Slide 1 Network & Technology Consulting
Network & Technology Consulting
System Engineer
WCDMA Radio Network Methods
EAB/RGT/M
HSDPA Basics
Filiz Gulkan
Slide 2 Network & Technology Consulting
Outline
HSDPA Principles
HSDPA Channel Structure
HSDPA Power Allocation
Architectural Impact
Summary and Conclusions
Abbreviations and references
Slide 3 Network & Technology Consulting
HSDPA Basics TTI=
2 ms
PRBS
HSDPA power
PDCH
PRBS_nom
R99 traffic power
PAdm
CPICH and control channel power
Channelization codes allocated
for HS-DSCH transmission
8 codes (example) SF=16
SF=8
SF=4
SF=2
SF=1
Slide 4 Network & Technology Consulting
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
Slide 5 Network & Technology Consulting
Key Idea in HSDPA
Fast adaptation of
transmission parameters to
fast variations in radio
conditions
Main functionality to support HSDPA
Fast link adaptation
Fast Hybrid ARQ
Fast channel-dependent scheduling
Slide 6 Network & Technology Consulting
Basic Features
Fast Link Adaptation and higher modulation
Data rate adapted to radio conditions
2 ms time basis
Fast Hybrid ARQ
Roundtrip time ~12 ms possible
Soft combination of multiple attempts
Shared Channel Transmission
Dynamically shared code resource
Fast Channel-Dependent Scheduling
2 ms time basis
2 ms
Short TTI (2 ms)
Reduced delays
Slide 7 Network & Technology Consulting
Short 2 ms TTI
Reduced air-interface delay
Improved end-user performance
Required by TCP at high data rates
Necessary to benefit from other HS-DSCH features
Fast Link Adaptation
Fast hybrid ARQ
Fast Channel-dependent Scheduling
10 ms
20 ms
40 ms
80 ms
Earlier releases
2 ms
Rel 5 (HS-DSCH)
2 ms
Slide 8 Network & Technology Consulting
Shared Channel Transmission
A set of radio resources dynamically shared among multiple users, primarily in the time domain
Efficient code utilization
Efficient power utilization
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
Slide 9 Network & Technology Consulting
Fast Channel-dependent Scheduling
Scheduling = which UE to transmit to at a given time instant and at what rate
Formally part of MAC-hs (a new MAC sub-layer in RBS)
Basic idea: transmit at fading peaks
May lead to large variations in data rate between users
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
Slide 10 Network & Technology Consulting
Fast Channel-dependent Scheduling
Examples of scheduling algorithms
Round Robin (RR)
Cyclically assign the channel to users without taking channel conditions into account
Simple but poor performance
Proportional Fair (PF)
Assign the channel to the user with the best relative channel quality
High throughput, fair
Max C/I Ratio
Assign the channel to the user with the best channel quality
High system throughput but not fair
Slide 11 Network & Technology Consulting
Fast Link Adaptation and higher modulation
Adjust transmission parameters to match instantaneous channel
conditions
HS DL Shared Channel: Rate control (no Fast Power control)
Adaptive coding
Adaptive modulation (QPSK or 16QAM)
Adapt on 2 ms TTI basis fast
R99: Power control (no Rate control constant data rate possible)
High data rate
Low data rate
Slide 12 Network & Technology Consulting
Higher Modulation
HS-DSCH supports both QPSK and 16QAM
16QAM is optional in RBS
16QAM is mandatory in the UE, except for the 2 lowest UE categories
16QAM gives approximately double data rates
16QAM is mainly useful at good radio conditions
16QAM typically requires more advanced receivers in the UE
16QAM
2 bits 4 bits
QPSK
Slide 13 Network & Technology Consulting
Fast Hybrid ARQ with Soft Combining
Rapid retransmissions of erroneous data
Hybrid ARQ protocol terminated in Node B short RTT (typical example: 12 ms)
Soft combining in UE of multiple transmission attempts reduced error rates for retransmissions
P1,1
P1,1
P1,2
P1,2
P2,1
P2,1
P2,2
P2,2
P3,1
P1,1 P2,1 P3,1
+ +
Transmitter
Receiver
Slide 14 Network & Technology Consulting
HS-DSCH Power Allocation
HS-DSCH must share the transmission power with all other channels
Dynamic power allocation
Allocate remaining power to HS-DSCH transmission
Best power utilization
HS-DSCH
Common channels (not power controlled)
Dedicated channels (power controlled)
To
tal
avail
ab
le c
ell p
ow
er
Slide 15 Network & Technology Consulting
Architectural Impact
Fast adaptation to varying radio conditions and fast retransmissions
new functionality in Node B!
New HW and SW in Node B
SW upgrade in RNC
HSDPA:
link adaptation, scheduling,
hybrid ARQ
R99: scheduling, TF selection,
link layer (ARQ)
Core
Network
RNC
Node B
Slide 16 Network & Technology Consulting
UE capabilities
HS-DSCH
category
Maximum number
of HS-DSCH
codes received
L1 peak rates
(Mbps)
User data
throughput P4 (Mbps)
QPSK / 16 QAM
Category 1 5 1.2 Both
Category 2 5 1.2 Both
Category 3 5 1.8 Both
Category 4 5 1.8 Both
Category 5 5 3.6 3.36 Both
Category 6 5 3.6 3.36 Both
Category 7 10 7.3 Both
Category 8 10 7.3 Both
Category 9 15 10.2 Both
Category 10 15 14.0 Both
Category 11 5 0.9 QPSK
Category 12 5 1.8 QPSK
P4 time frame
Slide 17 Network & Technology Consulting
HSDPA channel structure
RNC RNC Iur
Iub Iub
Iu Iu
Associated
Dedicated
Channels
Slide 18 Network & Technology Consulting
HSDPA Channel Structure
High-Speed Downlink Shared Channel HS-DSCH
High-Speed Shared Control Channel(s) HS-SCCH
Associated Dedicated Channel A-DCH
HS-DSCHHS-SCCH
A-DCH
RBS A
RBS B
HS-DSCHHS-SCCH
A-DCH
RBS A
RBS BRBS B
Slide 19 Network & Technology Consulting
High-Speed Shared Control Channel HS-SCCH
Control signalling to mobiles scheduled in a 2 ms interval
UE identity for which the HS-SCCH is intended (and HS-DSCH)
Informs the UE about:
HS-DSCH code set
Modulation scheme (QPSK/16QAM)
HS-DSCH transport format (number of transport blocks per TTI and number of bits per transport block)
Hybrid ARQ information
One or a few HS-SCCH per cell
Never in soft handover
SF = 128
Slide 20 Network & Technology Consulting
Associated Dedicated Channel A-DCH
One A-DCH per HSDPA enabled terminal in the cell
A-DCH DL
3.4 kbps SRB (control signalling: RRC & NAS)
A-DCH UL
384 kbps (or 64 kbps) DCH
3.4 kbps SRB (control signalling: RRC & NAS)
High-Speed Dedicated Physical Control Channel (HS-DPCCH)
ACK/NACK for H-ARQ
Channel Quality Indicator (CQI)
Never in soft handover (softer is possible)
Can be in
soft/softer handover
Slide 21 Network & Technology Consulting
Conclusions
No need for new sites, no need for new spectrum/carrier
No need for RBS configuration
End user data rate is adapted to radio conditions
We can have the same cell range as in R99
HSDPA cell border throughput better than DCH (R99)
More power gives most gain in improving the coverage
HSDPA gives ~3 times more downlink capacity than DCH
More power gives considerable capacity improvement
Substantial capacity gain when G-RAKE and Rx diversity is used in the future phases of HSDPA
Slide 22 Network & Technology Consulting
Abbreviations
A-DCH Associated Dedicated Channel
ARQ Automatic Repeat Request
CQI Channel Quality Indicator
DCH Dedicated Channel
G-RAKE Generalized RAKE
HS-SCCH High-Speed Shared Control Channel
HS-DPCCH High-Speed Dedicated Physical Control Channel
HS-DSCH High-Speed Downlink Shared Channel
MAC-hs Medium Access Control - High Speed
NAS Non-Access Stratum
PS Packet Switched
Slide 23 Network & Technology Consulting
Abbreviations (cont.)
QAM Quadrature Amplified Modulation
QPSK Quadrature Phase Shift Keying
R99 Release 99 of WCDMA specification
RA Rural Area
RRC Radio Resource Control
RTT Round Trip Time
RX Receiver
SF Spreading Factor
TF Transport Format
TTI Transmission Time Interval
TX Transmitter
Slide 24 Network & Technology Consulting
References:
WCDMA eveolved : High-speed packet-data
services, Stefan Parkvall, et al.
Slide 25 Network & Technology Consulting
Agenda
HSDPA Basics
Filiz Gulkan
System Engineer
WCDMA Radio Network Methods,
WCDMA Radio Network System
Management