HSDPA Basic Principles

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HSDPA Basic Principle www.huawei.com

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Learning Objectives ¾ HSDPA basic principle and feature ¾ HSDPA key technologies ¾ HSDPA physical channels

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Contents

Chapter 1 HSDPA Basic Concepts and Characteristics Section 2 Key Techniques Section 3 Physical Channel

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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

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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 HSDPA UMTS R9 9

GS M

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Contents

Chapter 1 HSDPA Basic Concepts and Characteristics Chapter 2 Key Techniques Chapter 3 Physical Channel

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HSDPA Key Techniques- Overview

AMC Adaptive Modulation and Coding

SF16, 2ms and CDM/TDM

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HARQ (Hybrid ARQ)

Fast Scheduling

Hybrid Automatic Repeat Request

16QAM

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3 New Physical Channels

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HSDPA Key Techniques ¾ Fast Scheduling(2ms short frame and scheduling) ¾ AMC (support QPSK and 16QAM) ¾ HARQ

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Fast Scheduling Basic Physical Layer 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.

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

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

z Scheduler may works based on CDM and/or TDM

z Some basic scheduler

Ö Channel condition

Ö Round Robin (RR)

Ö Amount of data waiting in the queue (delay) Ö Fairness

Ö Maximum C/I (MAXC/I) Ö Proportional Fair (PF)

Ö Cell throughout, etc

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Share and Scheduling of Shared Channel The following fig describes scheduling processing for 4 users.

All codes reserved for HSDPA transmission 2ms

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Fast Scheduling Process Available resource •Transmit power for which users Required resource

Scheduling Algorithm

•Channelization code •Data attributes

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: 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 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.

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RR Scheduling Algorithm (RR - Round Robin)

Note: User allocated resource

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.

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PF Scheduling Algorithm (PF- Proportional Fair) 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). 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.

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HSDPA Key Techniques

¾ Fast Scheduling(2ms short frame and scheduling) ¾ AMC (support QPSK and 16QAM) ¾ HARQ

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Adaptive Modulation and Coding (AMC) AMC could improve radio bandwidth and fit for high speed radio transmission. 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. Throughput ~ SIR Relationship

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Modulation Scheme ¾ HSDPA Modulation ¾ QPSK ¾ 16QAM

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CQI Mapping Table (Category 10) CQI value

Transport Block Size

0

N/A

1

137

1

QPSK

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

0

15

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

Number of HS-PDSCH

Reference power adjustment Δ

Modulation

NIR

XRV

28800

0

Out of range

¾AMC and modulation scheme recommend in protocol ¾Node-B chooses modulation scheme, transport block size and data rate based on CQI. HUAWEI TECHNOLOGIES CO., LTD.

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Link Emulation- AMC AMC Performance AMC gain

TU5(Fixed MCS) TU30(Fixed MCS) TU120(Fixed MCS)

TU5(AMC) TU30(AMC) TU120(AMC)

z AMC changes transmission parameters depending on channel

600

Throughput(kbps)

condition and optimize data rate. 500

z AMC performance is affected by

400

channel quality error and feedback delay in fading channel.

300

z For low data rate, AMC has better 200

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

100 0 -12

worse performance than fixed MCS. -11

-10

-9

-8

-7

-6

-5

-4

-3

HS-DSCH Ec/N0(dB)

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AMC Processing Flow

z z z z

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

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HSDPA Key Techniques

¾ Fast Scheduling(2ms short frame and scheduling) ¾ AMC (support QPSK and 16QAM) ¾ HARQ

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Hybrid Automatic Repeat Request (HARQ) HARQ helps minimize retransmission time and increase cell throughout. Tranditional ARQ

Hybrid ARQ

–decode received transport block

–decode received transport block

–detect if there is CRC error in decoded transport bolck

–Detect if there is CRC error in decoded transport bolck –If there is CRC error

–If there is CRC error

•Store error block(no discard)

•discard error block

•Request retransmission

•Request retransmission

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

Combined HARQ Block1

Block1

Block2

Soft Combine

Block1

Block1 Block1?

Increment redundancy

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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

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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 average coded bits after retransmission. Especially for high code rate, the HARQ gain is very evidence.

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Link Emulation- HARQ HARQ( Hybrid ARQ) Performance HARQ Gain over TU5(AMC+HARQ) TU30(AMC+HARQ) TU120(AMC+HARQ)

600

AMC TU5(AMC) TU30(AMC) TU120(AMC)

¾ HARQ may reduce effect by channel measure error and feedback delay, and provide AMC performance gain.

Throughput(kbps)

500

400

¾ Higher speed, higher HARQ gain.

300

200

100

0 -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)

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Contents

Chapter 1 HSDPA Basic Concepts and Characteristics Section 2 Key Techniques Section 3 Physical Channel

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HSDPA Relevant Physical Channel Three new HSDPA Physical Channel For each HS-PDSCH, SF=16

For each HS-SCCH, SF=128 Each cell is assigned up to 4 HSSCCH (limited by UE capability)

For each HS-DPCCH, SF=256 Each H has one HS-DPCCH.

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HSDPA Channel Mapping

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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 ode B

H S -P D S C H

H S -S C C H

DPCH

H S -D P C C H

UE

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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 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 HSPDSCH channels. Upon receiving an HS-PDSCH subframe for the UE, the UE physical layer will demodulates the subframe, otherwise do nothing.

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

3 slots in one TTI (2ms) SF=128, QPSK modulation Maps 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. 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. Data N data 1 bits

T slot = 2560 chips, 40 bits

Slot #0

Slot#1

Slot #2

HS-SCCH subframe: T = 2 ms

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Physical Channel Slot Format (HS-PDSCH) 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. Data Ndata1 bits k

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

Slot #0

Slot#1

Slot #2

1 subframe: Tf = 2 ms

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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. Tslot = 2560 chips

2×Tslot = 5120 chips

HARQ-ACK

CQI

One HS-DPCCH subframe (2 ms)

Subframe #0

Subframe #

Subframe #4

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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. 10 ms

Radio frame with (SFN modulo 2) = 0

P-CCPCH

Radio frame with (SFN modulo 2)=1

3 slots = 2 ms

HS-SCCH Subframe #0 Subframe #1 Subframe #2 Subframe #3 Subframe #4 3 slots = 2 ms

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

HS-PDSCH 2 slots

15 slots = 10 ms

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

DPCH

τDPCH

~7.5 slots

HS-DPCCH 3 slots = 2 ms

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UE Capacity Category( for reference)

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HSDPA Physical Channel Transmit Power z PHSDPA(HSDPA total transmit power)＝ PHS-PDSCH + PHS-SCCH 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. Ö Slot carrying HARQ-ACK/NACK or CQI may be set different power offset.

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HSDPA – Channel Mapping ÖWhen 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. ÖThe 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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