© SIEMENS Limited 1999ICN PLM CA NP
s
Frequency Planning
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
S p e i c h e r nM e n ü
GSM
S IE M E N S
S p e i c h e r nM e n ü
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
Reference Interference Performance GSM Recommendation 05.05
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
Interference Plots Example: C/I Example: C/A
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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
s
© SIEMENS Limited 1999ICN PLM CA NP
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