4 Frequency Planning

© SIEMENS Limited 1999ICN PLM CA NP

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Frequency Planning

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Main Topics

Frequency planning - task definition 2Specturm efficiency 2Frequency assignment methods 3Frequency reuse 4

Frequency reuse clusters 5Frequency reuse distance 5

Interference types 6Reference interference performance 6Co-channel interference factor 7Cluster size and co-channel interference 7Comparison between omni/sectorised cells 8Sectorisiation methods 8Calculation example 9Factors affecting the C/I ratio 9Effect of fading 10

Fading margin - C/I 10Simulations of cell configurations 11Interference analysis 12

Interference plots 12

Channel assignment 13Frequency reuse chain 13 Frequency groups 14

Base station identity code (BSIC) 14Interference analysis - aim and method 15Downlink and uplink interference 15Radio link control options 16

Power reduction (power control) 17Discontinuous transmission 18Frequency hopping 18Simulation results 20

System quality in FH-GSM 20Frequency planning strategies 21Frequency reuse with RLO 21

Frequency planning HCS 22Multiband operation 22Concentric cells 23Adaptive antenna principles 24

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S IE M E N S

S p e i c h e r nM e n ü

GSM

S IE M E N S


GSM

S IE M E N S


GSM

F1,F4

F2,F5

F3,F6

Frequency Planning

Task definition: Assign carriers to cells according to traffic demand while in a way as

to minimise interference

Minimise interference

Improve frequency reuse

Enhance capacity

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MHzKmErl

FATS

** 2For a given network it is an indicator for the quality of the network design (capacity limited areas)

Spectrum Efficiency

Definition

S = Spectral Efficiency T = Traffic A = Area F = Occupied Spectrum

Objectives: use spectrum efficiently in order to maximise capacity for a given

spectrum allocation minimise interference

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Frequency Assignment Methods

Dynamic Channel Assignments DECT:

no fixed channels are assigned to each cell. any channel in a composite of all radio channels can be assigned to the

mobile unit. mobile monitors all channels and chooses a frequency/ timeslot

combination with good signal strength and low interference frequency planning not necessary

GSM: directed retry is a form of dynamic channel assignment

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Frequency Assignment Methods Fixed Channel Assignments (e.g. GSM)

cells are allocated channels on a permanent basis in general: frequency planning is necessary

exception: allocation of all TCH frequencies to each cell, using frequency hopping

1/3 reuse patternA1 A1

A2A3 A3

A2

A1

A1

A2A3

A2A3

A1

A3A2

1/1 reuse patternA A

AA A

A

A

A

AA

AA

A

AA

A1

A2A3 B1

B2B3D3

D1 C1

C2C3

D2

4/12 reuse pattern

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R RD

C1 C2

f1 f1

Concept of Frequency Reuse

Use of radio channels on the same carrier frequency covering different areas

fn = Carrier frequency on each cell

Cn = Cell name

D = Distance between reuse cellsR = Cell radius

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Frequency Reuse Affected by interference between cells

Type of geographic terrain (radio propagation conditions) Antenna height / tilting Antenna types

Omnidirectional antenna 120 deg Directional (Rhomboidal) 60 deg Directional (Cloverleaf)

Transmission output power Radio Link Control features

Frequency Hopping Dynamic Power Control DTX / VAD

Frequency reuse efficiency

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Frequency Reuse ClustersLarger cluster size

Longer distance between interferers

13 4

2 13 4

2

13 4

213 4

2

13 4

2

K=4

15 4

367 2

15 4

367 2

15 4

367 2

15 4

367 2

K=715 4

367 2 8

9 15 4

367 2 8

9

15 4

367 2 8

9

15 4

367 2 8

9K=9

15 4

367 28 9 1011

12 15 4

367 28 9 1011

12

15 4

367 28 9 1011

12

K=12

13 2

13 21

3 2

13 2

13 2

K=3

Less interferenceBUT

Reduced capacitypotential

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Rr

D

D

ai

aj

R3

a

)60(Cosija2)aj()ai(D 0222 RKD 3

Rr 35.0

Ra 3

22 jijiK

Frequency Reuse distance

Reuse pattern in the Hexagonal grid

Outer Cell Radius : R Inner Cell Radius :

Distance between adjacent centers Minimum distance between the centers of reuse cells

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Interference Types C/Ic - common channel interference

The ratio of the level of the desired received signal to the level of unwanted received signals at the same frequency

Requirement : C/Ic > 9 dB.

C/Ia - adjacent channel intereference The ratio of the level of the desired received signal to the level of

unwanted received signals at frequencies n x 200 kHz apart. Requirement :

First adjacent channel interference (200 kHz apart): C/Ia1 > -9dB Second adjacent channel interference (400 kHz apart): C/Ia2 > -41dB Third adjacent channel interference (600 kHz apart): C/Ia3 > -49dB

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Reference Interference Performance GSM Recommendation 05.05

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Tranmission loss(dB)

Distance

C/I

HWN0

CoverageGuard zoneR D-R

H=Handover margin

Propagation path-loss equation:

where C = Received carrier powerR = Distance from transmitter to receiver

C R

= Constant = Propagation path-loss slope

= Frequency reuse distance to cell k = Number of cochannel interfering cells in the first tierIK

CI

R

kk

K

DI

1

Co-channel Interference Factor

11

1D

D-R

R

kD

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Six effective interfering cells from first tier

1

1

1

11

1

1

11

1 First tier

Second tier

Cochannel interference reduction factor:

KRDq 3

D

Average C/I : All interferers at D

IK

kk

KqR

IC

I

D

1

Worst case C/I : All interferers at D-R

I

K

kk

KqR

IC

I

D

1

1

Only first tier

Cluster Size and Co-channel Interference

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1 1

11

11

1

1

11

First tier

Second tier

Omni cells

1 43

23

21 43

2

1 43

2

1 43

21 43

2

120 deg. Directional Antennas

First tier

for first tier KI = 6 (theoretically) for first tier KI = 2 - 3 narrow beam antennas (e.g. 60º) better

than wide beam antennas (e.g. 120º)

Ex.3x4

Comparison between Omni / Sectorised Cells

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120 degree 3 dB beamwidth 60 degree 3 dB beamwidth

Sectorisiation Methods Rhomboidal sectorisation

better sidelobe coverage more interference

Cloverleaf sectorisation less interference than

Rhomboidal sectorisation

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Omni Sectored

Cluster size C/I(dB)

average

C/I(dB)

worst case

Cluster size C/I(dB)

worst case7 15.36 14.25 3x3 13.52

9 17.27 16.41 3x4 16.48

12 19.45 18.81 3x7 21.08

21 23.71 23.34

Sectorised sites suffer from lessinterference more capacity

Calculation Example C/I for various cluster sizes

path loss proportional to (distance)-3.5 (as in Hata formula) 120º antennas assumed in case of sectorised sites no fading included

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Factors Affecting the C/I Ratio Propagation path loss slope

range 20 dB/dec for free space 40 dB/dec for perfect ground reflection 50 dB/dec for highly attenuating environment from Hata: 35 dB/dec

larger slope less interference Site implementation Standard deviation of long term fading

larger values more margin needs to be planned for C/I Cluster size Handover margin

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Median level (50 %)

Median level (50 %)Rec

eive

d le

vel

Distance moved (within a small area - constant local mean received level

Worst case C/IMedian C/I

Effect of Fading Fading margin required

both wanted and interfering signals experience variations due to log-normal fading

C

I

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Fading Margin - C/I Assumption

wanted and interfering signals have log-normal distributions wanted and interfering signals are uncorrelated

Example:

2erfererint

2wantedtotal

dB6erfererintwanted

dB5.8total

Cell edgeprobability

Cell areaprobability

Margin for = 8.5 dB

50 % 74 % 0 dB

75 % 90 % 6 dB

87.5 % 95 % 10 dB

90 % 97 % 11 dB

95 % 99 % 14 dB

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standarddev. (dB)

areacoverage

90%

areacoverage

95%

areacoverage

98%4 3.6 5.6 7.85 5.4 7.9 10.56 7.4 10.4 13.57 9.6 12.9 16.18 11.8 15.6 18.4

Fading Margin - C/I Required fading margins from simulations

path loss proportional to (distance)-3.5 (as in Hata formula) fading conditions included simulation over whole cell assume 6 co-channel interferers

Add FM to 9 dBC/I requirement

Source: Lüders

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std. deviation > 5 dB 6 dB 7 dBcluster: % prob. % prob. % prob.

omni 7 92 87.5 82.5omni 9 95 92 88omni 12 (96.5) 95 92clover leaf 3/9 92.5 89 84clover leaf 4/12 95.5 93 89clover leaf 7/21 (98.5) 97.5 95.5

std. deviation > 5 dB 6 dB 7 dBcluster: reached C/I reached C/I reached C/I

omni 7 10 8 6omni 9 12 10 8omni 12 14 12 10clover leaf 3/9 10.5 8.5 6.5clover leaf 4/12 12.5 10.5 8.5clover leaf 7/21 16.5 14.5 12.5

Simulations of Cell Configurations Probability for C/Ic 9 dB

Larger cluster size higher probability of

acceptable C/I

C/Ic-ratio for 90 % probability

Larger cluster size higher C/I achieved

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Interference Analysis (I) C/I thresholds (dB) for analysis:

in this way thresholds can be derived for C/I analysis in planning tool

Qualityvaluation

callsaffected

%

=8dB

req. meanC/Ic

=7dB

req. meanC/Ic

=6dB

req. meanC/Ic

=8dB

req. meanC/Ia

=7dB

req. meanC/Ia

=6dB

req. meanC/Ia

excellent <=2 >=27.5 >=25 >=22.5 >=14.5 >=12 >=9.5

very good >2-5 24.5-27.5 22-25 19.5-22.5 11.5-14.5 9-12 6.5-9.5

good >5-10 21-24.5 18.5-22 16.5-19.5 9-11.5 6.5-9 3.5-6.5

fair >10-20 18-21 15.5-18.5 13.5-16.5 4.5-8.5 2.5-6.5 0.5-3.5

bad >20 <18 <15.5 <13.5 <4.5 <2.5 <0.5

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Interference Plots Example: C/I Example: C/A

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Frequencygroup

A1 B1 C1 D1 A2 B2 C2 D2 A3 B3 C3 D3

Channels 11325

21426

31527

41628

51729

61830

71931

82032

92133

102234

112335

122436

- A,B,C,D = Sites within cluster- 1,2,3 = Sector No.

A1

A2A3 B1

B2B3D3

D1 C1

C2C3

D2

Channel Assignment The allocation of specific channels to cell sites and mobile

units. Example: K = 4x3 cell pattern 4/12 Cell pattern

Swap to avoid C/Iabetween D3 / A1

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A1 B1C1

D1

A2B2C2D2

A3

B3

C3D3A1 B1

C1

A2B2C2

A3

B3C3

K = 3/9 K = 4/12

A1 B1 C1 D1E1

F1

G1A2

B2C2D2E2F2G2A3

B3C3

D3

E3 F3 G3

K = 7/21

Frequency group denomination for different reuse patterns

Frequency Reuse Chain

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A1

A2A3 C1

C2C3B1

B3

3/9 Cell Pattern

A1

A2A3 C1

C2C3B1

B3

A1

A2A3 C1

C2C3B1

B3

A1

A2A3 B1

B2B3D3

D1 C1

C2C3

4/12 Cell Pattern

A1

A2A3 B1

B2B3D3

D1 C1

C2C3

A1

A2A3 B1

B2B3D3

D1 C1

C2C3

D2B2

B2 B2

D2

D2

Frequency Groups

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Base Station Identity Code (BSIC)

BSIC = NCC + BCCNCC : Network Colour Code (0..7)BCC : Base Station Colour Code (0..7)

KONFERENZ?OK

32523 BARKMEY ER

1 DEF3

GHI4 MNO6

PQRS7 WXYZ9TUV8

ABC2

JKL5

0

R INT

F

f1f1

BCCH (f1,BSIC = 12)

f1

BCCH (f1,BSIC = 22) BCCH (f1,BSIC =

15)

Different country

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Interference Analysis The aim:

Push interference to areas which are not important (e.g. water, forests) Reduce interference in high traffic areas (e.g. downtown urban)

Method: Use weighting according to area type Traffic Weighting

Weighting factor between 0 and 1 to each pixel according to the traffic density

Clutter Weighting Urban : High weighting Suburban : Medium weighting Open : Low weighting Forest, Water : Zero

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KONFERENZ?OK

32523 BARKMEYER

1 DEF3

GHI4 MNO6

PQRS7 WXYZ9TUV8

ABC2

JKL5

0

R INT

F

KONFERENZ?OK

32523 BARKMEYER

1 DEF3

GHI4 MNO6

PQRS7 WXYZ9TUV8

ABC2

JKL5

0

R INT

F

Serv

ing si

gnal

U

L/DL

Interfering signal DL

Interfering signal UL

f1 f1

Downlink and Uplink Interference In general different for a given MS location at a given time Uplink interference analysis - complex because the source of

the interference may be moving not supported by most tools

external interference sources generally only affect one link co-channel interference intermodulation

Non-GSM interferer

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TighterFrequencyReuse

ENHANCEMENTSystem Capacity

Limitation

IncreaseI n t e r f e r e n c e

AVERAGINGAVERAGING

FHFH

PCPC

DTXDTX

REDUCTION

DIVERSITY

Radio Link Control Options

Source: ÖN MN ER 51, ÖN MN P 31

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Reduces interference due to minimum transmission power

Reduces interference due to no transmission during silence periods

Mitigates frequency selective Rayleigh fading for slow MSsAverages interference due to interference diversity

Capacity Enhancement by RLO Power Control (PC)

Discontinuous Transmission (DTX)

Frequency Hopping (FH)

Interference increase by tighter frequency re-usecan be compensated for by combination of FH, PC and DTX

Capacity increase via tight frequency re-use at moderate cost

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Advantages Save MS power

increase battery usage time of mobile

reduce radiation to user

Reduce interference enhanced capacity

BTS

MS 2

MS 1TXPWR

TXPWR

Power Reduction

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Power Control Decision

Power Increase

(bad quality)

Power Decrease

(good level)

Power Decrease

(good quality)

Power Increase

(bad level)

RXQUAL

RXLEV0

7

63

L_RXQUAL_XX_P

U_RXLEV_XX_P

L_RXLEV_XX_P

U_RXLEV_XX_P2*POW_RED_STEP_SIZE

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Discontinuous Transmission Why DTX?

on average people speak about 40 % of the time interference is related to traffic on the network avoid transmitting when

user is not active increased frequency and hence capacity possible every 480 ms a 20 ms frame containing background noise information is sent -

“comfort noise” save MS power

increase battery usage time of mobile reduce radiation to user

Voice Activity Detection (VAD) needed detect when user not active

PS! No benefit for data communications

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Frequency Hopping In GSM - slow hopping - 217 hops per second

cyclic or random Advantages

average out interference between users plan for average case, not worst case

provide frequency diversity combat flat fading mainly relevant for stationary or slow moving users improved performance of coder / interleaver

Implementations Baseband hopping:

Advantage: Can use filter combiner (low combiner losses)

Disadvantage: Require 1 TRX per frequency in hopping sequence

Synthesised hopping Advantage: Can hop over more

frequencies than no. of TRX’s Disadvantages: BCCH carrier cannot

hop, cannot use filter combiner

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10.07.56.56.0

8 FrequenciesYesYes

Yes

NoneNoneNoneNone

Frequency Hopping Diversity TU3 TU50 HT100None 11.5 6.8

2 Frequencies 6.74 Frequencies 8.3 6.68 Frequencies 7.5 6.0 6.6None Yes 6.8 - -

2 Frequencies 5.5 - -4 Frequencies 4.6 - -

4.1 - -

Frequency Diversity Averaging of short term fading S/N required to obtain 0.2 % residual BER for class 1b bits

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Frequency Hopping Cyclic hopping

Optimum frequency diversity Correlated hopping between cells,

but C and I channels change in an

uncorrelated way unequal no of frequencies for

different cells Interference averaging

Pseudo random hopping

Poor frequency diversity Uncorrelated hopping between

cells Good interference averaging

f1

f2

f3

f4

f1

f2

f3

f4

Frame sequence Frame sequence

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78.8%

47.0%29.5%

90.1%

56.6%

52.9%34.7%

PC on, DTX on PC off, DTX on PC on, DTX off PC off, DTX off

good interference diversity, but poor frequency diversity

good frequency diversity and

sufficient interference diversity

Random FH Cyclic FH

Simulation Results:

5 Carriers in High Traffic Network Dedicated Band Planning

Source: ICN CA MR EE6

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CHRHNH

System Quality in FH-GSM

With FH: C/I decreases, raw BER and RXQUAL get worse But: Voice quality (FER) improves

Source: ICN CA MR EE6

C/I [dB]per location

probability

FER [%]

probability

RxQual does not reflect quality as perceived by the user

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total operator bandwidth (8.6 MHz = 43 carriers)

43 carriers for both BCCH and TCH

Common band:

15 BCCH carriers

Dedicated band:

28 TCH carriers

Frequency Planning Strategies For the broadcast channel (BCCH) no RLO is possible

required cluster size BCCH channel > required cluster size TCH channels

dedicated band for BCCH channels sometimes used

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Frequency Reuse with RLO BCCH channel:

large reuse clusters (in theory 12 is possible, in practice 15 - 21) TCH channels

cluster size 1 x 3 or even 1 x 1 possible however

offered traffic may be limited by interference (soft blocking) rather than by number of TCH channels (hard blocking)

Offered traffic calculations capacity determined by simulations real (and not ideal) network simulations are needed

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Spectrum GA

Spectrum GB

Spectrum GC

Spectrum GD

Spectrum GE1/3 pattern

3/9 pattern

4/12 pattern

7/21 pattern

9/27 pattern

Frequency Planning HCS Challenge: Avoid

interference between layers allocate all frequencies to

all layers or

simplify planning / optimisation task by providing separate frequency bands for different layers

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Multiband Operation

GSM90025MHz

DCS180075MHz

e.g. 4MHz (ca. 20 carriers)each operator

e.g. 4MHz(ca. 20 carriers)each operator

8MHz(ca. 40 carriers)each operator

Different layers consisting of different frequency bands GSM900 GSM1800 can also include other GSM bands

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Concentric Cells TRX’s in cell split

outer area inner area BCCH covers both areas

Very efficient frequency reuse for inner area

1 x 3 possible Same antennae for both areas Handover criteria

level level and distance C/I (intelligent overlay /

underlay

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Conclusions higher capacity potential for hierarchical cells concentric cells for special application areas

Comparison with Hierarchical Cells

Concentric Cells

Advantages economical usage of sites &

antennas high frequency reuse high capacity gain if traffic

concentrated in inner area (Hot Spot Detection)

Disadvantages limited number of inner "cells" small gain for homogeneous

traffic inflexible installation:

no adaptation to traffic distribution

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Adaptive Antennae Principles Adaptation of "antenna diagram"

to reception condition Increase of antenna gain and cell

radius by small beams Reduction of interference ->

reduction of cluster size -> capacity gain

interference notching small beams

(less interference received in UL / less interference spread in DL)

Switching between beams Adaptive electronic beam forming BCCH carrier has to be

transmitted within the whole cell Space Division Multiple Access

SDMA: multiple usage of one physical

channel at same site additional capacity gain

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Adaptive Antennae Classification

smartantennas

fixedbeams

single channelusage per cell

multiple channelusage per cell

dynamic beamselectronically

dynamic beamselectronically

fixedbeams

sectorantennas

electronicallyformed

sectorantennas

electronicallyformed

Reduction of Cluster Size

SDMA

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Adaptive Antennae

What is the most appropriatepoint to perform beam selection

(combining & distribution) ?

by sector antennaselectronically formed

DSP 1

DSP 2

Combining &Distribution DSP 1

DSP 2

Combining &Distribution

K1 K2 K3

K1K3

K2

beam formingcoefficients

antenna array

fixed beamsMSI 1 I 2

I 3

Fixed Beams

Source: ÖN MN ER 51, ÖN MN P 31

4 Frequency Planning

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