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HSDPA Basic Principle

HUAWEI TECHNOLOGIES CO., LTD. Page 1Huawei Confidential

Learning Objectives

HSDPA basic principle and feature

HSDPA key technologies

HSDPA physical channels


Contents

Chapter 1 HSDPA Basic Concepts and Characteristics

Section 2 Key Techniques

Section 3 Physical Channel


HSDPA Basic Concepts

HSDPA = High Speed Downlink Packet AccessImportant Features of 3GPP R5Why HSDPA?

The subscribers request higher speed and better quality data accessCompetition challenge from CDMA EV/DO, WiMAXUp to now, the throughput request for downlink is much more higher than that of uplinkThe channel configuration of R99 lead a very low efficiency on the downlink capacity


HSDPA CharacteristicsHSDPA is the solution of WCDMA offering higher

speed downlink data services.Peak data rate in DL: 14.4Mbps (physical layer)Shorter delayHigher efficiency using downlink code and power and bigger downlink capacityFlexible cell resource allocationMore high speed user access

UMTS R99

GSM

HSDPA


Contents


Chapter 2 Key Techniques

Chapter 3 Physical Channel


HSDPA Key Techniques- OverviewHSDPA Key Techniques- Overview

AMC Fast SchedulingHARQ (Hybrid ARQ)

16QAMSF16, 2ms and CDM/TDM 3 New Physical Channels

Adaptive Modulation and Coding Hybrid Automatic Repeat Request


HSDPA Key Techniques

Fast Scheduling(2ms short frame and scheduling)AMC (support QPSK and 16QAM)HARQ


Fast Scheduling Basic

If a little part of received 10ms frame (15 slots - R99) can’t be decoded correctly, whole frame will be retransmit 10ms later.

An HSDPA frame is only 2ms(3 slots). If a 2ms frame can’t be decoded correctly, just this 2ms frame need be retransmitted. Other 2ms(up to 6) HARQ process may continue transmitting data, thus radio resource could be used more effectively.

Physical Layer Basic


Fast SchedulingFast Scheduling

Scheduling Principle: based on channel condition in short period; based on balance between throughout and proportional fair for all users in long period.

Some basic schedulerRound Robin (RR)

Maximum C/I (MAXC/I)

Proportional Fair (PF)

By fast scheduling, HSDPA cell can allocate the available HSDPA power resource and code resource among users effectively, to improves the throughout.

Scheduler may works based on CDM and/or TDM

Channel condition

Amount of data waiting in the queue (delay)

Fairness

Cell throughout, etc


Share and Scheduling of Shared Channel

The following fig describes scheduling processing for 4 users.

All codes reserved for HSDPA transmission

2ms


Fast Scheduling ProcessFast Scheduling Process

•Transmit power for which users•Channelization code•Data attributes

Scheduling Algorithm

Available resource

Required resource

Temporary statistic

Input:1. Available resource: power and channelization code2. Required resource: including users, user data, retransmission, air interface ability

estimate, etc.3. Temporary statistic of scheduling algorithm: waiting time, average C/I, etc.

Output:Transmit power for which users, power, channelization code, data attributes


Max C/I Scheduling AlgorithmMax C/I Scheduling Algorithm

Features:1) Allocates channel to the user with max C/I in one TTI.

2) Provides the highest cell throughout, because channel is allocated to the user in the best radio condition .

3) It is not fair for the users located in areas of poor coverage. By max C/I algorithm, the system hardly allocate channel for users under pool signal condition.


RR Scheduling Algorithm (RR - Round Robin)RR Scheduling Algorithm (RR - Round Robin)

Features:1) Every user has the same chance to occupy the channel and power.

2) It is very fair for every user, but it is not good to get a best cell throughput.

Note: User allocated resource


PF Scheduling AlgorithmPF Scheduling Algorithm

Features:1) A good balance scheme, whose fairness and resource allocation efficiency is between RR and max C/I scheduling algorithm.

2) Probability of serving all users is the same, although different users have different average channel quality.

3) This scheme accounts for balance between system throughout and fairness.

Priority for UE = R/r:R: required data rate of UE (calculated TB size per 2ms

based on CQI)

r: amount of effective data (not including data retransmitted ) transmitted by transport layer for this UE during the past 1.6s

The bigger the R/r, the higher the priority (more chance to get resource).

(PF- Proportional Fair)


Adaptive Modulation and Coding (AMC)Adaptive Modulation and Coding (AMC)

AMC is based on channel qualityAdjust data rate

Good channel condition – higher rate

Poor channel condition – lower rate

Adjust code rateGood channel condition – higher rate (e.g. 3/4 code)

Poor channel condition – lower rate (e.g. 2/4 code)

Adjust modulation schemeGood channel condition – 16QAM

Poor channel condition – QPSK

Channel Quality Feedback (CQI)UE measures channel quality (SNR) and reports to Node B every 2ms or longer time.

Node-B chooses modulation scheme, Transport Block size and data rate based on CQI.

Throughput ~ SIR Relationship

AMC could improve radio bandwidth and fit for high speed radio transmission.


HSDPA ModulationQPSK16QAM

Modulation SchemeModulation Scheme


CQI Mapping Table (Category 10)

016-QAM152555830

0…………

016-QAM121723726

016-QAM101441125

016-QAM81141824

016-QAM7971923

016-QAM5716822

016-QAM5655421

…….........

016-QAM5356516

0QPSK5331915

0QPSK4258314

0QPSK4227913

0QPSK3174212

……………

0QPSK26507

0QPSK14616

0QPSK13775

0QPSK13174

0QPSK12333

0QPSK11732

028800

0QPSK11371

Out of rangeN/A0

XRVNIRReference power adjustment ΔModulationNumber of HS-PDSCHTransport Block SizeCQI value

AMC and modulation scheme recommend in protocolNode-B chooses modulation scheme, transport block size and data rate based on CQI.


Link Emulation- AMC

AMC AMC PerformancePerformance

AMC changes transmission parameters depending on channel condition and optimize data rate.

AMC performance is affected by channel quality error and feedback delay in fading channel.

For low data rate, AMC has better performance than fixed MCS.

For high data rate, AMC has worse performance than fixed MCS.

AMC gain

0

100

200

300

400

500

600

-12 -11 -10 -9 -8 -7 -6 -5 -4 -3

HS-DSCH Ec/N0(dB)

Throughput(kbps)

TU5(Fixed MCS) TU5(AMC)




AMC Processing Flow

UE measure CPICH strengthUE reports the signal quality by CQI (channel quality indicator)Node B may filter and rectify CQI report to obtain actual CQIDetermine the channel number, transmit power and modulation scheme, etc, based on CQI, transmit data volume, available powerand code.


Hybrid Automatic Repeat Request (HARQ)Hybrid Automatic Repeat Request (HARQ)

Tranditional ARQ–decode received transport block

–detect if there is CRC error in decoded transport bolck

–If there is CRC error

•discard error block

•Request retransmission

Hybrid ARQ–decode received transport block

–Detect if there is CRC error in decoded transport bolck

–If there is CRC error

•Store error block(no discard)

•Request retransmission

•Combine the currently received retranmission with the previous failed decodes.

Soft Combine

Increment redundancy

HARQ helps minimize retransmission time and increase cell throughout.

Combined HARQ

Block1

Block1

Block1?

Block1

Block1

Block2


HARQ ConceptHARQ is a technique that transmitter sends new set of check bits if the previous transmission failed (NACK) while receiver buffers the failed decodes for soft combining with future retransmissions.

The RV parameter indicates different code bit transmit in IR buffer. Different RV parameter configuration supports:

CC (Chase Combining): retransmit the same coded data

PIR (Partial Incremental Redundancy): transmit systematic bits first

FIR (Full Incremental Redundancy): transmit parity bits first


HARQ Gain

One retransmission gain for different retransmission scheme

8.44.33.53.1FIR Gain (dB)

6.53.63.33.1PIR Gain (dB)

3.03.03.03.0CC Gain (dB)

3/42/31/21/3Code Rate

FIR scheme will transmit the check bits first, it has effective average coded bits after retransmission. Especially for high code rate, the HARQ gain is very evidence.


Link Emulation- HARQHARQ( Hybrid ARQ) Performance

HARQ may reduce effect by channel measure error and feedback delay, and provide AMC performance gain.

Higher speed, higher HARQ gain.

HARQ Gain over AMC

0

100

200

300

400

500

600

-12.5 -11.5 -10.5 -9.5 -8.5 -7.5 -6.5 -5.5 -4.5 -3.5

HS-DSCH Ec/N0(dB)

Throughput(kbps)

TU5(AMC+HARQ) TU5(AMC)




Contents


Section 2 Key Techniques

Section 3 Physical Channel


HSDPA Relevant Physical ChannelThree new HSDPA Physical Channel

For each HS-DPCCH, SF=256

Each H has one HS-DPCCH.

For each HS-SCCH, SF=128

Each cell is assigned up to 4 HS-SCCH (limited by UE capability)

For each HS-PDSCH, SF=16


HSDPA Channel Mapping


Associated Channel - DPCH

There is another dedicated physical channel named DPCH for each HSDPA user. DPCH is also called associated channel in HSDPA. It is used for signaling transport and power control.

Normally DPCH doesn’t carry service data, only sometimes carry real time services such as AMR (the user setup multiple RAB: CS+PS).

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

“Associated”? Or “Concomitant”?


HSDPA Physical Channel (HS-SCCH)HS-SCCH and HS-PDSCH

are downlink shared channel shared by all users. How can users know when and on which channel my

data is transported?

HS-SCCH is like soldiers holding flags at the first row of queue. UE keeps on monitoring the HS-SCCH channels to identify any HS-PDSCH subframes addressed to it on the sets of HS-PDSCH channels. Upon receiving an HS-PDSCH subframe for the UE, the UE physical layer will demodulates the subframe, otherwise do nothing.


Physical Channel Slot Format (HS-SCCH)HS-SCCH Slot Format Features

3 slots in one TTI (2ms)SF=128, QPSK modulationMaps user’s seven data attributes, including Xue, Xccs, Xms, Xrv, Xtbs, Xhap and Xnd;UE demodulates HS-SCCH and find out the received data addressed to the UE. Then UE demodulates the HS-PDSCH.In theory, one cell can configure up to 15 HS-SCCH. But now commercial UE can only monitor up to 4 HS-SCCH channels simultaneously. So one cell only configure up to 4 HS-SCCH channels.

Slot #0 Slot#1 Slot #2

T slot = 2560 chips, 40 bits

DataN data 1 bits

HS-SCCH subframe: T = 2 ms


Physical Channel Slot Format (HS-PDSCH)

Slot #0 Slot#1 Slot #2

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

DataNdata1 bits

1 subframe: T f = 2 ms

HS-PDSCH Slot Format Attributes:3 slots in one TTI (2ms)Fixed spreading factor SF16QPSK or 16QAM modulationOnly carry user dataUE may be assigned multi channelization codes to support multi-code transport

depending on UE capability.


Physical Channel Slot Format (HS-DPCCH)Uplink HS-DPCCH

TTI 2ms (3 slots), SF 256, Fixed rate of 15Kbps,carry 2 types of HSDPA uplink physical layer signaling: ACK/NACK and CQI.ACK and NACK notifies the NodeB if UE has received correct downlink data or not. The field defines like this:1-Nack, 0-AckCQI is a metric that reflects physical channel quality indicator based on CPICH, and reported by period ranging from 0, 2ms…. to 160ms (0 means no transmission). Usually the period is 2ms (one TTI).ACK/NAK and CQI having different function may be controlled independently by different parameters . ACK/NACK/CQI could be configured to repeat up to 4 times to improve TSTD gain.

Subframe #0 Subframe # Subframe #4

HARQ-ACK CQI

One radio frame Tf = 10 ms

One HS-DPCCH subframe (2 ms)

2×Tslot = 5120 chipsT slot = 2560 chips


Physical Channel TimingStart of HS-SCCH is aligned with the start of P-CCPCH, HS-PDSCH subframe is transmitted two slots after the associated HS-SCCH subframe. UE demodulates HS-PDSCH subframe according to HS-SCCH. HS-SCCH and PDSCH are common channels, so there are not timing between HS-SCCH/PDSCH and DPCH.

HS-SCCH

HS-PDSCH

3 slots = 2 ms

DPCH

τDPCH

Radio frame with (SFN modulo 2) = 0 P-CCPCH

2 slots

3 slots = 2 ms

Slot Slot Slot Slot Slot Slot Slot Slot Slot Slot Slot Slot Slot Slot Slot

15 slots = 10 ms

Subframe #0 Subframe #1 Subframe #2 Subframe #3 Subframe #4

Radio frame with (SFN modulo 2)=1 10 ms

Subframe #0 Subframe #1 Subframe #2 Subframe #3 Subframe #4

HS-DPCCH3 slots = 2 ms

~7.5 slots


UE Capacity Category( for reference)


HSDPA Physical Channel Transmit PowerPHSDPA(HSDPA total transmit power)＝ PHS-PDSCH + PHS-SCCH

The HS-PDSCH transmit power is adjusted by Node B according to the following factors:

CQI

Amount of data to be transmitted

Available power for HS-PDSCH

Available code resource for HS-PDSCH

HS-SCCH transmit power may use:Fixed power transmission (outdoor 5%, indoor 3% of the total power)

A fixed power offset between HS-SCCH and DL associated channel (PDCH). HS-PDSCH transmit power is usually bigger than the PDCH channel to keep a proper transmit power.

HS-DPCCH transmit power has a power offset based on UL DPCH.Slot carrying HARQ-ACK/NACK or CQI may be set different power offset.


HSDPA – Channel MappingWhen RAB is mapped onto HS-DSCH,

DPCH is needed to transport UL RLC AM information and possible UL data, no matter there is UL data to transport.

The following figure describes that DL TRB is carried on HS-DSCH SRB and SRB or UL service is carried on DCH. In soft handover, there may be one or more DCH, but only one HS-DSCH.

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