hsdpa basics.pdf

Network & Technology Consulting


System Engineer

WCDMA Radio Network Methods

EAB/RGT/M

HSDPA Basics

Filiz Gulkan


Outline

HSDPA Principles

HSDPA Channel Structure

HSDPA Power Allocation

Architectural Impact

Summary and Conclusions

Abbreviations and references


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


What is High Speed Downlink Packet Access (HSDPA)?

STANDARDIZED Integral part of WCDMA (3GPP Release 5)

REDUCED DELAY Reduced round trip time

CAPACITY 2 3 times improved system throughput

SPEED Higher bit rates: up to 14 Mbps

Smooth Upgrade Short time to market with existing sites


Key Idea in HSDPA

Fast adaptation of

transmission parameters to

fast variations in radio

conditions

Main functionality to support HSDPA

Fast link adaptation

Fast Hybrid ARQ

Fast channel-dependent scheduling


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


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


Shared Channel Transmission

A set of radio resources dynamically shared among multiple 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



Scheduling = which UE to transmit to at a given time instant and at what rate

Formally part of MAC-hs (a new MAC sub-layer in RBS)

Basic idea: transmit at 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



Examples of scheduling algorithms

Round Robin (RR)

Cyclically assign the channel to users without taking channel conditions 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


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 control constant data rate possible)

High data rate

Low data rate


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 UE categories

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


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 retransmissions

P1,1

P1,1

P1,2

P1,2

P2,1

P2,1

P2,2

P2,2

P3,1

P1,1 P2,1 P3,1

+ +

Transmitter

Receiver


HS-DSCH Power Allocation

HS-DSCH must share the transmission power with all other channels

Dynamic power allocation

Allocate remaining power to HS-DSCH transmission

Best power utilization

HS-DSCH

Common channels (not power controlled)

Dedicated channels (power controlled)

To

tal

avail

ab

le c

ell p

ow

er


Architectural Impact

Fast adaptation to varying radio conditions and fast retransmissions

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)

Core

Network

RNC

Node B


UE capabilities

HS-DSCH

category

Maximum number

of HS-DSCH

codes received

L1 peak rates

(Mbps)

User data

throughput 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


HSDPA channel structure

RNC RNC Iur

Iub Iub

Iu Iu

Associated

Dedicated

Channels


HSDPA Channel Structure

High-Speed Downlink Shared Channel HS-DSCH

High-Speed Shared Control Channel(s) HS-SCCH

Associated Dedicated Channel A-DCH

HS-DSCHHS-SCCH

A-DCH

RBS A

RBS B

HS-DSCHHS-SCCH

A-DCH

RBS A

RBS BRBS B


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 and number of bits per transport block)

Hybrid ARQ information

One or a few HS-SCCH per cell

Never in soft handover

SF = 128


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


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


Abbreviations

A-DCH Associated Dedicated Channel

ARQ Automatic Repeat Request

CQI Channel Quality Indicator

DCH Dedicated Channel

G-RAKE Generalized RAKE

HS-SCCH High-Speed Shared Control Channel

HS-DPCCH High-Speed Dedicated Physical Control Channel

HS-DSCH High-Speed Downlink Shared Channel

MAC-hs Medium Access Control - High Speed

NAS Non-Access Stratum

PS Packet Switched


Abbreviations (cont.)

QAM Quadrature Amplified Modulation

QPSK Quadrature Phase Shift Keying

R99 Release 99 of WCDMA specification

RA Rural Area

RRC Radio Resource Control

RTT Round Trip Time

RX Receiver

SF Spreading Factor

TF Transport Format

TTI Transmission Time Interval

TX Transmitter


References:

WCDMA eveolved : High-speed packet-data

services, Stefan Parkvall, et al.


Agenda

HSDPA Basics

Filiz Gulkan

System Engineer

WCDMA Radio Network Methods,

WCDMA Radio Network System

Management

[email protected]

hsdpa basics.pdf

Documents

ms slide

channel conditions

ms tti

fast variations

ms rel

fair slide

scheduled user slide

ms short tti