Lte High Capacity Event Parameters

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Lte High capacity event parameters

Prepared By: RAJESH KUMAR

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Focus areas

• LTE High Capacity Focus Areas

1. Control Channel Dimensioning • PUCCH Resources

• PDCCH Resources 2. UL Noise Rise

3. PRB Utilization / Cell Throughput Capacity 4. MP Load

• RRC Connection Setup Intensity – Due to UE releases by Inactivity

– Due to UE releases by RLC Supervision • Incoming Handover Intensity

• Hardware expansion 5. Connected Users License

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Focus areas

1. Control Channel Dimensioning

• PUCCH Resources • PDCCH Resources

2. UL Noise Rise

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Control channel resources

• UL Control Channel Resources

– PUCCH

• n_RB,PUCCH depends on number of SR and CQI resources  Focus Area for High Capacity Parameters

– PRACH

• n_RB,PRACH in 1 radio frame is independent of bandwidth and is fixed for different cell range

• DL Control Channel Resources

– PDCCH

• n_RE,PDCCH depends on CFI  Focus Area for High Capacity Parameters

– PCFICH

• n_RE,PCFICH in 1 radio frame is 160, independent of bandwidth and # of antenna ports – PHICH

• n_RE,PHICH in 1 radio frame depends on bandwidth and is fixed for different bandwidth – PBCH

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Pucch resources

intro

• PUCCH is used for transmitting

– SR, HARQ ACK/NACK (PUCCH Format 1) – CQI, RI (PUCCH Format 2)

• UE is allocated SR and CQI resources during setup procedure, and the

resources are kept as long as UE is UL synchronized.

– UE is not allowed to connect to a cell if there’s no free SR resources

• noOfPucchSrUsers and noOfPucchCqiUsers determine number of resources

for SR and CQI per cell

• PUCCH is allocated by

– 2 RB at the band edges (RB-pair)

– Time domain sharing, each PUCCH is assigned to a UE with a periodicity deciding which sub-frame UE can access PUCCH (default periodicity for CQI is 80ms, SR is 10ms)

• Current setting

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Pucch resources

highest pucch resources for sr & CQI

noOfPucchSrUsers (limited by n_CQI.res)=noOfPucchCqiUsers=640 This setting will reduce peak UL throughput

› 3rd_{attempt (n}

RB,format1 = 6, nRB,format2 = 2)

n_SR,res= (36*6-44)*10*10/10 = 1720 (>810)

n_CQI,res = 2*4*80*10/10 = 640 (<880)

T_SR = 10ms (SR periodicity)

n_SF,PUCCH = 10 (# sub-frames for PUCCH) n_cap = 4 (CQI resources/RB pair)

T_CQI = 80ms (CQI periodicity)

› 2nd_{attempt (n} RB,format1 = 5, nRB,format2 = 3) n_SR,res= (36*5-44)*10*10/10 = 1360 (>810) n_CQI,res = 3*4*80*10/10 = 960 (>880) • 1st_{attempt (n} RB,format1 = nRB,format2 = 4) n_SR,res= (36*4-44)*10*10/10 = 1000 (>810) n_CQI,res = 4*4*80*10/10 = 1280 (>880)

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Pucch resources

number of pucch rb-pairs

› Recommended setting (noOfPucchSrUsers = noOfPucchCqiUsers = 640)

n_PUCCH,SR = [640/10 * 10/10] = 64 n_RB,Format1 = [(64+44)/36] = 3

n_RB,Format2 = [640/(4*80) * 10/10] = 2 n_RB,PUCCH = 3 + 2 = 5 (even  6, < max RB pair per DU)

 Odd number will leave 1 RB-pair unused by PUCCH and PUSCH

• Current setting (noOfPucchSrUsers = noOfPucchCqiUsers = 320)

n_PUCCH,SR = [320/10 * 10/10] = 32 n_RB,Format1 = [(32+44)/36] = 3

n_RB,Format2 = [320/(4*80) * 10/10] = 1 n_RB,PUCCH = 3 + 1 = 4

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Pucch resources

observability

• pmPucchSrCqiResCongCqi

– The number of times a PUCCH allocation request

for CQI resource(s) could not be granted

• pmPucchSrCqiResCongSr

– The number of times a PUCCH allocation request

for SR resource(s) could not be granted

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Pdcch resources

adaptive pdcch (1/2)

• PDCCH is used for

– UL/DL scheduling assignments, e.g. PUSCH/PDSCH resource indication, transport format indication, HARQ info and PUCCH/PUSCH PC commands

• Number of OFDM symbols available for PDCCH in a sub-frame is CFI. Max

OFDM symbols, limited by pdcchCfiMode, is not exceeded

• Recommended setting:

– Bandwidth =< 10MHz : CFI_AUTO_MAXIMUM_3 (current setting), to handle peaks of PDCCH load

– Bandwidth > 10MHz : CFI_AUTO_MAXIMUM_2, since higher number of symbols for PDCCH can increase RB pairs for PUCCH, which leads to reduced UL peak rate

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Pdcch resources

observability

• pmPdcchCceUtil

– PDF of % of CCEs utilized compared with total CCEs available (at the maximum CFI permitted by pdcchCfiMode) each subframe, considering bandwidth and antenna configuration.

• pmPdcchCfiUtil

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Focus areas

• PDCCH Resources

2. UL Noise Rise

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Ul noise rise

pzeronominalpucch, pzeronominalpusch

• pZeroNominalPucch and pZeroNominalPusch can be used to adjust power control target, trade off between coverage and capacity

• Current setting

– pZeroNominalPucch = -117dBm

– pZeroNominalPusch = -96dBm (should be reduced to default -103dBm to reduce UL interference peaks at high load)

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Ul noise rise

observability

• pmSinrPucchDistr

– Distribution of the SINR values calculated for PUCCH

• pmSinrPuschDistr

– Distribution of the SINR values calculated for PUSCH

• pmRadioRecInterferencePwr

– The measured Noise and Interference Power on PUSCH, according to 36.214 of the SINR values calculated for PUSCH

• pmRadioRecInterferencePwrPucch

– The measured Noise and Interference Power on PUCCH, according to 36.214

• pmRadioTbsPwrRestricted

– The number of Transport Blocks on MAC level scheduled in uplink where the UE was considered to be power limited.

• pmRadioTbsPwrUnrestricted

– The number of Transport Blocks on MAC level scheduled in uplink where the UE was NOT considered to be power limited.

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Focus areas

3. PRB Utilization / Cell Throughput Capacity

4. MP Load

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Prb utilization / cell throughput capacity

schedulingalgorithm

System Fairness Cell Throughput

• Current setting schedulingAlgorithm = 3 (PROPORTIONAL_FAIR_MEDIUM),

propose to change to following at high load

– 4 (PROPORTIONAL_FAIR_LOW) or – 5 (MAXIMUM_C_OVER_I)

 Higher Cell Throughput  Higher TTI utilization  Higher PRB utilization

• Performance comparison between different schedulers

– Best cell throughput (from lowest to highest)

• RR < ER < PFH < PFM < PFL < MCI

– System fairness (from lowest to highest)

• MCI < PFL < PFM < PFL < ER < RR

For PFL or Max C/I, user at cell edge may have low throughput, as scheduler has higher weightage for RF condition

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Prb utilization / cell throughput capacity

observability

• Average Cell Throughput UL = pmUeThpVolUl/(pmSchedActivityCellUl/1000) • Average Cell Throughput DL = pmPdcpVolDlDrb/(pmSchedActivityCellDl/1000)

• pmPrbUtilUl

– A distribution that shows the uplink Physical Resource Block (PRB) pair utilization (total number of used PRB pairs by available PRB pairs) on the Physical Uplink Shared Channel (PUSCH)

• pmPrbUtilDl

– A distribution that shows the downlink Physical Resource Block (PRB) pair utilization (total number of used PRB pairs by available PRB pairs) on the Physical Downlink Shared

Channel (PDSCH)

• Average # Simultaneous Active UE UL = pmActiveUeUlSum/pmSchedActivityCellUl • Average # Simultaneous Active UE DL = pmActiveUeDlSum/pmSchedActivityCellDl

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Focus areas

3. PRB Utilization / Cell Throughput Capacity

4. MP Load

• RRC Connection Setup Intensity

– Due to UE releases by Inactivity

– Due to UE releases by RLC Supervision

• Incoming Handover Intensity

• Hardware expansion

5. Connected Users License

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Mp load

mp load control mechanism (new in L13A)

Main contributors (signaling) for MP Load • RRC Connection Setups

• Incoming Handovers • Paging Requests

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Mp load

1.1 RRC Connection setup intensity

(due to UE releases by inactivity)

• The time a UE can be inactive before it is released is controlled

by tInactivityTimer

• Current setting for tInactivityTimer is 10s, requirement from

UE vendor

• Recommend to change to 30s to reduce signaling load for high

capacity cells

For tInactivityTimer set to 30s,

• E-RAB drop rate will increase due to the E-RAB drops only consider the abnormal E-RAB Releases if there was data in buffer (i.e. active).

• Number of UEs stay in RRC_Connected state will be larger, thus lowering the number of available Connected Users License for new users

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Mp load

1.2 RRC Connection setup intensity (due to UE releases by rLC Supervision) – cont’

• As part of Radio Connection Supervision, RLC failures are caused by

– T310 expiry

– Max RLC re-transmissions reached

• T310 is controlled by

– After receiving N310 consecutive “out-of-sync” indications, start timer T310 – After receiving N311 consecutive “in-sync” indications, stop timer T310 – After T310 expired  Radio Link Failure

– Current settings:

• N310 = 20 (recommended, no change) • N311 = 1 (recommended, no change) • T310 = 2s (recommended, no change)  UE is released after T310 (2s) + T311 (3s)

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Mp load

1.2 RRC Connection setup intensity

(due to UE releases by rLC Supervision)

• RLC re-transmissions are controlled by

– Max # RLC re-transmissions before stopping and indicating to RRC max RLC re-tx reached

• SRB/DRB :: dlMaxRetxThreshold (Current setting: 8/8, recommended, no change) • SRB/DRB :: ulMaxRetxThreshold (Current setting: 8/8, recommended, no change)

– Poll timer for RLC re-Tx (if no status report received)

• SRB/DRB :: tPollRetransmitDl (Current: 45ms/50ms, recommend 80ms/80ms) • SRB/DRB :: tPollRetransmitUl (Current: 45ms/50ms, recommend 80ms/80ms)

Increase Poll timer may reduce SE/TTI usage for re-Tx and free SE/TTI for traffic, but re-Tx time is extended from 360-400ms to 640ms (80ms x 8) Re-Tx count #1 … #8 RLC Failure

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Mp load

2. incoming handovers intensity

• Current setting for handover is

– ReportConfigEUtraBestCell::a3offset = 3dB

– ReportConfigEUtraBestCell:: hysteresisA3 = 1dB

– ReportConfigEUtraBestCell:: timeToTriggerA3 = 40ms

• Propose to change a3offset to 5dB (handover margin increased to

6dB) for high capacity cells to reduce signaling load.

a3offsetAnrDelta remains unchanged

Increase handover margin reduces handovers and may impact

retainability

Will review feasibility to use

alternative approach on ‘UE Level Oscillating Handover Minimization’ feature

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Mp load

3. hardware expansion

• MP capacity for DUS is higher than MP capacity

on DUL

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Mp load

observability

• pmProcessorLoad

– The average CPU load on the whole MP system (all the CPU cores).

• pmProcessorLoadDistr

– A distribution of the CPU load of the MP corresponding to the definition of the CPU load used by MP Load Management.

– This counter also includes CPU load consumption from execution on priorities below traffic priority. This includes CPU load from performance management and some O&M tasks.

• pmPagS1Received

– This counter counts the number of received S1AP paging messages in the RBS.

• pmPagS1Discarded

– The number of discarded S1AP paging messages not routed to any cell due to high load (MP Load Control).

• pmRrcConnEstabFailHighLoad

– The total number of failed RRC connection establishments due to high load (MP Load Control).

• pmRrcConnEstabFailOverload

– The total number of failed RRC connection establishments due to overload (Procedure Latency Supervision).

• pmHoPrepRejInHighLoad

– The number of Handover Preparation Failure messages sent by the target eNodeB due to high load (MP Load Ccontrol).

• pmHoPrepRejInOverload

– The number of Handover Preparation Failure messages sent by the target eNodeB due to overload (Procedure Latency Supervision).

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Focus areas

• LTE High Capacity Focus Areas

1. Control Channel Dimensioning

• PUCCH Resources

• PDCCH Resources

2. UL Noise Rise

3. PRB Utilization / Cell Throughput Capacity

4. MP Load

• RRC Connection Setup Intensity

–

Due to UE releases by Inactivity

–

Due to UE releases by RLC Supervision

• Incoming Handover Intensity

• Hardware expansion

5. Connected Users License

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Connected users license

› Current Connected Users License is 800 per DUL

› Connected Users license should be topped-up for high traffic sites on demand basis Increase Connected Users License may have impact on signaling load

Connected Users License check is part of RRC

Setup procedure

DUL Rrc Conn user

DUL21 1500

DUL31 2500

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Connected users

observability

• pmRrcConnEstabFailLic

– The total number of failed RRC Connection

Establishments due to lack of connected users

license

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Focus areas

• LTE High Capacity Focus Areas

1. Control Channel Dimensioning

• PUCCH Resources

• PDCCH Resources

2. UL Noise Rise

3. PRB Utilization / Cell Throughput Capacity

4. MP Load

• RRC Connection Setup Intensity

–

Due to UE releases by Inactivity

–

Due to UE releases by RLC Supervision

• Incoming Handover Intensity

• Hardware expansion

5. Connected Users License

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Summary of high cap parameters

Parameter Current Recommended Objective

noOfPucchSrUsers 320 640 Maximize number of allowed SR users

noOfPucchCqiUsers 320 640 Maximize number of allowed CQI users

pdcchCfiMode (10MHz) CFI_AUTO_MAXIMUM _3

CFI_AUTO_MAXIMUM_3 (no change)

Recommended setting is already set, just monitor CCE and CFI usage

pZeroNominalPucch -117 -117 (no change) Recommended setting is already set

pZeroNominalPusch -96 -103 Reduce UL noise rise at high load

schedulingAlgorithm 3

(PROPORTIONAL_FAIR _MEDIUM)

4 (PROPORTIONAL_FAIR_LOW) or 5 (MAXIMUM_C_OVER_I)

Increase cell throughput and PRB utilization

tInactivityTimer 10s 30s Reduce signaling load

SRB/DRB::dlMaxRetxThreshold SRB/DRB::ulMaxRetxThreshold 8/8 8/8 8/8 (no change) 8/8 (no change)

Max # RLC re-Tx in UL/DL (control signaling load). Recommended setting is already set

SRB/DRB::tPollRetransmitDl SRB/DRB::tPollRetransmitUl 45ms/50ms 45ms/50ms 80ms/80ms 80ms/80ms

Increase poll timer for RLC re-Tx (if no status report received) to avoid RLC failures, reduce signaling load T310 / T311 20 / 1 20 / 1 (no change) Recommended setting is already set, for RLC

supervision

N310 / N311 2s / 3s 2s / 3s (no change) Recommended setting is already set, for RLC supervision

a3Offset 30 (3dB) 50 (5dB) (low priority) Reduce signaling load. Will review feasibility to use alternative approach on ‘UE Level Oscillating Handover Minimization’ feature

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