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WCDMA HSDPA
Principles
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References
3GPP Release 6 Specification References TS 25.308 HSDPA overall description stage2
TS 25.211 Physical channel and mapping of transport channels onto physical
channel (FDD)
TS 25.212 Multiplexing and channel coding (FDD)
TS 25.213 Spreading and modulation (FDD)
TS 25.214 Physical layer procedure (FDD)
TS 25.306 UE radio access capabilities
TS 25.321 Medium Access Control (MAC) protocol specification
TS 25.322 Radio Link Control (RLC) protocol specification
TS 25.331 Radio Resource Control (RRC) protocol specification
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Objectives
Upon completion of this course, you will be able to:
Define HSDPA protocol stack
Describe new channels for HSDPA
Explain the physical channel processing
HSDPA impact on protocol stack
Identify HSDPA UE categories
Define HSDPA protocols of Mac sub-layer
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Contents
1. HSDPA Introduction
2. HSDPA Key Techniques
3. HSDPA Physical Layer Channel
4. HSDPA Layer2 Protocol
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WCDMA Evolution
Downlink Peak Data Rate
(Typical Deployment)
Downlink Peak Data Rate
(Theoretical Maximum)
GSM 9.6kbps 9.6kbps
GPRS 40kbps 171kbps
EDGE 120kbps 473kbps
R99 WCDMA 384kbps 2.0Mbps
HSDPA 10.0Mbps 14.4Mbps
GSM GPRS
EDGE
WCDMA
R99
HSDPA
R5
HSUPA
R6
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High Speed Downlink Packet Access
What are the benefits of HSDPA
Higher Data Rates
Peak data rate up to 14Mbps per user
Higher Capacity More subscribers and throughput
Further reduces the cost per megabyte
Richer Application
Low latencyimprovement for streaming ,interactive, background
applications
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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
Node B
Node B
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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 change 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
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
2ms
HSDPA user#1
HSDPA user#2
HSDPA user#3
HSDPA user#4
Node B
a set of HS-PDSCHs
Code multiplexing for HSDPA
2ms
Big shared pipe
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High Speed Downlink Packet Access
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
Comparison Summary
Mode DCH FACH HSDPA
Channel Type Dedicated Shared Shared
Power Control Closed Inner Loopat 1500Hz &Closed Outer Loop
No Fixed Power withlink adaptation
Soft Handover Supported Not Supported Not Supported
Suitability for
BurstyPoor Good Good
Data Rate Medium Low High
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Contents
1. HSDPA Introduction
2. HSDPA Key Techniques
3. HSDPA Physical Layer Channels
4. 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 onCQI and fairness
Scheduling of user on 2ms
HARQHybrid ARQwithSoft combing
Reduce round trip time
16QAM
16QAM in complement to QPSKfor higher peak bit rates
SF16, 2ms and CDM/TDM
Dynamic 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 ( Adaptive Modulation and Coding ) in accordancewith CQI ( Channel Quality Indicator )
Adjust data rate to compensation channel condition
Good channel conditionhigher data rate
Bad channel conditionlower data rate
Adjust channel coding rate to compensation channel condition
Good channel conditionchannel coding rate is higher e.g. 3/4
Bad channel conditionchannel coding rate is lower e.g. 1/3
Adjust the modulation scheme to compensation channel condition Good channel conditionhigh order modulation scheme e.g. 16QAM
Bad channel conditionlow order modulation scheme e.g. QPSK
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Adaptive Modulation and Coding
AMC ( Adaptive Modulation and Coding ) based on CQI
( Channel Quality Indicator )
CQI ( channel quality indicator )
UE measures the channel quality and reports to NodeB every2ms 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 conditionless power
low data rate
high data rate
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CQI mapping table for UE category 10
CQI valueTransport
Block Size
Number of
HS-PDSCHModulation
Reference power
adjustment
0 N/A Out of range
1 137 1 QPSK 0
2 173 1 QPSK 0
13 2279 4 QPSK 0
14 2583 4 QPSK 0
15 3319 5 QPSK 0
16 3565 5 16-QAM 0
17 4189 5 16-QAM 0
18 4664 5 16-QAM 0
28 23370 15 16-QAM 0
29 24222 15 16-QAM 0
30 25558 15 16-QAM 0
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HSDPA UE Categories
UE 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
HSDPA RF performance depends on UE capability
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Hybrid Automatic Repeat reQuest
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 ( HARQ )
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
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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HARQ Combining
There are many different schemes for HARQ with soft
combining
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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HARQ Process
Each HSDPA assignment is handled by a HARQ process
runing in NodeB and UE
The UE HARQ process is responsible for:
Attempting to decode the data
Deciding whether to send ACK or NACK
Soft combining of retransmitted data
The NodeB HARQ process is responsible for:
Selecting the corrected bits to send according to the selectedretransmission scheme and UE capability
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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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Shared Channel Transmission
In HSDPA, a new DL transport channel is introduced call
HS-DSCH
A part of the total downlink code resource is dynamically
shared between HSDPA and Release 99
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Power Sharing for Channel Transmission
A part of the total downlink power resource is dynamically
shared between HSDPA and Release 99
Time
Allowed power for HSDPA
Total Power
DPCH
Power for CCH
Higher power utility
efficiency
TimePower margin for DCH power control
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Resource Allocation
Resources are assigned to HSDPA user only when they are
actually to be used for transmission, which leads to efficient
code and power utilization
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Higher-Order Modulation Scheme
HSDPA modulation scheme
QPSK
16QAM
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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
Scheduler may be based on: CDM, TDM
Channel condition
Amount of data waiting in the queue
Fairness (Satisfied users)
Cell throughput, etc
Some basic scheduler Round Robin (RR)
Maximum C/I (MAX C/I)
Proportional Fair (PF)
Enhanced Proportional Fair
(EPF)
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HSDPA New Physical Channels
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Contents
1. HSDPA Introduction
2. HSDPA Key Techniques
3. HSDPA Physical Layer Channels
4. HSDPA Layer2 Protocol
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R99 Channel Mapping
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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 Physical Control Channel
High Speed Physical Downlink Shared Channel ( HS-PDSCH )
Downlink Physical Channel
High Speed Dedicated Physical Control Channel ( HS-DPCCH )
Uplink Physical Control Channel
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R5 Channel Mapping
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Physical Layer Frame Duration
Frame Duration
10ms radio frame, 15 slots
2ms HSDPA sub-frame, 3 slots
1 HS-DSCH Transport Time interval (TTI)
Slot Duration
2560chips per slot
7680 chips per HSDPA sub-frame
Symbol Timing
QPSK: 2bits / symbol
16QAM: 4bits / symbol
R99 radio frame
10ms
HSDPA sub-frame
2ms
Time slot
0.67ms
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HS-PDSCH Sub-frame Structure
HS-PDSCH sub-frame structure
3 time slots constituted one TTI (2ms) , only one TB will be sent
during one TTI
Fixed spreading factor ( SF=16 )
May use QPSK or 16QAM modulation scheme
Up to 15 HS-PDSCH may be assigned simultaneously
All HS-PDSCH used to carry users data
UE can be assigned multiple OVSF code ( SF=16 ) based on UE
Categories
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HS-SCCH Sub-frame Structure
HS-SCCH sub- frame structure 3 time slots constitutes one TTI ( 2ms )
SF=128, QPSK only, Fixed rate of 60kbps
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 dataaddressed to the UE with Xue. Then UE demodulates HS-PDSCH
sub-frame with Xccs, Xms, Xrv, Xhap, Xtbs and Xnd are used for
HARQ Process
UE may need to simultaneous monitor up to four HS-SCCHs
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HS-DPCCH Sub-frame Structure
HS-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
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Uplink HS-DPCCH Preamble and
Postamble
Transmit Preamble and Postamble on HS-DPCCH around
ACK / NACK
Eases the decoding, which allows HS-DPCCH to operate at
lower power
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Associated Physical ChannelA-
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
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Fractional Dedicated Physical Channel
(F-DPCH)
The F-DPCH is a new physical channel in Release 6
Purpose of F-DPCH introduction is to keep the closed loop
power control working for HSDPA users without an
assigned DPCH (A-DPCH)
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F-DPCH Frame Structure
The F-DPCH carries control information generated at layer 1 (TPCcommands). It is a special case of downlink DPCCH
Each frame of length 10ms is split into 15 slots, each of length
Tslot = 2560 chips, corresponding to one power-control period,
SF=256
Each user occupy one Symbol in one slot to bear TPC command,
Pilot and TFCI is not needed
Up to 10 users can be multiplexed on one F-DPCH(Tx OFF)NOFF2bits
Slot #0 Slot #1 Slot #i Slot #14
Tslot= 2560 chips
1 radio frame: Tf= 10 ms
TPC
NTPCbits
(Tx OFF)
NOFF1bits
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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
HS-SCCH
HS-PDSCH
3 slots = 2 ms
DPCH
DPCH
Radio frame with (SFN modulo 2) = 0P-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-DPCCH
3 slots = 2 ms
~7.5 slots
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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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More Data Rate Factors
More factors that affect HSDPA data rate Inter- TTI interval
Retransmission
ACK / NACK Repetition
Assuming
5 OVSF code for HS-PDSCH
Consecutive assignment
QPSK
Turbo code rate =1/3
Retransmission
75% of data block decoded on first transmission
25% of data block decoded on second transmission
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Contents
1. HSDPA Introduction
2. HSDPA Key Techniques
3. HSDPA Physical Layer Channels
4. HSDPA Layer2 Protocol
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UMTS Protocol Stack
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HSDPA Protocol Stack
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MAC Architecture
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UTRAN MAC-hs Architecture
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UTRAN MAC-hs Functions
Flow Control
The flow control entity controls the HSDPA data flow between
RNC and NodeB
Purpose: to reduce the transmission time of HSDPA data on
the UTRAN side and to reduce the data discarded and
retransmitted when the Iub interface or Uu interface is
congested
The transmission capabilities of the Uu interface and Iub
interface are taken into account in a dynamic manner in the
flow control
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UTRAN MAC-hs Functions
Scheduling
The scheduling entity handles the priority of the queues and
schedules the priority queues or NACK HARQ processes of the
HS-DSCH UEs in a cell to be transmitted on the HS-DSCH
related physical channels in each TTI
Purpose: to achieve considerable cell throughput capability and
to satisfy user experience
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UTRAN MAC-hs Functions
HARQ
The HARQ entity handles the HARQ protocol for each HS-
DSCH UE
Each HS-DSCH UE has one HARQ entity on the MAC-hs of
the UTRAN side to handle the HARQ functionality
One HARQ entity can support multiple instances (i.e.HARQ
processes) of stop and wait HARQ protocols
Based on the status reports from HS-DPCCH, a new
transmission or retransmission is determined
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UTRAN MAC-hs Functions
TFRC selection
The TFRC selection entity selects an appropriate transport
format and resource for the data to be transmitted on HS-
DSCH
The transport format includes the transport block size and
modulation scheme. The resource includes the power resource
and code resource of HS-PDSCH
Transport Format and Resource Combination (TFRC) for each
UE is channel quality based, where AMC is the key technique
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UE MAC-hs Functions
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Summary
1. HSDPA Introduction
2. HSDPA Key Techniques
3. HSDPA Physical Layer Channels
4. HSDPA Layer2 Protocol
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