08_RA41218EN70GLA0_AMC.pdf

Nokia Academy LTE Radio Parameters 1 [RL70] Adaptive Modulation and Coding

RA41218EN70GLA0

© Nokia Solutions and Networks 2015

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Module Objectives

After completing this learning element, the participant should be able to describe discuss and analyze:

• Principles of OLQC • DL and UL Adaptive Modulation and Coding • UL link adaption

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Index • Outer Loop Quality Control

• DL Adaptive Modulation and Coding (AMC) • UL Adaptive Modulation and Coding (AMC) • Inner Loop Link Adaptation (ILLA) • Outer Loop Link Adaptation (OLLA)

• Adaptive Transmission Bandwidth (ATB) • Extended UL Link Adaptation (E-ULA) • Fast Uplink Adaptation (F-ULA)

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OLQC – CQI Adaptation Outer Link Quality Control (OLQC) Adapts the channel quality information that is used by the scheduler and link adaptation

to achieve the target block error ratio (BLER) for the first transmission of a Transport Block. • OLQC compensates any non-idealities of the link adaptation : • CQI estimation error of the UE

• CQI quantization error • CQI reporting error • Time delay between CQI measurement and the reception of the subsequent data block • CQI interpolation error • Errors due to CQI averaging of PRBs

dlOlqcEnable Enable/disable OLQC

LNCEL; false/true; true

- dlOlqcEnable parameter is used to enable/disable the outer link quality control. When outer link quality control is disabled then the corrected CQI values correspond to the reported CQI values.

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OLQC – CQI Adaptation • The picture below shows the principle of CQI adaptation

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OLQC – CQI Adaptation Single Code Word For a correct received transport block the CQI report will be increased by a value CQIstepup For an incorrect transport block the value will be decreased by CQIstepdown

No change will be done when no ACK/NACK is available or when it is a retransmission of the corresponding transport block. A maximum and a minimum CQI offset is defined (called DCQImax and DCQImin) in order to suppress very large fluctuations that may arise in extreme situations

CQIcorrected ( x, t )  CQIreported ( x, t )  CQI(t ) . for first HARQ feedback  ACK, min( CQI(t  1)  CQIstepup, CQImax ),  CQI(t )  max( CQI(t  1)  CQIstepdown, CQImin ), for first HARQ feedback  NACK, CQI(t  1), for first HARQ feedback  N/A.  dlOlqcDeltaCqiIni, dlOlqcDeltaCqiMax, dlOlqcDeltaCqiMin, dlOlqcDeltaCqiStepUp Hardcoded values

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OLQC – CQI Adaptation Two Code Words CQIcorrected ( x, t )  CQIreported ( x, t )  CQI(t ) .

min(CQI(t  1)  CQIstepup , CQImax ),  max(CQI(t  1)  CQIstepdown , CQImin ), min(max(CQI(t  1)  (CQIstepup  CQIstepdown ) / 2,  CQI(t )  CQImin ), CQImax ), min(CQI(t  1)  CQIstepup , CQImax ),  max(CQI(t  1)  CQIstepdown , CQImin ), CQI(t  1), 

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for new transmission HARQ feedbacks  ACK *  ACK*, for new transmission HARQ feedbacks  NACK * *  NACK * *, for new transmission HARQ feedbacks  ACK *  NACK * *, for new transmission HARQ feedbacks  ACK *  N/A, for new transmission HARQ feedbacks  NACK * *  N/A, for new transmission HARQ feedbacks  N/A  N/A.


OLQC – CQI Adaptation • OLQC algorithm targets to achieve a Target DL BLER (dlTargetBler)

• Based on the Target BLER, OLQC will determine whether the reported CQI is increased or decreased • CQI offset is defined by considering the CQI increase and decrease steps which should be balanced.

• Assuming that a CQI decrease will occur with a probability BLER target for the first transmission whereas a CQI increase occurs with the complementary probability (1-BLERtarget) the balance equation can be formulated as:

(1  BLER target )  CQIstepup  BLER target  CQIstepdown.

• Therefore, CQIstepdown can be calculated from the parameters CQIstepup and the dlTargetBler as:

CQIstepdown  CQIstepup 

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1 - BLER target BLER target

dlTargetBler

.

Target BLER DL

LNCEL; 0.1...99.9 %, step 0.1 % : default 10%





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DL AMC The target of the DL Adaptive Modulation and Coding (AMC) algorithm is to improve system capacity, peak data rate and coverage reliability The transmitted signal by a particular user is modified to account for the signal quality variation through link adaptation. The aim of the link adaptation is to estimate the transport block size for a UE and a certain set of allowed resource blocks (frequency resources) for transmission For the Downlink Data Channel a fast Adaptive Modulation and Coding (AMC) functionality based on UE reported CQI is performed by the AMC algorithm AMC selects a suitable Modulation and Coding Scheme (MCS) for the PRBs/RBGs assigned to a UE as indicated by the downlink scheduler.

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DL AMC DL AMC is enabled via

Start

dlamcEnable Retrieve Default MCS

For retransmissions the same MCS as for the

original transmission is

Dynamic AMC active? No Yes

applied

HARQ retransmission?

Yes

For new transmissions the MCS is decided based on CQI reports from the UE

No Use default MCS

Determine averaged CQI value for allocated PRBs

Determine MCS

dlamcEnable Enable Adaptive Modulation and Coding in DL LNCEL; true, false ; true

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End


Use same MCS as for initial transmission

DL AMC MCS Selection for new Transmissions For the first transmissions where no previous CQI information is available from the UE the DL AMC will provide the initial MCS to be used for the UE • Initial MCS is specified by iniMcsDl

-

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If DL AMC is disabled via dlamcEnable, then no link adaptation will be performed and a fixed MCS shall be applied according to iniMcsDl (Initial MCS for the DL) and the applied MCS shall never be changed over the time

dlamcEnable

iniMcsDl

Enable Adaptive Modulation and Coding in DL LNCEL; true, false ; true

Initial MCS in DL LNCEL; 0…28; 1 ; 4

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DL AMC MCS Selection for new Transmissions • In case of the averaged CQI value falling in-between two CQI indices with different corresponding modulation scheme, the scheme with the lower modulation order will be chosen

• For dual codeword transmission link adaptation has to be performed per codeword if CQI information per codeword is available (i.e., for closed loop MIMO transmission mode). • If only wideband CQI information is available for a UE the corresponding MCS level can be mapped directly (without a preceding averaging step). • If no new CQI values were received for a UE, and the UE is scheduled nevertheless, the MCS shall be determined as described above provided the latest available CQI information is not older than dlamcTHistCqi • If dlamcTHistCqi is exceeded (or CQI values are not yet available) the initial MCS (iniMcsDl) shall be applied. dlamcThistCqi

iniMcsDl Initial MCS in DL LNCEL; 0…28; 1 ; 4 16

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Time in TTIs for which historical CQI is remembered in AMC Vendor-specific parameter





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UL AMC and ATB • Used to adapt PUSCH to different link conditions by variable modulation and coding scheme, and variable bandwidth • Nokia Implementation • Inputs • Simple BLER based algorithm to select best - Ack/Nack information MCS according to UE specific Radio - SINR Measurements Conditions - Power Headroom reports • SINR Measurements are not required, only HARQ Ack/Nak output signaling used • Outputs - modulation

• Target BLER adjustable

- code rate

• Emergency Downgrade/Upgrade Feature combating very high or low BLER peaks

- maximum amount of PRBs

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• Adaptive Transmission Bandwidth (ATB) for controlling maximum PRB amount based on power headroom reports


UL AMC ulamcAllTbEn O&M switch for enabling/disabling the counting of all TBs instead of the 1st transmission TB for defining UL AMC inner loop factor. LNCEL; true, false; true

- The uplink AMC shall consist of 2 main components: 1.

An outer loop LA (OLLA) acting on the 1st Transmission Errors on TBs

2.

An inner loop LA based on BLER acting on either 1st Transmission Errors of TBs or on all TBs transmission errors derived from HARQ process.

- UL inner loop LA is a slow LA which will be performed every ulamcSwitchPer

- OLLA is an event based driven LA and will provide the capability to adjust to fast changing radio conditions by performing emergency downgrades or fast upgrades of the MCS

ulamcSwitchPer Period in sent Transport Blocks TBs when UL Inner Loop LA should be executed LNCEL; 10…500; 10; 30 TBs

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UL AMC - UL AMC can be enabled/disabled with actUlLnkAdp - If UL AMC is disabled, then no LA will be performed and a fixed MCS shall be applied according to iniMcsUl (Initial MCS for the UL) and the applied MCS shall never be changed over the time - If UL AMC is enabled then the data transfer of every UE shall start with iniMcsUl and the MCS shall change over time according to radio conditions. iniMcsUl - UL AMC shall provide the following functions: Initial MCS in UL LNCEL; 0…20; 1; 5

• BLER averaging

• OLLA which provides Emergency Downgrade (EDG) and Fast Upgrade (FUG) Events • MCS selection based on BLER providing the optimum MCS depending on radio link conditions

• UL ATB derived from selected MCS according to radio conditions. UL ATB process results in an upper PRB allocation limit submitted to the UL scheduler.

actUlLnkAdp Activates Uplink Link Adaptation and defines Link Adaptation mode LNCEL; off (0), slowAmcOllaATB (4), eUlLa (5), fUlLa (6); eUlLa (5)

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UL AMC - UL AMC shall select the MCS to be employed from the table below according to the radio conditions

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MCS Index I MCS

Modulation Order

TBS Index

Qm'

I TBS

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

2 2 2 2 2 2 2 2 2 2 2 4 4 4 4 4 4 4 4 4 4 6 6 6 6 6 6 6 6

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

Redundancy Version rvidx 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 2 3

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•

•

•

64 QAM modulation is not (yet) available in the UL, therefore selected MCS’s will be restricted from MCS 0 to MCS 20 (without LTE829) LTE829, introduced with RL30, allows for extending the range of MCSs used for 16QAM UEs beyond MCS20 to: • MCS21 • MCS22 • MCS23 • MCS24 Approximately 25% higher UL peak rates actModulationSchemeUL Enable 16QAM high MCS LNCEL; QPSK (0), 16QAM (1), 16QAMHighMCS (2)





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Inner Loop LA ulTargetBler LNCEL; 1…50%; 1%; 10%

• The target of the inner loop LA is to maintain a UE’s BLER close to the established target BLER , which is established by the parameter: ulTargetBler • Note that user data and L3 signaling are multiplexed together on PUSCH and will therefore have a common BLER Target

• Inner Loop LA is based on BLER measurements which are calculated based on the ack/nack feedback obtained from L1/L2 • Inner loop LA will be performed every time the timer ulamcSwitchPer expires

• Based on the UE’s actual BLER compared to the desired target BLER AM will make a decision whether to upgrade or downgrade the MCS

ulamcSwitchPer Period in sent Transport Blocks TBs when UL Inner Loop LA should be executed LNCEL; 10…500; 10; 30 TBs

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Inner Loop LA

ulTargetBler LNCEL; 1…50%; 1%; 10%

•

Thresholds for upgrade and downgrade of MCS are established by the following parameters:

• ulTargetBler : Target BLER for the Uplink • ulamcUpdowngrF: Upgrade/Downgrade Factor

ulamcUpdowngrF LNBTS; 1…3; 0.05; 1.2 Hard coded parameter

- High BLER Threshold (Downgrade) = Round(ulTargetBler * ulamcUpdowngrF) - Low BLER Threshold (Upgrade) = Round(ulTargetBler / ulamcUpdowngrF)

- Note Upgrade and downgrade are always performed by a single MCS step ensuring that the maximum and minimum possible MCS’s aren't surpassed

Target BLER

Low BLER

Upgrade MCS 24

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High BLER

Maintain MCS

Downgrade MCS


Inner Loop LA - Example: • ulTargetBler : 10%

• ulamcUpdowngrF: 1.5 - High BLER Threshold (Downgrade) = Round(ulTargetBler * ulamcUpdowngrF) = 15%

- Low BLER Threshold (Upgrade)= Round(ulTargetBler / ulamcUpdowngrF) =7%

7%

15 % Target BLER

Low BLER

Upgrade MCS

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High BLER

Maintain MCS

Downgrade MCS


ulamcAllTbEn

Inner Loop LA

O&M switch for enabling/disabling the counting of all TBs instead of the 1st transmission TB for defining UL AMC inner loop factor. LNCEL; true, false; true

•

There are 2 possibilities to calculate the BLER for the Inner Loop LA (ulamcAllTbEn): • Consider only 1st TB Transmissions: BLER does not take into account any HARQ gains achieved by soft combining • Consider all Transmissions: the HARQ gain is included leading to small decision errors

- Performance of the inner loop AMC is going to be highly dependent on UL AMC switch period (ulamcSwitchPer ): • High Values of this parameter will ensure more stability in the LA process but worst reaction to fast radio condition variations • Low values of this parameter will provide faster reactions of LA and additionally decrease the resolution the BLER measurements causing possibly more instability

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ulamcUpdowngrF

ulamcSwitchPer

LNBTS; 1…3; 0.05; 1.2

LNCEL; 10…500; 10; 30 TBs

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OLLA - OLLA is based on the 1st transmission ACK/NACK information provided by L1/L2 HARQ. - OLLA provides a quicker adaptation to radio conditions compared to the inner loop LA which typically will act every 100-500ms defined by ulamcSwitchPer - OLLA basically counts the BLER based on 1st transmissions (∆C) min( C(t  1)  Cstepup, C max ),  C(t )  max( C(t  1)  Cstepdown, C min ), C(t  1), 

for first HARQ feedback  ACK, for first HARQ feedback  NACK, for first HARQ feedback  N/A.

- Where:

• ∆ Cmax and ∆ Cmin give upper and lower limits on the compensation defined by parameters (ulamcDeltaCmax, ulamcDeltaCmin) •

Cstepup and Cstepdown are incremental compensation steps sizes, which obey to the 1 - BLER target following formula: C C  . stepdown

stepup

BLER target

- Where Cstepup and BLERtarget are parameters: ulamcCStepUp , ulTargetBler

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OLLA Every time OLLA is initialized or reset ∆C is set to ulamcDeltaCini

OLLA compensation value ∆ C is reset at each AMC period, EDG and FUG event. Emergency Downgrade (EDG) shall be triggered, whenever the compensation value ∆C is equal to ∆Cmin. AMC shall switch immediately to the next lower (i.e. more robust) MCS Fast Upgrade (FUG) shall be triggered, whenever the compensation value ∆C is equal to ∆C max. AMC shall switch immediately to the next higher (i.e. less robust) MCS

ulamcDeltaCini

ulamcDeltaCmin

ulamcDeltaCmax

ulamcCStepUp

LNBTS; 0

LNBTS;; -5

LNBTS;; 5

LNBTS;; 0.2

Hard coded parameter




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Inner Loop and Outer Loop Interaction OLLA Comp. C Max Cmax

FUG Event

Reduced AMC Period

ulamcSwitchPer 0

Time

AMC Switching Period

EDG Event

Min Cmin

Reduced AMC Period

Period in sent Transport Blocks TBs when UL Inner Loop LA should be executed

LNCEL; 10…500; 10; 30 TBs

- Inner loop LA is ‘periodical’ based on the parameter ulamcSwitchPer

- OLLA is event based - Every time a EDG or FUG event takes place the Inner loop LA is reset too, therefore the periodicity of the inner loop LA can be shortened by the OLLA events

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Inner Loop and Outer Loop Interaction Example:

- ulTargetBler =10%

ulamcDeltaCini =0

- ulamcCStepUp = 0.1 - ulamcCStepDown=0.1*(1-0.1)/0.1 = 0.9.

Cstepdown  Cstepup 

1 - BLER target BLER target

- So setting ulamcDeltaCmin=-9 means, that an EDG will be triggered after 10 unsuccessfully received consecutive 1st transmission TBs after every MCS upgrade/downgrade event

min( C(t  1)  Cstepup, C max ),  C(t )  max( C(t  1)  Cstepdown, C min ), C(t  1), 

for first HARQ feedback  ACK, for first HARQ feedback  NACK, for first HARQ feedback  N/A.

- By such an adjustment of the UL AMC with OLLA will be able to switch down the MCS after 10ms (10 TTIs) even if the ulamcSwitchPer is rather high with e.g. 50 TBs (equals to ~50ms).

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.

UL AMC During DRX/DTX • At the end of data transfer the currently selected MCS shall be stored and a Timer for “historical MCS” shall be started. • If the same UE proceeds with a data transfer within the time period ulamcHistMcsT, then the historical MCS shall be reloaded from memory and applied instead of the iniMcsUl iniMcsUl LNCEL; 0…20; 1; 5

• By setting ulamcHistMcsT = 0 the functionality of “historical MCS” can be switched off. • Before starting an UE specific DTX period or entering an Inactivity period the actual MCS shall be stored and a Timer for Inactivity shall be started. With every ulamcInactT period the MCS shall be decreased, but the selected MCS shall not go below the initial MCS iniMcsUl.

• If the currently selected MCS is below iniMcsUl then no action during DRX/DTX and/or Inactivity period shall be required.

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Adaptive Transmission Bandwidth (ATB) - Besides selecting the most appropriate MCS according to radio conditions, the UL AMC shall also perform slow ATB in parallel. (i.e. fast means every TTI) - ATB is necessary in case of lack of UE power to concentrate the remaining power on less PRBs, thus allowing a regular data transmission in UL even up to the cell edge.

- ATB will inform the scheduler about the maximum Number of PRBs per TTI that can be assigned to a UE based on the UE’s power headroom reports - The periodicity of ATB is defined by the parameter ulatbEventPer which defines a multiple of AMC events (periodic changes, EDG, FUG) after which ATB will be carried out - ATB functionality can be enabled/disabled with actUlLnkAdp ulatbEventPer Period in MCS increase/decrease events when UL ATB functionality should be performed. LNCEL; 1…50; 1; 1

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actUlLnkAdp Activates Uplink Link Adaptation and defines Link Adaptation mode LNCEL; off (0), slowAmcOllaATB (4), eUlLa (5), fUlLa (6); eUlLa (5)


Adaptive Transmission Bandwidth (ATB) •

Trigger conditions for UE to send Power headroom reports: - dlPathlossChg : When UE surpasses a defined threshold of power headroom it shall report it to the eNodeB. This event driven report will handle fast variations of the path loss - tPeriodicPhr: Parameter to set periodic reporting of the power headroom

- tProhibitPhr: Parameter to define minimum interval between power headroom reports sent to eNodeB dlPathlossChg

tPeriodicPhr

tProhibitPhr

This is a trigger condition for power headroom submission due to pathloss change

Period for periodic Power Headroom Reports

Minimum intermediate time between two consecutive Power Headroom Reports

LNCEL; 1 db (0), 3 db (1), 6 db (2), infinite (3); 3dB (1)

LNCEL; 10sf (0), 20sf (1), 50sf (2), 100sf (3), 200sf (4), 500sf (5), 1000sf (6), infinity (7); 20sf (1)

20sf = 20 ms

LNCEL; 0sf (0), 10sf (1), 20sf (2), 50sf (3), 100sf (4), 200sf (5), 500sf (6), 1000sf (7); 0sf (0) 0sf = 0 ms

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Adaptive Transmission Bandwidth (ATB) ATB Algorithm: 1. At call setup the maximum number of PRB’s that can be allocated to a single UE shall be limited by the parameter iniPrbsul iniPrbsul Initial amount of PRBs in UL LNCEL; 1…100; 1; 10

2. ATB events shall act synchronously with the slow AMC, based on ulatbEventPer

ulatbEventPer Period in MCS increase/decrease events when UL ATB functionality should be performed. LNCEL; 1…50; 1; 1

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Adaptive Transmission Bandwidth (ATB) ATB Algorithm: At call ATB calculates a running average filter acting continuously on all of the incoming power headroom reports of a certain UE. The averaging period is defined by means of ulatbPhrAvgF - Power head room reports depend on the number of PRB’s which were scheduled to the UE. Information on the number of scheduled PRB’s is obtained from the UL Scheduler - The equivalent possible PRBs derived from PWR_HEADR_UL and UE_PRBs_UL for a certain time instance t shall be given by: - PWR_HEADR_PRBs(t) = UE_PRBs_UL(t) * PWR_HEADR_UL(t). - For this PWR_HEADR_UL has to be linearized (converted from dB into linear scale), e.g. 3 dB is factor 2 and -3 dB is factor 1/2 and 0 dB is a factor 1. - The running average filter output is given by - RUNAVG_PRBs(0) = iniPrbsul. - RUNAVG_PRBs(n) = (1 - ulatbPhrAvgF)*RUNAVG_PRBs(n-1) + ulatbPhrAvgF *PWR_HEADR_PRBs(n). ulatbPhrAvgF Parameter used for time averaging of power headroom reports LNBTS; 0.9 Hard coded parameter 37

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Adaptive Transmission Bandwidth (ATB) Note: • with ulatbPhrAvgF = 1 always the last power headroom report is used • with ulatbPhrAvgF = 0 the ATB is disabled and always the initial setting is employed (this is a second possibility to switch the algorithm off).

4. At any ATB decision the present value of the running average filter is read and the max number of PRB’s is set to a rounded integer value by: - MAX_NUM_PRBs = floor( RUNAVG_PRBs ). 5.Ensure that PRB’s are within and upper and lower limit boundaries: • • • • •

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UPPER_LIMIT_PRBs = MAX_BITRATE_UL (given by Admission Control and QoS) / (MCS_THROUGHPUT_per_PRB*(1-ULAMC_TARGET_BLER)) The upper Limit shall not exceed #PRBs_UL given by the Carrier Bandwidth. The lower Limit is given by: LOWER_LIMIT_PRBs = MIN_BITRATE_UL (given by Admission Control and QoS) / (MCS_THROUGHPUT_per_PRB*(1-ULAMC_TARGET_BLER)) MCS_THROUGHPUT_per_PRB is the MCS dependent UE throughput under ideal radio conditions (0% BLER) assuming a fictive allocation of 1 PRB per TTI.

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ATB during DTX/DRX If no Power headroom indications are received during the previous reporting period, then ATB running average filter stays with the previous settings (no change).

If no Power headroom indications are received during the whole call at all, then ATB running average filter stays with the initial static setup iniPrbsul.

iniPrbsul Initial amount of PRBs in UL LNCEL; 1…100; 1; 10

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Uplink Link Adaptation entities The purpose UL LA is to improve system capacity, peak data rate and coverage reliability by the adaptation of transmission settings to the radio channel conditions - UL Adaptive Modulation and Coding (UL AMC) which selects appropriate MCS for UL transmission taking actual transmission reliability (BLER). UL-AMC is split into: • Inner Loop Link Adaptation (ILLA) – slow periodic AMC

OLLA

- Periodic ACK/NACK information is used for calculating BLER (Block Error Rate) after 1st transmission or nth retransmission

ILLA

ATB

• Outer Loop Link Adaptation (OLLA) – event-triggered aperiodic AMC

- Periodic ACK/NACK information is used for calculating BLER after 1 st transmission of a Transport Block in order to derive a compensation factor - Adaptive Transmission Bandwidth (ATB) • responsible for defining maximum number of PRBs that can be assigned to a particular UE by UL SCH

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Sync

OLLA

Slow ATB

Extended-Uplink Link Adaptation motivation It is more efficient to distribute the power over a wider bandwidth (more PRBs) using lower MCS • If a UE is power limited (corresponding to bad RF conditions) • This fact is due to Shannon‘s formula for the channel capacity of a bandwidth and power limited channel.

S  C  B w log 2 1    N More efficient Wider bandwidth (more PRBs)

Lower MCS

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Less efficient Few PRBs Higher MCS


E-ULA concept With LTE1034 the 3 processes (UL AMC, UL ATB and UL OLLA) that rule the UL Link Adaptation, work synchronized but independently to each other. Eliminate any possibility of BLER target drifting by: • stopping the SLOW AMC algorithm (ILLA) • leaving the MCS regulation the OLLA algorithm OLLA reacts relatively fast when it comes to reduce MCS index and slowly enough when it comes to upgrade MCS index

The main idea

Therefore OLLA algorithm is unchanged and become the only one ruling the MCS index up and down SlowA TB OLLA

AMC

ATB is no longer PHR based but BLER based (with PHR correction).

Most of all SlowATB is coordinated with OLLA.

It will become active only when the OLLA has already reached the lower possible limit for the MCSindex

This means that SlowATB acts only when OLLA has no longer margin left in terms of reaction.

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E-ULA algorithm overview START

• OLLA verifies BLER conditions and triggers FUG or EDG events when necessary as in former releases

OLLA

• Counter is incremented in every TTI when user is actively scheduled • ATB is triggered for:

Increment ttiEventCounter ATB Triggering ? Yes

Next slide 44

END

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No

• ttiEventCounter threshold for periodical ATB triggering (eUlLaAtbPeriod)

OR • EDG trigger - is sent by OLLA when EDG event happens and the lowest MCS Index has been already reached. Therefore EDG cannot further decrease this MCS index. In this case OLLA triggers the earlier activation of the SlowATB process. Abbreviated Name

Range (Stepsize/Granularity)

eUlLaAtbPeriod

{10, 15, 20, 30, 35, 40, 45, 50}


Default

30

BLER based ATB routines enhanced in E-ULA When UE being in bad RF goes to better RF conditions

TRIGGER No

When BLER is lower than the given target and OLLA has already set the MCS Index to the eUlLaLowMcsTh+ eUlLaDeltaMcs (value defined by the Operator).

When UE being in bad RF goes to worst RF conditions

BLER > blerTarget ?

No

Yes

No

Yes

Yes

Amount of PRBs is decreased by factor eUlLaPrbIncDecFactor

The number of PRBs is increased by factor eUlLaPrbIncDecFactor

provide MAX_NUM_PRB and NewMCS to other functions

END Abbreviated Name

Range

eUlLaLowPrbThr

{1, 2, 3, 4, 5}

eUlLaLowMcsThr

{1, 2, 3, 4}

eUlLaPrbIncDecFactor

{0.5...0.9, step 0.05}

eUlLaDeltaMcs 45

{1, 2, 3, 4, 5, 6}

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When BLER is higher than the given target and OLLA has already set the MCS Index to the eUlLaLowMcsTh, while MAX_NUM_PRB is still over the lowest PRB threshold (eUlLaLowPrbThr)

Remark

Default 1

1 0.8

3

This shall be always bigger than or equal to redBwMinRbUl

Defines how many MCS indexes above the minimum MCS index are required before ATB may increase the amount of © Nokia Solutions and Networks 2015 allocable PRBs

Resetting the algorithm after long pause between activescheduled TTIs 1/3 It is necessary to define how to react to long pauses between TTIs where UE is actively scheduled. • UL-AMC defines already the parameter/timer ulamcInactT (200 ms) for the purpose of resetting the MCS-index after the expiration of this timer.

Start decreasing PRBs

1

2

3

4

ulamcInactT

• To avoid parameter multiplications those parameters are utilized with a similar function in E-ULA but in E-ULA instead the algorithm acts as well on the number of allocable PRBs instead of the MCS Index only.

When PRBs decreased to initial, reset MCS

12 13 14 15

TTIs User scheduled

46

No transmission - long pause

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User actively scheduled again


Resetting the algorithm after long pause between activescheduled TTIs 2/3 If user is still not active after expiration of timer, its resource assignments should be gradually decreased

User is not scheduled Start decreasing PRBs

• No transmission – long pause • Wait until counter ulamcInactT is reached

• When counter reached and PRB > iniPrbsUl –> start decreasing PRBs by

eUlLaPrbIncDecFactor

• When PRBs already at iniPrbsUl set MCS to iniMcsUl Reset MCS

Abbreviated Name

47

If meantime user was scheduled again, the counter is reset and no further LA adjustment is done

Range(Stepsize/Granularity)

Reset counters and re-initialize OLLA in case of any recalculation

Default

iniPrbsUl

1, 2, ..., 100 / 1

10

iniMcsUl

MCS0, MCS1, …, MCS20

MCS5

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Resetting the algorithm after long pause between active-scheduled TTIs in E-ULA 3/3

START

Yes

Reset counter

Start when user get initial assignment

User scheduled ?

No

For every TTI

Reset MCS to initial if PRBs already resetted

Increment counter

Counter reached ulamcInactT ?

No

Yes

No

No CurrentMCS > iniMcsUl

MAX_NUM_PRB > iniPrbsUl

Yes

Yes

MAX_NUM_PRB = max ( iniPrbsUl, (MAX_NUM_PRB * eUlLaPrbIncDecFactor))

NewMCS = iniMcsUl

We shouldn’t decrease more, because PRB and MCS are already at initial default Leave MAX_NUM_PRB unchanged

Re-initialize OLLA Reset ttiEventCounter

In case of recalculation

END 48

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Decrease PRBs if not at initial yet

Uplink Link Adaptation for PUSCH (RL30) UE Power Headroom reporting • The UL AMC/ATB delivers to Telecom C-Plane the relevant configuration data for the UE Power Headroom Configuration − The UE shall be configured to report PERIODIC PWR_HEADR_UL reports. For this the period shall be configured by RRC - if applicable. The parameter tPeriodicPhr is available from O&M. Also the minimum time period in-between two reports is available by O&M with tProhibitPhr. Event driven Parameter such as rapid change in path loss shall be set according to dlPathlossChg. Also the latter data is taken from O&M parameter settings.

•

So the UE shall be configured as follows by: − event triggered reporting DL_PATHLOSS_CHANGE = dlPathlossChg with {dB1, dB3, dB6, infinity}

− periodical reporting PERIODIC_PHR_TIMER = tPeriodicPhr with {sf10, sf20, sf50, sf100, sf200, sf500, sf1000, infinity}

− report prohibit timer PROHIBIT_PHR_TIMER = tProhibitPhr with {sf0, sf10, sf20, sf50, sf100, sf200, sf500, sf1000}

• If the periodic PHR Timer is set to infinity and the DL path loss change, too, then no PWR_HEADR_UL indications are received during the whole call. Then in this case the ATB stays with the initial static setup ULATB_INIPRBs.

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E-ULA activation Parameter actUlLnkAdp activates Link Adaptation and defines its mode

ATB

actUlLnkAdp

ILLA

OLLA PHR based

off eUlLa slowAmc

slowAmcATB slowAmcOlla slowAmcOllaATB

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BLER based




51

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Fast Uplink Adaptation (F-ULA)

actUlLnkAdp Activate uplink link adaptation LNCEL; off (0), slowAmcOllaATB (4), eUlLa (5), fUlLa (6)

Before, E-ULA (LTE1034) as open loop link adaptation

ACK/NACK upper

FUG event (Fast upgrade)

Increase MCS +1

ΔC lower

EDG event

threshold is reached

(Emergency downgrade)

Decrease MCS -1

The mechanism to trigger a FUG or an EDG event is the same in E-ULA and FULA and is based on the defined BLER target.

After, F-ULA (LTE1495)

SINR is calculated based on measurements

SINR to MCS lookup table

+ OLLACF

FUG event

Increase OLLACF +1

(Fast upgrade)

SRS

DM-RS

ΔC

Final MCS

When threshold is hit

EDG event

(Emergency downgrade)

(+/- ATBCF)

Decrease OLLACF -1

ACK/NACK

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ATB is influenced by the power limitation of the UE

Fast Uplink Adaptation (F-ULA) Range of OLLACF is proportional to the maximum MCS index supported by the cell:

Calculation of OLLA correction factor (OLLACF): OLLACF,new = OLLACF,old + OLLAstep

OLLAstep = +1 if triggered by FUG or OLLAstep = -1 if triggered by EDG

LNCEL:actModulationSchemeUL QPSK 16QAM 16QAMHighMCS

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OLLACF range -10...+10 -20...+20 -24...+24


Fast Uplink Adaptation (F-ULA) Uplink OLLA (Outer Loop Link Adaptation)

ATBCF is calculated when the OLLACF has reached a certain value LNCEL:fUlLAAtbTrigThr,

default value = -2

Calculation of ATB correction factor (ATB CF):

Yes

OLLACF >

2 EDGs needed to trigger ATB

No

fUlLAAtbTrigThr

ATBCF,new = 0

ATBCF,new = min (0, ATBCF,old + ATBstep)

fUlLAAtbTrigThr is always < 0 ATBCF is always < 0

fUlLAAtbTrigThr Fast uplink link ATB trigger threshold

ATBstep = +1 if triggered by FUG or ATBstep = -1 if triggered by EDG

LNCEL; -10..0dB, step 1 dB: -2

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Fast Uplink Adaptation (F-ULA) System level simulation results

FULA immediate MCS adaptation

FULA high UE TP available

EULA slow MCS increasing

1 UE attached in good radio conditions

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EULA lower UE TP during transition phase


Fast Uplink Adaptation (F-ULA) Evolution of Link Adaptation: Link Adaptation

AMC

RL10 UL LA

RL30 E-ULA

RL60 F-ULA

ILLA

Slow AMC

Not used with E-ULA

Fast AMC

OLLA

OLLA

OLLA unchanged

Modified OLLA

Slow ATB - PHR based

New ATB - PHR and BLER based

Modified ATB

LNCEL:ulamcEnable = True LNCEL:ulatbEnable = True

LNCEL:actUlLnkAdp = eUlLa

LNCEL:actUlLnkAdp = fUlLa

OLLA and ATB synchronization

F-AMC core integrates all functional blocks

ATB Parameter activation

Comment

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RA41218EN70GLA0


08_RA41218EN70GLA0_AMC.pdf

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