HSDPA Basic Principles

Security Level: Internal Use Only

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Learning Objectives

¾

HSDPA basic principle and feature

¾

HSDPA key technologies

Contents

Chapter 1 HSDPA Basic

Concepts and Characteristics

Section 2 Key

Techniques

HSDPA Basic Concepts

z HSDPA = High Speed Downlink Packet Access

z

Important Features of 3GPP R5

z

Why HSDPA?

Ö The subscribers request higher speed and better quality

data access

Ö Competition challenge from CDMA EV/DO, WiMAX

Ö Up to now, the throughput request for downlink is much

more higher than that of uplink

Ö The channel configuration of R99 lead a very low

efficiency on the downlink capacity

HSDPA Characteristics

HSDPA is the solution of WCDMA offering higher

speed downlink data services.

¾ Peak data rate in DL: 14.4Mbps (physical layer)

¾ Shorter delay

¾ Higher efficiency using downlink code and power and bigger

downlink capacity

¾ Flexible cell resource allocation

¾ More high speed user access

UMTS R99

GSM

Contents

Chapter 1 HSDPA Basic

Concepts and Characteristics

Chapter 2 Key Techniques

HSDPA Key Techniques- Overview

HSDPA Key Techniques- Overview

AMC

HARQ (Hybrid ARQ)

Fast Scheduling

16QAM

SF16, 2ms and CDM/TDM

3 New Physical Channels

HSDPA Key Techniques

¾ Fast Scheduling(2ms short frame

and scheduling)

¾ AMC (support QPSK and 16QAM)

¾ 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.

Fast Scheduling

Fast Scheduling

Scheduling Principle:

based on channel

condition in short period; based on balance

between throughout and proportional fair for all

users in long period.

z

Some

basic

scheduler

Ö Round Robin (RR)

Ö Maximum C/I (MAXC/I)

Ö 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.

z

Scheduler may works based on CDM

and/or TDM

Ö Channel condition

Ö Amount of data waiting in the queue (delay)

Ö Fairness

Share and Scheduling of Shared Channel

The following fig describes scheduling processing for 4 users.

All codes reserved for HSDPA transmission

Fast Scheduling Process

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 ability

estimate, etc.

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

Output:

Max C/I Scheduling Algorithm

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 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 Algorithm

PF 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:

ÖR: required data rate of UE (calculated TB size per 2ms

based on CQI)

Ör: amount of effective data (not including data retransmitted )

transmitted by transport layer for this UE during the past 1.6s

ÖThe bigger the R/r, the higher the priority (more chance to

get resource).

HSDPA Key Techniques

¾

Fast Scheduling(2ms short frame and

scheduling)

¾ AMC (support QPSK and 16QAM)

Adaptive Modulation and Coding (AMC)

Adaptive Modulation and Coding (AMC)

z

AMC is based on channel quality

Ö Adjust data rate

‰ Good channel condition – higher rate ‰ Poor channel condition – lower rate

Ö Adjust code rate

‰ Good channel condition – higher rate (e.g. 3/4 code) ‰ Poor channel condition – lower rate (e.g. 2/4 code)

Ö Adjust modulation scheme

‰ Good channel condition – 16QAM ‰ Poor channel condition – QPSK

z

Channel Quality Feedback (CQI)

Ö UE measures channel quality (SNR) and reports to

Node B every 2ms or longer time.

Ö Node-B chooses modulation scheme, Transport Block

size and data rate based on CQI.

¾ HSDPA Modulation

¾ QPSK

¾ 16QAM

Modulation Scheme

CQI Mapping Table (Category 10)

Reference power adjustment Δ Modulation

Number of HS-PDSCH Transport Block

Size CQI value

Link Emulation- AMC

AMC

AMC

Performance

Performance

z

AMC changes transmission

parameters depending on channel

condition and optimize data rate.

z

AMC performance is affected by

channel quality error and feedback

delay in fading channel.

z

For low data rate, AMC has better

performance than fixed MCS.

z

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) Th roug hput( kbps) TU5(Fixed MCS) TU5(AMC) TU30(Fixed MCS) TU30(AMC) TU120(Fixed MCS) TU120(AMC)

AMC Processing Flow

z

UE measure CPICH strength

z

UE reports the signal quality by CQI (channel quality indicator)

z

Node B may filter and rectify CQI report to obtain actual CQI

z

Determine the channel number, transmit power and modulation

scheme, etc, based on CQI, transmit data volume, available power

and code.

HSDPA Key Techniques

¾

Fast Scheduling(2ms short frame and

scheduling)

¾

AMC (support QPSK and 16QAM)

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

HARQ helps minimize retransmission time and increase cell throughout.

Combined HARQ Block1 Block1 Block1? Block1 Block1 Block2

HARQ Concept

z

HARQ 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.

z

The RV parameter indicates different code bit transmit in IR buffer.

Different RV parameter configuration supports:

Ö CC (Chase Combining): retransmit the same coded data

Ö PIR (Partial Incremental Redundancy): transmit systematic bits first

Ö FIR (Full Incremental Redundancy): transmit parity bits first

HARQ Gain

One retransmission gain for different retransmission scheme

8.4

4.3

3.5

3.1

FIR Gain (dB)

6.5

3.6

3.3

3.1

PIR Gain (dB)

3.0

3.0

3.0

3.0

CC Gain (dB)

3/4

2/3

1/2

1/3

Code 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- HARQ

HARQ( Hybrid ARQ) Performance

¾

HARQ may reduce effect by

channel measure error and

feedback delay, and provide AMC

performance gain.

¾

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) Thr oughput (kbps) TU5(AMC+HARQ) TU5(AMC) TU30(AMC+HARQ) TU30(AMC) TU120(AMC+HARQ) TU120(AMC)

Contents

Chapter 1 HSDPA Basic

Concepts and Characteristics

Section 2 Key

Techniques

HSDPA Relevant Physical Channel

Three 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

Associated Channel - DPCH

¾

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.

¾

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

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)

z

HS-SCCH Slot Format Features

Ö 3 slots in one TTI (2ms)

Ö SF=128, QPSK modulation

Ö Maps user’s seven data attributes, including Xue, Xccs, Xms, Xrv, Xtbs, Xhap and Xnd;

Ö UE demodulates HS-SCCH and find out the received data addressed to the UE. Then

UE demodulates the HS-PDSCH.

Ö 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

Tslot= 2560 chips,

40

Data Ndata 1 bits

Physical Channel Slot Format (HS-PDSCH)

Slot #0 Slot#1 Slot #2 Tslot = 2560 chips, M*10*2k bits (k=4)

Data Ndata1 bits

1 subframe: Tf = 2 ms z

HS-PDSCH Slot Format Attributes:

Ö3 slots in one TTI (2ms)

ÖFixed spreading factor SF16

ÖQPSK or 16QAM modulation

ÖOnly carry user data

ÖUE may be assigned multi channelization codes to support multi-code transport

depending on UE capability.

Physical Channel Slot Format (HS-DPCCH)

z

Uplink HS-DPCCH

Ö TTI 2ms (3 slots), SF 256, Fixed rate of 15Kbps,carry 2 types of HSDPA uplink physical layer

signaling: ACK/NACK and CQI.

Ö ACK and NACK notifies the NodeB if UE has received correct downlink data or not. The field

defines like this:1-Nack, 0-Ack

Ö CQI 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).

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

parameters .

Ö 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 HS-DPCCH subframe (2 ms)

2

×T

= 5120 chips

Physical Channel Timing

z

Start 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.

z

HS-SCCH and PDSCH are common channels, so there are not timing between

HS-SCCH/PDSCH and DPCH.

HS-SCCH

HS-PDSCH

DPCH

τ

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-DPCCH

3 slots = 2 ms ~7.5 slots

HSDPA Physical Channel Transmit Power

z

P

HSDPA total transmit power)

＝ P

+ P

z

The HS-PDSCH transmit power is adjusted by Node B according

to the following factors:

Ö CQI

Ö Amount of data to be transmitted

Ö Available power for HS-PDSCH

Ö Available code resource for HS-PDSCH

z

HS-SCCH transmit power may use:

Ö Fixed power transmission (outdoor 5%, indoor 3% of the total power)

Ö 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.

z

HS-DPCCH transmit power has a power offset based on UL DPCH.

HSDPA – Channel Mapping

Ö

When 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.

Ö

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.

Thank you