Adaptive Modulation Modulation and Coding
Outer Loop Quality Quality Control Control
OLQC OL QC – CQ CQII Ad Adap apta tati tion on • Outer Link Quality Control (OLQC) adapts the channel quality information that is used by the the scheduler and link adaptation to achieve 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 dlOlqcEnable • CQI interpolation error Enable/disable OLQC • Errors due to CQI averaging of PRBs 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.
OLQC – CQI Adaptation •
The picture below shows the principle of CQI adaptation
OLQC – CQI Adaptation • OLQC adds a CQI offset to the CQI reports that are provided by the UE via the UL L1/L2 signaling. • The corrected CQI report will then be provided to the DL link adaptation and MIMO mode control for selection between Transmit diversity and Spatial Multiplexing
• Starting from the initial value the CQI offset will be adjusted in response to the ACK/NACK for the first transmission of a transport block that is provided by the UE via L1/L2 control signaling
• The averaging period for the CQI values reported by the UE are set by the MIMO mode Control parameters mimoClCqiAvg & mimoOlCqiAvg
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 CQI corrected ( x, t ) = CQI reported ( x, t ) + ∆CQI(t ) . for first HARQ feedback = ACK, min(∆CQI(t − 1) + CQIstepup , ∆CQI max ), ∆CQI(t ) = max(∆CQI(t − 1) − CQI stepdown , ∆CQI min ), for first HARQ feedback = NACK, ∆CQI(t − 1), for first HARQ feedback = N/A. dlOlqcDeltaCqiIni, dlOlqcDeltaCqiMax, dlOlqcDeltaCqiMin, dlOlqcDeltaCqiStepUp
OLQC – CQI Adaptation Two Code Words
CQI corrected ( x, t ) = CQI reported ( x, t ) + ∆CQI(t ) . min( ∆CQI(t − 1) + CQI stepup , ∆CQI max ), max( ∆CQI(t − 1) − CQI stepdown , ∆CQI min ), min(max( CQI ( 1 ) (CQI stepup − CQI stepdown ) / 2, t ∆ − + ∆CQI(t ) = ∆CQI min ), ∆CQI max ), min( ∆CQI(t − 1) + CQI stepup , ∆CQI max ), max( ∆CQI(t − 1) − CQI stepdown , ∆CQI min ), ∆CQI(t − 1),
for new transmisssion 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.
* the ACK feedback for a new transmission shall be mapped to N/A for the considered code word in the following two cases in order to supress an upgrade of the CQI offset: •The considered new transmission of the corresponding code word has been done with the maximum possible MCS that is possible for the considered UE (UE capabilities) and eNodeB (enabling/disabling of certain modulation of coding formats). In this case only a downgrade of the MCS and the CQI offset shall be allowed since the maximum possible MCS is reached and the channel conditions might be much better than indicated by the MCS. •MCS downgrade has been done for the considered new transmission of the considered code word (due to the fact that the selected transport block exceeds the peak data rate or the amount of buffered data of the considered UE). In this case only a downgrade of the MCS and the CQI offset shall be allowed since the channel conditions might be better than indicated by the MCS. ** the NACK feedback for a new transmission shall be mapped to N/A for the considered code word in order to suppress a downgrade of the CQI offset: •The considered new transmission of the corresponding code word has been done with the minimum possible MCS that is possible for the considered UE and eNodeB. In this case only an upgrade of the MCS and the CQI
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-BLER target) the balance equation can be formulated as:
(1 − BLER target ) ⋅ CQI stepup
=
BLER target ⋅ CQI stepdown .
• Therefore, CQIstepdown can be calculated from the parameters CQIstepup and the dlTargetBler as:
CQI stepdown
=
CQI stepup ⋅
1 - BLER target BLER target
dlTargetBler
.
Target BLER DL LNCEL;0.001…0.999;0.001; 0.1
DL Adaptive Modulation and Coding (AMC) (AMC)
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.
DL AMC • DL AMC is enabled via dlamcEnable
• For retransmissions the same MCS as for the original transmission is applied
• For new transmissions the MCS is decided based on CQI reports from the UE dlamcEnable Enable Adaptive Modulation and Coding in DL LNCEL; true, fal true
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 • 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
DL AMC MCS Selection for new Transmissions • An average channel state is determined from the CQI information corresponding to the PRBs/RBGs having been assigned (or are considered for being assigned) by the scheduler. • For this the CQI values have to be mapped to CIR values via link level simulation results. • The CIR values for the allocated PRBs/RBGs are averaged linearly. The resulting averaged CIR value is converted back into an averaged CQI value (but not quantized to full CQI steps; interpolation between full CQI steps needs to be applied). •The target for this mapping is to choose the transport block out of the group of possible transport blocks such that the difference of the code rate as derived from the averaged CQI value (according to the CQI table using interpolation to account for the non-quantized value of the averaged CQI) and the effective code rate corresponding to the considered transport block is minimized. •The MCS index as corresponding to the transport block as determined above shall be used and signaled accordingly.
•The mapping of the averaged CQI to an MCS level shall be performed by mapping the modulation scheme and code rate of the CQI table according to [3GPP-36.213]
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. iniMcsDl Initial MCS in DL LNCEL; 0…28; 1 4
dlamcThistCqi Time in TTIs for which historical CQI is remembered in AMC
DL Adaptive Modulation and Coding (AMC) – – for PDCCH
enableAmcpdcch
Main target of DL-AMC-CCH
Enable/disable CQI based AMC for PDCCH LNCEL; true; true
• Similar to data transmission, it is necessary to make a signaling (PDCCH) robust enough for poor UEs (low SINR, e.g. at the cell-edge) • Transmission with low ECR (Effective Coding Rate) leads to increased resource utilization which reduces the number of scheduled UEs; thus good UEs should occupy less PDCCH resources and operate with lower number of CCEs (higher ECR) – 7 UEs (5 MHz), 10 UEs (10 MHz), 20 UEs (20 MHz) • Any Link Adaptation technique must deal with a trade-off between signaling robustness (coverage) and signaling capacity • Macro cell case #1 • Uniform UE distribution
4-CCE 2-CCE
1-CCE
CQI-to-Aggregation Mapping unit CQI from DL-AMC/DL-OLQC
CQI filtering/processing
DLS_INPUT_LIST = { Broadcast, Tag, DCI-format, CSS, Prio-A; Paging, Tag, DCI-format, CSS, Prio-B; RACH Response, Tag, DCI-format, CSS, Prio-C; Preamble Assignment, Tag, DCI-format, CSS, Prio-D; Message 4 Assignment, Tag, DCI-format, CSS, Prio-E; UE-1, Tag, DCI-format, USS, Prio-X; UE-2, Tag, DCI-format, USS, Prio-Y; …; UE-k: ...; }
Filtered, compensated and shifted CQI
…; UE-k: ...;
All DCI formats… 1 1a
ULS_IINPUT_LIST = { UE-1, Tag, USS, Prio-X; UE-2, Tag, USS, Prio-Y;
}
CQI-to-Aggregation Mapping
…
REQUIRED_AGG_LIST = { UE-1: pdcchCQI, AGG-DCI0, AGG-DCI1, …; UE-2: pdcchCQI, AGG-DCI0, AGG-DCI1, …; …;
• CQI-to-Aggregation Mapping unit relies on UE-specific CQI information to build the list of required AGG levels for all possible DCI formats for every active UE (UE which appears on the DL/UL scheduling list). • REQUIRED_AGG_LIST must refer to all active UEs so that the schedulers know how many resources are needed to allocate them. • Common signaling (e.g. Broadcast, Paging, etc.) is not considered at this step; the mapping affects UE Search Space (USS) only
CQI-to-Aggregation Mapping unit rdPdcchAggTables •
• •
SINR-vs-BLER tables have been obtained from 4GMax LL simulator (EPA05, 2x2MIMO) for two representative payload sizes of 45 bits and 60 bits. The PDCCH performance should aim at 1% target BLER. SINR targets have to be translated to CQI thresholds. CQI = 0.51*SINR + 5.3
•
The mapping table is not sufficient. R&D in-built table must consist of thresholds for all possible DCI formats (various payload size). A scaling factor (SF) is applied. SFsmallDCI = 10*log10(DCI_size/45) SFlargeDCI = 10*log10(DCI_size/60) Mapping table for 45/60 bits payload composed based on CQI-to-SINR formula (4GMax)
CQI-to-Aggregation Mapping unit rdPdcchAggTables
pdcchAggDefUE PDCCH LA UE default aggregation; LNCEL; 1(0), 2(1), 4(2), 8(3); 4(2)
• After post-processing of 4GMax output, the table is ready to be used by the CQI-toAggregation Mapping unit. • The table is valid for 10MHz bandwidth, however the operator can adjust the thresholds by using O&M parameter pdcchCqiShift (if OLLA PDCCH is disabled, see below). • If PDCCH AMC is disabled or CQI is outdated, pdcchAggDefUe will be applied to all DCI pdcchCqiShift formats of all UEs. LNCEL; -10…10;0.1; 0
Mapping table for 45/60 bits payload composed based on CQI-to-SINR formula (4GMax)
CQI = 0.51*SINR + 5.3 SFsmallDCI = 10*log10(DCI_size/45) SFlargeDCI = 10*log10(DCI_size/60)
OLLA for PDCCH - Motivation • PDCCH carries information about the resources assignments for both Uplink (UL) and Downlink (DL) data channels . Downlink scheduling grant (MCS, PRBs, ..)
TTI n
PDCCH PDSCH
e-NB
Scheduling request
Uplink scheduling grant (MCS, PRBs, ..)
UE
TTI n
PUCCH/PUSCH
TTI n+x
PDCC H PUSCH
e-NB TTI n+y
Data
UE
Data
• If a PDCCH payload is missed the User Equipment (UE) cannot know whether it has been scheduled and on which time/frequency resources.
TTI n
? PDCCH
TTI n
PUCCH/PUSCH
TTI n+x
PDCCH
PDSCH e-NB
UE
e-NB TTI n+y
?
PUSCH
UE
OLLA for PDCCH – Principle • The PDCCH OLLA can be based on the PDSCH OLLA as follows: Offset_PDCCH = deltaCQI + pdcchCqiShift ,
• deltaCQI from OLQC is used to control the PDSCH and PDCCH inner loop link (ILLA) adaptation. It is the PDSCH OLQC offset available and calculated based on the Ack/Nack/DTX feedback from previous PDSCH transmission
• and pdcchCqiShift is a term needed to compensate for the difference in BLER target for the PDSCH (e.g. 10%) and PDCCH (e.g. 1%).
• • • • •
pdcchCqiShift is in use to fine tune the PDCCH BLER The value is controlled statically by O&M: pdcchCqiShift or
dynamically by the feature. In the latter case it’s computation is based on a similar algorithm as used for PDSCH OLLA and the target BLER PDCCH is O&M defined by pdcchHarqTargetBler
OLLA for PDCCH – Functional Model Decides #CCEs and trans-mission power per UE (more CCEs/ power to low SINR UEs)
PDCCH Link Adaptation PDCCH Inner Loop Link Adaptation
WideBand CQI
PDCCH Power and Aggregation Level
deltaCQIShift deltaCQI Adjusts the dynamic correction of UE SINR estimate per user
PDCCH Outer Loop Link Adaptation
New Existing
actOlLaPdcch OLLA for PDCCH: activation True, false HARQ
PDSCH Outer Link Quality Control
Feedback Ack/Nack/DTX
deltaCQI
PDSCH Inner Loop Link Adaptation
Frequency Selective CQI
PDSCH Link Adaptation /
(for initial DL transmission)
pdcchHarqTargetBler BLER target for PDCCH outer loop link adaptation 0.1 %, 0.2 % …3.0 %
PDCCH Scheduling • PDCCH carries DCI (Downlink Control Information) to inform UE – about UL and DL Resource Block allocation for user data transmission
• After UL and DL scheduling list was generated by UL and DL scheduler, this algorithm selects UEs for UL and DL physical resource block allocation
• Share between UL and DL can be set with parameter LNCEL: pdcchUlDlBal pdcchUlDlBal PDCCH allocation balance constant between UL and DL. The PDCCH UE-specific search space capacity is divided into UL and DL based on the parameter before dynamic schedulings LNCEL; 0…0.9; 0.05; 0.5
• ZIG-ZAG is not used anymore (trial approach) – only if entries have same priority level • UE specific search space can be limited by LNCEL: PDCCHAlpha – [0,5 .. 2], step 0,05, default = 0,8 (PDCCH UE search space capacity is multiplied with this parameter)
Usage based PDCCH adaptation (LTE616) Number of OFDM symbols for PDCCH is adapted to the required amount of CCEs
• Balance beteen D! and for "! may be adapted based on CCE bloc#in$ and used CCE • %cti&ation' by actLdPdcch (true) false* • symbols for PDCCH in a ++, is beteen the minimum reasonable (bandidth-dependent* and maxNrSymPdcch • +he parameter actLdPdcch can be set to True if all . conditions are fulfilled' �
• - phichDur is set to Normal • - maxNrSymPdcch &alue is $reater than
1
• - dlChBw &alue is $reater than 25 • +he !oad %dapti&e PDCCH al$orithm optimi/es the &alue dependin$ on the actual load distribution beteen D! and "!)
• pdcchUlDlBal parameter defines the initial &alue0
PDCCH scheduling • TOTAL_INPUT_LIST_DL_ AMC may AMC may be composed based on different joint list creation techniques however as mentioned on the previous slide, Priooriented solution has been chosen for RL10 • ZIG-ZAG solution is valid only in case of entries with the same priorities
“ZIG-ZAG approach” approach” Joint list Downlink list High priority
High priority
Uplink list High priority
Prio-oriented approach
Highest priority
Joint list Common signalling (CSS), Msg4 UL HARQ
Dedicated signalling (USS) Low priority
Scheduling requests
Low priority
Other DL/UL Low priority
Lowest priority
PDCCH scheduling
pdcchUlDlPrio PDCCH LA priorities LNCEL; 0…99; 1; Parameter is vendor specific
Structured Parameter: 15 single parameters – not configurable
UL Adaptive Modulation and Coding (AMC)
UL AMC and ATB Used to adapt PUSCH to different link conditions by variable modulation and coding scheme, and variable bandwidth Inputs • Ack/Nack information • SINR Measurements • Power Headroom reports Outputs • modulation • code rate • maximum amount of PRBs
NSN Implementation • Simple BLER based algorithm to select best • • • •
MCS according to UE specific Radio Conditions SINR Measurements are not required, only HARQ Ack/Nak output signalling used Target BLER adjustable Emergency Downgrade/Upgarde Feature combatting very high or low BLER peaks 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; true
• The uplink AMC shall consist of 2 main components: 1. An outer loop LA (OLLA) acting on the 1 st Transmission Errors on TBs 2. An inner loop LA based on BLER acting on either 1 st 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
UL AMC ulamcEnable Enable Adaptive Modulation and Coding in UL LNCEL; true, false ; true
• UL AMC can be enabled/disabled with ulamcEnable • 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. ulamcEdgFugEn O&M switch for enabling/disabling the 1st transmission BLER based Emergency Downgrade and Fast Upgrade functionality included in the UL AMC Outer Loop Link Adaptation.
UL AMC • UL AMC shall select the MCS to be employed from the table below according to the radio conditions MCSIndex I MCS
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
Modulation Order
TBS Index
'
Qm
I TBS
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
•In RL09/RL10 , 64 QAM modulation is not available in the UL, therefore selected MCS’s will be restricted from MCS 0 to MCS 20
UL AMC – Increased UL MCS Range • UL peak throughput can be enhanced (see table) • Additionally supported: MCS21-MCS24 (LTE829) • Applicable to 16QAM UEs (cat1-cat4) actModulationSchemeUL Enable 16QAM high MCS LNCEL; QPSK (0), 16QAM (1), 16QAMHighMCS (2)
BW / MHz
Max # PRB
UL Peak Rate / Mbps
Improvement / %
96 of 100
51.0
26
3 5 10 15 20
• Exercise: Please complete the table.
Inner Loop Link Adaptation (ILLA) (ILLA)
Inner Loop LA ulTargetBler LNCEL; 10…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 a 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
Inner Loop LA ulTargetBler LNCEL; 10…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 Vendor specific 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
High BLER
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
High BLER
Maintain MCS
Downgrade MCS
Inner Loop LA 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; 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 • Example: ulamcSwitchPer = 100 TBs ~ 100 ms there are 100 TBs and by that a BLER resolution of 1%, within 50 ms there are 50 TBs and the BLER resolution is 2% and for 20 ms there are 20 TBs and BLER resolution is 5%. This should be considered when setting ulamcUpdowngrF ulamcUpdowngrF
ulamcSwitchPer
Outer Loop Link Adaptation (OLLA)
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 1 st transmissions (∆C) ∆ C ( t ) =
min( ∆ C (t − 1) + C stepup , ∆ C max ), max( ∆ C ( t − 1) − C stepdown , ∆ 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 following formula: Cstepdown
=
Cstepup ⋅
1 - BLER target BLER target
.
• Where Cstepup and BLERtarget are parameters: ulamcCStepUp , ulTargetBler
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 •Note that ulamcDeltaCmin and ulamcDeltaCmax as well as ulamcCStepUp have to be configured carefully depending on adjusted ulTargetBler, for example a certain number of consecutive Nacks has to be assumed, which shall trigger the EDG
ulamcDeltaCini
ulamcDeltaCmin
ulamcDeltaCmax
LNBTS; -10..10; 0.1; 0
LNBTS; -10..10; 0.1; -5
LNBTS; -10..10; 0.1; 5
Vendor specific parameter
Vendor specific parameter
Vendor specific parameter
ulamcCStepUp LNBTS; 0..2; 0.05; 0.2 Vendor specific parameter
OLLA
ulamcEdgFugEn O&M switch for enabling/disabling the 1st transmission BLER based Emergency Downgrade and Fast Upgrade functionality included in the UL AMC Outer Loop Link Adaptation. LNCEL; true; true
•Emergency downgrades and fast upgrades functionality of the OLLA can be disabled with the parameter: ulamcEdgFugEn •If OLLA is disabled only the slow BLER based inner loop AMC shall control the MCS selection. •Gain of EDG is shown from the simulation results below: UL Throughput vs. SNR; 20 MHz LTE System, RX-Div, AWGN Channel 50000 45000 10% BLER Targets of 1st Transmission
40000 ] s p35000 b k [
30000
t u p25000 h g u20000 o r h15000 T
10000 5000 0 -16
-14
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
SNR [dB] QPSK 1/6
QPSK 1/3
QPSK 1/2
12
14
16
Inner Loop and Outer Loop Interaction OLLA Comp. ∆C Max ∆Cmax
FUG Event
Reduced AMC Period
ulamcSwitchPer 0
Time
AMC Switching Period Min ∆Cmin
EDG Event
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
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- BLERtarget BLERtarget
• 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 ∆ C ( t ) =
min( ∆ C ( t − 1) + C stepup , ∆ C max ), max( ∆ C ( t − 1) − C stepdown , ∆ 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). • Note that the BLER calculation is reset after each AMC period
.
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.
Adaptive ran!"i!!ion #and$idt% (A#)
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 ulatbEnabled • Note that after every EDG and FUG event the slow ATB limits have to be recalculated since the MCS might have changed. ulatbEventPer Period in MCS increase/decrease events when UL ATB functionality should be performed. LNCEL; 1…50; 1; 1
ulatbEnable O&M switch for enabling/disabling the UL ATB functionalities. LNCEL; true ; true
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
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
Adaptive Transmission Bandwidth (ATB) •ATB Algorithm: 3.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
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: – UPPER_LIMIT_PRBs = MAX_BITRATE_UL (given by Admission Control and QoS) / –
– 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)) The upper Limit shall not exceed #PRBs_UL given by the Carrier Bandwidth.
(MCS_THROUGHPUT_per_PRB*(1ULAMC_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.
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
&'tended UL Link Adaptation (& (&ULA)
Uplink Link Adaptation entities The purpose UL LA is to improve system capacity, peak data rate and coverage reliability by the adaptation of 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
ILLA OLLA ATB
Periodic ACK/NACK information is used for calculating BLER (Block Error Rate) after 1 st transmission or n th retransmission
– 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
Sync
OLLA
Slow ATB
Uplink Link Adaptation history New Uplink Link Adaptation concept has been introduced in RL30
RL10 UL LA
RL30 E-ULA
• OLLA
• OLLA • Remains unchanged
• ILLA
• ILLA • Not used when E-ULA is active • New PHR and BLER based ATB algorithm
• SlowATB PHR based
• OLLA and ATB synchronization algorithm
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
Less efficient Few PRBs Higher MCS
RL30 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
Therefore OLLA algorithm is unchanged and become the only one ruling the MCS index up and down
OLLA reacts relatively fast when it comes to reduce MCS index and slowly enough when it comes to upgrade MCS index
The main idea
Sl ow AT B 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 term of reaction.
E-ULA algorithm overview START
•OLLA verifies BLER conditions and triggers FUG or EDG events when necessary as in former releases •Counter is incremented in every TTI when user is actively scheduled •ATB is triggered for:
OLLA
Increment ttiEventCounter ATB Triggering ? Yes
• ttiEventCounter threshold for periodical ATB triggering No
(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
Next slide
END
Range (Stepsize/Granularity)
Default
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
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)
No
Yes
Yes
Amount of PRBs is decreased by factor eUlLaPrbIncDecFactor
The number of PRBs is increased by factor eUlLaPrbIncDecFactor
END Abbreviated Name
provide MAX_NUM_PRB and NewMCS to other functions
Range
eUlLaLowPrbThr
12) 5) .) 6) 47
eUlLaLowMcsThr
12) 5) .) 67
eUlLaPrbIncDecFactor
1304) 308) 309) 3094) 30:) 30:4) 30;7
Remark
Default 1
1 0.8
+his shall be alays bi$$er than or equal to redBwMinRbUl
-
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 for the purpose of resetting the MCS-index after the expiration of this timer. To avoid parameter multiplications those parameters are utilized with a similar function in E-ULA but in EULA instead the algorithm acts as well on the number of allocable PRBs instead of the MCS Index only. Start decreasing PRBs
1
2
3
4
T t c a n I c m a l u
When PRBs decreased to initial, reset MCS
12 13 14 15
TTIs User scheduled
Abbreviated Name ulamcInactT
No transmission - long pause
Range(Stepsize/Granularity) 10 ms, 20 ms, …., 1000 ms / 10 ms
User actively scheduled again Default 100 ms
Description
Timer for Inactivity and DRX/DTX Periods
Resetting the algorithm after long pause between activescheduled TTIs 2/3 If user is still not active after expiration of timer, its resource assigments should be gradually decreased
User is not scheduled Start decreasing PRBs
• No transmission – long pause • Wait until counter ulamcInactT is reached
If meantime user was scheduled again, the counter is reset and no further LA adjustment is done
• When counter reached and PRB > iniPrbsUl –> start decreasing PRBs by eUlLaPrbIncDecFactor
• When PRBs already at iniPrbsUl set MCS to iniMcsUl Reset MCS
Abbreviated Name iniPrbsUl
Range(Stepsize/Granularity) 1, 2, ..., 100 / 1
Reset counters and re-initialize OLLA in case of any recalculation
Default 10
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 initail if PRBs already resetted
Increment counter
Counter reached ulamcInactT ?
No
Yes
No
No CurrentMCS > iniMcsUl
MAX_NUM_PRB > iniPrbsUl
Yes
Yes
NewMCS = iniMcsUl
We shouldn’t decrease more, because PRB and MCS are already at initial default Leave MAX_NUM_PRB unchanged
MAX_NUM_PRB = max ( iniPrbsUl, ( MAX_NUM_PRB * eUlLaPrbIncDecFactor))
Re-initialize OLLA Reset ttiEventCounter
In case of recalculation
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.
E-ULA activation Parameter actUlLnkAdp activates Link Adaptation and defines its mode
ATB actUlLnkAdp
ILLA
OLLA PHR based
off eUlLa slowAmc slowAmcATB slowAmcOlla slowAmcOllaATB
BLER based
Controlled uplink paket !eg"entation
Controlled UL Packet Segmentation • UL coverage improvement algorithm as an extension to the UL LA. • PDCCH is better utilized by balancing new transmissions and retransmissions. • The enhancement in coverage throughput comes at the cost of cell throughput. • For a given modulation code scheme (MCS) as determined by the uplink link adaptation and configured transport block size (TBS), the uplink scheduler determines the PRB allocation. ulsMinTbs Defines the minimum UL TBS (segment size). LNCEL, 16... 1544, step 8, (bit) 104
ulsMinRbPerUe Minimum PRB allocation for UEs which are power Limited. LNCEL; 1…100, step 1, (1) 3
