hsdpa basic principle

8/12/2019 HSDPA Basic Principle

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HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential

Security Level: Internal Use Only

www.huawei.com

HSDPA Basic Principle


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HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 1

Learning Objectives

HSDPA basic principle and feature

HSDPA key technologies

HSDPA physical channels


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Contents

Chapter 1 HSDPA Basic

Concepts and CharacteristicsSection 2 Key Techniques

Section 3 Physical Channel


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HSDPA Basic Concepts

HSDPA = High Speed Downlink Packet Access

Important Features of 3GPP R5Why HSDPA?

The subscribers request higher speed and better qualitydata access

Competition challenge from CDMA EV/DO, WiMAXUp to now, the throughput request for downlink is muchmore higher than that of uplinkThe channel configuration of R99 lead a very lowefficiency on the downlink capacity


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HSDPA Characteristics

HSDPA is the solution of WCDMA offering higherspeed 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

HSDPA


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Contents


Concepts and CharacteristicsChapter 2 Key Techniques

Chapter 3 Physical Channel


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HSDPA 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


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HSDPA Key Techniques

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


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Fast Scheduling Basic

If a little part of received 10ms frame (15 slots - R99) cant bedecoded correctly, whole frame will be retransmit 10ms later.

An HSDPA frame is only 2ms(3 slots). If a 2ms frame cant bedecoded correctly, just this 2ms frame need be retransmitted. Other2ms(up to 6) HARQ process may continue transmitting data, thusradio resource could be used more effectively.

Physical Layer Basic


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Fast Scheduling

Scheduling Principle: based on channelcondition in short period; based on balancebetween throughout and proportional fair for allusers in long period.

Some basic scheduler

Round Robin (RR)Maximum C/I (MAXC/I)

Proportional Fair (PF)

By fast scheduling, HSDPA cell can allocate the available HSDPA power resource andcode 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


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Share and Scheduling of Shared Channel

The following fig describes scheduling processing for 4 users.

All codesreserved forHSDPAtransmission

2ms


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Fast 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 code

2. Required resource: including users, user data, retransmission, air interface abilityestimate, etc.

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

Output:

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


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Max 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 thebest 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.


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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 allocatedresource


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


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Adaptive Modulation and Coding (AMC)

AMC is based on channel quality Adjust 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 toNode B every 2ms or longer time.

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

Throughput ~ SIR Relationship

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


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HSDPA ModulationQPSK16QAM

Modulation Scheme


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CQI Mapping Table (Category 10)CQI value Transport BlockSize Number of HS-PDSCH Modulation Reference power adjustment NIR XRV

0 N/A Out of range

1 137 1 QPSK 0

28800 0

2 173 1 QPSK 0

3 233 1 QPSK 0

4 317 1 QPSK 0

5 377 1 QPSK 0

6 461 1 QPSK 0

7 650 2 QPSK 0

12 1742 3 QPSK 0

13 2279 4 QPSK 0

14 2583 4 QPSK 015 3319 5 QPSK 0

16 3565 5 16-QAM 0

... ... ...

21 6554 5 16-QAM 0

22 7168 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

0

30 25558 15 16-QAM 0

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


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Link Emulation- AMC

AMC Performance

AMC changes transmission

parameters depending on channel

condition and optimize data rate.

AMC performance is affected by

channel quality error and feedbackdelay 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)

T h

r o u g

h p u t

( k b

p s

)

TU5(Fixed MCS) TU5(AMC)T U30 (Fix ed MCS ) TU30 (AM C)TU120(F ixed MCS) TU120(AMC)


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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 modulationscheme, etc, based on CQI, transmit data volume, available powerand code.


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


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Hybrid Automatic Repeat Request (HARQ)

Tranditional ARQ decode received transport block

detect if there is CRC error in decodedtransport 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


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HARQ Concept

HARQ is a technique that transmitter sends new set of check bits ifthe previous transmission failed (NACK) while receiver buffers thefailed 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


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HARQ Gain

One retransmission gain for different retransmission scheme

Code Rate 1/3 1/2 2/3 3/4

CC Gain (dB) 3.0 3.0 3.0 3.0

PIR Gain (dB) 3.1 3.3 3.6 6.5

FIR Gain (dB) 3.1 3.5 4.3 8.4

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


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Link Emulation- HARQ

HARQ( Hybrid ARQ) Performance

HARQ may reduce effect bychannel measure error andfeedback 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)

T h

r o u g

h p u t

( k b

p s

)

TU5(AMC+HARQ) TU5(AMC)TU30(AMC+HARQ) TU30(AMC)TU120(AMC+HARQ) TU120(AMC)


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Contents


Concepts and CharacteristicsSection 2 Key Techniques

Section 3 Physical Channel


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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 Ch l M i


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HSDPA Channel Mapping


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Associated Channel - DPCH

There is another dedicated physical channel

named DPCH for each HSDPA user. DPCH isalso called associated channel in HSDPA. It isused for signaling transport and power control.

Normally DPCH doesnt carry service data, onlysometimes carry real time services such as

AMR (the user setup multiple RAB: CS+PS).

Node B

UE

HS-PDSCH HS-SCCH DPCH HS-DPCCH

Associated? Or Concomitant?


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

are downlink shared

channel shared by all users.How can users know whenand on which channel my

data is transported?

HS-SCCH is like soldiers holdingflags at the first row of queue. UEkeeps on monitoring the HS-SCCH channels to identify any HS-PDSCHsubframes addressed to it on the setsof HS-PDSCH channels. Uponreceiving an HS-PDSCH subframe forthe UE, the UE physical layer willdemodulates the subframe, otherwisedo nothing.


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Physical Channel Slot Format (HS-PDSCH)

Slot #0 Slot#1 Slot #2

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

Data N data 1 bits

1 subframe: T f = 2 ms

HS-PDSCH Slot Format Attributes:3 slots in one TTI (2ms)

Fixed spreading factor SF16QPSK or 16QAM modulation

Only carry user data

UE may be assigned multi channelization codes to support multi-code transportdepending on UE capability.


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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 layersignaling: ACK/NACK and CQI.

ACK and NACK notifies the NodeB if UE has received correct downlink data or not. The fielddefines like this:1-Nack, 0-AckCQI is a metric that reflects physical channel quality indicator based on CPICH, and reportedby period ranging from 0, 2ms. to 160ms (0 means no transmission). Usually the period is2ms (one TTI).

ACK/NAK and CQI having different function may be controlled independently by differentparameters .

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 T = 10 ms

One HS-DPCCH subframe (2 ms)

2 Tslot = 5120 chipsTslot = 2560 chips


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UE Capacity Category( for reference)


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HSDPA Physical Channel Transmit Power P HSDPA (HSDPA total transmit power) P HS-PDSCH + P HS-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.


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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 DLTRB is carried on HS-DSCH SRB andSRB or UL service is carried on DCH. Insoft handover, there may be one or moreDCH, but only one HS-DSCH.


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hsdpa basic principle

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