Hsdpa principles

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HUAWEI TECHNOLOGIES Co., Ltd. Huawei Confidential
The Overview of HSDPA
(High Speed Downlink Packet Access)

Page 2
Outline
Introduction
HSDPA New Techniques
Transport and Physical Channels
Spreading, Modulation and Coding
Protocol Architecture
Terminal Capabilities

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HSDPA Bit Rate Advantage
0
200
400
600
800
1000
1200
1400
1600
1800
2000
GPRS EDGE WCDMA EV-DO EV-DV HSDPA
1.5 Mbps
700 kbps
400 kbps
350 kbps
150 kbps
30 kbps
kbps
Typical average bit rate for different technologies in a medium loaded Macro cell.

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HSDPA Latency Advantage
0
100
200
300
400
500
600
700
GPRS/EDGE R99 WCDMA R99 HSDPA R5
ms
650 ms
200 ms
100 ms
Typical average round trip time for different technologies. Smaller round trip times
would benefit interactive applications.

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HSDPA Considerations
The same carrier can be shared between WCDMA and HSPDA. It’s the DL power
which should be intelligently divided between two services.
Unlike 3GPP2 standards, EV-DO and IS-95/1xRTT, which can not share a carrier.
An evolutionary rather than a revolutionary philosophy.
WCDMA networks can be upgraded with HSDPA hardware/software on Node-B by
Node-B basis.
Even HSDPA features can be added gradually, if required.
Priority to urban environments and indoor deployments.
Support full mobility but should be optimized for low and medium speed users.
Focus on streaming, interactive and background services.
HSDPA new features should show significant incremental gains over existing R’99
performance.
Consider value added to the user, cost to the operators, increased revenue for
operators, etc., in adding any new feature.

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Outline
Introduction

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Power Utilization in HSDPA
Efficient use of power: the unused power by dedicated/common channels is
exploited by HS-DSCH with use of dynamic power allocation.

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Channel Sharing in HSDPA
Efficient use of time: several packet data streams are time multiplexed and
sent over High Speed Downlink Shared Channel (HS-DSCH).

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Major New Techniques
Fast Scheduling
Fast Hybrid ARQ
Fast Link Adaptation

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Fast Scheduling

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Packet Scheduler
The packet scheduler’s task is to maximize the network throughput while satisfying
the QoS requirements of the users.
The packet scheduling method has significant impact on the cell throughput and on the
user-perceived quality of service.
The scheduler is located in the Node B and can respond quickly to channel
conditions, since the Iub and the RNC are not involved in the process.
Multi-user diversity:
Selection of the best users in the cell in terms of
the UE’s received signal strength is known as multi-
user diversity.
The scheduler may select for transmission in each
TTI (Transmission Time Interval) users that have
good signal to noise ratio and therefore ensure
better data reception and fewer retransmissions.
Multi-user diversity will increase the average cell
throughput by using the network resources more
efficiently.
TTI intervals
Channel
Quality
UE1
UE2
UE1
UE2
Node B

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Scheduling Methods
Round Robin
Users are served in cyclic order ignoring channel conditions. It is simple and ensures a fair resource
distribution among the users at the cost of cell capacity.
Maximum C/I (example shown in next page)
The cell serves in every TTI the user with the largest instantaneous supportable data rate. Users with
lower average radio conditions receive less resources but due to large fading dynamics, these users are
still able to receive service.
Average C/I
The cell serves in every TTI the user with the largest average C/I that has data to be transmitted.
Averaging windows can be as large as 50 TTI’s. This tends to average the short term fading conditions
for users.
Proportional Fairness
The cell serves the user with the largest relative channel quality, based on the short term data rate of the
user relative to its average data throughput. Users with better short term channel conditions will have
higher priority than users that are temporarily located in a fade.
Fair Throughput
Modifies the proportional fair algorithm to increase the priority of users that receive lower average
throughput, in an attempt to equalize the throughput to all users. A variant that does not use
instantaneous channel quality information and serves in every TTI the user with the lowest average
throughput.

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Example of Max C/I Scheduling Method
Example of Max C/I Scheduling

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Fast Hybrid ARQ

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Fast Retransmission
All Release 99 (pre-HSDPA) transport channels are terminated at the RNC.
Retransmission procedure is located in the serving RNC.
The serving RNC (SRNC) may not be the controlling RNC (or drift RNC),
and it may be several hops away from the controlling RNC, increasing
response times.
For high speed data, this potential delay is not acceptable.
The new high speed channel, the HS-DSCH, terminates at Node B.
A new MAC layer, the MAC-hs, is introduced in the Node B in order to
control all retransmissions in the high speed data channel and provide a
quick response to channel errors.

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Hybrid ARQ Types
HARQ is an implicit link adaptation technique
It uses ACK/NACKS to produce correct packets (implicit adaptation to channel
conditions).
It uses samples weighted by the signal to noise ratio to combine received versions
of the packets, which provides time-diversity.
There are three types of ARQ:
Type I ARQ - a pure repetition mode, the original data block is retransmitted.
Variants are called Chase Combining, when the data block is soft-combined with the original block and
Optimum Combining, where each block is weighted by the signal to noise ratio and then combined.
Type II ARQ - This is called Full Incremental Redundancy (FIR) combining.
A non-self decodable retransmission is sent. This retransmission must be combined with the original
block in order to decode. It consists of parity bits and does not include the original data.
Type III ARQ - This is called Partial Incremental Redundancy (PIR)
The retransmitted block must be self-decodable, that is, it must include the original version of the data
in addition to any other redundant information.

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Fast Link Adaptation

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Link Adaptation by Transport Format
The HS-DSCH does not use fast power control.
The transmitted power in the HS-DSCH is substantially constant, depending on
power sharing for other downlink channels in the Node-B.
The adaptation to channel conditions is done by selection of the transport format,
such as modulation and coding rate.
The transport format may be changed every TTI (2 ms).
UE Node B
Transport Format:
Modulation and
Coding
Power measurement, CQI
selection
CQI report every
1 to 80 TTI’s
Transport Format selection, new
modulation and coding

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Link Adaptation
The transmitter receives information on the channel conditions from the UE and selects an
appropriate transport format for transmission.
Selects QPSK or 16QAM modulation.
Selects a specific coding rate that works well in those conditions (approximately a 10% block error rate).
Lets the HARQ process fine-tune the coding rate by use of retransmissions to bring down the error rate.
Link adaptation is fast, since it all happens in the Physical layer between the UE and the Node-B.
Example of Adaptive Modulation and Coding:

Page 20
Outline
Introduction

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Channels and Layers
Radio Link Control
(RLC)
Medium Access Control
(MAC)
Physical Layer
Layer 1
Layer 2
Transport Channels: How data is sent
Logical Channels: Type of data sent
Physical Channels: Media used for data

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Transport Channels
Transport Channels
Broadcast
Channel (BCH)
(Downlink)
Common ChannelsDedicated Channels
Downlink Shared
Channel(DSCH)
(Downlink)
Common Packet
Channel (CPCH)
(Uplink)
Forward-Access
Channel (FACH)
(Downlink)
Paging
Channel (PCH)
(Downlink)
Random-Access
Channel (RACH)
(Uplink)
Dedicated Channel (DCH)
(Down & uplink)
High Speed Downlink
Shared Channel
(HS-DSCH)

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Downlink Data Transport Channels
DCH- Dedicated Channel
Voice, data up to 2 Mbps
Long channel set-up times, long channel release time, not good utilization for bursty traffic
Fixed Spreading Factor (SF), code tree is reserved for maximum data rate
Fast power control
Soft handoffs
FACH- Forward Access Channel
Common channel, no channel set-up time required
Suitable for small IP packets, infrequent packets for interactive gaming
High power channel - no feedback from UE
No fast power control, fixed SF
No soft handoffs - so cell reselection process takes time
DSCH- Downlink Shared Channel
Paired with a DCH that carries control information
Suitable for bursty traffic, channel is shared by UE’s
Dynamic SF
Fast power control
No soft handoffs
HS-DSCH- High Speed- Downlink Shared Channel
Supports HSDPA, associated with HS-SCCH and HS-DPCCH

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HS-DSCH Attributes (Summary)
High Speed downlink channel to support high data rates
Shared among UE’s
No fast power control
No soft handoffs
Fixed SF (SF=16)
Fixed CRC size (24 bits)
Uses Adaptive Modulation and Coding (AMC) to support different data rates
Uses Hybrid ARQ (HARQ) to provide error-free operation
Support multi-code operation (up to 15 codes) for data rates up to 10 Mbps
Uses Turbo code R1/3, with rate adaptation to support other coding rates
Uses a short Transmission Time Interval (TTI) 2 msec long, consisting of 3 timeslots
(TSs) in order to achieve a short round trip delay
Possible to use beam-forming for broadcast to part of a cell, or to the entire cell
Possible to vary transmit power
Always associated with a DPCH and one or more DSCHs

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HS-SCCH (High Speed Shared Control Channel)
A DL channel which carries the information required to demodulate the HS-DSCH.
Every UE using the HS-DSCH is assigned an HS-SCCH by the Node-B.
The HS-SCCH has a fixed rate of 60 kbps, fixed Spreading Factor (SF) of 128 and
uses rate 1/3 convolutional coding.
The HS-SCCH block consists of three Time Slots (1 TS = 667 microseconds) and is
transmitted two time slots before the start of the HS-DSCH transmission in order to
allow the UE to demodulate the data.
An HS-SCCH block carries necessary information in two separate coding chains:
Part 1 information:
Coding information, according to the UE’s capabilities
Modulation used for the HS-DSCH, i.e., QPSK or 16 QAM
Part 2 information:
Redundancy information, to allow the UE to combine with prior information
HARQ process information
New date indicator, whether the transmission is a first transmission or a re-transmission
Transport block size

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HS-DPCCH (HS Dedicated Physical Control Channel)
An uplink control channel which uses SF=256 code multiplexed with other uplink
control channels.
Channel used to provide constant feedback to the Node-B on signal quality and packet
errors.
Transmitted 5 msec after the reception of the HS-DSCH frame.
This packet is divided into two parts:
ACK/NACK information part - One bit long transmitted in one timeslot, provides the result
of the CRC check after packet decoding and indicates whether a retransmission is required
or not.
Downlink Channel Quality Indicator (CQI) - 5 bits long transmitted in two timeslots, to
indicate what block size, modulation and number of parallel codes could be received with
reasonable error rate based on measured channel conditions. This information is used by the
Node-B to determine the modulation and coding to be used in the next HS-DSCH
transmission.

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Outline
Introduction
Spreading and Coding

Page 28
Channelisation & Scrambling
Channelisation spreads the input bits or symbols into a chip sequence by a factor
equal to the spreading factor. It separates the transmissions within a single source
(i.e., a sector or a UE). It uses Orthogonal Variable Spreading Factor (OVSF) codes
which are built by Walsh codes.
Scrambling multiplies the already spread sequence by a second code that separates
the sources of the data (i.e., different sectors in DL or different UE’s in UL). It uses
Gold Codes or shorter codes.
Cell 1 Cell 2 Cell nCell 3 Cell 4
ScramblingChannelisation &
Spreading
1 2
3
n432
1

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DL Channelization and Modulation
Channelization codes are OVSF (Walsh) codes with SF=16 for HS-DSCH
and SF=128 for HS-SCCH.
Modulation mapper maps symbols to the I and Q branches
For QPSK, symbols are sent alternatively to the I and Q branches
For 16QAM, two pairs of symbols are first mapped to a constellation value and then sent to
the I and Q branches alternatively
I
Downlink
physical
channel
Serial to
Parallel
Converter
Channelization
code, SF value
j
Scrambling
code
Q
I+jQ S
Modulation
Mapper

Page 30
Outline
Introduction

Page 31
HSDPA Protocol Architecture
UE Node B SRNC
Uu
Air Interface
IUb
Layer 1
MAC-hs
MAC-d
RLC
Transport
Frame
Protocol
MAC-d
RLC
Layer 1
MAC-hs
Transport
Frame
Protocol

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MAC Layer and MAC-hs
The Medium Access Control (MAC) layer maps the logical channels coming from the
Radio Link Control (RLC) function to the transport channels connecting it to the
Physical layer.
The MAC layer is responsible for selecting an appropriate transport format for each
transport channel based on the requirements of the logical channels.
The MAC-hs is a new MAC entity located in the Node-B (in order to be closer to the
air interface) and the UE, to support the HSDPA high speed channel.
MAC-hs is responsible for:
Handling the new high speed shared channel, HS-DSCH.
Managing physical resources allocated to HSDPA.
Other MAC entities:
MAC-d is responsible for handling the dedicated channels (DCH transport channel). It is
located in the Serving RNC (SRNC).
MAC-b handles the broadcast channel (BCH). It is located in the Node-B.
MAC-c/sh handles the common and the shared channels, including the DSCH. It is located
in the SRNC.

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MAC Architecture
MAC-d
MAC Control
MAC-c/shMAC-hs
HS-DSCH
PCCH BCCH CCCH CTCH DCCH DTCH
PCH FACH RACH CPCH DSCH DCH
Associated Downlink Associated Uplink
Signaling Signaling

Page 34
Outline
Introduction

Page 35
HSDPA Terminal Capabilities
UE Power Class
Power Class III is 24 dBm and Class IV is 21 dBm. Initially, most UEs fall in Class IV.
There are UE Categories defined for HSDPA:
14.0QPSK, 16-QAM11510
0.9QPSK2511
QPSK
QPSK, 16-QAM
QPSK, 16-QAM
QPSK, 16-QAM
QPSK, 16-QAM
QPSK, 16-QAM
QPSK, 16-QAM
QPSK, 16-QAM
QPSK, 16-QAM
QPSK, 16-QAM
Modulation
Scheme
1.81512
10.01159
7.21108
7.21107
3.6156
3.6155
1.8254
1.8253
1.2352
1.2351
Max data rate
(Mbps)
Min. Inter-TTI
interval
Max number of
parallel codes
Category
Reference UE capability combinations:
1.2 Mbps class 3.6 Mbps class 7.2 Mbps class 10 Mbps class

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UE Capability Classes
Examples of UE capability classes proposed in 3GPP are listed in Table below. Note
that more combinations are still possible.
1.2 Mbps class
3.6 Mbps class
7.2 Mbps class
10 Mbps class

Page 37
Thank you!

Hsdpa principles

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