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Principles of HSDPA
ISSUE 1.0
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Objectives Upon completion of this course, you will be able to:
Review WCDMA and HSDPA evolution and standards Review R99 packet data service method Describe HSDPA physical channels HSDPA Network and UE protocol stack architecture
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Contents1.1. HSDPA ConceptsHSDPA Concepts
2. HSDPA Key Techniques3. HSDPA Physical Layer Channels4. HSDPA Layer2 Protocol
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WCDMA Evolution
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Release 99 Packet Data How is Packet Data handled in Release 99 (FDD) ?
DCH ( Dedicated Channel ) Spreading codes assigned per user Closed loop power control Soft handover
FACH ( Common Channel ) Common Spreading code No closed loop power control No soft handover
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Release 99 Downlink Limitation Dedicated Channel Features ( DCH )
Maximum implemented downlink of 384kbps OVSF code limitation for high data rate users Rate switching according to burst throughput is slow Outer loop power control responds slowly to channel
Common Channel Features ( FACH ) Good for burst data application Only low data rates supported Fixed transmit power
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High Speed Downlink Packet Access (HSDPA) The differences between HSDPA and R99
Set of high data rate channel Channels are shared by multiple users Each user may be assigned all or part of the resource
every 2 ms
Node B
HS-PDSCH
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High Speed Downlink Packet Access (HSDPA) How will HSDPA figure out the limitations of R99
Adaptive modulation and coding Fast feedback of Channel condition QPSK and16QAM Channel coding rate from 1/3 to 1
Multi-code operation Multiple codes allocated per user Fixed spreading factor
NodeB fast Scheduling Physical Layer HARQ ( Hybrid Automatic Repeat reQuest )
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High Speed Downlink Packet Access (HSDPA) Comparison Summary
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Contents1. HSDPA Concepts 2.2. HSDPA Key TechniquesHSDPA Key Techniques
3. HSDPA Physical Layer Channels4. HSDPA Layer2 Protocol
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HSDPA Key Techniques
AMC (Adaptive Modulation & Coding)Data rate adapted to radio condition on 2ms
Fast Scheduling based on CQI and fairness
Scheduling of user on 2ms
HARQ( Hybrid ARQ)with Soft combing
Reduce round trip time
16QAM16QAM in complement to QPSK
for higher peak bit rates
SF16, 2ms and CDM/TDMDynamic shared in Time and code domain
3 New Physical Channels
Block 1 Block 2Block 1
Block 1?
Block 1Block 1?
+
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Adaptive Modulation and Coding ( AMC )
AMC ( Adaptive Modulation and Coding ) based on CQI ( Channel Quality Indicator )
Adjust data rate to compensation channel condition Good channel condition – higher data rate Bad channel condition – lower data rate
Adjust channel coding rate to compensation channel condition Good channel condition – channel coding rate is higher e.g. 3/4 Bad channel condition –channel coding rate is higher e.g. 1/3
Adjust the modulation scheme to compensation channel condition Good channel condition – high order modulation scheme e.g. 16QAM Bad channel condition – low order modulation scheme e.g. QPSK
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Adaptive Modulation and Coding ( AMC ) AMC ( Adaptive Modulation and Coding ) based on CQI
( Channel Quality Indicator ) CQI ( channel quality indicator )
UE measures the channel quality and reports to NodeB every 2ms or more cycle
NodeB selects modulation scheme ,data block size based on CQI
Bad channel condition→ More power Node B Node B
Power Control Rate Adaptation
Good channel condition
Bad channel condition
Good channel condition
→ less power
→ low data rate
→ high data rate
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CQI mapping table for UE category 10
CQI valueCQI valueTransport Transport Block SizeBlock Size
Number of Number of HS-PDSCHHS-PDSCH
ModulationModulationReference power Reference power
adjustment adjustment
00 N/AN/A Out of rangeOut of range
11 137137 11 QPSKQPSK 00
22 173173 11 QPSKQPSK 00
………… ………… ………… ………… …………
1313 22792279 44 QPSKQPSK 00
1414 25832583 44 QPSKQPSK 00
1515 33193319 55 QPSKQPSK 00
1616 35653565 55 16-QAM16-QAM 00
1717 41894189 55 16-QAM16-QAM 00
1818 46644664 55 16-QAM16-QAM 00
………… ………… ………… ………… …………
2828 2337023370 1515 16-QAM16-QAM 00
2929 2422224222 1515 16-QAM16-QAM 00
3030 2555825558 1515 16-QAM16-QAM 00
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HSDPA UE CategoriesUE 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
Total Number of Soft Channel Bits
Category 1 5 3 7298 19200
Category 2 5 3 7298 28800
Category 3 5 2 7298 28800
Category 4 5 2 7298 38400
Category 5 5 1 7298 57600
Category 6 5 1 7298 67200
Category 7 10 1 14411 115200
Category 8 10 1 14411 134400
Category 9 15 1 20251 172800
Category 10 15 1 27952 172800
Category 11 5 2 3630 14400
Category 12 5 1 3630 28800
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Hybrid Automatic Repeat reQuest ( HARQ ) Conventional ARQ
In a conventional ARQ scheme, received data blocks that can not be correctly decoded are discarded and retransmitted data blocks are separately decoded
Hybrid ARQ In case of Hybrid ARQ with soft combining, received data
blocks that can not be correctly decoded are not discarded. Instead the corresponding received signal is buffered and soft combined with later received retransmission of information bits. Decoding is then applied to the combined signal.
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Hybrid Automatic Repeat reQuest ( HARQ ) Example for HARQ
The use of HARQ with soft combining increases the effective received Eb/Io for each retransmission and thus increases the probability for correct decoding of retransmissions, compare to conventional ARQ
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Hybrid Automatic Repeat reQuest ( HARQ ) There are many different schemes for HARQ with
soft combining. These scheme differ in the structure of
retransmissions and in the way by which the soft combining is carried out at the receiver
In case of Chase combining ( CC ) each retransmission is an identical copy of the original transmission
In case of Incremental Redundancy ( IR ) each retransmission may add new redundancy
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Hybrid Automatic Repeat reQuest ( HARQ ) Example for Chase Combining ( CC ) Scheme
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Hybrid Automatic Repeat reQuest ( HARQ ) Example for Incremental Redundancy ( IR ) Scheme
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Fast Scheduling Fast scheduling is about to decided to which
terminal the shared channel transmission should be directed at any given moment
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Short TTI (2ms) Shorter TTI ( Transmission Time Interval ) is to
reduce RTT ( round trip time ) Shorter TTI is necessary to benefit from other
functionalities such as AMC, scheduling algorithm and HARQ
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In HSDPA, a new DL transport channel is introduced call HS-DSCH. The idea is that a part of the total downlink code resource is dynamically shared between a set of HSDPA users
Shared Channel Transmission
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Shared Channel Transmission The codes are assigned to HSDPA user only when they ar
e actually to be used for transmission, which leads to efficient code and power utilizationAll
channelizationcodes available
for HSDPA
Time
Channelizationcode
UE1 data UE2 data UE3 data
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Higher-Order Modulation
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HSDPA New Physical Channels
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Contents1. HSDPA Concepts 2. HSDPA Key Techniques3.3. HSDPA Physical Layer ChannelsHSDPA Physical Layer Channels
4. HSDPA Layer2 Protocol
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R99 Physical Channels
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HSDPA Physical Layer Channels New HSDPA Channels
High Speed Downlink shared Channel ( HS-DSCH ) Downlink Transport Channel
High Speed Shared Control Channel ( HS-SCCH ) Downlink Control Channel
High Speed Physical Downlink Shared Channel ( HS-PDSCH ) Downlink Physical Channel
High Speed Dedicated Physical Control Channel ( HS-DPCCH )
Uplink Control Channel
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HSDPA Physical Channels
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HS-PDSCH sub-frame Structure HS-PDSCH sub-frame structure
3 time slots constituted one TTI (2ms) Fixed spreading factor ( SF=16 ) May use QPSK or 16QAM modulation scheme All HS-PDSCH used to carry user’s data UE can be assigned multiple OVSF code ( SF=16 ) based on UE
Categories
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
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HS-SCCH sub-frame Structure HS-SCCH sub- frame structure
3 time slots constitutes one TTI ( 2ms ) HS-SCCH SF=128, QPSK only HS-SCCH carries the following control messages: Xue, Xccs, Xms, Xrv, Xtbs,
Xhap and Xnd UE demodulates HS-SCCH sub-frame and find out the received data addres
sed to the UE with Xue. Then UE demodulates HS-PDSCH sub-frame with Xccs, Xms, Xrv, Xhp, Xtbs and Xnd are used for HARQ Process
UE may need to simultaneous monitor up to four HS-SCCH
Slot #0 Slot#1 Slot #2
T slot = 2560 chips, 40 bits
Data N data 1 bits
1 subframe: T f = 2 ms
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HS-DPCCH sub-frame StructureHS-DPCCH sub-frame structure
TTI=2ms ( 3 time slots ), SF=256, Fixed rate of 15kbps, carry 2 types of HSDPA uplink physical layer control message, including ACK/NACK CQI ACK and NACK notifies NodeB that UE has received correct downlink data or not. The field defines like this: 1-NACK, 0-ACK CQI reflects physical channel quality indicator based on CPICH strength, and reported by period range from 0 to 160ms ( 0 means no transmission ). Usually the period is 2ms ( one TTI ) ACK/NACK and CQI having different function may be controlled independently by different parameters.
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
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Associated physical channel - DPCH Besides 3 physical channels on top. There is another physical channel named DPCH, which is a dedicated channel . DPCH is also called associated channel used for signalling transmission and power control DPCH does not carry service generally, sometimes carry real time (RT) service such as AMR service
Node B
UE
HS-PDSCH HS-SCCH DPCH HS-DPCCH
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HSDPA Physical Channels Timing Start of HS-SCCH is aligned with the start of PCCPCH HS-PDSCH, subframe is transmitted two slots after the
associated HS-SCCH subframe
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Theoretical HSDPA Maximum Data Rate Theoretical HSDPA Maximum data rate is 14.4Mbps How do we get to 14.4Mbps ?
Multi-code transmission NodeB must allocate all 15 OVSF codes ( SF =16 ) to one UE
Consecutive assignments using multiple HARQ process NodeB must allocate all time slots to one UE UE must decode all transmission correctly on the first transmission
Low channel coding gain Effective code rate = 1 Requires very good channel conditions to decode
16QAM Requires very good channel condition
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Contents1. HSDPA Concepts2. HSDPA Key Techniques3. HSDPA Physical Layer Channels4.4. HSDPA Layer2 ProtocolHSDPA Layer2 Protocol
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HSDPA Protocol Stack
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UTRAN MAC Architecture
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UTRAN MAC-hs Architecture
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UE MAC-hs Architecture
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Implementation of MAC-hs
HS-DPCCH demodulation and decode
SRNC(MAC-d)
power monitor
CQI adjustment
Scheduler
Queues/flow control
HARQ
TFRC
Power management
Coding and modulation
OM parameters
Power limitation
Power for HSDPA
CQI Value
Stat. Of ACK/NACKACK/NACK
Waiting time
Queue filling info Queue priority
CQI ValueCode allocation
Code available
Data flow
Control signal
Thank You