05 ra41205en20gla0 lte link budget v03

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1 © Nokia Siemens Networks RA41205EN20GLA0

LTE RPESSLTE Link Budget

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Nokia Siemens Networks Academy

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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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Coverage Dimensioning

Introduction

DL Link Budget & Parameters

UL Link Budget & Parameters

Examples

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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 AreaCA Range

Coverage dimensioning requires multiple inputs:

Service typeTarget service probabilityInitial site configurationEquipment performancePropagation environment

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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

Lmax_DLLmax_UL

Tx Power+ Gains– Losses/Margins– Path Loss≥ minimum required Rx Power

max. Path Loss Lmax

Range

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Introduction



Examples

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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

LTE DL Link Budget (FDD case)

*PDSCH = Physical Downlink Shared Channel

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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 DL Link BudgetOperating 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.

Supported

operating

bands* &

bandwidth

s in RL 10

& 20

5 MHz, 10MHz, 15 MHz, 20 MHzBand 12100 MHz

5 MHz, 10MHz, 15 MHz, 20 MHzBand 3 & 91800 MHz

5 MHz, 10MHz, 15 MHz, 20 MHzBand 4 & 101700/2100 MHz

5 MHz, 10MHzBand 241600 MHz

Frequency band Band Index Supported Bandwidths

800 MHz Band 20 & 5 & 6 & 18 & 19 5 MHz, 10MHz(, 15 MHz, 20 MHz)

2600 MHZ Band 7 5 MHz, 10MHz, 15 MHz, 20 MHz

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 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 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

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 "proportional-fair-scheduled“ (LNCEL: dlsFdAlg). In UL "Round robin" and "exhaustive FD scheduler" is used (LNCEL: ulsFdPrbAssignAlg).

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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 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

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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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 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 Sensitivityrepresents the signal level that is required at the antenna port of the receiver to be able to achieve acceptable quality level in receiving

Receiver SensitivityReceiver Sensitivity = Handset Noise Figure + Thermal Noise + SINR Requirement

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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

10 log (kB *T) = -174dBm/Hz is the Thermal Noise Density not considering the bandwidth impact

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.

OFDMA / SC-FDMA

)#1215log(10/174 RBkHzHzdBmseThermalNoi ⋅⋅⋅+−=

Single RB bandwidth

Receiver bandwidth

#RB is the Number of Physical Resource Blocks

• DL: all available in the channel bandwidth

• UL: only those RBs allocated for transmission

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

Thermal noise density: 10*log (kT) in dBm, where k:1.38e-23 Joules/Kelvin; T:300 Kelvin

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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

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.

NII

SSINR

othown ++=

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SINR distribution

CDF = Cumulative Distribution Function *Source: "LTE Downlink Performance Results with Time-Domain Scheduling - Using UPRISE" by Klaus I Pedersen et al.

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

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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 SchemePRB: Physical Resource Block

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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

•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

Output: TBS (Transport Block Size) & Number of Required RBs (Resource Blocks) – see next slide

Cell Edge Throughput BLER MCS

STEP 1 for required SINR decision

TBS = Transport Block Size

#RBs = Number of Resource

Blocks

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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 MCSsMCS_index MCS Mod order ITBS

0 QPSK 2 01 QPSK 2 12 QPSK 2 23 QPSK 2 34 QPSK 2 45 QPSK 2 56 QPSK 2 67 QPSK 2 78 QPSK 2 89 QPSK 2 910 16QAM 4 911 16QAM 4 1012 16QAM 4 1113 16QAM 4 1214 16QAM 4 1315 16QAM 4 1416 16QAM 4 1517 64QAM 6 1518 64QAM 6 1619 64QAM 6 1720 64QAM 6 1821 64QAM 6 1922 64QAM 6 2023 64QAM 6 2124 64QAM 6 2225 64QAM 6 2326 64QAM 6 2427 64QAM 6 2528 64QAM 6 26

MCS: Modulation & Coding SchemePRB: Physical Resource Block

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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

• Example for the identification of the Number of PRBs per User and the Transport Block Size (TBS)

• Assumptions:

• Required cell edge throughput = 384Kbps

• MCS = 10-16QAM

Only a subset of the complete table

(3GPP TS 36.213 specifies 110 columns)

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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• 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 function of :– MCS = Modulation and Coding Scheme

– Number of RBs

Example:

SINR table for the case DL 2Tx-2Rx, EPA 5Hz Channel Model, BLER = 10%

EPA 5Hz Doppler frequency=5Hz for 1800MHz and 3km/h


Conditions for the table --- EPA5Hz + 2×2MIMO + 10%BLER

EPA: Enhanced Pedestrian A, ETU: Enhanced Typical Urban.

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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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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 = 3-QPSK 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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DL FDPS Gain (dB)Channel usage per

single UEGain (dB)

10.00% 3,7111.11% 3,6412.50% 3,5314.29% 3,4116,67% 3,25

20.00% 2,93

25.00% 2,5233.33% 2,1150.00% 1,68

100.00% 0

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.

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


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 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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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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DL Interference Margin

)/(/

NIIS

NSIM

otherown ++=

– 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

Interference margin IM• Interference Margin can be defined as a relation between signals received with & without interference

•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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DL Interference Margin

GSINR

IM11

1

⋅⋅−=

η

⋅⋅−⋅−=

GSINRIM

11log10 η

Neighbour cellload

G = S/I = Geometryfactor

After some analytical derivation the IM in DL could be written as:

• 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

• 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

•η(typical 50%).

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Interference MarginDownlink (simulation for 10MHz BW)

IM as a function of Neighbour Cell Load for different MCS and cell Edge User Throughputs

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 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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Building penetration loss

Pref = 0 dB

Pindoor = -3 ...-15 dB

Pindoor = -7 ...-18 dB

-15 ...-25 dB no coverage

rear side :-18 ...-30 dB

signal level increases with floor number :~1,5 dB/floor (for 1st ..10th floor)

• 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:Dense Urban: 20…25 dBUrban: 15…20 dBSuburban: 10…15 dB

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Slow Fading Margin SFM / Shadowing Margin

• Slow Fading is caused by signal shadowing due to

obstructions on the radio path

• A cell with a range predicted from maximum pathloss

(without “Slow Fading Margin SFM) will have a Cell

Area Coverage Probability of about 75 %

– this means: Lot of coverage holes due to shadowing

• SFM is required in order to achieve higher coverage

quality, better coverage probability

– Smaller cell, less coverage holes over cell area,

better coverage quality

max. pathlossfrom link budget

Pathlossprediction model

Cell Range

Cell Area Coverage probability = 75 %

large coverage holes, bad coverage quality

max: pathlossfrom link budget

Pathloss prediction model

Cell Range

Cell Area Coverage probability > 75 %,i.e. less coverage holes,Better coverage quality;

but: smaller cells

- Slow Fading Margin SFM

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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.

Area Location Probability: Cell Area / Cell Edge Probability

Cell Edge probability [ % ]

Cell Area probability [ % ]

50

75

84

90

95

75

90

94

97

99

Jakes, W.C.Jr. Microwave Mobile Communications. USA 1974, John Wiley & Sons. 473 p

Cell Edge Probability

Point Location Probability

Cell Area Probability:Location probability over whole cell area

W.C.Jake‘s formula is complex.

Typical value mapping is shown in the table.

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Cell Edge Probability: Point Location Probability at Cell Edge

• Slow Fading is normal distributed

with the gaussian distribution function

⋅−

⋅+=

⋅⋅⋅

= ∞

⋅−−

221

21

2

1

0

2)(

20

2

2

0

σ

σπσ

m

x

rr

x

rxerf

rdepm

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

• 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 :

2

2

2)(

22

1)( σ

σπ⋅−−

⋅⋅⋅

=mrr

erp

Slow Fading Margin, SFM

Field StrengthLevel [dBm]

Prob

abilit

y

σ σ

m

SFM = 1 σ - coverage

Coverage w/o SFM

Clutter Type

σ

DU 9 dB

U 8 dB

SU 8 dB

R 7 dB

• The standard deviation σ isempiricallydetermined

• Examples:

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FR

p dAu x=⋅

⋅1

2 0π

Cell Area Location ProbabilityPoint LocationProbabilities

px0

F erf a e erfa b

bu

a b

b= + + ⋅ − ⋅ +

⋅ ⋅ +

1

21 1 12 1

2( )

2)( 00

⋅−=

σPx

a2

log 10

⋅⋅=σ

γ eb

P0: field strength threshold value at cell edge

γ: path loss slope

Slow Fading Margin, SFM

Standard Deviation, σσ

From Point Location Probability to Area Location Probability

Jake Formula

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Slow fading margin SFM (Example)

Cell EdgeProbability

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

• 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

0.000

0.126

0.253

0.385

0.524

0.674

0.842

1.036

1.282

1.645

1.751

1.881

2.054

2.326

50

55

60

65

70

75

80

85

90

95

96

97

98

99

Factor Ffor

calculation

of SFM

Cell edge probability

in %

0.000

0.126

0.253

0.385

0.524

0.674

0.842

1.036

1.282

1.645

1.751

1.881

2.054

2.326

50

55

60

65

70

75

80

85

90

95

96

97

98

99

Factor Ffor

calculation

of SFM

Cell edge probability

in %

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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 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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Introduction



Examples

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LTE UL Link Budget

*PUSCH = Physical Uplink Shared Channel

Assumptions: same as in the DL

Transmitter – Handset

• UE Tx Powertypical 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

UE Tx capability :Power Class1 [+30] dBmPower Class2 [+27] dBm

Power Class3 [+23 +/-2 dB] dBmPower Class4 [+21] dBm

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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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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 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 Shadowingare the same as in DL

Isotropic Power Required = Receiver Sensitivity –RxAntennaGain + Interference Margin + Cable

Loss –Benefit of using MHA – Gain Against Shadowing + BPL + SFM

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Interference MarginUplink

• 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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Introduction



Examples

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Assumptions

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 = 1Number of RX antennas = 2

Number of TX antennas = 1Number 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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Pathloss as a function of Cell Edge Throughput DL

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Pathloss as a function of Number of PRBsDL

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Pathloss as a function of Number of PRBsUL

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