11 Principles of HSDPA

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Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Principles of HSDPA

ISSUE 1.0

Page1Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.

Objectives

� Upon completion of this course, you will be able to:

� Review WCDMA and HSDPA evolution and standards

� Review R99 packet data service method

� Describe HSDPA physical channels

� HSDPA Network and UE protocol stack architecture


Contents

1.1. HSDPA ConceptsHSDPA Concepts

2. HSDPA Key Techniques

3. HSDPA Physical Layer Channels

4. HSDPA Layer2 Protocol


WCDMA Evolution


Release 99 Packet Data

� How is Packet Data handled in Release 99 (FDD) ?

� DCH ( Dedicated Channel )

� Spreading codes assigned per user

� Closed loop power control

� Soft handover

� FACH ( Common Channel )

� Common Spreading code

� No closed loop power control

� No soft handover


Release 99 Downlink Limitation

� Dedicated Channel Features ( DCH )

� Maximum implemented downlink of 384kbps

� OVSF code limitation for high data rate users

� Rate switching according to burst throughput is slow

� Outer loop power control responds slowly to channel

� Common Channel Features ( FACH )

� Good for burst data application

� Only low data rates supported

� Fixed transmit power


High Speed Downlink Packet Access (HSDPA)

� The differences between HSDPA and R99

� Set of high data rate channel

� Channels are shared by multiple users

� Each user may be assigned all or part of the resource every 2 ms

Node B

HS-PDSCH



� How will HSDPA figure out the limitations of R99

� Adaptive modulation and coding

� Fast feedback of Channel condition

� QPSK and16QAM

� Channel coding rate from 1/3 to 1

� Multi-code operation

� Multiple codes allocated per user

� Fixed spreading factor

� NodeB fast Scheduling

� Physical Layer HARQ ( Hybrid Automatic Repeat reQuest )



� Comparison Summary


Contents

1. HSDPA Concepts

2.2. HSDPA Key TechniquesHSDPA Key Techniques




HSDPA Key Techniques

AMC (Adaptive Modulation & Coding)

Data rate adapted to radio condition on 2ms

Fast Scheduling based on CQI and fairness

Scheduling of user on 2ms

HARQ（（（（Hybrid ARQ））））with

Soft combing

Reduce round trip time

16QAM

16QAM in complement to QPSK for higher peak bit rates

SF16, 2ms and CDM/TDM

Dynamic shared in Time and code domain

3 New Physical Channels

Block 1 Block 2Block 1

Block 1?

Block 1Block 1?

+


Adaptive Modulation and Coding ( AMC )

� AMC ( Adaptive Modulation and Coding ) based on CQI ( Channel

Quality Indicator )

� Adjust data rate to compensation channel condition

� Good channel condition – higher data rate

� Bad channel condition – lower data rate

� Adjust channel coding rate to compensation channel condition

� Good channel condition – channel coding rate is higher e.g. 3/4

� Bad channel condition –channel coding rate is higher e.g. 1/3

� Adjust the modulation scheme to compensation channel condition

� Good channel condition – high order modulation scheme e.g. 16QAM

� Bad channel condition – low order modulation scheme e.g. QPSK


Adaptive Modulation and Coding ( AMC )

� AMC ( Adaptive Modulation and Coding ) based on CQI

( Channel Quality Indicator )

� CQI ( channel quality indicator )

� UE measures the channel quality and reports to NodeB every 2ms or

more cycle

� NodeB selects modulation scheme ,data block size based on CQI

Bad channel condition→→→→ More power

Node B Node B

Power Control Rate Adaptation

Good channel condition

Bad channel condition

Good channel condition→→→→ less power

→→→→ low data rate

→→→→ high data rate


CQI mapping table for UE category 10

Out of rangeOut of rangeN/AN/A00

001616--QAMQAM151525558255583030

001616--QAMQAM151524222242222929

001616--QAMQAM151523370233702828

……………………………………………………

001616--QAMQAM55466446641818

001616--QAMQAM55418941891717

001616--QAMQAM55356535651616

00QPSKQPSK55331933191515

00QPSKQPSK44258325831414

00QPSKQPSK44227922791313

……………………………………………………

00QPSKQPSK1117317322

00QPSKQPSK1113713711

Reference power Reference power

adjustment adjustment ∆∆∆∆∆∆∆∆ModulationModulation

Number of Number of

HSHS--PDSCHPDSCH

Transport Transport

Block SizeBlock SizeCQI valueCQI value


HSDPA UE Categories

28800363015Category 12

14400363025Category 11

17280027952115Category 10

17280020251115Category 9

13440014411110Category 8

11520014411110Category 7

67200729815Category 6

57600729815Category 5

38400729825Category 4

28800729825Category 3

28800729835Category 2

19200729835Category 1

Total Number of Soft Channel Bits

Maximum Number of Bits of an HS-DSCH Transport Block

Received Within an HS-DSCH TTI

Minimum Inter-TTI Interval

Maximum Number of HS-DSCH Codes

Received

UE Category


Hybrid Automatic Repeat reQuest ( HARQ )

� Conventional ARQ

� In a conventional ARQ scheme, received data blocks that can not be

correctly decoded are discarded and retransmitted data blocks are

separately decoded

� Hybrid ARQ

� In case of Hybrid ARQ with soft combining, received data blocks that can

not be correctly decoded are not discarded. Instead the corresponding

received signal is buffered and soft combined with later received

retransmission of information bits. Decoding is then applied to the

combined signal.



� Example for HARQ

� The use of HARQ with soft combining increases the effective received

Eb/Io for each retransmission and thus increases the probability for

correct decoding of retransmissions, compare to conventional ARQ



� There are many different schemes for HARQ with soft

combining.

� These scheme differ in the structure of retransmissions and in

the way by which the soft combining is carried out at the

receiver

� In case of Chase combining ( CC ) each retransmission is an

identical copy of the original transmission

� In case of Incremental Redundancy ( IR ) each retransmission may

add new redundancy



� Example for Chase Combining ( CC ) Scheme



� Example for Incremental Redundancy ( IR ) Scheme


Fast Scheduling

� Fast scheduling is about to decided to which terminal the

shared channel transmission should be directed at any given

moment


Short TTI (2ms)

� Shorter TTI ( Transmission Time Interval ) is to reduce RTT

( round trip time )

� Shorter TTI is necessary to benefit from other functionalities

such as AMC, scheduling algorithm and HARQ


� In HSDPA, a new DL transport channel is introduced call HS-

DSCH. The idea is that a part of the total downlink code

resource is dynamically shared between a set of HSDPA users

Shared Channel Transmission


Shared Channel Transmission

� The codes are assigned to HSDPA user only when they are

actually to be used for transmission, which leads to efficient

code and power utilization

Allchannelization

codes availablefor HSDPA

Tim e

Channelizationcode

UE1 data UE2 data UE3 data


Higher-Order Modulation


HSDPA New Physical Channels


Contents

1. HSDPA Concepts


3.3. HSDPA Physical Layer ChannelsHSDPA Physical Layer Channels



R99 Physical Channels


HSDPA Physical Layer Channels

� New HSDPA Channels

� High Speed Downlink shared Channel ( HS-DSCH )

� Downlink Transport Channel

� High Speed Shared Control Channel ( HS-SCCH )

� Downlink Control Channel

� High Speed Physical Downlink Shared Channel ( HS-PDSCH )

� Downlink Physical Channel

� High Speed Dedicated Physical Control Channel ( HS-DPCCH )

� Uplink Control Channel


HSDPA Physical Channels


HS-PDSCH sub-frame Structure

� HS-PDSCH sub-frame structure

� 3 time slots constituted one TTI (2ms)

� Fixed spreading factor ( SF=16 )

� May use QPSK or 16QAM modulation scheme

� All HS-PDSCH used to carry user’s data

� UE can be assigned multiple OVSF code ( SF=16 ) based on UE Categories

Slot #0 Slot#1 Slot #2

Tslot = 2560 chips, M*10*2 k bits (k=4)

DataNdata 1 bits

1 subframe: T f = 2 ms


HS-SCCH sub-frame Structure

� HS-SCCH sub- frame structure

� 3 time slots constitutes one TTI ( 2ms )

� HS-SCCH SF=128, QPSK only

� HS-SCCH carries the following control messages: Xue, Xccs, Xms, Xrv, Xtbs, Xhap

and Xnd

� UE demodulates HS-SCCH sub-frame and find out the received data addressed to

the UE with Xue. Then UE demodulates HS-PDSCH sub-frame with Xccs, Xms, Xrv,

Xhp, Xtbs and Xnd are used for HARQ Process

� UE may need to simultaneous monitor up to four HS-SCCH

Slot #0 Slot#1 Slot #2

T slot = 2560 chips, 40 bits

Data N data 1 bits

1 subframe: T f = 2 ms


HS-DPCCH sub-frame Structure

�HS-DPCCH sub-frame structure

� TTI=2ms ( 3 time slots ), SF=256, Fixed rate of 15kbps, carry 2 types of HSDPA uplink

physical layer control message, including ACK/NACK CQI

� ACK and NACK notifies NodeB that UE has received correct downlink data or not. The

field defines like this: 1-NACK, 0-ACK

� CQI reflects physical channel quality indicator based on CPICH strength, and reported

by period range from 0 to 160ms ( 0 means no transmission ). Usually the period is 2ms

( one TTI )

� ACK/NACK and CQI having different function may be controlled independently by

different parameters.

S u b f r a m e # 0 S u b f r a m e # i S u b f r a m e # 4

H A R Q - A C K C Q I

O n e r a d i o f r a m e T f = 1 0 m s

O n e H S - D P C C H s u b f r a m e ( 2 m s )

2 × T s lo t = 5 1 2 0 c h i p s T s lo t = 2 5 6 0 c h i p s


Associated physical channel - DPCH

� Besides 3 physical channels on top. There is another physical channel

named DPCH, which is a dedicated channel . DPCH is also called associated

channel used for signalling transmission and power control

� DPCH does not carry service generally, sometimes carry real time (RT)

service such as AMR service

N o d e B

U E

H S -P D S C H H S -S C C H D P C H H S -D P C C H


HSDPA Physical Channels Timing

� Start of HS-SCCH is aligned with the start of PCCPCH

� HS-PDSCH, subframe is transmitted two slots after the associated

HS-SCCH subframe


Theoretical HSDPA Maximum Data Rate

� Theoretical HSDPA Maximum data rate is 14.4Mbps

� How do we get to 14.4Mbps ?

� Multi-code transmission

� NodeB must allocate all 15 OVSF codes ( SF =16 ) to one UE

� Consecutive assignments using multiple HARQ process

� NodeB must allocate all time slots to one UE

� UE must decode all transmission correctly on the first transmission

� Low channel coding gain

� Effective code rate = 1

� Requires very good channel conditions to decode

� 16QAM

� Requires very good channel condition


Contents

1. HSDPA Concepts



4.4. HSDPA Layer2 ProtocolHSDPA Layer2 Protocol


HSDPA Protocol Stack


UTRAN MAC Architecture


UTRAN MAC-hs Architecture


UE MAC-hs Architecture


Implementation of MAC-hs

HS-DPCCH demodulation and decode

SRNC(MAC-d)

power monitor

CQI adjustment

Scheduler

Queues/flow control

HARQ

TFRC

Power management

Coding and modulation

OM parameters

Power limitation

Power for HSDPA

CQI Value

Stat. Of ACK/NACKACK/NACK

Waiting time

Queue filling info Queue priority

CQI ValueCode allocation

Code available

Data flow

Control signal

Thank YouThank You

11 Principles of HSDPA

Documents

channel quality

bad channel

received data

hsdpa layer2

physical channels

hs architecture

dedicated

soft combining