hsdpa principles

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Principles of HSDPA

HUAWEI TECHNOLOGIES CO., LTD. HUAWEI Confidential

Objectives

Similarities and Differences Between HSDPA and GPRS

Basic Concepts and Features of HSDPA

Key Technologies of HSDPA

Physical Channels of HSDPA

Data Transmission and Flow Control of HSDPA

In this course, you will learn:


Contents

Chapter 1 HSDPA vs GPRS

Chapter 2 Basic Concepts and Features of HSDPA

Chapter 3 Key Technologies of HSDPA

Chapter 4 Physical Channels of HSDPA

Chapter 5 Data Transmission and Flow Control of HSDPA


HSDPA vs GPRS&EGPRS

Multiple access technology: TDMA+CDMA

Multiple access technology: FDMA+TDMA

AMC: Adaptive modulation and coding

MCS1 to MCS9 ， CS1 to CS4 coding

Modulation:

16QAM, QPSK

Modulation:

GMSK, 8PSK

Physical channel:

HS-DSCHPhysical channel:

PDTCH

Scheduling: Channel condition, delay, fairness

Scheduling:

User priority

HSDPA GPRS&EGPRS


Contents







HSDPA Basic Concepts

HSDPA = High Speed Downlink Packet Access

An Important Feature of the 3GPP R5


HSDPA Features

HSDPA is a WCDMA solution offering higher speed downlink data services.

Peak data rate in DL: 14.4 Mbit/s

Shorter delay

Higher downlink code and power efficiency and larger downlink capacity

Flexible cell resource allocation

More high speed user access


Contents







Overview of HSDPA Key Technologies

AMC Fast SchedulingHARQ (Hybrid ARQ)

16QAMSF16, 2ms and CDM/TDM 3 New Physical Channels


HSDPA Key Technologies

Fast scheduling (2 ms subframe and scheduling)

AMC (supporting QPSK and 16QAM)

HARQ


Fast Scheduling Basic

If a little part of the 10 ms frame (15 timeslots) cannot be decoded properly, the whole frame is retransmitted 10 ms later.

If a 2 ms subframe (3 timeslots) cannot be decoded properly, only this 2 ms subframe is retransmitted. The HARQ process of other 2 ms subframes (a maximum of 6) can continue transmitting data. This greatly improves the resource usage on the air interface.


Fast Scheduling

Scheduler can be based on

CDM, TDM

Channel condition

Amount of data in the queue (delay)

Fairness

Cell throughput

Scheduling principle:

• Based on channel conditions in short terms;

• Based on the throughput and fairness for users in long terms.

Basic schedulers

Round Robin (RR)

Max-C/I

Proportional Fair (PF)

All codes to whichHSDPA transmissionis mapped(5 in this example)

Data to UE #1 Data to UE #2 Data to UE #3 CodeCode

Time

Fast scheduling enables effective allocation of available cell and code resources and improves the cell throughput.


Share and Scheduling of the Shared Channel

Scheduling with four users

CDM+TDM

All codes reserved for HSDPA transmission 2m

s


• Users to transmit data

• Power• Channel code• Data attributes

Fast Scheduling Process

（ Scheduling Algorithm ）

Available resources

Required resources

Middle statistics

Input of the scheduling algorithm:1. Available resources, including power and channel code resources2. Required resources, including users, data, retransmission, capability evaluation of the air interface, channel power, uplink and downlink compression gap of the channel, and discard timer.3. Middle statistics of the scheduling algorithm, such as the waiting time and average C/I.Output of the scheduling algorithm:User to transmit data, power, channel code, data attributes (including queue ID, Xrv, invalid data packet discarded)


Max C/I Scheduling Algorithm

Features:1. The max C/I scheduling algorithm allocates resources to the user with the max C/I in one TTI.

2. This scheme provides the maximum cell throughput, because the users provided with services are in best channel conditions.

3. The scheme, however, fails to guarantee fairness for users. In fact, users on the cell edge receive large penalty and great impact because of too much service delay and signal quality deterioration.


RR Scheduling Algorithm

Features:

1) The RR scheduling algorithm adopts the "First in First Allocated" principle for users.2) The users have high fairness at the cost of high system overhead and high expense of system throughput (spectral efficiency ).


PF Scheduling AlgorithmOld algorithm (V1.5)The PF is expressed as follows:Pi = a*f1 + b*f2 + c*f3 + d*f4f1: level of data streamf2: CQIf3: Waiting timef4:Queue lengtha/b/c/d: weight factor, which be flexibly configured. The default values are a=0.3; b=0.4; c=0.2; d=0.1 Exceptional cases:b=1, a=c=d=0, MaxC/I

C=1, a=b=d=0 ， RR Features:1) This scheme provides a balanced algorithm, of which the fairness and resource allocation efficiency are between the RR and Max C/I algorithms.2) The probability of serving all users is equal, although users may experience different average channel qualities.

3) The balance between the system throughput and the fairness is guaranteed.

New algorithm (V1.6)

Priority is based on the R/r

R: UE request rate (TB Size / 2ms, calculated based on the CQI)

r: amount of effective data (retransmitted data excluded) transmitted by the transport layer before this UE (in 1.6s)



Fast Scheduling (2 ms subframe and scheduling)

AMC (Supporting QPSK and 16QAM) HARQ


Adaptive Modulation and Coding (AMC)

AMC, based on channel quality feedbackAdjust data rate to compensate the channel condition.

− Good channel condition: higher data rate

− Poor channel condition: lower data rateAdjust code rate to compensate the channel condition.

− Poor channel condition: 1/3 coding

− Good channel condition: 3/4 codingAdjust modulation scheme to compensate the channel condition.

− Good channel condition: 16QAM

− Poor channel condition: QPSK

Channel Quality Feedback (CQI)The UE measures the channel quality (SNR) and reports the results to the NodeB every 2 ms or longer.The NodeB chooses the modulation scheme, transport block size, and data rate based on the CQI.

Throughput - SIR relationship

AMC improves radio bandwidth at the air interface and applies to high-speed radio transmission.


Modulation HSDPA Modulation

QPSK

16QAM


CQI Mapping Table (Category 10)CQI value Transport Block Size Number of

HS-PDSCHModulation Reference power adjustment NIR XRV

0 N/A Out of range

1 137 1 QPSK 0 28800 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

AMC scheme recommended by the protocolAdopt corresponding TB size, modulation mode, and TX power based on the CQI


Link Emulation - AMCAMC (AMC (Adaptive modulation and channel codingAdaptive modulation and channel coding) ) PerformancePerformance

The AMC modifies the TX parameters based on the instantaneous channel condition and optimizes the data rate.The AMC performance is affected by channel quality strategy error and feedback delay in channel fading.For low data rate, the AMC has better performance than the fixed MCS.For high data rate, the AMC has worse performance than the fixed MCS

AMC gai n

0

100

200

300

400

500

600

- 12 - 11 - 10 - 9 - 8 - 7 - 6 - 5 - 4 - 3HS- DSCH Ec/ N0(dB)

Thro

ughp

ut(k

bps)

TU5(Fi xed MCS) TU5(AMC)TU30(Fi xed MCS) TU30(AMC)TU120(Fi xed MCS) TU120(AMC)


AMC Process

The UE measures the RX channel.

The UE provides the CQI.

The NodeB filters and corrects the reported CQI to obtain the actual CQI (Channel Quality Indicator).

Configure the number of channels, TX power, modulation mode based on the CQI, amount of data to be transmitted, and available power and code resources.



Fast Scheduling (2 ms short frame and scheduling)

AMC (supporting QPSK and 16 QAM)

HARQ


Hybrid Automatic Repeat Request (HARQ)

Traditional ARQ

– Decode received transport blocks

– Check for the CRC errors in the decoded transport blocks

– Errors exist

• Discard the block with errors

• Request retransmission

Hybrid ARQ

– Decode received transport blocks

– Check for the CRC errors in the decoded transport blocks

– Errors exist

• Store instead of discard the block with errors

• Request retransmission

• Combine the newly received retransmission block with the previous blocks

Combined processing

Increment redundancy

HARQ helps reduce retransmission time and increase cell throughput.


HARQ Concept HSDPA is a technique where the transmitter sends the new set of parity bits if the

previous transmission fails (NACK) and receiver buffers the failed decodes for soft combing with future retransmissions.

The RV parameter indicates different code bits transmit in IR buffer. Different RV parameter configurations support:

Chase Combining (CC) (retransmission of the same coded data)

PIR （ Partial Incremental Redundancy (PIR) (systematic bits transmission first)

Full Incremental Redundancy (FIR) ( parity bits transmission first)

Use different r parameters and set of puncture bits for different retransmission. This ensures average coded bits transmission.


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

The IR scheme, which preferentially transmits parity bits, has average effective codes bits after retransmission. The HARQ gain is prominent especially in high coded rate.


Link Emulation - HARQHARQ Performance

HARQ reduces the impact HARQ reduces the impact by channel measurement by channel measurement errors and feedback delay errors and feedback delay and provides the AMC and provides the AMC performance gain.performance gain.

Higher Speed, higher Higher Speed, higher HARQ gainHARQ gain

HARQ Gai n 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. 5HS-DSCH Ec/ N0(dB)

Thro

ughp

ut(k

bps)

TU5(AMC+HARQ) TU5(AMC)TU30(AMC+HARQ) TU30(AMC)TU120(AMC+HARQ) TU120(AMC)


Link Emulation – CC and IR

The HARQ-based IR provides the performance gain.The HARQ-based IR provides the performance gain.

Static Channel

0.1

1

Ec/Ior

BLER

First Transmission CC Full IR Partial IR

PA3

0. 1

1

Ec/ I or

BLER

Fi rst Transmi ssi on CC Ful l I R Parti al I R


Contents







HSDPA Related Physical Channel

New HSDPA Physical Channels

Each HS-PDSCH: SF=16

Each HS-SCCH: SF=128

Each UE is assigned up to 4 HS-SCCHs (limited to UE capability)

Each HS-DPCCH:SF=256

Each H user is assigned 1 HS-DPCCH


HSDPA Physical Channel Mapping Transport Channels

DCH

RACH

CPCH

BCH

FACH

PCH

Physical Channels

Dedicated Physical Data Channel (DPDCH)

Dedicated Physical Control Channel (DPCCH)

Physical Random Access Channel (PRACH)

Physical Common Packet Channel (PCPCH)

Common Pilot Channel (CPICH)

Primary Common Control Physical Channel (P - CCPCH)

Secondary Common Control Physical Channel (S - CCPCH)

Synchronisation Channel (SCH)

Acquisition Indicat or Channel (AICH)

Access Preamble Acqu isition Indicator Channel (AP - AICH)

Paging Indicat or Channel (PICH)

CPCH Status Indicator Channel (CSICH)

Collision - Detection /Channel - Assig nment Indicator

Channel (CD /CA - ICH )

DSCH Physical Downlink Shared Channel (PDSCH)

HS-DSCH-related Shared Control Channel (HS-SCCH)

HS-DSCH High Speed Physical Downlink Shared Channel (HS-PDSCH)

Dedicated Physical Control Channel (uplink) for HS-DSCH (HS-DPCCH)


Associated Channel DPCH

Besides the 3 physical channels, there is anther dedicated channel DPCH, which is called associated channel in the HSDPA. The DPCH is used for signaling transmission and power control.

The DPCH normally does not carry services, but it can carry real-time services such as the AMR (multiple RABs: CS+PS)


HSDPA Physical Channel

HS-SCCH and HS-PDSCH are both downlink shared channels

shared by all user. How can users know when and on which

channel the user’s data is transmitted?

HS-SCCH is like a soldier holding the flag at the first row of the queue. The UE continuously

monitors the HS-PDSCH subframes addressed to it on the sets of the HS-PDSCHs. Upon receiving an HS-PDSCH frame for the UE, the UE physical

layer demodulates the subframe. Otherwise, no response is performed.


Physical Channel Slot Format (1): HS-SCCH

Features of the HS-SCCH slot format:3 slots (2 ms) constitute one TTI.HS-SCCH SF=128 ， QPSK only.HS-SCCH maps the seven data attributes of the user: Xue, Xccs, Xms, Xrv, Xtbs, Xhap, and Xnd ；For TT data, the UE demodulates HS-SCCH subframe and finds out the received data addressed to the UE with Xue. Then, the UE demodulates the HS-PDSCH subframe with Xccs, Xms, Xrv, and Xtbs. Xhp and Xnd are used for HARQ processing.A UE monitors a maximum of 4 HS-SCCHs.

Slot #0 Slot#1 Slot #2

T slot = 2560 chips, 40 bits

Data N data 1 bits

1 HS - SCCH subframe: T f = 2 ms


Physical Channel Slot Format (2): HS-PDSCH

Slot #0 Slot#1 Slot #2

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

Data N data 1 bits

1 subframe: T f = 2 ms

Features of the HS-PDSCH slot format 3 slots (2 ms) constitute one TTI.

Fixed SF: 16

Modulation scheme: QPSK and 16QAM

All HS-PDSCH are used to carry data.

A UE may be assigned multiple channel codes to support multi-code transport, depending on the HS-DSCH UE category.

Subframe and slot format of the HS-PDSCH


Physical Channel Slot Format (3): HS-DPCCHFeatures of the uplink HS-DPCCCH

2 ms TTI (3 slots), SF=256, rate: 15 kbit/s, bearing 2 types of HSDPA uplink physical layer signaling, including the ACK/NACK and CQIACK and NACK notify the NodeB of the UE has received correct downlink data. Definition of the field: 1-Nack, 0-AckCQI is a metric that reflects the physical channel quality indicator based on the CPICH, and is reported periodically. The period ranges from 0 to 160 ms. 0 means no transmission. Normally the period is 2 ms (every TTI).ACK/NACK and CQI have different functions and therefore can be controlled independently by different parameters.ACK/NACK/CQI can be configured with the number of repeat transmission (max: 4) to improve the TSTD gain.

Subframe #0 Subframe # i Subframe #4

HARQ-ACK CQI

One radio frame T f = 10 ms

One HS-DPCCH subframe (2 ms)

2 T slot = 5120 chips T slot = 2560 chips


UE Category (For Reference)HS-DSCH category

Maximum number of HS-DSCH

codes received

Minimum inter-TTI interval

Maximum number of bits of an HS-DSCH transport block received within

an HS-DSCH TTI

NOTE 1

Total number of soft channel bits

Supported modula-tions without MIMO

operationor dual cell operation

Supported modula-tions

with MIMO operation and without dual

cell operation

Supported modula-tions with dual cell

operation

Supported modula-tions with simulta-

neous dual cell and MIMO operation

Category 1 5 3 7298 19200

QPSK, 16QAMNot applicable

(MIMO not supported)

Not applicable (dual cell

operation not supported)

Not applicable (simultaneous dual cell and

MIMO operation not supported)

Category 2 5 3 7298 28800Category 3 5 2 7298 28800Category 4 5 2 7298 38400Category 5 5 1 7298 57600Category 6 5 1 7298 67200Category 7 10 1 14411 115200Category 8 10 1 14411 134400Category 9 15 1 20251 172800Category 10 15 1 27952 172800Category 11 5 2 3630 14400 QPSKCategory 12 5 1 3630 28800Category 13 15 1 35280 259200 QPSK, 16QAM,

64QAMCategory 14 15 1 42192 259200

Category 15 15 1 23370 345600 QPSK, 16QAMCategory 16 15 1 27952 345600

Category 17 NOTE 2 15 1

35280 259200 QPSK, 16QAM, 64QAM –

23370 345600 – QPSK, 16QAM

Category 18 NOTE 3 15 1

42192 259200 QPSK, 16QAM, 64QAM –

27952 345600 – QPSK, 16QAMCategory 19 15 1 35280 518400 QPSK, 16QAM, 64QAMCategory 20 15 1 42192 518400Category 21 15 1 23370 345600

- -QPSK, 16QAMCategory 22 15 1 27952 345600

Category 23 15 1 35280 518400 QPSK, 16QAM, 64QAMCategory 24 15 1 42192 518400

Category 25 15 1 23370 691200 - - - QPSK, 16QAMCategory 26 15 1 27952 691200Category 27 15 1 35280 1036800

- - -QPSK, 16QAM, 64QAMCategory 28 15 1 42192 1036800


Transmit Power of the HSDPA Physical ChannelsPHSDPA (HSDPA total transmit power) ＝ PHS-PDSCH+PHS-SCCH

The HS-PDSCH transmit power can be adjusted by the NodeB according to the following factors:

CQIAmount of transmitted dataAvailable power allocated to the HS-PDSCHAvailable codes allocated to the HS-PDSCH

The transmit power of the HS-SCCH can use:Fixed power transmission (outdoor: 5%; indoor: 3%)A fixed power offset between the HS-SCCH and the DL associated channel. The transmit power of the HS-PDSCH is usually greater than that of the associated channel to ensure that the associated channel keeps a proper transmit power.

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

The slot bearing the HARQ-ACK/NACK and that bearing the CQI can have different power offsets.


HSDPA – Channel Mapping (1)

When RAB is mapped to the HS-DSCH, the DCH is required to be configured to transport UL RLC ACK information and possible UL data, regardless of whether there is UL data to be transported.

The figure in the next page describes the scenario of DL TRB carried on the HS-DSCH and SRB and UL services on the DCH. In soft handovers, there may be one or more DCHs, but there is only one HS-DSCH.


HSDPA – Channel Mapping (2)


Scheduling Working with HARQ

Priority

Queue1

Priority

Queue2

Priority

Queue3

Scheduler Determine the priority, and then allocate resources to the corresponding process in order.

If TB from UE1 is not received properly, the 1st frame of TB is retransmitted once UE1 is scheduled.

Priority

Queue3

Priority

Queue3


Contents







Concepts of HSDPA Flow Control

What is flow control? What are functions?

HSDPA users in different radio conditions may receive different air bandwidth. The function of flow control is to adjust relevant DL flow according to user’s air capacity.

For users, flow control ensures sufficient data in the NodeB buffer for transmission and prevents too much data in the NodeB buffer from discarding or retransmission.


HSDPA Flow Control Process

Periodical flow control Flow shaping at receiver

based on pre-allocation Single queue pre-allocation

based on queue flow rate

Flow control timer out

MAC-hs queue cycle starts

MAC-hs queue flow pre-allocation

MAC-hs queue flow pre-allocation Vin,pre

MAC-hs cycle ends

Flow shaping

MAC-hs queue flow allocation final result Vin, final

Send capacity allocation frame

End


Flow Control for a Single User


HSDPA Data Transmission and Flow Control

HSDPA flow control is implemented in the MAC-hs. The MAC-hs has four functional entities: flow control, scheduling/priority handling, HARQ, and TFRI.Flow control is used to control data flow from MAC-d or MAC-c/sh to satisfy air interface capability and reduce delay and congestion. Flow control of the data stream from MAC-d with individual priority is independent.

Position of flow control in the MAC-hs entity

Position of flow control in the MAC-hs entity

Flow control

Scheduling/Priority handling

Resource allocation &HARQ

TFRC

hsdpa principles

Documents

simultaneous

dual cell

good channel

hsdpa channel

hsdpa key

channel condition

transmit power

link emulation