View
92
Download
0
Category
Preview:
DESCRIPTION
GSM PLANNING
Citation preview
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
Table of Contents
Table of Contents ................................................................................................................... 1
List of Figures ................................................................................................................... 2
List of Tables ..................................................................................................................... 3
Chapter 6 GSM Frequency Planning ................................................................................... 4
6.1 Overview .................................................................................................................... 4
6.2 Frequency Division and C/I Requirement .................................................................. 5
6.2.1 Frequency Division .......................................................................................... 5
6.2.2 C/I ................................................................................................................... 5
6.3 Frequency Planning Principle .................................................................................... 9
6.4 Normal Frequency Reuse Technology ..................................................................... 10
6.4.1 C/I under 4 x 3 Frequency Reuse Pattern ..................................................... 10
6.4.2 10MHz Bandwidth 4 x 3 Frequency Reuse ................................................... 12
6.4.3 19MHz Bandwidth 4 x 3 Frequency Reuse ................................................... 13
6.4.4 6MHz Bandwidth 4 x 3 Frequency Reuse ..................................................... 13
6.4.5 4 x 3 Frequency Reuse Conclusion .............................................................. 14
6.5 Aggressive Frequency Reuse Technology ............................................................... 15
6.5.1 3 x 3 Frequency Reuse Pattern ..................................................................... 15
6.5.2 2 x 6 Reuse Pattern ...................................................................................... 16
6.5.3 2 x 3 Frequency Reuse Pattern ..................................................................... 19
6.5.4 1 x 3 Frequency Reuse Pattern ..................................................................... 20
6.5.5 1 x 1 Frequency Reuse Pattern ..................................................................... 24
6.5.6 A + B Frequency Reuse Pattern .................................................................... 24
6.6 Concentric Cell Technology ..................................................................................... 26
6.6.1 Concept ......................................................................................................... 26
6.6.2 General Underlay Overlay ............................................................................. 27
6.6.3 Intelligent Underlay Overlay .......................................................................... 28
6.6.4 Characteristics of Concentric Cell Technology .............................................. 29
6.7 Multiple Reuse Pattern Technology ......................................................................... 30
6.7.1 Basic Principle ............................................................................................... 30
6.7.2 MRP Sequence Grouping ............................................................................. 33
6.7.3 MRP Space Grouping ................................................................................... 34
6.7.4 Characteristics of MRP Technology ............................................................... 35
6.7.5 Comparison between MRP and 1 X 3 Frequency Reuse Pattern ................. 36
6.8 Network Capacity Comparison ................................................................................ 36
11/12/2010 All rights reserved Page1 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
List of Figures
Figure 1.1Intra-frequency reuse of the omni-directional base station ..............................6
Figure 1.2Intra-frequency interference for the omni-directional base station...................7
Figure 1.3Normal 4 x 3 frequency reuse pattern................................................................11
Figure 1.43 x 3 frequency reuse pattern.............................................................................15
Figure 1.52 x 6 frequency reuse pattern.............................................................................17
Figure 1.62 x 3 frequency reuse pattern.............................................................................19
Figure 1.71 x 3 frequency reuse pattern.............................................................................21
Figure 1.8A + B frequency reuse pattern............................................................................25
Figure 1.9Schematic diagram of concentric cell................................................................26
Figure 1.10Structure of general underlay overlay..............................................................28
Figure 1.11Structure of intelligent underlay overlay..........................................................28
Figure 1.12Layering aggressive frequency reuse..............................................................30
Figure 1.13Frequency planning under MRP (7.2MHz bandwidth).....................................32
Figure 1.14Frequency planning under MRP space grouping............................................34
11/12/2010 All rights reserved Page2 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
List of Tables
Table 3.1Frequency planning under 4 x 3 frequency reuse pattern (a)............................12
Table 3.2Frequency planning under 4 x 3 frequency reuse pattern (b)............................13
Table 3.3Frequency planning under 4 x 3 frequency reuse pattern (c)............................14
Table 4.1Frequency planning under 3 x 3 frequency reuse pattern.................................15
Table 5.1Frequency planning under 2 x 6 frequency reuse pattern.................................17
Table 6.1Frequency planning under 2 x 3 frequency reuse pattern.................................20
Table 7.11 X 3 frequency reuse space grouping (a)..........................................................21
Table 7.21 x 3 frequency reuse sequence grouping (a).....................................................22
Table 7.31 x 3 frequency reuse space grouping (b)..........................................................22
Table 7.41 x 3 frequency sequence grouping (b)...............................................................23
Table 7.5Frequency planning under 1 x 1 frequency reuse pattern.................................24
Table 8.1Frequency planning under A + B frequency reuse pattern................................25
Table 9.1Channel number grouping for 6MHz bandwidth concentric cell (a)..................27
Table 9.2Channel number grouping for 6MHz bandwidth concentric cell (b)..................27
Table 11.1A comparison between GUO and IUO................................................................29
Table 12.1Channel number allocation for each layer.........................................................30
Table 13.1MRP sequence grouping.....................................................................................33
Table 14.1Comparison of the network capacity under various frequency reuse pattern
................................................................................................................................................36
11/12/2010 All rights reserved Page3 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
Chapter 6 GSM Frequency Planning
6.1 Overview
Frequency resource is scarce for the mobile communication, so how to maximize
the spectrum utilization ratio is a great concern for many carriers, equipment
providers, and scholars. And their research into this problem has accelerated the
development of the communication technologies. By now, the mobile
communication has experienced three phases: analog TACS/AMPS,
GSM/CDMA IS95, and WCDMA/CDMA2000.
The purpose to enhance the spectrum utilization ratio is to expand the network
capacity based on the limited spectrum resource while ensuring the network
quality. If not considering adding frequencies to the network, you can expand the
capacity of a GSM network using the two methods. One is to increase the
number of base stations in the network; the other is to use the frequency reuse
technologies. This chapter mainly describes the GSM frequency reuse
technologies, namely, frequency planning technologies.
To expand the network capacity, you must reuse the limited frequency resources.
Though frequency reuse is beneficial for network expansion, it brings into
another problem. That is, it deteriorates the conversation quality. The more
aggressive the frequencies are reused, the greater the interference will arise in
the network. Therefore, how to seek a balance between network capacity and
conversation quality is a demanding task in frequency planning.
Currently, the 4 x 3, 3 x 3, 2 x 6, 1 x 3, 1 x 1, MRP, and concentric circles are the
GSM frequency technologies in common use. For the 4 x 3 frequency reuse
pattern, the frequency utilization ratio is relatively low, but the higher carrier-to-
interference ratio (C/I) can be obtained, so you can enjoy better conversation
quality. Compared with the 4 x 3 frequency reuse pattern, the 1 x 3 frequency
reuse pattern ensures a relatively high frequency utilization ratio, but the reuse
distance is shorter, so interference is greater and the conversation quality is
poorer. In this case, you should take some measures, such as the frequency
hopping and DTX, against the interference.
The frequency planning is a key technology for GSM network, so the quality of
the frequency planning will determine the network quality.
This chapter introduces the rules of frequency reuse based on the frequency
reuse patterns and the network requirement. Meanwhile, it also provides
11/12/2010 All rights reserved Page4 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
examples to detail the frequency division, C/I, frequency reuse degree under
each reuse pattern.
6.2 Frequency Division and C/I Requirement
6.2.1 Frequency Division
The GSM cellular system can be divided into GSM 900MHz system and DCS
1800MHz system in terms of the band to be used. The carrier spacing is 200
KHz.
I. GSM 900MHz
It has 124 channel numbers. The absolute radio frequency channel number
(ARFCN) is 1–124, and a protection band with 200 KHz in width is reserved at
the two ends. According to the documents prescribed by the relative government
department of China, China Mobile uses the 890–909/936–954MHz band, and
the corresponding ARFCN is 1–95 (generally, the channel number 95 is for
reservation only). For China Unicom, it uses the 909–915/954–960MHz band,
and the corresponding ARFCN is 96–124. For the bands defined for the carriers
from other countries, they can be calculated by the following formulas:
Base station reception: f1 (n) = [890.2 + (n – 1) x 0.2] MHz
Base station transmit: f2 (n) = [f1 (n) + 45] MHz
II. DSC 1800MHz
It has 374 channel numbers. The ARFCN is 512–885. The relationship between
the frequency and the channel number (n) are listed in the following:
Base station reception: f1 (n) = [1710.2 + (n – 512) x 0.2] MHz
Base station transmit: f2 (n) = [f1(n) + 95] MHz
China Mobile uses the 1710–1720 MHz band, and the corresponding ARFCN is
512–561. China Unicom uses the 1745–1755 MHz, and the corresponding
ARFCN is 687–736.
6.2.2 C/I
C/I stands for carrier-to-interference ratio. In the GSM system, frequency reuse
will cause intra-frequency interference. The intra-frequency is related to both the
reuse distance and the cell radius. Hereunder is an example.
6.2.2 shows the intra-frequency reuse of the omni-directional base station.
11/12/2010 All rights reserved Page5 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
Figure 1.1 Intra-frequency reuse of the omni-directional base station
Suppose that the coverage radius of all base stations is the same, the
relationship of the intra-frequency reuse distance (D), the cell radius (R), and
number of each frequency reuse cluster (N) can be expressed by the following
equation:
NRDq 3/ ==
Here,
22 jijiN ++= (“i” and “j” are positive integers)
“q” is the intra-frequency interference attenuation factor.
For the directional cell, the physical meaning of the N stands for the number
of base stations in the frequency reuse clusters.
If the intra-frequency cell and the service cell work at the same time, the MS
locating in the center of the service cell will receive both the useful signals from
this service cell and the interfering signals from the intra-frequency cells. In this
case, the C/I can be expressed by the following equation:
∑=
=k
ikI
C
I
C
1
11/12/2010 All rights reserved Page6 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
Here, kI is the Kth interfering signal. This equation can also be expressed as:
∑=
−= k
i
rkq
I
C
1
)(
1
Here,
kq is the intra-frequency interference attenuation factor of the Kth intra-
frequency interference cell.
r is the path loss slop according to actual geographical environment. In
moving environment, it ranges from 3 to 5. Generally, it is 4.
As shown in 6.2.2, for the omni-directional base station with regular frequency
reuse, there are 6 intra-frequency interference sources at the first layer, namely,
the 6 intra-frequency reuse cells in orange. There are 12 intra-frequency
interference sources at the second layer, namely, the 12 intra-frequency reuse
cells in yellow. However, the 12 intra-frequency interference sources has only a
little effect on the 6 interference sources at the first layer, so it can be neglected.
Figure 1.2 Intra-frequency interference for the omni-directional base station
11/12/2010 All rights reserved Page7 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
If the radio propagation environment between the 6 intra-frequency reuse cells
and the service cell is the keeps stable, the following three equations are
present:
rqI
C−=
6
1
r
I
Cq
1
)6( ×=
6
rq
I
C =
Based on the three equations, the relationship between the C/I and the number
of the base station in the frequency reuse clusters can be expressed by the
following equation:
6
)3( rN
I
C =
When the MS locates at the edge of the service cell, it will receive the poorest
signals form the service cell but the strongest interfering signals. In this case, the
needed C/I can be expressed by the following equation:
6
)1( rq
I
C −=
If the cellular layout is improperly designed, the interfering sources will increase
and the C/I will decrease. According to the previous equations, the more the cells
in each cluster, the greater the C/I and the better the network quality are, but the
frequency utilization ratio will be lower. In addition, the GSM interference is
related to the traffic load. The intra-frequency interference reaches the greatest
when the traffic load reaches the peak.
Generally, the 4 x 3 frequency reuse pattern is used in GSM frequency planning.
For the areas where the traffic is great, you can use other frequency reuse
patterns, such as 3 x 3 and 1 x 3. No matter which frequency reuse pattern you
take, you must meet the requirement on interference-to-protection ratio.
Apart from the intra-frequency interference caused by normal frequency reuse,
there are other abnormal interferences. They are listed in the following:
Multipath signal interference (It occurs when useful signals fall outside the
delay equalizer of the system.)
Outside signal interference (It refers to the signals from the radar, illegal
wireless equipments, and environment noises.)
In the GSM system, the requirements on the C/I are listed in the following:
11/12/2010 All rights reserved Page8 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
For intra-frequency C/I, it must be equal to greater than 9 dB. In actual
projecting, a margin of 3 dB is needed, namely, it is equal to or greater than
12 dB.
For adjacent-frequency C/I, it must be equal to or greater than -9 dB. In
actual projecting, a margin of 3 dB is needed, namely, it is equal to or
greater than -6 dB.
When the carrier offset reaches 400 KHz, the C/I must be equal to or
greater than -41 dB.
6.3 Frequency Planning Principle
Generally, when planning the frequency for the network, you will divide the
geographic area into smaller slices, but you must reserve a certain amount of
channel number at the intersection area between slices if the frequency resource
is adequate.
The intersection area must be far away from the areas where the traffic is great
and the areas where the networking is complex. Generally, you should begin the
planning with the area where base stations are intensively distributed. If there
are rivers or big lakes in the planning area, you must consider the refection effect
of the surface.
Generally, base stations irregularly distributed, so you cannot perform the
frequency planning completely according to 4 x 3 frequency reuse pattern or 3 x
3 frequency reuse pattern. Instead, you must make flexible adjustment according
to actual conditions.
No matter which reuse pattern you take, you must obey the following principles:
Generally, the intra-frequencies and adjacent channel numbers are allowed
to appear within a base station.
The frequency spacing between the BCCH and TCH must be greater than
400 KHz within a cell.
The frequency spacing between the TCHs must be greater than 400 KHz
within a cell. (When frequency hopping is used, you can meet this by
properly setting the mobile allocation index offset.)
The adjacent base stations cannot use the same frequency.
Considering the complexity of the antenna height and radio propagation
environment, the base stations near each other cannot use the same
frequency.
Generally, if using the 1 x 3 frequency reuse pattern, you must ensure that
the number of frequency hopping channel numbers is at least twice that of
the frequency hoping carriers.
Pay special attention to the intra-frequency reuse. The adjacent areas are
not allowed to share the BCCH and the BSIC.
11/12/2010 All rights reserved Page9 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
6.4 Normal Frequency Reuse Technology
6.4.1 C/I under 4 x 3 Frequency Reuse Pattern
The spectrum utilization ratio can be expressed by frequency reuse degree,
which reveals the aggressiveness of the frequency reuse. The frequency reuse
degree can be expressed by the following equation:
TRX
ARFCNreuse N
Nf =
Here NARFCN is the total number of the available channel numbers, and NTRX is the
number of TRXs configured for the cell.
For the n x m frequency reuse pattern, “n” indicates the number of the base
stations in the reuse clusters, and “m” indicates the number of the cells under
each base station. In this case, the frequency reuse degree can be expressed by
the following equation:
reusef = n x m
In actual planning, however, the allocated number of channel numbers will be
greater than n x m, so the actual reusef is usually greater than n x m.
Therefore, the smaller the reusef , the more aggressive the frequency is reused
and the higher the frequency utilization ratio is. As the aggressiveness of the
frequency reuse grows, however, it will bring greater interference to the network.
In this case, you must enable the technologies, including DTX and power control,
to solve this problem. The more aggressive the frequency is reused, the lower
the spectrum utilization ratio is, but the conversation quality is better at this time.
The purpose the frequency planning is to reach a balance between the
frequency utilization ratio and the network capacity. Based on the assurance of
the network quality, you must take measures to maximize the network capacity.
In the GSM system, the 4 x 3 frequency reuse pattern is in basic use. Here “4”
indicates 4 base stations (each base station consists of 3 cells), and “3” indicates
11/12/2010 All rights reserved Page10 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
the 3 cells under the control of each base station. Therefore, there are 12 sectors
are available. And the 12 sectors makes up of a frequency reuse cluster, but the
frequency in the same cluster cannot be reused.
For the 4 x 3 frequency reuse pattern, the intra-frequency spacing is great, so it
can meet GSM system’s requirement on the intra-frequency interference
protection ratio and adjacent frequency interference protection ratio. As a result,
this frequency reuse pattern is good for the network quality and security. Under
the 4 x 3 frequency reuse pattern, the frequency reuse aggressiveness is 12.
For the aggressive reuse introduced hereunder, because the BCCH plays an
important role in the network and you cannot use the apply the anti-interference
measures, such as downlink power control and DTX, to the BCCH, you must
apply the 4 x 3 frequency reuse pattern or looser reuse patterns to the BCCH
carriers.
6.4.1 shows the normal 4 x 3 frequency reuse pattern.
Figure 1.3 Normal 4 x 3 frequency reuse pattern
Under this frequency reuse pattern, N is 4, so the following equation is present:
46.3433 =×== Nq
Under this frequency reuse pattern, each cell is a 120º-directional cell. At this
time, the number of the interference source is reduced by 2, sot the C/I in the
poorest condition can be expressed by the following equation:
dBqq
IC 20)7.0(
1/
44=
++= −−
In actual conditions, because the base station are irregularly distributed, the
antenna height is different, and the effect from the radio environment, the C/I
cannot reach a so high value.
11/12/2010 All rights reserved Page11 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
6.4.2 10MHz Bandwidth 4 x 3 Frequency Reuse
Hereunder are several assumptions:
The available bandwidth is 10MHz.
The channel number is 45–94.
If the channel numbers ranging from 81–94 (14 channel numbers in total)
are allocated to the BCCH, and the other channel numbers are allocated to
TCH.
If the previous assumptions are present, the frequency planning under 4 x 3
frequency reuse pattern is provided in 6.4.2.
Table 3.1 Frequency planning under 4 x 3 frequency reuse pattern (a)
Frequency group
number
A1 B1 C1 D1 A2 B2 C2 D2 A3 B3 C3 D3
Channel number of
each frequency
group
94 93 92 91 90 89 88 87 86 85 84 83
80 79 78 77 76 75 74 73 72 71 70 69
68 67 66 65 64 63 62 61 60 59 58 57
56 55 54 53 52 51 50 49 48 47 46 45
According to this table, the channel numbers in the first line are BCCH numbers,
in which the channel numbers 81 and 82 are standby channel numbers. The
frequency groups correspond to the cell numbers in 6.4.1. The channel number
of BCCH of the cell A1 is 94. It is 80, 68 and 56 for other carriers, and so on.
In a cluster which contains 12 cells, the frequency group for base station A is
{A1, A2, and A3}; the frequency group for base station B is {B1, B2, and B3}; the
frequency group for base station C is {C1, C2, and C3}; and the frequency group
for base station D is {D1, D2, and D3}.
Therefore, as listed in this table, no channel number is reused within a cluster. In
addition, the intra-frequency and adjacent frequency are not available for the
adjacent cells and the same cell.
However, the drawbacks of this frequency reuse pattern are that the frequency
reuse ratio is low and the capacity expansion needs a great amount of the
frequency resources. Therefore, this reuse pattern is not used in the areas where
the network capacity needs to be constantly expanded.
If the bandwidth is 10MHz, the maximum base station configuration is S4/4/4
under the normal 4 x 3 frequency reuse pattern, and the frequency reuse degree
is 12.5 (50/4 = 12.5).
11/12/2010 All rights reserved Page12 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
Note:
The maximum base station type mentioned in the chapter refers to the
configuration type that most continuous base stations can reach. It does not
include standalone base station.
6.4.3 19MHz Bandwidth 4 x 3 Frequency Reuse
For the 19MHz frequency (1 to 94) used by China Mobile, the 4 x 3 frequency
reuse pattern are used for the frequency planning. The channel numbers ranging
from 79 to 94 (16 channel numbers in total) are allocated to the BCCH, and other
channel numbers are allocated to TCH. No channel number is reserved for micro
cells. In this case, the frequency planning solution is provided in 6.4.3.
Table 3.2 Frequency planning under 4 x 3 frequency reuse pattern (b)
Frequency group
number
A1 B1 C1 D1 A2 B2 C2 D2 A3 B3 C3 D3
Channel number of
each frequency
group
94 93 92 91 90 89 88 87 86 85 84 83
78 77 76 75 74 73 72 71 70 69 68 67
66 65 64 63 62 61 60 59 58 57 56 55
54 53 52 51 50 49 48 47 46 45 44 43
42 41 40 39 38 37 36 35 34 33 32 31
30 29 28 27 26 25 24 23 22 21 20 19
18 17 16 15 14 13 12 11 10 9 8 7
6 5 4 3 2 1
As listed in this table, the channel numbers ranging from 79 to 82 are standby
channel numbers. For the 19MHz bandwidth, the maximum base station type
can be S8/7/7 under 4 x 3 frequency reuse pattern. The frequency reuse
degrees are 11.75, 13.43, and 13.43, so the average value is 12.87.
6.4.4 6MHz Bandwidth 4 x 3 Frequency Reuse
For the 6MHz frequency (96 to 124) used by China Unicom, the 4 x 3 frequency
reuse pattern is used for the frequency planning. The channel numbers ranging
from 111 to 124 (14 channel numbers in total) are allocated to the BCCH, and
other channel numbers are allocated to TCH. No channel number is reserved for
micro cells. In this case, the frequency planning solution is provided in
11/12/2010 All rights reserved Page13 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
Table 3.3 Frequency planning under 4 x 3 frequency reuse pattern (c)
Frequency group
number
A1 B1 C1 D1 A2 B2 C2 D2 A3 B3 C3 D3
Channel number of
each frequency
group
124 123 122 121 120 119 118 117 116 115 114 113
110 109 108 107 106 105 104 103 102 101 100 99
98 97 96
As listed in this table, the channel numbers ranging from 111 to 112 are standby
channel numbers. For the 6MHz bandwidth, the maximum base station type can
be S3/2/2 under 4 x 3 frequency reuse pattern. The frequency reuse degrees are
9.67, 13.5, and 13.5, so the average value is 12.22.
6.4.5 4 x 3 Frequency Reuse Conclusion
The 4 x 3 frequency reuse pattern is a basic technology applied in frequency
planning. It is applicable to other frequency aggressive reuse technologies that
are used for the BCCH.
Theoretical analysis shows that when the base stations are regularly distributed
and azimuths of the cells are consistent with each other, the interference can be
reduced to the minimum. Therefore, if you intend to expand the network capacity,
you can keep the base stations to be distributed as regular as possible and plan
the azimuths of the cells along the same direction. In addition, you can also
maintain the antennas at a similar height. However, sometimes you need to
adjust the azimuth of the antenna to improve the coverage, which seems
contradicts to the capacity expansion. Therefore, sometimes you must make find
a balance between the coverage and capacity.
If the network capacity needs to be further expanded, you can take the following
measures:
Split a cell into smaller cells. At present, however, the average coverage
radius of the macro cell base stations in urban areas is already shorter than
500m, so further cell splitting will meet difficulty in cost and technology.
Utilize new frequency resources. For example, you can employ the
1800MHz band to establish a DSC 1800MHz network.
Under the current 900MHz network, use more aggressive frequency reuse
technology to expand the network capacity.
At present, the aggressive frequency reuse technology works as the most
economical and convenient way to expand the network capacity, so it is also the
most popular with carriers.
11/12/2010 All rights reserved Page14 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
The typical frequency reuse technology includes 3 x 3, 2 x 6, 2 x 3, 1 x 3, and 1 x
1.
6.5 Aggressive Frequency Reuse Technology
6.5.1 3 x 3 Frequency Reuse Pattern
The 3 x 3 frequency reuse pattern can be used in the areas with high traffic. That
is, three base stations form a group, and each base station has three cells, so
there are 9 cells, which form a frequency reuse cluster. However, the 9 cells use
different frequencies. Compared with the 4 x 3 frequency reuse pattern, the intra-
frequency reuse distance under the 3 x 3 frequency reuse pattern is small, so
on-line interference is greater.
6.5.1 shows the 3 x 3 frequency reuse pattern.
Figure 1.4 3 x 3 frequency reuse pattern
If the available bandwidth is 10MHz and the channel numbers are from 45 to 94,
you can use normal 4 x 3 frequency reuse pattern on BCCH. In this case, the
frequency ranges from 81 to 94, so 14 channel numbers are available. For TCH,
you can use 3 x 3 frequency reuse pattern. In this case, the frequency ranges
from 45 to 80, so 36 channel numbers are available.
For the frequency planning under 3 x 3 frequency reuse pattern, see 6.5.1.
Table 4.1 Frequency planning under 3 x 3 frequency reuse pattern
Frequency group
number
A1 B1 C1 A2 B2 C2 A3 B3 C3
Channel number of
each
80 79 78 77 76 75 74 73 72
71 70 69 68 67 66 65 64 63
11/12/2010 All rights reserved Page15 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
frequency group
62 61 60 59 58 57 56 55 54
53 52 51 50 49 48 47 46 45
If 3 x 3 reusing the 10MHz band, you can configure the maximum base station
type as S5/5/5, and the frequency reuse degree is 10.
According to previous equations, because the number of base stations is 3 (N =
3), the intra-frequency interference attenuation factor is 3 (q = 3). In this case,
the number of the intra-frequency interference sources is 2 at the first layer. If the
radius of the cell is 4, the theoretical carrier-to-interference ratio (C/I) can be
expressed by the following equation:
dBq
IC 07.162
1/
4=
⋅= −
In actual conditions, because base stations are irregularly distributed, the
antenna height varies, and the effect from the radio environment, the value of C/I
can not be as high as 16.07 dB.
When the bandwidth is 10MHz, the base station type can be configured as
S5/5/5 under 3 x 3 frequency reuse pattern. For 4 x 3 frequency reuse pattern,
the maximum base station configuration type can only be configured as S4/4/4/.
Therefore, network capacity under 3 x 3 frequency reuse pattern is greater than
that under 4 x 3 frequency reuse pattern when the bandwidth is the same.
When the number of subscribers in a network is not great, you can use the 3 x 3
frequency reuse pattern to ease the pressure of network capacity. In actual
conditions, however, because base stations are irregularly distributed, the
antenna height is different, and the coverage area of each base station varies,
the interference in the network will increase. In this case, if you intend to obtain
better voice quality, you must take some anti-interference measures, such as
using frequency hopping and DTX.
The characteristic of the 3 x 3 frequency reuse pattern are as follows:
The adjustment for network structure is unnecessary.
The frequencies can be easily grouped and the system capacity is great.
Compared with 4 x 3 frequency reuse pattern, 3 x 3 frequency reuse pattern
brings greater interference, but the overall interference can be controlled to
a lower level.
If frequency hopping is used, adequate bandwidth is needed.
6.5.2 2 x 6 Reuse Pattern
The 2 x 6 frequency reuse pattern is developed from the 4 x 3 frequency reuse
pattern. Under the 4 x 3 frequency reuse pattern, you can add anther 2 cells to
11/12/2010 All rights reserved Page16 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
each base station, so 2 base stations (each base station has 6 60°-sectorized
cells) has 12 cells, which form a frequency reuse cluster. In this case, a
frequency reuse cluster contains 12 60°-sectorized cells, and this is defined as 2
x 6 frequency reuse pattern.
6.5.2 shows the 2 x 6 frequency reuse pattern.
Figure 1.5 2 x 6 frequency reuse pattern
Under the 2 x 6 frequency reuse pattern, 45.2233 =×== Nq .
Because each cell is 60°-directional cell under 2 x 6 frequency reuse pattern, the
interference source of each cell is reduced to 1 at the first layer. In this case, the
theoretical C/I can be expressed by the following equation:
dBq
IC 6.151
/4
== −
In actual conditions, because base stations are irregularly distributed, the
antenna height is different, and the effect from radio environment, the value of
C/I cannot be as high as 15.6 dB.
If the available bandwidth is 10MHz, the channel numbers range from 45 to 94,
you can also use 2 x 6 frequency reused pattern. Considering the characteristics
of the 2 x 6 cellular structures, you can also use the 2 x 6 frequency reuse for
BCCH. The frequencies are from 81 to 94, 14 channel numbers in total, and the
others are TCH numbers.
For the frequency planning under 2 x 6 frequency reuse pattern, see 6.5.2.
Table 5.1 Frequency planning under 2 x 6 frequency reuse pattern
Frequency group
number
A1 B1 A2 B2 A3 B3 A4 B4 A5 B5 A6 B6
11/12/2010 All rights reserved Page17 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
Channel number of
each frequency
group
94 93 92 91 90 89 88 87 86 85 84 83
80 79 78 77 76 75 74 73 72 71 70 69
68 67 66 65 64 63 62 61 60 59 58 57
56 55 54 53 52 51 50 49 48 47 46 45
As listed in this table, when allocating frequency to the base station, you can
select the frequency according to the regularity of {A1, A2, A3, A4, A4, A6} and
{B1, B2, B3, B4, B5, B6}. Note that intra-frequency and neighbor frequency
cannot be present within the same cell and adjacent cells.
Under the 2 x 6 frequency reuse pattern, you can enhance the system capacity
by adding new cells to the base station. Compared with 4 x 3 frequency reuse
pattern, the maximum base station type can be configured as S4/4/4/4/4/4 under
2 x 6 frequency reuse pattern, so the capacity of a single base station is twice
that of the base station under the 4 x 3 frequency reuse pattern.
Under this frequency reuse pattern, however, the intra-frequency reuse distance
is further shortened, which increases network interference greatly. In addition, as
the number of cells increases, the requirements on the half-power angle and
other antenna indexes are higher. Moreover, you must add antenna feeders to
the system if using the 2 x 6 frequency reuse pattern, which brings great difficulty
to project implementation. Therefore, the 2 x 6 frequency reuse pattern is seldom
used.
For the 2 x 6 frequency reuse pattern, the frequency reuse degree is 12.5. And
its characteristics are listed in the following:
Through add more cells to each base station, you can enhance the capacity
of the base station greatly.
The antennas with smaller half-power angle and good performance are
needed and the requirement on antenna and base station address is strict.
The signals radiated by antennas are more concentrated, which is good for
indoor coverage.
The BSS system must support 6 sectors.
More antennas are needed under the 2 x 6 frequency reuse pattern than
that under 4 x 3 frequency reuse pattern, so you must adjust and optimize
the planning for antenna system and frequencies.
The times of handovers under the 2 x 6 frequency reuse pattern are more
than that under the 4 x 3 frequency reuse pattern.
The intra-frequency reuse distance is small, so the interference within the
network is great. Therefore, you must take anti-frequency measures, such
as using DTX and frequency hopping.
11/12/2010 All rights reserved Page18 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
6.5.3 2 x 3 Frequency Reuse Pattern
Under 2 x 3 frequency reuse pattern, there are 2 base stations. Each one has 3
cells, so 6 cells form a frequency reuse cluster. The cells in the same cluster use
the different frequencies, and the cells in different clusters use the same
frequency group. This is defined as the 2 x 3 frequency reuse pattern.
6.5.3 shows the 2 x 3 frequency reuse pattern.
Figure 1.6 2 x 3 frequency reuse pattern
Under 2 x 3 frequency reuse pattern, each intra-frequency cell is interfered by 3
cells. Because the number of base stations in each frequency cluster is 2 (N =
2), the intra-frequency interference attenuation factor (q) can be expressed by
the following equation:
45.22*33 === Nq
For regularly-arranged cells, the theoretical carrier-to-interference ratio (C/I) can
be expressed by the following equation:
dBq
IC 8.103
1/
4=
⋅= −
Even if the cells are regularly arranged, however, the value of C/I cannot meet
the requirement of the network. Therefore, you must take anti-frequency
measures, such as frequency hopping, power control, and DTX.
For 10MHz bandwidth, the available channel numbers are from 45 to 94. If the
14 channel numbers (81-94) are BCCH numbers, and the others are TCH
numbers, the frequencies are planned according to 6.5.3 under 2 x 3 frequency
reuse pattern.
11/12/2010 All rights reserved Page19 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
Table 6.1 Frequency planning under 2 x 3 frequency reuse pattern
Frequency group number
A1 B1 A2 B2 A3 B3
Channel number of each frequency
group
80 79 78 77 76 75
74 73 72 71 70 69
68 67 66 65 64 63
62 61 60 59 58 57
56 55 54 53 52 51
50 49 48 47 46 45
You can use looser 4 x 3 frequency reuse pattern and allocate 14 channel
numbers for BCCH. If the bandwidth is 10MHz, you can configure the maximum
base station type as S7/7/7 under the 2 x 3 frequency reuse pattern. In this case,
the frequency reuse degree is 7.14.
The network capacity is great under the 2 x 3 frequency reuse pattern, but small
intra-frequency reuse distance will cause great interference. In addition, the cell
traffic cannot 100% reach the designated value. In actual conditions, therefore,
you can use the looser 4 x 3 frequency reuse pattern for BCCH and the 2 x 3
frequency reuse pattern for TCH.
The characteristics of the 2 x 3 frequency reuse pattern are listed below:
The network capacity is relatively great.
The adjustment for the network structure is unnecessary.
The network capacity can be expanded without wide frequency band.
Small intra-frequency reuse distance will cause great interference, so you
must take anti-interference measures to ensure network quality.
Radio frequency (RF) hopping technology must be used to support the
equipments.
The antennas must be directed to the same direction as much as possible.
6.5.4 1 x 3 Frequency Reuse Pattern
1 x 3 frequency reuse pattern is also called fractional reuse. For 1 x 3 or 1 x 1
frequency reuse pattern, the reuse distance is quite small, so the interference in
the network is quite great. Therefore, to avoid frequency collision, you must use
RF hopping technology and set the parameters, including MA (mobile allocation),
HSN (hopping sequence number), and MAIO (mobile allocation index offset).
The ratio of number of the TRXs to that of the frequency hopping is FR LOAD
(generally, it is smaller than 50%).
Under the 1 x 3 frequency reuse pattern, the interference in the network can also
11/12/2010 All rights reserved Page20 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
indicates the probability of the collision of intra-frequencies and neighbor
frequencies. Emulation shows that probability of the collision is related to FR
only.
According to 1 x 3 frequency reuse pattern, the 3 cells of a base station form a
frequency reuse cluster. The same-directional cells of each base station use the
same frequency group.
6.5.4 shows the 1 x 3 frequency reuse pattern.
Figure 1.7 1 x 3 frequency reuse pattern
For the 1 x 3 frequency reuse pattern, the number of base station is 1 (N = 1), so
73.13 == Nq , and dBq
IC 8.43
1/
4=
⋅= − .
Because the value of C/I here is far lower than the protection value required by
the system, you must take anti-interference measures, such as frequency
hopping, power control, and DTX, to enhance the value of C/I.
If the available bandwidth is 10MHz, the available channel numbers are from 45
to 94. Because RF hopping must be used under 1 x 3 frequency reuse pattern,
considering the importance of BCCH, you can use 4 x 3 frequency reuse pattern
for BCCH and 1 x 3 frequency reuse pattern for TCH.
For BCCH, 14 channel numbers (81-94) are available; for TCH, 36 channel
numbers (45-80) are available.
The channel numbers used for TCH are divided according to two ways. They are
space grouping and sequence grouping. For the 1 x 3 frequency reuse spacing
grouping, see 6.5.4.
Table 7.1 1 X 3 frequency reuse space grouping (a)
Frequency group number
Channel number MAIO
A 80, 77, 74, 71, 68, 65, 62, 59, 56, 53, 50, 47 0, 2, 4,6, 8, 10
11/12/2010 All rights reserved Page21 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
B 79, 76, 73, 70, 67, 64, 61, 58, 55, 52,49, 46 1, 3, 5, 7, 9, 11
C 78, 75, 72, 69, 66, 63, 60, 57, 54, 51, 48, 45 0, 2, 4, 6, 8, 10
For the 1 x 3 frequency reuse sequence grouping, see 6.5.4.
Table 7.2 1 x 3 frequency reuse sequence grouping (a)
Frequency group number
Channel number MAIO
A 80, 79, 78, 77, 76, 75, 74, 73,72, 71, 70, 69 0, 2, 4, 6, 8, 10
B 68, 67, 66, 65, 64, 63, 62, 61, 60, 59, 58, 57 0, 2, 4, 6, 8, 10
C 56, 55, 54, 53, 52, 51, 50, 49, 48, 47, 46, 45 0, 2, 4, 6, 8, 10
Because the ratio of the number of carriers to that of frequency hopping is
required to be 1 to 2, if the bandwidth is 10MHz, you can configure the maximum
base station type as S7/7/7. In this case, the frequency reuse degree is 7.14.
The 3 cells of the same base station use the same HSN, and the cells of different
base stations use different HSNs. To avoid the interference from neighbor
frequencies, you can configure a proper MAIO for the cells of the same base
station.
If the available bandwidth is 6MHz, the available channel numbers are from 96 to
124. In this case, you can use 4 x 3 frequency reuse pattern for BCCH (the
available channel numbers are from 111 to 124, namely, 14 in total). For TCH,
you can use 1 x 3 frequency reuse pattern (the available channel numbers are
from 96 to 110, namely, 15 in total.
For the 1 x 3 frequency reuse space grouping when the bandwidth is 6MHz, see
6.5.4.
Table 7.3 1 x 3 frequency reuse space grouping (b)
Frequency group number
Channel number MAIO
A 96, 99, 102, 105, 108 0, 2, 4
B 97, 100, 103, 106, 109 1, 3
C 98, 101, 104, 107, 110 0, 2
When the bandwidth is 6MHz, you can configure the maximum base station type
as S4/3/3 under 1 x 3 frequency reuse space grouping. In this case, the
frequency reuse degree is 7.25/9.67/9.67, with 8.86 in average.
11/12/2010 All rights reserved Page22 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
For the 1 x 3 frequency reuse sequence grouping, see
Table 7.4 1 x 3 frequency sequence grouping (b)
Frequency group number
Channel number MAIO
A 96, 97, 98, 99, 100 0, 2
B 101, 102, 103, 104, 105 0, 2
C 106, 107, 108, 109, 110 0, 2
Because the ratio of the number of carriers to that of frequency hopping is
required to be 1 to 2, if the bandwidth is 6MHz, you can configure the maximum
base station type as S3/3/3. In this case, the frequency reuse degree is 9.67.
For TCH, both the space grouping and sequence grouping have drawbacks.
Generally, for the urban areas where base stations are regularly and densely
distributed, you should better use sequence grouping. For the areas where base
stations are fragmentary and irregularly distributed, you should better use space
grouping.
The characteristics of 1 x 3 frequency reuse pattern are listed below:
The frequencies are more aggressively reused, so the network capacity is
great.
The network capacity under space grouping is a little greater than that under
sequence grouping.
When planning a network, you need to plan channel numbers for BCCH
only.
Re-planning for frequencies is unnecessary during network optimization.
The efficiency for network planning is high.
Wideband combiner must be used, but the cavity combiner with frequency
selectivity is inapplicable.
This frequency reuse pattern requires wideband repeater.
The interference among intra-frequencies and neighbor frequencies
increases as the frequency reuse distance decreases.
RF hopping must be used, and the channel numbers participating frequency
hopping is twice that of the number of carriers at least.
In actual conditions, you cannot take anti-interference measures, such as
RF hopping, DTX, and power control, for BCCH. Therefore, to ensure
network quality, you can use the looser 4 x 3 frequency reuse pattern for
BCCH only.
11/12/2010 All rights reserved Page23 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
6.5.5 1 x 1 Frequency Reuse Pattern
One cell of one base station forms a frequency reuse cluster, and this is defined
1 x 2 frequency reuse pattern. Other cells and this cell use the same frequency
group.
If the available bandwidth is 6MHz, the available channel numbers are from 96 to
124. Because RF hopping must be used under 1 x 1 frequency reuse pattern,
considering the importance of BCCH, you can use 4 x 3 frequency reuse pattern
for BCCH and 1 x 1 frequency reuse pattern for TCH.
If 4 x 3 frequency reuse pattern is used for BCCH, the available channel
numbers are from 111 to 124, 14 in total. The channel numbers from 96 to 110
are used for TCH, 15 in total.
For the frequency planning under 1 x 1 frequency reuse pattern, see 6.5.5.
Table 7.5 Frequency planning under 1 x 1 frequency reuse pattern.
Frequency group
number
Channel number MAIO
A 96,97,98,99,100,101,102,103,104,105,106,107,108,109,110 0,2,4
B 96,97,98,99,100,101,102,103,104,105,106,107,108,109,110 6,8
C 96,97,98,99,100,101,102,103,104,105,106,107,108,109,110 10,12
If the bandwidth is 6MHz, you can configure the maximum base station type as
S4/3/3/ under 1 x 1 frequency reuse pattern. In this case, the frequency reuse
degree is 7.25/9.67/9.67, so the average value is 8.86.
Therefore, the maximum base station configuration under 1 x 1 frequency reuse
pattern is the same as that under 1 x 3 frequency reuse space grouping pattern,
so is the network capacity.
6.5.6 A + B Frequency Reuse Pattern
The A + B frequency reuse pattern is developed from 1 x 3 frequency reuse
pattern. When the bandwidth is narrow but the capacity is great, you can use this
frequency reuse pattern. In this case, you must use RF hopping. Under the A + B
frequency reuse pattern, the frequencies can be divided into three groups. They
are {f1}, {f2}, and {f3}. For frequency planning, see 6.5.6.
11/12/2010 All rights reserved Page24 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
Figure 1.8 A + B frequency reuse pattern
According to A + B frequency reuse pattern, you can increase frequency diversity
gain by increasing the number of channel numbers participating frequency
hopping within the cell, because the increase of the frequency diversity gain can
improve the carrier-to-interference ratio. To avoid interference among intra-
frequencies and neighbor frequencies, you can configure a proper MAIO for the
cells within the same base station. The probability of the collision of the intra-
frequencies and neighbor frequencies will decrease as the number of channel
numbers participating frequency hopping increases among cells of different base
stations.
If the available bandwidth is 6MHz, the available channel numbers are 96 to 124.
For A + B frequency reuse pattern, you must use RF hopping, but the BCCH
does not participate in RF hopping. Therefore, in actual planning, to ensure good
network quality, you can use looser 4 x 3 frequency reuse pattern for BCCH and
A + B frequency reuse pattern for TCH.
If you use 4 x 3 frequency reuse for BCCH, the available channel numbers are
111 to 124, 14 in total, in which two channel numbers are standby ones. For
TCH, the available channel numbers are 96 to 110, 15 in total.
For the frequency planning under A + B frequency reuse pattern, see 6.5.6.
Table 8.1 Frequency planning under A + B frequency reuse pattern
Frequency group number
Channel number MAIO
A 96, 97, 98, 99, 100, 101, 102, 103, 104, 105 0, 2, 4
B 101, 102, 103, 104, 105, 106, 107, 108, 109, 110 1, 3
C 96, 97, 98, 99, 100, 106, 107, 108, 109, 110 5, 7
11/12/2010 All rights reserved Page25 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
When the bandwidth is 10MHz, you can configure the maximum base station
type as S4/3/3 under A + B frequency reuse pattern. In this case, the frequency
reuse degree is 7.25/9.67/9.67, so the average value is 8.86.
In actual conditions, the irregular distribution of base stations and antenna height
may deteriorate the performance of parts of the network. Therefore, the A + B
frequency reuse pattern are not recommended in large networks.
6.6 Concentric Cell Technology
6.6.1 Concept
In the GSM network, concentric cell technology is used to divide the service area
into two parts: overlay and underlay. In essence, the concentric cell technology
concerns channel allocation and handover. When combining this technology with
various frequency planning technologies, you can both expand network capacity
and improve network quality.
The underlay covers the traditional cells, and the overlay covers the areas near
the base station. Generally, 4 x 3 frequency reuse pattern is used for the
underlay. For overlay, the frequency reuse patterns, such as 3 x 3, 2 x 3, or 1 x 3,
are used. Therefore, all carriers can be divided into two groups, one for underlay,
and the other one for overlay. The overlay and underlay share the same base
station address, one set of antenna feeder system, and one BCCH, so you must
set the BCCH on the underlay.
6.6.1 shows the schematic diagram of the concentric cell.
Figure 1.9 Schematic diagram of concentric cell
If the capacity of the overlay is great, you can group the channel numbers
according to 6.6.1. In this case, the overlay has more channel numbers, which is
beneficial for the base station to absorb nearby traffic volume.
11/12/2010 All rights reserved Page26 of 37
Overlay
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
Table 9.1 Channel number grouping for 6MHz bandwidth concentric cell (a)
If traffic volume is evenly distributed, you can enhance the underlay capacity
through grouping the channel numbers according to 6.6.1. In this case, the
underlay can absorb more traffic volume.
Table 9.2 Channel number grouping for 6MHz bandwidth concentric cell (b)
6.6.2 General Underlay Overlay
General underlay overlay (GUO) aims to restrict the intra-frequency interference.
To realize this purpose, you can reduce the overlay coverage area. That is, if the
transmit power of the overlay carriers is lower than that of the underlay carriers,
the coverage area of the overlay is smaller than that of the underlay.
The handover between the overlay and underlay is related to the receiving level
of the MS and the TA (timing advance) from the MS to the base station. You
should allocate the channel numbers (such as BCCH number) with looser
frequency reuse aggressiveness to the MSs in the underlay. For the MSs in the
overlay, you should allocate the channel numbers with aggressive frequency
reuse to them. In this case, you can expand the network capacity by using
aggressive frequency reuse pattern in overlay.
6.6.2 shows the structure of the general underlay overlay.
11/12/2010 All rights reserved Page27 of 37
Logical channel
Channel number
Underlay
(12)
66 67 68 69 70 71 72 73 74 75 76 77
Overlay (18)
78 79 80 81 82 83 84 85 86 87 88 98 90 91 92 93 94 95
Logical channel
Channel number
Underlay (24)
66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89
Overlay (6 )
90 91 92 93 94 95
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
Figure 1.10 Structure of general underlay overlay
For general underlay overlay, the coverage area of the underlay is inconsistent
with that of the overlay, so problems concerning traffic and handover control are
often caused. The general underlay overlay is applicable to the areas near the
base station where the traffic is concentrated. The more concentrated the traffic
near the base station, the more apparent the effect of capacity expansion is.
However, the transmit power of the carriers in the overlay is low, so it is hard for
the base station to absorb indoor traffic volume. In this case, when the traffic
volume is evenly distributed, the general underlay overlay has little effect on
capacity expansion.
6.6.3 Intelligent Underlay Overlay
Intelligent underlay overlay (IUO) technology can ensure that the coverage areas
of call carriers are the same. For an IUO, the transmit power of the carriers in the
underlay and overlay is the same. For the structure of the IUO, see 6.6.3.
Figure 1.11 Structure of intelligent underlay overlay
In an IUO, the frequencies of a base station are divided into two layers: one is
regular layer, and the other one is supper layer. At the regular layer, the
frequency reuse distance is large, so you can use looser frequency reuse
pattern, such as 4 x 3 frequency reuse pattern. At the supper layer, the frequency
reuse distance is relatively small, so you can use aggressive frequency reuse
patterns, such as 2 x 3 and 1 x 3 frequency reuse pattern.
11/12/2010 All rights reserved Page28 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
In an IUO, the interference at the supper layer is great, so designated
equipments and handover algorithms on C/I must be provided.
In an IUO, the conversation is first established at the supper layer, and then the
BSC monitors the C/I of the channels at the supper layer without any stop. If the
C/I is greater than the Good C/I Threshold, the conversation seizes a channel at
the supper layer. If the C/I is smaller than the Bad C/I Threshold, the
conversation seizes a channel at the regular layer. In addition, you can control
the traffic volume at the supper layer and the regular layer by adjusting the
handover threshold.
For an IUO, the transmit power of the carriers at the regular layer is the same as
that at the supper layer, so the network can absorb the traffic flexibly, which is
beneficial for the expansion for actual network capacity.
If the IUO technology is used, you must add the functions, including the
estimation of intra-frequency protection C/I for downlink channels and the
handover algorithms related to IUO, to the system.
6.6.4 Characteristics of Concentric Cell Technology
The characteristics of concentric cell technology are listed below:
Any change of the network structure is unnecessary.
Special software and designated algorithms on channel allocation and
handover are needed.
The system has no special requirement on hardware.
GUO is applicable to the areas near the base station where the traffic is
concentrated.
The overlay coverage of the GUO is small, so the intra-frequency reuse
attenuation factor (q) is great, which increases interference in the network.
The transmit power of the overlay carriers in the GUO is low, so it is hard for
the carriers to absorb indoor traffic.
The transmit power of the underlay carriers in the GUO is the same, so the
carriers can absorb indoor traffic, which contributes to network capacity
expansion and good conversation quality.
For the comparison between the GUO and IUO, see 6.6.4.
Table 11.1 A comparison between GUO and IUO.
Coverage area
Frequency reuse pattern
Transmit power
Logical channel allocation
Handover algorithm
GUO Underlay 4 x 3 High BCCH/TCH Power& Distance
Overlay 3 x 3/2 x 3/1 x 3 Low TCH
11/12/2010 All rights reserved Page29 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
IUO Underlay 4 x 3 Same BCCH/TCH C/I
Overlay 3 x 3/2 x 3/1 x 3 Same TCH
6.7 Multiple Reuse Pattern Technology
6.7.1 Basic Principle
According to multiple reuse pattern (MRP), the carriers are divided into several
groups. The carries in each group work as an independent layer, and each layer
uses a different frequency reuse pattern. During frequency planning, you can
configure the carriers layer by layer, with reuse aggressiveness increases layer
by layer, as shown in 6.7.1.
Figure 1.12 Layering aggressive frequency reuse
In this figure, the ellipse in the same color indicates a frequency group, in which
the frequencies are reused, and the size of an ellipse indicates its coverage
area. L1, L2…L3 indicates frequency layers in the cell. As shown in this figure,
the degree of frequency reuse aggressiveness is greater at upper layers. If the
bandwidth is certain, the number of carriers is greater under the layering
aggressive frequency reuse pattern than that under the frequency reuse pattern
where the reuse degree is the same between layers.
MRP has no special requirement on hardware. It is developed from the concept
of carrier layering. That is, the available channel numbers are divided into
multiple groups, and each group works as a carrier layer. According to the rules
of the aggressive frequency reuse pattern, the channel numbers allocated for
each layer are listed in 6.7.1.
Table 12.1 Channel number allocation for each layer
Layer Channel number
BCCH n1
11/12/2010 All rights reserved Page30 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
TCH 1 n2
TCH 2 n3
… …
TCHm-1 nm
Note:
n1 ≥ n2 ≥ n3 ≥ n4 ≥…≥nm.
For MRP, first you must divide an available band into several sub-bands.
Generally, the sub-bands work as the bands for BCCH. The reasons are listed
below:
BSIC decoding will not be affected by traffic. TCH numbers cannot affect
separated BCCH numbers, which is helpful for the MS to decode the BSIC.
The planning for adjacent cell list can be simplified. The separated BCCH
numbers contributes the simplification of adjacent cell list, so the MS can
capture the useful BCCH quickly.
Maximum gain can be obtained from power control and DTX. Downlink
power control and DTX can be applied to TCH carriers only, so the
separated BCCH numbers can maximize the function of downlink power
control and DTX.
The re-planning for TCH numbers will not affect BCCH. When a TRX is
added to the system, if not considering the isolation of combiner and
adjacent frequency interference, you do not have to change the BCCH
numbers.
After that, you must divide the remaining channel numbers into multiple TCH
bands. For MRP, different frequency reuse patterns must be used for different
TCH bands.
According to the carrier allocation in the network, you can decide the average
frequency reuse degree. According to the maximum number of carriers
configured in each cell and the number of cells configured in the network, you
can adjust the average frequency reuse degree to a proper value. In this way,
you can effectively control network quality.
The increase of the carries has little effect on the frequency allocation plan. The
increased channel numbers affect other cells that have more carriers than the
service cell has. For example, if a cell has four carriers, the cells that have been
configured with more than four cells will be affected.
MRP technology enables carriers to be configured flexibly. According to MRP, the
frequencies of a cell can never be completely identical with that of the adjacent
cells. Therefore, the MRP improves both the intra-frequency interference
protection ratio and frequency hopping effect.
11/12/2010 All rights reserved Page31 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
According to the requirements defined in GSM protocols, all the downlink
timeslots of the BCCH carriers must transit with full power and the interference
features of the BCCH are different from that of the TCH. Therefore, to ensure
network quality and security, you are recommended to use 4 x 3 frequency reuse
pattern for BCCH. In this case, the channel numbers used for BCCH are equal to
or more than 12. In actual conditions, they are from 12 to 15.
If the available bandwidth is 7.2MHz, the available channel numbers are from 60
to 95, 36 in total, and they can be divided into 4 groups, as shown in 6.7.1.
Figure 1.13 Frequency planning under MRP (7.2MHz bandwidth)
As shown in this figure, 12 channel numbers can be reused for BCCH. Traffic
channels are divided into TCH1, TCH2, and TCH3. For TCH1, 9 channel
numbers can be reused; for TCH2, 8 channel numbers can be reused; and for
TCH3, 7 channel numbers can be reused.
To ensure network security, you must finish BCCH number allocation first. To be
specific, plan the 12 channel numbers according to 4 x 3 frequency reuse pattern
11/12/2010 All rights reserved Page32 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
and allocate 1 BCCH number to each of the 12 cells. After that, you should
allocate 1 carrier at the TCH3 layer to each cell, and then you should allocate the
TCH2 and TCH1 numbers to the cells. In this case, you can configure four
channel numbers for each cell of a base station (S4/4/4). The remaining 3
channel numbers can be configured for micro cells or mini-micro cells.
6.7.2 MRP Sequence Grouping
Because BCCH numbers and TCH numbers are selected in different ways, the
MRP can be divided into two types. They are MRP sequence grouping and MRP
space grouping, the first of which is introduced hereunder.
If the available bandwidth is 10MHz, the channel numbers are from 46 to 94. In
this case, you can plan the frequencies at the BCCH and TCH carrier layers
according to the sequence of the channel numbers. If using the sequence
planning, you should add 1 to 2 extra channel numbers to the BCCH numbers.
For the MRP sequence grouping, see
Table 13.1 MRP sequence grouping
Carrier type ARFCN of the available channel number
Available channel numbers
BCCH 83–94 12
TCH1 74–82 9
TCH2 66–73 8
TCH3 58–65 8
TCH4 52–57 6
TCH5 46–51 6
Note:
ARFCN stands for absolute radio frequency channel number.
According to this table, the channel numbers can be divided into 6 groups. For
BCCH, 12 channel numbers can be reused at the carrier layer. Traffic channels
can be divided into 5 groups, from TCH1 to TCH5. For TCH1, 9 channel
numbers can be reused; for TCH2 and TCH3, 8 channel numbers can be
reused; and for TCH4 and TCH5, 6 channel numbers can be reused.
Therefore, when the bandwidth is 10MHz, the base station type can be
configured as S6/6/6. If the traditional 4/12 frequency reuse pattern is used, the
maximum base station type can be configured as S4/4/4 only.
For MRP sequence grouping, intra-frequency and neighbor frequency
interference may exist within the frequency layer, and the interference between
11/12/2010 All rights reserved Page33 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
frequency layers exist at the critical points of the frequencies.
6.7.3 MRP Space Grouping
6.7.3 shows the frequency planning under MRP space grouping. According to
this figure, 37 channel numbers are available for the BCCH, 12 of which are
allocated to the BCCH, and the remaining of which are allocated to TCH1, TCH2,
TCH3, and MICRO.
For MRP space grouping, neighbor frequency interference does not exist within
the frequency layer, but exist between frequency layers. When the traffic is not
busy, this frequency reuse pattern can reduce network interference.
Figure 1.14 Frequency planning under MRP space grouping
If the available bandwidth is 10MHz, the available channel numbers are from 46
to 94. In this case, the frequencies can be allocated according to
Carrier type
ARFCN of the available channel number Available channel numbers
BCCH 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68 12
TCH1 70, 72, 74, 76, 78, 80, 82, 84, 86 9
TCH2 88, 90, 92, 94, 47, 49, 51, 53 8
TCH3 55, 57, 59, 61, 63, 65, 67, 69 8
TCH4 71, 73, 75, 77, 79, 81 6
TCH5 83, 85, 87, 89, 91, 93 6
11/12/2010 All rights reserved Page34 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
Note:
ARFCN stands for absolute radio frequency channel number.
At the very beginning, not each cell needs the TRX of the last layer, so the TRX
of the last layer can reuse the frequencies more aggressively. In addition, though
interference increases after the MRP is enabled, the TRXs in the cells also
increase. In this case, more the channel numbers will participate in frequency,
which enhances frequency hopping gain.
If both the channel numbers with a little interference and the channel numbers
with great interference exist simultaneously within a cell, the frequency hopping
technology will average the interference through mixing these channel numbers.
In this case, the system can still decode the signals normally.
When allocating the frequencies according to MRP, you must notice that the
minimum frequency reuse degree at the TCH layer must be equal to or greater
than 6. In actual conditions, however, the minimum average frequency reuse
degree at the TCH layer ranges from 7 to 8. Therefore, when the frequency
resource is adequate, you can reserve some channel numbers to for future use
during frequency planning.
Fixed MRP means that the channel numbers allocated to each TCH are fixed.
They are independent of each other, as shown in 6.7.3. For MRP, you should
plan the channel numbers layer by layer so that the TCH numbers can be easily
adjusted. In this case, if interference is present at a TCH layer, you need to
adjust the channel numbers allocated to that layer only.
6.7.4 Characteristics of MRP Technology
MRP technology can enables you to plan the frequencies flexibly according to
traffic distribution. Compared with 3 x 3 frequency reuse pattern, MRP
contributes to greater network capacity. Compared with 2 x 3 and 1 x 3
frequency reuse pattern, MRP has little effect against network quality. In addition,
MRP technology is compatible with the technologies, such as frequency hopping,
power control, DTX. Moreover, it has no special requirement on hardware and
software.
Generally, the advantages of the MRP are listed below:
The network capacity is great and frequency utilization rate is high.
The channel configuration is flexible. The frequency reuse pattern is
selected according to network capacity and traffic distribution. In the areas
where the traffic is high, you can add carriers to these areas.
No two cells have the same channel numbers, so no intra-frequency cell
exists in the system if the MRP is used.
11/12/2010 All rights reserved Page35 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
Baseband hopping and RF hopping can be used.
The base station type can be configures flexibly, which is good for network
quality.
The channels to be allocated are weighted, which enhances the network
quality.
6.7.5 Comparison between MRP and 1 X 3 Frequency Reuse Pattern
In fact, 1 x 3 frequency reuse pattern is a special kind of MRP. The configuration
for the equivalent MRP is 12/3/3/3/3/3. The following is a comparison between
MRP and 1 x 3 frequency reuse pattern.
The network capacity under 1 x 3 frequency reuse pattern is greater than
that under MRP.
For 1 x 3 frequency reuse pattern, you need to plan a group of frequencies
for TCH only. If you have to add new carriers to the system without adding
new base stations, you do not have to re-plan the frequencies. Therefore,
the frequency planning is simpler under 1 x 3 frequency reuse pattern than
that under MRP.
If the network is irregular in landforms and traffic distribution, you should
better not use 1 x 3 frequency reuse pattern. In most cases, a base station
is interfered by many base stations nearby. If the 1 x 3 frequency reuse
pattern is used, you will find it hard to position the interference source.
Therefore, when adding new base stations to the network, you cannot
eliminate the interference by adjusting some channel numbers only. If using
MRP, however, you can easily solve this problem.
6.8 Network Capacity Comparison
For the comparison of the network capacity under various frequency reuse
patterns, see
Table 14.1 Comparison of the network capacity under various frequency reuse pattern
Bandwidth Frequency reuse
pattern
Frequency
reuse
degree
Base station
configuration
type
Loadable
traffic
volume
Admissible
subscribers
Capacity
ratio
6MHz 4×3 12 3/2/2 27.9 1188 1
3×3 9 3/3/3 34.5 1380 1.16
4×3 + 1×3 7.5 4/4/3 53.5 2140 1.8
MRP(12, 9, 6) 9 3/3/3 34.5 1380 1.16
2 × 6 12 2/2/2/2/2/2 49.2 1968 1.66
11/12/2010 All rights reserved Page36 of 37
GSM Radio Network Planning and Optimization Chapter 6 GSM Frequency Planning
For internal use only
IUO: 4 × 3 + 2 × 3 9 4/4/3 53.5 2140 1.8
7.2MHz 4 × 3 12 3/3/3 34.5 1380 1
3 × 3 9 4/4/4 62 2480 1.8
4 × 3 + 1 × 3 7.5 5/5/5 81.9 3276 2.37
MRP(12, 9, 8, 7) 9 4/4/4 62 2480 1.8
2 × 6 12 3/3/3/2/2/2 60.1 2404 1.74
IUO: 4 × 3 + 2 × 3 9 5/5/5 81.9 3276 2.37
9.6MHz 4 × 3 12 4/4/4 62 2480 1
3 ×3 9 5/5/5 81.9 3276 1.32
4 × 3 + 1 × 3 7.5 7/7/7 123.6 4944 1.99
MRP(12,9,8,7,6,6) 8 6/6/6 104.1 4164 1.70
2 × 6 12 4/4/4/4/4/4 126 5040 2.03
IUO: 4 × 3 + 2 × 3 9 7/7/7 123.6 4944 1.99
Note:
GoS = 0.02; a = 0.025 Erl.
11/12/2010 All rights reserved Page37 of 37
Recommended