Ericsson HSDPA Introduction and Troubleshooting for Low Throughput

Ericsson Internal 2008-11-281

HSDPAIntroduction and Troubleshooting

for Low Throughput

Sadok Ben Ali28 Nov 2008


Key characteristics of HSDPA

High data rate

Low data rate

HS-DSCH with dynamic power allocationt

Dedicated channels (power controlled)Common channels

HS-DSCH (rate controlled)

Tot

al c

ell

pow

er

Power

high data rate

low data rateTime

#2#1 #2 #2#1 #1 #1

User 2

Scheduled user

User 1

Fast Link Adaptation

Scheduling


Shared Channel Transmission (1)

� A set of radio resources dynamically shared among multiple users, primarily in the time domain

� Up to 15 codes (SF16) can be allocated and shared between the users. It also depends on what the UE can support.

SF4

SF8

SF16

SF32

SF64

SF128

SF256

HS-PDSCH Cell CCH(s)

HS-SCCH

p-CCPCH

p-CPICH

PICH

AICH

s-CCPCH(PS32Kbps on FACH)


HSDPA channel structure

RNC RNCIur

Iub Iub

Iu Iu

Associated Dedicated Channels

HS-DSCHHS-SCCHHS-DPCCH

� DL: High-Speed Downlink Shared Channel – HS-DSCH

� DL: High-Speed Shared Control Channel(s) – HS-SCCH (SCHEDULING)� Associated Dedicated Channel – A-DCH bidirectional DCH for SRB3.4 signaling (

DPCCH+DPDCH)

� UL :HS Dedicated Physical Common Control Channel - HS-DPCCH (CQI, HARQ ACK/NACK)

Shared Channel Transmission (2)


CQI – Channel Quality Indicator� UE sends CQI info in the UL to aid rate adaptation and scheduling� CQI (1-30) provides the Node B with a measure of the UE's perceived channel quality and the UE receiver

performance� The CQI report estimates the number of bits that can be transmitted to the UE using a certain assumed

power with a block error rate of (blerQualityTargetDl =1%)� UE assumes a HS- PDSCH power to calculate CQI : PHS_assumed = RSCPCPICH +

hsMeasurementPowerOffset + ∆ (3GPP 25214)� CQI = 0 if SNR <= -16, CQI=SNR/1.02 + 16.62 if -16<SNR<14, CQI = 30 if SNR=>14

Fast Link Adaptation (1)


Fast Link Adaptation (2)

� Rate control– Adjusts data rate based on the Radio conditions (CQI)– Fast Adaptation : 2 ms TTI basis– Adaptive Modulation (QPSK and 16 QAM) and Coding– Use “available power”

High data rate

Low data rate

HS-DSCH with dynamic power allocationt

Dedicated channels (power controlled)

Common channels

HS-DSCH (rate controlled)

Tot

al c

ell p

ower

Power


Fast Hybrid ARQ with Soft Combining

� Rapid retransmissions of erroneous data– Hybrid ARQ protocol terminated in Node B

⇒ short RTT (typical example: 12 ms)– Soft combining in UE of multiple transmission attempts

⇒ reduced error rates for retransmissions


Fast Channel-dependent Scheduling (MAC-hs)

� Scheduling => which UE to transmit to at a given time instant and at what rate

– MAC-hs (a new MAC sub-layer in RBS)

� Basic idea: transmit at fading peaks– May lead to large variations in data rate between users

high data rate

low data rateTime

#2#1 #2 #2#1 #1 #1

User 2

User 1

Scheduled user


MAC-hs FunctionsResource Estimation

Queue Validation

• Estimation for available HS-PDSCH power and codes• PHS = Pmax - hsPowerMargin - Pnon-HS• PHSPDSCH = PHS - PHSSCCH

• HS-SCCH power is set with reference to CPICH• Code information available from RNC

• Data to transmit is available• ADCH in uplink in synch for the UE• UE’s minimum TTI capability is ok• Adjusted CQI exists for the UE• Suitable HARQ process exists• MAC-hs transmission window is not full

Queue Selection

• f(CQI) • f(C/I ) • f(average rate)


Queue Selection Algorithms� Ericsson supports the following Scheduling Algorithms

and is configurable per Node B (queueSelectAlgorithm)

– Round Robin (RR)� Cyclically assign the channel to users without taking channel

conditions into account� Simple but poor performance

– Proportional Fair (PF)� Assign the channel to the user with the best relative channel quality� High throughput, fair

– Max C/I Ratio� Assign the channel to the user with the best channel quality� High system throughput but not fair


Channel Switching (New in P5)

IDLE

HS

64/HS

hsd

sch

inac

tivi

tyT

imer

P4

Switching between HS-DSCH and DCH happens to support Iur, IRAT and IFHO Mobility…

P5


HSDPA Throughput

• HS L1 Throughput = W * Number of codes * Modulation scheme /SF=(3.84 M cps 5 * 4 )/16 = 4.8 Mbps

• Max HS MAC-d user data = ( Tbsize (7168) / 2ms) = 3.584 Mbps

The deference between MAC-d and L1 throughput due to Rate matching & turbo code

•The real Max HS MAC-d user data = ( Tbsize / TTI)*(1 - BLER)

CQI valueTransport Block Size

Number of HS-PDSCH

ModulationReference power

adjustment ∆∆∆∆NIR XRV

0 N/A Out of range

1 137 1 QPSK 0 9600 0

2 173 1 QPSK 0

3 233 1 QPSK 0

4 317 1 QPSK 0

5 377 1 QPSK 0

6 461 1 QPSK 0

7 650 2 QPSK 0

8 792 2 QPSK 0

9 931 2 QPSK 0

10 1262 3 QPSK 0

11 1483 3 QPSK 0

12 1742 3 QPSK 0

13 2279 4 QPSK 0

14 2583 4 QPSK 0

15 3319 5 QPSK 0

16 3565 5 16-QAM 0

17 4189 5 16-QAM 0

18 4664 5 16-QAM 0

19 5287 5 16-QAM 0

20 5887 5 16-QAM 0

21 6554 5 16-QAM 0

22 7168 5 16-QAM 0

23 7168 5 16-QAM -1

24 7168 5 16-QAM

25 7168 5 16-QAM -3

26 7168 5 16-QAM -4

27 7168 5 16-QAM -5

28 7168 5 16-QAM -6

29 7168 5 16-QAM -7

30 7168 5 16-QAM -8

HS-DSCH categoryMaximum

number of HS-DSCH codes

received

Minimum inter-TTI interval

Modulation CoderThroughputMbit/s

Category 1 5 3 QPSK&16QAM 1.2










Category 11 5 2 QPSK only 0.9

Category 12 5 1 QPSK only 1.8


• Radio Environment

• Low CQI or Low Modulation rate : it could be due to no enough power (Much power allocated for R99), bad coverage....

• High DTX : UE is not being scheduled. It could be that are many users in the cell

• ACK/NACK rate : UE is not receiving well the data and is sending NACKs, it can be due to improper parameters setting

• USIM• HLR need to be verified for the USIM profile (DL throughput /UL

throughput)

• UE Capability• ueCapability-Info : UE category shall be more than 6

HSDPA Throughput Analysis


HSDPA Throughput Analysis � Laptop

� TCP Window Size should be 102400，MTU=1460

� RBS� Check RBS parameters

� IMA configuration(number of E1s)

� AtmTrafficDescriptor on AAL2 (aal2QoSAvailableProfiles ) in RBS and RNC side� AAL2 Path parameters such as PCR, SCR...

� Check Hardware (some times replacing the HSDPA board can resolve the problem)

• Iub Flow control• Proper Setting for maxHsRate

• The HSDPA Iub flow control algorithm adjusts to the Iub congestion by adapting a reference value (targetHsRate) every second. The reference value is initially set to maxHsRate, which also determines the maximum value for targetHsRate. The more congestion detections, the lower the available bit rate over Iub

• Iub flow capacity is affected by quality of the transport network


• CN

In R4 GGSN by default there is limitation 2M bps in the downlink. To allow more bandwidth, the maximum-bandwidth-downlink has to be set to a bigger value with the policing in the PDP context definition.

RAB-Assignment Request:

{ trafficClass interactive, rAB-AsymmetryIndicator asymmetric-bidirectional, maxBitrate

{ 2048000, (>>> DL)

384000 }, (>>> UL)}

� In SGSN, check if the correct QoS profile has been linked to the IMSI series that were used in the test;

� In GGSN, verify the policing with the PDP context to see if there is any limitation on the downlink.

� The link between the GGSN and the IP router in the IP backbone has to have enabled the auto-negotiation and fixed 100 Mbit/s speed in full-duplex mod



Aal2PathVccTp pmBwErrBlocks

pmBwLostCells

pmBwMissinsCells

pmFwErrBlocks

pmFwLostCellspmFwMissinsCells

pmLostBrCells

pmLostFpmCells

HsDschResources pmAckReceivedpmAverageUserRate

pmIubMacdPduCellReceivedBits

pmNackReceived

pmNoActiveSubFrames

pmNoInactiveRequiredSubFramespmReportedCqi

pmSumAckedBits

pmSumNonEmptyUserBuffers

pmSumTransmittedBits

pmTransmittedCarrierPowerNonHspmUsedCqi

IubDataStreams pmCapAllocIubHsLimitingRatio

pmHsDataFramesLostpmHsDataFramesReceived

pmIubMacdPduRbsReceivedBits

pmTargetHsRate

VplTp pmReceivedAtmCellspmTransmittedAtmCellspmSecondsWithUnexp

VclTp pmReceivedAtmCellspmTransmittedAtmCells

RncFunction pmSentPacketDataHs1 (is stepped only if < 1kB)pmSentPacketDataHs2 (is stepped only if < 10kB but > 1kB)pmSentPacketDataHs3 (is stepped only if < 100kB but > 10kB)pmSentPacketDataHs4 (is stepped only if > 100kB).pmTotalPacketDurationHs1 - duration for data < 1kB.pmTotalPacketDurationHs2 - duration for data < 10kB but > 1kBpmTotalPacketDurationHs3 - duration for data < 100kB but > 10kBpmTotalPacketDurationHs4 - duration for data > 100kB

HSDPA Throughput Analysis Counters :


RNC :� HsTputAverg = 8 * 1000 * ( pmSentPacketDataHs1 / 1000 + pmSentPacketDataHs2 / 1000 +

pmSentPacketDataHs3 + pmSentPacketDataHs4 ) / ( pmTotalPacketDurationHs1 + pmTotalPacketDurationHs2 + pmTotalPacketDurationHs3 + pmTotalPacketDurationHs4 )

� HsTputGt100KbAverg = 8 * 1000 * (pmSentPacketDataHs4) / (pmTotalPacketDurationHs4)

HsTputAverg is looking at HS throughput over all data transmission sizes, even if a small amount of data is sent. HsTputGt100KbAverg is for data transmissions > 100kB, the HsTputGt100KbAverg should give a better indication of the performance achieved with HS because you'd be most interested in the speed when performing large downloads rather than when using smaller transmission sizes where you may not be utilizing the full 2ms air interface frame.

RBS :� The average MAC-hs throughput per PS Interactive HSDPA user:

pmSumAckedBits / (TTI * pmSumNonEmptyUserBuffers)� The average MAC-hs Data rate per PS Interactive HSDPA user:

pmSumTransmittedBits / (TTI * pmSumNonEmptyUserBuffers)� The MAC-hs throughput on cell level:

pmSumAckedBits / (TTI * pmNoActiveSubFrame)� The MAC-hs data rate on cell level:

pmSumTransmittedBits / (TTI * pmNoActiveSubFrame)


If MAC-hs Data rate mush bigger than MAC-hs throughput per user there is a high NACK subframe, we need to check BLER, R99 used power…

KPIs:


HSDPA Throughput Analysis IubDataStreamsIs to check capacity limitation in the Iub Interface : � pmCapAllocIubHsLimitingRatio : is the relative number of occurrences when the calculated Capacity Allocation

figure is limited by the Iub HS bandwidth during a 100 ms period (compared to the total number of 100 ms periods in the PM interval. This is related to Physical throughput, so it will include all the overheads, retransmissions, and the HSDSCH throughput is not mapped to this counter directly. If the counter is pegging, that means the Iub bandwidth limit as been met sometimes, so the configuration of the Iub, i.e., the AtmTrafficDescriptor on AAL2 VC's should be verified.

� pmtargetHsRate : is real capacity of the Iub interface is calculated by the Iub Flow Control according to retransmission ratio and MaxHsRate

Transport Network� VplTp and VclTp counters are used to verify that everything is sent from RNC is received in RBS.� Is to check the quality of transport network.


HSDPA PARAMETRS (1)

MO Class Parameter Value According to…ChannelSwitching downswitchThreshold 0 E/// DefaultChannelSwitching downswitchTimerThreshold 1 BaseLine 1.6ChannelSwitching hsdschInactivityTimer 8 BaseLine 1.6Rcs hsDschRcLostT 100 E/// DefaultRncFunction hsCellChangeAllowed 1 BaseLine 1.6RncFunction hsOnlyBestCell 1 BaseLine 1.6RncFunction hsToDchTrigger. servHsChangeInterRnc ON BaseLine 1.6RncFunction hsToDchTrigger. servHsChangeIntraRnc ON BaseLine 1.6RncFunction hsToDchTrigger. changeOfBestCellIntraRnc ON BaseLine 1.6RncFunction hsToDchTrigger. poorQualityDetected ON BaseLine 1.6UeMeasControl hsQualityEstimate 1 BaseLine 1.6UeMeasControl hsTimeToTrigger1d 1280 BaseLine 1.6

MO Class Parameter Value According to…IubDataStream maxHsRate 29 BaseLine 1.6, 2 E1s linksNodeBFunction flexibleSchedulerOn TRUE BaseLine 1.6NodeBFunction supportOf16qam TRUE BaseLine 1.6


MO Class Parameter Value According to…Carrier cqiAdjustmentOn 1 BaseLine 1.6Carrier hsScchMaxCodePower -20 E/// DefaultCarrier queueSelectAlgorithm 1 BaseLine 1.6HsDsch codeThresholdPdu656 0 BaseLine 1.6HsDsch deltaAck1 5 BaseLine 1.6HsDsch deltaAck2 7 BaseLine 1.6HsDsch deltaCqi2 6 BaseLine 1.6HsDsch deltaNack1 5 BaseLine 1.6HsDsch deltaNack2 7 BaseLine 1.6HsDsch hsMeasurementPowerOffset 80 E/// RecommendedHsDsch numHsPdschCodes 5 BaseLine 1.6HsDsch numHsScchCodes 3 BaseLine 1.6RbsLocalCell dynamicHsPdschCodeAdditionOn 1 BaseLine 1.6RbsLocalCell maxNumHsdpaUsers 16 BaseLine 1.6RbsLocalCell maxNumHsPdschCodes 15 BaseLine 1.6UtranCell beMarginDlCode 1 BaseLine 1.6UtranCell dlCodeAdm 85 BaseLine 1.6UtranCell hsdpaUsersAdm 12 BaseLine 1.6

HSDPA PARAMETRS (2)


Documents

Ericsson HSDPA Introduction and Troubleshooting for Low Throughput