High-Speed Downlink Packet Access (HSDPA) · PDF fileHigh-Speed Downlink Packet Access (HSDPA) ... UMTS Networks Andreas Mitschele-Thiel, ... Advanced transmission to increase data

High-Speed Downlink Packet Access (HSDPA)

HSDPA Background & BasicsPrinciples: Adaptive Modulation, Coding, HARQChannels/ UTRAN ArchitecturePrinciples: Fast scheduling, MobilityPerformance Results

UMTS Networks 2Andreas Mitschele-Thiel, Jens Mückenheim Nov. 2011

Motivation (as of 2000)

As the UMTS networks are rolled out, the demand for high bandwidth services is expected to grow rapidly. By 2010, 66% of the revenues will come from data services (source: UMTS forum).Release 99/4 systems alone will not be capable to meet these demands. (Realistic outdoor data rates will be limited to 384kbps).A more spectral efficient way of using DL resources is required.Competition with CDMA 2000 1x EV-DO/DV

GSM/GPRS

UMTS Rel. 99

Voice, low speed packet data No Multimedia, Limited QOS

Medium rate Packet data Theoretical 2 Mbps but ~384 kbps subjected to practical constraints


HSDPA Background

Initial goalsEstablish a more spectral efficient way of using DL resources providing data rates beyond 2 Mbit/s, (up to a maximum theoretical limit of 14.4 Mbps)Optimize interactive & background packet data traffic, support streaming serviceDesign for low mobility environment, but not restrictedTechniques compatible with advanced multi-antenna and receivers

Standardization started in June 2000Broad forum of companiesMajor feature of Release 5

Enhancements in R7 HSPA+Advanced transmission to increase data throughputSignaling enhancements to save resources


HSDPA Basics

Evolution from R99/ R45MHz BWSame spreading by OVSF and scrambling codesTurbo coding

New concepts in R5Adaptive modulation (QPSK vs. 16QAM), coding and multicodes (fixed SF = 16)Fast scheduling in NodeB (TTI = 2ms)Hybrid ARQ

Enhancements in R7 HSPA+Signaling enhancements64QAMMIMO techniques, increase of the bandwidth


Higher Order Modulation

Standard modulation scheme in UMTS networksQPSK 2 bit per symbol

With HSDPA, modulation can be switched between two schemesQPSK 2 bit per symbol16-QAM 4 bit per symbol

Low bitrate robust High bitrate Sensitive to disturbances


Key Principles

Adaptive Modulation and Coding(Mother Turbo code rate = 1/3)

For wireless data, link adaptation through Rate Control is more effective then Power Control.Users in favorable channel conditions (based on Channel Quality indication) are assigned higher code rates and higher order modulation (16QAM).This means higher data rates = Reduced latency

But what about when channel is changing at high rate;Can AMC guarantee reliability?


Hybrid ARQ

H-ARQ automatically adapts to instantaneous channel conditions by:fast retransmissions at physical layeradding redundancy only when needed

The retransmitted packets are combined with original packet to improve the decoding probability.Simple form of Hybrid ARQ shows significant gains over link adaptation alone. Different schemes can be used for retransmission of original data packet.

Chase combiningIncremental Redundancy

No. In fast fading conditions, AMC alone is not enough.


Fast Scheduling

Channels are uncorrelated Multi-user diversityAssign the resources to the best user(s) in time to maximise throughputGains increase with number of users

Max C/IProportional fair Round Robin

10

With HSDPA Scheduling function is moved from RNC to Node-B.

Fading is good in multi-user environment!!


HS-DSCH Principle I

Channelization codes at a fixed spreading factor of SF = 16Up to 15 codes in parallel

OVSF channelization code tree allocated by CRNCHSDPA codes autonomously managed by NodeB MAC-hs scheduler

Example: 12 consecutive codes reserved for HS-DSCH, starting at C16,4

Additionally, HS-SCCH codes with SF = 128 (number equal to simult. UE)

SF=8

SF=16

SF=4

SF=2

Physical channels (codes) to which HS-DSCH is mapped CPICH, etc.

C16,0C16,15


HS-DSCH Principle II

Resource sharing in code as well as time domain:Multi-code transmission, UE is assigned to multiple codes in the same TTIMultiple UEs may be assigned channelization codes in the same TTI

Example: 5 codes are reserved for HSDPA, 1 or 2 UEs are active within one TTI

Data to UE #1 Data to UE #2 Data to UE #3

Time (per TTI)

Code

not used


UMTS Channels with HSDPA

Cell 1

UE

Cell 2

R99 DCH (in SHO)UL/DL signalling (DCCH)UL PS serviceUL/DL CS voice/ data

Rel-5 HS-DSCHDL PS service(Rel-6: DL DCCH)

= Serving HS-DSCH cell


HSDPA Channels

HS-PDSCHCarries the data trafficFixed SF = 16; up to 15 parallel channelsQPSK: 480 kbps/code, 16QAM: 960 kbps/code

HS-SCCHSignals the configuration to be used next: HS-PDSCH codes, modulation format, TB informationFixed SF = 128Sent two slots (~1.3msec) in advance of HS-PDSCH

HS-DPCCHFeedbacks ACK/NACK and channel quality information (CQI)Fixed SF = 256, code multiplexed to UL DPCCHFeedback sent ~5msec after received data


Timing Relations (DL)

NodeB Tx viewFixed time offset between the HS-SCCH information and the start of the corresponding HS-DSCH TTI: HS-DSCH-control (2 Tslot= 1.33msec)HS-DSCH and associated DL DPCH not time-aligned

TB size & HARQ Info

Downlink DPCH

HS-SCCH

DATA HS-PDSCH

3 Tslot (2 msec)

HS-DSCH TTI = 3 Tslot (2 msec)

HS-DSCH-control = 2 Tslot

Tslot (2560 chips)

ch. code & mod


Timing Relations (UL)

UE Rx viewAlignment to m 256 to preserve orthogonality to UL DPCCHHS-PDSCH and associated UL DPCH not time-aligned (but “quasi synch”)

DATA

Uplink DPCCH

HS-PDSCH

HS-DPCCH

3 Tslot (2ms)

m 256 chips

UEP = 7.5 Tslot (5ms) 0-255 chips

Tslot (0.67 ms)

CQI A/NCQI A/NCQI A/NCQI A/N


HSDPA Architecture

MAC-c/sh

MAC-d

RLC

RRC PDCP

Logical Channels

Transport Channels

MAC-b

BCH

BCCHDCCHDTCH

SRNC

CRNC

NodeB

DCH

Upper phy

DSCHFACH

Evolution from R99/R4

• HSDPA functionality is intended for transport of dedicated logical channels

• Takes into account the impact on R.99 networks

MAC-hs

HS-DSCH

HSDPA in R5

• Additions in RRC to handle HSDPA

• RLC nearly unchanged(UM & AM)

• Modified MAC-d with link to MAC-hs entity

• New MAC-hs entity located in the Node B

w/o

MAC

-c/s

h


MAC-hs in NodeB

MAC-hs

MAC – Control

HS-DSCH

Priority Queue distribution

MAC-d flows

Scheduling

Priority Queue

Priority Queue

Priority Queue

UE #1 UE #2

UE #N

MAC-hs FunctionsPriority handlingFlow Control

To RNCTo UE

SchedulingSelect which user/queue to transmitAssign TFRC & Tx powerHARQ handling

Service measurementse.g. HSDPA provided bitrate

TFRC: Transport Format and Resource Combination


MAC-hs in UE

MAC-hs

MAC – Control

Associated Uplink Signalling HS-DPCCH

To MAC-d

Associated Downlink Signalling HS-SCCH

HS-DSCH

HARQ

Reordering Reordering

Re-ordering queue distribution

Disassembly Disassembly

MAC-hs Functions

HARQ handling

ACK/ NACK generation

Reordering buffer handling

Associated to priority queues

Flow control per reordering buffer

Memory can be shared with AM RLC

Disassembly unit


Data Flow through Layer 2

Higher Layer

L1

Higher Layer PDU

RLC SDU

MAC-d SDU

MAC-d PDU

…RLCheader

RLCheader…

MAC-d SDU

MAC-d PDU

CRC

……

MAC-dheader

MAC-dheader L2 MAC-d

(non-transparent)

L2 RLC(non-transparent)Segmentation

&Concatenation

Reassembly

Higher Layer PDU

RLC SDU

MAC-hs SDU MAC-hs SDU…MAC-hsheader L2 MAC-hs

(non-transparent)Transport Block (MAC-hs PDU)

…


Hybrid Automatic Repeat Request

HARQ is a stop-and-wait ARQUp to 8 HARQ processes per UE

Retransmissions are done at MAC-hs layer, i.e. in the Node BTriggered by NACKs sent on the HS-DPCCH

The mother code is a R = 1/3 Turbo codeCode rate adaptation done via rate matching, i.e. by puncturing and repeating bits of the encoded dataTwo types of retransmission

Incremental RedundancyAdditional parity bits are sent when decoding errors occuredGain due to reducing the code rate

Chase CombiningThe same bits are retransmitted when decoding errors occuredGain due to maximum ratio combining

HSDPA uses a mixture of both types


HARQ Processes

HARQ is a simple stop-and-wait ARQ Example

RTTmin = 5 TTISynchronous retransmissions (MAC-hs decides on transmission)

UE support up to 8 HARQ processes (configured by NodeB)Min. number: to support continuous receptionMax. number: limit of HARQ soft bufferNumber of HARQ processes configured specifically for each UE category

1

1

2 2

2

3 4 5 3

3 4 5

1

RTTHARQ

DataHS-PDSCH

ACK/NACKHS-DPCCH


HSDPA UE Categories

The specification allows some freedom to the UE vendors

12 different UE categories for HSDPA with different capabilities (Rel.5)

The UE capabilities differ inMax. transport block size (data rate)Max. number of codes per HS-DSCHModulation alphabet (QPSK only)Inter TTI distance (no decoding of HS-DSCH in each TTI)Soft buffer size

The MAC-hs scheduler needs to take these restrictions into account


HSDPA – UE Physical Layer Capabilities

HS-DSCH Category

Maximum number of HS-DSCH

multi-codes

Minimum inter-TTI interval

Maximum MAC-hs TB size

Total number of soft channel

bits

Theoretical maximum data rate (Mbit/s)

Category 1 5 3 7298 19200 1.2

Category 2 5 3 7298 28800 1.2

Category 3 5 2 7298 28800 1.8

Category 4 5 2 7298 38400 1.8

Category 5 5 1 7298 57600 3.6

Category 6 5 1 7298 67200 3.6

Category 7 10 1 14411 115200 7.2

Category 8 10 1 14411 134400 7.2

Category 9 15 1 20251 172800 10.1

Category 10 15 1 27952 172800 14.0

Category 11* 5 2 3630 14400 0.9

Category 12* 5 1 3630 28800 1.8

cf. TS 25.306Note: UEs of Categories 11 and 12 support QPSK only


Channel Quality Information (CQI)

Signalled to the Node B in UL each 2ms on HS-DPCCH

Integer number from 0 to 30 corresponds to a Transport Format Resource Combination (TFRC) given by

ModulationNumber of channelisation codesTransport block size

For the given conditions the BLER for this TFRC shall not exceed 10%

Mapping defined in TS 25.214 for each UE category


CQI – Mapping Table

CQI value Transport Block Size

Number of HS-PDSCH Modulation

Reference power adjustment

NIR XRV

0 N/A Out of range

1 137 1 QPSK 0

6 461 1 QPSK 0

7 650 2 QPSK 0

15 3319 5 QPSK 0

16 3565 5 16-QAM 0

23 9719 7 16-QAM 0

24 11418 8 16-QAM 0

25 14411 10 16-QAM 0

26 17237 12 16-QAM 0

27 21754 15 16-QAM 0

28 23370 15 16-QAM 0

29 24222 15 16-QAM 0

30 25558 15 16-QAM 0

28800 0

Tables specified in TS 25.214

For each UE categoryCondition: BLER 10%

Example for UE category 10


3G (Rel.99)with dedicated channels

C/IC/I

C/I

CQI

CQI

CQI

2 TTI @1.2M

2 TTI @76k

7 TTI @614k

1 TTI @1.2M

64k64k

64k

Note: No fast channel quality feedback

3G with high speed feedback/scheduling on shared channels

HSDPA Fast Scheduling


Scheduler Inputs

Scheduler

QoS & Subscriber ProfileQoS: guar. bitrate, max. delay

GoS: gold/ silver/ bronce

Feedback from UL (CQI, ACK/NACK)

HistoryHow long hadthe user been

waiting?

Traffic ModelMorning AfternoonEvening Off peak

UE capability

Radio resourcesPower, OVSF codesBuffer Status

Scheduled Users & Packet Formation Strategy


Packet Formation Strategy

Scheduler Outputs

Selected UserAdaptive Transport Block size

Adaptive Coding

or redundancy

Adaptive Modulation

(QPSK, 16 QAM)

# of OVSFcodes

So thatQoS/GoS constraints are satisfied andNetwork throughput is maximized, while

Subject to constraints (standards restrictions and service requirements)Maintain fairness across UEs and traffic streams


Classical Scheduling Disciplines

Round Robin: allocate the users consecutivelyAdvantage: - Offers fair time allocation

- One of the simplest solutionsDisadvantage: - Low cell and user throughput

Best Effort scheduler: prefer the users with good channel conditionsAdvantage: - Highest system throughput and easy to

implementDisadvantage: - Starvation to users with low C/I

Proportional Fairness: equalise the channel rate / throughput ratio Advantage: - Higher throughput than Round RobinDisadvantage: - Does not use QoS information

HSDPA scheduler runs every TTI (2 msec)


Comparison of Schedulers

Simple Round Robin doesn’t care about actual channel rateProportional Fair offers higher cell throughputQoS aware algorithm offers significantly higher user perceived throughput than PF with similar cell throughput

aggregated cell throughput

0

500

1000

1500

2000

2500

Round Robin Proportional Fair QoS aw are

aver

age

thro

ughp

ut [k

bps]

user perceived throughput

0%

20%

40%

60%

80%

100%

0 100 200 300 400 500 600average throughput [kbps]

Perc

enta

ge o

f use

rs

rece

ivin

g th

roug

hput

Round Robin

Proportional Fair

QoS aw are


Mobility Procedures I

HS-DSCH for a given UE belongs to only one of the radio links assigned to the UE (serving HS-DSCH cell)The UE uses soft handover for the uplink, the downlink DCCH and any simultaneous CS voice or data

Using existing triggers and procedures for the active set update (events 1A, 1B, 1C)

Hard handover for the HS-DSCH, i.e. Change of Serving HS-DSCH Cell within active set

Using RRC procedures, which are triggered by event 1D


Mobility Procedures II

Inter-Node B serving HS-DSCH cell changeNote: MAC-hs needs to be transferred to new NodeB !

NodeB

NodeB

MAC-hs

NodeB

NodeB

MAC-hs

Source HS-DSCH Node B

Target HS-DSCH Node B

Serving HS-DSCH radio link

Serving HS-DSCH radio link

s t

CRNC CRNC


HS-DSCH Serving Cell Change

Event 1D: change of best cell within the active setHysteresis and time to trigger to avoid ping-pong(HS-DSCH: 1…2 dB, 0.5 sec)

Reporting event 1D

Measurement quantity

Time

CPICH 2

CPICH 1

CPICH3

Hysteresis

Time to trigger


Handover Procedure

Example: HS-DSCH hard handover (synchronized serving cell change)

SRNC =

DRNC Target

HS-DSCH cell UE

RL Reconfiguration Prepare RL Reconfiguration Ready

Radio Bearer Reconfiguration

Radio Bearer Reconfiguration Complete

Source HS-DSCH cell

ALCAP Iub HS-DSCH Data Transport Bearer Setup If new NodeB

Synchronous Reconfiguration with Tactivation RL Reconfiguration Commit

ALCAP Iub HS-DSCH Data Transport Bearer Release

DATA

Reset MAC-hs entity

Serving HS-DSCH cell change decision i.e. event 1D

RL Reconfiguration Prepare RL Reconfiguration Ready

RL Reconfiguration Commit


HSDPA – Managed Resources

a) OVSF Code Tree

b) Transmit Power

SF=8

SF=16

SF=4

SF=2

Codes reserved for HS-PDSCH/ HS-SCCH

C16,0 C16,15

Codes available for DCH/ common channels

Border adjusted by CRNC

Tx power available for HS-PDSCH/ HS-SCCH Tx power available for DCH/ common channels

Border adjusted by CRNC

Note: CRNC assigns resources to Node B on a cell basis


Cell and User Throughput vs. Load

36 cells networkUMTS composite channel modelFTP traffic model (2 Mbyte download, 30 sec thinking time)

The user throughput is decreased when increasing load due to the reduced service time

The cell throughput increases with the load because overall more bytes are transferred in the same time

Load Impact

0

500

1000

1500

2000

2500

4 6 8 10 12 14 16 18

Number of Users/ Cell

Thro

ughp

ut [

kbit

/sec

]

Mean User ThroughputAggregated Cell Throughput


HSDPA Performance per Category

36 cells networkUMTS composite channel modelFTP traffic model (2 Mbyte download, 30 sec thinking time)

Higher category offers higher max. throughput limit

Cat.6: 3.6 MBit/secCat.8: 7.2 MBit/sec

Max. user perceived performance increased at low loadingCell performance slightly better

Cat 6 - Cat 8 Comparison

0

500

1000

1500

2000

2500

Cat 6/ 10 users Cat 8/ 10 users Cat 6/ 20 users Cat 8/ 20 users

thro

ughp

ut (k

bps)

Mean User ThroughputPeak User ThroughputAggregated Cell Throughput


Coverage Prediction with HSDPA

Example Scenario15 users/cellPedestrian A channel modelPlot generated with field prediction tool

HSDPA Throughput depends on location


HSDPA Summary

New downlink transmission conceptOptimised for interactive & background, support of streamingDesign for indoor & urban environment

Improved PHY approachNew DL transport channel: HS-DSCHAdditional signalling channels to support fast adaptation

Advanced architectureMAC-hs entity located in NodeB

Radio Resource Control procedures similar to DCHHSDPA Resource Management

Cell resources managed by Controlling-RNCRe-use of principles for DCH control (handover, state transition)

Significant improved performance


HSDPA References

Papers:Arnab Das et al: “Evolution of UMTS Toward High-Speed Downlink Packet Access,” Bell Labs Technical Journal, vol. 7, no. 3, pp. 47 – 68, June 2003A. Toskala et al: “High-speed Downlink Packet Access,” Chapter 12 in Holma/ Toskala: WCDMA for UMTS, Wiley 2010T. Kolding et al: “High Speed Downlink Packet Access: WCDMA Evolution,” IEEE Veh. Techn. Society News, pp. 4 – 10, February 2003

H. Holma/ A. Toskala (Ed.): “HSDPA/ HSUPA for UMTS,” Wiley 2006

StandardsTS 25.xxx series: RAN AspectsTR 25.858 “HSDPA PHY Aspects” TR 25.308 “HSDPA: UTRAN Overall Description (Stage 2)”TR 25.877 “Iub/Iur protocol aspects”


Abbreviations

ACK (positive) AcknowledgementALCAP Access Link Control Application

ProtocolAM Acknowledged (RLC) ModeAMC Adaptive Modulation & CodingCAC Call Admission ControlCDMA Code Division Multiple AccessCQI Channel Quality InformationDBC Dynamic Bearer ControlDCH Dedicated ChannelDPCCH Dedicated Physical Control ChannelFDD Frequency Division DuplexFEC Forward Error CorrectionFIFO First In First OutGoS Grade of ServiceHARQ Hybrid Automatic Repeat RequestH-RNTI HSDPA Radio Network Temporary

IdentifierHSDPA High Speed Downlink Packet AccessHS-DPCCH High Speed Dedicated Physical Control

ChannelHS-DSCH High Speed Downlink Shared ChannelHS-PDSCH High Speed Physical Downlink Shared

ChannelHS-SCCH High Speed Signaling Control Channel

IE Information ElementMAC-d dedicated Medium Access ControlMAC-hs high-speed Medium Access ControlMux MultiplexingNACK Negative AcknowledgementNBAP NodeB Application PartOVSF Orthogonal Variable SF (code)PDU Protocol Data UnitPHY Physical LayerQoS Quality of ServiceQPSK Quadrature Phase Shift KeyingRB Radio BearerRL Radio LinkRLC Radio Link ControlRRC Radio Resource ControlRRM Radio Resource ManagementSDU Service Data UnitSF Spreading FactorTB Transport BlockTFRC Transport Format & Resource

CombinationTFRI TFRC IndicatorTTI Transmission Time IntervalUM Unacknowledged (RLC) Mode16QAM 16 (state) Quadrature Amplitude

Modulation

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High-Speed Downlink Packet Access (HSDPA) · PDF fileHigh-Speed Downlink Packet Access (HSDPA) ... UMTS Networks Andreas Mitschele-Thiel, ... Advanced transmission to increase data