LTE Link Budget
LTE RPESS
LTE Link Budget
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LTE Link Budget
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LTE Link Budget
Module Objectives
After completing this module, the participant should be able to:
• Calculate link budget for different bit rates
• Understand link budgets and parameters
• Understand planning margins
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LTE Link Budget
Coverage Dimensioning
Introduction
DL Link Budget & Parameters
UL Link Budget & Parameters
Examples
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LTE Link Budget
Introduction
• Link Budget is the basis of coverage dimensioning, aiming to calculate UL / DL maximum
allowed path loss (MAPL) for a certain type of service.
• With the MAPL and a suitable propagation model, which can be generally seen as a
function about path loss (PL) and distance between UE and eNB, average cell coverage
radius can be calculated.
• With cell coverage radius, radio network planners can easily figure up the site coverage
area and site count for given area. That’s the target of coverage dimensioning.
Coverage Area
CA
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Range
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Coverage dimensioning requires multiple inputs:
Service type
Target service probability
Initial site configuration
Equipment performance
Propagation environment
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LTE Link Budget
Link budget
• Target of the Link Budget calculation: estimate the maximum allowed path loss on radio path from
transmit antenna to receive antenna
• The minimum SINR requirement is achieved with the maximum allowed path loss and transmit
power both in UL & DL
• The maximum allowed Path Loss can be used to calculate cell range
Tx Power
+ Gains
– Losses/Margins
– Path Loss
≥ minimum required Rx Power
Lmax_UL
 max. Path Loss Lmax
Lmax_DL
Range
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LTE Link Budget
Coverage Dimensioning
Introduction
DL Link Budget & Parameters
UL Link Budget & Parameters
Examples
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LTE Link Budget
LTE DL Link Budget (FDD case)
In LTE, similar like in HSDPA Link Budget,
one of two approaches can be adopted:
1. Cell Edge User Throughput
LTE bit rate can be specified and link
budget completed from top to bottom to
determine the maximum allowed path
loss
2. Existing maximum allowed path loss can
be specified and link budget completed
from bottom to top to determine the
achievable LTE bit rate at cell edge
*PDSCH = Physical Downlink Shared
Channel
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LTE Link Budget
LTE DL Link Budget
Assumptions:
• Operating Band
– 3GPP TS 36.104 specifies 16 operating bands
for FDD
– Defined by customer
• Channel Bandwidth
– 3GPP TS 36.104 specifies values of 1.4, 3, 5,
10, 15 & 20 MHz
– Defined by customer.
• Channel Model
– The SINR is based on link level simulations
results which are available for:
– Enhanced Pedestrian A 5Hz (EPA05) valid for
low speed mobiles in general, i.e. 3 Km/h at
1800 MHZ (5Hz Doppler)
– Enhanced Typical Urban (ETU70) valid for
higher speed mobiles
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LTE Link Budget
LTE DL Link Budget
Operating Band
– For simplicity only the main centre frequencies (e.g. 1700, 2100, 2600 ...) are considered for the link budget
calculation
– It is also assumed that there is no bandwidth separation between UL & DL (i.e. 2600 MHz assumed both
UL & DL )
Channel Bandwidth
– The bandwidth configuration impacts factors such as Thermal Noise, overhead ratio & total cell throughput.
The wider the working band is, the better the network performance (max. peak rate & cell throughput) is.
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Frequency band
Band Index
Supported Bandwidths
800 MHz
Band 20 & 5 & 6 & 18 & 19
5 MHz, 10MHz(, 15 MHz, 20 MHz)
1600 MHz
Band 24
5 MHz, 10MHz
1800 MHz
Band 3 & 9
5 MHz, 10MHz, 15 MHz, 20 MHz
1700/2100 MHz
Band 4 & 10
5 MHz, 10MHz, 15 MHz, 20 MHz
2100 MHz
Band 1
5 MHz, 10MHz, 15 MHz, 20 MHz
2600 MHZ
Band 7
5 MHz, 10MHz, 15 MHz, 20 MHz
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Supported
operating
bands* &
bandwidth
s in RL 10
& 20
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LTE uses a channel raster of 100 kHz, which means that the carrier centre frequency must be an integer
multiple of 100 kHz. Uplink E-UTRA Absolute radio Frequency Channel Numbers (EARFCN) are
allocated sequentially from 0 starting from the lowest frequency in the uplink of operating band 1.
Downlink EARFCN are allocated sequentially from 13000 starting from the lowest frequency in the
downlink of operating band 1.
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LTE Link Budget
LTE DL Link Budget
Assumptions:
• Scheduling
– Two options possible: round robin &
proportional fair
– Proportional fair is possible only in DL for
RL10
→ See next slide
•
Clutter Type
– Typical: dense urban, urban, suburban,
rural
– Impact on propagation parameters like
slow fading margin or building penetration
loss
•
Cell Edge Throughput
– Either defined by the network operator or
derived from the given pathloss
– Central input parameter
→ See next slide
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LTE Link Budget
LTE DL Link Budget
Scheduling
– Round Robin (RR) algorithm in time and frequency – random allocation
– Proportional Fair (PF) in time and frequency domain – allocation based on metrics assigned to
UE (e.g. Channel conditions)
– RL 20 RRM uses Proportional Fairness as the default scheduling algorithm for DL.
 Frequency Domain Packet Scheduling (FDPS) provides some SINR improvement for PF.
Cell Edge User Throughput [kbps]
– Target throughput requirement to be achieved at the cell edge; minimum net single UE
throughput requirement
– Determines the service that can be provided at the cell border
– It can limit the MCS (Modulation & Coding Scheme) to be used
– Normally customer requirement
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In LTE the scheduling is done on a per sub-frame basis: 180KHz in frequency domain and 1ms
in time domain --- PRB pair.
For each time interval the scheduler controls which resources will be allocated to which users
(considering the buffer status, pending retransmissions, ...) HARQ retransmissions and Signaling
Radio Bearers (SRB) have a higher priority than the first transmission for data radio bearers.
The frequency domain scheduler takes into account the channel conditions for every user and
makes the best possible assignment. It applies in DL "throughput-to-average" and "proportionalfair-scheduled“ (LNCEL: dlsFdAlg). In UL "Round robin" and "exhaustive FD scheduler" is used
(LNCEL: ulsFdPrbAssignAlg).
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LTE Link Budget
LTE DL Link Budget
Transmitter: eNodeB
• Tx. Power per Antenna
− Typical value: 43dBm (20W)
• Antenna TX Gain
–
–
Antenna gain changes with the antenna type and
frequency band
Common value: 18 dBi for a directional antenna
• Cable Loss
• Feederless solution considered
• MHA Insertion Loss
• Mast Head Amplifier MHA: Pre-Amplifier for UL
receive path
• Typical 0.5 dB
• EIRP represents the Effective Isotropic
Radiated Power from the transmit
antenna.
EIRP = Tx. Power per Antenna +
Antenna Gain – Cable Loss – MHA
Insertion Loss
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LTE Link Budget
LTE DL Link Budget
Tx. Power per Antenna Connector
–
–
–
–
Depends on the Flexi Radio Module selected
Typically 8, 20, 40 & 60 Watts
8, 40 & 60W are SW licensed
In case of transmit diversity techniques like MIMO transmit diversity the power could be increased with 3dB in
DL
Antenna Gain
–
–
–
–
Proportional to the physical size, signal frequency and antenna vertical & horizontal beamwidth
Large size & High frequency → Narrow beam → High gain
In 2100 MHz bandwidth typical gains are between 12 dBi - 20 dBi
BTS Antennas vary in frequencies, sizes & configuration
 smaller antenna beam  higher Antenna Gain
 larger size (e.g. 1m → 2 m)  higher Antenna Gain (at same frequency)
 lower frequency  lower Antenna Gain
– Typical values:
 18 dBi for eNodeB directional antenna (3-sector)
 19.5 dBi for eNodeB directional high gain antenna (6-sector)
 8 dBi for eNodeB omni-directional antenna
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Flexi multiradio BTS provides high radio downlink output power when using Flexi 3-sector RF module
with the total of 210w power amplifiers, or RRH.
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LTE Link Budget
Cable loss
Cable Loss
is the sum of all signal losses caused by the antenna line
outside the base station cabinet
• Jumper losses
• Feeder cable loss
• MHA (or TMA) insertion loss in DL when MHA is used
– Typical 0.5 dB
– No MHA is used with Feederless solution*
Typical values for the cable loss:
• 0.4 dB with Feederless solution* (jumper losses only)
• 2 dB feeder solution w/o TMA
• 2.4 dB if feeders with TMA used (2 dB feeders + 0.4dB additional
jumpers for TMA) + 0.5dB MHA Insertion loss
• * in the case of feederless solution the Flexi RF Module is
mounted closed to the antenna. There is only a jumper cable
connection between the RF module and the antenna system
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LTE Link Budget
LTE DL Link Budget
Receiver: UE
• Handset Noise Figure
• depends on the receiver equipment design and
represents the additive noise generated by various HW
components
• Typical 7dB for the UE
• Thermal Noise
–
–
Depends on the channel bandwidth
See next slide
• SINR Requirement
–
See next slides
• Receiver Sensitivity
represents the signal level that is required at the
antenna port of the receiver to be able to
achieve acceptable quality level in receiving
Receiver Sensitivity = Handset Noise
Figure + Thermal Noise + SINR
Requirement
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LTE Link Budget
Thermal Noise Calculation
Thermal Noise = kB x T x B
Where:
• kB = Boltzmann’s constant, 1.38 E-23 Ws/K
• T = Receiver temperature, 293 K
• B = Bandwidth
Single RB bandwidth
ThermalNoise = −174dBm / Hz + 10 ⋅ log(15kHz ⋅12⋅# RB)
Receiver bandwidth
#RB is the Number of Physical Resource Blocks
• DL: all available in the channel bandwidth
• UL: only those RBs allocated for transmission
OFDMA / SC-FDMA
DL: OFDM receiver looks at the whole bandwidth, thus all available
Resource Blocks should be considered.
UL: SC-FDMA receiver looks only at the allocated bandwidth, thus not all
but only assigned Resource Blocks are assumed in sensitivity formula.
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10 log (kB *T) = -174dBm/Hz is the Thermal
Noise Density not considering the bandwidth
impact
Example:
For 10MHz there are 50 RBs in DL
Thermal noise = -174dBm/Hz + 10log(15 *
1000 * 12 * 50) =
= -174 dBm/Hz + 69,54 dB=
= -104.45dBm
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Thermal noise density: 10*log (kT) in dBm, where k:1.38e-23 Joules/Kelvin; T:300 Kelvin
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LTE Link Budget
SINR: Signal-to-Interference + Noise Ratio
SINR: Signal to Interference plus Noise Ratio
– Minimum relation between useful signal and sum of interferences coming from own and
neighboring cells and the received noise power
SINR =




S
I own + I oth + N
S : useful signal (received power)
Iown : own cell interference (close to zero in LTE due to the orthogonality of subcarriers)
Ioth : other cell interference
N : noise power
– In LTE the PDSCH “required SINR” replaces the “required Eb/No” of the UMTS Rel. 99 DCH
Link Budget; Eb/No is not helpful in case of Fast Link Adaptation
– SINR requirement is practically obtained from link level simulations, which depend
on channel mode, MIMO scheme, BLER requirement.
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LTE Link Budget
SINR distribution
The simulation scenarios and
parameters are provided in
3GPP TR25.814
Bandwidth = 2000MHz
Speed = 3Km/h
Macro Case 1 – Inter-site
distance = 500m
Macro Case 3 – Inter-site
distance = 1732m
Cell load is 100% which is
affecting the inter-cell
interference
CDF = Cumulative Distribution Function
*Source: "LTE Downlink Performance Results with Time-Domain Scheduling - Using UPRISE" by Klaus I Pedersen et al.
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LTE Link Budget
Required SINR
In order to meet the defined quality requirements (BLER) a certain average required SINR is needed
Required SINR depends on:
•
•
Cell Range (Pathloss)
Cell Edge User Throughput
•
•
Based on the Cell Edge Throughput the number of allocated PRBs and the MCS could be defined → see next slides
OFDM specific channel models
•
•
–
–
•
Channel model is a way to consider UE mobility and environment in the link budget calculation
2 main groups of channel models are available:
Enhanced Pedestrian A 5Hz (EPA05) valid for low speed mobiles in general, i.e. 3 Km/h at 1800 MHz (5Hz Doppler)
Enhanced Typical Urban (ETU70) valid for higher speed mobiles
Considered Antenna Scheme for the DL:
•
•
1Tx – 2Rx; 2TX – 2RX Transmit Diversity ; 2TX – 2RX Spatial Multiplexing (not expected at cell edge)
L1 overhead of the physical channels
•
The impact is the reduced number of resource blocks which could be used for user data
• Scheduling gain
→ see next slides
MCS: Modulation & Coding Scheme
PRB: Physical Resource Block
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LTE Link Budget
Required SINR decision sequence (1/7)
STEP 1 for the required SINR decision:
Input:
• Cell Edge User Throughput
•
The target cell edge throughput is used to select the
least robust MCS with good balance of coverage &
resource consumption of the air interface
STEP 1 for required
SINR decision
Cell Edge
Throughput
BLER
MCS
•BLER at first HARQ retransmission
•
•
Assumption: to be 10% for the first HARQ
retransmission, i.e. 10% probability to complete 1 or
more retransmissions
The actual effect is the increase of the cell edge
throughput
•
MCS = Modulation & Coding Scheme
•
•
3GPP TS 36.211 specifies QPSK, 16QAM & 64QAM for the DL
Affects the amount of resources that will be used for user data
TBS =
Transport
Block Size
#RBs = Number
of Resource
Blocks
Output: TBS (Transport Block Size) & Number of Required RBs (Resource Blocks) – see next
slide
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LTE Link Budget
Required SINR decision sequence (2/7)
TBS set
• Number of user data bits transmitted to single user
during 1 TTI (1ms)
• The TB occupies 2 PRBs in time domain
3GPP TS 36.213 specifies tables to:
• link the MCS Index -> Modulation Order (modulation type) and
TBS Index
• link the TBS Index -> Transport Block Size (TBS) for a specific
number of PRBs
MCS index - from 0 to 28
• it is decided by the scheduler which should translate a specific
CQI in an MCS index
ITBS = TBS index
• The TBS Index is mapped to a specific TBS size for a specific
•
•
#PRBs
Uses a different table (3GPP TS 36.213)
See next slide for an example
DL MCSs
MCS_index
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
MCS
QPSK
QPSK
QPSK
QPSK
QPSK
QPSK
QPSK
QPSK
QPSK
QPSK
16QAM
16QAM
16QAM
16QAM
16QAM
16QAM
16QAM
64QAM
64QAM
64QAM
64QAM
64QAM
64QAM
64QAM
64QAM
64QAM
64QAM
64QAM
64QAM
Mod order
2
2
2
2
2
2
2
2
2
2
4
4
4
4
4
4
4
6
6
6
6
6
6
6
6
6
6
6
6
ITBS
0
1
2
3
4
5
6
7
8
9
9
10
11
12
13
14
15
15
16
17
18
19
20
21
22
23
24
25
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MCS: Modulation & Coding Scheme
PRB: Physical Resource Block
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LTE Link Budget
Required SINR decision sequence (3/7)
• Example for the identification of the Number of PRBs per User and the Transport
Block Size (TBS)
• Assumptions:
• Required cell edge throughput = 384Kbps
Only a subset of the complete table
(3GPP TS 36.213 specifies 110 columns)
• MCS = 10-16QAM
MCS = 10-16QAM  TBS_index = 9
Air Interface User Throughput =
= 384 / (100% - 10%) = 427 kbps
…search for TBS in ITBS9 ≥ Air Interface User
Throughput
#RB_used = 3  TBS = 456 bits
456 bits/TTI = 456 bits/1 ms = 456 kbps ≥ 427
kbps
Conclusion: # RB used= 3
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Identifies the number of Resource Blocks (RB) required to achieve the target Cell Edge User Throughput
Uses the already defined MCS to identify the appropriate row within the transport block size
table
The target Cell Edge User Throughput is used to determine the minimum transport block size
requirement
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LTE Link Budget
Required SINR decision sequence (4/7)
STEP 2 for required
SINR decision
• STEP 2 for the required SINR
decision:
• The selected MCS & #PRBs from Step 1 is
associated with a defined Required SINR
• The actual SINR requirement is obtained from
link level simulations
• Several look-up tables results are available for
several cases:
–
–
–
Specific channel models (EPA 5Hz & ETU70Hz
channel models)
Different SINR requirements are specified for
different antenna schemes (1TX – 2RX or 2TX –
2RX)
Block Error Rate BLER typical 10%
• In the SINR look-up table result the SINR is a
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function of :
Example:
–
–
SINR table for the case DL 2Tx-2Rx, EPA 5Hz Channel Model, BLER =
10%
MCS = Modulation and Coding Scheme
Number of RBs
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EPA 5Hz  Doppler frequency=5Hz for 1800MHz and 3km/h
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Conditions for the table --- EPA5Hz + 2×2MIMO + 10%BLER
EPA: Enhanced Pedestrian A, ETU: Enhanced Typical Urban.
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LTE Link Budget
Required SINR decision sequence (5/7)
The selection of MCS is a trade-off between coverage & resource utilization:
The more robust the selected MCS (e.g. 0-QPSK) the lower the allowed required SINR which
is improving the coverage. But on the same time the higher the resource consumption (42
PRBs out of 50 for 10 MHz bandwidth for 1024Kbps) which leaves less resources for the rest
of the scheduled users.
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LTE Link Budget
Required SINR decision sequence (6/7)
Note that not all MCS are suitable to achieve a certain cell edge throughput.
If high target cell edge throughput are required then the selection of a very robust MCS (with
correspondingly large overhead portion) may lead to a situation where the resource consumed by the
coded user data traffic exceeds the amount of the resources provided by the entire cell (e.g. MCS = 3QPSK for a cell edge throughput 4096Kbps requires more than 50 PRBs for 10 MHz bandwidth)
It is recommended for a specific cell edge throughput to select the MCS which is maximizing the allowed
pathloss.
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LTE Link Budget
Required SINR decision sequence (7/7)
STEP 3 for required SINR decision:
• Consider additional SINR improvements features like FDPS
(Frequency Domain Packet Scheduling)
• System level simulations are used to show the gain of Proportional Fair
algorithm in DL over Round Robin (see the table)
• The table could be read as follows: when UE occupies 100% of
resources there is no gain from particular scheduling strategy because
RRM cannot play with frequency resources.
STEP 3 for required
SINR decision
DL FDPS Gain (dB)
Channel usage per
single UE
Gain (dB)
10.00%
11.11%
12.50%
14.29%
16,67%
20.00%
25.00%
33.33%
50.00%
100.00%
3,71
3,64
3,53
3,41
3,25
2,93
2,52
2,11
1,68
0
The more UEs could be scheduled in the same TTI (that means less resource allocation per
user), the more certain gain can be observed.
Example:
Cell edge Throughput is 1024Kbps, Number of allocated PRBs per user is selected to be 13 out of 50
available in 10 MHz (for MCS = 5-QPSK)
The channel usage per TTI of the user is 26%. Thus, Required SINR = 1,11 dB(Required SINR from table)
– 2,47 dB (FDPS gain for 26% channel usage) = -1,36dB
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The larger the amount of resources (subcarriers) available for the scheduling of a single user, the higher
the chance to avoid channel quality gaps
For example when 50 PRBs are available (10MHz bandwidth) and 10 full user buffer UEs are scheduled
per TTI then it results 5 PRBs per user that is 10% of resources allocated per UE.
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LTE Link Budget
LTE DL Link Budget
Receiver: UE
• Rx Antenna Gain
• 0 dBi for UE Antenna
• DL Load
– Average Resource Utilisation
– Assumed to be 50%
– Defined by the customer
• Interference Margin
– Depends on the neighbor cell interference
– Frequency reuse 1 will be used
– Higher reuse schemes are possible but
there is no significant gain in network
performance
– See next slides
• Body Loss
• 2-3 dB for VoIP users & 0 dB for data
users
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LTE Link Budget
Cell Load
Cell Load [%]
• Cell load represents the average resource utilization in terms of PRBs
– It accounts for the average load of the system over longer time period (minutes, hours,...)
– For the link budget calculation, which is a single cell-edge user case to estimate maximum possible
coverage, cell load reflects the average neighbour load but it does not impact own cell resource allocation
– In other words a cell edge user occupying 100% resources per TTI (100% of PRBs) does not mean 100%
load (i.e. over long time period)
• Affects the Interference Margin (IM)
– Higher cell load means higher interference from the neighbour cells
– High neighbour cell load increases the IM that in terms reduces the MAPL*
– High neighbour cell load limits the possibility of selecting high MCS
• Recommended value: 50% (subject to change)
• Customer may provide this value
*MAPL = Maximum Allowed Path Loss
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LTE Link Budget
DL Interference Margin
Interference margin IM
• Interference Margin can be defined as a relation between signals received with & without interference
IM =
S/N
S /(Iown + Iother + N)
– S: useful signal (received power)
– Iown: own cell interference (≈ 0 in LTE due to the orthogonality of subcarriers)
– Ioth: other cell interference
– N: noise power
• 100% orthogonality could be assumed in UL & DL due to OFDM & SC-FDMA so that the Intra-cell
interference is close to zero
• The only interference which counts is the Inter-cell interference
• DL Interference Margin could be derived analytically
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•IM = (1/N) / [1 / (I+N)] = 1 / [N / (I+N)] = 1 / [1 – I / (N + I)] = 1 / [1 – S/(N+I) · I/S] = 1 / [1 – SINR·(1/G)],
and now η can be introduced on the right part.
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LTE Link Budget
DL Interference Margin
After some analytical derivation the IM in DL could be written as:
1
IM =
1 − SINR ⋅ η ⋅
1
G
Neighbour cell
load
1

IM = −10 ⋅ log1 − SINR ⋅η ⋅ 
G

G = S/I = Geometry
factor
• Geometry Factor G explanation:
• At cell edge the noise N could be neglected in comparison to Iother so that SINR  S/I which is
also called G geometry factor
• SINR < G (G is the Maximum SINR at cell edge)
• G depends on the network geometry (cell area location probability) and antenna configuration but
not on the cell range
• G = -0.03 dB
•
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Obtained from system level simulations (with the NSN Morse Simulator for the 3GPP Macro cell case 1
simulation environment with ISD (inter-site distance) = 500m
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•η(typical 50%).
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LTE Link Budget
Interference Margin
Downlink (simulation for 10MHz BW)
IM as a function of Neighbour Cell Load for different MCS and cell Edge User
Throughputs
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By selecting high neighbour cell load we are limiting to the usage of low ( robust) MCS since for higher
MCS the IM increases a lot.
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LTE Link Budget
LTE DL Link Budget
• Building penetration loss BPL
– Loss for Indoor Coverage due to walls, etc.
– clutter specific between 12 dB (Rural) and more than
20 dB (Urban / Dense Urban)
• (Indoor) Location Probability
– Area Location probability, giving the service
probability of connection (here: indoor)
– applied values depend on clutter & area, vary from
85 – 95%
• Indoor standard deviation
– The standard deviation σ represents the dispersion
of the path loss or received power measured over the
coverage area.
– clutter & area dependent; differing for Indoor /
Outdoor; varies from 5 - 12 dB.
• Shadowing Margin or Slow Fading Margin
– often also denominated as “Log-normal Fading
Margin”
– calculated from indoor location probability and
standard deviation. Typical values for slow fading
margins for 90-95% coverage probability are:
 outdoor: 6 – 8 dB
 indoor: 10 – 15 dB
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LTE Link Budget
Building penetration loss
• Signal levels from outdoor Base stations into buildings are estimated by applying a “Building
Penetration Loss (BPL)” margin
• Slow fading standard deviation is higher inside buildings due to shadowing by building
structures
– There are big differences between rooms with window and “deep indoor” (10 ..15 dB)
Typical values for BPL:
In-car/Rural 5… 10dB
In building:
signal level increases with floor
number :~1,5 dB/floor (for 1st
..10th floor)
Dense Urban: 20…25 dB
Urban:
15…20 dB
Suburban: 10…15 dB
Pindoor = -3 ...-15 dB
-15 ...-25 dB
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rear side :
-18 ...-30 dB
Pindoor = -7 ...-18 dB
Pref = 0 dB
no coverage
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LTE Link Budget
Slow Fading Margin SFM / Shadowing Margin
• Slow Fading is caused by signal shadowing due to
obstructions on the radio path
max. pathloss
from link budget
max: pathloss
from link budget
• A cell with a range predicted from maximum pathloss
(without “Slow Fading Margin SFM) will have a Cell
- Slow Fading
Margin SFM
Area Coverage Probability of about 75 %
– this means: Lot of coverage holes due to shadowing
• SFM is required in order to achieve higher coverage
Pathloss
prediction model
Pathloss prediction
model
quality, better coverage probability
– Smaller cell, less coverage holes over cell area,
Cell Range
Cell Range
better coverage quality
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Cell Area Coverage
probability = 75 %
Cell Area Coverage
probability > 75 %,
large coverage holes, bad
coverage quality
i.e. less coverage holes,
Better coverage quality;
but: smaller cells
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LTE Link Budget
Area Location Probability: Cell Area / Cell Edge Probability
The Location Probability means the probability that the average received field strength is better than
the minimum required received signal strength (in order to make a successful phone call).
For Radio Network Planning & Dimensioning, two different types of location probabilities are used:
• Cell Area Probability: coverage probability over the whole cell area;
• Cell Edge Probability: point location probability at the cell edge.
The Jake’s formula can be used to convert the Cell Area into a Cell Edge Probability.
Point Location Probability
Cell Area Probability:
Cell Edge Probability
Location probability
over whole cell area
Cell Edge
probability [ % ]
50
75
84
90
95
Cell Area
probability [ % ]
75
90
94
97
99
Jakes, W.C.Jr. Microwave Mobile Communications. USA 1974, John Wiley & Sons. 473 p
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W.C.Jake‘s formula is complex.
Typical value mapping is shown in the table.
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LTE Link Budget
Cell Edge Probability: Point Location Probability at Cell Edge
Probability
• Slow Fading is normal distributed
with the gaussian distribution function
p(r)=
1
2⋅π ⋅σ2
(r −r )2
− m2
⋅e 2⋅σ
px0 =

x0
1
2⋅ π ⋅ σ 2
Field Strength
Level [dBm]
m
• The probability Pxo that r exceeds some threshold xo at a given
point inside the cell is called the Point Location Probability. The
point location probability can be written as the upper tail probability
of the above equation :
∞
σ σ
−
⋅e
(r −rm )2
2⋅σ
2
dr
 x −r 
1 1
= + ⋅ erf 0 m 
2 2
σ⋅ 2
Slow Fading
Margin, SFM
Coverage w/o SFM
SFM = 1 σ - coverage
• The standard
deviation σ is
empirically
determined
• Examples:
Clutter
Type
σ
DU
9 dB
U
8 dB
SU
8 dB
R
7 dB
Refer to Cellular Radio Performance Engineering, Chapter 2, e.g. 2.9 Page 29
Jakes, W.C.Jr. Microwave Mobile Communications. USA 1974, John Wiley & Sons. 473 p
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LTE Link Budget
From Point Location Probability to Area Location Probability
Point Location
Probabilities
px
1
⋅ p dA
π ⋅ R2  x0
Cell Area Location Probability
Fu =
0
 2 ⋅ a ⋅b +1

 
1 
2
 a ⋅ b + 1 
Fu = 1 + erf (a ) + e b  ⋅ 1 − erf 

 b  
2 


Slow Fading
Margin, SFM
Standard
Deviation, σ
a=
( x0 − P0 )
σ⋅ 2
b=
γ ⋅ log 10 e
σ⋅ 2
P0: field strength threshold value at cell edge
γ: path loss slope
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Jake Formula
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LTE Link Budget
Slow fading margin SFM (Example)
• SFM values presented for the different Cell Edge & Cell Area Probabilities
• Jake’s formula used to convert Cell Area into Cell Edge Probability
• F: Factor to adapt SFM to required Cell Edge Probability
• Standard deviation assumed to be 8 dB
SFM = σ x F
Cell edge
probability
in %
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Cell Edge
Probability
Cell Area
Probability
Factor F
SFM
50%
75%
0
0 dB
75%
90%
0.67
5.5 dB
84%
94%
1.00
8 dB
90%
97%
1.28
10 dB
95%
99%
1.65
13.2 dB
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Factor F
for
calculation
of SFM
50
55
60
65
70
75
80
85
90
0.000
0.126
0.253
0.385
0.524
0.674
0.842
1.036
1.282
95
96
97
98
99
1.645
1.751
1.881
2.054
2.326
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LTE Link Budget
Gain Against Shadowing
Gain Against Shadowing is considered at the cell edge
Also called multi server gain (because of multi-cell coverage probability)
For the previous calculation of the Shadowing Margin the key assumption was a single, isolated cell
However, if there are several cells providing coverage in an area then the probability of having enough
field strength increases
The Gain Against Shadowing reflects the possibility of switching to another cell available at a certain
position
Example:
Assume that there are 2 cells providing coverage and
both cells are providing at the cell edge 50% location
probability (A = B =50% are the location probabilities for
the 2 cells)
If the assumption is that the signals from the cells are
uncorrelated then a joint probability could be calculated:
P = (A+B) – (A*B) = (50%+50%) – (50%*50%) = 75%
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LTE Link Budget
LTE DL Link Budget
• Isotropic power required:
– Required signal power is calculated to take
into account the building penetration loss and
indoor standard deviation as well as receiver
sensitivity and additional margins.
Isotropic Power Required = Receiver
Sensitivity – RxAntennaGain + Interference
Margin + Body Loss – Gain Against
Shadowing + BPL + SFM
Max. allowed Path Loss Lpmax =
Allowed Prop. Loss =
EIRP – Isotropic Power Required
max. Pathloss Lpmax
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LTE Link Budget
Coverage Dimensioning
Introduction
DL Link Budget & Parameters
UL Link Budget & Parameters
Examples
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LTE Link Budget
LTE UL Link Budget
Assumptions: same as in the DL
Transmitter – Handset
• UE Tx Power
typical value: 23dBm (UE Class 3)
• Antenna TX/RX gain
• typically assumed to be 0 dBi
• for data card 2 dBi possible
• Body Loss
• UE: 0 dB (data user); 2-3dB (VoIP users)
• Otherwise (card) : 0dB
UL EIRP = UE Tx Power +
UE Antenna Gain – Body Loss
*PUSCH = Physical Uplink Shared Channel
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UE Tx capability :
Power Class1 [+30]
Power Class2 [+27]
Power Class3 [+23
Power Class4 [+21]
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dBm
+/-2 dB] dBm
dBm
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LTE Link Budget
LTE UL Link Budget
Receiver – eNodeB
• NodeB Noise Figure
• vendor-specific
• for Flexi-BTS default values: 2.2 dB (w/o MHA) / 2
dB (with MHA)
• Thermal Noise
• same formula as in DL
• only RBs considered which are allocated for UL
transmission (1RB for 64Kbps, 15RBs for 384Kbps,
27 RBs for 1024 Kbps)
• SINR Requirement
• same decision sequence as in the DL
• based on link level simulations
• differences in UL coming from different
MCS allocation strategy
• see next slide
Receiver Sensitivity = eNodeB Noise
Figure + Thermal Noise + SINR
Requirement
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LTE Link Budget
Required SINR in UL
The selection of MCS in UL is a trade-off between a lower required SINR value and the number of allocated
PRBs per UE:
UE output power is shared between the subcarriers assigned for transmission.
The smaller the number of used subcarriers the higher is the power per subcarrier so the higher the coverage.
On the other hand, lower number of PRBs per UE (lower number of subcarriers) requires a higher order MCS increasing the required SINR.
In this case, despite of a higher required SINR, a greater cell range could be obtained due to the accumulation
of the total power on less PRBs used for the transmission.
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LTE Link Budget
LTE UL Link Budget
Receiver – eNodeB
• Rx Antenna Gain
• Antenna gain changes with the antenna type &
frequency band
• typical value: 18 dBi for a 3-sectored site /
directional antenna
• UL Load
• same assumption as in DL
• Interference Margin
• based on system level simulations (analytical
formula like in DL isn’t trivial because of the
interference nature in UL which is more complex
due to UE mobility)
• see next slide
• Cable Loss, Building Penteration Loss, Indoor
Location Probability, Indoor Standard Deviation,
Shadowing Margin & Gain Against Shadowing
are the same as in DL
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Isotropic Power Required = Receiver Sensitivity –
RxAntennaGain + Interference Margin + Cable
Loss –Benefit of using MHA – Gain Against
Shadowing + BPL + SFM
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LTE Link Budget
Interference Margin
Uplink
• Uplink Interference Margin
– Currently obtained from system level simulations. Due to the non-deterministic
characteristic of uplink interferences it is difficult to make a mathematical model (like in
downlink)
– It is a function of cell load
IM as a function of Cell Load
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LTE Link Budget
Coverage Dimensioning
Introduction
DL Link Budget & Parameters
UL Link Budget & Parameters
Examples
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LTE Link Budget
Assumptions
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Parameter/Feature
UL
DL
Operating Band
2600 MHz
2600 MHz
Transmission power
max UE power 23dBm
43 dBm (20W Flexi RF Module)
Antenna Scheme
Number of TX antennas = 1
Number of RX antennas = 2
Number of TX antennas = 1
Number of RX antennas = 2
Noise Figure
UE: 7dB
eNodeB: 2,2dB
Cell Load
50%
50%
Scheduling
Channel unaware with Round
Robin strategy
Channel aware with Proportional
Fairness
Mast Head Amplifier
Not Considered
(Feederless solution)
Not Considered
(Feederless solution)
Antenna Gain
0 dBi
18 dBi
UE speed
3Km/h
3Km/h
Planning Margins
Building Penetration Loss,
Shadowing Margin & Gain Against
Shadowing NOT considered
Building Penetration Loss,
Shadowing Margin & Gain Against
Shadowing NOT considered
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LTE Link Budget
Pathloss as a function of Cell Edge Throughput
DL
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LTE Link Budget
Pathloss as a function of Number of PRBs
DL
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LTE Link Budget
Pathloss as a function of Number of PRBs
UL
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