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High-Speed Downlink Packet Access (HSDPA)

u HSDPA Background & Basics

u Principles: Adaptive Modulation, Coding, HARQ

u Channels/ UTRAN Architecture

u Principles: Fast scheduling, Mobility

u Performance Results

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UMTS Networks 2Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2012

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 to

384kbps).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 data

No Multimedia, Limited QOS

Medium rate Packet data Theoretical 2 Mbps but ~384 kbps

subjected to practical constraints

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HSDPA Background

u Initial goals

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

data rates beyond 2 Mbit/s, (up to a maximum theoretical limit of 14.4Mbps)

u Optimize interactive & background packet data traffic, support streamingservice

u Design for low mobility environment, but not restricted

u Techniques compatible with advanced multi-antenna and receivers

u Standardization started in June 2000

u Broad forum of companies

u Major feature of Release 5

u Enhancements in R7 HSPA+

u Advanced transmission to increase data throughputu Signaling enhancements to save resources

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HSDPA Basics

u Evolution from R99/ R4

u 5MHz BW

u Same spreading by OVSF and scrambling codesu Turbo coding

u New concepts in R5

u 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 HSPA+

u Signaling enhancements

u 64QAM

u MIMO techniques, increase of the bandwidth

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HSDPA Techniques

u Adaptive modulation and coding(AMC)

u Modulation can be switchedbetween QPSK and 16QAM

u Adaptation of FEC coding rate

u Fast feedback from UE aboutchannel quality (CQI)

u Hybrid ARQ

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

u Retransmitted packetscombined with original ones

u Adaptive redundancy

u Fast scheduling

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

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HS-DSCH Principle I

u Channelization codes at a fixed spreading factor of SF = 16

u Up to 15 codes in parallel

u OVSF channelization code tree allocated by CRNC

u 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

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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 within oneTTI

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

Time (per TTI)

Code

not used

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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)

= Serving

HS-DSCH cell

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HSDPA Channels

u HS-PDSCH

u Carries the data traffic

u Fixed SF = 16; up to 15 parallel channelsu QPSK: 480 kbps/code, 16QAM: 960 kbps/code

u HS-SCCH

u Signals the configuration to be used next: HS-PDSCH codes, modulationformat, TB information

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

u HS-DPCCH

u Feedbacks ACK/NACK and channel quality information (CQI)

u Fixed SF = 256, code multiplexed to UL DPCCH

u Feedback sent ~5msec after received data

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Timing Relations (DL)

u NodeB Tx view

u

Fixed time offset between the HS-SCCH information and the start of thecorresponding HS-DSCH TTI: tHS-DSCH-control (2 Tslot= 1.33msec)

u HS-DSCH and associated DL DPCH not time-aligned

TB size & HAR 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

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Timing Relations (UL)

u UE Rx view

u Alignment to m 256 to preserve orthogonality to UL DPCCH

u HS-PDSCH and associated UL DPCH not time-aligned(but quasi synch)

DATA

Uplink DPCCH

HS-PDSCH

S-DPCCH

3Tslot(2ms)

m 256 chips

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

Tslot(0.67 ms)

CQIA/NCQIA/NCQIA/NCQI A/N

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HSDPA Architecture

MAC-c/sh

MAC-d

RLC

RRC PDCP

Logical Channels

Transport Channels

MAC-b

BCH

BCCHDCCHDTCH

SRNC

CRNC

NodeB

DCH

Upper phy

DSCH

FACH

Evolution from R99/R4

HSDPA functionality isintended for transport of

dedicated 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/oMAC-c/sh

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MAC-hs in NodeB

MAC-hs

MAC Control

HS-DSCH

Priority Queuedistribution

MAC-d flows

Scheduling

PriorityQueue

PriorityQueue

PriorityQueue

UE #1

UE #2

UE #N

MAC-hs Functions

u Priority handling

u Flow Control

u To RNC

u To UE

u Scheduling

u Select which user/queueto transmit

u Assign TFRC & Txpower

u HARQ handling

u Service measurements

u e.g. HSDPA providedbitrate

TFRC: Transport Format and Resource Combination

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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

u HARQ handling

u ACK/ NACK generation

u Reordering buffer handling

u Associated to priority

queues

u Flow control per

reordering buffer

u Memory can be shared

with AM RLC

u Disassembly unit

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Data Flow through Layer 2

Higher Layer

L1

Higher Layer PDU

RLC SDU

MAC-d SDU

MAC-d PDU

RLCheader

RLC

header

MAC-d SDU

MAC-d PDU

CRC

MAC-dheader

MAC-d

headerL2 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)

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Hybrid Automatic Repeat Request

u HARQ is a stop-and-wait ARQ

u Up to 8 HARQ processes per UE

u Retransmissions are done at MAC-hs layer, i.e. in the Node B

u Triggered by NACKs sent on the HS-DPCCH

u The mother code is a R = 1/3 Turbo code

u Code rate adaptationdone via rate matching, i.e. by puncturing andrepeating bits of the encoded data

u Two types of retransmission

u Incremental Redundancy

uAdditional parity bits are sent when decoding errors occured

u Gain due to reducing the code rate

u Chase Combining

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

u HSDPA uses a mixture of both types

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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

Data

HS-PDSCH

ACK/NACK

HS-DPCCH

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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 in

u Max. transport block size (data rate)

u Max. number of codes per HS-DSCH

u 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

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HSDPA UE Physical Layer Capabilities

HS-DSCHCategory

Maximumnumber of

HS-DSCHmulti-codes

Minimum inter-TTI interval

MaximumMAC-hs TB size

Total number ofsoft channel

bits

Theoreticalmaximum 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

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Channel Quality Information (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 by

u Modulation

u Number of channelisation codes

u 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

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CQI Mapping Table

CQI value

Transport

Block Size

Number of

HS-PDSCHModulation

Reference power

adjustmentNIR 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

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

BLER 10%

u Example forUE category 10

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3G (Rel.99)with dedicated channels

C/I

C/I

C/I

CQI

CQI

CQI

2 [email protected]

2 TTI@76k

7 TTI

@614k1 TTI

@1.2M

64k64k

64k

Note: No fast channel quality feedback

3G with high speed feedback/schedulingon shared channels

HSDPA Fast Scheduling

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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 metrics

Throughput, 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

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Scheduling Disciplines

u Task

u 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 categories

u Round Robin: allocate each user equal amount of time

u Proportional Fair: equalise the channel rate / throughput ratio

u Max C/I: prefer the users with good channel conditionsu To provide GoS/ QoS additional inputs are to be used

u Additional scheduling weights and rate constraints based on therequested GoS/ QoS

u This can be traded-off with channel conditions

u Special scheduling schemes are needed for providing delay critical

services, e.g. VoIP

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Comparison of Schedulers

u Simple Round Robin doesnt care about actual channel rate

u Proportional Fair offers higher cell throughputu QoS aware algorithm offers significantly higher user perceived throughput than

PF with similar cell throughput

aggregated cell throu ghput

0

500

1000

1500

2000

2500

Round Robin Proportional Fair QoS aw are

averag

e

throughput[kbps]

user perceived throughput

0%

20%

40%

60%

80%

100%

0 100 200 300 400 500 600

average throughput [kbps]

Per

centage

ofusers

receiving

throughput

Round Robin

Proportional Fair

QoS aware

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Mobility Procedures I

u HS-DSCH for a given UE belongs to only one of the radio links assigned to

the UE (serving HS-DSCH cell)u The UE uses soft handover for the uplink, the downlink DCCH and any

simultaneous CS voice or data

u 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 set

u Using RRC procedures, which are triggered by event 1D

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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 BTarget HS-

DSCH Node B

ServingHS-DSCH

radio link

ServingHS-DSCH

radio link

s t

CRNC CRNC

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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: 12 dB, 0.5 sec)

Reporting

event 1D

Measurement

quantity

Time

CPICH 2

CPICH 1

CPICH3

Hysteresis

Time to

trigger

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Handover Procedure

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

SRNC=

DRNC

Target

HS-DSCH cellUE

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 TactivationRL Reconfiguration Commit

ALCAP Iub HS-DSCH Data

Transport Bearer Release

DATA

Reset MAC-

hs entity

Serving HS-DSCHcell change decision

i.e. event 1D

RL Reconfiguration Prepare

RL Reconfiguration Ready

RL Reconfiguration Commit

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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

C16,0C

16,15

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

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Cell and User Throughput vs. Load

u

36 cells networku UMTS composite channel model

u FTP traffic model (2 Mbytedownload, 30 sec thinking time)

u The user throughput is decreasedwhen increasing load due to the

reduced 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

Throughput

[kbit/s]

Number of Users/ Cell

Load Impact

Mean User Throughput

Aggregated Cell Throughput

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HSDPA Performance per Category

u 36 cells network

u UMTS composite channel model

u FTP traffic model (2 Mbytedownload, 30 sec thinking time)

u Higher category offers highermax. throughput limit

u 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

throug

hput(kbps)

Mean User Throughput

Peak User Throughput

Aggregated Cell Throughput

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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 by

uThe RLC window size, whichis limited to 2047 PDUs

uRound-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

Throughput

[kbit/s]

Higher Layer Impact

Max. RLC Throughput, RTT = 120msec

Max. RLC Throughput, RTT = 80msec

Max. MAC-hs Throughput

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Coverage Prediction with HSDPA

uExample Scenario

u 15 users/cell

u Pedestrian A channelmodel

u Plot generated with fieldprediction tool

HSDPA Throughput

depends on location

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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 2006u Standards

u TS 25.xxx series: RAN Aspects

u TR 25.858 HSDPA PHY Aspects

u TR 25.308 HSDPA: UTRAN Overall Description (Stage 2)

u

TR 25.877 Iub/Iur protocol aspects

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Abbreviations

ACK (positive) Acknowledgement

ALCAP Access Link Control ApplicationProtocol

AM Acknowledged (RLC) Mode

AMC Adaptive Modulation & Coding

CAC Call Admission Control

CDMA Code Division Multiple Access

CQI Channel Quality Information

DBC Dynamic Bearer Control

DCH Dedicated Channel

DPCCH Dedicated Physical Control Channel

FDD Frequency Division DuplexFEC Forward Error Correction

FIFO First In First Out

GoS Grade of Service

HARQ Hybrid Automatic Repeat Request

H-RNTI HSDPA Radio Network TemporaryIdentifier

HSDPA High Speed Downlink Packet Access

HS-DPCCH High Speed Dedicated Physical Control

ChannelHS-DSCH High Speed Downlink Shared Channel

HS-PDSCH High Speed Physical Downlink SharedChannel

HS-SCCH High Speed Signaling Control Channel

IE Information Element

MAC-d dedicated Medium Access Control

MAC-hs high-speed Medium Access Control

Mux Multiplexing

NACK Negative Acknowledgement

NBAP NodeB Application Part

OVSF Orthogonal Variable SF (code)

PDU Protocol Data Unit

PHY Physical Layer

QoS Quality of Service

QPSK Quadrature Phase Shift Keying

RB Radio BearerRL Radio Link

RLC Radio Link Control

RRC Radio Resource Control

RRM Radio Resource Management

SDU Service Data Unit

SF Spreading Factor

TB Transport Block

TFRC Transport Format & Resource

CombinationTFRI TFRC Indicator

TTI Transmission Time Interval

UM Unacknowledged (RLC) Mode

16QAM 16 (state) Quadrature AmplitudeModulation

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