GSM Frequency Planning Guide: Optimize Network Capacity with Tight Reuse Patterns

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Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
GSM Frequency
Planning

Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved. Page2
Contents
1. Frequency Planning
2. Normal Frequency Reuse Technology
3. Tight Frequency Reuse
4. Multiple Reuse Pattern Technology
5. Concentric Cell Technology
6. Frequency Hopping

Contents
1. Frequency Planning Basic
1.1 Frequency Resource of GSM System
1.2 Concept of Frequency Reuse
1.3 Reuse Density
1.4 C/I Ratio

P-GSM 900 :
DCS 1800 :
1710 1785 1805 1880
Duplex distance : 95 MHz
890 915 935 960
Duplex distance : 45 MHz
Frequency Resource of GSM System

Frequency Resource of GSM System
Frequency
Spectrum
Range
(MHz)
Uplink
Frequency Value
ARFCN
Downlink
Frequency Value
P-GSM900
890~915
935~960
Fu(n)=890+0.2n 1≦n ≦ 124 Fd(n)=Fu(n)+45
E-GSM900
880~915
925~960
Fu(n)=890+0.2n
Fu(n)=890+0.2(n-1024)
0 ≦ n ≦ 124
975 ≦ n ≦ 1023
Fd(n)=Fu(n)+45
R-GSM900
876~915
921~960
Fu(n)=890+0.2n
Fu(n)=890+0.2(n-1024)
0 ≦ n ≦ 124
955 ≦ n ≦ 1023
Fd(n)=Fu(n)+45
DCS1800
1710~1785
1805~1880
Fu(n)=1710.2+0.2(n-512) 512 ≦ n ≦ 885 Fd(n)=Fu(n)+95
PCS1900
1850~1910
1930~1990
Fu(n)=1850.2+0.2(n-512) 512 ≦ n ≦ 810 Fd(n)=Fu(n)+80

{fi,fj..fk}
{fi,fj..fk} {fi,fj..fk} {fi,fj..fk}.. ..
Macro-cell system
d
Micro-cell system
Concept of Frequency Reuse

Example of Frequency Reuse
 Frequency resource is limited. If there is 8MHz frequency
resource, 8 MHz = 40 channels × 8 timeslots = 320
 Max. 320 users can access the network at the same time.
 If every frequency is reused N times
 Max. 320×N uses can access the network at the same time.

 The spectrum utilization ratio can be expressed by frequency reuse
density (freuse), which reveals the tightness of the frequency reuse and
can be expressed by the following equation
 NARFCN is the total number of the available channel numbers,
 NTRX is the number of TRXs configured for the cell.
Reuse Density
TRX
ARFCN
reuse
N
N
f

Question
(1) Frequency bandwidth is 12MHZ, if frequency reuse density
is 4x3,each cell has how many TRX?
(2) Frequency bandwidth is 6MHZ, if frequency reuse density
is 2x3,each cell has how many TRX?

Looser reuse
Higher frequency reuse efficiency,
but interference is serious.
More technique is needed.
Tighter reuse
0 12 20
Little interference,
but frequency reuse efficiency is low.
Reuse Density
 Reuse density is the number of cells in a basic reuse cluster.
 For the n x m frequency reuse pattern,
 n: The number of BTSs in the reuse clusters
 m: The number of the cells under each BTS.
mnfreuse

4×3 Frequency Reuse
A1
C1
B1
D1
A2
A3
B2
B3
C2
C3
D2
D3
A1
C1
B1
D1
A2
A3
B2
B3
C2
C3
D2
D3
A1
C1
B1
D1
A2
A3
B2
B3
C2
C3
D2
D3
A1
C1
B1
D1
A2
A3
B2
B3
C2
C3
D2
D3
A1
C1
B1
D1
A2
A3
B2
B3
C2
C3
D2
D3
A1
C1
B1
D1
A2
A3
B2
B3
C2
C3
D2
D3

Requirement for C/I Ratio
All useful signals Carrier
All useless signals Interference=
Useful signal Noise from environment
Other signals
C/I =

Requirement for C/I Ratio
Interference C/I
C/I in Actual Project
(3 dB margin is needed )
Co-channel ≥ 9dB ≥ 12dB
Adjacent-channel ≥- 9dB ≥- 6dB
Carrier offset reaches 400 KHz ≥- 41dB

Exercise
Cell A fre 5
Cell C fre 4
Cell D fre 3
Cell B fre 5?dB<
?dB<
?dB<
-70dB

Contents

Example of 4 x 3 Frequency Reuse
Hereunder are several assumptions
The available bandwidth is 10MHz. The channel number is 45~94
 BCCH 81~94 (14 channel numbers in total, 81~82 are reserved)
 The other channel numbers are allocated to TCH
 So the maximum base station configuration is S4/4/4, and the
frequency reuse density is 12.5 (50/4 = 12.5)
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

4 x 3 Frequency Reuse Conclusion
 The 4 x 3 frequency reuse pattern is a basic technology applied in frequency planning.
Which must be applied to the BCCH in frequency aggressive reuse technologies
 If the network capacity needs to be further expanded, the following measures can be
taken:
 Split a cell into smaller cells.
 Utilize new frequency resources. For example, you can establish a DSC 1800MHz
network.
 Under the current 900MHz network, use more tight frequency reuse technology to
expand the network capacity.
 At present, the tight 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.
 The typical frequency reuse technology includes 3 x 3, 2 x 6, 2 x 3, 1 x 3, and 1 x 1.

Contents

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
available frequency hopping is FR LOAD
(generally, it is smaller than 50%).
A1
A2
A3
A1
A2
A3
A1
A2
A3
A1
A2
A3

 If the available bandwidth is 10MHz ,the channel numbers are 45~94
 For BCCH carriers, channel numbers is 81~94, frequency reuse pattern is 4×3
 For TCH carriers, channel numbers is 45~80, frequency reuse pattern is 1×3
 Because FR LOAD 1 to 2, if the bandwidth is 10MHz, the maximum base station
type can be configured as S7/7/7. In this case, the frequency reuse degree is 7.14
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
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
space
grouping
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
sequence
grouping

Example of 1×3 Frequency Reuse
 Suppose 900 band: 96～124
 BTS configuration: S3/3/3
 BCCH layer: 96～109 reuse pattern: 4×3
 TCH layer: 110～124 reuse pattern: 1×3

TCH Consecutive Allocation Scheme
MAIO
CELL1(MA1) 110 111 112 113 114 0,2
CELL2(MA2) 115 116 117 118 119 0,2
CELL3(MA3) 120 121 122 123 124 0,2
MA1
MA2 MA3
Cell1
Cell2Cell3
MA1
MA2 MA3
Cell1
Cell2Cell3
MA1
MA2 MA3
Cell1
Cell2Cell3
(110,112)
(110,112)
(110,112)
(115,117)
(115,117)
(115,117)
(120,122)
(120,122)
(120,122)

TCH Interval Allocation Scheme
MAIO
CELL1(MA1) 110 113 116 119 122 0,1
CELL2(MA2) 111 114 117 120 123 2,3
CELL3(MA3) 112 115 118 121 124 4,0
MA1
MA2 MA3
Cell1
Cell2Cell3
MA1
MA2 MA3
Cell1
Cell2Cell3
MA1
MA2 MA3
Cell1
Cell2Cell3
(110,113) (110,113)
(110,113)
(117,120) (117,120)
(117,120)
(124,112)
(124,112)
(124,112)

The Characteristics of the 1 x 3
 The frequencies are more tightly reused, so the network capacity is great.
 When planning a network, only need to plan BCCH, while it’s unnecessary to re-
plan frequencies. So the efficiency for network planning is high.
 Wideband combiner must be used, but the cavity combiner with frequency
selectivity is inapplicable.
 Co-channel and neighbor channel interference 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, BCCH cannot take measures, such as RF hopping, DTX, and
power control, therefore, in order to ensure network quality, BCCH can only use
the looser 4 x 3 frequency reuse pattern.

 One cell of one base station forms a frequency reuse cluster
 If the available bandwidth is 6MHz ,the channel numbers are 96~124
 For BCCH carriers, channel numbers is 111~124, frequency reuse pattern is 4×3
 For TCH carriers, channel numbers is 96~110, frequency reuse pattern is 1×1
 the maximum base station type can be configured 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.
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

BCCH14+TCH36：
1BCCH+3TCH
1BCCH+3TCH 1BCCH+3TCH
1BCCH+12TCH
4×3
1×3
1×3 and 1×1
1BCCH+TCH
1×1

TRX1 TRX2 ... TRX7
TRX8 TRX9... TRX14 TRX15 TRX16...TRX21
TRX1 TRX2 ... TRX7
TRX8 TRX9... TRX14 TRX15 TRX16...TRX21
The red items are BCCH RCs
Illustration of 1×3 or 1×1

Contents

Conception of MRP Technology
 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, configure the carriers layer by
layer, with reuse density increases layer by layer, as shown
in the next slide.

Conception of MRP Technology

 Capacity increase when reuse density is multiplied:
 Supposing there are 300 cells
 Bandwidth: 8 MHz (40 frequency)
 Normal 4×3 reuse: reuse density=12
 Network capacity = (40/12)×300 = 1000 TRX
 Multiple reuse:
BCCH layer: re-use =12, (14 frq.)
Normal TCH layer: re-use =10, (20 frq.)
Aggressive TCH layer: re-use = 6, (6 frq.)
 Network capacity = (1 +2 +1)×300 = 1200 TRX
Example of MRP

Example of MRP
 Capacity increase when reuse density is multiplied:
 Supposing there are 300 cells
 Bandwidth: 8 MHz (40 frequency)
 Normal 4×3 reuse: reuse density=12
 Network capacity = (40/12)×300 = 1000 TRX
 Multiple reuse:
BCCH layer: reuse density=12, (14 frequency)
Normal TCH layer: reuse density=10, (20 frequency)
Aggressive TCH layer: reuse density= 6, (6 frequency)
 Network capacity = (1 +2 +1)×300 = 1200 TRX

Contents

Conception of Concentric Cell Technology
 In the GSM network, concentric cell technology is used to divide the
service area into two parts: overlaid and underlaid.
 Essentially, the concentric cell technology concerns channel allocation and
handover, but when combining this technology with various frequency
planning technologies, both expand network capacity can be improved
network quality.
Overlaid-cell
Underlaid-cell

Overlaid/Underlaid Frequency Configuration
Super fn
Regular fm Regular fm Regular fm
Super fn
BCCH 15f Regular 24f Super 12f
BCCH TRX reuse density: 12
Regular TCH TRX reuse density: 12
Super TCH TRX reuse density: 6
Super fn

Conception of Concentric Cell Technology
 Generally, 4 x 3 frequency reuse pattern is used for the underlaid. For
overlaid, 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
underlaid, and the other one for overlaid.
Underlaid Overlaid

Contents

Contents
6.1 Classification of hopping
6.2 Advantages of hopping
6.3 Parameter of hopping
6.4 Collocation of hopping data

Frequency Hopping

Advantages of Hopping
 Get an agreeable radio environment.
 Provide a similar communication quality for every user.
 Tighter reuse patterns are possible to be used for larger
capacity.

Smoothen the rapid fading (Rayleigh fading)
Frequency Diversity of Hopping

Smoothen and average the interference
Interference Diversity of Hopping

Classification of Hopping
 According to implementation mode
 Base-band hopping
 RF hopping
 According to the minimum hopping time unit
 Timeslot hopping
 Frame hopping

Base Band Hopping Principle
FH bus

 BCCH carrier attends hopping, on which TS0 can not attend hopping
No Hopping
TRX0
TRX1
TRX2
TRX3
TS 0 TS 1 TS 2 TS 3 TS 4 TS 5 TS 6 TS 7 ARFCN
5(BCCH carrier)
10(TCH carrier)
15(TCH carrier)
20(TCH carrier)
MA={5,10,15,20}MA={10,15,20}

 BCCH carrier does not attends hopping
TRX0
TRX1
TRX2
TRX3
TS 0 TS 1 TS 2 TS 3 TS 4 TS 5 TS 6 TS 7
MA={10,15,20}
ARFCN
5(BCCH carrier)
10(TCH carrier)
15(TCH carrier)
20(TCH carrier)
No Hopping No Hopping No Hopping No Hopping No Hopping No Hopping No Hopping No Hopping

RF Hopping Principle

RF Hopping Principle
 BCCH carrier does not attends hopping
TRX0
TRX1
TRX2
TRX3
TS 0 TS 1 TS 2 TS 3 TS 4 TS 5 TS 6 TS 7
No Hopping No Hopping No Hopping No Hopping No Hopping No Hopping No Hopping No Hopping
MA={10,15,20}
MA={10,15,20}
MA={10,15,20}
(BCCH carrier)
(TCH
carrier)

Classification of Hopping
 Frame hopping
 Frequency changes every TDMA frame.
 The different channel of one TRX uses the same MAIO.
 Timeslot hopping
 Frequency changes every timeslot.
 The different channel of one TRX uses the different MAIO.

Frame Hopping
f 0
Frame 0
f 1
f 2
f 3
f 4
Frame 1 Frame 2 Frame 3 Frame 4 ……
One TRX (none BCCH carrier) hopping on 5 frequencies
•RF hopping and baseband hopping without BCCH carrier

Timeslot Hopping
f 0
Frame 0
f 1
f 2
f 3
f 4
•5 timeslots on 1 TRX hopping on 5 frequencies

Hopping Parameters
 All the parameters which are related to hopping are
configured in Cell Attributes/Frequency Hopping.
 Hopping mode: the mode used by the BTS system
 No hopping
 Base band hopping
 RF hopping

Hopping Parameters
 HSN：Hopping Sequence Number（0～63）
 HSN=0：cycle hopping.
 HSN≠0：random hopping. Every sequence number
corresponds a pseudo random sequence.

Hopping Parameters
 MA (Mobile Allocation Set):
 MA is the set of available RF bands when hopping, containing at most 64
frequency carriers. The frequency being used must be those of the available
frequency
 MAIO (Mobile Allocation Index Offset)
 MAIO is used to define the initial frequency of the hopping.
 Be careful to configure the MAIO of same timeslot in all channels, otherwise
interference occurs.
 MAI (Mobile Allocation Index)
 At the air interface, the frequency used on a specific burst is an element in MA
set. MAI is used for indication, referring to a specific element in the MA set.
 MAI is the function of TDMA FN, HSN and MAIO.

Example of MAIO
No Hopping
0
2
1
2
2
2
3
2
0
2
1
2
2
2
0 1
1
2
2
2
3
2
0
2
1
2
2
2
3
2
1 1
2
2
3
2
0
2
1
2
2
2
3
2
0
2
2 1
3
2
0
2
1
2
2
2
3
2
0
2
1
2
TRX0
TRX1
TRX2
TRX3
5(BCCH carrier)
10(TCH carrier)
15(TCH carrier)
20(TCH carrier)
MA2={5,10,15,20}MA1={10,15,20}
MAIO 0 1 2 MAIO 0 1 2 3
MAIO MAI

Example of MAIO
No Hopping
0
2
1
2
2
2
3
2
0
2
1
2
2
2
0 1
1
2
2
2
3
2
0
2
1
2
2
2
3
2
1 1
2
2
3
2
0
2
1
2
2
2
3
2
0
2
2 1
3
2
0
2
1
2
2
2
3
2
0
2
1
2
0 3
1
3
2
3
3 3
0
3
1
3
2
3
3
3
1 3
2
3
3
3
0
3
1
3
2
3
3
3
0
3
2 3
3
3
0
3
1
3
2
3
3
3
0
3
1
3
0 1 2 3 0 1 2
TRX0
TRX1
TRX2
TRX3
5(BCCH carrier)
10(TCH carrier)
15(TCH carrier)
20(TCH carrier)
MA2={5,10,15,20}
MA1={10,15,20}
MA3={510,515,520,525}
510(TCH carrier)
515(TCH carrier)
520(TCH carrier)
525(TCH carrier)
TRX4
TRX5
TRX6
TRX7

Example of MAIO
5
Frame 0
10
15
20
25
MA={5,10,15,20,25}
• 5 TRXs separately belongs to the same MA hopping on 5
frequencies, and uses same HSNs

Example of Hopping Parameters
f 0
Frame 0
f 1
f 2
f 3
f 4
• 8 timeslots of 1 TRX separately belongs to different MAs hopping
on 5 frequencies, and uses different HSNs.

Example of Hopping Parameters
f 0
Frame 0
f 1
f 2
f 3
f 4
• 5 TRXs separately belongs to different MAs hopping on 5
frequencies, and uses different HSNs

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