cell cluster with six sectors per cell)
C/I =4
4
)R7.0D(
R
I
C
+= = 779 = 29 dB
(7-cell cluster with three sectors per cell)
C/I =44
4
D)R7.0D(
R
I
C
++
= = 282 = 24.5 dB
A disadvantage is that the channel sets are divided
between sectors and trunking efficiency is reduced.
However, improved C/I ratio allows the system to use a
smaller reuse pattern N. The net effect of sectorizationis an increase in the total system capacity (Table 5.1).
After sectorization, the original cell coverage is no
more valid. Fig. 5.7 shows the radiation pattern and
coverage of the new 120o sectored cell. Fig. 5.8 shows
the 3-site, 9-cell cluster and the 4-site, 12-cell cluster
which are evolved from the 3-cell and 4-cell clusters.
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System
(396 ch)
N Channels
per sector
Offered
load / site
Mean
C/I (dB)
4 99 86.7 13.8
Omni 7 56 / 57 45.9 / 46.9 18.712 33 24.7 23.3
4 33 74.1 19.8
120o 7 19 36.9 24.5
Sector 12 11 17.4 29
4 16 / 17 64.2 / 58.8 24.8
60o 7 9 25.8 28.9
Sector 12 6 13.8 33GoS = 2%
Table 5.1 Omni vs. sectorized cellular system
performance
d d
d= maximum service distance
Figure 5.7 Cell and 120o sectored cell
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3-cell cluster 3/9-cell cluster
4-cell cluster
4/12-cell cluster
Figure 5.8 Examples of reuse patterns
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5.6 Frequency Channel Assignment
Frequency assignment scheme is used to control
adjacent channel interference (ACI). Main assignmentcriterion is to maintain frequency separation between
channels in the same cell and in the adjacent cells.
Consider the 4-cell cluster in Fig. 5.1 as an example, a
simple frequency assignment will be:
f1 cell A, f2 cell B, f3 cell C, f4 cell D,
f5 cell A, f6 cell B, f7 cell C, f8 cell D .
The main advantage of this arrangement is that all
frequencies within one cell are widely separated (e.g.,
in B: f2, f6, f10 ). It will greatly reduce the ACI.
ACI also appears when two adjacent frequencies (e.g.,
f3 and f4) are assigned to two adjacent cells. It can be
shown that a careful frequency assignment provides
smaller ACI but cannot eliminate ACI. In general, ACI
decreases with the increase of cluster size N.
For sectored cases, the cells are numbered as shown in
Fig. 5.9. Consider the 4/12-cell cluster as an example, a
simple frequency assignment will be:
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f1 cell A1, f2 cell B1, f3 cell C1, f4 cell D1,
f5 cell A2, f6 cell B2, f7 cell C2, f8 cell D2,
f9 cell A3, f10 cell B3, f11 cell C3, f12 cell D3,
f13 cell A1, f14 cell B1, f15 cell C1, f16 cell D1,
f17 cell A2, f18 cell B2, f19 cell C2, f20 cell D2 .
It can be shown that there is no adjacent frequency in
adjacent cells when cluster is equal or larger than 4/12-
cell cluster.
3/9-cell cluster 4/12-cell cluster
A1
A3 A2
B3 B2
C1
C3 C2
B1C2
A3 A2
C3 C3
B2 A1
A3
B1
C1
C2 B1
B2 A1 B3
D1 D2
B2 A1 C3 C2
C1 A3 A2 B1 D1
C2 D3 B3 B2 A1
B1 D1 D2 C1 A3
D3C2C3A1B2
D1B1A2
Figure 5.9 Frequency assignments of 3/9, 4/12-cell
clusters
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5.7 Reuse Pattern Selection
7/21 reuse pattern:
It provides ideal isolation of co-channel and adjacentchannel interference.
4/12 reuse pattern:
Most GSM systems are planned around this reuse
pattern over flat terrain.
3/9 reuse pattern:This pattern can be used by GSM in theory, but it has
the problem of the adjacent channel interference.
5.8 Antenna Arrangement
Fig. 5.10a is a typical antenna configuration layout for a
3-sector cell site. Two receive antennas provide space-
diversity against multi-path fading. Fig. 5.10b shows
the 6-sector antenna array.
Figure 5.10 Antenna array of cell site
R RT R RT
R RT
R
R
T
R
R
T
R
R
T
R
R
T
R
R
T
R
R
T
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6 Adding Capacity
Once a cellular network has been planned to provide
overall coverage, there are a number of ways of addingadditional capacity.
6.1 Cell Architecture Approach
6.1.1 Sectorization
60o and 120o cell sectorization are commonly
employed. It reduces the number of prime interference
sources to one and two respectively. A better overall
C/I ratio then allows a smaller reuse pattern, N to be
used to increase the overall traffic capacity.
6.1.2 Regular Grid
A regular and consistent reuse pattern provides better
overall C/I ratio as compared with non-regular reuse
pattern.
6.1.3 Cell Splitting
By reducing the size of cells, more cells (hence
channels) per area will be available and traffic capacity
will increase. But as cell sizes decrease, it becomes
difficult to find suitable base station sites.
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Figure 6.1 Example of cell splitting for omni-cell.
Figure 6.2 Example of cell splitting for 3-sector cell.
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6.1.4 Microcell, Picocell and Hierarchical
Structure
Marcocells refer generally to cells with large coveragethat serve fast moving vehicle.
Minicells refer generally to cells with antennas just
above local clutter and therefore their coverages are
smaller than that of the macrocells.
Microcells refer generally to cells of small coverage
that are able to serve slower moving pedestrian.
Picocells refer generally to cells that serve indoor area.
Smaller cell size brings up the traffic density per unit
area but the problems are:
It needs new techniques to handle handover. Site locations are difficult to find.Hierarchical layered cell structure with macrocells on
the top and picocells in the bottom provides (i) widearea coverage, (ii) capacity, and (iii) less handover.
However, a careful frequency planning is needed.
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6.2 Dual Networks with Dual-mode Mobiles
Network can be combined for example, GSM800 +
PCS1800, GSM800 + DECT, AMPS + CDMA.Alternative routing between the two networks will
increase trunking efficiency and capacity. Of course, it
needs dual-mode mobiles and the underlay
infrastructure should be able to handle the handover.
6.3 Frequency Utilization Approach
Half rate voice codec is available in GSM specification.
It doubles the channel capacity but the voice quality of
such codec is poorer than the full rate codec and
therefore is still not employed.
6.4 Interference Reduction Approach
Frequency hopping and DTX can be utilized together to
reduce interference and a smaller reuse pattern can be
used.
6.4.1 Frequency Hopping
Frequency hopping has a time averaging effect which
provides extra protection against both channel fading
and co-channel interference. It will reduce dropped-callrate but increase average Bit-Error-Rate, BER.
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6.4.2 Discontinue Transmission (DTX)
Transmission is stopped during the silent period of
conversation. This may account for 60% of thetransmission time in a conversation and a 60%
interference reduction can be obtained. In addition,
mobile power consumption is reduced.
6.5 Frequency Reuse Approach
6.5.1 Intelligent Underlay/Overlay (IUO)
Fig. 6.3 shows the IUO operation. There are additional
overlay cells at the centers of normal underlay cells.
When a mobile moves into the overlay cell coverage
region, the call will be handover from the underlay cell
to the overlay cell and vice versa.
All the overlay cells use some sets of channel known as
super channels. These super channels are arranged in
smaller re-use pattern (e.g. 1/3, 2/6 as shown in Fig.
6.4) and will increase the overall traffic capacity. On
the other hand, co-channel interference among overlaycells is also increased with the short reuse distance.
However, the small overlay cells provide stronger field
strengths and give satisfy C/I ratio.
The network will measure the co-channel interference
and adjust the overlay cell boundaries dynamically and
this is what we call intelligent. This allows maximumutilization of overlay cells to increase system capacity.
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Main advantage of using IUO is that there is no extra
hardware added to the system.
MS
MS
MS
Overlay
Underlay
Overlay
Underlay
BS
BS
Co-channel
interference fsfs
fr
Figure 6.3 Intelligent Underlay-Overlay in Omni
cells
Figure 6.4 Intelligent Underlay-Overlay in sectorized
cells
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7 Cellular System Design Procedure
7.1 Coverage Planning
From the terrain data and selected propagation model,
determine the path loss and fade margin at cell edge.
With the maximum allowable transmitter power and
receiver sensitivity, determine the maximum allowable
distance which gives the maximum coverage of the cell
or sector. The total number of cells or sectors is then
determined by repeating the process until full coverage
is achieved.
7.2 Capacity Planning
From population, land usage and other statistics,
forecast the traffic distribution of the covered region.Together with the coverage plan, determine the traffic
density of each cell in the region.
7.3 Frequency Planning
Select a reuse pattern and then allocate the channels toeach cell. This process should satisfy the required cell
traffic densities and the C/I ratio requirements at the
same time. Several iterations of the above processes
may be needed to finalize a basic cellular plan.
7.4 Traffic Growth
Use the mentioned techniques to handle traffic growth.
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Appendix 1 Erlang-B Formula
Let A = mean traffic (Erlangs)
= mean arrival rate of all callsh = mean service time of a call
N = number of trunk lines
A = h
For a group of N trunks the number of calls in progress
follows a birth and death process known as regular
Markov chain.
The probability of a call arriving during t:
P(a) = At/h
The probability of a call ending during t when k calls
are in progress:
P(e) = kt/h
The probability of a transition from k-1 to k busy trunksduring t is:
P(k-1 k) = P(k-1)P(a) = P(k-1) At/h
The probability of a transition from k to k-1 busy trunks
during t is:
P(k k-1) = P(k)P(e) = P(k) kt/h
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The assumption of statistical equilibrium requires that
P(k k-1) = P(k-1 k)
P(k) =k
AP(k-1)
and in general
P(x) = !x
Ax
P(0)
where P(x) is equal to the probability of x calls in
progress, then
=0xP(x) =
=0x !x
Ax
P(0) = 1
P(0) = 1/=0x !x
Ax
then
P(x) =!x
AxP(0) =
=0k
k
x
!k
A
!x
A
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If the system has N circuits, then
P(x) =
=
N
0k
k
x
!k
A!x
A
A call will not find a free trunk line when all N circuits
are occupied, then
Blocking Probability, B = P(N) =
=
N
0k
k
N
!k
A
!N
A
References
1. CY Lee, Mobile Cellular Telecommunications Systems, McGraw-Hill,
2nd edition, 1995
2. JE Flood, Telecommunications Switching, Traffic and Networks, Prentice
Hall, 1995