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GSM Frequency Planning and Neighbor Cell
Planning
V1.0
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Chapter 1 Chapter 1 Frequency planningFrequency planning
Chapter 2 Chapter 2 Tight frequency reuseTight frequency reuse
Chapter 3 Chapter 3 Frequency hoppingFrequency hopping
Chapter 4 Neighbor Cell PlanningChapter 4 Neighbor Cell Planning
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Content of Frequency planning
Frequency resource of GSM system
Requirement for interference and carrier-to-interference ratio
Signal quality grade coding
Concept of frequency reuse
4*3 frequency reuse
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GSM 900 :
GSM 1800 :
1710 1785 1805 1880
Duplex distance : 95 MHz
890 915 935 960
Duplex distance : 45 MHz
Frequency Resource of GSM System
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Frequency Band Configuration
GSM900:
BTS receiver (uplink ): f1 (n) =890.2+ (n-1)*0.2 MHz
BTS transmitter (downlink ): f2 (n) =f1 (n) +45 MHz
GSM1800:
BTS receiver (uplink ): f1 (n) =1710.2 + (n-512) * 0.2 MHz
BTS transmitter (downlink ): f2 (n) =f1 (n) +95 MHz
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All useful signals carrierAll useless signals interference=
GSM standard: C / I >= 9 dB
In practical projects: C / I >= 12dB
Useful signal Noise from environment
Other signals
Requirement for Interference and Carrier-to-Interference Ratio
C/I =
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Requirement for Interference and Carrier-To-Interference RatioRequirement for Interference and Carrier-To-Interference Ratio
All useful signals carrierAll useless signals interference=
GSM standard: C / I >= 9 dB
In practical projects: C / I >= 12dB
Useful signal Noise from environment
Other signals
C/I =
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Effect of Interference
Decrease of signal quality
Bit error
− Recoverable: channel coding, error correction
− Irrecoverable: phase distortion
System interference model
− Unbalanced: uplink interference ≠ downlink interference
− Asymmetrical: the interference is different at the MS and
BTS ends
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RXQUAL Mean BER BER rangeclass (%) from... to0 0.14 < 0.2%1 0.28 0.2 ... 0.4 %2 0.57 0.4 ... 0.8 %3 1.13 0.8 ... 1.6 %4 2.26 1.6 ... 3.2 %5 4.53 3.2 ... 6.4 %6 9.05 6.4 ... 12.8 %7 18.1 > 12.8 %
Fairly good
Intolerable
Good
Acceptable
Signal Quality
Receiving quality (RXQUAL parameter)
Level of receiving quality (0 ... 7)
Bit error rate before decoding and error correction
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{fi,fj..fk}
{fi,fj..fk} {fi,fj..fk} {fi,fj..fk}.. ..
Macro-cell system
dMicro-cell system
Concept of Frequency Reuse
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The Reason 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.
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Looser reuse
Higher frequency reuse
efficiency, but interference
is serious. More technique
Is needed.
Tighter reuse
0 10 20
Little interference, but frequency
reuse efficiency is low.
Reuse Density Reuse density is the number of cells in a basic reuse cluste
r.
− 4*3 : 12
− n*m : n*m
− n: BTS number in a basic reuse cluster
− m: Frequency group number in a BTS
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[fn]
[fn]
D
[fn]
R
Reuse of a frequency causes the co-channel interference
Problem of Frequency Reuse
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Interference (C/I) Estimation
6
1 q
I
C
1/2
q = D/R = ( 3 k )
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R
D
This old-fashioned frequency distribution mode is not recommended
Frequency Reuse Patterns
Purpose: to minimize the interference in the whole network with
the final frequency allocation plan
Theoretically
− Regular hexagon cell
− Regular network distribution
− Cell cluster
− Multiplexing distance
D = R *sqrt(3*K)
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A1C1
B1D1
A2A3
B2B3
C2C3
D2D3
A1C1
B1D1
A2A3
B2B3
C2C3
D2D3
A1C1
B1D1
A2A3
B2B3
C2C3
D2D3 A1
C1
B1D1
A2A3
B2B3
C2C3
D2D3
A1C1
B1D1
A2A3
B2B3
C2C3
D2D3
A1C1
B1D1
A2A3
B2B3
C2C3
D2D3
4*3 Frequency Reuse
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A1 B1 C1 D1 A2 B2 C2 D2 A3 B3 C3 D3
34 34 35 36 37 38 39
40 41 42 43 44 45 46 47 48 49 50 51
52 53 54 55 56 57 58 59 60 61 62 63
64 65 66 67 68 69 70 71 72 73 74 75
76 77 78 79 80 81 82 83 84 85 86 87
88 89 90 91 92 93 94 95
Illustration of Frequency Allocation of 4*3 Frequency Reuse
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Chapter 1 Chapter 1 Frequency planningFrequency planning
Chapter 2 Chapter 2 Tight frequency reuseTight frequency reuse
Chapter 3 Chapter 3 Frequency hoppingFrequency hopping
Chapter 4 Neighbor Cell PlanningChapter 4 Neighbor Cell Planning
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Tight Frequency Reuse Technology
Multi-layer reuse pattern
Underlaid and overlaid cell
1*3
1*1
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Multi-layer Reuse Pattern
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BCCH: n1
TCH1: n2
TCH2: n3
TCHm-1: nm
n1 ≥n2≥n3 ≥n4 ≥...... ≥ nm
And n1+n2+...+nm=n
Multi-layer Reuse Pattern
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Multi-layer Reuse Pattern Frequency Allocation
Suppose that the available frequency carrier is 10MHZ, channel nu
mber is 46 ~ 94, the Multi-layer reuse pattern should be:
RC type Allocated
frequencies
Number of available
frequencies
BCCH 46~57 12
TCH1 58~66 9
TCH2 67~74 8
TCH3 75~82 8
TCH4 83~88 6
TCH5 89~94 6
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BCCH TCH1 TCH2 TCH3 TCH4
{f1,f3,f5...f23}
{f1,f2,f3,f4,f5...f40}
{f2,f4..f22,f24...f40}
Multi-layer Reuse Pattern Frequency Allocation
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cap NBW
re usei
i
.
Advantages of Multi-layer Reuse Pattern 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 =14, (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
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cap NBW
re usei
i
.
Advantages of Multi-layer Reuse Pattern Capacity increases 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 =14, (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
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The inner circle covers a smaller area, and the frequency can be reused more tightly.
Underlaid/Overlaid Frequency Allocation
Overlaid-cellUnderlaid-cell
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Super fn
Regular fm Regular fm
Regular fm
Super fn
BCCH 15f Regular 24f Super 12f
BCCH Reuse density: 15
R TCH TRX reuse density: 12
S TCH TRX reuse density: 6
Overlaid/Underlaid Frequency Configuration
Super fn
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BCCH14+TCH36 :
1BCCH+3TCH
1BCCH+3TCH 1BCCH+3TCH
1BCCH+12’TCH
1BCCH+12’TCH 1BCCH+12’TCH
1*3 1*1
1*3 and 1*1 Reuse Patterns
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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 TCH Frequency Allocation
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Frequency Planning Principle There should be no co-channel frequency carriers in one BTS.
The frequency separation between BCCH and TCH in the same cell should be not less than 400K.
When frequency hopping is not used, the separation of TCH in the same cell should be not less than 400K.
In non-1*3 reuse mode, co-channel should be avoided between the immediately neighbor BTS.
Neighbor BTS should not have co-channels facing each other directly.
Normally, with 1*3 reuse, the number of the hopping frequencies should be not less than twice of the number of frequency hopping TRX in the same cell.
Pay close attention to co-channel reuse, avoiding the situation that the same BCCH has the same BSIC in adjacent area.
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.Example of Frequency Planning An example network in a specific place, BTS are densely
located. The topography is plain. The maximum BTS
configuration is S3/3/2
Initial planning:
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Example of Frequency Planning− Final frequency planning:
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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
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Group 1 (MA1): 110 111 112 113 114 Cell1
Group 2 (MA2): 115 116 117 118 119 Cell2
Group 3 (MA3): 120 121 122 123 124 Cell3
TCH Consecutive Allocation Scheme
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TCH Interval Allocation Scheme
Group 1 (MA1): 110 113 116 119 122 Cell1
Group 2 (MA2): 111 114 117 120 123 Cell2
Group 3 (MA3): 112 115 118 121 124 Cell3
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Comparison Between Multi-layer reuse and 1*3
For Multi-layer reuse pattern, either Base band hopping or RF hopping can
be used. But for 1x3 reuse, only RF hopping can be used.
Multi-layer reuse pattern is a gradual process for TCH frequency planning.
In other words, the reuse is rather loose in TCH1 layer and it is quite close
in the last TCH layer (such as TCH5). The reason for this pattern is that
base band hopping is used in the Multi-layer reuse pattern. When there are
rather few frequency carriers, the hopping gain is small. Therefore, more
frequency carriers should be allocated for the layer with small TCH and
then the reuse coefficient is relatively large. When RF hopping is used in
the Multi-layer reuse pattern and there are a large number of frequency
carriers, the hopping gain is high and the reuse coefficient can be very
small. In addition, the Multi-layer reuse pattern is of a free pattern. It is
different from base band hopping, in which the reuse must be loose in the
first TCH layer and more close in inner layers.
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Comparison Between Example of Frequency Planning and 1*3
The frequency planning for the 1x3 mode is simple and it is easy to plan
the frequency for new added BTS.
1x3 mode requires a rather regular BTS location distribution.
For the cells with fixed number of TRX, when the traffic is heavy, the 1x3
provides higher service quality than that of Multi-layer reuse pattern.
TRX can be easily added to the 1x3 network, but TRX number of hopping
should not exceed the product of the allocated hopping frequency
number and the max RF load ratio.
BCCH of Multi-layer reuse pattern can take part in the frequency
hopping, while BCCH in 1x3 mode can not.
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Chapter 1 Chapter 1 Frequency planningFrequency planning
Chapter 2 Chapter 2 Tight frequency reuseTight frequency reuse
Chapter 3 Chapter 3 Frequency hoppingFrequency hopping
Chapter 4 Neighbor cell planningChapter 4 Neighbor cell planning
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Content of Frequency Hopping
Class of hopping
Advantages of hopping
Parameter of hopping
Collocation of hopping data
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Content of Frequency Hopping
Class of hopping
Advantages of hopping
Parameter of hopping
Collocation of hopping data
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Frequency Hopping
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Class of Hopping
Hopping can be implemented in two ways
Base-band hopping
RF hopping
Class according to the min hopping time unit
Timeslot hopping
Frame hopping
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Base Band Hopping Principle
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RF Hopping Principle
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Class 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.
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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.
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Smoothen the rapid fading (Rayleigh fading)
Frequency Diversity of Hopping
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Smoothen and average the interference
Interference Diversity of Hopping
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Hopping Parameters
All the parameters which are related to hopping are configured
in cell/configure Hopping data
Hopping mode: the mode used by the BTS system, including
three options: not hopping, base band hopping and RF
hopping.
MA (Mobile Allocation Set): 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
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Description of Hopping Parameters
HSN : hopping sequence number ( 0 ~ 63 ) .
HSN=0 : cycle hopping.
HSN≠0 : random hopping. Every sequence number correspo
nds a pseudo random sequence.
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Hopping Parameters
MAIO (Mobile Allocation Index Offset): used to define the initial frequency
of the hopping.
Be careful to configure the MAIO of same timeslot in all channels,
otherwise interference occurs.
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Description Hopping Parameters
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.
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Chapter 1 Chapter 1 Frequency planningFrequency planning
Chapter 2 Chapter 2 Tight frequency reuseTight frequency reuse
Chapter 3 Chapter 3 Frequency hoppingFrequency hopping
Chapter 4 Neighbor cell planningChapter 4 Neighbor cell planning
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Why Handover is based on the neighbor relationship.
Existing problem of neighbor planning
No neighbor relationship, no handover
Co-BCCH and co-basic between adjacent cells lead to handover
failure.
redundant neighbors
missing neighbor
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Neighbor Cell Description
There are table BA1 and table BA2.
Table BA1 describes BCCH frequencies of the adjacent cells to be
measured when the MS is in idle mode.
Table BA2 describes BCCH frequencies of the adjacent cells to be
measured when the MS is in dedicated mode.
There are two kinds of neighbors
bidirectional neighbors
unidirectional neighbors
Bidirectional neighbors are common, and unidirectional neighbors are
used in special condition, such as overshooting
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B
C
A
A
• The signals of cell A covers some areas far away from this
cell. It is overshooting. • When MS moves from this area towards B and C
in dedicated mode, the signal is worse and worse.• since cell B and C is not the cell A’s neighbor,
call drop will occur finally. • There are three solution:
• Adjust the downtilt of the antenna• Adjust the transmitting power of the BTS • Add B and C as the neighbor of cell A, no need to add
A to B and C, that is unidirectional neighbor.
(make sure that there are no co-BCCH and co-BSIC in neighbor list)
Overshooting and Unidirectional Neighbor
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The cells of co-site must be set as neighbor cells
The cells confronting directly must be added to neighbor list
The cells facing toward the same direction should be neighbors
The cells shooting by the original cell
The cells shooting at the original cell
The cells, one site apart, face to face should be neighbor cells.
Neighbor Planning Principle
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Demonstration (ideally)
co-site cellConfronting cellsame directional cellone site apartface to face cell
Original cell
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