Qualcomm Lte Performance Challenges 09-01-2011 130905182126

8/12/2019 Qualcomm Lte Performance Challenges 09-01-2011 130905182126

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LTE Performance Expectations& Challenges

Engineering Services GroupSeptember 2011


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Agenda

Overview of ESG LTE Experience

ESG AT&T Engagements for LTE

LTE Performance Expectations

Factors Impacting LTE Performance

Key Areas To Be Considered for LTE Launch

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ESG LTE Experience Overview

ESG

EUTRAVendor IOTs

R&D

3GPP SA5Participation

Chipset LabTesting

Technology trial participations RFP development

LTE Protocols trainings & hands-onoptimization workshops delivered to2600+ engineers

LTE design guidelines

LTE capacity & dimensioning

Performance assessment &troubleshooting in commercial LTE

networks

Performance studies & evaluationsusing ESG simulation platforms

Early exposure to LTE through Qualcomms leadership position in technology

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ESG-AT&T LTE Partnership HighlightsMultiple engagements with NP&E and A&P teams

LTE Technology Trial (2009) ESG SME in Dallas for 6 months Participation in Phase I & II Trial SME support and technical oversight of

execution by vendors

Review results and progress of the trialwith the vendors

RAN Architecture & Planning Team

Field testing in BAWA & Dallas FOA clusters, labtesting in Redmond

RAN Design Team

LTE Design OptimizationGuidelines LTE Design System Studies

LTE Design & ACP ToolStudies

Antenna Solutions Group

LTE capacitycalculator forvenues

IDAS/ODAS design& optimizationguidelines

CSFB Performance Assessment (starting next week)

LTE Realization Group

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Expected LTE Performance


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Key Areas of LTE Performance

LTE Call Setup and Registration

LTE Single-user Throughput

LTE Cell Throughput

User Plane Latency

Handover Success Rates and Data Interruption

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Expected LTE Performance Dependencies

LTE System Bandwidth1.4 -> 20 MHz

FDD/TDDThroughput expectations

LTE UE Category Current category 3 DevicesDeployment Considerations

Number of eNodeB Transmit AntennasBackhaul Bandwidth

System ConfigurationTransmission Modes used for DL (Diversity, MIMO schemes)Control channel reservation for DLResource Reservation for ULSystem Parameters

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LTE Call Setup, Registration

UE NW

UE Power Up

Initial acquisitionPSS, SSS, PBCH, SIBs

Idle, camped

RRC Connection Setup

Attach request incl. PDN connectivityrequest

Attach response (accept)Incl. Activate Default Bearer Ctxt

RequestAttach complete

RRC connectedRRC Connection SetupDuration, Success rates

Attach and PDN Connectivity

Duration, Success Rates

RRC Connection Request (Msg3)

RRC Conn. Setup Complete (Msg4)

Idle, not camped

RACH (Msg1, Msg2)

Authentication,Integrity, CipheringSecurity Procedures

Number of RACH Attempt,RACH Power, ContentionProcedure Success rates

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Key LTE Call Setup Metrics

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Metric Typical ExpectedValues

Reasons for Variability

Number of RACH and RACHPower

RACH Attempts 99% Poor RF conditions, Limited number of

RRC Connected users allowed causingRRC Rejects, large RRC inactivity timers

RRC Connection SetupDuration (Including RACHduration)

30-60ms Multiple RACH attempts, Msg3retransmission, delayed contentionprocedure

Attach and PDN Connectivity

Success Rates

>99% Failure of ATTACH procedure (EPC issues)

or EPS Bearer setup, poor RF conditions,Integrity/Security failures

Attach and PDN ConnectivityDuration

250-550ms Multiple Attach Request, Authenticationor Security related failures, EPC issues,delayed RRC Reconfiguration to setupDefault RB


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Peak Single User DL Throughput 10 MHz

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Ideal case 0% BLER, 100% scheduling

Near Cell field location 5% BLER, 100% scheduling

Scenario LTE-FDD Cat 3 UE 2x2 MIMO Max DL MCS 28 used with 50

RBs and Spatial Multiplexing


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Peak Single User UL Throughput 10 MHz

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Ideal case 0% BLER, 100% UL scheduling UL MCS 23 and 50 RBs

Near Cell field location 5% BLER, 100% scheduling UL MCS 24 and 45 RBs (some

RBs reserved for PUCCH)

Scenario LTE-FDD Cat 3 UE Max UL MCS 23/24 depending

on number of UL RBs


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LTE DL Cell Throughput Multiple Devices

Device-RUN

Throughput [Mbps] Sched.Rate[%]

BLER[%]

MCS NumRB

CQI RI RSRP[dBm]

RSRQ[dB]

FTP L1 Norm.L1**

T2 13.90 14.44 46.71 30.91 5.74 23.31 49.4 14.18 2 -73.85 -9.06

P2 16.58 16.65 53.04 31.39 5.40 25.12 49.76 14.48 2 -71.01 -8.98

P2 17.34 17.87 60.0 29.68 1.52 26.47 49.80 14.87 2 -68.87 -9.06

Total(3 devices)

47.82 48.96 91.98

All 3 devices are scheduled almostequally (~30% each)

Device with highest CQI reportedreceives highest MCS and low BLERand consequently highest DL L1Throughput Total L1 Cell Throughput ~49 Mbps

Total Scheduling rate ~92% (


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User Plane Latency

Ave (ms) Min (ms) Max (ms) STD (ms)

42.1 36 62 4.3

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30 40 50 60 70 80

D i s t r i b u t i o n

User Plane Latency (ms)pdf cdf

Stationary, Near cell conditionsPing size = 32 Bytes

Ping Server: Internal server

Ping Round-Trip-Time distribution from one commercial network above is concentrated between 40 -50 ms Lower Ping RTT ~25 ms have been observed in some networks Ping RTT can be dependent on CN delays, backhaul, system parameters and device

Ping Round-Trip Time (RTT) in an unloaded system should be ~20-25ms Such Ping tests are done to an internal server one hop away from LTE PGW (avoid internet delays)


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LTE Intra-frequency Handover Success Rate

DL Test Run Total HO HO Failure(case)

Run 1 125 2 ( A, B)

Run 2 108 0

Run 3 95 1 ( A)

Total 328 3

UL Test Run Total HO HO Failure(case)

Run 1 106 0

Run 2 118 0

Run 3 98 1 ( A)

Total 320 1

Some Handover failure cases:

A) RACH attempt not successful andT304 expires

B) HO command not received after

Measurement Report

HO Success Rate is high in both UL and DL

99.05

99.69

99.37

98.4098.60

98.80

99.00

99.20

99.40

99.60

99.80

100.00

P e r c e n t a g e

[ % ]

HO Success rate

HO Success Rate

Download Upload Total

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LTE Intra-frequency Handover/Data Interruption

Ave (ms) Min (ms) Max (ms) STD (ms)

78 38 199 34

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0.20.3

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0 25 50 75 100 125 150 175 200

D i s t r i b u t i o n

HO Interrupt Time (ms)pdf cdf

HO Interrupt Time:Interval betweenLast DATA/CONTROLRLC PDU onsource cellandFirst DATA/CONTROLRLC PDU on target cell

Data Interruption Time:Interval betweenonly DATA RLC PDUs

becomes much higherthan 199 ms

Current LTE Networks have higher HO and Data Interruption Times eNodeB buffer optimization and data forwarding support needed

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Factors Affecting LTE Performance

Deployment

Pilot Pollution,Interference

Neighbor ListIssues, ANR

Parameters(Access, RRC

Timers)

EUTRAN, EPCImplementation

and SoftwareBugs

Unexpected RRC

ConnectionReleases

DL MCS andBLER, Control

Channel impacts

eNodeBSchedulerlimitations

Mobility

Intra-LTEReselection, HO

Parameters minimize Ping-

pongs

Inter-RAT HOBoundaries and

Parameters

DataPerformance

BackhaulConstraints

TCP Segmentlosses in CN

MTU Sizesettings on

devices

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RF Issues Impacting Call Setup Performance - 1

Sub-optimal RF optimizationdelays LTE call-setup

Mall served by PCI 367 PCI 212 leaking in partly

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RF Issues Impacting Call Setup Performance - 2

UE NW

UE Power Up

Initial acquisition(incl. attempt on PCI 367) Idle, camped: PCI 212

RRC Connection RequestRRC Connection Setup

RRC connected

RRC Setup Duration:60 ms

RRC Conn. Setup Complete

PSS, SSS, PBCH, SIBs

Idle, not camped

1st Attach request incl. PDNconnectivity request

2nd Attach request incl. PDNconnectivity request

Duration:4.533 sec

UL data to sendRACH not successful

RACH (Msg1, Msg2)

RACH (Msg1-Msg4)

UE Reselects to PCI 367

No attach response (accept)

PCI 212: RSRP = -110 dBmPCI 367: RSRP = -104 dBm

3 rd Attach request incl. PDNconnectivity request Attach Accept is sent

Pilot Pollution can impact call-setup, causing intermediate failures impacting KPIs, reselections and highercall-setup time

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RF Issues Causing LTE Radio Link Failure - 1

PCIs 426, 427,428 are notdetected (site is missing)Lack of dominant server =>Area of Pilot pollution

PCI 376

PCI 42 & PCI 142

Missing sites during initial deployment phase requires careful neighbor planning or optimal use of ANR

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RF Issues Causing LTE Radio Link Failure - 2

1. UE is connected to PCI 4112. UE reports event A3 twice for PCI 142 (Reporting int. = 480 ms)3. UE reports event A3 for PCI 142 & 4634. No Neighbor relation exists between PCI 411 and 142 (Clear

need for ANR) . UE does not receive handover command, RLFoccurs

5. RRC Re-establishment is not successful, UE reselects to PCI 42

RLF DL BLER increases to 70%UL power increases to 23 dBm

RSRP & SINR decrease to -110 dBm & -8 dB

MRM A3

RLF

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Backhaul Limitations Reduce LTE DL Throughput

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

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

L 1 T

h r o u g

h p u t

( k b p s

)

SINR (dB)

L1 Throughput vs SINR Throughput is alwayslower than 50 Mbps,even at high SINR

Backhaul limitationnegatively

Impacts theallocation of radioresources

Statistics are calculated by using metricsaveraged at 1 sec intervals

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0 .0 0 0 .0 0 0.00 0 .0 0 0 .0 0 0 .0 0 0.02

0.12

0.18

0.64

0 .0 0 0 .0 0 0 .0 00.04

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0.2

0.4

0.6

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0.4

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MCS

PDF CDF

eNodeB Scheduler: MCS and BLER Relationship

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 0 0 .0 0 0 .0 0 0.00 0.01

0.43

0.56

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0.2

0.4

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CQI

PDF CDF

Highest CQI is 15 and highest DL MCS is 28 Although we see a significant number of

CQI=15 reported, scheduler hardly assignsany MCS=28!

Whenever DL MCS 28 is scheduled BLER on1st Tx is 100%, hence scheduler uses MCS 27

Number of symbols for PDCCH is fixed at 2

and results in higher code-rate for MCS 28

MCS=28: TBS = 36696 (@49&50 PRB) MCS=27: TBS = 31704 (@49&50 PRB)

10 Mbps L1 throughput difference!(2x2 MIMO, 2 Code Words)

P D F

C D F

P D F

C D F

Lower than expected Peak DL throughput as eNodeB scheduler avoids MCS 28 due to high BLER and fixedcontrol channel symbol assignment

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Lower eNodeB Scheduling reduces DL Throughput

P1_AvgL1Throughput P1_AvgScheduledRate P1_AvgMCS_DL P1_AvgL1BLER

Time19:13:1519:13:1019:13:0519:13:0019:12:5519:12:5019:12:4519:12:4019:12:3519:12:3019:12:2519:12:2019:12:1519:12:1019:12:0519:12:0019:11:55

k b p s

50,000

40,000

30,000

20,000

10,000

0

p e r c e n

t a g e

1009080

70605040302010

0

N / A

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24

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p e r c e n

t a g e

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L1 thpt >50 Mbps Following scheduling rate and DL MCS

Scheduling rate ~ 85-90% (< 100%) Linked to lack of DL scheduling when SIB1

is transmitted and only 1 user/TTI support

MCS ~26-27

Low BLER negligible impact on throughput

Scheduling dip after ~78 sec

L 1 T p u t

S c h e

d u l i n g

M C S

B L E R

Internal Modem Time

eNodeB Scheduler implementation results in lower scheduling rate and lower DL throughput

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Impact of MTU Size and TCP Segment Losses

TCP MSS: 1460, TCP MTU:1500

TCP packet stats: Re-tx: 765 (0.2%) ooOrder: 5380 (1.5%)

TCP graph shows quite someslow starts and irregularities

MTU of 1500 can also result infragmentation of IP segmentson backhaul given GTP-Uheaders => Negatively impactsDL throughput

TCP graph shows quite someslow starts and irregularities

due to TCP segment losses inCore Network => Negativelyimpacts DL Applicationthroughput

Setting device MTU sizes correctly and minimizing CN packet losses is important to avoid negativeApplication layer throughput impacts

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Key Areas to be considered LTE Initial Launch

Optimize pilot polluted areas Verify neighbor list planning,use ANR if available Optimization study of systemparameters is critical forhandling increased load

Deployment

Insufficient backhaul can

reduce DL throughput Sporadic packet discards inCore Network Correct MTU size enforcementon all devices

Data Performance

Optimize HO parameters to ensurehigh Handover Success rates andreduce handover ping-pongs Unexpected Radio Link Failures canimpact performance

Inter-RAT optimization to ensuresuitable user-experience duringInitial build-out

Mobility

Unexpected RRC related dropsand RACH failures may need tobe investigated Several RAN limitations exist Scheduler limitations must beaddressed before demandincreases

Implementation

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Qualcomm Lte Performance Challenges 09-01-2011 130905182126

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