Section 6
Wideband CDMA Radio Network Planning
Radio Network Planning
A radio network planning consists of three phases:
1. Network Dimensioning (using link budgets)
2. Detailed capacity and coverage planning (using planning tools)
3. Network optimisation (using optimisation tool)
Phase 1 :Network Dimensioning
•
Dimensioning the WCDMA radio network includes radio
link budget and coverage analysis, capacity estimation
and estimation of the amount of network equipment
(such as number of BSs and RNCs) required.
•
These estimations will be based on the operator’s
requirements on coverage, capacity and quality of
service.
•
WCDMA-specific parameters in the link budget
compared to those parameters used in a TDMA-based
radio systems are:
-Interference margin
The value of the interference margin used in the link
budget depends on the loading of the cell. Higher is the
value of the interference margin in the uplink, the
smaller is the coverage area. Typical values are 1.0-3.0
dB in the coverage-limited cases, corresponding to 2050% loading.
-Fast fading margin
For slow-moving mobiles, to take care of fast fading
effect, a fast fading margin in the range of 2.0-5.0 dB
should be included in the link budget.
-Soft handover gain
Due to uncorrelated channels from the MS to the BSs,
handover gives a gain against slow fading. Also, soft
handover gives an additional macro diversity gain
against fast fading. The total handover gain can be
assumed to be in the range of 2.0-3.0 dB.
Link budget approach
Coverage requirement for a specific data rate with uniform load
Derive Link Budget
Input existing 2G sites that can be
Upgraded to 3G
Coverage satisfied?
Yes
End
No
Refine design, put new sites using
Planner’s individual judgment
Uplink Link Budget Example
A
B
C
D
E
F
G
H
Mobile transmit power (125 mW)
21 dBm
Mobile antenna gain
0 dBi
Body loss
3 dB
Mobile EIRP (A+B-C)
18 dBm
Thermal noise density
-174 dBm/Hz
Base station receiver noise figure
5 dB
Receiver noise density (E+F)
-169 dBm/Hz
Chip rate
3.84 Mchip/s
I
J
K
L
M
N
O
P
Receiver noise power (G + 10log H)
-103.2 dBm
Interference Margin (noise rise)
3 dB
Total effective noise & interference (I+J)
-100.2 dBm
Data rate
12.2 Kb/s
Processing gain (10 log (H/L) )
25 dB
Required Eb/No
5 dB
Base station receiver sensitivity (K-M+N) -120.2 dBm
Base station antenna gain
14 dBi
Q
R
S
T
U
Cable losses in the base station
2 dB
Lognormal shadowing margin
9 dB
In-car loss
8 dB
Soft handover gain
4 dB
Maximum path loss for cell range
(D-O+P-Q-R-S+T)
137.2 dB
Cell range
From the link budget, the cell range R can be easily calculated
using a known propagation model, for example the Okumura-Hata
model. The Okumura-Hata propagation model for an urban
macro-cell with base station antenna height of 30m, mobile antenna
Height of 1.5m and carrier frequency of 1950 MHz is given by:
L = 137.4 + 35.2 log10 ( R)
where L is the path loss in dB and R is the cell range in Km.
For suburn areas we assume an additional area correction factor of
8 dB and therefore the path loss is:
L = 129.4 + 35.2 log10 ( R)
Some Definitions
• Ratio of other cell to own cell interference
i
I oth
I own
In the uplink, it is calculated for the
i  BS, therefore i is similar for all
connections within one cell. However in the downlink, it is calculated
for each MS and therefore depends on the MS location.
i ranges from 0.15 (very well isolated microcells) to 1.2 ( poor radio
network planning.)
For the downlink, i is defined as:
i = I other
Pj
where I other is the power received from other BSs and pj is the power
received from the serving BS.
• Noise rise
I total
noise rise =
PN

Pj  Iown  Iother  PN
PN
Capacity estimation
The second part of dimensining is to estimate the capacity per cell i.e.,
supported traffic per BS. The capacity per cell depends on the amount
of interference per cell, hence it can be calculated from the load equations.
- Uplink load factor equation
 Eb
  W
 N o  j  j R j
Pr , j
I total  Pr , j
(1)
where W is the chiprate, pr,j is the received signal power for mobile user j,
 j is the activity factor of user j, Rj is the bit rate of user j and I totalthe
total received wideband power including thermal noise power in the BS.
Equation (1) can be rewritten as:
Pr, j 
1
1 


we define
I total
w
(2)

Eb N o   R j  j
j
Pr , j  L j I total
where L j is the load factor of one connection.
Using this equation and equation (2), one can obtain L j as:
Lj 
1
1 


w



Eb N o  R j  j
j
(3)
The total received interference, excluding the thermal noise PN ,can
be written as:
N
N
I total  PN   Pr, j   L j I total
j 1
j 1
(4)
The noise rise is defined as:
Noise rise

I total
PN
and using (4), we can obtain
(5)
Noise rise

I total
PN

1
N
1  L j
 11
(6)
UL
j 1
where
UL is defined as the uplink load factor and equals to:
UL
N
  Lj
j 1
(7)
when UL becomes close to 1, the corresponding noise rise approaches
to infinity and system has reached its pole capacity.
If the interference from the other cells is taken into account, then one
can write
UL
N
N
 (1  i )  L j  (1  i ) 
j 1
j  11 





1
W
Eb
No





j
(9)
 R j  j
where i is the ratio of other cells to own cell interference.
The interference margin used in the link budget must be equal to the
maximum planned noise rise i.e., -10 log(1-UL ).
For an all – voice service network, where all N users in the cell have
a low bit rate of R, we can write
W
 Eb
R


N
o

1
and hence equation (9) is simplified to
UL 
E
 b


W
No
R




N    (1  i )
- Downlink load factor
In the absence of intra- and inter- cell interferences, one can write
Pr, j
 Eb

 W


No 
 j R j PN

j
In the absence of interferences, we defined Pr, j  L j PN
and hence,
Pr, j
 Eb

1
Lj 

 j 

No 
PN



j
W

Rj



when we take into account both intra- and inter- cell interferences,
we have
 Eb

1




L j   1   j   i j   j  
 
N




o  j  W


 Rj


where  j is the orthogonality of the channel of mobile user j.
Its value depends on the channel multipath fading ; where  j = 1
means no multipath fading. i j is the ratio of other cell to own
cell base station power, received by the mobile user j.
The downlink load factor is defined as:
 DL
N
  Lj
j 1
N
  j
j 1
E
 b


W


N o 
Rj
j 


1



i




j
j



since, in the uplink, i and  j depends on the location of the mobile
user and they should ; therefore, be approximated by their average
values across the cell, i and  j .
j
The average value of the downlink load can then be approximated as:
 DL
N
  j
j 1
E

b



W
No





j
1     i 
Rj
the noise rise is given by:
noise rise
when


 10 log 1  DL  Interference margin
DL 
1
noise rise 
the system approaches its pole capacity.
Total BS transmission power
The total BS transmission power can be written as:
N
Pto ta l 
L  Pr , j
j 1
1 DL
where L is the average attennation between the BS and mobile
receiver (6 dB less than the maximum path loss)
E

since


Pr , j   j



b
W
N o 
Rj
j
PN
and
PN  NoW
then
N
N oW L 
j 1
Ptotal 

E
 b
j


W



1DL
No
Rj




j





where N o is the power spectral density of the mobile receiver and is
given by:
No  KTo F
where F is the noise figure of the mobile receiver with typical values
of 5-9 dB.
Throughput per cell
Throughout  N  R  1  BLER 
where N is the number of users per cell, R is the bit rate and
BLER is the block error rate.
Link budget approach
• Pros
- Enables fast planning of coverage for a pre-specified uniform load
- Skilled 3G staff not a requirement
• Cons
- Too simplistic for WCDMA where coverage/capacity/QoS are
closely related
- The final performance of the network cannot be derived based on
this method
- Mix of traffic cannot be taken into account
Phase2 :Detailed capacity and coverge planning
• In this phase, real propagation data from the planned area and the
estimated user density and user traffic are used.
• The output of this phase are the base station locations, configuration and
network parameters.
Static simulation approach
Coverage/traffic/QoS requirements
Input existing 2G sites which can be
upgraded to 3G
Refine design, put new sites using
Planner’s individual judgment
WCDMA static simulator
Coverage/capacity/QoS
Satisfied?
End.
Yes
No
Static simulation approach
•Pros
- Average QoS, capacity and coverage may be assessed for a mix
of traffic
•Cons
- Can only be run on a limited area, typical figures for running time
for a 3 Km x 3 Km area is ~5-8 hours on a Unix work station
- Manual judgment must be exercised in interpreting the results and
making decisions to improve the plan.
- Plans may need to be iterated several times (on average 5 times)
before the desired capacity/QoS/ coverage is achieved. This takes
total planning time for a 3 Km x 3 Km to ~1 to 2 working days at best!
- Skilled 3G a prerequisite
Phase 3 : Optimisation Phase
Network optimiser
•Optimises WCDMA FDD network plan minimising the number of sites
required to achieved the coverage/traffic/QoS targets set by the user.
•An Optimiser also automatically selects the most appropriate antenna
tilt, direction and sectorisation in order to achieve the required
coverage/traffic/QoS.
Network optimiser
Feed in your site portfolio
Set optimisation criteria
Run Optimiser algorithms
End
Optimisation phase
Coverage information
Optimised site
locations
WCDMA FDD
parameters
Traffic information
Site locations
Optimisation criteria
Optimiser
Coverage,
Capacity/QOS
statistics
Reference
“WCDMA for UMTS”, Edited by Harri Holma and Antti Toskala,
Second edition, John Wiley & Son Ltd, ISBN 0-470-84467-1.