WCDMA Radio Link Budget Principle and Case Study
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WCDMA RNP
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WCDMA Radio Link Budget Principle and
Case Study
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2007-12-10
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WCDMA Radio Link Budget Principle and Case Study
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WCDMA Radio Link Budget Principle and Case Study
Table of Contents
1 Introduction ............................................................................................................................ 4
2 R99 Link Budget ..................................................................................................................... 4
2.1
Maximum Allowable Path Loss....................................................................................... 4
2.2
Main R99 Link Budget Parameters ................................................................................. 5
2.3
Case Study ...................................................................................................................... 10
3 HSDPA Link Budget ............................................................................................................. 11
3.1
HSDPA Link Budget Procedure .................................................................................... 11
3.2
Case Study ...................................................................................................................... 12
4 HSUPA Link Budget ............................................................................................................. 13
4.1
HSUPA Link Budget Procedure .................................................................................... 13
4.2
Case study ...................................................................................................................... 14
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WCDMA Radio Link Budget Principle and Case Study
WCDMA Link Budget Principle and Case Study
Abstract：This article first presents an overview of WCDMA link budget procedure
and then fundamental parameters used in link budget are explained in detail.
1 Introduction
The purpose of this document is to illustrate the link budget principle and at the same time
provide detailed introduction to certain fundamental link budget parameters and some case
study.
The document is organized as follows:
Chapter 2 presents the R99 link budget principle and case study.
Chapter 3 shows the HSDPA link budget principle and case study.
Chapter 4 presents the HSUPA link budget principle and case study.
2 R99 Link Budget
2.1
Maximum Allowable Path Loss
Link Budget is the first step for radio network dimensioning. For an actual network, the
effective coverage of NodeB depends on not only the coverage requirement but also the TX
power and Rx sensitivity of NodeB and UE. Since the properties of NodeB and UE are
different from each other considerably, the actual permitted uplink and downlink path loss
vary too. Because the actual effective coverage range will depend on the lower value of them,
it is necessary to calculate the permitted maximum allowable propagation path loss of both
uplink and downlink.
The Maximum Path loss of uplink and downlink can be described by the formulas below:
PL _ DL  Pout _ BS  Lf _ BS  Ga _ antenna  Lp  Lb  IM  SFM  FFM  S _ UE
PL _ UL  Pout _ UE  Lf _ BS  Ga _ antenna  Lp  Lb  IM  SFM  FFM  S _ BS
Where:
PL _ DL : Downlink maximum path loss
PL _ UL : Uplink maximum path loss
Pout _ BS : Maximum TX power of BS traffic channel
Pout _ UE : Maximum TX power of UE
Lf _ BS : Cable loss
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Ga _ antenna : BS antenna gain
Lp : Building penetration loss (required in indoor coverage)
Lb : Human body loss
IM : Interference margin (related to system design capacity)
SFM : Slow fading margin or Log-Normal Fading (including soft handover gain against SFM)
FFM : Fast fading margin (including soft handover gain against FFM)
S _ BS : Sensitivity of BS receiver (related to factors like the service and multi-path condition)
S _ UE : Sensitivity of UE receiver (related to factors like the service and multi-path condition)
2.2
Main R99 Link Budget Parameters
In the following sections, a detailed description of the main parameters used in link budget is
provided.
1.
Receiver sensitivity (S_BS, S_UE)
Receiver sensitivity is mainly dependent upon noise figure and Eb/No and service bearer
rate R (kbps). The calculation formulas of S_BS and S_UE are:
S_BS = Thermal Noise Power + Noise Figure of NodeB + Eb/No + Processing Gain
S_UE = Thermal Noise Power + Noise Figure of UE + Eb/No + Processing Gain
* R is the service bearer rate.

Thermal Noise Power (Nth)
Thermal noise Power is the noise density generated by environment and equals to
N th  K  T  W
With K being Boltzmann’s constant 1.38*10-23 and T the temperature in Kelvin. When T is
293 in Kelvin (20 in Celsius), K  T is (-174dBm/Hz), W is 10×log (3840000), and N th is
(-108dBm/3.84MHz.)

Noise Figure (Nf)
Noise figure is the additional amount of noise generated by a receiver. For UE of 2100MHz,
typical noise figure is 7dB. For Huawei’s NodeB, latest noise figure is 1.6dB. It should be
noticed that noise figure of NodeB is equipment related and may be different for various
vendors.

Eb/No
Eb/No is the required bit energy over the density of total noise to maintain service quality.
The Eb/No values are related with the service type, the target BLER, the channel models and
the user speed. The table below shows the required Eb/No under different conditions.
Table1 Eb/NO requirement
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Service
BLER
AMR12.2k
1.00%
CS64k
0.10%
CS64k
1.00%
Channel
Model
Uplink
Eb/NO
Downlink
Eb/NO
TU3
RA120
TU3
RA120
TU3
RA120
5.4dB
4.5 dB
2.8 dB
2.8 dB
2.5 dB
2.3 dB
7.8 dB
8.3 dB
6.3 dB
6.8 dB
5.4 dB
6 dB
In dense urban and urban scenarios TU (Typical Urban) channel model is often used with
user speed being 3km/h or 50km/h, while in the rural environment the RA channel model is
often used with 120km/h speed.
Since two receiving antenna is typical configuration of NodeB, the uplink Eb/No that HUAWEI
provided above already includes two antenna receiving diversity gain.

Processing Gain (PG)
Processing gain is related with the service bearer rate, and the detail formula is present
below:
Processing Gain = 10 × log (3840 / R (Kbps)), R is the service bearer rate.
Service
AMR 12.2K
CS64K / PS64K
PS128K
PS 384K
2.
Processing Gain
25.0
17.8
14.8
10.0
Body Loss
Body loss is the loss at UE due to the presence of human body. Typical value is 3dB for
voice and low data rate services. For services with data rates no less than 64kbps, no body
loss is taken into account considering that terminals are usually held kept a distance from the
subscribers’ body.
3.
Penetration Loss
When indoor coverage is required to coverage by outdoor macro NodeBs, buliding
penetration loss needs to be considered. Building penetration loss is related to such factors
as incidence angle of the radio wave, the building construction (the construction materials
and number and size of windows), the internal building layout and Frequency. Building
penetration loss is highly dependent on specific environment and morphology and varies
greatly. For instance, the wall thickness in Siberian tends to be larger than that of Singapore
in order to resist coldness and hence the former’s building penetration loss is
correspondingly larger.
In addition, sometimes vehicular coverage may be required and consequently vehiculare
penetration loss also needs to be included in link budget process. In fact, only one
penetration loss, the maximum of building penetration loss and vehicular penetration loss, is
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included in link budget. Since typical vehicular penetration loss is around 8dB which is
smaller than building penetration loss, building penetration loss rather than vehicular
penetration loss is usually included in link budget process.
4.
Interference Margin (IM)
Interference margin is the required margin in the link budget due to the noise rise caused by
system load (the noise rise due to other subscribers).The higher the system load, the larger
the interference margin.
For uplink, the relationship between uplink load and interference margin is
IM uplink  10 * log10 (1  UL )
And depicted in the picture below
For downlink, the calculation of downlink interference margin is more complicated than uplink.
Many factors besides downlink load also have impact on downlink interference margin, such
as maximum transmission power of NodeB, cell coupling loss, orthogonal property of channel
model and adjacent-to-own cell interference ratio at cell edge.
5.
Fast fading margin
In WCDMA, user signals should be received at the BS with equal power all the time and for
downlink the transmitted TCH power should be as small as possible while maintaining the
required Qos. This implies that fast fading dips are compensated by the power control
algorithm, which requires additional headroom at both UE and NodeB in order to let UE and
NodeB following the power control commands at cell edge. Simulation results prove that the
required fast fading margin equals to the gain of fast power control. Obviously, no fast fading
margin is needed if fast power control brings no gain at all.
Since it’s a margin against fast fading, it decreases with user speed and the number of
multi-path.

SHO gain over fast fading
In SHO more than one branch exists and the multiple received signals are combined. As a
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result, the fast power control no longer has to compensate for the deepest fade and both the
required transmission power and received signal level can be reduced.
SHO gain over fast fading refers to the gains of combining the multiple received signals
(MDC gain) and less peaky fast power control due to SHO. In other words, SHO gain against
slow fading is not included.
6.
SFM (Slow Fading Margin)
The log normal fading margin (also known as slow or shadow fading margin) corresponds to
the variation in mean signal level caused by shadowing effect of physical environments such
as buildings and hills.
The fading margin is the amount of margin necessary to achieve the required area reliability
for a given standard deviation. Obviously, the higher area coverage reliability requires the
larger SFM. In addition, the value of standard deviation will also influence the required fading
margin and the larger the standard deviation, the larger the required SFM.
Coverage Probability:
P COVERAGE (x) = P [F(x) > Fthreshold ]
Probability Density
SFM required
Without SFM
With SFM
Fthreshold

Received Signal Level [dBm]
SFM without SHO
The following equation is Jake’s singe cell reliability equation that determines the area
reliability of a single cell which is commonly used to approximate the reliability of a site.
Fu 
1 
1  2ab 
1  ab  
 1  erf (a)  exp(
)  1  erf (
) 
2
2 
b  
b

Where:
a
x0  Pr
 2 ,
b
10  n  log 10 e
 2
,
Fu is cell coverage probability, Pr is the received signal mean at cell edge, n is the
propagation constant, x 0 is the average signal strength threshold,
 is the slow fading
standard deviation and erf is the error function.
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
STD (Slow Fading Standard Deviation)
The standard deviation is a measured value that is obtained from various clutter types. It
basically represents the variance (log-normally distributed around the mean value) of the
measured RF signal strengths at a certain distance from the site.
Therefore, the standard deviation would vary by clutter type. Depending on the propagation
environment, the log-normal standard deviation can easily vary between 6 and 8 dB or even
greater. Assuming flat terrain, rural or open clutter types would typically have lower standard
deviation levels than the suburban or urban clutter types. This is due to the highly obstructive
properties encountered in an urban environment that in turn will produce higher standard
deviation to mean signal strengths than that experienced in a rural area.
A composite standard deviation can be obtained by the following formula:
 c   12   22     n2
where  n is the log normal standard deviation for environment n. This composite standard
deviation may sometimes be used if there are two or more environments (for instance,
outdoors and in-building) which have their own standard deviation. For example, if the
standard deviation is 8 dB for outdoors and 10 dB for in-building, the composite standard
deviation to use in Jake’s equation would be ~ 12 dB.

SHO gain over slow fading
SHO gain over slow fading is also known as the Multi-Cell gain because in soft handover
more than 1 branch exists and hence the coverage probability increases which would result
in the decreasing of required slow fading margin.
Suppose that soft handover has 2 branches, and the orthogonality of the two radio link
branches on slow fading is 50%. We can calculate the slow fading margin required with soft
handovers based on the former assumptions, and compare it with the slow fading margin
required without soft handover to get the SHO gain over slow fading.
It should be noted that in a real network more than 2 branches may be involved in a soft
handover, though this probability is rather slow, the corresponding SHO gain is slightly higher
than that of a 2 branch soft handover. Therefore, the SHO gain derived from the above
supposition on 2-brance handovers is relatively conservative.
SHO gain over slow fading is dependent on the required area coverage probability, the
propagation path loss slope and the STD. The following table gives the calculated SHO gain
over slow fading and the propagation path loss slope equals to 3.59.
Table2 SHO gain over slow fading
Standard
Deviation(Indoor)
Coverage
Probability
Slow Fading
Margin(Non SHO)
SHO Gain over
Slow Fading
Slow Fading
Margin(With SHO)
11 (Dense Urban)
9 (Urban)
0.95
0.95
13.1dB
10.2dB
5.6dB
4.6dB
7.5dB
5.6dB
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8 (Suburban)
2.3
0.95
8.7dB
4.7dB
4dB
Case Study
Assumption:
Cable Loss: 0.5 dB (Distribution system)
Cell Load: 50% for uplink and 90% for downlink (considering HSPA services)
Antenna Gain: 18 dBi
Penetration Loss: 20 dB (Dense urban)
Maximum UE transmitting power: 21 dB
Propagation Model: SPM (Standard propagation model)
BS average antenna height: 30 meters
Procedures of uplink and downlink link budget are provided in the following table:
Table3 Uplink and Downlink Link Budget Procedures
Link Budget
AMR12.2k
CS64k
Calculation Formula
Uplink
Downlink
Uplink
Downlink
Transmitting Power(dBm)
21
30
21
36
a
BS Antenna Gain (dBi)
18
18
18
18
b
Cable Loss(dB)
0.5
0.5
0.5
0.5
c
Body Loss(dB)
3
3
0
0
d
Load Factor
0.5
0.9
0.5
0.9
Interference Margin(dB)
3.01
5.44
3.01
5.44
e
Fast Fading Margin(dB)
0.8
0
1.8
0
f
Area coverage probability
95%
95%
Slow fading standard deviation (dB)
11
11
Slow Fading Margin(dB)
7.54
7.54
7.54
7.54
g
Penetration Loss(dB)
20
20
20
20
h
Thermal Noise (dBm/3.84MHz)
-108.13
-108.13
-108.13
-108.13
j
Receiver Noise Figure(dB)
1.6
7
1.6
7
k
Required Eb/NO(dB)
5.4
7.8
2.8
6.3
l
Processing Gain(dB)
24.98
24.98
17.78
17.78
m=W/R
Receiver Sensitivity(dB)
-126.11
-118.31
-121.51
-112.61
i=j+k+l-m
Maximum Path Loss
130.26
129.83
127.66
133.13
PL=a+b-c-d-e-f-g-h-i
According to the maximum path loss, BS antenna high and propagation model, the cell
radius can be obtained.
Coverage Service
Cell Radius (Km)
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AMR12.2k
CS64k
Uplink
Downlink
Uplink
Downlink
0.47
0.45
0.39
0.57
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WCDMA Radio Link Budget Principle and Case Study
3
HSDPA Link Budget
3.1
HSDPA Link Budget Procedure
The HSDPA link budget is usually base on the R99 link budge to get the cell edge throughput
in downlink. The link budget for HSDPA is more complex than R99, and the cell edge
throughput need to be calculated depend on simulation result, which is closed related with
cell edge Ec/No.
For HSDPA, soft handover gain and fast fading margin should not be considered in link
budget, since neither fast power control nor soft handover is adopted in HS-PDSCH channel.
The figure below shows the procedure of HSDPA link budget:
Cell Radius
Downlink Coupling Loss
Cell Edge Ec/No
HSDPA Power Allocation
Simulation
UE Category,
Receiver Type…
Ec/No => Throughput
Cell Edge Throughput
The main step of HSDPA link budget is present below:
1.
According to the cell radius comes from R99 dimensioning, the downlink coupling loss
can be calculated.
2.
Cell edge Ec/No will be carry out base on the formula below:
Ec
 10 * log(
No
PHS  DSCH
  f  DL  Pmax  10
DL _ CoupleLoss＋NF＋Nt
10
)
Where:
PHS  DSCH
: Total power of HS-DSCH channel
 : Non-orthogonality Factor
f
: Neighbor cell interference factor
DL _ CoupleLoss ：Downlink coupling loss
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 DL : Downlink target load, including R99 and HSDPA service
Pmax : Max transmitter power of downlink
Nt : Thermal noise power spectral density, typical value is -108.16dBm
Nf
3.
: Receiver noise Figure, typical value is 7dB
Cell edge throughput can be calculated base on the simulation result, while more
factors have been considered, such as UE Category and HSDPA codes allocation.
3.2
Case Study
Assumption:
Channel type: TU3
Non-orthogonality factor: 0.5
Neighbor cell interference factor: 1.78
HSDPA code resource: 5
Cell radius: 0.36 Km
UE Category: 8
Max transmitter power of downlink: 20000 mw
Total power of HSDPA: 6000 mw (30% downlink power allocation)
According to the assumption above, the DL_CoupleLoss for HSDPA is calculated below:
DL _ CoupleLoss  PL _ DL  Lf _ BS  Ga _ antenna  Lb  SFM NSHO  Lp
 (127.69  1.37)  0.5 - 18  0  13.1  20  144.66
Where:
PL _ DL : Downlink maximum path loss
Lf _ BS : Cable loss
Ga _ antenna : BS antenna gain
Lp : Building penetration loss (required in indoor coverage)
Lb : Human body loss
SFM NSHO : Slow fading margin or Log-Normal Fading (without soft handover gain against SFM)
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Ec
 10 * log(
No
PHS  DSCH
  f   DL  Pmax  10
DL _ CoupleLoss＋NF＋Nt
10
6000
 10 * log(
(0.5  1.78) * 0.9 * 20000  10
144.66108.16 7
10
)
)  10.2dB
Base on the simulation result, the cell edge throughput for HSDPA can be obtained as
173.80 Kbit/S.
4
HSUPA Link Budget
4.1
HSUPA Link Budget Procedure
The procedure of HSUPA link budget is almost the same with HSDPA. The cell edge
throughput is also depended on the simulation result. The main difference between HSUPA
and HSDPA is that power control, soft handover gain and UE power back off are needed to
be considered in the cell edge Ec/No evaluation.
For HSUPA, the UE power PAR (Peak to average rate) is increase due to the multi-code
transmission of uplink users, and power back off is needed to protect UE’s PA (Power
amplifier).
The figure below shows the procedure of HSUPA link budget.
Cell Radius
Cell Edge Ec/No
Simulation
Ec/No => Throughput
UE Maximum Power
UE Category,
Receiver Type…
Cell Edge Throughput
The main step of HSUPA link budget is present below:
1.
Cell edge Ec/No for HSUPA can be calculated base on the formula below:
R _ signal  Pout _ UE  Pbackoff  PL _ UL  Lp  SFM  IM  FFM  Ga _ antenna
Ec
 R _ signal  ( Nt  Nf  Lf _ BS )
No
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Where:
R _ signal : Minimal receive signal level required
Pout _ UE : Maximum TX power of UE
Pbackoff
: UE power back off
PL _ UL : Uplink path loss
Lf _ BS : Cable loss
Ga _ antenna : BS antenna gain
Lp : Building penetration loss (required in indoor coverage)
Lb : Human body loss
IM : Interference margin (related to system design capacity)
SFM
: Slow fading margin or Log-Normal Fading (including soft handover gain against SFM)
FFM
: Fast fading margin (including soft handover gain against FFM)
Nt : Thermal noise power spectral density, typical value is -108.16dBm
Nf
2.
: NodeB Receiver Noise Figure, typical value is 1.6dB for Huawei
Cell edge throughput can be calculated base on the simulation result, while more
factors have been considered, such as UE Category, receiver type. Part of simulation
result is presented as below:
TU3_SBLER70%
TU3_SBLER30%
TU50_SBLER70%
TU50_SBLER30%
RA3_SBLER70%
RA3_SBLER30%
10
5
0
-10
Ec/N0
-5
-15
-20
Bearer Rate
-25
69
4.2
507.6
978
1353
1927.8
2706
4050
Case study
Assumption:
Channel type: TU3
Cell radius: 0.36 Km
Pout _ UE : 24 dBm
Pbackoff
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: 1.5 dB
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WCDMA Radio Link Budget Principle and Case Study
IM : 3 dB for 50% uplink load
According to the assumption above, the Ec/No for HSUPA can be calculated below:
Ec
 Pout _ UE  Pbackoff  PL _ UL  Lp  SFM  IM  FFM  Ga _ antenna  ( Nt  Nf  Lf _ BS )
No
 24  1.5  127.69  20  7.54  3  0  18  (108.16  1.6  0.5)  11.67
Base on the simulation result, the cell edge throughput for HSUPA can be obtained as 255.6
Kbit/S.
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