High-Speed Downlink Packet Access (HSDPA) Downlink Packet Access (HSDPA) uHSDPA Background & Basics uPrinciples: Adaptive Modulation, Coding, HARQ uChannels/ UTRAN Architecture uPrinciples:

High-Speed Downlink Packet Access (HSDPA)

u HSDPA Background & Basicsu Principles: Adaptive Modulation, Coding, HARQu Channels/ UTRAN Architectureu Principles: Fast scheduling, Mobilityu Performance Results

Cellular Communication Networks 2Andreas Mitschele-Thiel, Jens Mueckenheim Nov. 2014

Motivation (as of 2000)

u As the UMTS networks are rolled out, the demand for highbandwidth services is expected to grow rapidly.

u By 2010, 66% of the revenues will come from data services(source: UMTS forum).

u Release 99/4 systems alone will not be capable to meet thesedemands. (Realistic outdoor data rates will be limited to384kbps).

u A more spectral efficient way of using DL resources is required.u Competition with CDMA 2000 1x EV-DO/DV

GSM/GPRS

UMTS Rel. 99

Voice, low speed packet dataNo Multimedia, Limited QOS

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


HSDPA Background

u Initial goalsu Establish a more spectral efficient way of using DL resources providing

data rates beyond 2 Mbps, (up to a maximum theoretical limit of14.4 Mbps)

u Optimize interactive & background packet data traffic, support streamingservice

u Design for low mobility environment, but not restrictedu Techniques compatible with advanced multi-antenna and receivers

u Standardization started in June 2000u Broad forum of companiesu Major feature of Release 5

u Enhancements in R7 à HSPA+u Advanced transmission to increase data throughputu Signaling enhancements to save resources


HSDPA Basics

u Evolution from R99/ R4u 5MHz BWu Same spreading by OVSF and scrambling codesu Turbo coding

u New concepts in R5u Adaptive modulation (QPSK vs. 16QAM), coding and multicodes

(fixed SF = 16)u Fast scheduling in NodeB (TTI = 2ms)u Hybrid ARQ

u Enhancements in R7 à HSPA+u Signaling enhancementsu 64QAMu MIMO techniques, increase of the bandwidth


HSDPA Techniques

u Adaptive modulation and coding(AMC)u Modulation can be switched

between QPSK and 16QAMu Adaptation of FEC coding rateu Fast feedback from UE about

channel quality (CQI)u Hybrid ARQ

u Fast retransmission in MAC-layer (S&W protocol)

u Retransmitted packetscombined with original ones

u Adaptive redundancyu Fast scheduling

u Allocate resources to userswith good channel quality® Multi-user diversity gain


HS-DSCH Principle I

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

u OVSF channelization code tree allocated by CRNCu HSDPA codes autonomously managed by NodeB MAC-hs scheduler

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

u 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

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

u Example: 5 codes are reserved for HSDPA, 1 or 2 UEs are active withinone 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)u UL/DL signalling (DCCH)u UL PS serviceu UL/DL CS voice/ data

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

= ServingHS-DSCH cell


HSDPA Channels

u HS-PDSCHu Carries the data trafficu Fixed SF = 16; up to 15 parallel channelsu QPSK: 480 kbps/code, 16QAM: 960 kbps/code

u HS-SCCHu Signals the configuration to be used next: HS-PDSCH codes, modulation

format, TB informationu Fixed SF = 128u Sent two slots (~1.3msec) in advance of HS-PDSCH

u HS-DPCCHu Feedbacks ACK/NACK and channel quality indicator (CQI)u Fixed SF = 256, code multiplexed to UL DPCCHu Feedback sent ~5msec after received data


Timing Relations (DL)

u NodeB Tx viewu Fixed time offset between the HS-SCCH information and the start of the

corresponding HS-DSCH TTI: tHS-DSCH-control (2 ´ Tslot= 1.33msec)u HS-DSCH and associated DL DPCH not time-aligned

TB size & HARQ Info

Downlink DPCH

HS-SCCH

DATAHS-PDSCH

3 ´ Tslot (2 msec)

HS-DSCH TTI = 3 ´ Tslot (2 msec)

tHS-DSCH-control = 2 ´ Tslot

Tslot (2560 chips)

ch. code & mod


Timing Relations (UL)

u UE Rx viewu Alignment to m ´ 256 to preserve orthogonality to UL DPCCHu HS-PDSCH and associated UL DPCH not time-aligned

(but “quasi synch”)

DATA

Uplink DPCCH

HS-PDSCH

HS-DPCCH

3 ´ Tslot (2ms)

m ´ 256 chips

tUEP = 7.5 ´ Tslot (5ms)0-255 chips

Tslot (0.67 ms)

CQIA/NCQIA/NCQIA/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 isintended for transport ofdedicated logical channels

• Takes into account theimpact on R.99 networks

MAC-hs

HS-DSCH

HSDPA in R5

• Additions in RRC to handleHSDPA

• RLC nearly unchanged(UM & AM)

• Modified MAC-d with link toMAC-hs entity

• New MAC-hs entity locatedin the Node B

w/o

MAC

-c/s

h


MAC-hs in NodeB

MAC-hs

MAC – Control

HS-DSCH

Priority Queuedistribution

MAC-d flows

Scheduling

PriorityQueue

PriorityQueue

PriorityQueue

UE #1UE #2

UE #N

MAC-hs Functionsu Priority handlingu Flow Control

u To RNCu To UE

u Schedulingu Select which user/queue

to transmitu Assign TFRC & Tx

poweru HARQ handling

u Service measurementsu e.g. HSDPA provided

bitrate

TFRC: Transport Format and Resource Combination


MAC-hs in UE

MAC-hs

MAC – Control

Associated Uplink SignallingHS-DPCCH

To MAC-d

Associated Downlink SignallingHS-SCCH

HS-DSCH

HARQ

Reordering Reordering

Re-ordering queue distribution

Disassembly Disassembly

MAC-hs Functions

u HARQ handling

u ACK/ NACK generation

u Reordering buffer handling

u Associated to priorityqueues

u Flow control perreordering buffer

u Memory can be sharedwith AM RLC

u 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

u HARQ is a stop-and-wait ARQu Up to 8 HARQ processes per UE

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

u The mother code is a R = 1/3 Turbo codeu Code rate adaptation done via rate matching, i.e. by puncturing and

repeating bits of the encoded datau Two types of retransmission

u Incremental Redundancyu Additional parity bits are sent when decoding errors occuredu Gain due to reducing the code rate

u Chase Combiningu The same bits are retransmitted when decoding errors occuredu Gain due to maximum ratio combining

u HSDPA uses a mixture of both types


HARQ Processes

u HARQ is a simple stop-and-wait ARQu Example

u RTTmin = 5 TTIu Synchronous retransmissions (MAC-hs decides on transmission)

u UE support up to 8 HARQ processes (configured by NodeB)u Min. number: to support continuous receptionu Max. number: limit of HARQ soft bufferu Number 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

u The specification allows some freedom to the UE vendors

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

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

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


HSDPA – UE Physical Layer Capabilities

HS-DSCHCategory

Maximumnumber ofHS-DSCH

multi-codes

Minimum inter-TTI interval

MaximumMAC-hs TB size

Total number ofsoft channel

bits

Theoreticalmaximum datarate (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 Indicator (CQI)

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

u Integer number from 0 to 30 corresponds to a Transport Format ResourceCombination (TFRC) given byu Modulationu Number of channelisation codesu Transport block size

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

u Mapping defined in TS 25.214 for each UE category


CQI – Mapping Table

CQI value TransportBlock Size

Number ofHS-PDSCH Modulation

Reference poweradjustment D

NIR XRV

0 N/A Out of range

1 137 1 QPSK 0

¼

6 461 1 QPSK 0

7 650 2 QPSK 0

¼

15 3319 5 QPSK 0

16 3565 5 16-QAM 0

¼

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

u Tables specified in TS25.214u For each UE categoryu Condition:

BLER £ 10%u Example for

UE category 10


3G (Rel.99)with dedicated channels

C/IC/I

C/I

CQI

CQI

CQI

2 [email protected]

2 TTI@76k

7 TTI@614k

1 [email protected]

64k64k

64k

Note: No fast channel quality feedback

3G with high speed feedback/schedulingon shared channels

HSDPA Fast Scheduling


HSDPA Resource Allocation

Scheduler

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

GoS: gold/ silver/ bronze

Feedback from ULCQI, ACK/NACK

UE capabilitiesmax. TFRC

Radio resourcesPower, OVSF codes

UE service metricsThroughput, Buffer Status

Scheduler Output• Scheduled Users• TFRC: Mod., TB size, # codes, etc.• HS-PDSCH power

• Scheduling targets- Maximize network throughput- Satisfy QoS/ GoS constraints- Maintain fairness across UEs and traffic streams


Scheduling Disciplines

u Tasku Select UEs (and associated priority queues) to transmit within next TTIu Usually this is done by means of ranking lists

u Depending on the ranking criterion it can be distinguished between threemajor categoriesu Round Robin: allocate each user equal amount of timeu Proportional Fair: equalise the channel rate / throughput ratiou Max C/I: prefer the users with good channel conditions

u To provide GoS/ QoS additional inputs are to be usedu Additional scheduling weights and rate constraints based on the

requested GoS/ QoSu This can be traded-off with channel conditionsu Special scheduling schemes are needed for providing delay critical

services, e.g. VoIP


Comparison of Schedulers

u Simple Round Robin doesn’t care about actual channel rateu Proportional Fair offers higher cell throughputu QoS 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

geof

user

sre

ceiv

ing

thro

ughp

ut

Round Robin

Proportional Fair

QoS aw are


Mobility Procedures I

u HS-DSCH for a given UE belongs to only one of the radio links assigned tothe UE (serving HS-DSCH cell)

u The UE uses soft handover for the uplink, the downlink DCCH and anysimultaneous CS voice or datau Using existing triggers and procedures for the active set update

(events 1A, 1B, 1C)

u Hard handover for the HS-DSCH, i.e.Change of Serving HS-DSCH Cell within active setu Using RRC procedures, which are triggered by event 1D


Mobility Procedures II

u Inter-Node B serving HS-DSCH cell changeu Note: 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

ServingHS-DSCHradio link

ServingHS-DSCHradio link

s t

CRNC CRNC


HS-DSCH Serving Cell Change

u Event 1D: change of best cell within the active setu Hysteresis and time to trigger to avoid ping-pong

(HS-DSCH: 1…2 dB, 0.5 sec)

Reportingevent 1D

Measurementquantity

Time

CPICH 2

CPICH 1

CPICH3

Hysteresis

Time totrigger


Handover Procedure

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

SRNC=

DRNCTarget

HS-DSCH cellUE

RL Reconfiguration Prepare

RL Reconfiguration Ready

Radio Bearer Reconfiguration

Radio Bearer Reconfiguration Complete

SourceHS-DSCH cell

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

SynchronousReconfigurationwith TactivationRL Reconfiguration Commit

ALCAP Iub HS-DSCH DataTransport Bearer Release

DATA

Reset MAC-hs entity

Serving HS-DSCHcell change decisioni.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

C16,0C16,15

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

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


Cell and User Throughput vs. Load

u 36 cells networku UMTS composite channel modelu FTP traffic model (2 Mbyte

download, 30 sec thinking time)

u The user throughput is decreasedwhen increasing load due to thereduced service time

u The cell throughput increaseswith the load because overallmore bytes are transferred in thesame time

0

500

1000

1500

2000

2500

4 6 8 10 12 14 16 18

Thro

ughp

ut[k

bit/

s]

Number of Users/ Cell

Load Impact

Mean User Throughput

Aggregated Cell Throughput


HSDPA Performance per Category

u 36 cells networku UMTS composite channel modelu FTP traffic model (2 Mbyte

download, 30 sec thinking time)

u Higher category offers highermax. throughput limitu Cat.6: 3.6 MBit/secu Cat.8: 7.2 MBit/sec

uMax. user perceived performanceincreased at low loading

u Cell 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


Impact from Higher Layers

uMaximum MAC-hs throughput isdetermined by the MAC-d PDUsize and the max. number ofMAC-d PDUs, which fit into themax. MAC-hs PDU

uMaximum RLC throughput isfurther limited byuThe RLC window size, which

is limited to 2047 PDUsuRound-trip time RTT

0

2000

4000

6000

8000

10000

12000

14000

Cat.6 – 336bit Cat.8 – 336bit Cat.8 – 656bit Cat.10 – 336bit Cat.10 – 656bit

Thro

ughp

ut[k

bit/

s]

Higher Layer Impact

Max. RLC Throughput, RTT = 120msec

Max. RLC Throughput, RTT = 80msec

Max. MAC-hs Throughput


Coverage Prediction with HSDPA

uExample Scenariou 15 users/cellu Pedestrian A channel

modelu Plot generated with field

prediction tool

HSDPA Throughputdepends on location


HSDPA References

u Papers:u Arnab Das et al: “Evolution of UMTS Toward High-Speed Downlink Packet

Access,” Bell Labs Technical Journal, vol. 7, no. 3, pp. 47 – 68, June2003

u A. Toskala et al: “High-speed Downlink Packet Access,” Chapter 12 inHolma/ Toskala: WCDMA for UMTS, Wiley 2010

u T. Kolding et al: “High Speed Downlink Packet Access: WCDMAEvolution,” IEEE Veh. Techn. Society News, pp. 4 – 10, February 2003

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

u Standardsu TS 25.xxx series: RAN Aspectsu TR 25.858 “HSDPA PHY Aspects”u TR 25.308 “HSDPA: UTRAN Overall Description (Stage 2)”u 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 IndicatorDBC 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

Documents

High-Speed Downlink Packet Access (HSDPA) Downlink Packet Access (HSDPA) uHSDPA Background & Basics uPrinciples: Adaptive Modulation, Coding, HARQ uChannels/ UTRAN Architecture uPrinciples: