HSDPA Technical HighlightsHSDPA (High Speed Downlink Packet Access)Next evolution step of UMTS, 3.5GDefined in 3GPP Rel5 specsOffers peak data rates up to 14 Mbit/s (2 Mbit/s with R99 UMTS) and 50-100% increase in system capacityHSDPA is a set of new features in base station and terminal:AMC (Adaptive Modulation and Coding)HARQ retransmissionsFast schedulingFast power control and variable SF are replaced with AMC, multicode transmission, and HARQNo SHOHSDPA features are applied to new HS-DSCH (High Speed Downlink Shared Channel) transport channelRel99 channels can co-exist with HS-DSCH

HSDPA terminal categoriesHSDPA offers up to 5.4 Mbps throughput with QPSK coding, and up to 14.4 Mbps throughput with 16QAM codingCategory 7/8 currently availableCalled Multi coding

HSDPA in Nemo ToolsNemo Outdoor supports HSDPA measurementsNemo Handy for Nokia N95 supports HSDPA measurementsNemo Analyze supports post-processing of HSDPA measurementsSupported terminals:Qualcomm TM6280 and MSM7200TM based terminals, data cards and USB modemsNokia N85, N95 &N96Nokia 6120/ 6121Motorola V3XX& V9(EMEA& NA versions)Samsung G800 (7.2Mbps)Huawei E169

Recorded HSDPA parameters include: Cellular system Carrier number HSDPA UE category Power offset between pilot power and HSDPA MAX downlink power Number of monitored signalling channels Packet data technology Packet state

Serving HSDPA cell (SC) Transport Block Size distribution Effective coding rate Modulation Number of codes MAC layer throughput and transmission TTI CQI distributionRequested Physical ThroughputHS-DSCH Activity rateHS-SCCH Usage

HSDPA Performance AnalysisQuestion: What is the end-user performanceAnswer: Throughput and delay (RTT)

Question: If the performance is not good, why so?Answer: There is following potential reasons for low performance:Terminal capability. Terminal does not support high throughputsBad radio conditions (parameters: Ec/N0, RSCP, G-factor), link adaptationOther HSDPA users in the cell. (Indicators: HS-DSCH activity rate (High Speed Downlink Shared channel), HS-SCCH usage rate (High-Speed Shared Control channel )). Bottleneck elsewhere than in radio interface. E.g. Iub transmission, Application). (Indicators: HS-DSCH activity rate, HS-SCCH usage rate).

HSDPA parameters in Nemo tools 1/5All release 99 parameters available earlier with Qualcomm are supported E.g. Application throughput, PPP throughput, CPICH Ec/No etc..Blue colored parameters are supported only with Nemo AnalyzeRest of the parameters are supported both with Nemo Outdoor and Nemo Analyze

List of parameters:CQI percentage histogramChannel quality indicator (CQI), reported by terminal to the NWReported in every 2ms by the terminal, histogram event written to measurement file in every 200msCQI modeThe most common CQI value among in histogram

HSDPA parameters in Nemo tools 2/5Link adaptation parameters (percentage histogram)ModulationEffective codingTransport block sizeFirst channelisation code usedNumber of codes

Modulation (mode)Effective coding (mode)Number of codes (mode)

HSDPA parameters in Nemo tools 3/5HS-DSCH 1st retransmission ratePercentage of blocks retransmitted onceHS-DSCH 2nd retransmission ratePercentage of blocks retransmitted twiceHS-DSCH 3rd retransmission ratePercentage of blocks retransmitted 3 timesMAC block rate downlinkNumber of radio blocks received in measurement period (200ms with Qualcomm)# Number of ACK/NACKsTotal number of ACK/NACK status messages sent to uplinkMAC-HS (L1) BLERNumber of NACK messages from total in percentage (that is, percentage of erroneous blocks before HARQ)HSDPA HS-SCCH usage (high-speed shared control channel )Percentage of time over the measurement period (200ms) when HS-SCCH has indicated incoming data to the terminalPhysical layer requested throughputComputational throughput based on CQI value. The throughput that would have been achieved, if network would have sent with the link adaptation parameters defined by the CQI

HSDPA parameters in Nemo tools 4/5Packet technologyHSDPA/UMTS/EDGE/GPRSHSDPA UE categoryHS-DSCH scrambling codeServing HS-DSCH cell scrambling code# HS-SCCHsNumber of HS-SCCH channels listened by the phonePower offsetPower offset in dB between HS-DSCH and CPICHMAC-HS(L1) throughput downlinkThroughput provided by the L1/MAC-HS to the upper layersHS-DSCH activity ratePercentage of time when HS-DSCH channel has been allocated to the measured user (max 100% with inter-TTI interval 1)G-factor estimateBest active set RSCP / (Other cell1 RSCP + other cell2 RSCP + + Thermal noise)

HSDPA parameters in Nemo tools 5/5HS- PDSCH throughput (High Speed Physical Downlink Shared Channel throughput)CQI feedback cycleControls how often the UE transmits new CQI information on the uplink (see 3GPP TS 25.214 s6A.1.2).CQI repetition factorControls how often the UE repeats CQI information on the uplink (see 3GPP TS 25.214 s6A.1.2).Ack/Nack repetition factorControls how often the UE repeats each ACK or NACK (see 3GPP TS 25.214 s6A.1.1).HSDPA HARQ process informationHARQ uses incremental redundancy, where user data is transmitted multiple times using different codings. When a corrupted packet is received, the user device saves it and later combines it with the retransmissions, to recover the error-free packet as efficiently as possible. Even if the retransmitted packets are corrupted, their combination can yield an error-free packet.

Perfecting Wireless Communications

*HSDPA key parameters examples

Verification of Link Adaptation

Variations in channel conditions (CPICH Ec/No) affect link adaptation parametersKey parameters: L1 throughputEffective coding rateModulationNumber of multicodesHARQ retransmission ratePhysical Channel Quality Indicator (CQI)HS-DSCH power offsetCPICH Ec/No

Verification of Link AdaptationHARQ Retransmissions

Key parameters: 1st, 2nd, and 3rd MAC-HS retransmission rate1st retransmission rate should be in reasonable levelLow rate can indicate too conservative link adaptation2nd and 3rd retransmission rates should be near to 0

The effect of all link adaptation parameters is seen in throughputMAC- HS throughput vs. radio conditions gives the best overall picture of link adaptationChannel Quality Indicator (CQI) indicates the channel quality seen by the terminalHS-DSCH radio condition measurements other than CQI are not availableCPICH Ec/No together with HS-DSCH power offset indicates the channel quality of HS-DSCHThroughput may also vary due to other than radio reasons: Core/transmission network bottlenecksApplication protocol effects, etc.HS-DSCH power offset to CPICH: 4.5dBHS-DSCH power offset to CPICH: 3dBHS-DSCH power offset to CPICH: 0dBVerification of Link AdaptationMAC- HS Throughput vs. Radio Channel Conditions

ThroughputTransmission/Core NW Limitation or Other HSDPA users in the CellPhysical layer requested throughput is 5.34MB (computational throughput based on CQI)Actual MAC-HS throughput is ~235kBRadio conditions would allow ~5MB higher throughputHS-SCCH usage is 12% 88% of the time the HSDPA channel has been idle or allocated to another user

Packet Scheduling VerificationTrade-off between system capacity and service coverage with packet schedulingPerformance and scalability of HSDPA depends strongly on the vendor-specific packet scheduling algorithmTesting needed!Multiple test terminals in the same cell downloading bulk dataDifferent channel conditions and/or QoS profilesKey parameters:HS-DSCH activity rate End-user/cell throughput HSDPA DTX percentage

Switching from HS-DSCH to DCHRunning out of HSDPA capacity, or defined coverage, or some other RRM reasonSwitching is an RRC procedure, where at least transport channel is reconfiguredChannel switching causes a break in the data flowMAC-HS buffer in Node B is flushed, and the data is retransmitted in RLC layerFrom application perspective the switch is seamless

HS-DSCH Cell ChangeHS-DSCH is not in SHOHS-DSCH is transmitted from one of the active set cellsHS-DSCH channel changed to other active set cell with RRC signalingChannel switching causes a break in the data flowRNC stops sending DL data before channel reconfiguration Data is not lostFrom application perspective the switch is seamless

R99 vs. HSDPA ExampleR99 terminal and HSDPA terminal, both downloading data in the same cellStationary test

Example: Increased Interference Due to HSDPAR99 384kbps bearer (SF8), lowers CPICH Ec/No about 1dBHSDPA transfer decreases CPICH Ec/No about 4dBHSDPA typically takes up a large share of the power resources InterferenceHS-DSCH power offset to CPICH: 4.5dB

HSDPA Field TestsExpected HSDPA Performance Based on R99 MeasurementsG-factor or Ior/Ioc together with HS-DSCH Tx power are the variables in most of the HSDPA performance simulations

G-factor or Ior/Ioc can be estimated based on CPICH measurements from serving and neighboring cellsEqually loaded cells are assumed

Estimation of:HSDPA performance in existing R99 networkHSDPA performance in loaded network

Microcell environment (antennas on the walls)Macrocell environment (antennas on masts and rooftops

HSDPA Field TestsChallenge in Radio Network PlanningServing cell dominance has a relatively big effect on throughput compared to R99HSDPA makes the deployment scenario (micro/macro, etc.), and the radio network planning visible to the end-user

HSDPA Field TestsGeographical Visualization

Results can be visualized on a mapFor example, MAC-HS DL throughputProblem areas can be pinpointed geographicallyBest active set cell Ec/No below -15dBNumber of HS-DSCH multicodes less than 3

HSDPA Field TestsStatistics Per CellThroughput statistics per cell Modulation statistics per cellProblem/worst cells can be pinpointed

ConclusionsPerformanceMAC-HS throughputRLC/PPP/App. throughputRTT (Ping)

Radio conditionsCPICH Ec/NoHS-DSCH power offsetCQI

Link adaptationCoding rateModulationNumber of multi codesMAC BLERHS-DSCH activity rate

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