4. HSDPA, short for High-Speed Downlink Packet Access,
is a new protocol for mobile telephone data
transmission. Essentially, the HSDPA provide download
speeds on a mobile phone equivalent to an ADSL
(Asymmetric Digital Subscriber Line) line in a home .
HSDPA for WCDMA feature was included in 3GPP Rel. 5
specification. It is also referred as 3.5 G network.
What is HSDPA?
5. • HSPA features/properties include e.g.
– Higher order modulation and coding
• Higher throughput and peak data rates
– In theory up to 5,8 Mbps in the uplink and 14 Mbps
in the downlink without Multiple Inputs and
Multiple Outputs (MIMO)
– Multiple Inputs and Multiple Outputs (MIMO)
• Roughly speaking equals to additional transmitter and
receiver antennas
– Fast scheduling in the Node B
• Possibility to take advantage of channel conditions with
lower latency
What is HSDPA?
6. • To improve packet data throughput.
• Introduction of new transport channel.
• Peak data rate 14 Mbps.
• Two most fundamental features of WCDMA , variable
SF
and fast power control are disabled.
• Shared channel transmission.
• High order modulation.
HSDPA Features
7. • Fast radio channel dependent scheduling.
• Hybrid ARQ with soft combining.
• Shorter TTI.
• Dynamic power allocation.
• Shared channel transmission.
• Fast link adaptation.
HSDPA Features
8. 8
8
8
Terminal Changing caused by HSDPA
Powerful 3G terminals
Much more powerful, attractive HSDPA terminals
faster processor
larger memory
advanced receive and process algorithm
16QAM demodulation, multiple decoding
MAC-hs process
multiple codes
HSDPA terminal, first choice for high-end commercial application
9. 9
9
9
HSDPA, Mature technology
2002.6 R5 released
2003.6 HSDPA (High Speed Downlink Packet Access) was
added into R5
HSDPA is smoothly evolved from WCDMA R99 without any big
effect to the existing R99 network
1 new transport channel: HS-DSCH
3 new physical channels：HS-PDSCH, HS-SCCH and HS-DPCCH
MAC-hs sub-layer, HARQ (Fast Hybrid Automatic Repeat reQuest),
Fast Scheduling and AMC (Adaptive Modulation and Coding)
HSDPA --Max. downlink data rate:
14.4Mbps
11. 1 - Shared Channel Transmission (1/2)
• Shared-channel transmission implies that a
certain amount of radio resources of a cell
(codes and power) is seen as a common
resource that is dynamically shared between
users.
Channelization codes allocated
for HS-DSCH transmission
5 codes (example)
SF=16
SF=8
SF=4
SF=2
SF=1
12. 1 - Shared Channel Transmission (2/2)
• The Shared-channel transmission allows:
–Higher peak bit rate:
–all the resource can be allocated to a
single user in case of low load.
13. 2 - Short 2 ms TTI (1/2)
• The Transmission Time Interval becomes
extremely short in HSDPA; 2 ms compared to the
10 ms used by R99 high bit rate radio bearer.
• The HS channels are organised in sub-frame of 3
slots each; this means that the slot time 2/3
ms/slot is the same as for R99 slots (10/15
ms/slot).
14. 2 - Short 2 ms TTI (2/2)
• The shorter TTI allows:
– Reduced air-interface delay: this is required by the the TCP at
high data rates to Improved end-user performance
• The shorter TTI is necessary to benefit from
other HSDPA features:
– Fast Link Adaptation
– Fast hybrid ARQ with soft combining
– Fast Channel-dependent Scheduling
2 ms
16. 3 - HSDPA – Power Allocation
• HS-DSCH adjusts the data rate to
match the instantaneous radio
conditions and the available
transmission power in the RBS
– No closed loop power control is
specified for HS-DSCH, unlike the DCH
channel
• The system adjusts the data rate by
– changing the modulation scheme
• This leads to a higher efficiency in
the usage of power.
19. 19
19
19
4 - Fast Link Adaptation (2/4)
• Adjust transmission parameters to
match instantaneous channel
conditions
• HSDPA: Adapt on 2 ms TTI basis the Rate
(“constant” power)
– Adaptive coding
– Adaptive modulation (QPSK or 16QAM)
20. 4 - Fast Link Adaptation (3/4)
• In order to estimate current channel
conditions, an estimate of the Channel
Quality is reported by the UE to RBS (CQI).
21. • UE informs the Node B regularly of its channel
quality by CQI messages (Channel Quality
Indicator)
4 - Fast Link Adaptation (4/4)
22. • Scheduling = which UE to transmit to at a
given time instant
• There is a main tradeoff to choose between:
fairness vs. cell throughput
5 - Fast Channel-dependent Scheduling (1/2)
Every user has the
same “rights to
access the
resource”
The user with
better radio
condition transmit
more
User1 User2 User3 User4
time
2 ms 2 ms
23. 5 - Fast Channel-dependent Scheduling (1/2)
• 2 opposite strategies are:
– Round Robin: radio resources are allocated to
communication links on a sequential basis.
– Proportional Fair: transmit at fading peaks. This
may lead to large variations in data rate
between users.
high data rate
low data rate
Time
#2
#1 #2 #2
#1 #1 #1
User 2
User 1
Scheduled
user
24. 6 - Fast Hybrid ARQ with Soft Combining
• This new “level” allows 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 retransmissions
25. Fast Retransmissions
• Radio Link Control (RLC) layer ACK/NACKs also possible with HSPA
Packet
RLC
ACK/NACK
Retransmisson Packet
Layer 1
ACK/NACK
Retransmisson
Rel ‘99 HSPA
RNC
NodeB
UE
26. 26
26
26
HSDPA working procedure
RNC
Node B
(AMC and HARQ)
Data Packet
AMC, modulation and coding
selection
HARQ, lowers the time delay,
improves the data throughput
Fast scheduling, quick decision
②Evaluation, HS-DSCH parameters setting
④Receive data from HS-
DSCH according to
Detecting HS-SCCH
27. 27
27
27
Protocol stacks (1/4)
UE RBS SRNC
PHY
AAL2
ATM
FP
MAC-hs
L1
RLC
User Data
PHY PHY
AAL2
ATM
AAL5
ATM
GTP-U
UDP/IP
FP
RLC
MAC
CN
PHY
AAL5
ATM
GTP-U
UDP/IP
User Data
Uu Iub Iu
The figure shows the R99 protocol stack.
Note in particular that MAC is a protocol between the RNC and
the UE
MAC
L1
28. 28
28
28
Protocol stacks (2/4)
UE RBS SRNC
PHY
L1
AAL2
ATM
MAC-hs
HS-DSCH
FP
MAC-d
MAC-hs
L1
RLC
User Data
PHY PHY
AAL2
ATM
AAL5
ATM
GTP-U
UDP/IP
HS-DSCH
FP
RLC
MAC-d
CN
PHY
AAL5
ATM
GTP-U
UDP/IP
User Data
Uu Iub Iu
The new radio interface layer 2 functionality required by the HS-
DSCH (hybrid ARQ signaling, scheduling, etc) was placed in a new
functional entity of the MAC layer, called MAC-hs.
The physical layer was updated with new functionalities for HS-
DSCH (soft combining of retransmitted transport blocks, new
physical channels, etc.).
29. • RBS
– New TX board in RBS
• RNC
– No HW upgrades
– Only SW!!
HSDPA Node Impacts
R99:
• Scheduling,
• Link layer
retransmission
(ARQ)
Core
Network
RNC
Node B
HSDPA:
• Scheduling,
• Link
Adaptation,
• Hybrid ARQ
30. 30
30
30
Advantage of HSDPA
Comparing item R99/R4 HSDPA
System capacity (Mbps) 2.668 14.4
Spectrum efficiency
(Kbit/(MHz*Cell))
537.6 2795.2
System handover
Inter-frequency hard HO
Intra-frequency soft HO
Intra-frequency softer HO
Inter-system HO (GSM)
Only hard handover
Power control
Open loop, Close loop (Inner loop, Outer loop)
PC, Quick, Slow PC
HS-PDSCH adopts slow PC or even
no power control
Modulation QPSK QPSK, 16QAM
Link adaptive technology Quick PC and soft HO
AMC, HARQ, Short TTI and Quick
channel feedback
MAC-hs N/A For faster scheduling
Provides various speed
with stable power
(stable power,
adjustable speed)
Adjust power to
guarantee service speed
(stable speed,
adjustable power)
HSDPA R99/R4
31. Conclusions
• High Speed Packet Access evolution for WCDMA
was introduced in Release 5 and 6 for downlink
and uplink, respectively
• HSPA offers much higher peak data rates,
reaching in theory up to 14 Mbps in the downlink
and 5,4 Mbps in the uplink, in addition to
reduced delays
• Key technologies with HSPA are
– Fast Layer 1 retransmissions i.e. HARQ
– Node B scheduling
– Shorter frame size (2ms in DL and 2/10ms UL)
– Higher order modulation and coding along with
link adaptation in downlink
– Real support for multicodes in the uplink
