03 - lte dimensioning guidelines - indoor link budget - fdd - ed1.1 - internal

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LTE Dimensioning Guidelines – Indoor Link Budget

July 2010

< LTE DIMENSIONING GUIDELINES – INDOOR LINK BUDGET> <JUL.2010>

Alcatel-Lucent – Proprietary Version 1.1

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Copyright © 2010 by Alcatel-Lucent. All Rights Reserved.

About Alcatel-Lucent

Alcatel-Lucent (Euronext Paris and NYSE: ALU) provides solutions that enable service providers, enterprises and governments worldwide, to deliver voice, data and video communication services to end-users. As a leader in fixed, mobile and converged broadband networking, IP technologies, applications, and services, Alcatel-Lucent offers the end-to-end solutions that enable compelling communications services for people at home, at work and on the move. For more information, visit Alcatel-Lucent on the Internet.

Notice

The information contained in this document is subject to change without notice. At the time of publication, it reflects the latest information on Alcatel-Lucent’s offer, however, our policy of continuing development may result in improvement or change to the specifications described.

Trademarks

Alcatel, Lucent Technologies, Alcatel-Lucent and the Alcatel-Lucent logo are trademarks of Alcatel-Lucent. All other trademarks are the property of their respective owners. Alcatel-Lucent assumes no responsibility for inaccuracies contained herein.



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History

Changes Date Author

Ed 1.0 – 1st Release (based on LTE Dimensioning Guidelines – Outdoor Link Budget - Ed2.6)

Apr 2010 Keith Butterworth

Ed 1.1 – Updated to align with LTE Dimensioning Guidelines - Outdoor Link Budget - Ed2.7

July 2010 Keith Butterworth

Reviewed by ARFCC (Advanced RF Competence Centre)



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CONTENTS

1 INTRODUCTION .................................................................................................... 8

2 UPLINK LINK BUDGET........................................................................................... 10

2.1 UPLINK LINK BUDGET PARAMETERS ...............................................................................11 2.1.1 UE Characteristics ...................................................................................12 2.1.2 Indoor Distribution Solutions.......................................................................12 2.1.3 eNode-B Receiver Sensitivity.......................................................................13 2.1.4 Noise Figure...........................................................................................13 2.1.5 SINR Performances ...................................................................................13

2.1.5.1 Multipath Channel........................................................................................ 13 2.1.5.2 Number Resource Blocks & Modulation & Coding Scheme.......................................... 14 2.1.5.3 Hybrid Automatic Repeat request (HARQ)............................................................ 15 2.1.5.4 Selection of Optimal MCS Index & NRB................................................................. 16 2.1.5.5 Typical SINR Performances .............................................................................. 19

2.1.6 Handling of VoIP on the Uplink ....................................................................20 2.1.6.1 VoIP and TTI Bundling.................................................................................... 21 2.1.6.2 VoIP and RLC Segmentation ............................................................................. 21

2.1.7 Uplink Explicit Diversity Gains.....................................................................22 2.1.8 Interference Margin .................................................................................23 2.1.9 Shadowing Margin....................................................................................25 2.1.10 Handoff Gain / Best Server Selection Gain ......................................................26 2.1.11 Frequency Selective Scheduling (FSS) Gain ......................................................28 2.1.12 Macro Diversity Gain ................................................................................29

2.2 FINAL MAPL AND CELL RANGE...................................................................................30 2.2.1 Propagation Model ...................................................................................30

2.3 UPLINK BUDGET EXAMPLE ........................................................................................31 2.4 UPLINK COMMON CONTROL CHANNEL CONSIDERATIONS ...........................................................32

2.4.1 Attach Procedure ....................................................................................32

3 DOWNLINK LINK BUDGET ...................................................................................... 35

3.1 DOWNLINK BUDGET PARAMETERS.................................................................................36 3.1.1 SINR.....................................................................................................36 3.1.2 RSRQ....................................................................................................38 3.1.3 Geometry..............................................................................................39 3.1.4 Downlink SINR Performances.......................................................................42

3.1.4.1 Multipath Channel........................................................................................ 43 3.1.4.2 Number Resource Blocks & Modulation & Coding Scheme.......................................... 43 3.1.4.3 Hybrid Automatic Repeat request (HARQ)............................................................ 43 3.1.4.4 Selection of the Optimal MCS Index ................................................................... 44 3.1.4.5 Downlink Explicit Diversity Gains ...................................................................... 45 3.1.4.6 Spatial Multiplexing / MIMO Gain...................................................................... 46

3.1.5 Resource Element Distribution ....................................................................47 3.1.6 Energy Per Resource Element (EPRE) .............................................................48 3.1.7 Shadowing Margin & Handoff Gain ................................................................49

3.2 DOWNLINK BUDGET EXAMPLE.....................................................................................50

4 SUMMARY ......................................................................................................... 52


EXECUTIVE SUMMARY

The purpose of this series of dimensioning guidelines is to describe details of Alcatel-Lucent’s dimensioning rules for the LTE Frequency Division Duplex (FDD) air interface and eNode-B modem hardware.

A first step of the network design process consists of determining the number of sites required and deployment feasibility according to the following information:

Site density of any legacy network deployments, Frequency band(s) used by the legacy system(s), if applicable Frequency band(s) used by the LTE system, Bandwidth available for LTE (1.4, 3, 5, 10, 15 or 20 MHz), Requirements in terms of LTE data rates at cell edge (e.g. uplink data edge to be

guaranteed, best effort data, VoIP coverage requirements, etc.).

This initial number of sites is then typically refined by means of a Radio Network Planning (RNP) study, taking into account site locations, accurate terrain databases and calibrated propagation models. The figure below illustrates key inputs and outputs of the Alcatel-Lucent eNode-B dimensioning process:


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Coverage Inputs

• Area to be covered

• Targeted service at cell edge

• Indoor penetration level

Traffic Inputs

• Number of subscribers

• Traffic profile per subscriber

Network Information

• Incumbent network info

• LTE Frequency

• LTE Maximum bandwidth

eNodeB Configuration

• LTE Bandwidth

• MIMO Scheme, Output Power

Coverage Outputs

• Cell Range

•Legacy Site Reuse

•Number of Sites

+ Traffic Inputs

Link Budget RF Planning

Air InterfaceCapacityAnalysis

Traffic ModelModem

Dimensioning

Traffic ModelModem

DimensioningOptional Requirements

• Peak Throughput per Site

eNodeB configuration

• Number of modems

• Modem configuration

- No. connection tokens

- UL & DL Throughput tokens

Coverage Inputs




Traffic Inputs

• Number of subscribers

• Traffic profile per subscriber

Network Information


• LTE Frequency


eNodeB Configuration

• LTE Bandwidth

• MIMO Scheme, Output Power

Coverage Outputs

• Cell Range


•Number of Sites

+ Traffic Inputs


Air InterfaceCapacityAnalysis

Traffic ModelModem

Dimensioning

Traffic ModelModem

Dimensioning

eNodeB configuration

• Number of modems

• Modem configuration

- No. connection tokens

- UL & DL Throughput tokens

Optional Requirements

• Peak Throughput per Site

Figure 1: Alcatel-Lucent Dimensioning Process

As implied in the figure, Alcatel-Lucent’s process relies on advanced dimensioning rules for Link Budget Analysis, Air Interface Capacity Analysis, eNode-B Modem Dimensioning, and Multi-service traffic modeling. The dimensioning process takes into account product release functionalities and will be updated regularly to follow product evolutions.

As background to further discussion of this process, a qualitative overview of dimensioning challenges regarding the FDD radio interface and multi-service traffic mix is provided.



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Internal: These rules are implemented in the dedicated LTE tools used by Network Designers: “Alcatel-Lucent LTE Link Budget” for link budget analysis, “9955 and ACCO” for radio network planning studies and “LTE eNode-B Dimensioning Tool” for air interface capacity and modem dimensioning.



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References

[1] Jakes W.C., “ Microwave Mobile Communications”, IEEE Press, 1994

[2] K.M Rege, S. Nanda, C.F. Weaver, W.C. Peng, “ Analysis of Fade Margins for Soft and Hard Handoffs”, PIMRC, 1996

[3] K.M Rege, S. Nanda, C.F. Weaver, W.C. Peng, “Fade margins for soft and hard handoffs”, Wireless Networks 2, 1996



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1 INTRODUCTION

This document forms one part of a series of network dimensioning guidelines, as detailed in Table 1.

Table 1: Design Topics Covered in the LTE Dimensioning Guidelines Package

Design Topic Document

Deployment Strategy LTE Dimensioning Guidelines - Deployment Strategy

Radio Features LTE Dimensioning Guidelines – Radio Features

Outdoor Link Budget LTE Dimensioning Guidelines – Outdoor Link Budget

Indoor Link Budget LTE Dimensioning Guidelines – Indoor Link Budget

Peak Throughput LTE Dimensioning Guidelines – Peak Throughput

Radio Network Planning LTE Dimensioning Guidelines – RNP

Air Interface Capacity LTE Dimensioning Guidelines – Air Interface Capacity

eNode-B Dimensioning LTE Dimensioning Guidelines – Modem

Token & Licensing Dimensioning LTE Dimensioning Guidelines – Token & Licensing

S1/X2 Dimensioning LTE Dimensioning Guidelines – S1 & X2

Frequency Reuse Considerations LTE Dimensioning Guidelines – Frequency Reuse

Diversity & MIMO LTE Dimensioning Guidelines – Diversity & MIMO

Traffic Power Control LTE Dimensioning Guidelines – Power Control

Traffic Aggregation Modeling LTE Dimensioning Guidelines – Traffic Aggregation Modeling

The purpose of this document is to detail the formulation of Alcatel-Lucent’s LTE link budget for dedicated indoor deployments.

Link budgets are used by Alcatel-Lucent primarily to derive the expected LTE performances at cell edge on the uplink and compare them with legacy systems in the case of an overlay of an existing network. This enables the estimation of the viability of reusing existing distributed antenna systems (additional constraints such as space for hardware deployment, etc, have to be considered on top of this) and/or the required number of radiating points for a Greenfield deployment.

Figure 2 illustrates the main inputs and outputs for an LTE link budget coverage analysis.



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Coverage Inputs




Network Information


• LTE Frequency


Coverage Outputs

• Cell Range


•Number of Sites


Figure 2: Link Budget Coverage Analysis Inputs/Outputs

Key factors influencing the link budget analysis include the frequency band for LTE operation, the cell edge performance requirements.


2 UPLINK LINK BUDGET

On the uplink, a cell is generally dimensioned by its coverage, the maximum cell range at which a mobile station is received with enough quality by the base station.


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cell radius

MAPL

Required Received Signal

Max UE transmit Power

Figure 3: Uplink Link Budget Concept

The signal threshold at which a signal is received with enough quality is called the eNode-B receive sensitivity. This sensitivity figure will depend upon the:

Data rate targeted at cell edge, Target quality / HARQ operating point (such as Block Error Rate (BLER), maximum

number of retransmissions), Radio environment conditions (multipath channel, mobile speed), eNode-B receiver characteristics (Noise Figure).

As for 2G and 3G systems, the uplink link budget involves the calculation of the Maximum Allowable Propagation Loss (or Pathloss), denoted as the MAPL, that can be sustained over the link between a mobile at cell edge and the eNode-B, while meeting the required sensitivity level at the eNode-B. As for 2G/3G systems, the uplink link budget calculations consider all the relevant gains and losses encountered on the link between the mobile and the eNode-B.

The uplink link budget is formulated such that one service (UL_Guar_Serv) is targeted at the cell edge, while for more limiting service rates, link budgets are formulated under the assumption they are not guaranteed at cell edge but at a reduced coverage footprint, as is illustrated in Figure 4).



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RangeUL_Guar_Serv

128kbps

256kbps

512kbps

UL Rates

Figure 4: Rationale behind the Uplink LKB Formulation

2.1 Uplink Link Budget Parameters

The power, Cj(UL), received at the eNode-B from a mobile (UE) located at cell edge transmitting with its maximal power, PMaxTX_PUSCH, is given by:

dBdBdB

dBdBdBdBdBm

sityMacroDiverRxRx

Body)Service(ULnPropagatioTxTxHMaxTX_PUSCdBmj(UL)

GainLossGain

LossRLossesLossGainPC

MaxTXP

where

dBmPUSCH_ is the maximum transmit power of the UE (see section 2.1.1),

GainTx and LossTx, the gains and losses at the transmitter side such as UE antenna gain,

GainRx and LossRx represent the gains and losses at the receiver side such as the eNode-B antenna gain and the feeder losses between the eNode-B and the antenna,

LossBody is the body losses induced by the user, typically 3dB body losses are considered for voice services and 0 dB for data services (handset position is far from the head when using data services),

GainMacroDiversity is the gain considered for solutions that are comprised of multiple distributed antennas connected to the same sector, i.e. this is a combining gain (see Section 2.1.12),

For the assumed indoor propagation model (see section 2.2.1), the propagation losses can be expressed according to the cell range, LossesPropagation:

).log(RKKLosses )Service(UL21nPropagatio dB .

To ensure reliable coverage, the received power at the eNode-B should be higher than the eNode-B receiver sensitivity:

dBdBdBdBdBm FSSHOShadowingIoTdBmj(UL) GainGainMarginMarginySensitivitC

where

MarginShadowing is a margin that compensates for the slow variability in mean path loss about that predicted using the indoor propagation model (see section 2.1.9)

GainHO is a handoff gain or best server selection gain that models the benefits due to the ability to reselect to the best available serving site at any given location (see section 2.1.10)


GainFSS is a frequency selective scheduling gain that is due to the ability of the scheduler to select best frequency blocks per UE depending on their channel conditions

For each service to be offered by the operator, this relationship allows computation of the maximum propagation losses that can be afforded by a mobile located at the cell edge, that is to say the Maximum Allowable Path Loss (MAPL):


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dBdBdB

dBdB

dBdBdBdBdBdBm

sityMacroDiverFSSHO

ShadowingIoTdBm

BodyRxRxTxTxHMaxTX_PUSCdBj(UL)

GainGainGain

MarginMarginySensitivit

LossossLGainossLGainPMAPL

2.1.1 UE Characteristics

The maximum transmit power of an LTE UE, PMaxTX_PUSCH, depends on the power class of the UE. Currently, only one power class is defined in 3GPP TS 36.101:

a 23dBm output power is considered with a 0 dBi antenna gain.

Internal: This is the case in the TS 36.101 version of March 2010. Only one class defined (Class 3) with 23dBm output power (with ±2dB tolerance, but we should not account for such a tolerance to define the UE output power).

2.1.2 Indoor Distribution Solutions

There is a wide range of possible solutions for deploying dedicated indoor coverage to a particular indoor environment, these include:

Passive: Solutions where a relatively high power eNode-B is used to drive a passive distribution network of coaxial cable, splitters, couplers and antennas.

Hybrid: Solutions that are a cross between Passive and Active solutions where remote radio heads are used to drive small passive distributed antenna systems

Active: Solutions where a low power eNode-B is used to drive a filly active distribution network consisting of, for example, optical fiber fed remote radio modules that are directly connected to antennas.

Distributed: Solutions that are comprised of multiple low power eNode-B’s that are distributed across the coverage area, for example, Pico eNode-B’s, Femto eNode-B’s, etc.

The key factors associated with the above solutions that impact the LTE indoor link budget are as follows:

Table 2: Key Link Budget Factors Influenced by Indoor Solution Type

Passive Hybrid Active Distributed

Feeder Losses High Low Negligible Negligible

eNode-B Noise Figure No Impact Negligible Moderate Moderate

Downlink Output Power High Power Medium Power Low Power Low Power

SINR Performances No Impact No Impact No Impact Minimal Impact

< LTE DIMENSIONING GUIDELINES – INDOOR LINK BUDGET> <JUL.2010> 2.1.3 eNode-B Receiver Sensitivity

The sensitivity level can be derived from SINR figures calculated or measured for some given radio channel conditions (multipath channel, mobile speed) and quality target (e.g. 10-2 BLER):

RBRB(UL)theNode_B10PUSCH_dBdBm .W.N.NFLog10 SINRySensitivit

where:

SINRPUSCH_dB is the signal to interference ratio per Resource Block, required to reach a given PUSCH data rate and quality of service,

FeNode-B.Nth.NRB(UL).WRB is the total thermal noise level seen at the eNode-B receiver within the required bandwidth to reach the given data rate, where:

FeNode-B is the noise figure of the eNode-B receiver after accounting for any impact due to an active distributed antenna system (using Friss formula, see section 2.1.4),

Nth is the thermal noise density (-174dBm/Hz), NRB(UL) is the number of resource blocks (RB) required to reach a given data rate – it

can be deduced from link level simulations selecting the best combination (e.g. the one that requires lowest SNR or lowest number of RB to maximize the capacity),

WRB is the bandwidth used by one LTE Resource Block. One Resource Block is composed of 12 subcarriers, each of a 15kHz bandwidth – so WRB is equal to 180kHz.

2.1.4 Noise Figure

The Noise Figure of the eNode-B is supplier dependent. Typical Noise Figures of an eNode-B range from 2.5 to 3dB, depending upon the product variant.

If an active distribution solution (see Section 2.1.2) is used for an indoor deployment then the effective noise figure of the distribution solution plus the eNode-B must be computed. As with any active element inserted in the reception chain of an eNode-B, the impact of active elements on the link budget can be assessed by means of the Friis formula.

Module_Active

BeNodeModule_Activeoverall g

1nnn

with 10

NF

element

element

10n and 10

G

element

element

10g ,

The typical active elements characteristics, NFActive_element and GActive_Element are dependent upon the specific active distribution solution that is deployed.

2.1.5 SINR Performances

The SINR figures are derived from link level simulations or better from equipment measurements (lab or on-field measurements). They depend on the eNode-B equipment performance, radio conditions (multipath fading profile, mobile speed), receive diversity configuration for the indoor solution (see section 2.1.2, 1 branch for most distributed antenna systems, 2 branch for distributed solutions and exceptionally 4 branches), targeted data rate and quality of service.

2.1.5.1 Multipath Channel

For link budget analysis, the most typical UE speed and multipath profiles are considered according to the type of environment (e.g. dense urban, rural, etc).


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< LTE DIMENSIONING GUIDELINES – INDOOR LINK BUDGET> <JUL.2010> In terms of multipath channel, the indoor environment is considered to be well approximated by the ITU Vehicular multipath profile, with mobiles moving at 3km/h for indoor environments.

Choosing one multipath channel for a given environment is a modeling assumption. In reality, in a cell, various multipath conditions exist. A better representation would be to consider a mix of multipath channel models (even though there is no one unique mix to represent a typical indoor environment that has been agreed across the radio community). However for a coverage assessment, the worst case model should be considered. The ITU VehA multipath channel model (2 equivalent main paths) is correspondingly a good compromise for a reasonable, worse case, link budget analysis.

For LTE some evolved multipath channel models have been defined such as EVA5Hz or EPA5Hz. These are an extension of the VehA and PedA models used in UMTS to make them more suitable for the wider bandwidths encountered with LTE, e.g. >5MHz. Main difference lies in the definition of a doppler frequency instead of a speed, making the model useable for different frequency bands. All SINR performances used in Alcatel-Lucent indoor link budgets are for EVehA3 channel models.

For the purposes of the link budget the underlying assumption is that the UE is at the cell edge and the main driver is to maximize the coverage.

2.1.5.2 Number Resource Blocks & Modulation & Coding Scheme

For a given target data rate the required target SINR depends upon (see Figure 5 for some definitions of the LTE channel structure):

Number Resource Blocks, NRB Modulation & Coding Scheme Index (MCS)


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t

f

one OFDM symbol

one Subcarrier

subframePhysical Resource Block (RB)

= 14 OFDM Symbols x 12 Subcarrier

This is the minimum unit of allocation in LTE

15 kHz

RB

Slot (0.5 ms)

Subframe (1 ms)

Slot (0.5 ms)

Figure 5: LTE Channel Structure - Some Definitions

The Modulation & Coding Scheme Index (MCS) determines the Modulation Order which in turn determines the Transport Block Size (TBS) Index to be used (see Table 3).



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Table 3: Extract from the Modulation and TBS index table for PUSCH (from 36.213)

MCS Index, IMCS Modulation Order, QM TBS Index, ITBS

0 QPSK 0

1 QPSK 1

2 QPSK 2

3 QPSK 3

… … …

For a given MCS Index the Transport Block Size (TBS) is given by Table 4 for different numbers of resource blocks

Table 4: Extract from the Transport Block size table (from 36.213)

ITBS NRB = 1 NRB = 2 NRB = 3 NRB = 4 NRB = …

0 16 32 56 88 …

1 24 56 88 144 …

2 32 72 144 176 …

3 40 104 176 208 …

4 56 120 208 256 …

5 72 144 224 328 …

6 328 176 256 392 …

… … … … … …

For example, for an MCS Index = 2 and NRB = 3 the corresponding TBS = 144 bits.

2.1.5.3 Hybrid Automatic Repeat request (HARQ)

A key characteristic of the LTE air interface is the utilization of HARQ, a combination of ARQ and channel coding which provides greater robustness against fast fading; these schemes include incremental redundancy, whereby the code rate is progressively reduced by transmitting additional parity information with each retransmission.

In LTE, asynchronous adaptive HARQ is used for the downlink, and synchronous HARQ for the uplink. In the uplink, the retransmissions may be either adaptive or non-adaptive, depending on whether new signaling of the transmission attributes is provided.

In an adaptive HARQ scheme, transmission attributes such as the modulation and coding scheme, and transmission resource allocation in the frequency domain, can be changed at each retransmission in response to variations in the radio channel conditions. In a non-adaptive HARQ scheme, the retransmissions are performed without explicit signaling of new transmission attributes – either by using the same transmission attributes as those of the previous transmission, or by changing the attributes according to a predefined rule. Accordingly, adaptive schemes bring more scheduling gain at the expense of increased signaling overheads.

There are multiple HARQ operating points that can be utilized for an LTE system:

Either, a lower initial BLER with a correspondingly fewer overall number of HARQ transmissions, resulting in a higher SINR requirement with reduced latency and better spectral efficiency (e.g. 10% iBLER target for the 1st HARQ transmission)


Or, a higher initial BLER with a correspondingly greater overall number of HARQ transmissions resulting in a lower SINR requirement with an increased latency and poorer spectral efficiency (e.g. 1% pBLER target after up to 4 HARQ transmissions – iBLER ~50-70%).

The former operating point is currently recommended by Alcatel-Lucent, this corresponds to a 10% iBLER target for the 1st HARQ transmission.

Internal: Ideally the later operating point is considered at cell edge locations (for which we perform the link budget) where the objective is to tradeoff spectral efficiency and latency for an improved SINR and receiver sensitivity. Whereas in locations that are not link budget constrained, e.g. closer to the eNode-B, the former HARQ operating point is more appropriate. The current Alcatel-Lucent implementation considers only a 10% iBLER, eventually a different operating point is likely to be supported, maybe even a dynamic operating point.

2.1.5.4 Selection of Optimal MCS Index & NRB

For each targeted uplink data rate there will be an optimal combination of NRB and MCS Index that will maximize the receiver sensitivity for the relevant HARQ operating point. Figure 6 provides an example of the selection of the optimal MCS and number of RB, NRB, for a given target effective data rate. This plot illustrates for the full range of possible MCS indices the corresponding required NRB and the resultant eNode-B receiver sensitivity.

-120.0 dBm

-115.0 dBm

-110.0 dBm

-105.0 dBm

-100.0 dBm

-95.0 dBm

-90.0 dBm

MCS 0 MCS 5 MCS 10 MCS 15 MCS 20 MCS 25 MCS 30

ode-

B R

x Se

nsit

ivit

y

1 RB

2 RB

3 RB

4 RB

5 RB

6 RB

7 RB

Req

uire

d #

RB

for

Ser

viceMCS 2 provides the optimal

tradeoff between Rx. Sens and NRB required

eN

Figure 6: Selection of Optimal MCS and NRB for a target rate of 128kbps with 10% iBLER, EVehA3

From Figure 6 it can be seen that MCS 2 with 3 RB’s is optimal, as this provides the best receiver sensitivity while minimizing utilization of RB’s. Table 5 provides a comparison between the 10% iBLER operating point performance with that for a 1% pBLER operating point, for the same 128kbps target effective data rate:


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Table 5: Example of Different HARQ Operating Points (128kbps)

1% pBLER

(high initial BLER) 10% iBLER

(low initial BLER)

MCS Index MCS 8 MCS 2 NRB 3 RB 3 RB

TBS Size 392 bits 144 bits Effective Coding Rate 0.556 0.242

Average #HARQ Transmissions 3.06 1.13 Post HARQ Throughput 128 kbps 128 kbps

Required SINR -3.0 dB -0.3 dB Receiver Sensitivity -117.2 dBm -114.5 dBm

Note: The 1% pBLER HARQ operating point (1% BLER after 4 HARQ Tx) corresponds to an iBLER (BLER for the 1st HARQ transmission) much greater than 10%.

It can be seen from the example summarized in Table 5, that the same required data rate can be achieved with different combinations of NRB, MCS Index and number of HARQ transmissions. The receiver sensitivity comparison below highlights the different coverage for the same targeted data rate due to the different HARQ operating points:

RBRB(UL)


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theNode_B10PUSCH_dBdBm .W.N.NF10log SINRySensitivit

Sensitivity1% BLER after 4 HARQ Tx = -3.0 + 10xlog10( 2.5dBxNthx3RBx180kHz ) = -117.2dBm Sensitivity10% BLER after 1 HARQ Tx = -0.3 + 10xlog10( 2.5dBxNthx3RBx180kHz ) = -114.5dBm

While the two solutions utilize the same number of resource blocks, the trade-off between the two is in the number HARQ transmissions versus the receiver sensitivity. While the utilization of more HARQ transmissions enhances the receive sensitivity it also requires the same air interface resources for a longer period of time (more transmission time intervals). Note that the difference between the receiver sensitivities in Table 5 is due only to the difference in the required SINR (as the NRB is equal).

Figure 7 shows an identical analysis to that presented in Figure 6 with the exception that here an effective data rate of 512kbps is targeted.



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-115.0 dBm

-110.0 dBm

-105.0 dBm

-100.0 dBm

-95.0 dBm

-90.0 dBm

MCS 0 MCS 5 MCS 10 MCS 15 MCS 20 MCS 25 MCS 30

eNod

e-B

Rx

Sens

itiv

ity

1 RB

6 RB

11 RB

16 RB

21 RB

26 RB

Req

uire

d #

RB

for

Ser

viceMCS 4 provides the optimal

tradeoff between Rx. Sens and NRB required

Figure 7: Selection of Optimal MCS and NRB for a target rate of 512kbps with 10% iBLER, EVehA3

From Figure 7 it can be seen that now MCS 4 with 9 RB’s is optimal as this provides the best receiver sensitivity while minimizing utilization of RB’s.

Table 6 provides a comparison between the 10% iBLER operating point performance with that for a 1% pBLER operating point, for the same 512kbps target effective data rate:

Table 6: Example of Different HARQ Operating Points (512kbps)

1% pBLER


(low initial BLER)

MCS Index MCS 10 MCS 4 NRB 10 RB 9 RB

TBS Size 1736 bits 632 bits Effective Coding Rate 0.676 0.286

Average #HARQ Transmissions 3.39 1.23 Post HARQ Throughput 512 kbps 512 kbps

Required SINR -3.1 dB 0.6 dB Receiver Sensitivity -112.1 dB -108.8 dB

Making the same comparison of the receiver sensitivity:

RBRB(UL) theNode_B10PUSCH_dBdBm .W.N.NF10log SINRySensitivit

Sensitivity1% BLER after 4 HARQ Tx = -3.1 + 10xlog10( 2.5dBxNthx10RBx180kHz ) = -112.1dBm Sensitivity10% BLER after 1 HARQ Tx = 0.6 + 10xlog10( 2.5dBxNthx9RBx180kHz ) = -108.8dBm

Here the difference between the receiver sensitivities is due to the combination of the differences in the required SINR and in the required bandwidth (dictated by the number of resource blocks, NRB). Thus it is important when comparing the required SINR for two services to consider also the required number of resource blocks.



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2.1.5.5 Typical SINR Performances

Based on link level simulations, for a HARQ operating point that targets 1% pBLER, the optimal combination of NRB, MCS Index and the corresponding SINR target for the typical data rates considered in Alcatel-Lucent uplink link budgets are summarized in Table 7 (for EVehA3 and EVehA50 channel conditions with 2-way Rx Diversity).

Table 7: Typical Rates Considered in Uplink Link Budget (for EVehA3 channel conditions @ 2.6GHz with 2.5dB Noise Figure, 1% post HARQ BLER)

Post HARQ Peak T’put 8 kbps 64 kbps 128 kbps 256 kbps 512 kbps 1000 kbps 2000 kbps

MCS Index MCS 0 MCS 6 MCS 8 MCS 10 MCS 10 MCS 10 MCS 10

Modulation QPSK QPSK QPSK QPSK QPSK QPSK QPSK

NRB(UL) 1 RB 2 RB 3 RB 5 RB 10 RB 20 RB 40 RB

HARQ Operating Point 1% pBLER 1% pBLER 1% pBLER 1% pBLER 1% pBLER 1% pBLER 1% pBLER

TBS Size 16 bits 176 bits 392 bits 872 bits 1736 bits 3496 bits 6968 bits

Effective Coding Rate 0.242 0.424 0.556 0.697 0.676 0.671 0.667

Average # HARQ Tx 2.00 2.75 3.06 3.41 3.39 3.50 3.48

SINR Target (EVehA3) -3.4 dB -3.6 dB -3.0 dB -2.4 dB -3.1 dB -2.9 dB -3.3 dB

Rx Sensitivity (EVehA3) -122.3 dBm -119.6 dBm -117.2 dBm -114.4 dBm -112.1 dBm -108.8 dBm -106.2 dBm

Internal: If quoting SINR performances to customers the 10% iBLER figures (Table 8) should be presented (as they are more representative of current product characteristics) in preference to the 1% pBLER figures (Table 7).

The above SINR figures have been derived from link level simulations which assume ideal scheduling and link adaptation, the reality in the field will not be as good. To compensate for such ideal assumptions, there are currently two key elements to the margins incorporated into in the SINR performances used in uplink budgets today:

Implementation Margin: to account for the assumptions implicit in the link level simulations used to derive the SINR performances

o Currently considered to be ~1dB o No variability is assumed for different environments or UE mobility

conditions o Will be tuned based on SINR measurements (not yet performed)

ACK/NACK Margin: to account for the puncturing of ACK/NACK onto the PUSCH o A 1dB margin is applied for VoIP services and 0.5dB for higher data

throughputs

The SINR performances quoted in Table 7 and subsequently in Table 8 account for the above mentioned implementation and ACK/NACK margins.

Table 8 summarizes the same for a 10% iBLER HARQ operating point.

< LTE DIMENSIONING GUIDELINES – INDOOR LINK BUDGET> <JUL.2010> Table 8: Typical Rates Considered in Uplink Link Budget (for EVehA3 channel conditions

@ 2.6GHz with 2.5dB Noise Figure, 10% iBLER)

Post HARQ Peak T’put 8 kbps 64 kbps 128 kbps 256 kbps 512 kbps 1000 kbps 2000 kbps

MCS Index MCS 0 MCS 5 MCS 2 MCS 5 MCS 4 MCS 4 MCS 4

Modulation QPSK QPSK QPSK QPSK QPSK QPSK QPSK

NRB(UL) 1 RB 1 RB 3 RB 4 RB 9 RB 16 RB 32 RB

HARQ Operating Point 10% iBLER 10% iBLER 10% iBLER 10% iBLER 10% iBLER 10% iBLER 10% iBLER

TBS Size 16 bits 72 bits 144 bits 328 bits 632 bits 1128 bits 2280 bits

Effective Coding Rate 0.242 0.455 0.242 0.356 0.286 0.278 0.276

Average # HARQ Tx 1.1 1.1 1.1 1.1 1.1 1.1 1.1

SINR Target (EVehA3) -1.7 dB 2.4 dB -0.3 dB 2.1 dB 0.6 dB -0.5 dB -1.1 dB

Rx Sensitivity (EVehA3) -120.7 dBm -116.5 dBm -114.5 dBm -110.8 dBm -108.8 dBm -107.4 dBm -105.0 dBm

Figure 8 illustrates the receiver sensitivity figures quoted in Table 8 for a 10% iBLER and EVehA3 channel conditions.

-125 dBm

-120 dBm

-115 dBm

-110 dBm

-105 dBm

-100 dBm

-95 dBm

-90 dBm

-85 dBm

-80 dBm

VoI

P A

MR

12.

2

(TT

I Bu

ndli

ng)

PS 8

PS 3

2

PS 6

4

PS 1

28

PS 2

56

PS 3

84

PS 5

12

PS 7

68

PS 1

000

PS 2

000

PS 5

700

PS 1

0000

PS 2

0000

eNod

e-B

Rec

eive

r Se

nsit

ivit

y

EVehA50

EVehA3

Figure 8: Receiver Sensitivity for Typical Rates Considered in Uplink Link Budget (for EVehA3 channel conditions @ 2.6GHz with 2.5dB Noise Figure, 10% iBLER)

2.1.6 Handling of VoIP on the Uplink

For VoIP, various approaches (L2 segmentation and TTI bundling) were discussed at 3GPP to offer good coverage performances of VoIP (see Figure 9). TTI bundling was adopted in 3GPP Rel8 (36.321).

With TTI bundling, as opposed to RLC Segmentation, larger transport blocks are used. Relying on incremental redundancy, HARQ Transmissions are performed in consecutive TTIs without waiting for HARQ feedback. The HARQ receiver accumulates the received energy of all transmissions and responds with HARQ feedback only once after the entire bundle has been received and evaluated.


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RLC Segmentation 4ms TTI Bundling

Figure 9: RLC Segmentation and 4ms TTI Bundling Operating Modes

2.1.6.1 VoIP and TTI Bundling

No segmentation of VoIP packets required Enhances link budget compared to transmission of a single packet by supporting

more HARQ transmissions in short time period Not supported in initial UEs and product Otherwise known as VoIP with QoS

The VoIP packet size for an AMR 12.2 VoIP codec, after accounting for RLC, MAC and CRC overheads, is ~328 bits. The VoIP codec generates such packets with ~20ms periodicity. With 4ms TTI bundling each 328 bit VoIP packet is sent in 4 consecutive TTI’s with 4 different redundancy variants (think of this as doing 4 HARQ transmissions in successive TTI’s). These four transmissions can be sent up to a maximum of 4 times and on average 2 times.

For each TTI, MCS Index 6 is utilized with a single RB. This yields a TBS (Transport Block Size) of 328 bits (MCS 6 & 1 RB is a special combination created especially for VoIP services). The average effective air interface rate for active transmission for an AMR 12.2 VoIP service over the air interface is 328 bits / 4 successive TTIs / 2 average transmissions = 41 kbps, with the maximum of 4 transmissions this drops to 20.5kbps. However, if we average the codec payload of 328 bits over the 20ms periodicity, the average throughput is 328 bits / 20ms = 16.4 kbps. Table 9 summarizes the VoIP with TTI bundling performance characteristics that are considered in UL budgets:

Table 9: VoIP with TTI Bundling (1% pBLER target)

AMR 12.2

Nominal Codec Rate 12.2kbps

VoIP Packet Size (with overheads) 328 bits

MCS / NRB / SINR (EVehA3) Rx Sensitivity

MCS 6 / 1 RB / -3.7 dB -122.7 dBm

2.1.6.2 VoIP and RLC Segmentation

Segments VoIP packets into multiple smaller segments


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Enhances link budget compared to transmission of a single packet as the smaller segments result in a more favorable required MCS and NRB

Substantially higher overheads in terms of required grants and signaling Otherwise known as “Over the Top” best effort VoIP Very poor link budget without substantial levels of segmentation

There are a wide range of possible VoIP codec’s that could be used for such solutions, e.g. G711 (64kbps) and G729 (8kbps), in fact it is possible to use RLC segmentation with an AMR 12.2 VoIP codec. Table 10 provides a summary of the performance characteristics that are considered in UL budgets:

Table 10: “Over the Top” Best Effort VoIP (assuming IPv4, 10% iBLER target)

G711 Codec G729 Codec

Nominal Codec Rate 64kbps 8kbps

VoIP Packet Size (no oveheads) 160 Bytes 20 Bytes

VoIP Packet Size (with oveheads) 1664 bits 536 bits

8 way segmentation 250 bits 109 bits

MCS / NRB / SINR (EVehA3) Rx Sensitivity

MCS 4 / 4 RB / 1.8dB -111.1 dBm

MCS 8 / 1 RB / 5.4dB -113.6dBm

Comparing the receiver sensitivity figures in Table 9 and Table 10, the link budget benefits attributable to TTI bundling combined with more HARQ transmissions are immediately apparent.

2.1.7 Uplink Explicit Diversity Gains

The SINR performance figures considered by Alcatel-Lucent in uplink and downlink budgets are based on link level simulations that already account for the corresponding transmit and receive diversity gains. For the uplink the default assumption is 1x2 receive diversity (2RxDiv), the gain associated with 2RxDiv is accounted for directly in the SINR figures.

Note: Most indoor distribution solutions (see section 2.1.2) are unlikely to support 2 RF paths, as such the SINR performances in such cases must be offset to account for the lack of receive diversity at the eNode-B. Table 11 summarizes the impact on the SINR figures considered with different numbers of UL receive paths:

Table 11: SINR Impact Due to UL Receive Diversity

UL Rx Diversity Scheme SINR Impact

1 RxDiv -2.5 dB

2 RxDiv 0.0 dB

4 RxDiv 2.5 dB

For example, to account for 1x4 receive diversity (4RxDiv) on the uplink an additional 2.5dB gain is considered on the (2RxDiv) SINR figures from link level simulations.

< LTE DIMENSIONING GUIDELINES – INDOOR LINK BUDGET> <JUL.2010> 2.1.8 Interference Margin

Generally, sensitivity figures are derived considering only thermal noise. However, in a link budget analysis, the real interference, Ij(UL), should be considered and not only the thermal noise. This means that the received power, Cj(UL), should satisfy the following condition:

dBdBm ceInterferendBmj(UL) MarginySensitivitC

where


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WN

WNI10logMargin

th

thj(UL)ceInterferen dB

The MarginInterference is the interference rise over that of thermal noise due to inter-cell interference. Nth is the thermal noise (-174 dBm/Hz) and W is the used PRB bandwidth (Hz). Note that the assessment of the interference margin is totally different from the classical relationship between uplink cell load and noise rise considered in CDMA and WCDMA systems. Ij(UL) is the interference due to adjacent cells utilizing the same PRB at the same time. Note that this interference could also be considered to comprise of external interference from other systems such as MediaFLO or DTC Channel 51.

LTE resources are divided into resource blocks (set of OFDM symbols and frequencies). The interference per resource block will depend on the probability that resource blocks of same frequency are simultaneously used in the surrounding cells. However, LTE system is likely to be deployed with a frequency reuse of 1. The interference on a given resource block can therefore be high.

Assessing the interference level enables the derivation of the interference margin to be accounted for in link budgets used for coverage (cell range) evaluation. In CDMA or WCDMA systems, the interference margin was derived from power control equations, these equations established a linkage between the number of users transmitting in the cell (or the cell load) to the interference margin (or noise rise). In LTE some specific power control schemes are defined with some flexibility in the definition of the parameters offering various power control strategies to be adopted and consequently impacting the interference margin, IoT, to be considered in link budget analyses.

A typical IoT target considered in LTE link budgets is 3dB. Such an IoT target will have a corresponding loading for adjacent cells for the cell range computed using the link budget formulation presented in this document.

The average IoT is dependent upon the cell edge data rate (SINR) that is targeted by UEs in adjacent cells.

Higher cell edge SINR targeted by UEs in adjacent cells Higher average IoT Larger cell sizes Lower cell edge rates can be achieved by UEs in adjacent cells Lower average IoT (e.g. NGMN Case 3)

Smaller cell sizes Higher cell edge rates can be achieved by UEs in adjacent cells Higher average IoT (e.g. NGMN Case 1)

An example from some macro cellular system level simulations performed under NGMN Case 3 conditions (a coverage/link budget limited scenario) is presented in Figure 10 (assuming 100% resource block loading, 10 UEs per sector, full buffer simulations, 10MHz bandwidth).


0 kbps

1000 kbps

2000 kbps

3000 kbps

4000 kbps

5000 kbps

6000 kbps

7000 kbps

1.0 dB 1.5 dB 2.0 dB 2.5 dB 3.0 dB 3.5 dB

IoT

Cel

l T

hro

ugh

put

Figure 10: NGMN Case 3 – Coverage limited scenario, 100% resource block loading, 10 UEs per sector, full buffer simulations

Figure 10 illustrates the impact of allowing a different average IoT on the spectral efficiency of the uplink. It can be seen that for this particular scenario the optimal IoT is between 2.5 and 3dB. Such scenarios are more typical of deployments that are more coverage rather than interference limited which is typical of the cases commonly considered in link budget analyses.

A further example performed under NGMN Case 1 conditions (an interference/capacity limited scenario) is presented in Figure 11 (assuming 100% resource block loading, 10 UEs per sector, full buffer simulations, 10MHz bandwidth).

0 kbps

1000 kbps

2000 kbps

3000 kbps

4000 kbps

5000 kbps

6000 kbps

7000 kbps

8000 kbps

9000 kbps

10000 kbps

0 dB 5 dB 10 dB 15 dB 20 dB

IoT

Cel

l T

hro

ugh

put

Figure 11: NGMN Case 1 – Interference/capacity limited scenario, 100% resource block loading, 10 UEs per sector, full buffer simulations


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< LTE DIMENSIONING GUIDELINES – INDOOR LINK BUDGET> <JUL.2010> Figure 11 illustrates the impact of allowing a different average IoT on the spectral efficiency of the uplink. It can be seen that for this particular scenario the optimal IoT is greater than 5dB. However, in this case the link budget is not constraining and thus from a link budget perspective there is no issue with tolerating a higher IoT.

Note that while the simulations indicate there are gains to be had at IoTs of up to 15dB or more, operating points greater ~5.5dB are not currently recommended by Alcatel-Lucent.

2.1.9 Shadowing Margin

From the previous section, the link budget should satisfy the following equation:


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dBdBm ceInterferendBmj(UL) MarginySensitivitC

This equation should be satisfied from a statistical point of view with a given probability, Pcov, (coverage probability) within the cell. Typically, the received power should be better than the sensitivity over more than 95% of the cell area:

covceInterferendBmj(UL) PMarginySensitivitCProbadBdBm

Generally, a target of 95% cell coverage is considered in dense urban, urban and suburban environments, while 90% is considered in rural environments, but this is dictated by the operator’s coverage quality objectives.

The received power from a mobile within the cell will depend upon the shadowing conditions due to obstacles between the UE and the base station antennas. These slow shadowing variations (in dB) can be represented as a Gaussian random variable with a zero-mean and a standard deviation that is dependent upon the environment (typically between 5 to 10 dB).

Due to the Gaussian properties of the shadowing, a margin called the “shadowing margin” can be computed and incorporated in the link budget calculations to consider the coverage probability requirement, either probability at cell edge or over the cell. The following formulas are used to derive the shadowing margins according to the specified coverage probability:

2σ

Marginerfc

21

1P dBShadowingborder cell cov

bab1

erf1eaerf121

P 2b

2ab1

area cell cov

Where

2σ

Margina

Shadowing

2σ10ln

b K2

K2 is the propagation model coefficient.

More details on the way these equations are derived can be found in [1].

Table 12 summarizes some typical shadowing margins for a typical path loss slope, K2 =35:



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Table 12: Example of Shadowing Margins

Shadowing Standard Deviation

Cell Area Coverage

Probability

Cell Edge Coverage

Probability

Shadowing Margin

95% 87.7% 11.7 dB 10 dB

90% 77.7% 7.7 dB

95% 86.2% 8.7 dB 8 dB

90% 75.1% 5.4 dB

95% 84.9% 7.2 dB 7 dB

90% 73.3% 4.3 dB

95% 83.9% 5.9 dB 6 dB

90% 70.9% 3.3 dB

2.1.10 Handoff Gain / Best Server Selection Gain

Unlike UMTS/WCDMA or CDMA, there is no soft-handoff functionality for LTE. Therefore, no soft-handoff gain should be considered for LTE.

However it would be too pessimistic to only consider the shadowing margin computed with one cell as in section 2.1.9: a mobile at the cell edge can still handover to or originate a call on a neighboring cell with more favorable shadowing, i.e. a lower path loss.

Some models have been derived to compute such a hard handoff gain, taking into account handoff hysteresis thresholds and connection delays [2] [3]. Such a model collapses to that of soft-handoff computations when the handoff threshold and the connection delays are equal to zero. It is also important to note that while this is referred to in the link budget as a “handoff gain” it could equally well be referenced as a “best server selection gain”.

Note that this hard handoff gain can be considered for any system without soft handoff. So this is the case for GSM. Note that the handoff gain for LTE should be somewhere in between that which may be considered for GSM and that for a soft handoff scenario for WCDMA or CDMA.

A shadowing margin, which is partially mitigated by the handoff gain, is only considered in the link budget due to uncertainties in the estimation of the path loss and cell range. As the uncertainty in the prediction of the path loss is reduced (a reduction in the standard deviation of shadowing) the shadowing margin and handoff gain will also be reduced. If there are no uncertainties in the estimation of the path loss and the corresponding cell range, there will be no need to consider any shadowing margin or handoff gain.

Internal: However we are not used to considering such a gain in GSM. It is highly recommended to consider such a hard handoff gain, above all to have favorable link budget comparison with CDMA or WCDMA, both of which consider a soft handoff gain in their link budgets.

Table 14 provides some examples of the shadowing margin and handoff gain for different coverage probability targets and shadowing standard deviations. This example is based on the assumptions listed in Table 13:



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Table 13: Assumptions for Hard Handoff Gain Computations

Antenna Height 30 m

K2 Propagation Model 35.2

Shadowing Correlation 0.5

Hysteresis 3 dB

HO sampling time 20 msec

# of samples to decide HO 4 samples

Correlation distance 50 m

Note that the assumptions in Table 13 for the Hysteresis and HO sampling time are relatively conservative so as to ensure that the handoff gains considered in the LKB are evaluated with a reasonable degree of confidence.

Table 14: Example of Hard Handoff Gain

Shadowing Standard Deviation

Cell Area Coverage

Probability

Cell Edge Coverage

Probability

Shadowing Margin

Soft Handoff

Gain

Handoff Gain

6 dB 90% 71% 3.3 dB 2.7 dB 2.3 dB

6 dB 95% 84% 5.9 dB 2.8 dB 2.5 dB

7 dB 90% 73% 4.3 dB 3.1 dB 2.8 dB

7 dB 95% 85% 7.2 dB 3.4 dB 3.1 dB

8 dB 90% 75% 5.4 dB 3.6 dB 3.4 dB

8 dB 95% 86% 8.7 dB 3.9 dB 3.6 dB

10 dB 90% 78% 7.7 dB 4.7 dB 4.4 dB

10 dB 95% 88% 11.7 dB 5.0 dB 4.8 dB

Based on these results, a 3.6dB handoff gain can be assumed for typical indoor deployment conditions (95% area reliability, 8dB shadowing standard deviation and 3km/h). If the indoor solution (see section 2.1.2) consists of a distributed antenna system with minimal overlapping coverage with adjacent cells then a 0dB gain is considered.

Note that the full handoff gain is only applicable for UE’s located at the cell edge. In the uplink link budget we consider one service (data rate) that is guaranteed at the cell edge, the more demanding services are supported in a subset of the coverage area. Consequently, the other services will not take benefit of the full handoff gain. Figure 12 illustrates the handoff gains computed for UE locations between the eNode-B and the cell edge. Note that this is an example for the same assumption as shown in Table 13 for a shadowing standard deviation of 8dB and 95% coverage reliability.



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0.0 dB

0.5 dB

1.0 dB

1.5 dB

2.0 dB

2.5 dB

3.0 dB

3.5 dB

4.0 dB

0% 20% 40% 60% 80% 100%

% of Cell Range

Han

dof

f G

ain

Figure 12: Handoff Gains for UE Locations between the eNode-B and the Cell Edge

2.1.11 Frequency Selective Scheduling (FSS) Gain

There are a number of ways the LTE system can manage the potentially considerably frequency selective channel:

Schedule the best groups of RBs (Resource Blocks) to individual UEs according to the channel conditions for specific UEs (frequency selective scheduling)

Make no specific consideration to the frequency selectivity o Frequency non-selective scheduling o A variant upon this is to randomly hop frequencies (RBs) for retransmissions

and/or successive TTIs

For frequency selective scheduling, consider as an example, an uplink where an eNode-B is serving 3 contending UEs. For each UE, the eNode-B has knowledge of the quality of the radio channel (by means of the uplink SRS) and as such can form quality metrics for each individual RB for each UE on the UL. Based on these quality metrics the scheduler can formulate which resource block or group of resource blocks is most advantageous to allocate to each of the contending UEs on the uplink. This process is highlighted Figure 13.

12

34

56

78

9

UE 1

UE 2

UE 3

0

2

4

6

8

10

12

1 2 3 4 5 6 7 8 9

PRB Index

Pri

ori

ty M

etri

c

0

1

2

3

4

5

6

7

8

Priority Metric

PRB Index

UE 1

UE 2

UE 3

Figure 13: Per UE quality metrics for each RB and the consolidated priority metric for each RB

< LTE DIMENSIONING GUIDELINES – INDOOR LINK BUDGET> <JUL.2010> By allocation of the RB groupings according to the right hand diagram in Figure 13 it is possible to ensure that each UE is more likely to get allocated individual resource blocks that have more favorable channel conditions, thus resulting in enhanced link budget performances. This can be thought of a type of interference co-ordination scheme, whereby it is possible for the system to avoid interference by appropriate resource block allocation. A similar principle also applies on the downlink.


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One alternative to such a frequency selective scheduling approach is to consider only an average of the channel qualities across the entire band for each UE, see Figure 14.

12

34

56

78

9

UE 1

UE 2

UE 30

1

2

3

4

5

6

Priority Metric

Resource Unit Index

UE 1

UE 2

UE 3

Figure 14: Frequency Non-Selective Scheduling

With such an approach the scheduler losses the ability to differentiate the best RB or group of RBs depending on the channel quality of individual resource blocks. Thus as a consequence the system can not take benefit of the corresponding link budget benefits.

The gains attributable to frequency selective scheduling are dependent upon the channel model and the HARQ operating point. The gains can be estimated by means of system level simulations performed both with and without consideration of frequency selective scheduling. The difference in cell edge performances dictates the link budget gain that can be attributed to frequency selective scheduling.

Table 15 summarizes the frequency selective scheduling gains, derived from simulations, for two HARQ operating points and three different channel models.

Table 15: Frequency Selective Scheduling Gains

Channel Model 1% pBLER


(low initial BLER)

VehA3 0.5 dB 1.8 dB

Consider as an example from Table 15:

10% iBLER HARQ operating point, VehA3 channel conditions FSS Gain = 1.8dB This means the throughput with FSS is 50% greater than the case without FSS

2.1.12 Macro Diversity Gain

As detailed in Section 2.1, a macro diversity combining gain considered for indoor distribution solutions that are comprised of multiple distributed antennas connected to the same sector. In such cases it is assumed that there is a degree of overlapping coverage

< LTE DIMENSIONING GUIDELINES – INDOOR LINK BUDGET> <JUL.2010> between adjacent antennas connected to the same sector and as such there is a statistical gain that helps partially mitigate the shadowing margin.

The default macro diversity combining gain for such deployment scenarios is 2.0dB.

2.2 Final MAPL and Cell Range

The final uplink link budget equations become:


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dBdBdB

dBdBdBdBdBm

sityMacroDiverRxRx

BodynPropagatioTxTxHMaxTX_PUSCdBmj(UL)

GainLossGain

ssLoLossesLossGainPC

And

dBdBdBdBdBm FSSHOShadowingIoTdBmj(UL) GainGainMarginMarginySensitivitC

For each service to be offered by the operator, this relationship allows computation of the maximum propagation losses that can be afforded by a mobile located at the cell edge, that is to say the Maximum Allowable Path Loss (MAPL):

dBdBdB

dBdB

dBdBdBdBdBdBm

sityMacroDiverFSSHO

ShadowingIoTdBm

BodyRxRxTxTxHMaxTX_PUSCdBj(UL)

GainGainGain

MarginMarginySensitivit

LossossLGainossLGainPMAPL

Transmit Power

Reference Sensitivity

Losses and Margins

Gains

•= MAPL

Interferencecell radius

Maximum Allowable Pathloss

Reference Sensitivity

Max UE transmit Power

Interference marginextra cell interference

Gains - Losses- Margins

Figure 15: Uplink Link Budget Elements

Considering the most demanding service for which contiguous coverage is to be offered, the following can be used to determine the maximum allowable cell range for deployment of the system:

)Service(UL102(UL)1(UL)dBj(UL)(UL)dB RLogKKMAPLMinMAPL

2.2.1 Propagation Model

K1 and K2 characterize the propagation model. For Indoor coverage, the following propagation models are used:



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Table 16: Default Alcatel-Lucent Indoor Propagation Models

Environment Description K1 K2

Open Parking Garage, Convention Center 36 - 8.55 x Log10( Hb )

Moderately Open Warehouse, Airport, Manufacturing 40 - 8.55 x Log10( Hb )

Mildly Dense Retail, Office Space w/ approx 80%

cubes/20% hard-walled offices 44 - 8.55 x Log10( Hb )

Moderately Dense Office Space w/ approx 50%

cubes/50% hard-walled offices 48 - 8.55 x Log10( Hb )

Dense Hospital, Office Space w/ approx

20% cubes/80% hard-walled offices

20 x Log10( 4..FMHz /300 )

52 - 8.55 x Log10( Hb )

FMHz represents the operating frequency in MHz. Hb is the height of the indoor antenna in meters.

Indoor propagation is notoriously difficult to estimate. A very simple statistical model such as this model should not be relied upon for accurate estimates of indoor cell range. Rather more accurate indoor propagation modeling tools or ideally field measurements should be used to validate the achievable cell range.

2.3 Uplink Budget Example

Table 17 presents an example of the uplink budget analysis for a moderately dense indoor environment for a range of services.

The key objective of the air interface coverage analysis is to formulate a link budget from which the per-service MAPLs and the corresponding cell ranges can be computed (see the rows in red in Table 17).

< LTE DIMENSIONING GUIDELINES – INDOOR LINK BUDGET> <JUL.2010> Table 17: Typical PUSCH link budgets for a RRH feeding a Passive Distribution Solution

in a Moderately Dense Environment at 700MHz (128kbps guaranteed at cell edge)

The cell ranges computed above are for an Alcatel-Lucent indoor propagation model (see section 2.2.1) for an 8m indoor antenna height, a 1.5m UE antenna height. Where PL=K1+K2xlog10(dm), K1=30.3 and K2=40.3.

Internal: The default ALU indoor link budget can be found on the intranet: Alcatel-Lucent LTE-FDD Link Budget.

Based on the services to be guaranteed at cell edge the limiting Maximum Acceptable Path Loss (MAPL) can be derived.

2.4 Uplink Common Control Channel Considerations

The main common channel consideration that should be assessed for an LTE network design is the Attach Procedure.

2.4.1 Attach Procedure

Figure 16 illustrates the procedure that the UE must go through to Attach to an LTE network. From a link budget perspective the limiting message from messages 1, 2, 3, 4, 5, 15 and 16 (that involve the air interface) must be considered to assess any link budget constraints.


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https://all1.us.alcatel-lucent.com/teams/nd-cc-radio/lte/03_Design%20toolbox/FDD/01%20-%20LTE%20FDD%20LKB%20Tool/Indoor



eNBUE MME

RACH Preamble (1)

Grant and TA (2)

RRC Connection Request (3)

RRC Connection Setup (4)

RRC Connection Setup Complete (5)

SGW PGW

Attach request (6)

Authentication (optional)/ security (7-8)Create Default Bearer

Request (9) CDB Request (10)

Attach accepted (13)

Create Default Bearer Response (12)

CDB Response (11)

RRC Connection reconfiguration (14)

RRC Connection reconfiguration complete (15)

Attach complete (16)

No MME Relocation

1st UL bearer packet

Update Bearer Request (20)

Update Bearer Response (21)

1st DL bearer packet

eNBUE MME

RACH Preamble (1)

Grant and TA (2)

RRC Connection Request (3)

RRC Connection Setup (4)

RRC Connection Setup Complete (5)

SGW PGW

Attach request (6)

Authentication (optional)/ security (7-8)Create Default Bearer

Request (9) CDB Request (10)

Attach accepted (13)

Create Default Bearer Response (12)

CDB Response (11)

RRC Connection reconfiguration (14)

RRC Connection reconfiguration complete (15)

Attach complete (16)

No MME Relocation

1st UL bearer packet

Update Bearer Request (20)

Update Bearer Response (21)

1st DL bearer packet

Figure 16: LTE Attach Procedure

The limiting message of the attach procedure over the air interface is message 3 (RRC Connection Request). This message utilizes 2 resource blocks with MCS 3, delivering an average effective data rate of 20.8 kbps after 5 HARQ transmissions. The SINR requirements for this message is -4.4 dB (including margins), based on link level simulation studies.

Figure 17 summarizes an uplink budget formulated for a moderately dense indoor environment in the 700MHz band. This link budget compares the Attach link budget with VoIP, 8, 32 and 64kbps services.


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Figure 17: LTE Link Budget for Message 3 of the LTE Attach Procedure (compared with VoIP, 8, 32 and 64kbps services

It can be seen from Figure 17 that the Attach link budget is only slightly more limiting than an 8kbps cell edge service, the difference is considered to be insignificant.


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3 DOWNLINK LINK BUDGET

For typical eNode-B output powers and deployment scenarios with the classical UE output power class of 23dBm, link budgets should remain uplink limited. The downlink cell edge performances depend primarily upon the scheduler parameters (e.g. tuning of the fairness of the proportional fair scheduler algorithm) or the available bandwidth (e.g. 10MHz vs 5MHz).

For the downlink, link budgets need to be carefully tuned with system level simulations to well assess the interference margin that is location dependent. The preferred approach by Alcatel-Lucent is to perform system level simulations to well assess the downlink performances with or without MIMO. Alcatel-Lucent extensively contributed to such system-level performances assessment at 3GPP and in the NGMN initiative.

In addition to system level simulations it is the preferred practice of Alcatel-Lucent to rely upon Radio Network Planning (RNP) analysis.

However, it is possible to formulate a reasonably meaningful downlink budget. The approach preferred by Alcatel-Lucent is as follows:

Downlink cell range is defined by the uplink cell edge service link budget, i.e. the same cell ranges as those considered for the uplink are also considered for the downlink. On the uplink the objective was to compute the cell range for a target data rate, on the downlink the objective is to compute the data rate for a known cell range.

Downlink throughputs computed for coverage reliabilities associated with each corresponding uplink service

Geometry distributions (see section 3.1.3) are used to determine the cell edge SINR for the PDSCH, from which an estimate of the downlink cell edge throughput can be made

Figure 18 illustrates the downlink link budget approach utilized by Alcatel-Lucent. Section 0 described the methodology used to compute the cell range for different uplink services. Some examples of such services and their relative cell ranges are illustrated in blue in Figure 18. Also shown in Figure 18 are the downlink data rate estimates, illustrated in purple, corresponding to the various uplink data rates.


RangeUL_Guar_Serv

128kbps (3RB) - guaranteed at cell edge

256kbps (4RB)

512kbps (9RB)

UL Rates

DL Rates

6281kbps (50RB)

8834kbps (50RB)

2033kbps (50RB)

Figure 18: Rationale behind the Downlink LKB Formulation

The example shown in Figure 18 is for a moderately dense indoor environment, indoor 0dBi omni UE configuration, cell range fixed for uplink 128kbps, 100% adjacent cell downlink resource block loading, no TMA. This example illustrates the concept behind downlink link budget approach that is described in this section.

Note: The diagram shown in Figure 18 is not to scale and does not include all rates.

3.1 Downlink Budget Parameters

3.1.1 SINR

The measure of quality used on the downlink is the SINR. It is important to note that no consistent standards or industry defined measure of SINR exists, that is a completely unambiguous and can be used as a concise reference measure of downlink signal quality in the field.

For example, the SINR can be quantified both with and without inclusion of a combining gain at the UE (the default for Alcatel-Lucent is to incorporate such a combining gain). While Alcatel-Lucent link level performances are quantified in terms of the SINR, the reference to be used, measured and validated in the field is the RSRQ (see section 3.1.2), which is unambiguously defined.

Unlike the uplink the downlink SINR performances are dependent on the UE location, i.e. the signal to interference plus noise ratio for the PDSCH channel, SINRPDSCH, is dependent on the user location. Thus for a given UE location, SINRPDSCH, for a number of transmit paths, PathDL, is given by:

(DL)j(DL)

DL)j_PDSCH(DLPDSCH NI

PathsCINRS

The worst performances will be experienced when the UE is at cell edge far from the eNode-B. The relationship between the SINRPDSCH, and downlink throughput is discussed in more detail in section 3.1.4.


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< LTE DIMENSIONING GUIDELINES – INDOOR LINK BUDGET> <JUL.2010> Cj_PDSCH(DL) is the PDSCH power received at the UE located at the uplink service cell range, RService(UL), per Resource Element (RE) from the UE’s serving eNode-B, that is transmitting with its maximal power and is given by:

PDSCHdBmj_RS(DL)dBm)j_PDSCH(DL OffsetCC

dBdBdBdBdB

dBdBdBdB

HOShadowingsityMacroDiverRxRx

Body)UL(ServicenPropagatioTxTxRSdBmj_RS(DL)

GainMarginGainLossGain

LossRLossesLossGainEPREC


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where

EPRERS is the Energy Per Resource Element for the reference symbol (see Section 3.1.6)

OffsetPDSCH is the margin by which PDSCH RE’s are offset in power from the EPRERS GainTx and LossTx, represent the gains and losses at the transmitter side such as the

eNode-B antenna gain and the feeder losses between the eNode-B and the antenna, GainRx and LossRx, the gains and losses at the receiver side such as UE antenna gain, LossBody is the body loss induced by the users proximity to the UE, typically 3dB

body losses are considered for voice services and 0 dB for data services (handset position is far from the head when using data services),

The downlink MAPL, MAPL(DL)dB, that corresponds to an uplink service cell range, RService(UL) (as computed in section 2.2), is dependent upon the propagation model differences (K1(DL) & K2(DL)) due to the frequency duplex difference between uplink and downlink,

GainMacroDiversity is the gain considered for solutions that are comprised of multiple distributed antennas connected to the same sector, i.e. this is a combining gain (see Section 2.1.12),

MarginShadowing is a margin that compensates for the slow variability in mean path loss about that predicted using the propagation model, e.g. Hata (see section 3.1.7)

GainHO is a handoff gain or best server selection gain that models the benefits due to the ability to reselect to the best available serving site at any given location (see section 3.1.7)

)Service(UL2(DL)1(DL)nPropagatio RlogKKLossesdB .

Ij(DL), is the average received interfering power at the UE from all adjacent cells per RE. Averaging is based upon the average number of RE allocated to the various interfering channels (see Section 3.1.5 for details of the RE distribution).

SINR_ShadPercentileDLj_RS(DL)DLAvg)j_Other(DLAvg)j_PDSCH(DLdBmj(DL) inargMGeometry -PathsC LoadingCCIAvg

where

Ij_PDSCH(DL) is the average interference contribution due to RE’s allocated to PDSCH channels and is given by:

TTI_Total

TTI_PDSCHPDSCHdBmj_RS(DL)Avg)j_PDSCH(DL RE

REOffsetCC ,

Ij_RS(DL) is the average interference contribution due to RE’s allocated to RS’s and is given by (Note: The 3rd and 4th antennas, if present, only transmit the RS on half the number of RE’s as the 1st two antennas):

TTI_Total

TTI_RSDLj_RS(DL)j_RS(DL) RE

RE1Else75.0Then,4PathsIfCC

Avg ,


Ij_Other(DL) is the average interference contribution due to RE’s allocated to PDCCH, PCFICH, PHICH and P/S-SCH, PBCH channels and is given by (Note: it is assumed that the interference due to PDCCH from adjacent cells will be reduced with reduced loading):

TTI_Total

TTI_OtherPDCCHj_RS(DL)Avg)j_Other(DL RE

REOffsetCC ,

LoadingDL is the assumed average resource blocking loading of adjacent cells on the downlink.

GeometryReliability, represents the downlink geometry that corresponds to the UL cell range, RService(UL) (discussed in more detailed in section 3.1.3),

MarginShad_SINR is the shadowing margin applied to the SINR distribution to account for the fact that the desired and interfering signals are not perfectly correlated with each other (see section 3.1.7)

The thermal noise for NRB resource blocks is given by:

SC10UEthdBm)DL( WLog10FNN

where

Nth is the thermal noise density (-174dBm/Hz), FUE is the noise figure of the UE receiver (8dB by default), WSC is the bandwidth used by one subcarrier, each of a 15kHz bandwidth.

3.1.2 RSRQ

While, SINRPDSCH, is a meaningful measure of the cell edge quality (see section 3.1.1), this is not a measure that is standardized by 3GPP and as such is somewhat open to interpretation when it comes to measurement in the field, i.e. whether a power combining gain is accounted for in the computation of SINR. The standardized measure of the downlink quality is RSRQ (Reference Symbol Receive Quality) and is given by:

TotalRB10)Service(UL RSSI)N(log10 SRPRRSRQ

where

RSRP is the Reference Signal Received Power at the UE from its serving cell and is given by Cj_RS(DL) (see above)

NRB is the maximum number of RB’s for the consider carrier bandwidth RSSITotal is the total received power at the UE from its serving cell and all adjacent

cells across the entire bandwidth and is given by:

RB#sSubCarrierNISSIRRSSI RB)DL()DL(jCell_OwnTotal

SubCarriersRB is the number of sub carries per RB, this is defined by the standards to be 12 sub-carriers per RB

RSSIOwn_Cell is the average power received at the UE from its serving cell per RE. The averaging is based upon the average number of RE allocated to the various interfering channels (see Section 3.1.5 for details of the RE distribution) and is given by:

SINR_ShadPercentileDLj_RS(DL)DL)j_Other(DL)j_PDSCH(DLOwn_Cell inargMGeometry -PathsCLoadingC CRSSIAvgAvgAvg

Note: RSRQ is dependent upon the number of downlink transmit paths, PathsDL.


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< LTE DIMENSIONING GUIDELINES – INDOOR LINK BUDGET> <JUL.2010> 3.1.3 Geometry

The geometry at a specific UE location is defined as the ratio between the total power received from the eNode-B serving that location and the total power received from all adjacent eNode-Bs, under the assumption that all eNode-Bs are transmitting at the same power.

Figure 19: Signals Contributing to the Downlink Geometry (serving site is solid green and adjacent sites are dashed maroon color)

The geometry at a given UE location is given by:

AllSiteAdjacent

SiteServing

PowerRx

PowerRxGeometry

Consequently the geometry is influenced by the parameters such as the relative positioning of adjacent sites, degree of overlapping coverage, variability of the propagation environment and directivity of eNode-B and UE antennas.

The geometry distributions considered in the link budget are based upon the geometry distributions computed with the 9955 Radio Network Planning (RNP) tool, for a range of LTE trial network deployments, across a number of markets. These geometry distributions are considered to be representative of the typical geometries that are expected in a well optimized LTE deployment.

Note: The downlink geometries do not account for lognormal shadowing as such an additional shadowing margin must be applied to SINR and RSRQ computations (see section 3.1.7)

A significant factor influencing the geometry distribution is the directivity and placement of the UE antenna. While the majority of LTE deployments are focused on a typical cellular mobility deployment model there is also interest in considering fixed wireless deployment scenarios where it is not uncommon to consider a directional non-zero gain UE antenna that can be roof mounted and directed at the best serving site.

Figure 20 provides some examples of the geometry distributions used in the downlink budget for omni directional as well as direction UE antenna configurations.

Internal: Currently the indoor link budget uses a geometry distribution for a typical macro cellular deployment, clearly this is a gross approximation that will be rectified in the future with indoor deployment specific geometry distributions.


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0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

-5 dB 0 dB 5 dB 10 dB 15 dB 20 dB 25 dB 30 dB 35 dB 40 dB

Geometry

Indoor - 0 dBi - Omni

Outdoor - 4 dBi - Direc.



Figure 20: Geometry Distributions Considered in Link Budget (for Different UE Antenna Configurations)

In the computation of the Cell Edge SINR (as mentioned in section 3.1.1), the average received interfering power, Ij(DL), at the UE from all adjacent cells per RE is given by:

SINR_ShadPercentileDLj_RS(DL)DLAvg)j_Other(DLAvg)j_PDSCH(DLdBmj(DL) inargMGeometry -PathsC LoadingCCIAvg

The percentile of the geometry distribution shown in Figure 20 is approximated to be dependent upon the targeted coverage reliability, PCov, and the percentage of the overall coverage area for which the downlink service is to be guaranteed.

2e(UL)eed_ServicUL_Guarant

2(UL)UL_Service

CovR

RPPercentile

Where RUL_Service(UL) is the cell range for the uplink service for which the equivalent downlink data rate is being computed and RUL_Guaranteed_Service(UL) is the uplink service that is guaranteed at the cell edge on the uplink. See the example in Figure 21 (based on the uplink budget summarized in Table 17) where RUL_Guaranteed_Service(UL) = 64m is for a 128kbps cell edge service and the Percentile is computed for the UL cell range, RUL_Service(UL) = 52m, that corresponds to an uplink 256kbps service.


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RangeUL_Guar_Serv(UL)= 64m

128kbps (3RB) - guaranteed at cell edge

256kbps (4RB)

UL Rates

DL Rates

6281kbps (50RB)

2033kbps (50RB)

RangeUL_Serv(UL)= 52m

Figure 21: Example of Geometry Percentile Computation for 256kbps UL Cell Range within a 128kbps Coverage Footprint

In this example the cell area reliability is 95%. Thus the percentiles can be calculated as follows:

For 128kbps uplink cell range, 95% x 0.642 / 0.642 = 95% For 256kbps uplink cell range, 95% x 0.522 / 0.642 = 62%

Referring to Figure 22, estimates of the corresponding geometries can be read off the chart for these two uplink cell ranges, i.e. percentiles of 95% and 62% yield GeometryPercentile values of -2.2 & 4.1dB, respectively, for a 0dBi omni UE configuration.


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0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

-5 dB 0 dB 5 dB 10 dB 15 dB 20 dB 25 dB 30 dB 35 dB 40 dB

Geometry

Indoor - 0 dBi - Omni



Outdoor - 10 dBi - Direc.95% Geometry %’ile

-2.2dB

62% Geometry %’ile

4.1dB

Figure 22: Example of Geometry Distributions

3.1.4 Downlink SINR Performances

The downlink SINR figures, like those for the uplink (see section 2.1.5), are derived from link level simulations or from equipment measurements (lab or field measurements). They depend on the UE performance, radio conditions (multipath fading profile, mobile speed), antenna scheme (TxDiv/SFBC, spatial multiplexing, closed loop rank 1, etc), targeted data rate and the quality of service. Figure 23 illustrates a sample set of link level simulation results for the full set of MCS Indices for a wide range of SINR conditions.


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4000 kbps

6000 kbps

8000 kbps

10000 kbps

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-15 dB -10 dB -5 dB 0 dB 5 dB 10 dB 15 dB 20 dB 25 dB 30 dB

SINR

Thro

ugh

put

MCS 0 MCS 1 MCS 2 MCS 3MCS 4 MCS 5 MCS 6 MCS 7MCS 8 MCS 9 MCS 10 MCS 11MCS 12 MCS 13 MCS 14 MCS 15MCS 16 MCS 17 MCS 18 MCS 19MCS 20 MCS 21 MCS 22 MCS 23MCS 24 MCS 25 MCS 26 MCS 27

Figure 23: Example of link level simulations results for downlink, NRB=25, 10MHz Bandwidth (TxDiv / SFBC)

3.1.4.1 Multipath Channel

The equivalent channel model to that considered on the uplink (see section 2.1.5.1) is also assumed on the downlink, i.e. EVehA 3km/h.

3.1.4.2 Number Resource Blocks & Modulation & Coding Scheme

For the uplink, the focus was to determine the required SINR for a given target data rate (see section 2.1.5.4). For the downlink, the reverse is performed, the data rate that is achievable for a given SINR value is determined. However, the same principles apply.

For a given SINR and Number of Resource Blocks, NRB, there will be an optimal Modulation & Coding Scheme Index (MCS) that maximizes the data rate while also satisfying the targeted HARQ operating point.

The same process is used for determining the Transport Block Size (TBS) that corresponds to a given combination of NRB and MCS Index (as described in section 2.1.5.2, with the exception that the PDSCH version of the MCS to TBS index mapping is used instead of the PUSCH version shown in Table 3).

3.1.4.3 Hybrid Automatic Repeat request (HARQ)

As mentioned in section 2.1.5.3, asynchronous adaptive HARQ is used for the downlink where transmission attributes such as the modulation and coding scheme, and transmission resource allocation in the frequency domain, can be changed at each retransmission in response to variations in the radio channel conditions.

Like the uplink there are multiple HARQ operating points that can be utilized (with the corresponding tradeoffs), the current recommended operating point for the downlink is a 10% iBLER.

Figure 24 illustrates the average effective L2 post HARQ frame averaged throughput versus the BLER for the 1st HARQ transmission for MCS index 27.


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13 dB 15 dB 17 dB 19 dB 21 dB 23 dB 25 dB

SINR

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ough

put

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BLE

R

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INR

13.3 Mbps Throughput

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BLE

R

Throughput

BLER

10 % BLER

19.9

dB S

INR

13.3 Mbps Throughput

Figure 24: Throughput mapping for 19.9dB SINR, respecting 10% iBLER HARQ operating point for 25 RB, MCS Index 27, TxDiv / SFBC and 5MHz Bandwidth

For the recommended 10% iBLER HARQ operating point it can be seen that an SINRPDSCH = 19.9dB is required which corresponds to a throughput of 13.3Mbps.

This is an example for MCS index 27, the same can be done for the full range of MCS indices resulting in the plot shown in Figure 25 in Section 3.1.4.4.

3.1.4.4 Selection of the Optimal MCS Index

In order to select the optimal MCS index for the SINRPDSCH conditions at a specific UE location. First the same process to that identified in Figure 24 must be performed for the full range of MCS indices. Figure 25 illustrates for a range of SINRPDSCH values the corresponding optimal MCS indices and post HARQ average effective frame throughputs for a 10% iBLER HARQ operating point.


0 kbps

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20000 kbps

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ugh

put

MCS 0

MCS 5

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10dB

SIN

R13 Mbps

MCS 16

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MCS 0

MCS 5

MCS 10

MCS 15

MCS 20

MCS 25

MCS 30

Throughput

MCS Index

10dB

SIN

R13 Mbps

MCS 16

Figure 25: Optimal MCS Index Selection for a 10dB cell edge SINR, 25 RB, 5MHz Bandwidth, TxDiv / SFBC

Assuming a specific UE location the cell edge SINR can be computed (see section 3.1.1), SINRPDSCH, the next step is to select the optimal MCS index for such conditions. As an example here it is assumed that for the considered UE location the SINRPDSCH is computed to be 10dB.

Referring to Figure 25 it can be seen that the optimal MCS Index = 16 and the corresponding post HARQ throughput is 13Mbps for SINRPDSCH = 10dB.

Note: This relationship has been derived based on TxDiv / SFBC link level performances. On top of these performances there will be additional gains in very good channel conditions, due to spatial multiplexing / Rank 2 MIMO (this is discussed in more detail in section 3.1.4.6).

3.1.4.5 Downlink Explicit Diversity Gains

The default SINR performances considered in the Alcatel-Lucent downlink budgets are for a 2x2 Tx Diversity / SFBC configuration, these performances account for SFBC pre-coding gains and a 2RxDiv gain at the UE.

The choice to base the link budget on TxDiv / SFBC link level performances was been made as the channel conditions typical of the cell edge are not generally conducive to effective utilization of Spatial Multiplexing.

However, when in very good SINR conditions, a spatial multiplexing is applied in the downlink budget. This gain is applied on top of the 2x2 TxDiv/SFBC performances (see section 3.1.4.6).

Note: An additional over the air power combining gain is also considered on the downlink, e.g. a 3dB gain is applied in the downlink budget for PathsDL≥2 to account for the fact that the same RE’s are transmitted on each transmit path (with the exception of the RS).

Note: Most indoor distribution solutions (see section 2.1.2) are unlikely to support 2 RF paths, as such the SINR performances in such cases must be offset to account for the lack of receive diversity at the eNode-B depending on the number of transmit paths, as detailed in Table 18:


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Table 18: Approximation for Impact of <> 2 Transmit Paths

Downlink Transmit Paths, PathDL SINR Impact

1 path -1.0 dB

2 paths 0.0 dB

4 paths 1.0 dB

Warning: the SINR impact detailed in Table 18 is a very rough approximation to the expected performances with 1 and 4 transmit paths. To ensure higher confidence in the link budget results requires consideration of dedicated link level results for those configurations.

3.1.4.6 Spatial Multiplexing / MIMO Gain

As outlined in section 3.1.4.5, the underlying link level performances used to select the optimal MCS Index and the corresponding throughput for a given number of resource blocks are for a TxDiv / SFBC configuration. In very good channel conditions (channel rank >1 and high SINR) an additional spatial multiplexing gain on top of the underlying link level simulation performances is applied.

Such a gain is based upon a comparison of the TxDiv / SFBC link level performances with the link level performances for a Rank2 spatial multiplexing configuration.

Figure 26 illustrates a summary of the gain computed from such a comparison for two different antenna correlation assumptions (low and high) as well as two different channel conditions (VehA3 and VehA50km/h):

1.0

1.2

1.4

1.6

1.8

2.0

2.2

10 dB 15 dB 20 dB 25 dB 30 dB 35 dB 40 dB 45 dB

SINR

Ran

k 2

Sp

atia

l Mu

ltip

lexi

ng

Gai

n VehA 3km/h - Low

VehA 3km/h - Med

VehA 50km/h - Low

VehA 50km/h - Med

Figure 26: Gains Associated with Spatial Multiplexing (MIMO Rank 2)

Note: The antenna correlation that best represents what has been seen in the field to date is best represented by the medium correlation assumptions.

Internal: The above note is for outdoor deployments. Indoor measurements are not yet available to better refine this assumption for typical indoor deployments.


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From Figure 26 it can be seen that spatial multiplexing gains become significant beyond an SINRPDSCH = 15dB (the spatial multiplexing switch point) and progressively increase with increasing SINRPDSCH. The precise gain attributable to spatial multiplexing is dependent upon the SINR, the antenna correlation and the channel model.

As an example, consider an SINRPDSCH = 35dB, medium antenna correlation and VehA3 channel conditions. Referring to Figure 26 the estimated spatial multiplexing gain is slightly less than 1.8. If we the TxDiv / SFBC link level performances indicated a 30,440kbps throughput for 50RB and a 10MHz bandwidth then the final throughput after accounting for the spatial multiplexing gain would be 30,440kbps x 1.78 = 54,174kbps.

Note: One thing that is not possible to compute from a link budget analysis is whether the channel can support rank 2 transmissions. The best that can be done is to assume/approximate that with a high SINR there is a reasonable probability that the channel rank will also be sufficiently good. For example, high SINR is most commonly observed close to the serving eNode-B and so is higher channel rank.

3.1.5 Resource Element Distribution

Computation of the downlink SINR and RSRQ detailed in sections 3.1.1 and 3.1.2 is dependent upon the average resource element allocation to the various downlink channels.

An example of the RE distribution for 2 transmit paths, Control Format Indicator (CFI) = 3, and 10MHz bandwidth is summarized in Table 19.

Table 19: Example Average RE Distribution Across the 14 OFDM Symbols of a Single TTI (2 Transmit Paths, CFI=3, 10MHz Bandwidth)

Type of RE OFDM Symbol RERS

1 REP-SCH RES-SCH REPBCH4 REPDCCH REPCFICH REPHICH REPDSCH_A REPDSCH_B REUnused

6

Sym 0 100 RE 0 RE 0 RE 0 RE 300 RE5 16 RE 84 RE 0 RE 0 RE 100 RE

Sym 1 0 RE 0 RE 0 RE 0 RE 600 RE 0 RE 0 RE 0 RE 0 RE 0 RE




Sym 5 0 RE 0 RE 25 RE3 0 RE 0 RE 0 RE 0 RE 0 RE 571 RE 4 RE

Sym 6 0 RE 25 RE2 0 RE 0 RE 0 RE 0 RE 0 RE 0 RE 571 RE 4 RE








Notes: 1 Two RE allocated per Resource Block (RB) for OFDM symbols 0, 4, 7 and 11 2 P-SCH is always located in the last OFDM symbol of the 1st and 11th slots of each radio frame for the center 6 RB's (figures averaged across 1 radio frame)

< LTE DIMENSIONING GUIDELINES – INDOOR LINK BUDGET> <JUL.2010> 3 S-SCH is always located in the last OFDM symbol of the 2nd and 12th slots of each radio frame for the center 6 RB's (figures averaged across 1 radio frame) 4 For the centre 6 RB's (72 subcarriers) of the 2nd slot of each radio frame the non-RS RE are used for the PBCH (figures averaged across 1 radio frame) 5 PDCCH RE after accounting for RS, PCFICH and PHICH REs 6 There remains some unused RE due primarily to RE reserved for RS transmission on the 2nd transmit path and also some RE reserved around the SCH RE

A summary of the average number of Resource Elements (REs) that are transmitted per TTI for 1, 2 and 4 transmit paths is presented in Table 20. This is based on equivalent analyses to that presented in Table 19. The averaging is performed over one radio frame (10msec).

Table 20: Average Number of RE Transmitted per TTI per Transmit Path

1 Tx Path 2 Tx Paths 4 Tx Paths

RETotal_TTI 8390 RE 7990 RE 7790 RE

REPDSCH_TTI 6216 RE 5916 RE 5816 RE

RERS_TTI 400 RE 400 RE 400 RE

REOther_TTI 1774 RE 1674 RE 1574 RE

REPDCCH_TTI 1600 RE 1500 RE 1400 RE

RESCH_BCH_TTI 74 RE 74 RE 74 RE

REPCFICH_PHICH_TTI 100 RE 100 RE 100 RE

3.1.6 Energy Per Resource Element (EPRE)

The Energy Per Resource Element (EPRE) is the transmitted energy associated with a single resource element. This parameter is dictated by the overall output power setting for the eNode-B, the carrier bandwidth and the product variant.

For each product variant the following set of information is defined (as summarized in Table 21):

PowerRef – the reference downlink eNode-B transmit power per transmit path BWRef – Reference bandwidth EPRERS(Ref) –the EPRERS for the corresponding reference power and bandwidth

Table 21: Product EPRE Reference

Hardware PowerRef BWRef EPRERS(Ref)

RRH40 30 W 10 MHz 17.0 dBm

TRDU40 40 W 10 MHz 18.0 dBm

As it is possible to use the same power amplifier with a different power setting, PowerCurrent and different bandwidth, BWCurrent, in such cases the EPRERS is given by:

Current

fRe10

Current

fRe10)f(ReRSRS BE

BWLog10

PowerPower

Log10EPREEPRE


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< LTE DIMENSIONING GUIDELINES – INDOOR LINK BUDGET> <JUL.2010> For example, consider for PowerCurrent = 40W and BWCurrent = 20MHz. The ERPERS for RRH40 hardware is given by:

dBm2.15MHz20MHz10

Log10W40W30

Log10dBm17EPRE 1010RS

Table 22 summarizes the power offsets from the EPRERS power setting for channels other than the RS:

Table 22: Power Offsets from EPRERS

RE Type Power Offset from EPRERS

OffsetPDSCH 0.0 dB

OffsetPDCCH 1.0 dB

OffsetSCH/BCH 0.0 dB

3.1.7 Shadowing Margin & Handoff Gain

For the downlink the same assumptions are considered to hold true, for reasons of reciprocity, when computing the received signal level at the UE, as they do on the uplink when computing the received signal level at the eNode-B. Thus the same relationships and rationale to those presented in section 2.1.9 (shadowing margin) and section 2.1.10 (handoff gain) are assumed to be equally applicable on the downlink.

The only exception arises when considering the SINR and RSRQ on the downlink. For such computations the above mentioned shadowing margin and handoff gains are applied equally to both the desired and interfering signals and thus the net effect is only to bring the signal closer to the noise floor. In reality the desired and interfering signals are not perfectly correlated with each another.

To account for such non-ideal correlation an approximation is applied in the downlink link budget to account for an additional shadowing margin on the SINR and the RSRQ. The shadowing standard deviation considered for the SINR shadowing margin is determined by the standard deviation considered for the given environment. Table 23 summarizes the mapping from the environment shadowing standard deviation to that considered for the computing the SINR shadowing margin.

Table 23: Mapping from Environment Shadowing Standard Deviation to the Shadowing Standard Deviation Used for Computing SINR Shadowing Margin

Environment Shadowing Std. Dev.

DL SINR Shadowing Std.

Dev.

6 dB 0 dB

7 dB 1 dB

8 dB 2 dB

44The same method as detailed in section 2.1.9 is used to compute the SINR shadowing margin based on the SINR shadowing standard deviations presented in Table 23.


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< LTE DIMENSIONING GUIDELINES – INDOOR LINK BUDGET> <JUL.2010> Note: Close agreement has been observed when comparing field measured SINR and RSRQ distributions with predicted SINR and RSRQ distributions that account for a shadowing margin based on the standard deviations presented in Table 23.

3.2 Downlink Budget Example

Table 24 presents some example of the entire downlink budget analysis for a dense indoor environment for a range of services. Note that this is the downlink link budget that corresponds to the uplink budget presented in Table 17.

The key objective of the downlink link budget analysis is to formulate estimates of the data rate expectations for the cell ranges of some nominal uplink data rates (see the rows in red in Table 24).

Table 24: Typical PDSCH link budget for a RRH feeding a Passive Distribution Solution in a Moderately Dense Environment at 700MHz (uplink 128kbps guaranteed at cell edge)

It is important to note that the downlink data rate estimates presented in the last row of Table 24 are achievable with 95% coverage reliability over the downlink cell ranges indicated in the row titled “UL Service Cell Range”. Note also that the same data rates are achieved over the entire coverage area (70m cell range) with reduced reliabilities for the higher data rates.


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Internal: The default ALU link budget can be found on the intranet: Alcatel-Lucent LTE-FDD Link Budget.





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4 SUMMARY

This document has introduced the detailed formulation of Alcatel-Lucent’s LTE link budget for indoor deployments for both the uplink and the downlink.

LTE coverage is not considered to be limited by the downlink for typical eNode-B output powers and deployment scenarios. Link budgets should remain uplink limited and as such link budgets are used by Alcatel-Lucent primarily to derive the expected LTE performances at the cell edge on the uplink and compare them with legacy systems in the case of an overlay of an existing network and/or the required number of radiating points for a Greenfield deployment. In the case of overlay deployments, this allows for the estimation of the viability of reuse of existing distributed antenna systems (additional constraints such as space for hardware deployment, etc, have to be considered on top of this).

The downlink link budgets that have been detailed here are indicative of what rates are achievable within the corresponding uplink service coverage areas. It is important to understand that downlink cell edge performances are strongly dependent upon scheduler parameters (e.g. tuning of the fairness of the proportional fair scheduler algorithm) or the available bandwidth (e.g. 10MHz vs 5MHz)

Downlink performances in the link budget are based only on long term average PDSCH SINR values and do not account for dynamic channel variations that can be addressed with frequency selective scheduling functionalities

Better estimates of downlink performances can be achieved by means of system level simulations and/or Radio Network Planning (RNP) analysis.

END OF DOCUMENT

03 - lte dimensioning guidelines - indoor link budget - fdd - ed1.1 - internal

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