Long Term Evolution
Part 5: Radio Link Budget
J. Hämäläinen, 2016
Department of Communications and Networking
Contents
1 Principles of RLB
2 LTE downlink RLB
3 Some details on RLB
a) eNodeB powers and antennas
b) Path loss and shadowing margin
c) Interference, SINR and data rate
4 DL Link Budget Examples
5 LTE Uplink Radio Link Budget
Network Planning
Our focus area
Network planning consists of 3 phases:
- Dimensioning, detailed planning and optimization
Dimensioning
Note: We omit core network
150
140
Path Loss [dB]
130
+
120
110
100
90
0
0.2
0.4
0.6
0.8
Distance from BS [km]
1
1.2
EIRP
58dB
Margins
23dB
Sensitivity -100dB
Allowed PL 135 dB
1000 x
5000 x
1.4
Area and propagation information
Radio Link budget
# Network elements
Detailed planning
TX power 43dBi
Antennas 2
Antenna tilt 5o
Parameter x, y, z
Input from
dimensioning
Network planning tools
System simulations
BS + RS Configurations and
topology plan
Optimization
+
Operating network
(drive tests, monitoring)
Optimized system
1. Principles of RLB
Background
• Radio Link Budget (RLB) is a basic tool in radio engineering. It is used to
compute estimates for e.g.
Can be used to estimate
– Received power in terminal/eNodeB
user rates
– Allowed propagation loss
– Connection range between transmitter and receiver
• RLB take into account the gains and losses from the transmitter, the
communication medium (wireless channel in our case) and the receiver.
• Typical parameters are related to the propagation model (radio
environment), antennas (antenna directivity/gains), feedlines (cable
attenuation) and the receiver properties (product specific sensitivity, noise
figure)
Example: RLB in LTE cell coverage
estimation
LTE eNodeB
with 3-sector
transmission
User on the distance where
minimum required rate can be
provided – assuming a certain
load.
Example: We require that user
should reach 1Mbit/s data rate when
10% of the cell resources are
allocated for him/her.
Question: How far from eNodeB
user can be? This distance gives cell
range under above constraint
Simplified RLB
EIRP = Effective Isotropic Radiated Power,
contains transmitted power and antenna gain
Transmitter
characteristics
BS Transmitter
BS to MS
Total transmission power
43 dBm (20 W)
Transmitter antenna gain
15 dBi
EIRP
58 dBm
Margins
Channel
characteristics
Receiver
characteristics
Number that is
used to estimate
the cell range
Shadow fading margin
7 dB
Interference margin
4 dB
Penetration loss
10 dB
Total Margin
21 dB
UE Receiver
(Max coverage)
Receiver sensitivity
-100.7 dBm
System gain
158.7 dB
Allowed Propagation Loss
137.7 dB
Simplified RLB: Terminology
• dBi = dB(isotropic). It is the forward gain of a certain antenna compared to
the ideal isotropic antenna which uniformly distributes energy to all
directions.
• dBm = dB(1 mW) is a measured power relative to 1 mW (e.g. 20W is
10*log(1000*20)= 43 dBm
• Effective isotropic radiated power is the amount of power that would have
to be emitted by an isotropic antenna (that evenly distributes power in all
directions and is a theoretical construct) to produce the peak power density
observed in the direction of maximum antenna gain.
– EIRP can take into account the losses in transmission line and connectors and
includes the gain of the antenna.
RLB through equations
• In this case the Allowed Propagation Loss (APL) can be calculated as
follows:
APL = EIRP - min { PRX } - M Total
= PTX + GA - min { PRX } - M SF - M I - M Penetration
Here
min { PRX } = Receiver sensitivity [dBm]
PTX = Transmission power in BS [dBm]
GA = BS antenna gain [dBi]
M SF = Shadow fading margin [dB]
M I = Interference Margin [dB]
M Penetration = Indoor penetration loss [dB]
Penetration loss simply depends on the expected building wall losses.
10
The RLB principle
TX/RX parameters
Data rate requirement
User resource allocation
• TX/RX parameters depend on
the network deployment
– Equipments (eNodeB, UE,
antennas), site properties
• Data rate requirement
Link budget
Allowed propagation loss
– Depends on the service
– Data rate can be mapped to
required signal to interference
and noise ratio (SINR)
• User resource allocation
Path loss model
– Traffic expectations
• Path loss model
System range
– Environment/clutter type
2. LTE Downlink Radio Link Budget
12
LTE Downlink RLB
• In the following we go
through this LTE
downlink radio link
budget in details
• This is a snapshot from
excel tool that is given
for participants
• There will be some
solved examples
discussed later.
Resource allocation and rate
requirements
Parameter
Comment
Number of
PRBs
This is estimated by assuming the operation
bandwidth and number of users served at the same
time. In case of 10MHz band we have 50 resource
blocks (48 for data). Then 10PRB takes 10/48 of all
resources
Data rate
In this case we assume 2Mbits/s target rate
Remark on rate requirement
• In case of constant bit rate service (like real time video) the
2Mbits/s requirement defines how much resources user
continuously employs
• In usual case (e.g. web browsing, file downloading, streaming
video) the data transfer happens in bursts so instantaneous rate
can be high while there are time gaps between transmissions
for user (time multiplexing of users)
• Example: If user on cell edge download 1 Mbit file
– (s)he needs round 0.1 seconds for all 48 PRBs OR
– (s)he is given 5PRBs for 1 second time period
– Other options – of course – are possible as well
Transmission characteristics
Parameter
eNodeB TX
power
Comment
Typical value is 20W-60W (43dBm-48dBm)
20W on 5MHz band (as in WCDMA/HSPA)
40W on 10MHz band (most usual test case for Rel.8 LTE)
60W on 20MHz band
Antenna
gain
Discussed later in more details. Typical 1.3 m high panel
antenna at 2 GHz band gives 18 dBi gain in main
direction
Cable loss
Loss between the eNodeB antenna and the low noise
amplifier. The cable loss value depends on the cable
length, cable type and frequency band.
UE receiver (1/2)
Parameter
Comment
UE Noise
Figure (NF)
NF measures of degradation of the SNR by the
components in the RF receiver chain, product specific.
Typical values: 6-11dB
Thermal noise = Boltzmann constant x T (Kelvin) x Effective
bandwidth. Here
Boltzmann constant = 1.38 x 10^(-23) J/K (J = Ws)
Reference temperature 20 Celsius = 290 Kelvin
Effective bandwidth = Number of PRB’s x 180kHz
Thermal
Noise
Receiver
Noise Floor
Receiver noise floor = UE NF + Thermal noise
UE receiver (2/2)
PHICH = Physical HARQ Indicator Channel
PBCH = Physical Broadcast Channel
PDCCH = Physical DL Control Channel
Parameter
Comment
SINR
Required Signal to Interference and Noise Ratio
depends on the data rate, number of PRBs and link
efficiency. We consider this in more details later in
this slide set
Minimum required power in receiver required to detect
the signal. Receiver sensitivity = Receiver Noise Floor +
SINR
Receiver
sensitivity
Control channel
overhead
Control channel overhead includes the overhead
from reference signals, PBCH, PDCCH and PHICH.
5%-25% leads to 1dB-4dB overhead.
RX antenna gain
Depends on the receiver antenna, usually 0dBi for
Margins and losses
Parameter
Comment
Body loss
Body loss is typically included for voice link budget
where the terminal is held close to the user’s head.
3-5dB for voice.
Depends on the propagation environment. Typical values:
4-7dB. Will be discussed later in more details.
Shadowing loss
Interference
margin
Interference margin accounts for the increase in the
terminal noise level caused by the other cell
interference. If we assume a minimum G-factor of −4
dB, that corresponds to 5.5dB IM
(10*log10(1+10^(4/10)) = 5.5 dB). Typical values for
IM: 3dB – 8dB.
Indoor
penetration loss
Depends on the building types. In urban area 20dB,
in suburban/rural area with light buildings 10dB.
Allowed propagation loss
APL = PTX + GA( NodeB) - LCable + GA(UE) - min { PRX }
- M SF - M I
- LC - Lbody - LPenetration
3. Some details on RLB
RLB elements:
a) eNodeB powers and antennas
eNodeB transmission power
• For macro eNodeB typical value is 20W-60W (43dBm-48dBm)
– 20W on 5MHz band (as in WCDMA/HSPA)
– 40W on 10MHz band (most usual test case for Rel.8 LTE)
– 60W on 20MHz band
• For micro eNodeB typical value is 5-10W (37dBm-40dBm)
• For pico eNodeB typical value is 100mW-2W (20dBm-33dBm)
– 3GPP limit for pico eNodeB TX power is 250mW (24dBm)
– There are many ‘pico’ products with TX power 250mW-2W
• For femto eNodeB TX power is limited to 100mW (20dBm)
– Typical values are some tens of milliwatts
Example eNodeB products
Ericsson 6201 multi-standard
macro base station, indoor
installation
Nokia macro base station,
outdoor wall installation
Macro eNodeB antennas: 3-Sector site
solutions
• Site = location for base
station, antennas, cables, etc.
• The use of 3 sectors in each
site is the most common
approach
• Omnidirectional antennas can
be used in cells with low load
• Here color code refers to
coverage areas of different
antennas (frequencies can be
same or different in different
sectors)
1
2
3
1
1
2
3
2
3
1
1
2
24
3
2
3
Typical macro eNodeB site antenna
• Dual band X-polarization antenna for each sector
– 2 transmission branches in downlink and uplink in
each sector antenna
– Dual band: 800MHz and 2100 MHz
– Design contains only 3 antennas but still 6 feeder
cables needed
25
Panel antenna example: Kathrein 742 215
• Kathrein multi-band dual-polarization
panel antenna (model 742 215)
• Typical macrocell eNodeB antenna
– Round 18dBi antenna gain
– Support 2100MHz and 800MHz bands
• Let us look this antenna in more details
and compare antenna measurements with
the general 3GPP modeling used in
simulations (see antenna slides for more
details)
26
Horizontal and vertical gain patterns
27
Comparison with Gmain
18dBi
3GPP model
q3dB(V )
q3dB(H ) GFB
65 deg
30dB
6.2 deg
SLL
-18dB
Kathrein 742215
Simple gain model
Source: F. Gunnarsson et al: “Downtilted Base Station
Antennas – A Simulation Model Proposal and Impact on
HSPA and LTE Performance”, IEEE VTC 2008
q tilt
= 10 degrees
29
‘High power’ pico eNodeB
• Ericsson indoor pico (6401), multistandard
• TX output power: 1W
• http://www.ericsson.com/ourportfolio/products/rbs-6401
30
Model for pico eNodeB antenna gain
pattern 1/2
• Horizontal gain pattern
GH ( )
5dBi
0dBi
-180deg
-10dBi
-100deg-70deg
-15deg 15deg
70deg
100deg
180deg
Model for pico eNodeB antenna gain
pattern 2/2
• Vertical gain pattern
GV ( )
0dBi
-3dBi
-180deg
-100deg -70deg
-15deg 15deg
• Total gain pattern
G ( , )  GH ( )  GV ( )
70deg
100deg
180deg
32
Example
• Two 2W indoor
nodes with given
antenna gain
patterns
• Received wideband
powers simulated
by WinProp tool
• 2GHz carrier
• Excellent indoor
coverage obtained
‘Low power’ Femto base stations
Nokia 3G femto
base station
Vodafone 3G femto
base station
RLB elements:
b) Path loss and shadowing margin
b1) Average path loss
Single slope model
• The most commonly used average path loss model is the
so-called single-slope model
where
– “L0” is the average path loss at reference distance “r0”
– “n” is the path loss exponent (which depends on antenna heights,
carrier frequency, and propagation environment)
– In free space n = 2
➢ The single-slope model is valid, e.g., when
dealing with homogeneous environments
Free space model
• Free space propagation is an example of a single slope
model, i.e.,
In this situation, we have that
Dual-slope model
• Another path loss modeling approach is provided by the dualslope model, i.e.,
where “r0” is known as the break-point distance
Linear loss model
• In waveguide propagation and absorbing propagation
environments, the linear loss model can be sometimes used
• Linear model is suitable for tunnels, and indoor propagation
through walls (i.e., excellent signal propagation)
Environment types (1)
– Outdoor propagation environments:
Subdivision is done into:
• Base station antenna located above roof tops, and
• Base station antenna located below roof tops
Environment types (2)
– Outdoor to indoor propagation
environments
Subdivision is done again into same
categories as outdoor case:
• Base station antenna located
above roof tops
• Base station antenna located
below roof tops
Environment types (3)
– Indoor propagation environments
Subdivision is done, e.g., into:
• Number of floors in a building to be covered,
• Landscape of the (office) building, and so on
– Offices or flats with many rooms
– Corridors, tunnels, etc.
Okumura-Hata Model (1)
• (Okumura-) Hata model is one of most common models
for signal prediction in large macrocells
– This model exists in many version, and is defined for limited
ranges of parameters
• Originally, this model is valid for:
– Distances: 1-100 km
– Frequency ranges: 150-1500 MHz (it was extended later)
43
Okumura-Hata Model (2)
• Okumura used extensive
measurements of base station-tomobile signal attenuation in the
city of Tokio (Japan)
– He developed a set of curves that
gives the median attenuation
(relative to free space) of signal
propagation in irregular terrain
– The base station heights for these
measurements were 30-100 m
➢ The Hata model is an empirical formulation of the graphical
path-loss data provided by Okumura (model is isotropic)
– Closed-form formulas provided by Hata simplify path loss calculations
(four different environments were defined)
44
Okumura-Hata Model (3)
• The original Hata model is given by
where the parameters (and their corresponding units) are
150 and 1500 MHz
Okumura-Hata Model (4)
• The correction factor for the mobile antenna height
“ai(hMS)” depends on the size of the coverage area:
– Large/dense city (i.e., “i = 1”),
– Medium/small size city (i.e., “i = 2”),
– Suburban area (i.e., “i = 3) and rural/open area (i.e., “i = 4”)
Okumura-Hata Model (5)
➢ Correction factor for the mobile antenna height (cont’d)
Okumura-Hata Model: PL vs. Range (1)
Carrier frequency
48
Okumura-Hata Model: PL vs. Range (2)
Carrier frequency
49
Okumura-Hata Model: PL vs. BS Antenna Height
Carrier
frequency
50
Okumura-Hata Model (6)
• In mobile communication systems (like GSM and
3G), base station antennas are rarely placed on
locations over 40 meters in height
• Systems like television and radio broadcasting
may use towers that higher than 100 meters
– The height of the FM- and TV-mast (Helsinki-Espoo)
located in Latokaski (Espoo), has a current height of 326
meters (third highest structure in Finland)
• In the next slide, we illustrate the impact of the
environment type in the path loss attenuation
– It is found that difference between large and medium
size cities is small, while
– Path loss attenuation in suburban and open areas is far
more smaller than in city environments
Okumura-Hata Model: PL vs. Range (3)
Environment Type
52
Okumura-Hata Model (7)
• Later on, Okumura-Hata model was extended to the 15002000 MHz frequencies, in the COST 231 research program
– The distance interval was also extended
• ITU-R sector adopted this model in Recommendation P.529
where MS antenna height correction factor is the same as in
the previous model, and the additional term is given by
Okumura-Hata Model (8)
• Finally, an extension to the Okumura-Hata model for
distances between 20-100km is given by the expression
where the “β” parameter is given by
Note: The COST 231 extension of the Okumura-Hata model is
a single slope model for distances in the range of 1-20 km
Remark on path loss models
• Okumura-Hata model represents the most well-know macrocell
model
• Walfisch-Ikegami model is an other well-known model for urban
area
• In network planning tools above-mentioned models are used with
additional clutter corrections
– Several different clutter types can be defined with different additional
dB/m loss factors
– Planning tool design companies are usually not publishing all their
models
• There are also several models for small outdoor and indoor cells
– Yet, the smaller are the cells, the worse are the ‘isotropic models’ that
don’t take into account the environment (e.g. building) structure.
– When high carrier frequency communication take place in cellular
systems (5G) ray tracing models become more important.
55
b2) Shadow fading
56
Example: Path loss measurements
Shadow fading (1)
• Obstacles with a size from tens to hundreds of
wavelengths (on the different propagation paths)
cause a variation of the path loss around the
average path loss “L”
• This variation is random but, however, it is
correlated when measured in nearby locations
• Shadowing, caused for e.g. by big buildings, can
be critical for mobile users located in cell edge
areas
Shadowing
Tx
Rx
– The effect of shadow fading may create large
coverage holes
➢ In many measurements, it has been observed that shadow fading “Ls”
can be described with a log-normal distribution*, and the probability
density function is given by
1
f ( Ls ) 
e
2  s

L2s
2 s2
* Loss measured in logarithmic scale (i.e., [dB]) is normally distributed
Shadow fading (2)
• Values obtained in shadow fading measurements*
– Carrier frequency: 2.0 GHz
Network area/
Parameter
Standard
deviation
Dense urban /
Urban
8,5 dB
Sub-urban
7,2 dB
Rural
6,5 dB
* Values reported in different sources vary generally from 6-10 dB
Shadow fading (3)
1
Scaled probability distribution function (PDF)
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
-30
-20
-10
0
10
Shadow fading value [dB]
20
30
Probability distribution function for shadow fading when SF
standard deviation “σs” is 4 dB (o), 8 dB (*), and 12dB (x)
Shadow fading (4)
• The cumulative distribution function (CDF) is given by
PLs  L0  
L0

0
 L0 
f (t ) dt  1  Q  ,
s 
where “Q(x)” is the Marcum Q-function,
Q( x) 
1
2

e
x
t2

2
dt 
1
 x 
erfc 

2
 2
erfc(x) = complementary error function
Shadow fading (5)
1
Cumulative distribution function (CDF)
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
-30
-20
10
0
-10
Shadow fading value [dB]
20
30
Cumulative distribution function for shadow fading when SF
standard deviation “σs” is 4 dB (o), 8 dB (*), and 12dB (x)
Combined path loss and shadowing (1)
• In network planning, a Shadow Fading Margin (SFM) is
added on top of average path loss
• This margin is based on the required target power level
(i.e., maximum allowed path loss in the link budget) to
guaranteed a given outage probability in the system
• Let us denote
– “Lmax” = maximum allowed attenuation (link budget parameter)
– “Pout” = allowed outage probability at cell edge (QoS of network)
– “Ltot” = Total loss including shadowing and average path loss
• Then we set
(*)
PLtot  Lmax   Pout
S-72.3216 RC Systems I (5
Ltot  L  Ls
cr) Lecturesattenuation
3-5, Autumn
”Lmax” = maximum allowed
(system specific parameter)
2013
63
”Ltot” = Total loss at cell
edge (network design parameter)
Combined path loss and shadowing (2)
• From formula (*) we obtain
1  PLs  Lmax  L   Pout
• Then, using the Marcum function representation we get
 Lmax  L 
  Pout
Q 
 s 
• It is common to use the inverse Marcum’s function to obtain
the (average) path loss that fulfill target requirements, i.e.,
L  Lmax   sQ1 Pout 
• Yet, note that the inverse Marcum’s function does not exist in
closed-form
S-72.3216 RC Systems I (5
cr) Lecturesattenuation
3-5, Autumn
”Lmax” = maximum allowed
(system specific parameter)
2013
64
”Ltot” = Total loss at cell
edge (network design parameter)
Inverse Marcum’s function
0
10
-1
10
-2
Q(x)
Q(x)
10
-3
10
-4
10
-5
10
0
0.5
1
1.5
2
x
x
2.5
3
3.5
4
Combined path loss and shadowing (3)
• Revisiting the derived formula that combines path loss and
shadowing,
L  Lmax   sQ
1
Pout 
• The (average) path loss on the left-hand side depends on:
– Distance between transmitter and receiver,
– Antenna heights of both, transmitter and receiver,
– Carrier frequency, environment type, …
OkumuraHata model
• The value on the right-hand side depends on:
– Standard deviation of shadow fading (environment type),
– Allowed attenuation (system specific parameter: link budget)
– Outage probability (network target performance: guaranteed QoS)
In link budget calculations,
so-called SF margin is given by
M SF   s  Q
1
Pout 
Combined path loss and shadowing (4)
Lmax
Path Loss
L
Ltot
50%
Edge reliability (i.e., “Pout”) depends on
assumed “σSF” and shadow fading margin
Path Loss + shadowing
90%
Lmax
Ltot
Shadow fading standard
devidation (σSF) grows
L
➢ As “σSF” grows for same fading margin, the edge reliability is reduced
➢ As “σSF” grows, a larger fading margin is required to maintain the
same edge reliability
67
RLB elements:
c) Interference, SINR and data rate
Co-channel interference: general formulation (1)
• General formulation for the
received signal:
Interfering TX #1
K
r  S 0   S k  nW
d1
k 1
where “S0” is the desired
signal, “Sk” refers to the
interfering signal originated
in the k-th (co-channel)
transmitter, and “nW” is
additive white Gaussian
noise (i.e., Thermal noise)
Receiver
d2
Interfering
TX #2
d0
dK
Interfering
TX #K
Source
of desired
signal
Interference in LTE, illustration
Desired signal from
serving eNodeB
Interfering signal from
other eNodeB
Interfering signal from
adjacent sector
S-72.3216 RC Systems I (5
cr) Lectures 11-12, Autumn
2013
70
UE
eNodeB
Co-channel interference: general formulation (2)
• Let us compute the expected powers:
  P
E S0
2
RX
0
P
TX
0
  P
/ L0 E S k
2
RX
k
P
TX
k
/ Lk
  P
E nW
2
N
Here “L0” refers to the path loss attenuation between the
receiver and the source of desired signal, “Lk” corresponds
to the path loss attenuation between the “k-th” interfering
transmitter and the receiver, “PN” the AWGN power
• The instantaneous path loss can be written as follows:
Antenna gain
x
Shadow fading
Lk =
Lk (dk )
Gk (j k )× L × hk
SF
k
Average path loss
2
Fast fading
Co-channel interference: general formulation (3)
• The shadow fading follows a lognormal distribution, i.e.,
k
10
linear scale
LSF

10
k
where “ξk” is a sample from a zero mean Gaussian process,
with standard deviation “σk”
– If it is assumed that all TX-RX pairs admit the same shadow fading
characteristics, then
k 
k
• Shadow fading in different links is usually correlated
– In most studies of cellular systems, the correlation between shadow
fading in different links is assumed to be the same
– A typical value for correlation, which corresponds to BS antennas
located above the roof-top of buildings, is 0.5
– Correlation between adjacent sector antennas is 1.0
LTE: General formulation of SINR
• Now, the general formula for the SINR is given by
SINR=
P L × h0 G0 (j 0 ) L0 (d0 )
TX
0
K
åP
2
SF
0
L × hk × dk ×Gk (j k ) / Lk (dk ) + PN
TX SF
k
k
2
k=1
• This formula can be used in simulations. We have
PkTX =transmission power of kth eNB (for certain PRB)
LSF
k =SF towards kth eNB
hk = kth eNB signal fast fading channel power response (for certain PRB)
2
Gk = Antenna gain pattern towards kth eNB
dk = 1 if kth eNB is transmitting on this PRB, otherwise 0
Lk (dk ) = Distance dependent path loss towards kth eNB
PN = AWGN power
General formulation of SINR
• If we ignore shadow and fast fading, and assume
transmission on all PRB’s, then we obtain wideband SINR
that is also called as Geometry-factor (G-factor)
Gfactor =
P0TX LSF
0 G0 (j 0 ) L0 (d0 )
K
TX SF
P
å k Lk dkGk (j k ) / Lk (dk ) + PN
k=1
• G-factor can be used to describe the network deployment,
see the next slide
– 30% of UEs with ITU modified Vehicular A at 30 km/h and
– 10% of UEs with ITU modified Vehicular A at 120 km/h
Cell selection
Best cell selected with 0 dB margin
Transmission power
Uplink: Max 24 dBm (latest 3GPP specifications use 23 dBm
Antenna configuration
Downlink: 1 × 2, 2 × 2
Uplink: 1 × 2, 1 × 4
Receiver algorithms
Downlink: LMMSE (Linear Minimum Mean Square Error)
Geometry factor
• G-factor distribution depends on the network
G-factor
Uplink: deployment.
LMMSE receiver with Maximal
Ratio Combining
depends on
– Antennas, sectorization
– Applied average path loss model
1
0.9
0.8
– Frequency reuse (e.g. δ )
0.7
• Example:
– 3GPP macro 1 (ISD = 500m)
– 3GPP macro 3 (ISD = 1700m)
– 3GPP micro
CDF
0.6
0.5
0.4
0.3
0.2
Cell edge: 5%-ile level
Interference margin for 3GPP Macro 1:
M I =10× log10 (1+10
-G
)
3GPP, macro 1
3GPP, macro 3
3GPP, micro indoor:outdoor = 50:50
0.1
0
-10
-5
0
5
10
15
Geometry (dB)
20
25
30
G-factor has value -4dB
=Figure
5.5dB
9.9 Distribution
the average
wide-band channel SINR (geometry factor) macro ca
onof cell
edge
3 and micro
The corresponding downlink system performance numbers for LTE SIMO and 2 ×
Source (picture): transmission
Holma, Toskala:
for inUMTS,
Wiley
schemes areLTE
presented
Figure 9.10
and Figure 9.11, respecti vely.
Notes on the G-factor distribution
• Distribution shows that G-factor varies in macrocell
deployment between -5dB and 15dB
– Thus, in fully loaded macro network the (average) SINR is
limited to 15dB and data rates are limited accordingly
– The 50% level of G-factor CDF indicates that (average) SINR in
fully loaded macro network is close to 4dB
• If microcells are added to the network much higher SINR
values can be reached
• In e.g. indoor small cells very high SINR values are
possible
Mapping between SINR/G-factor and
throughput in LTE
• When creating RLB we require a certain bit rate on the cell edge.
– We may, for example, require that rate on cell edge is 1Mbps when user can be
allocated 10% of the radio resources.
• We can use the following very simple approximation for a bit rate
(throughput):
(*)
TP = BW× M × A× log2 (1+ SINR/ B) = NPRB × BWPRB × SE
where SE is the Spectral Efficiency and
– BW is the allocated bandwidth (in terms of PRBs)
– A and B are factors that are selected such that SE approximates the LTE link
spectral efficiency.
– Factors A and B depend on the number of antennas and physical layer
performance.
– M = number of data streams
Mapping between SINR and throughput
• Previous spectral efficiency formula provides an approximation for the
Adaptive Modulation and Coding (AMC) schemes (also called as
Modulation and Coding Schemes (MCS)) applied in the system.
Resulted parameters of the
configurations
MIMO
M
A
B
SIMO 1x2
1
0.62
1.8
MIMO 2x2
2
0.42
0.85
MIMO 4x4
4
0.40
1.1
MIMO 8x8
8
0.33
1.4
• We note that these parameters represent
approximations based on certain simulations. Thus,
different assumptions on channel estimation and
detection algorithms may lead to slightly different
results.
Spectral efficiency
30
Max SE
Max SE
Spectral efficiency [bits/s/Hz]
25
20
SIMO (1x2)
15
MIMO (2x2)
MIMO (4x4)
MIMO (8x8)
10
5
Max SE
0
-10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34
SINR [dB]
81
LTE Rel.8 peak bit rate examples
Modulatio
n
Stream
s
Ideal SE
[bits/s/Hz]
Practical
SE
[bits/s/Hz]
LTE Max bit
rate (20MHz)
64QAM
1
6.0
3.75
75Mbps
64QAM
2
12.0
7.5
150Mbps
64QAM
4
24.0
15.0
300Mbps
• If carrier aggregation approach is used (LTE-Advanced), then rate
can be multiplied by number of carriers.
• Maximum spectral efficiencies may take place only when SINR is
extremely large => reachable in practical macrocellular networks
only in special cases.
• Note the difference between ideal and practical SE
• These spectral efficiencies set upper limit for SE growth in previous
slide
4. DL Link Budget Examples
Urban area example (DL)
•
Assume the link budget parameters below, 10MHz band, 2GHz carrier, 35 meter
Radio antenna
Communication
base station
height andSystems
1.5 meterII,
UEExercise
height. 3, 2014
•
Compute the coverage in case of large city for 2Mbps service when eNodeB
allocates 4 PRBs for the user (12 users/cell served simultaneously).
–
–
Problem
downlink
RLB
(excelcan
in Noppa):
thePRBs
following
link b
What
happens1.
forLTE
the service
coverage
if eNodeB
allocate allAssume
available 48
for this user
(target
rate being
the same
2 Mbps)?
2.1GHz
carrier,
25 meter
base station antenna height and 1.5 meter UE height:
Increase the user rate 5Mbps and solve problem again
Parameter
BS TX power
BS antenna gain
BS cable loss
UE noise figure
Interference margin
RX antenna gain
RX body loss
Control channel overhead
Indoor penetration loss
Shadow fading margin
BS antenna configuration
Value
40W
18dBi
2dB
7dB
4dB
0dBi
0dB
1dB
20dB
7dB
2x2/4x4 MIMO
Results
• Case 2Mbit/s and 4 PRB’s:
– Range in large city = 300 meters
– Range in suburban area = 680 meters
• Case 2Mbit/s and 48 PRB’s:
• Case 5Mbit/s and 4 PRB’s:
– Range in large city = 880 meters
– Range in suburban area = 2.0 km
– Range in large city = 110 meters
– Range in suburban area = 240 meters
• Case 5Mbit/s and 48 PRB’s:
– Range in large city = 650 meters
– Range in suburban area = 1.5 km
Remark on range (1/3)
• Question: We increase the amount of radio resources 12 times (4
PRB ->48 PRB) but range is not increasing directly proportionally.
Why range increase is so small?
• Answer: If more PRB’s are used, less data needs to be loaded per
PRB => SE and accordingly SINR requirement decreases
– In 2Mbit/s case SINR requirement decreases from 8.8dB to -7.5dB, the
difference being 16.3dB (see next slide)
– In 5Mbit/s case SINR requirement decreases from 24.2dB to -2.8dB, the
difference being 27.0dB (see next slide)
– This increases allowed propagation loss with same amounts. Yet, if distance
from/to eNodeB is short, then the path loss increases fast as a function of
distance (see next slides)
Remark on range (2/3)
10
LTE 2x2 MIMO maximum
spectral efficiency
(7.5bits/s/Hz)
9
Spectral efficiency [bits/s/Hz]
8
SISO Spectral
Efficiency
7
6
5
MIMO Spectral
efficiency (2x2)
4
3
Shannon AWGN
bound (SISO)
2
1
0
-10
-8
-6
-4
-2
0
2
4
6
8 10
SINR [dB]
12
14
16
18
20
22
24
26
Remark on range (3/3)
16.3dB
27.0dB
Other remarks
• In 4 PRB case we can serve 12 users at the same time while in 48
PRB case we can serve only single user.
– Range extension by using more resources per user can take place only
when cell load is low.
• User usually needs 2-5Mbit/s rates just during very short time
periods
– In e.g. web browsing/streaming video data is transferred in bursts.
– Thus, if instantaneous rate is high, user will have good use experience.
Rural area example
• In suburban area LTE is used on 800MHz to provide mobile
broadband for single houses
– Note: interference margin is decreased to 2dB.
• Assume three cases:
1. User is inside a light single house with 10dB indoor penetration loss
2. User is outside the house
3. User has a LTE based fixed wireless system containing directive antenna with
10dBi gain (2dB cable loss) on the house rooftop (7 meters height). LTE
receiver is connected to indoor WiFi (through cable) that provides indoor
connectivity.
• What is the maximum distance from eNodeB to receiver (= rooftop
antenna) for 2Mbit/s and 5Mbit/s services if receiver can apply 4/8
PRBs?
Illustration of connection options
eNodeB
Yagi antenna
(10dBi gain)
Antenna cable
(2dB loss)
LTE receiver
and WiFi
router
Outdoor UE
See, e.g.: http://www.smartcoverage.eu/4G-antenna/4g-lte-aerial-antenna.html
Results
4 PRB case:
8 PRB case:
•
•
Indoor user with 10dB penetration loss
–
–
•
–
–
•
•
2Mbit/s, suburban area, range = 25.0km
5Mbit/s, suburban area, range = 9.0km
•
2Mbit/s, suburban area, range = 4.6km
5Mbit/s, suburban area, range = 2.6km
Outdoor user with 0dB penetration loss
–
–
2Mbit/s, suburban area, range = 5.9km
5Mbit/s, suburban area, range = 2.2km
Rooftop directive antenna + indoor
distribution
–
–
–
–
2Mbit/s, suburban area, range = 3.1km
5Mbit/s, suburban area, range = 1.1km
Outdoor user with 0dB penetration loss
Indoor user with 10dB penetration loss
2Mbit/s, suburban area, range = 8.9km
5Mbit/s, suburban area, range = 5.0km
Rooftop directive antenna + indoor
distribution
–
–
2Mbit/s, suburban area, range = 37.6km
5Mbit/s, suburban area, range = 20.9km
Remarks
• If cell dimensioning is done based on outdoor coverage,
then indoor coverage can be achieved using additional
directive rooftop antenna
– Costs falling on the user/subsidized by operator or government?
– Shared directive antennas + local distribution one good option
(village case)
• If only fixed wireless based connectivity is assumed very
large cells can be used
– There will be large coverage holes outdoors and especially for
direct indoor coverage
– Doubling the cell range decreases the required number of
eNodeB’s to ¼ from original case.
5. LTE Uplink Radio Link Budget
LTE Uplink RLB
• Note that besides
data rate the same
parameters are
used as in DL
• The UL data rate
with 10PRB’s is
1Mbit/s while it was
2Mbit/s in DL.
• Yet the ALP is
almost the same as
in DL.
UE resource allocation and rate
Parameter
Comment
Number of
PRBs
This is decided by eNodeB after estimating the
required bandwidth and scheduling uplink users that
are served at the same time. Thus, in this case 1
Mbit/s takes 10/50 of all resources. In (Rel.8/9)
uplink PRB’s are given continuously in frequency.
Data rate
In uplink we have 1Mbit/s while in DL we assumed
2Mbits/s target rate (APL will be almost the same)
UE transmission characteristics
Parameter
UE TX
power
Comment
In uplink maximum TX power is 23dBm. It is assumed here since
this RLB consider cell edge user. Power control is used in uplink
=> TX power can be less than 23dBm as well.
UE
antenna
gain
UE antenna gain depends on the device type. Typical value
is 0dBi while fixed wireless LTE transceivers may have even
10dBi antenna gain.
Body loss
Not visible in this UL RLB but 3-5dB body loss can be
subtracted.
EIRP
EIRP = TX power + antenna gain (-body loss)
TX power
UE power is divided between PRB’s. Thus, with larger
eNodeB receiver (1/2)
Parameter
Comment
eNodeB
Noise
Figure
NF measures of degradation of the SNR by the
components in the RF receiver chain, product specific.
The minimum performance requirement is approximately
5 dB but the practical performance can be better like 2 dB.
Thermal noise = Boltzmann constant x T (Kelvin) x Effective
bandwidth. The bandwidth depends on the number of
allocated resource blocks. With 10 PRB’s we have 121dBm.
Thermal
Noise
Receiver
Noise Floor
Receiver noise floor = eNodeB NF + Thermal noise
eNodeB receiver (2/2)
Parameter
Comment
SINR
Required Signal to Interference and Noise Ratio
depends on the data rate, number of PRBs and link
efficiency.
Minimum power in receiver required to detect the signal.
Receiver sensitivity = Receiver Noise Floor + SINR (in
UL this is given per PRB)
eNodeB antenna gain, same as in DL
Receiver
sensitivity
RX antenna gain
Margins and losses
Parameter
Comment
eNodeB cable
loss
Same as in DL.
Shadowing
loss
As in downlink. Values: 4-7dB.
Interference
margin
Interference margin reflects the increase in the eNodeB
receiver noise level caused by the interference from (other
cell) users. Since LTE uplink is orthogonal, there is no intracell interference but we still need a margin for the other cell
interference. This margin depends on the UL target capacity.
That is, there is a tradeoff between capacity and coverage.
Penetration
loss
As in downlink
Allowed propagation loss
APL = PTX + GA(UE) - LBody + GA(eNodeB) - min { PRX }
- M SF - M I
- LCable - LPenetration
Example: Recall the first DL example
•
Assume the previous link budget parameters (from DL example) 10MHz
band, 2GHz carrier, 35 meter base station antenna height and 1.5 meter
UE height
–
–
eNodeB Noise Figure = 2dB (In DL for UE it was 7dB)
Antenna configuration is now 1x2 SIMO (2 eNodeB antennas, 1 UE TX antenna)
•
Compute the coverage in case of large city for 1.3Mbps service when
eNodeB allocates 5 PRBs for the user (10 users/cell served
simultaneously)
•
Ranges when assuming 1.3Mbit/s and 5 PRB’s:
– Range in large city = 300 meters
– Range in suburban area = 680 meters
Rural area example (UL)
• In suburban area LTE is used on 800MHz to provide mobile
broadband for single houses
– Note: interference margin is decreased to 2dB.
• Assume three cases:
1. User is inside a light single house with 10dB indoor penetration loss
2. User is outside the house
3. User has a LTE based fixed wireless system containing directive antenna with
10dBi gain (2dB cable loss) on the house rooftop (7 meters height). LTE
transceiver is connected to indoor WiFi (through cable) that provides indoor
connectivity.
• What is the maximum distance from transmitter to eNodeB for
1.3Mbit/s service if receiver can apply 5/10 PRBs?
Illustration of connection options
eNodeB
Yagi antenna
(10dBi gain)
Antenna cable
(2dB loss)
LTE receiver
and WiFi
router
Outdoor UE
See, e.g.: http://www.smartcoverage.eu/4G-antenna/4g-lte-aerial-antenna.html
Results
5 PRB case:
10 PRB case:
•
•
Indoor user with 10dB penetration loss
–
•
–
•
•
1.3Mbit/s, suburban area, range = 25.3km
•
1.3Mbit/s, suburban area, range = 4.35km
Outdoor user with 0dB penetration loss
–
1.3Mbit/s, suburban area, range = 6.0km
Rooftop directive antenna + indoor
distribution
–
–
1.3Mbit/s, suburban area, range = 3.1km
Outdoor user with 0dB penetration loss
Indoor user with 10dB penetration loss
1.3Mbit/s, suburban area, range = 8.4km
Rooftop directive antenna + indoor
distribution
–
1.3Mbit/s, suburban area, range = 35.5km