![Page 1: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/1.jpg)
Cellular Network Planningand Optimization
Part III: InterferenceJyri Hämäläinen,
Communications and Networking Department, TKK, 18.1.2007
![Page 2: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/2.jpg)
2
Interference classification
![Page 3: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/3.jpg)
3
Co-channel interference
� Co-channel interference arise when same radio resources are used in different cells (nearby each other) at the same time. � If there is no co-channel interference or amount of co-
channel interference is small then system is said to benoise limited (here noise = AWGN)
� If co-channel interference is limiting the systemoperability then system is said to be interferencelimited.
� In cellular networks there is always co-channelinterference. By using various radio resource reusetechniques the impact of interference can be removed. Yet, the cost of such resource reuse is usually loweroverall capacity in the system.
![Page 4: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/4.jpg)
4
Adjacent channel interference� Adjacent-channel interference is interference that is
caused by power leakage from a signal in an adjacen t channel.
� Adjacent channel interference can be attenuated by adequate filtering� For each cellular system there are certain RF specifications
that put requirements to adjacent channel filtering
� Adjacent channel interference should be also taken into account in network planning.� Adjacent channel interference can be mitigated also through
proper frequency planning
� Adjacent-channel interference is also sometimes cal led as crosstalk. � In analog systems (e.g. NMT) there can be crosstalk (literally)
between adjacent channels
![Page 5: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/5.jpg)
5
Co-channel/adjacent channel interference
� In the following we mainly concentrate on co-channelinterference. � Co-channel interference is a system issue: By proper
system design and network planning we can mitigate the co-channel interference partly.
� There will be always trade-off between co-channelinterference and system efficiency
� Adjacent channel interference is more related to hardware. � Adjacent channel interference is usually taken into account
in specifications regarding to HW requirements� Adjacent channel interference needs to be kept in mind also
in network planning.
![Page 6: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/6.jpg)
6
Co-channel interference
� Co-channel interference is one of the main limitingfactors for cellular systemcapacity
� Co-channel interferencecan be mitigated bysystem level design (frequency planning) and/or by receiverprocessing (interferencecancellation)
Down link co-channelinterference
Wanted signalUnwanted signal=co-channel interference
MSBS
![Page 7: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/7.jpg)
7
Co-channel interference/frequency planning
� Frequency planning is the conventionalapproach. In frequency planning each cell is assigned a subset of the available frequencies.� Frequency allocation can be fixed: Each cell has a
fixed number of frequencies� Frequency allocation can be dynamic so that each cell
may use all (or almost all) frequencies according to some rule that take into account the traffic variations in the network
1
32
![Page 8: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/8.jpg)
8
Frequency planning
� In the following we consider in more details� Reuse distance and clustering. This is a basic
concept that is very important from FDMA/TDMA perspective. Example technologies: GSM/EDGE, WiMAX
� Reuse partitioning and fractional reuse. Due to increased capacity and coverage requirements these concepts are gaining importance. Example technologies: WiMAX, LTE
![Page 9: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/9.jpg)
9
Reuse distance and clustering
![Page 10: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/10.jpg)
10
Frequency planning based on SINR
� Service area is subdivided into cells. � To simplify analysis cells are usually modeled as
hexagons or squares.� Each cell is assigned a subset of the available
frequencies from the bundle assigned to the mobile network operator.
� Cells utilizing the same frequency cause co-channel interference to each other.
� In order to achieve tolerable signal-to-interferenc e+noiseratio (SINR) cells using the same frequency must be separated by distance D (reuse distance)
� When a mobile is moving from cell to another an automatic channel/frequency change (handover) occurs.
![Page 11: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/11.jpg)
11
Cellular radio system
�Isotropic antennas�Radio range of the base station is R�Distance to co-channel cell i is D i
Mobile
R√3
R
Di=3R
Handover region
![Page 12: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/12.jpg)
12
Frequency reuse
� Example: Number of available frequencies is 3
1
3
2
Cluster size K =3
1
32
1
321
32
1
32
1
32
1
32
1
32
Cluster formation
ReuseDistanceD
![Page 13: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/13.jpg)
13
Hexagonal cell vs true cell
![Page 14: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/14.jpg)
14
Hexagonal cells vs true cells
Three hexagons Three cells
![Page 15: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/15.jpg)
15
Frequency reuse
� Example: Number of available frequencies is 4
4
1
3
2
41
32
41
32
41
32
41
32
41
32
41
32
41
32
41
324
1
32 D
ReuseDistance
Cluster size K =4
![Page 16: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/16.jpg)
16
Frequency reuse
� Example: Number of available frequencies is 7
4
1
3
2
7
6
5
Cluster size K =7
41
32
76
5
41
32
76
5
41
32
76
5
41
32
76
5
41
32
76
5
41
32
76
54
1
32
76
5
41
32
76
5
DReuseDistance
![Page 17: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/17.jpg)
17
4 1
3 2
7
65
4 1
3 2
7
65
Frequency reuse
� Not all cluster sizes are possible� Feasible cluster sites
i=0,1,2,…j=0,1,2,…i=0, j=0 excluded
� Reuse distance
i=1, j=0 => k=1i=1, j= 1=> k=3i=2, j=0 => k=4i=2, j=1 => k=7i=3, j=0 => k=9i=2, j=2 => k=12…
i and j denote distance in terms of cells
i=2 x=5√3/2R
j=1 y=3/2RD=√21R
![Page 18: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/18.jpg)
18
1
3
11
1
31
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
21
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
21
3
2
1
3
2
1
3
2
1
3
2
1
3
2
1
3
2
2
2
1 1 1 1
![Page 19: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/19.jpg)
19
SINR/uplink
� Mobile positions are uniformly distributed in the c ell. The average interference is obtained by considering interferenc e sources at the middle of the cell.
Two first tires of co-channel interferers
α attenuation exponentα=2 in free spaceα up to 4 in macro cell environment
P Transmit powerN Noise powerR cell radiusD reuse distanceDi distance from base station i
T
D
3D
R
![Page 20: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/20.jpg)
20
� Distance to base station iDi≈D for i ∈ [1,6]Di≈D√3 i ∈ [7,12]Di≈D√4 i ∈ [13,18]Di≈D√7 i ∈ [19,24]etc.
� Interference power
SINR
111
1 1 1
111
D
√3 DT
Di Di+1
1 2
3
45
6
7
8
9
10
11
12
First tire
Second tire
Third tire
Fourth tire
![Page 21: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/21.jpg)
21
SINR
�Define
If α>2, C(α)<1� The larger α, the smaller
co-channel interference. That is, the better the isolation between cells.
�In macro cellular environment
α < 4 and C(α) > 7
2.5 3 3.5 4 4.5 56
7
8
9
10
11
12
13
α
C( α
)
![Page 22: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/22.jpg)
22
SINR
� The SINR can now be written as
� If N/P → 0, the system capacity is interference limited
� Recall that
![Page 23: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/23.jpg)
23
Frequency planning example
� Number of channels C=100� Required SINR = 20 dB =>
� Propagation exponent α = 4 => C(α) ~ 7
� Solving for K yields� The closest is K=9
� Hence the cluster size K=9� Number of channels per cell is then
41
32
76
59
8
c
![Page 24: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/24.jpg)
24
SINR
� If N/P>> C(α) the system is called range limitedor noise limited
� Cell radius R is bounded by
� The larger the required SINR, the smaller the cell radius.
![Page 25: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/25.jpg)
25
Frequency planning
� SINR as a function of cluster size K
1 5 10 15 20 25 30 35 390
5
10
15
20
25
Cluster size K
SIN
R
SNR = 10 dB
SNR = 25 dB
SNR = 15 dB
SNR = 20 dB
SNR = R-αP/N
Signal-to-noise ratio
on the cell edge
Interference limited region
Noise limited region
( ) SNRRDCR
D1)(
1α
α
α +
=
KRD 3/ =
![Page 26: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/26.jpg)
26
SINR
� The derived interference model can serve as an approximation for downlink interference
111
1 1 1
111
D
√3 DT
Di Di+1
1 2
3
45
6
7
8
9
10
11
12
Interference isoverestimated
Interference isunderestimated
Aggregate interference isclose to the real value
![Page 27: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/27.jpg)
27
SINR/uplink, worst case
� In worst case interference comes from users on the cell edge
T
Worst caseinterferencein uplink
α attenuation exponentα=2 in free spaceα up to 4 in macro cell environment
P Transmit powerN Noise powerR cell radiusD reuse distanceDi distance to base station i
( )jj
PR
D R P N
α
α
−
−Γ ≥− +∑
![Page 28: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/28.jpg)
28
Worst case analysis
5 10 15 20 25 30 35-10
-5
0
5
10
15
20
25
Cluster size K
SIN
R SNR = 10 dB
SNR = 25 dB
SNR = 15 dB
SNR = 20 dB
SNR = R-αP/N
Signal-to-noise ratio
on the cell edge
Average uplink interference < downlink caseWorst case uplink interference (dotted line)
![Page 29: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/29.jpg)
29
Reuse partitioning and fractional reuse
![Page 30: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/30.jpg)
30
Reuse Partitioning
�Overlaid cell plans with different reuse distances chose channel based on received signal strength RSS.�Mobiles with high RSS may use channels with higher interference while mobiles with low RSS use low interference channels.
r1
r2
r3
rK
1
2
3
Kr_L
L
( )1
3
ll
ll
l l
DNr C DP
D K R
α
αα
Γ =
+
=
![Page 31: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/31.jpg)
31
Reuse Partitioning
� Number of channels in zone l: cl� Cluster size utilized in zone l: Kl� Total number of channels allocated to cell
� Total number of channels
� Gains of 50 -100% in capacity
� Most gain achieved by going from one to two “zones”
![Page 32: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/32.jpg)
32
Reuse Partitioning
� Reuse partitioning will increase the average number of channels available to the mobiles.
� The number of mobiles in a zone is smaller than in single zone case. This will cause traffic variation s to increase.
� In low traffic load, the effect of increased traffi c variations will dominate leading to worse performance in terms of blocking than conventional scheme. (Trunking loss)
� In high traffic load, the effect of increased avera ge number of channels will dominate leading to increas ed performance.
![Page 33: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/33.jpg)
33Zander, J., "Generalized reuse partitioning in cell ular mobile radio," Vehicular Technology Conference, 1993 IEEE
43rd , vol., no.pp.181-184, 18-20 May 1993
Channel AssignmentFailure
BlockingProbability
Offered traffic
Reuse Partitioning
![Page 34: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/34.jpg)
34
Fractional reuse
� In OFDMA systems the available sub-carriers constitute the channel pool that can be divided among the different zones.
� Typically close to the base station we want to have reuse K1=1 and use larger reuse on the edge of the cell to improve coverage.
f
Cell 1 Cell 2 Cell 3K2=3
K1=1
![Page 35: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/35.jpg)
35
Frequency planning example
� Number of channels C=256� Required SINR = 3 dB
� Propagation exponent α = 4 => C(α) ~ 7 � Cell radius R=700 m � Transmit power per channel P= 16 dBm
� Noise power per channel -104 dBm� Two zones
� Zone 1: Universal reuse K 1=1, determine r1
� Zone 2: Determine K2, r2=R=700 m
![Page 36: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/36.jpg)
36
Frequency planning example
� Required SINR
� Zone 1:
( ) ( )
1
1 1l ll l
l ll l
D Dr
N Nr C D C DP P
αα α
α αα α
Γ = ≥ Γ ⇔ ≤ Γ + +
1 3D R=
( )
1
1586 ml
ll
l
Dr
NC D
P
αα
αα
≤ ≈ Γ +
![Page 37: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/37.jpg)
37
Frequency reuse example
� Zone 2� SINR
( )2
22
2
1DNr C DP
α
αα
Γ = ≥ Γ
+
2 23D K r=
( )( ){
( )
( )
1
2
1
21
2
13
3
115.75 16
13
KN
C r KP
CK K
α
αα
γ
α
α
αγ
−
−
Γ =+
Γ = ≈ ⇒ = − Γ
Pr
Nαγ = SNR on the cell edge
![Page 38: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/38.jpg)
38
Frequency reuse example
� Frequency planC=256K1c1+K2c2=Cc2=(C-c1)/K2
� Feasible allocations� No reuse partitioning:
c=c2=C/K2 = 16 channels per cell� Reuse partitioning:
c2=(C-c1)/K2 = 1,2,…,15 channels per zone and cellc1=240, 224,…, 16 channels per zone and cell
r1= 586 m r2=700 m
K1=1
K2=15
![Page 39: Cellular network planning and optimization part3 - Aalto · 3 Co-channel interference Co-channel interference arise when same radio resources are used in different cells (nearby each](https://reader030.vdocuments.net/reader030/viewer/2022041207/5d60faf588c993a2558b5a7f/html5/thumbnails/39.jpg)
39
Frequency reuse example
Distance
Number of Channels Capacity
Zone 1 Zone 2Cell border
Distance
Number of Channels Capacity
Zone 1 Zone 2Cell border
16
8
256
16