WCDMA

1. HSDPA Overview
Christofer Lindheimer
WRAN System Management

2. Commercial in confidence HSDPA Overview 2005-09-27
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Outline
 HSDPA Principles
 HSDPA Channels and Bearers
– Power Setting of new channels
 Capacity Management
 HS-DSCH Mobility
 Flow Control & Transport
 Questions and Answers

3. Commercial in confidence HSDPA Overview 2005-09-27
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What is High Speed Downlink Packet
Access (HSDPA)
STANDARDIZED Integral part of WCDMA (3GPP Release 5)
REDUCED DELAY Reduced round trip time
CAPACITY 2 – 3 times improved system throughput
SPEED Higher bit rates: up to 14 Mbps
Smooth Upgrade Short time to market with existing sites

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Key Idea in HSDPA
Fast adaptation of
transmission parameters to
fast variations in radio
conditions

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Shared Channel Transmission
 HSDPA data channel is called HS-DSCH
 A set of radio resources dynamically shared among multiple users
– In the time domain
– In the code domain
Channelization codes allocated
for HS-DSCH transmission
8 codes (example)
SF=16
SF=8
SF=4
SF=2
SF=1
User #1 User #2 User #3 User #4
TTI
Shared
channelization
codes
User #5 (CODE MUX!)

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Short TTI (2 ms)
 Reduced air-interface delay
– Improved end-user performance
– Required by TCP at high data rates
 Increases benefit from other HS-DSCH features
– Fast Link Adaptation
– Fast hybrid ARQ with soft combining
– Fast Channel-dependent Scheduling
10 ms
20 ms
40 ms
Earlier releases
2 ms
Rel 5 (HS-DSCH)
2 ms

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Higher Order Modulation
 16 QAM to be used when radio quality is good
– E.g., close to base stations
 Enables higher rates
16QAM
2 bits/symbol 4 bits/symbol
QPSK

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Fast Link Adaptation
 Adjust transmission parameters to match
instantaneous channel conditions
 HS-DSCH: Rate control
– Based on Quality reports from UE
(CQI= Channel Quality Indicator)
– Adaptive coding rate
– Adaptive modulation
– Adapt on 2 ms TTI basis
– Use “available power”
 Compare
– Release 99: Power control (constant
rate)
C
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Good channel
conditions

high data rate
Bad channel
conditions

low data rate
rate adaptation

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Dynamic Power Allocation
Dedicated channels (power controlled)
Common channels
Power usage with dedicated channels
t
Unused power
Power
HS-DSCH with dynamic power allocation
t
Dedicated channels (power controlled)
Common channels
HS-DSCH (rate controlled)
Total
cell
power
Power
Total
cell
power
3GPP Release 99 3GPP Release 5

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Fast channel-dependent
Scheduling
 Scheduling = which UE to transmit to at a given time instant and at
what rate
 Basic idea: transmit at fading peaks
– Tradeoff: fairness vs cell throughput
high data rate
low data rate
Time
#2
#1 #2 #2
#1 #1 #1
User 2
User 1
Scheduled
user

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Fast channel-dependent
Scheduling
 Examples of scheduling algorithms
– Round Robin (RR)
 Cyclically assign the channel to users
 Channel quality variance unexplored
– Proportional Fair (PF)
 Assign the channel to the user with the best relative
channel quality
 Improved cell throughput
– Max C/I Ratio
 Assign the channel to the user with the best channel
quality
 High system throughput but not fair

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P1,1
+
Fast Hybrid ARQ with Soft
Combining
 Rapid retransmissions of erroneous data
– Hybrid ARQ protocol terminated in RBS
 short RTT
– Soft combining in UE of multiple transmission attempts
 reduced error rates for RLC retransmissions
P1,2
P1,2
P2,1
P1,1
P1,1 P2,1
P2,2
P2,2
P3,1
P2,1 P3,1
+
Transmitter
Receiver
RTT

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HSDPA Basic Principles
Shared Channel Transmission
Dynamically shared in time & code
domain
Higher-order Modulation
16QAM in complement to QPSK for
higher peak bit rates
2 ms
Short TTI (2 ms)
Reduced round trip delay
Fast Hybrid ARQ with
Soft Combining
Reduced round trip delay
Fast Radio Channel
Dependent Scheduling
Scheduling of users on 2 ms time
basis
Fast Link Adaptation
Data rate adapted to radio
conditions on 2 ms time basis
t
P
Dynamic Power Allocation
Efficient power &
spectrum utilisation

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Node Impacts
 RBS
– HS-DSCH functionality
 Scheduling, Link Adaptation, Hybrid ARQ…
- …all implemented in RBS
 RNC
– Impact
 Setup of HS-DSCH/HS-SCCH
 Setup of users on HS-DSCH
 Capacity Management, Cell change handling

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Outline
 HSDPA Principles
 HSDPA Channels and Bearers
– Power Setting of new channels
 Capacity Management
 HS-DSCH Mobility
 Flow Control & Transport
 Questions and Answers

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HSDPA Channel Structure
RBS A
RBS A
High-Speed Downlink Shared Channel – HS-DSCH
-High-Speed Physical Downlink Shared Channel – HS-PDSCH : DL Data
-High-Speed Shared Control Channel – HS-SCCH: Scheduling
Associated Dedicated Channel- A-DCH: Data in UL and control in DL
RBS B
RBS B
RBS B
A-DCH
-Multiplexed with High-Speed Dedicated Physical Control Channel:
ACK/NACK + CQI

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HS-DSCH and A-DCH
 Shared channel:
– HS-DSCH
 Per HS-DSCH user:
– A-DCH DL
 3.4 kbps SRB (control signalling)
 Also needed for power controlling the UL
– A-DCH UL
 64 (or 384) kbps DCH
 3.4 kbps SRB (control signalling)
 High-Speed Dedicated Physical Control Channel
(HS-DPCCH)

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HS-DPCCH and HS-SCCH power
 HS-DPCCH (UL)
– ACK, NACK, CQI
 Power offsets in relation to DPCCH
 Repetition of ACK, NACK, CQI based on performance
 HS-SCCH (DL)
– Fixed Power (relative to CPICH)

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UE capabilities
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
Total
number of
soft channel
bits
Modulation
Category 1 5 3 7298 19200 QPSK/16QAM
Category 2 5 3 7298 28800 QPSK/16QAM
Category 3 5 2 7298 28800 QPSK/16QAM
Category 4 5 2 7298 38400 QPSK/16QAM
Category 5 5 1 7298 57600 QPSK/16QAM
Category 6 5 1 7298 67200 QPSK/16QAM
Category 7 10 1 14411 115200 QPSK/16QAM
Category 8 10 1 14411 134400 QPSK/16QAM
Category 9 15 1 20251 172800 QPSK/16QAM
Category 10 15 1 27952 172800 QPSK/16QAM
Category 11 5 2 3630 14400 QPSK
Category 12 5 1 3630 28800 QPSK

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HSDPA Services and RABs first
HSDPA release
 New RABs
– PS Interactive
64/HS
– PS Interactive
384/HS
 16QAM is optional
 1–5 HS-PDSCH
codes (configurable)
 All HS capable UEs
use HSDPA
regardless of CN
requested bit-rate
Theoretical max: BLER operating level 10 % will
decrease values accordingly

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Outline
 HSDPA Principles
 HSDPA Channels and Bearers
– Power Setting of new channels
 Capacity Management
 HS-DSCH Mobility
 Flow Control & Transport
 Questions and Answers

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Admission control
Load
non-guaranteed
/
non-handover
non-guaranteed
/
handover
guaranteed
/
non-handover
guaranteed
/
handover
Admission Granted
Admission Rejected
 Admission thresholds varies
depending on:
– Request class
 Guaranteed
- Conversational
- Streaming
 Non-guaranteed
- Interactive
- Background
– Request type
 Handover
 Non-handover

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Admission control
Power
non-guaranteed
/
non-handover
non-guaranteed
/
handover
guaranteed
/
non-handover
guaranteed
/
handover
A-DCH
/
non-handover
A-DCH
/
handover
Admission Granted
Admission Rejected
Congestion threshold
Handover threshold
Guaranteed threshold
Non-guaranteed threshold
High load situations
should still allow for
access to remaining
power
MAX number of HS-
DSCH users criterion

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Congestion control
Cell(s)
Congestion
Control
Admission
Control
“DL Congestion”
Block ALL new requests
Start congestion resolve actions in the cell
Periodically:
•Downswitch non-guaranteed users to
Cell_FACH
•Downswitch HS-users to idle state
•Drop guaranteed users
Most resource-consuming users are targeted first

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Outline
 HSDPA Principles
 HSDPA Channels and Bearers
– Power Setting of new channels
 Capacity Management
 HS-DSCH Mobility
 Flow Control & Transport
 Questions and Answers

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RNC RNC
Iur
Iub Iub
Iu Iu
Associated
Dedicated
Channels
•Serving HS-DSCH Cell
Selection (Intra and Inter-
Frequency)
•No Soft/Softer HO for
HS-DSCH
•Serving HS-DSCH Cell
Change (Intra-RNC)
Iub
Overview of HSDPA Mobility

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Serving HS-DSCH Cell Change, -Mobility
 The following events will trigger a serving HS-DSCH cell
change
– A change of best cell within AS (event 1d)
– SHO removal (event1b)
– SHO replacement (event 1c)
RNC RNC
Iur
Iub Iub
Iu Iu
Associated
Dedicated
Channels
Iub
No support for HS-DSCH over Iur

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Outline
 HSDPA Principles
 HSDPA Channels and Bearers
– Power Setting of new channels
 Capacity Management
 HS-DSCH Mobility
 Flow Control & Transport
 Questions and Answers

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Purpose of Iub flow control
 Pre-buffer data in RBS to allow fast
scheduling
 Avoid buffer overflow or empty buffers in RBS
 Keep an appropriate amount of data buffered
in RBS
– Conflicting requirements
 Keep the RBS priority queues short in
order to avoid excessive RLC RTT
 Keep enough data in queue to ensure
throughput when scheduled
 Ensure that the flow is within Iub Transport
Network limits
SDU buffer
RNC
RBS
UE
RBS buffer
HARQ buffer
TN
(Scheduler)
RLC buffer
Iub flow control

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HSDPA enablers in the Transport
Iub solution optimized for efficient bandwidth utilization
– With AAL2 Switching and UBR for HSDPA
New Best Effort AAL2 QoS class for handling HS traffic
– Class C
AAL2 QoS separation between different traffic classes
– A, B, C
User traffic Flow control for HSDPA
IMA for trunking gains
– For >1.5Mbps HS bandwidth to a single user

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Iub Configuration with AAL2 Switching,
UBR, IMA
T1
T1
3 Mbps
Class B:
DCH best effort
Class C: HSDPA best effort
Class A:
Strict QoS
Voice, Video, CS64,
Common Channels
R99 PS
Data
AAL2/
CBR
B
A
AAL2/UBR
C
ET-MC1 /
MC41
HSDPA Peak rate of up to 2.2Mb/s

32. Questions and Answers

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