1

HSDPA

by

Devendra Sharma

2

Sequence of Presentation

• History / Motivation

• Introduction to New Features/ Transport Ch

• Feature Explanation

– AMC

– HARQ

– Scheduler

• Transport / Control Channel Explanation

– HS DPCCH

– HS SCCH

– HS DSCH

3

Sequence of Presentation

• Architectural Changes

- RAN Architecture

- MAC (hs, sh/c/m, d)

- UE

• Mobility in HSDPA

- Intra & Inter Node B HS DSCH Handover

- HS DSCH to DCH Handover

✓ Q&A

4

Motivation

• Sophisticated UE applications need higher bit rates

• Primary target of HSDPA is to enhance system throughput with minimum changes in network architecture

• Is an extension to WCDMA Release ’(”99”)

Release 5 - HSDPA (High Speed Downlink Packet Access)

5

Transition from Present UMTS system

• Current WCDMA network can be upgraded to support

HSDPA

• Does not change network architecture dramatically

• There can be HSDPA supported cells and regular cells

• If HSDPA is not accessible at UE location it will use

normal Release 99 (DCH) to communicate at regular

service speeds

6

HSDPA Research

• Motorola and Nokia supporting the start of work on HSDPA from the vendor side and BT/Cellnet, T-Mobile and NTT DoCoMo from the operator side

• Physical layer retransmissions, BTS-based scheduling and adaptive modulation and coding were studied.

• Investigations were done for multi-antenna transmission and reception technology, titled ‘multiple input multiple output’ (MIMO), as well as on fast cell selection

• Based on the above study the specifications were developed

7

HSDPA Introduction

• HSDPA was standardised as 3GPP release 5

• The HSDPA peak data rate available in the terminals is initially 1.8Mbps and will

increase to 3.6 and 7.2 Mbps during 2006 and 2007, and potentially beyond 10Mbps.

• HSDPA can share same CN element

8

Radio Capability Evolution

9

Transition from Present UMTS system

• Current WCDMA network can be upgraded to support

HSDPA

• Does not change network architecture dramatically

• There can be HSDPA supported cells and regular cells

• If HSDPA is not accessible at UE location it will use

normal Release 99 (DCH) to communicate at regular

service speeds

10

HSDPA Introduction

• Relase 99 provide data rates of 384Mbps to 2Mbps

• HSDPA

- Increase peak data rates upto 14Mbps

- Reduce the round trip delay

- Will increase the UTRAN network capacity

11

Radio resource management architecture

• Relase 99 RRM Architecture

12

Radio resource management architecture -

cont

• HSDPA/HSUPA RRM architecture

13

HSDPA Impact on UTRAN Interfaces

Presentation on HSDPA…Continues

14

HSDPA Impact on UTRAN Interfaces - ctd

• HSDPA flow control

15

HSDPA Impact on UTRAN Interfaces - ctd

• HSDPA added functionalities

16

HSDPA Impact on UTRAN Interfaces - ctd

• HSDPA protocol states

17

HSDPA Principles

Introduction/New Features

18

Release 99 DL Packet Capabilities

• Dedicated Channel( DCH )

• Downlink-shared Channel( DSCH )

• Forward Access Channel( FACH )

19

HSDPAWhat comes in? & What goes out?

• Two fundamental features of WCDMA are disabled:

– Variable SF

– Fast Power Control

• These two features are replaced by

– Adaptive Modulation and Coding (AMC)

– Fast retransmission strategy (HARQ)

– Scheduling Algorithm

20

New Channels Introduced

in HSDPA (R – 5)

• HS-DSCH (High Speed Down link Shared Channel)

TO support the HS-DSCH Operation

Two Control Channels are added

• HS-SCCH (High Speed Shared Control Channel)

DL channel

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

UL Channel

21

Comparison of

DSCH and HS_DSCH

Feature DCH HS-DSCH

Variable Spreading Factor No No

Fast Power Control Yes No

AMC No Yes, Extended

Multi Code Operation Yes Yes

Physical Layer Retransmission No Yes

BTS based Scheduling and Link

AdaptationNo Yes

22

Node B Protocol Stack In R99

E1

ATM

AAL2 AAL5

SSCOP

SSCF – UNI

STC.2 NBAP

ALCAP

FP

PHY

23

Node B Protocol Stack In R-5

E1

ATM

AAL2 AAL5

SSCOP

SSCF – UNI

STC.2 NBAP

ALCAP

FP

PHY

MAC - hs

24

UE Protocol Stack In R-5

CM

MM

RRC

RLC

MAC

PHY – UP

PHY

MAC - hs

25

Feature Explanation

Presentation on HSDPA…Continues

26

BTS Retransmission Handling

27

Adaptive Modulation & Coding

• Aimed at changing the modulation and coding format with variations in the

channel conditions

• Role: Continuously Optimisation of :

• Code Rate – 3/4 rate or 1/4 rate Turbo Code or Convolution Coding

• Modulation Scheme (16 QAM, QPSK)

→ (Based on CQI Feedback from UE) or transmission power of other DL

channels under power control

•Hence different Combinations of:

• Modulation

• Ch Code Rate

(Based on TFRC, Transport Format & Resource Combination)

Can provide different Peak Data Rates.

28

Adaptive Modulation & Coding

The main benefits are:

• Higher data rates for users in favourable condition, which in turn increases the average throughput of the cell,

• Since the transmit power is fixed (no fast power control) , the interference to other users is significantly reduced

(chip rate) (16QAM) (SF) (Codes) (Turbo) (Puncture)

3.84M chips/s * 4 bits/chip * 1/16 *15 * 1/3 * 3/1 = 14.4M bits/sec

This Rate in a real system Remains very unlikely as it would require an unloaded

system serving a single User extremely close to the Node B

29

HARQHARQ schemes combine the conventional ARQ with FEC

• Role

➢ It is the Re-Tx Mechanism selected for HSDPA

➢ Allows UE to Re-Tx rapidly of erroneous transport block until are

successfully Rx.

• Location

➢ HARQ is implemented at the MAC-hs (in Node B).

➢ Terminated at Node B as opposed to the SRNC (RLC) . Hence

Re-TX delays is much lower in HSDPA than in Rel 99.

➢ How?

✓ NACk may require less than 10msec at the MAC Layer.

✓ Approx.100msec is required at the RLC layer when Iub

signalling is involved.

30

HARQ

• Waiting Time Utility

➢ Multiple processes can run for the same UE using separate TTIs.

• HARQ Types

➢ Type I: Same PDU is retransmitted

➢ Type II: Incremental redundancy is employed

➢ Type III: Consistent redundancy (codes) is employed. Also called chase combining.

• The scheduler in UTRAN determines the redundancy version parameters for HARQ functional entities in NODE Bs

31

HARQ

HSDPA is the Combination of AMC and HARQ

• leads to an integrated, robust and high performance solution,

• AMC provides the coarse data rate selection,

• HARQ provides for fine data rate adjustment based on channel condition

32

Scheduler

• It’s the key element in HSDPA

• Scheduler base it’s decisions on

➢Channel quality as used by link adaptation,

➢current load of the cell,

➢traffic priority classes

• Scheduler for HSDPA is fast

➢ Compared to R99 scheduler is moved from RNC to Node B

• Fundamental task of scheduler is to schedule the transmission for users

• For each TTI, it determines which terminal or terminals HS-DSCH should be transmitted to and inconjunction with the AMC

33

SchedulerTypes

• Round Robin (RR):▪ Schedules USers to a 1st in 1st out approach,

▪ No of time slots allocated are inversely propotional to user data rates,

▪ Provides higher degree of fairness between users,

▪ But at an expense of overall Through-put of the system,

▪ No differentiation in the quality of services for different classes of users.

• Max carrier-to-interface(C/I):▪ Schedules Users with the highest C/I during current TTI.

▪ Naturally leads to a higher Through-put of the system, as users with best channels are served.

▪ Fairness is effected in this scheduler, specially users at cell edge will have service delays and significant Outage.

34

SchedulerTypes

– Proportioanl Fair (PF):

• Offers good trade between RR & Max C/I.

• Schedules Users according to the Ratio between their

Instantaneous achievable Data rate and their Average

Served Data rate.

• Results in all Users having equal probability of being served

even though they may experience very different average

Chanel quality.

• Good Balance between System Through-put & Fairness.

35

Transport / Control

Channel

36

HS-DSCH - Basics

• Lack of fast power control. Instead, link adaptation

selects the suitable combination of codes, coding

rates and modulation to be used.

• Support of higher order modulation than the DCH.

• User allocation with base station based

scheduling every 2ms, with fast physical layer

signalling

• Use of physical layer retransmissions and

retransmission combining.

37

HS-DSCH - Basics

• Lack of soft handover hence data are sent from one

serving HS-DSCH cell only.

• Lack of physical layer control information on the HS-

PDSCH.

• Multicode operation with a fixed spreading factor of 16.

• With HSDPA only turbo-coding is used.

• No discontinuous transmission (DTX) on the slot level. The

HS-PDSCH is either fully transmitted or not transmitted at all

during the 2-ms TTI.

38

HS-DSCH - Basics

•No discontinuous transmission (DTX) on the slot

level. The HS-PDSCH is either fully transmitted or

not transmitted at all during the 2-ms TTI.

39

HS-DSCH

• HS-DSCH consists of:

– With in each TTI = 2ms

– SF = 16 is made fixed

– Channelization (spreading) codes=15: Shared by active HSDPA terminals

in a cell

• Users can Share Resources, all users in a Particular sector as users

are allocated within different TTIs

• Transmission Time Interval (TTI) = 2ms as compared to 10ms in R99

• By reducing TTI reduces :

– The Round Trip delay &

– Improve Link Adaptation Rate/ efficient AMC

40

HS-DSCH – Coding Chain

41

HS-DSCH

• Turbo Coding is used for HS-DSCH

– With in each TTI = 2ms

– SF = 16 is made fixed

– Channelization (spreading) codes=15: Shared by

active HSDPA terminals in a cell

• 16 QAM is used by HS-DSCH

• Bit Scrambling on the physical layer for

HS_DSCH

42

• HSPDA codes allocated by CRNC• Example: 12 consecutive codes reserved for HS-DSCH, starting at C16,4

• Real-time allocation of these codes by NodeB scheduler• Transmit power set by scheduler, constant during one TTI

Channelisation codes at a fixed spreading factor of SF = 16

Up to 15 codes in parallel

SF=8

SF=16

SF=4

SF=2

Physical channels (codes) to which HS-PDSCH is mappedCPICH, etc.

C16,0C16,15

43

HS-DSCH

The Codes can all be assigned to One User in 2ms or Split across Several Users.

The assigning of Codes Depends of following Factors:

• Cell Load

• QoS requirement

• UE Code Capabilities

HSDPA permits sumultaneous transmissions i.e. two or four users can can be supported within the same TTI by using different subset of the channelization codes allocated to HS-DSCH

44

DL-DPCH & UL-DPCH

• The DL-DPCH carries HSDPA Indicatior (HI)

• HI indicates which HS-SCCH subset the terminal should monitor in order to obtain the signalling information

• The UL_DPCH carries power control signals for the DL-DPCH

• The UL-DPCH power control signal information and feedback information from HS-DPCCH can be used by the network to estmate the channel quality.

45

HS-SCCH

46

HS-SCCH

47

HS-SCCH

• Two slots offset compared to HS_DSCH

48

• The first part contains the following information:– Information needed to be availbale to enable de-spreading of correct codes.

– Modulation information

• Second part contains less urgent information such as – Which ARQ process is being tramsmitted

– An indication whether the transmission is new or related to an earlier transmitted packet is also included.

– Iformation on the redundancy version and the contellation.

– Transport block size

HS-SCCH

49

• The HS-SCCH coding and multiplexing chain

HS-SCCH

50

• The first part contains the following information:– UE – ID – 16 bits

– HARQ related Information – 3 bits

– Parameters of the HS-DSCH Transport Format Selection by the Link

Adaptation Mechanism – 6 bits

• UE can be assigned upto ”4” HS-SCCH out of 32 parallel HS-SCCH. Which needs monitoring continuously

• When HSDPA is operated using the time multiplexing principle, then only one HSSCCH can be configured. In this case only one user receives data at a time.

HS-SCCH

51

• In any given TTI:

– Max. of ”1” of HS-SCCH may address a particular UE

– UE detects msg addressed to him on a Specific HS-SCCH

– It may restrict its monitoring of HS-SCCH to only that one

HS-SCCH in next TTI.

• Contents per channel per TTI:–RNTI of selected UE (masked in)

–HS-PDSCH code(s) - up to 15

–Modulation (QPSK or 16QAM)

–TB size (TFRI) 137-27952 bits

–Hybrid-ARQ information (retransmission or new block)

–CRC

HS-SCCH

52

HS-DPCCH

HS-DPCCH Usage – ACK/NACK

There is one HS-DPPCH for each active terminal using HSDPA services

53

HS-DPCCH

HS-DPCCH Usage – CQI

54

HS-DPCCH

55

CQI

• Information is Based on (Cpich) Common Pilot Channel

• Is used to estimate the following:– Transport Block Size

– Modulation Type

– No. of Channelisation Codes (that can be supported at a given

reliability level)

• The feedback of CQI can be set as Network parameter in a

Predefined steps of 2ms

• When longer feedback cycles are used, the (PDCH) Power Control

Command can be used to update the channel quality estimation

• CQI (0-30) => UEs estimates highest value with probability of TB

error < 10% for the next transmission slot, and with various power

assumptions

56

Architectural Changes

57

HSDPA Architecture

58

Node B Protocol Stack In R99

E1

ATM

AAL2 AAL5

SSCOP

SSCF – UNI

STC.2 NBAP

ALCAP

FP

PHY

59

Node B Protocol Stack In R99

E1

ATM

AAL2 AAL5

SSCOP

SSCF – UNI

STC.2 NBAP

ALCAP

FP

PHY

MAC - hs

60

Radio Access Network Architecture

• All Release 4 transport channels

are terminated at the RNC

– Retransmission procedure is

located in serving RNC

• In Release 5 an additional

HSDPA MAC layer (MAC-HS) is

installed in the Node B

– Retransmissions will happen closer

to air interface - in the Node Bs

– Faster retransmissions

– Shorter delays with packet data

operation

• Flow control mechanism is

needed in Iub interface between

Node B and RNC to ensure

correct Node B data buffering (to

prevent data losses at Node B)

61

Radio Access Network Architecture

• RNC handles RLC (Radio Link Control)

functionalities

– If e.g. HS-DSCH TX from Node B fails for some

reason

62

MAC-hs (UTRAN side)• One MAC-hs entity in UTRAN for each cell

that support HS-DSCH transmission

• Scheduling/priority handling

– Manages HS-DSCH resources

between HARQ entities and data

flows according to their priority

– Determines either to send a new

transmission or a retransmission

based on uplink signalling

– Determines QueueID and TSN for

each new MAC-hs PDU

• HARQ

– One HARQ entity per user

– Multiple instances of stop and wait

HARQ protocols supported for each

HARQ entity

• TFRC selection

– Selection of appropriate transport

format and resource for the data

MAC-hs

MAC – Control

HS-DSCH

TFRC selection

Priority Queuedistribution

Associated DownlinkSignalling

Associated UplinkSignalling

MAC-d flows

HARQ entity

Priority Queuedistribution

PriorityQueue

PriorityQueue

PriorityQueue

PriorityQueue

Scheduling/Priority handling

To UE

From network

63

MAC-hs (UE side)

• HARQ

– Handles all the tasks that are required for hybrid ARQ

– Generates ACKs or NACKs

– Configurations of the H-ARQ protocol is provided by RRC over the MAC-Control SAP

• Re-ordering queue distribution

– Reorders incoming MAC-hs PDUs to ordering buffer based on queue ID

• Reordering

– Reorders received PDUs according to received transmission sequence number (TSN)

– Delivers complete objects to disassembly function

– PDUs are not delivered if PDUs with lower TSN are missing

• Disassembly

– Removes MAC-hs header and padding bits and passes the MAC-d PDU to higher layers

MAC-hs

MAC – Control

Associated Uplink Signalling

To MAC-d

Associated Downlink Signalling

HS-DSCH

HARQ

Reordering Reordering

Re-ordering queue distribution

Disassembly Disassembly

UE side MAC-hs details

From network

To UE

64

MAC - hs in Node B

MAC-hs

MAC – Control

HS-DSCH

Priority Queue distribution

MAC-d flows

Scheduling

Priority Queue

Priority Queue

Priority Queue

UE #1

UE #2

UE #N

MAC-hs Functions

• Priority handling

• Flow Control• To RNC

• To UE

• Scheduling

• HARQ handling

• (CQI) Service

measurements• e.g. HSDPA

provided bitrate

65

MAC - hs PDU

66

Node B conceptual per-UE data flow

Scheduler

Qual/Ack-Nak

DL

Queue

Xmit Info

Bearer Data

Bearer Data

Bearer Data

UE

Qual/Ack-Nak

RNC

(reported

user buffer

size)

(HS-DPCCH)

(HS-SCCH)

(HS-PDSCH)

Coding/

Modulation

67

Mobility in HSDPA

HSPA does not support soft handovers

68

Mobility in HSDPA

• No soft handovers in HS-DSCH

• HSDPA control channels are sent via only one of the radio links assigned to UE

(from serving HS-DSCH cell)

• UTRAN determines the serving HS-DSCH cell for an HSDPA capable UE

• Synchronized change of serving HS-DSCH cell is supported between UTRAN and

UE connectivity is achieved if UE moves from one cell to another

• Serving HS-DSCH cell change is triggered by UE measurement reports and

determined by UTRAN

• UTRAN (RNC) dictates the time moment when serving cell is changed

• This gives full mobility and coverage to exploit the advantages for HSDPA over

Release 4 channels

• Serving HS-DSCH cell can be changed:

– Without changing user’s active set for Release 4 dedicated channels

– In combination with establishment, release or reconfiguration of Release 4 dedicated

channels

• A new UE measurement event is needed to provide these properties

69

Mobility in HSDPA

• Three handover types

– Intra-Node B HS-DSCH to HS-DSCH

handover

– Inter-Node B HS-DSCH to HS-DSCH

handover

– HS-DSCH to DCH handover

70

Mobility in HSDPA

• All transmission from the source cell stops at that specified time and the packet scheduler in the target cell is then allowed to control transmission to UE

• MAC-hs preservation:

– Buffered data (for H-ARQ protocol: data waiting acknowledgement or new PDUs) in source cell is moved to target cell inside the Node B no data loss!

– H-ARQ manager will continue without breaks or retransmissions

– No higher layer retransmissions (e.g. from RLC protocol)

Intra-Node B HS-DSCH to HS-DSCH Handover

UE-L1

Node B-L1

SRNC-RRC

UE-RRC

measurement

Measurement report

Serving HS-DSCH cell change decision

Prepare reconfiguration

Reconfiguration ready

CUPHY-RL-commit-REQ

Physical channel reconfiguration

CUPHY-Modify-Req

Physical channel reconfiguration complete

71

Mobility in HSDPAIntra-Node B HS-DSCH to HS-DSCH Handover

Target node B

Source Node B SRNC

UE-RRC

measurementMeasurement report

Serving HS-DSCH cell change decision

Radio link setup

Radio link setup ready

CUPHY-RL-commit-REQ

transport channel reconfiguration

transport channel reconfiguration complete

Prepare reconfiguration

Reconfiguration ready

Radio link deletion req

Deletion complete

• At the time of cell change (usually 300-500ms from the RNC decision), the MAC-hs for the user in the source cell is reset (user data in buffers is deleted)

• The reset of the MAC-hs entity is indicated by the flag in transport channle reconfiguration.

• The RLC or Tx/Rx on HSDCH is be stopped at both the UTRAN and UE side prior to recinfiguration and continued when reconfiguration is complete

• If RLC is used in UM mode and if user application does not have retransmission mechanisms, some data is lost forever when a handover occurs

72

Mobility in HSDPA

• Needed when user moves from HSDPA capable cell to a cell that

does not support HSDPA

• Node Bs, target cell RNC and the user are informed about

incoming handover event

• Buffers in Node B are reset as in previous case and similar

retransmissions are required because of lost buffer data

HS-DSCH to DCH Handover

• Transmission continues in DCH

73

Beyond HSDPA and HSUPA

• 3GPP has started a feasibility study on the UMTS Terrestrial Radio Access Network

(UTRAN)long-term evolution (LTE).

•The work has been started with the following targets defined:

• Radio network user plane latency below 5 ms with 5-MHz or higher spectrum allocation.

With smaller spectrum allocation below, latency below 10 ms should be facilitated.

• Reduced control plane latency.

• Scalable bandwidth up to 20 MHz, with smaller bandwidths covering 1.25MHz, 2.5 MHz,

5 MHz, 10MHz and 15MHz for narrow allocations.

• Downlink peak data rates up to 100 Mbps.

• Uplink peak data rates up to 50Mbps.

• Two to three times the capacity of existing Release 6 reference scenarios with HSDPA or

HSUPA.

• Improved end user data rates at the cell edge.

• Support for the PS domain only.

74

Beyond HSDPA and HSUPA - contd

• 3GPP has started a feasibility study on the UMTS Terrestrial Radio Access Network

(UTRAN)long-term evolution (

•The work has been started with the following targets defined:

• Radio network user plane latency below 5 ms with 5-MHz or higher spectrum allocation.

With smaller spectrum allocation below, latency below 10 ms should be facilitated.

• Reduced control plane latency.

• Scalable bandwidth up to 20 MHz, with smaller bandwidths covering 1.25MHz, 2.5 MHz,

5 MHz, 10MHz and 15MHz for narrow allocations.

• Downlink peak data rates up to 100 Mbps.

• Uplink peak data rates up to 50Mbps.

• Two to three times the capacity of existing Release 6 reference scenarios with HSDPA or

HSUPA.

• Improved end user data rates at the cell edge.

• Support for the PS domain only.

75

Beyond HSDPA and HSUPA

• Further work for long-term evolution is based on pursuing single-carrier

frequency division multiple access (SC-FDMA)for the uplink transmission

and orthogonal frequency division multiplexing (OFDM)in the downlink

direction.

•To be added:

• To be added

76

Any Questions & Comments ?

?