01 hsdpa principles
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The Overview of HSDPA
(High Speed Downlink Packet Access)
HUAWEI TECHNOLOGIES Co., Ltd.
Huawei Confidential
Page 1
Page 1
Outline
Introduction
HSDPA New Techniques
Transport and Physical Channels
Spreading, Modulation and Coding
Protocol Architecture
Terminal Capabilities
HUAWEI TECHNOLOGIES Co., Ltd.
Huawei Confidential
Page 2
Page 2
HSDPA Bit Rate Advantage
Typical average bit rate for different technologies in a medium loaded Macro cell.
2000
1800
1.5 Mbps
1600
1400
1200
kbps 1000
700 kbps
800
400 kbps
600
350 kbps
400
200
150 kbps
30 kbps
0
GPRS
HUAWEI TECHNOLOGIES Co., Ltd.
EDGE
WCDMA
EV-DO
Huawei Confidential
EV-DV
HSDPA
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HSDPA Latency Advantage
Typical average round trip time for different technologies. Smaller round trip times
would benefit interactive applications.
700
650 ms
600
500
ms
400
300
200 ms
200
100 ms
100
0
GPRS/EDGE R99
HUAWEI TECHNOLOGIES Co., Ltd.
WCDMA R99
Huawei Confidential
HSDPA R5
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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.
HUAWEI TECHNOLOGIES Co., Ltd.
Huawei Confidential
Page 5
Page 5
Outline
Introduction
HSDPA New Techniques
Transport and Physical Channels
Spreading, Modulation and Coding
Protocol Architecture
Terminal Capabilities
HUAWEI TECHNOLOGIES Co., Ltd.
Huawei Confidential
Page 6
Page 6
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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Huawei Confidential
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Page 7
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).
HUAWEI TECHNOLOGIES Co., Ltd.
Huawei Confidential
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Major New Techniques
Fast Scheduling
Fast Hybrid ARQ
Fast Link Adaptation
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Huawei Confidential
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Page 9
Fast Scheduling
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Huawei Confidential
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Page 10
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:
Channel
Quality
Selection of the best users in the cell in terms of
the UE’s received signal strength is known as multiuser 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.
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Huawei Confidential
UE1
UE2
TTI intervals
Node B
UE2
UE1
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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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Huawei Confidential
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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:
HUAWEI TECHNOLOGIES Co., Ltd.
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Outline
Introduction
HSDPA New Techniques
Transport and Physical Channels
Spreading, Modulation and Coding
Protocol Architecture
Terminal Capabilities
HUAWEI TECHNOLOGIES Co., Ltd.
Huawei Confidential
Page 20
Page 20
