HSDPA Fundamental

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HSDPA Fundamental

January 25th, 2011


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Outline

HSDPA Principles

HSDPA Channel Structure

HSDPA Power Allocation

Architectural Impact

Summary and Conclusions Abbreviations and references


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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


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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


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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


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Shared Channel Transmission

A set of radio resources dynamically shared amongmultiple 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


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Fast Channel-dependent Scheduling

Examples of scheduling algorithms Round Robin (RR)

Cyclically assign the channel to users without taking channelconditions 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


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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 controlconstant data rate possible)

High data rate

Low data rate


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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 UEcategories

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


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Ericsson AB 2009 | EricssonInternal | X (X) | Date

Higher Order ModulationAdding 64QAM on the Downlink

16QAM

4 bits/symbol2 bits/symbol

QPSK

64QAM

6 bits/symbol

1.8

3.6

7.2

21

Mbps

14.4

5 codes

5 codes

10 codes

15 codes

15 codes

Chip Rate = 3.84 Mchip/s

SF =16Code =15

Bit Rate = (3.84/16)*6*15

= 21.6 Mbps


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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 retransmissionsP1,1

P1,1

P1,2

P1,2

P2,1

P2,1

P2,2

P2,2

P3,1

P1,1 P2,1 P3,1

+ +

Transmitter

Receiver


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Architectural Impact

Fast adaptation to varying radio conditions and fastretransmissions 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)

CoreNetwork

RNC

Node B


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UE capabilities

HS-DSCHcategory

Maximum numberof HS-DSCHcodes received

L1 peak rates(Mbps)

User datathroughput P4(Mbps)

QPSK / 16 QAM

Category 1 5 1.2 Both




Category 5 5 3.6 3.36 Both

Category 6 5 3.6 3.36 Both





Category 11 5 0.9 QPSK

Category 12 5 1.8 QPSK

P4 time frame


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HSDPA Channel Structure

High-Speed Downlink Shared Channel HS-DSCH

High-Speed Shared Control Channel(s)

HS-SCCH Associated Dedicated Channel A-DCH

HS-D

SCHHS-SCCH

A-DCH

RBS A

RBS B

HS-D

SCHHS-SCCH

A-DCH

RBS A

RBS BRBS B


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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 andnumber of bits per transport block)

Hybrid ARQ information

One or a few HS-SCCH per cell

Never in soft handover SF = 128


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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


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The HSPA trace possibilities

Corporate ISP/Internet

RBS

RBS

RNC

HLR

Gi

Router /

Firewall

External

IP network

Gn

External

IP network

Services Network

(Application Server)

IuPS

Drive testing:

-TEMS-Wireshark/Ethereal

Passive measurements:

-RBS & RNC counters

Passive measurements:

-IuPS, Gn, Gi tracesPassive measurements:

-Wireshark/Ethereal

-Moniq


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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

HSDPA Fundamental

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