GSM Frequency Planning & Neighbor Cell Planning

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GSM Frequency Planning and Neighbor Cell

Planning

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HUAWEI TECHNOLOGIES CO., LTD. All rights reserved

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


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


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


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


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 =


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 =


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


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


{fi,fj..fk}

{fi,fj..fk} {fi,fj..fk} {fi,fj..fk}.. ..

Macro-cell system

dMicro-cell system

Concept of Frequency Reuse


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.


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


[fn]

[fn]

D

[fn]

R

Reuse of a frequency causes the co-channel interference

Problem of Frequency Reuse


Interference (C/I) Estimation

6

1 q

I

C

1/2

q = D/R = ( 3 k )


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)


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


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





Chapter 4 Neighbor Cell PlanningChapter 4 Neighbor Cell Planning


Tight Frequency Reuse Technology

Multi-layer reuse pattern

Underlaid and overlaid cell

1*3

1*1


Multi-layer Reuse Pattern


BCCH: n1

TCH1: n2

TCH2: n3

TCHm-1: nm

n1 ≥n2≥n3 ≥n4 ≥...... ≥ nm

And n1+n2+...+nm=n

Multi-layer Reuse Pattern


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


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


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


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


The inner circle covers a smaller area, and the frequency can be reused more tightly.

Underlaid/Overlaid Frequency Allocation

Overlaid-cellUnderlaid-cell


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


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


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


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.


.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:


Example of Frequency Planning− Final frequency planning:


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


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


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


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.


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.





Chapter 4 Neighbor cell planningChapter 4 Neighbor cell planning


Content of Frequency Hopping

Class of hopping

Advantages of hopping

Parameter of hopping

Collocation of hopping data


Frequency Hopping


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


Base Band Hopping Principle


RF Hopping Principle


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.


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


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


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.


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.


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.





Chapter 4 Neighbor cell planningChapter 4 Neighbor cell planning


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


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


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


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


Demonstration (ideally)

co-site cellConfronting cellsame directional cellone site apartface to face cell

Original cell

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GSM Frequency Planning & Neighbor Cell Planning

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