Transcript Tietoliikennetekniikka

Capacity planning exercise
M.Sc. Mika Husso
9.2.2007
1
Traffic reviewed …
• The unit of traffic is E [erlang]
– Single line or sever can handle up to 1 E traffic.
• Offered Traffic (total traffic created by subcribers)
– A= h = call intensity * mean service time
• Carried Traffic (or served traffic) = Total amount of
traffic the network is able to serve
• Lost Traffic (or rejected traffic)
= Offered Traffic – Carried Traffic
• Potential traffic: Offered traffic if there would be no
restrictions on the use of the service.
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… Traffic reviewed
• In practice, it is not feasible for mobile network to
have the capacity to handle any possible load at
all times.
• Fortunately, not all subscribers place calls at the
same time and so it is reasonable to size the
network to be able to handle some expected
level of load.
– > planner has to design the network to meet a
predefined blocking probability (e.g. 2 %), which
depends on the desired GoS
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Capacity planning process (TDMA/FDMA)
1. Considering the available resources (number of carriers etc.)
and the GoS requirements (blocking prop., )
2. Estimating the amount of Offered Traffic on each area
3. Estimating how many cells (BSs) and how many traffic
channels per cell are needed to serve the offered traffic on the
area with the given blocking propability (e.g. 2 %)
-> Determining the CAPACITY based cell area (and radius)
4. Checking if also COVERAGE can be granted for the capacity
based cell (i.e. can the signal reach the user/BS without
attenuating too much?)
-> if not the cell radius is decreased so that COVERAGE can
be granted
4
1. Considering the resources
• There are available resources
–
–
–
–
Number of carriers (channels)
Multiplexing (TDMA, FDMA, CDMA)
Duplexing (TDD, FDD)
…
• There are also requirements for GoS
– Blocking propability
– Call dropping propability
–…
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2. Estimating the traffic …
• Offered voice traffic from a user group can be
predicted as follows
Ttot  N * C *Tuser * F
, where
•
•
•
•
N is the number of persons
C denotes the penetration
T is the average traffic generated by one user
F denotes the area coverage probability (users not on
the network coverage area can’t offer traffic)
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… Estimating the traffic
• The traffic offered by each user is:
A = μH Erlangs
, where
H is the average holding time of a call
μ is the average number of calls requested/time
unit by the user
For example
H = 2 minutes and μ = 0.8 calls / hour
-> A = 2 * (0.8/60) ≈ 26.7 mErlang
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Traffic estimate
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•
Penetration CP = 0.25
Offered traffic per user: TO,1=TO,2=20 mErlang
Coverage probability: F1=0.8 (Pedestrian), F2=0.95 (Vehicular)
Distance between pedestrians S1=4 m
Distance between vehicles S2=25 m
Number of people in a car 2=1 (1=1)
Number of pedestrians
N1 = 1 Ls/S1 = 1•10000/4=2500
Number of cars
N1 = 2 Ls/S2 = 1•10000/25=400
Traffic offered by pedestrian users
T1=F1CP TO,1 N1 = 0.8•0.25•0,02•2500=10 Erlang
Traffic offered by vehicular users
T2=F2CP TO,2 N2 = 0.95•0.25•0,02•400=1.9 Erlang
Offered traffic A= T1+T2 = 11.9 Erlang
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3. Estimating the number of BSs needed
• Assuming we have estimated a total traffic of 20 Erlang
on a given area, how many BSs do we need if the smax
number of tranceivers (channels) on a BS is 5 and the
desired blocking level is 3 %?
– Using Erlangs B formula (or table)
 We need 27 channels, which can serve a total of 20.31
Erlang (from the Erlang B table)
 We need 27 / 5 = 5.4 -> 6 Base Stations (using 5 transceivers
in a BS)
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4. Can coverage be granted?
• Will be dealt with in the coverage planning
exercise
• Based on the calculation of a link budget
– Can the signal be received with adequate power?
• If the signal attenuates too much, the maximum distance
between BS and user (i.e. cell radius) must be reduced
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Example of capacity planning
• System parameters
– Penetration (all user groups): 25 %
– Offered traffic/user (all user groups): 20 mErlang
– Coverage probability target: vehicular users 95%, 1 user/car,
pedestrian users 80%
– Multiple access method: FDMA, 28 TRX/cell
– Blocking probability target: 2 %
– Service area divided into 4 homogenous Regions with spatially
uniformly distributed users
– In Region A the vehicular generated traffic is handled by
macrocells and pedestrian generated traffic by microcells, in
other Regions all traffic is handled by macrocells
• Approach: Minimum excess capacity, starting from
Region with highest traffic density, cells possibly
overlapping to adjacent Regions will reduce the area in
these to be covered correspondingly
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Geometry of the service area
D
Region types:
A: dense city
B: city
C: suburban
D: rural
C
B
A
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Parameters of the Regions in the Service Area
Regio
n
Size, L1L2-area of
o3ther Regions
Block size,
LB1LB2
Vehicle
spacing, Sv
Pedestrian
spacing,
Sp
A
55 km2 = 25 km2
0.20.2 km2
25 m
4m
B
1515  25 km2 =
200 km2
0.250.25 km2
50 m
10 m
C
4040  225 km2 =
1375 km2
0.1250.25 km2 200 m
125 m
D
120120  1600
km2 = 12800 km2
22 km2
550 m
1000 m
Basic assumption: Vehicles, pedestrians, and traffic are assumed to
be spatially uniformly distributed in each Region.
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Choosing the cell structure
An ideal cell would
have a circular shape.
To get complete coverage
a certain overlapping
must be allowed.
 Minimum overlapping with
hexagonal structure, which
is the most common in
theoretical investigations
 Another possible cell
structure giving complete
coverage is the quadratic cell
structure
 In this example the
quadratic cell structure gives
easier calculations and will be
used
 FROL = Fractional
Overlapping
FROL  1 
6
R 3 R

2 2
 R2
 0.173
hex_quad_cells
FROL  1 
2 R2
 R2
 0.363
hex_quad_cells
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Estimating the population in the regions
Estimation of population in the Regions
Length of street/road
network
Number of cars
Region L  L1 L2  L2 L1  2 A
N = L/S
LB1
LB 2 LB 1
A
B
C
2  25
 250 km
0 .2
2  200
L
 1600 km
0.25
L
L
F1375  1375I
H0.125 0.25 K
Number of
pedestrians
N2= L/S
250
250
 10000 N 2 
 62500
0.025
0.004
1600
1600
N1 
 32000 N 2 
 160000
0.050
0.010
N1 
N1 
16500
16500
 82500 N 2 
 132000
0.2
0.125
 16500 km
2  12800
L
12800
12800
 23273
2
N1 
 12800 N 2 
D
0.55
1
 12800 km
Hint. Don't forget to subtract the area of inner Regions
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Estimating the offered traffic
Estimation of offered traffic in the Regions
Vehicle originated
traffic
T1  F1C p1To N 1
Pedestrian originat- Total traffic and
ed traffic
traffic density
T2  F2C p 2To N 2
Region
T  T1  T2 /Erlang
 0.95  0.25  0.02N 1  0.80  0.25  0.02N 2
T T T
2

  1  2 /Erl/km
 0.00475 N 1
 0.004 N 2
A A A
T1  0.00475  10000 T2  0.004  62500 T  47.5  250.0  297.5
A
 47.5 Erlang
 250.0 Erlang   1.90  10.00  11.90
T1  0.00475  32000 T1  0.004  160000 T  152.0  640.0  792.0
B
 152.0 Erlang
 640.0 Erlang   0.76  3.20  3.96
T1  0.00475  82500 T1  0.004  132000 T  391.9  528.0  919.9
C
 391.9 Erlang
 528.0 Erlang   0.285  0.384  0.669
T  60.8  93.1  153.9
T1  0.00475  12800 T1  0.004  23273
  0.00475  0.00727
 93.1 Erlang
D
 60.8 Erlang
 0.0120
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Estimating the amount of traffic channels
and BSs to be used
Minimum number of cells with different number of
TCs/BS.
Region Offered Offered Traffic channels/BS and maximum traffic/BS
Traffic traffic
4
8
12
16
20
24
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density
B
Amacro
C
D
Amicro
Erlang Erl/km2 1.09
792.0
3.96
47.5
1.90
919.9
0.669
153.9
0.012
250.0 10.00
3.63
6.61 9.83 13.18 16.63
80.57 60.09 47.62
2.86
55.32
9.25
15.03
20.15
39.31
2.36
45.65
7.64
12.41
The Region with the highest traffic density is treated first, as this approach
would minimise equipment in most cases. In this case Region B is
investigated first, because the traffic density is highest there
(In Region A only car generated traffic is served by macrocells, while
pedestrian generated traffic is served by microcells)
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Dimensioning cells …
Cell dimensioning in Region B, 1/3
Region B cell size of cell completely inside the region:
Region B total area
200 km 2
x 

 5.09 km 2
minimum cell number
39.31
 x  2.26 km  RB  2.26 2  1.59 km
2
Offered traffic in edge cells partly covering Region C (overlapping area
from geometrical considerations):
Cells B1,B2,B3,B4,B5,B6,B14,B21,B28,B35,B40,B45:
T   B S B   C SC
 3.96  2.26  ( 2.26  0.82)  0.669  2.26  0.82  14.13 Erlang
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… Dimensioning cells …
Cell dimensioning in Region B, 2/3
From the Erlang B-table:
 22 TRXs in the FDMA-system giving a capacity of 14.90 Erlang/cell
Corner cell B7 partly covering Region C:
T   B S B   C SC
 3.96  ( 2.26  0.82) 2  0.669  2.26 2  ( 2.26  0.82) 2  10.24 Erlang
 17 TRXs in the FDMA-system giving a capacity of 10.66 Erlang
Offered traffic in edge cells B29,B30,B36,B41 partly covering Region A:
T   B SB   AS A
 3.96  2.26  ( 2.26  0.48 )  1.90  2.26  0.48  17.99 Erlang
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… Dimensioning cells …
Cell dimensioning in Region B, 3/3
 26 TRXs in the FDMA-system giving a capacity of 18.38 Erlang/cell
Corner cell B31 partly covering Region B:
T   B SB   AS A
e
j
 3.96  2.26 2  0.48 2  1.90  0.48 2  19.75 Erlang
 28 TRXs in the FDMA-system giving a capacity of 20.15 Erlang
In all other 27 Region B cells completely inside the region:
T   B S B  3.96  2.26 2  20.15 Erlang
 28 TRXs in the FDMA-system giving a capacity of 20.15 Erlang
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… Dimensioning cells
• When region B is dimensioned, it usually partly
overlaps regions A, C and D and therefore also
serves some of their offered traffic
– > When dimensioning regions A, C and D the traffic
already served by region B should not be served
again (equipment should be minimized)
• Otherwise the dimensioning process is done
exactly as for region B
• When the next region is dimensioned (in this
case D), the traffic served by it in other regions
should also not be served again
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Macrocell layout (capacity planning)
D1
D2
D3
D4
D5
D6
D7
D8
C1 C2 C3 C4 C5 C6 C7 C8
C9 C10 C11 C12 C13 C14 C15 C16
C17 C18 C19 C20 C21 C22 C23 C24
C25 C26 C27 C28 C29 C30 C31 C32
C33 C34 C35 C36 C37 C38 C39 C40
B4 B5 B6 B7
B1
B2 B3
B8
B9 B10 B11 B12 B13 B14
C41 C42 C43 C44 C45
B15 B16 B17 B18 B19 B20 B21
B22 B23 B24 B25 B26 B27 B28
B29 B30 B31 B32 B33 B34 B35
A1
A2
B36 B37 B38 B39 B40
B41 B42 B43 B44 B45
C46 C47 C48 C49 C50
C51 C52 C53 C54 C55
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Dimensioning microcells
• The procedure is similar, but
– In the city area, buildings cause significant
attenuation to the signal
– To minimize equipment, the BSs should generally be
located at the street crossings
– Usually pedestrian originated traffic on the area is
served using microcells and vehicular originated
using macrocells
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Microcell layout (capacity planning)
Coverage area (path loss <150 dB) calculated with
COST231 Walfisch Ikegami model
90 80
110 100
1.4
km
120
1.2
130
f=960 MHz
hbs=15 m
hms=1.6 m
hroof=30 m
w=25 m
b=100 m
60
1.5
Am4
50
30
0.6
160
Am6
Am5
40
0.8
150
Am3
Am2
70
1.0
140
Am1
Am7
20
Am9
Am8
WI_coverage.dsf
0.4
170
10
0.2
180
0
Am10
Am11
Am12
350
190
200
340
210
Am13
Am14
Am15
330
220
320
230
310
240
250
260 270 280
290
300
Am16
Am17
Am18
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