8.HSDPAOverview

1 © Nokia Siemens Networks Presentation / Author / DateFor internal use

HSDPA High Speed Downlink Packet Access

Agenda

-> Introduction

General Principal

• HSDPA Key Characteristics, New Features

Architectural Changes, Impact on RAN

Link Adaptation

HSDPA Channel Structure

HARQ Principle

HSDPA – Operating Principle

Packet Scheduling

HSDPA Mobility

What is HSDPA ?

High Speed Downlink Packet Access (HSDPA) is a packet swithed DL data service in WCDMA with data rate up to 10Mbps over a 5MHz Bandwidth

3GPP Rel5 specifications

Builds on distributed architecture that gives Node-B more control when to transmit, to which terminal to transmit and also to handle the retransmission

Nokia RAN05 feature

Improvements and new functionalities coming in RAN05.1 and in RAN06

Why HSDPA?

Improved

• cell throughput

• maximum user throughput

• round trip time

• spectral efficiency

HSDPA Peak Data Rates

5 codes QPSK 1.6 Mbps

# of codes Modulation Max RLC data rate

5 codes 16-QAM 3.36 Mbps




1.8 Mbps

Max L1 data rate

3.6 Mbps

7.2 Mbps

10.1 Mbps

14.0 Mbps

Phase 1

Phase 2

Phase 3

Phase 4

15 codes, MIMO 16-QAM 26.6 Mbps 28.0 Mbps 3GPP R7

15 codes, MIMO? 64-QAM 3GPP R7

HSDPA TX-power

Common channels

DCH RT

DCH NRT

HSDPA NRT

PtxTarget

Max power

Power control head-room

Non-controllable power

Controllable power

Total transmittedcarrier power

NEW non-HSDPApower measurements

Power measurementsfrom the Node-B to

the RNC

In addition to power also code resource shared!

Agenda

Introduction

-> General Principal



Link Adaptation


HARQ Principle


Packet Scheduling

HSDPA Mobility

HSDPA key characteristics (1)

Basic WCDMA Technology

Enhanced in HSDPAIncluded in HSDPA

Excluded from HSDPA

AMC

H-ARQ

TTI = 2 ms

Advanced PS

SHO

PC

Variable SF

Multi-code operation

HSDPA key characteristics (2)

The physical layer retransmission (ARQ function)

• R’99: RNC-based ARQ

• HSDPA: Node-B based fast H-ARQ

Packet scheduling

• R’99: RNC-based

• HSDPA: NodeB-based

Power control

• R’99: Fast PC

• HSDPA: Link adaptation function and AMC (adaptive modulation and coding)

Good spectral efficiency

• HSDPA: up to 15 multi-codes in parallel.

SF = 128

SF = 256

SF = 64

SF = 32

SF = 8

SF = 16

SF = 4

SF = 2

SF = 1

Codes for the cell common channels

Code for oneHS-SCCH

Codes for 5HS-PDSCH's

Downlink Code Allocation

•166 codes @ SF=256 available for the associated DCHs and non-HSDPA uses

•HSDPA with 5 codes allocated at cell MAC-hs start-up when HSDPA is enabled

•Code allocation is dynamic in future releases when more than 5 codes are allocated

New features (1/2)

Shared channel transmission

• HS-DSCH (high speed downlink shared channel)

• Supports up to 15 codes parallel

• Fixed spreading factor (16)

• Works in parallel to DCH

Higher-order modulation

• QPSK

• 16-QAM

Short transmission time interval (TTI)

• Dynamic channel code allocation interval of 2 ms

New features (2/2)

Fast link adaptation• Adjusts transmission parameters – not TX

power!• Users near Node B: QPSK 16-QAM (for

example)

Fast scheduling• Allocates the use of shared channel to UEs

with best radio conditions at certain time moment (Multi User Diversity)

• Scheduling is done at Node-B instead of RNC

Fast hybrid automatic-repeat-request (H-ARQ)• Request and retransmit missing data (UE

Node-B)• Combine information from original

transmission (Soft Combining)• Signalling with ACKs and NACKs

HSDPA Operating Prinicple

HSDPA - General Principle

Channel quality(CQI, Ack/Nack, TPC)

Data

BTS Tx pwr

Tx power for HSDPA

is constant

Tx power for HSDPA

is constant

Throughput

Throughput varies according

to channel quality

HSDPAR99-DCH

BTS Tx pwr

Tx power varies according to

channel quality (BLER)

Throughput

Throughput is “maintained”

Throughput is “maintained”

#channelisationCodes per UE

Only 1 variable SF code used per user

Only 1 variable SF code used per user

1

#channelisationCodes per UE

2

4

6

8

0-15 codes of SF16 used based on channel quality and UE/network capability

0-15 codes of SF16 used based on channel quality and UE/network capability

Agenda

Introduction

General Principal


-> Architectural Changes, Impact on RAN

Link Adaptation


HARQ Principle


Packet Scheduling

HSDPA Mobility

Key Architectural ChangeThe PDCP, RLC and MAC-d layers are unchanged from the Release '99 and Release 4 architectureThe new functionalities of hybrid ARQ and scheduling/priority handling are included in the MAC layer• In the UTRAN side, these functions are included in a new entity called MAC-hs, which is located in the BTS• A new type of transport channel, the HS-DSCH, is introduced for HSDPA– It is controlled by the MAC-hs.

Iub

Affected by HSDPA

RNC

RRMAC

PS

HCLC

RM

PDCP

RLC

MAC

FP

Transport

Node B

FP

Transport

MAC-hs

WCDMAL1

O&M

Not affected by HSDPA

New entity for HSDPA

HSDPA Protocol Architecture

New MAC entity, MAC-hs added to the Node B

RNC still retains the RLC functionalities

WCDMA L1

UE

Iub/Iur

SRNCNode B

Uu

MAC-hs

RLC

NAS

HSDPA user plane

WCDMA L1

MAC-hs

TRANSPORT

FRAMEPROTOCOL

TRANSPORT

FRAMEPROTOCOL

MAC-dRLC

IuMAC-d

PHY

ATM

AAL2

HS - DSCH FP

MAC - d

RLC

PDCP

SRNC

PHY

ATM

AAL5

IP

UDP

GTP - U

PHY

ATM

AAL5

IP

UDP

GTP - U

User IP data

CN UE

PHY

WCDMA L1

WCDMA L1 ATM

AAL2

HS - DSCH FP MAC - hs MAC - hs

Node B MAC - d

RLC

PDCP

User IP data

PHY

ATM

AAL2

HS - DSCH FP

MAC - d

RLC

PDCP

SRNC

PHY

ATM

AAL5

IP

UDP

GTP - U

PHY

ATM

AAL5

IP

UDP

GTP - U

User IP data

CN UE

PHY

WCDMA L1

WCDMA L1 ATM

AAL2

HS - DSCH FP MAC - hs MAC - hs

Node B MAC - d

RLC

PDCP

User IP data

Uu Iub Iu - PS

HSDPA Protocol Stack incl. PS Core NW

HSDPA impact on RAN

Additional intelligence (HSDPA MAC – MAC hs) is installed at the NodeB.

Retransmission controlled by the NodeB leads to faster execution and shorter delay in case of retransmissions.

The Iub interface (NodeB-RNC) requires a flow control mechanism to ensure that NodeB buffers are used properly and there is no buffer overflow.

Pac

ket

Pac

ket

RLC ACK/NACK

L1 ACK/NACK

R’99 DCH / DSCH R’5 HS-DSCH

New Node B functionality for HSDPA

TerminalsNode BRNC

PacketsScheduler

& Buffer

ARQ &

Coding

ACK/NACK & Feedback Decoding

Flow Control

New Node B functions:Scheduler: Terminal scheduling, Coding & Modulation selection (16QAM as

new modulation)

ARQ Retransmissions Handling

Uplink Feedback Decoding

Flow Control towards SRNC

New terminal functionality for HSDPA

TerminalNode BRNC

PacketsARQ

Decoding

Soft Buffer

& Combining

ACK/NACK & Feedback

Generation

Flow Control

New terminal functions:

16 QAM demodulation

ARQ Retransmissions Handling

Soft buffer & combining

Fast Uplink Feedback Generation & encoding

Initial HSDPA terminals are data cards without voice capability

Sub frame Structure

WCDMA : 10ms frame (15 slots)

HSDPA: 2ms (3slots) -> Subframe

slot#0 slot#1 slot#2

HSDPA subframe (2 ms)

Quick Snapshot: Changes Introduced by HSDPA

Shorter radio frame ( 2ms TTI)

Use of 16QAM modulation in addition to QPSK modulation

Code multiplexing combined with time multiplexing

New Channels in DL and UL

Use of hybrid automatic-repeat-request (HARQ)

MAC-hs functionality in Node-B

Agenda

Introduction

General Principal



-> Link Adaptation


HARQ Principle

Cell Change order

Link adaptation: Modulation

QPSK

2 bits / symbol =480 kbit/s/HS-PDSCH =

max. 7.2 Mbit/s

16QAM

4 bits / symbol =960 kbps/HS-PDSCH =

max. 14.4 Mbit/s

1011 1001

10001010

0001 0011

00100000

0100 0110

01110101

1110 1100

11011111

Q

I

10 00

0111

Q

I

Fast Link Adaptation in HSDPA

0 2 0 4 0 6 0 8 0 1 00 1 20 1 40 1 60- 202468

10121416

Time [number of TTIs]

QPSK1/4

QPSK2/4

QPSK3/4

16QAM 2/4

16QAM 3/4

Inst

anta

neou

s Es

No

[dB]

C/I received by UE

Link adaptation

mode

C/I varies with fading

BTS adjusts link adaptation mode with a few ms delay based on channel quality

reports from the UE

Agenda

Introduction

General Principal



Link Adaptation

-> HSDPA Channel Structure

HARQ Principle


Packet Scheduling

HSDPA Mobility

HS-SCCH

HS-PDSCH

HS-DPCCH

Associated DPCH DL: 1 DPDCH & 1 DPCCH

HS-SCCH: High speed shared control channel. It indicates the recipient UE Id, modulation, number of codes, relevant HARQ info. 1 HS-SCCH per cell in case of no code multiplexing.

HS-PDSCH: High speed physical downlink shared channel. Carries a variable amount of user data, for a single user in case of no code multiplexing.

HS-DPCCH: High speed dedicated physical control channel. Used by the UE to send ACK / NACK and CQI (Channel Quality Indicator)

Associated DPCH UL: DCH channel used to send UL user data, e.g. RLC and TCP ACKs, HTTP requests etc.

Associated DPCH DL: DCH channel used to transmit power control information for the UL associated DCH and other potentially needed signalling (e.g. bearer reconfgurations etc.)

Node-BUE

1

5

3

2

1

5

3

2

per cell

per user 4

4

Associated DPCH UL: 1 DPDCH & 1 DPCCH

New Channels on Air-Interface introduced for HSDPA

HSDPA Channels – Transport Channel

HS-DSCH

WCDMA System normally operates on DCH which brings maximum system

performance with continuous data.

HSDPA introduces new transport channel, HS-DSCH, which makes efficient use of radio resources and takes into account bursty packet data

HS-DSCH shares multiple codes among several users

Time Multiplexing in HSDPA

HSDPA Physical Channels (1/4)

HSDPA channels – Physical Channel (2/4)

HS-PDSCH (High Speed DL Shared Channel)

• Carries the user data in the DL.

• Higher modulation scheme (16QAM), lower encoding redundancy leading to high peak data rates.

• TTI (Transmission Time Interval), interleaving period = 2 ms (In R’99, TTI = 10/20/40/80 ms).

• Fixed SF (16), support multi-code transmission, as well as multiplexing of different users (15 – maximum capability, depends on the UE category: 5/10/15).

• Users check the information on the HS-SCCH to determine which HS-DSCH codes to despread.

• HS-PDSCH has always DL DPCH associated (signal radio bearer for layer 3 signaling, power control command for UL HS-DPCCH, etc.)

HSDPA Channels- physical channels (3/4)

HS-SCCH (High Speed Shared Control Channel)

• Carries the information needed for HS-DSCH demodulation

• If there is no data on HS-DSCH, HS-SCCH is not assigned.

• The HS-SCCH uses SF 128, accomodating 40 bits per slot.

• Each HS-SCCH block has a three–slot duration divided into 2 functional parts:

– First part (first slot) carries the time-crucial information needed to start the demudaltion process in due time: HS-DSCH codes, indication if QPSK or 16QAM modulation is used on HS-DSCH.

– Second part (next two slots) contains CRC (cyclic redundancy check) for checking HS-SCCH, ARQ process number, redundancy version.

HSDPA Channels - physical channels (4/4)

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

• Carries ACK/NACK information for the L1 retransmissions.

• Carries CQI (DL Channel Quality Indicator) to be used by NodeB scheduler to determine to which terminal to transmit and at which rate.

• Intensively discussed in the 3GPP forum, feedback method is not easy to be standardized due to differences in the terminals.

CQI Reporting from UECQI TBS codes M (dB)1 137 1 QPSK 02 173 1 QPSK 03 233 1 QPSK 04 317 1 QPSK 05 377 1 QPSK 06 461 1 QPSK 07 650 2 QPSK 08 792 2 QPSK 09 931 2 QPSK 010 1262 3 QPSK 011 1483 3 QPSK 012 1742 3 QPSK 013 2279 4 QPSK 014 2583 4 QPSK 015 3319 5 QPSK 016 3565 5 16QAM 017 4189 5 16QAM 018 4664 5 16QAM 019 5287 5 16QAM 020 5887 5 16QAM 021 6554 5 16QAM 022 7168 5 16QAM 023 7168 5 16QAM -124 7168 5 16QAM -225 7168 5 16QAM -326 7168 5 16QAM -427 7168 5 16QAM -528 7168 5 16QAM -629 7168 5 16QAM -730 7168 5 16QAM -8

UE should report the CQI for which the BLER probability would not exceed 10% on HS-DSCH in measured condition (PCPICH +

Algorithm to calculate CQI value is not specified by 3GPP.

CQI reporting can have UE specific differences.

TS25.214 says :

“Based on an unrestricted observation interval, the UE shall report the highest tabulated CQI value for which a single HS-DSCH sub-frame formatted with the transport block size, number of HS-PDSCH codes and modulation corresponding to the reported or lower CQI value could be received in a 3-slot reference period ending 1 slot before the start of the first slot in which the reported CQI value is transmitted and for which the transport block error probability would not exceed 0.1. “

Agenda

Introduction

General Principal



Link Adaptation


-> HARQ Principle


Packet Scheduling

HSDPA Mobility

Stop and Wait Protocol (SAW)

Transmission of new blocks is stopped until and ACK/NACK is received

• Minimal protocol overhead (no sequence numbers needed)

• Reduced storage requirements at UE

• Problem: Channel is unused until ACK/NACK is received

N Channel Hybrid ARQ (HARQ)

H-ARQ principles (1)Fast H-ARQ algorithm rapidly requests the retransmission of missing data entities.

Retransmitted data entities are soft combined with the original transmission before message decoding.

Since, the H-ARQ mechanism resides in the NodeB (MAC-hs), requests can be done immediatly.

This way, probability of successful combining is increased.

If all data is correctly decoded, the ACK message is sent on the associated UL channel (HS-DPCCH).

H-ARQ requires some memory in the UE to buffer the soft information.

Two strategies of H-ARQ:• IR (incremental redundancy)

• CC (chase combining)

H-ARQ principles (2)

The idea of the CC is to transmit the same packet again

• Receiver combines these two copies prior to decding

The idea of the IR is to transmit additional redundant information that is incrementally transmitted if the decoding fails on the first attempt.

• Causes increase of the effective coding gain with the number of retransmissions.

• Full IR (inlcudes parity bits in every coded word) requires significant UE memory capabilities.

H-ARQ

HARQ is one of the most important features in HSDPA concept to enhance the packet data transmission capability of WCDMA system

It controls the packet retransmission on layer 1 level to reduce the retransmission delay

There is one HARQ entity per UE in UTRAN side

• Each HARQ entity consists of several HARQ processes (i.e. the so called SAW channels)

HS-DSCH Physical Layer Category

Number of HARQProcesses

NIR(in bits)

Category 1 2 9600

Category 2 2 14400

Category 3 3 9600

Category 4 3 12800

Category 5 6 9600

Category 6 6 11200

Category7 6 19200

Category8 6 22400

Category9 6 28800

Category10 6 28800

Category 11 3 4800

Category 12 6 4800

• A number of parallel HARQ processes are established at the same time to support the HARQ protocol

• The number of HARQ processes is determined by MAC-hs as shown in table on the right

• MAC-hs gets the HS-DSCH Physical Layer Category information in the NBAP: RADIO LINK SETUP REQUEST message or the NBAP: RADIO LINK RECONFIGURATION PREPARE message

Agenda

Introduction

General Principal



Link Adaptation


HARQ Principle

-> HSDPA – Operating Principle

Packet Scheduling

HSDPA Mobility

HSDPA Operating Prinicple

HSDPA Peak Bit Rates

Coding rateCoding rate

QPSKQPSK

Coding rateCoding rate

1/41/4

2/42/4

3/43/4

5 codes5 codes 10 codes10 codes 15 codes15 codes

600 kbps600 kbps 1.2 Mbps1.2 Mbps 1.8 Mbps1.8 Mbps

1.2 Mbps1.2 Mbps 2.4 Mbps2.4 Mbps 3.6 Mbps3.6 Mbps


16QAM16QAM

2/42/4

3/43/4

4/44/4




RAN05

RAN05.1

UE categories

12 different UE categories

Possible receiver types Rake, Equalizer, 2-Equalizer

Theoretical peak bit rate up to 14 Mbps

1.8 Mbps and 3.6 Mbps capability expected initially

10

9

7/8

5/6

3/4

1/2

12

11

UE Category

-

-

-

3.6 Mbps

1.8 Mbps

1.2 Mbps

1.8 Mbps

0.9 Mbps

5 Codes

--36302QPSK only

--36301QPSK only

QPSK/16QAM

QPSK/16QAM

QPSK/16QAM

QPSK/16QAM

QPSK/16QAM

QPSK/16QAM

Modulation

14.0 Mbps

10.1 Mbps

-

-

-

-

15 Codes

-279521

-202511

7.2 Mbps144111

-72981

-72982

-72983

10 CodesTransportBlock sizeInter-TTI

(First one has smaller HARQ memory.)

Inter-TTI interval

Inter-TTI interval: Number of sub frames between transmissions to a UE

DTXData DTX DTXData

Inter-TTI = 3

DTXData Data DataDTX

Inter-TTI = 2

HSDPA Cell throughput

780 kbps

DCH: 410 kbps

1090 kbps

HSDPA: 670 kbps

DCH: 410 kbps

1320 kbps

HSDPA: 910 kbps

DCH: 780 kbps

HSDPA: N.A.

HSDPA 16QAMRR scheduling

HSDPA 16QAMPF scheduling

No HSDPA

43% Gain

21% Gain

Simulated cell throughput with mixed HSDPA and Rel.99 traffic.

5 codes assumed.

Pedestrian propagation channel.

Packet Scheduling in HSDPA

Reasons why UE sometimes cannot be scheduled:

• Some UEs do not support reception in consecutive TTIs.

• BTS cannot receive Ack/Nack because of poor uplink quality.

• All HARQ processes of UE are full and next transmission would be a new one.

1st TTI

2nd TTI

3rd TTI

Some Scheduler TypesProportional Fair Resource (P-FR)

• UE with best radio condition is chosen

• On short time-scale, different UEs get different resources.

• On medium time-scale, similar fairness to Round-Robin.

• Implemented in RAN05.1

Maximum Throughput (M-TP)

• The UE with the highest instant-aneous throughput is chosen.

• Average throughput and cell capacity maximised.

• Lots of UEs get zero throughput.

• Not “fair” among queues on short or even medium time-scale.

Round-Robin (RR) = Fair Resource (FR)

• UE in front of queue is scheduled, then moved to back of queue.

• Each UE gets same amount of resources. The throughput depends on its link conditions.

• Simple.

• Used in RAS05

Fair Throughput (FT)

• Each UE gets same throughput.

• UE in bad conditions has to be given more resources.

• Cell capacity is bad.

UE2



Data

Data

UE1

WBTS scheduling operates at 2ms rate and can utilize information on the instantanous channel conditions for each user

WBTS scheduling operates at 2ms rate and can utilize information on the instantanous channel conditions for each user

Multi-user selection diversity(give shared channel to “best” user)

TTI 1 TTI 2 TTI 3 TTI 4

USER 1 Es/N 0USER 2 Es/N 0

Scheduled user

Proportional Fair Idea (RAS05.1)

Agenda

Introduction

General Principal



Link Adaptation


HARQ Principle


Packet Scheduling

-> HSDPA Mobility

HSDPA mobility in RAS05

• Serving Cell Change switches the user from HS-DSCH to Cell_FACH then back to HS-DSCH

HS-DSCH coverage HS-DSCH coverage

Service in

HSDPA

Switching to Cell_FACH within the SHO area

UE on HS-DSCH

Cell A Cell B

HSDPA

DCH

0

Throughput

64kbps

128kbps or 384kbps according to parameter settings

Details on Cell Change via cell-FACH

•HSDPA Serving Cell Change via Cell-FACH feature is used only in intra frequency handover cases, in case of IFHO or ISHO the original DCH switching procedures are used

•If the user was moved to Cell-FACH because of intra frequency handover no HSDPA user penalty timers are used on Cell-FACH, the user will be immediately switched to a new HSDPA connection when there is a data volume request either from the UE or RNC

•If the user was moved to Cell-FACH because of low throughput then the HSDPA user penalty timers are used on Cell-FACH

•If the HSDPA user moves to non-HSDPA cell, the user in HO area will be moved to Cell-FACH. The user will be immediately switched to the DCH of the requested bit rate when there is a data volume request either from the UE or RNC (no need for first DCH0/0 DCH Initial bit rate DCH Final bit rate)

In RAS05, UE goes to cell_FACH in the current serving cell. Possible cell reselection to best server happens in cell_FACH.

Improved HS-DSCH to cell_FACH switching

Target cell (cell with best CPICH Ec/No in the measurement set) informed in the RB reconfiguration message, when UE is commanded to cell_FACH

There is no need for cell reselection in cell_FACH, as the UE goes directly to strongest cell in cell_FACH.

Scrambling code of the strongest cell in the measured set informed

to UE.

Establishment of HSDPA Call

AAL2SIG:ECF

AAL2SIG:ERQ

Radio Link Reconfigure Ready

UE RNC SGSNNode B

NBAP: Radio Link Reconfigure Prepare

PDP Established

Measurement Report: e4a

FP: Downlink Sync

FP: Uplink Sync

Radio Link Reconfiguration Commit

RRC: Radio Bearer Reconfiguration (DCH)

RRC: Radio Bearer Reconfiguration Complete (DCH)

Measurement Control

AAL2SIG:ECF

AAL2SIG:ERQ

FP: Downlink Sync

FP: Uplink Sync

HSDPA Traffic

HS-DSCH: Capacity Request

HS-DSCH: Capacity Allocation

1. Intra Node-B serving HS-DSCH cell change

2. Inter Node-B serving HS-DSCH cell change

3. HS-DSCH to DCH switch (needed if the UE is moving to a cell without HSDPA support)

RAS05.1 provides full intra-frequency mobility for HSDPA users and enables HSDPA also in SHO

region

HSDPA capable cellHSDPA not supported

12

3

HSDPA Handover UL/DL DCH = soft/softer HO ; DL HS-DSCH = serving cell change

Mobility in RAS05.1

Agenda

Introduction

General Principal



Link Adaptation


HARQ Principle


Packet Scheduling

HSDPA Mobility

-> Measurement Results

32-B Ping Measurements Average Round Trip Time 78 ms

Reply from 10.20.143.10: bytes=32 time=83ms TTL=126












…















Round trip time

0

10

20

30

40

50

60

70

80

90

100

1

Samples

[ms]

Round trip time 71-84

ms

Multiuser Capacity Sharing Works

0

200

400

600

800

1000

1200

1400

1600

1800

1 2 3 4 16

Number of users

kb

ps

Total cell throughputUser throughput

Throughput per user decreases when more

users download data (as expected)

Total cell throughput remains constant

regardless of the number of simultaneous users

0

200

400

600

800

1000

1200

1400

1600

1800

-110-108-106-104-102-100-98-96-94

RSCP [dBm]

kbp

s

Simulated flat fading UE noise -101 dBmMeasured OptionSimulated flat fading UE noise -99 dBmMeasured Novatel

Throughput in Low Signal Power in the Field

700-900 kbps at RSCP = –108 dBm

level

6 W HSDPA power assumed

8.HSDPAOverview

Documents

Transcript of 8.HSDPAOverview