hsdpa basic principle
TRANSCRIPT
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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 CharacteristicsSection 2 Key Techniques
Section 3 Physical Channel
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HSDPA Basic Concepts
HSDPA = High Speed Downlink Packet Access
Important Features of 3GPP R5Why HSDPA?
The subscribers request higher speed and better qualitydata access
Competition challenge from CDMA EV/DO, WiMAXUp to now, the throughput request for downlink is muchmore higher than that of uplinkThe channel configuration of R99 lead a very lowefficiency on the downlink capacity
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HSDPA Characteristics
HSDPA is the solution of WCDMA offering higherspeed 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
HSDPA
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Contents
Chapter 1 HSDPA Basic
Concepts and CharacteristicsChapter 2 Key Techniques
Chapter 3 Physical Channel
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HSDPA 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 frameand 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) cant bedecoded correctly, whole frame will be retransmit 10ms later.
An HSDPA frame is only 2ms(3 slots). If a 2ms frame cant bedecoded correctly, just this 2ms frame need be retransmitted. Other2ms(up to 6) HARQ process may continue transmitting data, thusradio resource could be used more effectively.
Physical Layer Basic
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Fast Scheduling
Scheduling Principle: based on channelcondition in short period; based on balancebetween throughout and proportional fair for allusers in long period.
Some basic scheduler
Round Robin (RR)Maximum C/I (MAXC/I)
Proportional Fair (PF)
By fast scheduling, HSDPA cell can allocate the available HSDPA power resource andcode 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 codesreserved forHSDPAtransmission
2ms
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Fast 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 code
2. Required resource: including users, user data, retransmission, air interface abilityestimate, 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 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 thebest 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)
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 allocatedresource
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HSDPA Key Techniques
Fast Scheduling(2ms short frame andscheduling) AMC (support QPSK and 16QAM)HARQ
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Adaptive Modulation and Coding (AMC)
AMC is based on channel quality Adjust 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 toNode B every 2ms or longer time.
Node-B chooses modulation scheme, Transport Blocksize 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 Scheme
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CQI Mapping Table (Category 10)CQI value Transport BlockSize Number of HS-PDSCH Modulation 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 015 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 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 Performance
AMC changes transmission
parameters depending on channel
condition and optimize data rate.
AMC performance is affected by
channel quality error and feedbackdelay 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)
T h
r o u g
h p u t
( k b
p s
)
TU5(Fixed MCS) TU5(AMC)T U30 (Fix ed MCS ) TU30 (AM C)TU120(F ixed 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 modulationscheme, etc, based on CQI, transmit data volume, available powerand code.
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HSDPA Key Techniques
Fast Scheduling(2ms short frame andscheduling)AMC (support QPSK and 16QAM)HARQ
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Hybrid Automatic Repeat Request (HARQ)
Tranditional ARQ decode received transport block
detect if there is CRC error in decodedtransport 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 Concept
HARQ is a technique that transmitter sends new set of check bits ifthe previous transmission failed (NACK) while receiver buffers thefailed 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
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
FIR scheme will transmit the check bits first, it has effective averagecoded bits after retransmission. Especially for high code rate, theHARQ gain is very evidence.
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Link Emulation- HARQ
HARQ( Hybrid ARQ) Performance
HARQ may reduce effect bychannel measure error andfeedback 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)
T h
r o u g
h p u t
( k b
p s
)
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 CharacteristicsSection 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
HSDPA Ch l M i
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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 isalso called associated channel in HSDPA. It isused for signaling transport and power control.
Normally DPCH doesnt carry service data, onlysometimes carry real time services such as
AMR (the user setup multiple RAB: CS+PS).
Node B
UE
HS-PDSCH HS-SCCH DPCH HS-DPCCH
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 whenand on which channel my
data is transported?
HS-SCCH is like soldiers holdingflags at the first row of queue. UEkeeps on monitoring the HS-SCCH channels to identify any HS-PDSCHsubframes addressed to it on the setsof HS-PDSCH channels. Uponreceiving an HS-PDSCH subframe forthe UE, the UE physical layer willdemodulates the subframe, otherwisedo nothing.
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Physical Channel Slot Format (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
HS-PDSCH Slot Format Attributes:3 slots in one TTI (2ms)
Fixed spreading factor SF16QPSK or 16QAM modulation
Only carry user data
UE may be assigned multi channelization codes to support multi-code transportdepending 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 layersignaling: ACK/NACK and CQI.
ACK and NACK notifies the NodeB if UE has received correct downlink data or not. The fielddefines like this:1-Nack, 0-AckCQI is a metric that reflects physical channel quality indicator based on CPICH, and reportedby period ranging from 0, 2ms. to 160ms (0 means no transmission). Usually the period is2ms (one TTI).
ACK/NAK and CQI having different function may be controlled independently by differentparameters .
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 T = 10 ms
One HS-DPCCH subframe (2 ms)
2 Tslot = 5120 chipsTslot = 2560 chips
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UE Capacity Category( for reference)
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HSDPA Physical Channel Transmit Power P HSDPA (HSDPA total transmit power) P HS-PDSCH + P HS-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 DLTRB is carried on HS-DSCH SRB andSRB or UL service is carried on DCH. Insoft handover, there may be one or moreDCH, but only one HS-DSCH.
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