Rev A Commercial in confidence 1
WCDMA Evolved:
HighSpeed Downlink Packet Access
Mechanisms and Capabilities
WCDMA Evolved: WCDMA Evolved:
High High Speed Downlink Packet Access Speed Downlink Packet Access
Mechanisms and Capabilities Mechanisms and Capabilities
Alexander Wang
Technical Solutions Manager
Alexander Wang
Technical Solutions Manager
Rev A Commercial in confidence 2
HSDPA Improving the WCDMA downlink
STANDARDIZED Integral part of WCDMA (3GPP Rel.5)
LATENCY Quicker response time with interactive services
CAPACITY 2 – 3 times improved system capacity
SPEED Higher bit rates: up to 14 Mbps
TIME TO MARKET Short time to market with existing sites
Rev A Commercial in confidence 3
End user benefit: File Download Performance
Delay for average user (in seconds) 4.3 1.41
JPEG image, 30 kB (VGA)
26.7 5.1
1.9
Slideshow, 200 kB (PowerPoint)
132 22.4
4.1
MP3, 1000 kB (1 min audio)
3G (64 kbps) 3G (384 kbps)
HSDPA
3G (64 kbps) 3G (384 kbps)
HSDPA
3G (64 kbps) 3G (384 kbps)
HSDPA
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Latency (radioaccess network)
Latency (roundtrip)
≈150 ms R99 based equipment
Tighther implementation requirements
WCDMA Evolved R5 (HSDPA)
<100 ms
3050 ms
WCDMA Evolved Beyond R5
Rev A Commercial in confidence 5
Basic Principles
• Shared Channel Transmission
• Higherorder Modulation
• Short Transmission Time Interval (2 ms)
• Fast Hybrid ARQ with Soft Combining
• Fast Radio Channel Dependent Scheduling
• Fast Link Adaptation
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Shared Channel Transmission
• New transport channel type, using multicode transmission
• Radio resources dynamically shared among multiple users in time & code domain
• Efficient code utilization
Channelization codes allocated for HSDSCH 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
Speed Latency Capacity
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Higher Order Modulation
• 16QAM may be used as a complement to QPSK • 16QAM allows for twice the peak data rate compared to QPSK • 16QAM more sensitive to interference
=> Higher data rate in good radio channel conditions (high C/I, Little or no dispersion, Low speed) e.g. Close to cell site & Micro/Indoor cells
16QAM
2 bits/symbol 4 bits/symbol
QPSK
Speed Latency Capacity
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Short 2 ms Transmission Time Interval (TTI)
• Reduced round trip delay on the air interface • Enables HSDPA features to operate at 500 times per second!
– Fast Link Adaptation – Fast Radio Channeldependent Scheduling – Fast hybrid ARQ with soft combining
10 ms 20 ms 40 ms 80 ms
Earlier releases
2 ms Rel 5 (HSDSCH) 2 ms
Speed Latency Capacity
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Fast Hybrid ARQ with Soft Combining
• Fast retransmissions of erroneous packets processed in the RBS => Reduced round trip delay on the air interface
• Soft combining of multiple transmission attempts in the UE => Improved performance
P1,1
P1,1
NACK
P1,2
P1,2
ACK
P2,1
P2,1
P3,1
ACK
P1,1 +
Transmitter
Receiver
Speed Latency Capacity
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Fast Link Adaptation (I)
• Adjust transmission parameters to match instantaneous radio channel conditions – Path loss and shadowing – Interference variations – Fast multipath fading
• HSDSCH is rate controlled – Encoding rate, number of channelization codes & modulation type adapted based on available power
– Adaptation on 2 ms TTI basis ⇒ 500 times/sec!
High data rate
Low data rate
Speed Latency Capacity
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Fast Link Adaptation (II) HSDSCH Power Utilization
Dedicated channels (power controlled)
Common channels
Power usage with dedicated channels channels
t
Unused power
Power
HSDSCH with dynamic power allocation t
Dedicated channels (power controlled)
Common channels
HSDSCH(rate controlled)
Total cell p
ower
Power
Total cell p
ower
– No need for extra spectrum/carrier – Voice and data on same carrier
3GPP Release 99 3GPP Release 5
Effecient power & spectrum utilisation
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Fast Radio channel dependent Scheduling (I)
• Scheduling = which UE to transmit to at a given time instant • Basic idea:
– Transmit to users based on radio channel quality, targeting 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
Speed Latency Capacity
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Fast Channeldependent Scheduling (II)
Examples of scheduling algorithms – Round Robin (RR)
• Cyclically assign the channel to users without taking channel conditions into account
• Simple but poor performance – Max C/I
• Assign the channel to the user with the best channel quality • High system throughput but not fair
– Proportional Fair (PF) • Assign the channel to the user with the best relative channel quality • High throughput, fair
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Terminal Capability HSDSCH category
Maximum number of HSDSCH codes
received
L1 peak rates (Mbps)
QPSK/16QAM
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 Both Category 6 5 3.6 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
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Summary
• Shared Channel Transmission Dynamically shared in time & code domain
• Higherorder Modulation 16QAM in complement to QPSK for higher peak bit rates
2 ms • Short Transmission Time Interval (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
Rev A Commercial in confidence 16
Thank you for your attention!