1. HSDPA Version 3.0

Proprietary and Confidential

HSDPAHSDPAHigh Speed Downlink Packet High Speed Downlink Packet

AccessAccess

UMTS Training GroupVersion 3.0

Proprietary and Confidential Slide 2

IntroductionIntroduction

• HSDPA – High Speed Downlink Packet Access

• Part of release 5 3GPP specifications

• HSxPA can also be referred to as 3.5G as it is an adaptation of the 3G standards

• HSDPA increases air interface data rates from 384kbps to 14Mbps

• HSDPA is suited to high data rates and bursty applications


What’s New with HSDPAWhat’s New with HSDPA

• Fast Link Adaptation– Instead of using power control to compensate for varying radio environment, the

data rate can be adjusted every 2ms.

• Fast HARQ with soft combining– Instead of handling all retransmissions at the RNC, a new HARQ process is

introduced at the Node B to realize rapid retransmission of erroneous data

• Fast Channel Dependent Scheduling– Scheduler is implemented at the Node B as opposed to the RNC to allow for fast

scheduling to accommodate the user environment.


HSDPA Channels - NewHSDPA Channels - New

• HS-PDSCH – High Speed Physical Downlink Shared Channel

– Carries user data– 1 – 15 codes per channel– Always SF16– QPSK or 16QAM

• HS-SCCH – High Speed Shared Control Channel

– Informs the UE of how and when to receive the HS-PDSCH

– SF128

• HS-DPCCH – High Speed Dedicated Control Channel

– ACK/NACK– CQI report– SF256

UE

NodeB

Ass

oci

ate

d

DPC

H1-1

5 x

HS-

PD

SC

H

1-

4 x

HS-S

CC

H

HS

-DPC

CH


HSDPA Channels - ExistingHSDPA Channels - Existing

• A-DCH – Associated Dedicated Channel– One A-DCH is required per HSDPA user– Carries signaling and uplink data– Typically has a downlink rate of 0– Uplink rate can vary, minimum is 64kbps

up to 384kbps and peak HSDPA rates will require EUL

– Uplink data rate usually 5-6% of downlink rate (higher layer signaling).

UE

NodeB

Ass

oci

ate

d

DPC

H1-1

5 x

HS-

PD

SC

H

1-

4 x

HS-S

CC

H

HS

-DPC

CH


HSDPA Protocol StackHSDPA Protocol Stack


HARQ &Coding

Flow Control

New NodeB HSDPA FunctionalityNew NodeB HSDPA FunctionalityTerminalNode B

RNC

• Scheduler & Buffer: Buffering of data, Terminal scheduling, Coding & Modulation selection – QPSK is still used and a new modulation type 16QAM introduced

• HARQ, Retransmission Handling and coding

• Uplink Feedback Decoding

• Flow Control towards the SRNC

PacketsScheduler& Buffer

ACK/NACK &FeedbackDecoding


TerminalNode BRNC

Packets

Flow Control

New terminal functions:

• 16 QAM demodulation

• HARQ decoding and Retransmissions Handling

• Buffering & Soft combining

• Fast Uplink Feedback Generation & encoding

New Terminal HSDPA FunctionalityNew Terminal HSDPA Functionality

Soft buffer & combinin

g

ACK/NACK &

Feedbackgeneration

16QAM demodulatio

n

HARQdecodin

g


UE CategoriesUE Categories

• 12 Categories of UE have been specified

• UE category is sent in the UE Capability message transmitted to RNC during call setup

• RNC & Node B restrict data, number of codes or air interface coding schemes depending on the UE Capability

• Due to processor limitations in some implementations, processing of consecutive TTIs is not possible.


UE CategoriesUE Categories

10

9

7/8

5/6

3/4

1/2

12

11

HSDPACategory

-

-

-

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 size

(bits)Inter-TTI (MS)


ModulationModulation

QPSK

2 bits / symbol480 kbit/s/HS-PDSCH

max. 7.2 Mbit/s

10 00

0111

Q

I

Q

1011 1001

10001010

0001 0011

00100000

0100 0110

01110101

1110 1100

11011111

I

16QAM

4 bits / symbol 960 kbit/s/HS-

PDSCHmax. 14.4 Mbit/s


Downlink HSDPA Code AllocationsDownlink HSDPA Code Allocations

• SF16 codes assigned to HS-PDSCH, 5, 10 or 15 (3GPP)• SF128 assigned to the HS-SCCH (3GPP) (up to 4)• Maximum of 15 codes in Ericsson and Nokia• HS-PDSCH code resources are assigned to one user at a time

HS-PDSCH

SF=1

SF=2

SF=4

SF=8

SF=16

SF=32

SF=64

SF=128

SF=256

CPICH P-CCPCH

S-CCPCH

HS-SCCH

S-CCPCH

Free code that can be allocated to e.g. DPCH, HS-PDSCH (SF16) or HS-SCCH (SF128).

Code that cannot be allocated due to allocations lower in the code-tree / branch.

Code reserved for a common channel.

Legend:


Hybrid ARQ (HARQ)Hybrid ARQ (HARQ)

• ARQ = Automatic Repeat Request – uses error detection to determine if a PDU is received in error

• Hybrid ARQ uses forward error correction as well as error detection resulting in improved performance over ARQ.

• Employed between the UE and the Node B

• UE transmits ACK/NACK to indicate the successful / unsuccessful reception of a PDU.

• HARQ round trip time is longer (approx. 12ms) than a TTI period and as such multiple HARQ processes are used to prevent waiting for ACK/NACK before sending the next PDU

• Retransmissions are combined with original transmissions using soft combining (called chase combining) to improve error correction.


Hybrid ARQ and Soft CombiningHybrid ARQ and Soft Combining

NB. If more than 4 NACK are received for the same packet, the coding rate is changed to higher error correction or the buffer in Node B is flushed and re-filled from the RNC.


Link AdaptationLink Adaptation

• Transport Format Resource Combination (TFRC) changes on the air interface are adapted depending on a Channel Quality Indicator (CQI) sent from the UE.

• The Node B uses this reported CQI as a reference but fine tunes the actual TFRC assignment depending on the last series of ACKs or NACKs, UE capability, actual transmit power, amount of buffered data etc.

• CQI levels change depending on UE type. Attached is the CQI mapping for a CAT 8 UE.

• The TFRC can be modified in each TTI. -516-QAM101441130

-416-QAM101441129

-316-QAM101441128

-216-QAM101441127

-116-QAM101441126

016-QAM101441125

016-QAM81141824

016-QAM7971923

016-QAM5716822

016-QAM5655421

016-QAM5588720

016-QAM5528719

016-QAM5466418

016-QAM5418917

016-QAM5356516

0QPSK5331915

0QPSK4258314

0QPSK4227913

0QPSK3174212

0QPSK3148311

0QPSK3126210

0QPSK29319

0QPSK27928

0QPSK26507

0QPSK14616

0QPSK13775

0QPSK13174

0QPSK12333

0QPSK11732

019200

0QPSK11371

Out of rangeN/A0

XrvNIRReference power adjustment Modulation

Number of HS-PDSCH

Transport Block Size

CQI value

-516-QAM101441130

-416-QAM101441129

-316-QAM101441128

-216-QAM101441127

-116-QAM101441126

016-QAM101441125

016-QAM81141824

016-QAM7971923

016-QAM5716822

016-QAM5655421

016-QAM5588720

016-QAM5528719

016-QAM5466418

016-QAM5418917

016-QAM5356516

0QPSK5331915

0QPSK4258314

0QPSK4227913

0QPSK3174212

0QPSK3148311

0QPSK3126210

0QPSK29319

0QPSK27928

0QPSK26507

0QPSK14616

0QPSK13775

0QPSK13174

0QPSK12333

0QPSK11732

019200

0QPSK11371

Out of rangeN/A0

XrvNIRReference power adjustment Modulation

Number of HS-PDSCH

Transport Block Size

CQI value


Link AdaptationLink Adaptation


Power ControlPower Control

• Fast Link Adaptation provides a mechanism to adequately accommodate changes in the radio environment.

• Initially power control of the HS-PDSCH was not used, however vendors have now implemented various degrees of power control to reduce HSDPA impact to other services.

• Ericsson – HS-SCCH has power control– HS-DSCH has power control

• For Nokia– HS-SCCH has power control – HS-DSCH is set at minimum power but can absorb extra power if available to increase

throughput.

• Associated DCH is power controlled using fast power control.


SchedulersSchedulers• The scheduler schedules the information that will be sent from the

Node B to the UE.• The scheduler requires important information from the uplink HS-

DPCCH and other sources

Scheduler

QoS and Subscriber ProfileWho is the subscriber? Platinum, Gold,Silver, Normal.What type of service is the subscriber allowed? High priority, Besteffort

Uplink FeedbackCQI and Ack/Nackinformation

Node B buffer statusHow much data is in bufferHow fast is the data arriving

User HistoryHow long has userbeen waiting

Traffic ModelWhat type of traffic model shouldbe used - according to periodof the day – Peak/Off Peak

Available Radio ResourcesPowerCodes

UE Capability

Users are scheduled according to theirrequirements for transmission by theNode B over the air interface


• Simplest form of scheduler

• First in First out principle

• Advantages:

• Easy to implement

• Minimises waiting time

• Fair

• Disadvantage:

• System Throughput not optimal.

UE 1 Datasent

UE 2 Datasent

UE 1

UE 6

UE 5

UE 4

UE3

UE 2

UE 3 Datasent

UE 4 Datasent

UE 5 Datasent

UE 6 Datasent

UE 1 DataRequest

UE 2 DataRequest

UE 3 dataRequest

UE 4 Data Request

UE 5 DataRequest

UE 6 DataRequest

NodeB PacketScheduler

Round Robin SchedulerRound Robin Scheduler

NodeB Buffers


Max CQI (Best Effort)Max CQI (Best Effort)

UE 4 Datasent

UE 3 Datasent

UE 1 Datasent

UE 2 Datasent

UE 5 Datasent

UE 6 Datasent

UE 1CQI = 14

UE 2CQI = 8

UE 3CQI = 18

UE 4CQI = 20

UE 5CQI = 6

UE 6CQI = 4

UE 4

UE 6

UE 5

UE 2

UE1

UE 3

NodeB Packet Scheduler

Check which user

has requestedhighest

data rate.Prioritisedelivery

accordingly

• Highest CQI (greatest throughput) user schedule first.

• Users with best radio conditions are given preference

• Advantages:

• Easy to implement

• Highest system throughput

• Disadvantage:

• Due to bad CQI users may be starved of data

NodeB Buffers


Proportional Fair SchedulerProportional Fair Scheduler

• Schedules users based on– CQI – Average throughput – Retransmission (time between NACK reception and retransmission)– Delay (time since last scheduled)


Proportional Fair SchedulerProportional Fair Scheduler

• Provides improved system throughput over round robin by scheduling users when they are experiencing good radio conditions.

• Provides improved fairness over maximum CQI by considering average throughput and delay in the scheduling decision.

• The “fairness” of the algorithm can be adjusted using parameters.


HSDPA MobilityHSDPA Mobility

• There is no SHO for HSDPA

• This is due to – Location of the scheduler (Node B level)– Resource requirements on Iub / Channel Elements (CE)

• There are 3 methods for continuing data while HSDPA is in SHO area1. Suspend data till SHO area has expired

2. Radio Bearer reconfiguration to a DCH in SHO area, then re-attempt a HSDPA call setup when SHO area expires

3. SHO of the A-DCH and effectively do a cell reselection for the HS channel to the new best server (depends on vendor support)

• Ericsson Supports SHO of A-DCH in P5, Nokia Supports in RAS 5.1


SHO of Associated DCHSHO of Associated DCH• New HSDPA mobility parameters have been introduced to allow the

manipulation of the HSDPA handover separately from RT and R99 NRT services in both E/// and Nokia

• These parameters can be used to adjust the branch replacement window (Event 1d) for HSDPA sessions

• This allows the A-DCH to be manipulated using the standard R99 parameters (and hence allows the A-DCH to enter into SHO)

• The Branch Replacement for HSDPA can then be placed well into the neighbors cell to ensure a good CQI report when switched.


HSDPA Mobility - SHO for Associated DCHHSDPA Mobility - SHO for Associated DCH


HSDPA Priority or DCH PriorityHSDPA Priority or DCH Priority

• In some Vendor RAN it is possible to set the priority for either DCH or HSDPA traffic

• When the priority is set for either DCH or HSDPA and the RAN reaches an over load event for the following, then either DCH or HSDPA traffic is reduced or dropped to free capacity:

1. Iub Overload

2. Downlink Power

3. Downlink Orthogonal Codes

• The decision on priority depends largely on the penetration of devices in the market.


Performance of HSDPA compared to R99 Performance of HSDPA compared to R99 DCHDCH

• HSDPA offers multiple advantages over R99 DCH

– Improved Air interface efficiency

– Faster Download speeds for users

– Improved Latency

• HSDPA is a shared resource, and user data rates vary greatly according to the number of users in a cell


Air Interface Efficiency - codesAir Interface Efficiency - codes

• Users are time multiplexed onto the shared channels giving a more efficient use of code resource.


Air Interface Efficiency – inactivity Air Interface Efficiency – inactivity timerstimers

Idle

DCH

FACH

Data Transmission

t t tt

DCH holding timeAir interface, node B and Iub resources are reserved

even though there is no data transmission

FACH hold timeIub resources reserved

wastage


Air Interface Efficiency – fixed rate Air Interface Efficiency – fixed rate bearersbearers

• Only fixed rate DCH bearers are available

• Available bearers - 8,16,32,64,128,256,384 kbps

• Hence if the data to be transmitted is in between these bearers, the higher bearer rate is assigned and the bearer is not full utilized

Wasted Resource

SF32 Bearer (64kbps)

SF16 Bearer (128kbps)

User Data (75kbps)

User Data


HSDPA assignmentHSDPA assignment

• When HSDPA is enabled on a cell – DSP capacity is permanently assigned as a pool, this resource can not be used by other services.

• Only transmits when data is ready to transmit

• Power, code and transmission resource are temporarily reserved as required

• No Hold times in HSDPA state (FACH hold time is applied but no Iub reservation)

• HSDPA is a more efficient way of transporting bursty PS data than DCH ever could be.


Q & AQ & A

Documents

1. HSDPA Version 3.0