HSDPA Basic Principles
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HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential
Security Level: Internal Use Only
www.huawei.com
HSDPA Basic Principle
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Learning Objectives
HSDPA basic principle and feature
HSDPA key technologies
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
HSDPA = High Speed Downlink Packet AccessImportant Features of 3GPP R5Why HSDPA?
The subscribers request higher speed and better quality data accessCompetition challenge from CDMA EV/DO, WiMAXUp to now, the throughput request for downlink is much more higher than that of uplinkThe channel configuration of R99 lead a very low efficiency on the downlink capacity
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HSDPA CharacteristicsHSDPA is the solution of WCDMA offering higher
speed downlink data services.Peak data rate in DL: 14.4Mbps (physical layer)Shorter delayHigher efficiency using downlink code and power and bigger downlink capacityFlexible cell resource allocationMore high speed user access
UMTS R99
GSM
HSDPA
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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- OverviewHSDPA Key Techniques- Overview
AMC Fast SchedulingHARQ (Hybrid ARQ)
16QAMSF16, 2ms and CDM/TDM 3 New Physical Channels
Adaptive Modulation and Coding Hybrid Automatic Repeat Request
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HSDPA Key Techniques
Fast Scheduling(2ms short frame and scheduling)AMC (support QPSK and 16QAM)HARQ
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Fast Scheduling 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.
Physical Layer Basic
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Fast SchedulingFast Scheduling
Scheduling Principle: based on channel condition in short period; based on balance between throughout and proportional fair for all users in long period.
Some basic schedulerRound Robin (RR)
Maximum C/I (MAXC/I)
Proportional Fair (PF)
By fast scheduling, HSDPA cell can allocate the available HSDPA power resource and code resource among users effectively, to improves the throughout.
Scheduler may works based on CDM and/or TDM
Channel condition
Amount of data waiting in the queue (delay)
Fairness
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 ProcessFast Scheduling Process
•Transmit power for which users•Channelization code•Data attributes
Scheduling Algorithm
Available resource
Required resource
Temporary statistic
Input:1. Available resource: power and channelization code2. 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 AlgorithmMax 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)RR Scheduling Algorithm (RR - Round Robin)
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.
Note: User allocated resource
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PF Scheduling AlgorithmPF Scheduling Algorithm
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.
Priority for UE = R/r:R: required data rate of UE (calculated TB size per 2ms
based on CQI)
r: amount of effective data (not including data retransmitted ) transmitted by transport layer for this UE during the past 1.6s
The bigger the R/r, the higher the priority (more chance to get resource).
(PF- Proportional Fair)
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HSDPA Key Techniques
Fast Scheduling(2ms short frame and scheduling)AMC (support QPSK and 16QAM)HARQ
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Adaptive Modulation and Coding (AMC)Adaptive Modulation and Coding (AMC)
AMC is based on channel qualityAdjust data rate
Good channel condition – higher rate
Poor channel condition – lower rate
Adjust code rateGood channel condition – higher rate (e.g. 3/4 code)
Poor channel condition – lower rate (e.g. 2/4 code)
Adjust modulation schemeGood channel condition – 16QAM
Poor channel condition – QPSK
Channel Quality Feedback (CQI)UE measures channel quality (SNR) and reports to Node B every 2ms or longer time.
Node-B chooses modulation scheme, Transport Block size and data rate based on CQI.
Throughput ~ SIR Relationship
AMC could improve radio bandwidth and fit for high speed radio transmission.
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HSDPA ModulationQPSK16QAM
Modulation SchemeModulation Scheme
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CQI Mapping Table (Category 10)
016-QAM152555830
0…………
016-QAM121723726
016-QAM101441125
016-QAM81141824
016-QAM7971923
016-QAM5716822
016-QAM5655421
…….........
016-QAM5356516
0QPSK5331915
0QPSK4258314
0QPSK4227913
0QPSK3174212
……………
0QPSK26507
0QPSK14616
0QPSK13775
0QPSK13174
0QPSK12333
0QPSK11732
028800
0QPSK11371
Out of rangeN/A0
XRVNIRReference power adjustment ΔModulationNumber of HS-PDSCHTransport Block SizeCQI value
AMC and modulation scheme recommend in protocolNode-B chooses modulation scheme, transport block size and data rate based on CQI.
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Link Emulation- AMC
AMC AMC PerformancePerformance
AMC changes transmission parameters depending on channel condition and optimize data rate.
AMC performance is affected by channel quality error and feedback delay in fading channel.
For low data rate, AMC has better performance than fixed MCS.
For high data rate, AMC has worse performance than fixed MCS.
AMC gain
0
100
200
300
400
500
600
-12 -11 -10 -9 -8 -7 -6 -5 -4 -3
HS-DSCH Ec/N0(dB)
Throughput(kbps)
TU5(Fixed MCS) TU5(AMC)
TU30(Fixed MCS) TU30(AMC)
TU120(Fixed MCS) TU120(AMC)
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AMC Processing Flow
UE measure CPICH strengthUE reports the signal quality by CQI (channel quality indicator)Node B may filter and rectify CQI report to obtain actual CQIDetermine the channel number, transmit power and modulation scheme, etc, based on CQI, transmit data volume, available powerand code.
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HSDPA Key Techniques
Fast Scheduling(2ms short frame and scheduling)AMC (support QPSK and 16QAM)HARQ
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Hybrid Automatic Repeat Request (HARQ)Hybrid Automatic Repeat Request (HARQ)
Tranditional ARQ–decode received transport block
–detect if there is CRC error in decoded transport bolck
–If there is CRC error
•discard error block
•Request retransmission
Hybrid ARQ–decode received transport block
–Detect if there is CRC error in decoded transport bolck
–If there is CRC error
•Store error block(no discard)
•Request retransmission
•Combine the currently received retranmission with the previous failed decodes.
Soft Combine
Increment redundancy
HARQ helps minimize retransmission time and increase cell throughout.
Combined HARQ
Block1
Block1
Block1?
Block1
Block1
Block2
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HARQ ConceptHARQ 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.
The RV parameter indicates different code bit transmit in IR buffer. Different RV parameter configuration supports:
CC (Chase Combining): retransmit the same coded data
PIR (Partial Incremental Redundancy): transmit systematic bits first
FIR (Full Incremental Redundancy): transmit parity bits first
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HARQ Gain
One retransmission gain for different retransmission scheme
8.44.33.53.1FIR Gain (dB)
6.53.63.33.1PIR Gain (dB)
3.03.03.03.0CC Gain (dB)
3/42/31/21/3Code Rate
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- HARQHARQ( Hybrid ARQ) Performance
HARQ may reduce effect by channel measure error and feedback delay, and provide AMC performance gain.
Higher speed, higher HARQ gain.
HARQ Gain 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 -3.5
HS-DSCH Ec/N0(dB)
Throughput(kbps)
TU5(AMC+HARQ) TU5(AMC)
TU30(AMC+HARQ) TU30(AMC)
TU120(AMC+HARQ) TU120(AMC)
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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 ChannelThree new HSDPA Physical Channel
For each HS-DPCCH, SF=256
Each H has one HS-DPCCH.
For each HS-SCCH, SF=128
Each cell is assigned up to 4 HS-SCCH (limited by UE capability)
For each HS-PDSCH, SF=16
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HSDPA Channel Mapping
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Associated Channel - DPCH
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.
Normally DPCH doesn’t carry service data, only sometimes carry real time services such as AMR (the user setup multiple RAB: CS+PS).
N o d e B
U E
H S -P D S C H H S -S C C H D P C H H S -D P C C H
“Associated”? Or “Concomitant”?
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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 HS-PDSCH 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)HS-SCCH Slot Format Features
3 slots in one TTI (2ms)SF=128, QPSK modulationMaps 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.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.
Slot #0 Slot#1 Slot #2
T slot = 2560 chips, 40 bits
DataN data 1 bits
HS-SCCH subframe: T = 2 ms
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Physical Channel Slot Format (HS-PDSCH)
Slot #0 Slot#1 Slot #2
Tslot = 2560 chips, M*10*2 k bits (k=4)
DataNdata1 bits
1 subframe: T f = 2 ms
HS-PDSCH Slot Format Attributes:3 slots in one TTI (2ms)Fixed spreading factor SF16QPSK or 16QAM modulationOnly carry user dataUE may be assigned multi channelization codes to support multi-code transport
depending on UE capability.
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Physical Channel Slot Format (HS-DPCCH)Uplink HS-DPCCH
TTI 2ms (3 slots), SF 256, Fixed rate of 15Kbps,carry 2 types of HSDPA uplink physical layer signaling: ACK/NACK and CQI.ACK and NACK notifies the NodeB if UE has received correct downlink data or not. The field defines like this:1-Nack, 0-AckCQI 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).ACK/NAK and CQI having different function may be controlled independently by different parameters . ACK/NACK/CQI could be configured to repeat up to 4 times to improve TSTD gain.
Subframe #0 Subframe # Subframe #4
HARQ-ACK CQI
One radio frame Tf = 10 ms
One HS-DPCCH subframe (2 ms)
2×Tslot = 5120 chipsT slot = 2560 chips
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Physical Channel TimingStart 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. HS-SCCH and PDSCH are common channels, so there are not timing between HS-SCCH/PDSCH and DPCH.
HS-SCCH
HS-PDSCH
3 slots = 2 ms
DPCH
τDPCH
Radio frame with (SFN modulo 2) = 0 P-CCPCH
2 slots
3 slots = 2 ms
Slot Slot Slot Slot Slot Slot Slot Slot Slot Slot Slot Slot Slot Slot Slot
15 slots = 10 ms
Subframe #0 Subframe #1 Subframe #2 Subframe #3 Subframe #4
Radio frame with (SFN modulo 2)=1 10 ms
Subframe #0 Subframe #1 Subframe #2 Subframe #3 Subframe #4
HS-DPCCH3 slots = 2 ms
~7.5 slots
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UE Capacity Category( for reference)
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HSDPA Physical Channel Transmit PowerPHSDPA(HSDPA total transmit power)= PHS-PDSCH + PHS-SCCH
The HS-PDSCH transmit power is adjusted by Node B according to the following factors:
CQI
Amount of data to be transmitted
Available power for HS-PDSCH
Available code resource for HS-PDSCH
HS-SCCH transmit power may use:Fixed power transmission (outdoor 5%, indoor 3% of the total power)
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.
HS-DPCCH transmit power has a power offset based on UL DPCH.Slot carrying HARQ-ACK/NACK or CQI may be set different power offset.
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HSDPA – Channel MappingWhen 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.
The 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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