Broadband Wireless Access – HSPA and LTE - 3G, 4G · PDF fileBroadband Wireless Access – HSPA and LTE Dr Stefan Parkvall Senior Specialist, Adaptive Radio Access ... but many basic

© Ericsson AB 2008 1

Broadband Wireless Access –HSPA and LTE

Dr Stefan ParkvallSenior Specialist, Adaptive Radio AccessEricsson Research


Mobile Broadband

HSPAHSPA

LTELTE

TurboTurbo--3G3G


936 HSPA Devices from 120 Suppliers!

Source: GSMA, November 2008


HSPA – The Global Broadband Standard

278 Operators in 93 Countries

Source: GSMA, November 2008

So…what is HSPA and LTE?


Trend – Data is overtaking Voice

4 million new HSPA subscribers per month, 56 million in total

>240 million WCDMA/HSPA subscribers world wide

High speed packet data Packet data Speech

Source: GSMA and NetQB, September 2008

Data is overtaking voice......but previs cellular systems designed primarily for voice


HSPA and LTE = Mobile Broadband

HSPA – High-Speed Packet Access– Evolution of 3G/WCDMA to enhance packet-data support – Gradually improved performance at a low additional cost– Data rates up to ~40 Mbit/s in 5 MHz

LTE – Long-Term Evolution– Significantly improved performance in a wide range of spectrum allocations– Data rates up to ~300 Mbit/s in 20 MHz– Takes Mobile Broadband into IMT-Advanced (”4G”)

Different systems – but many basic principles are similar!

HSPAHSPA HSPA evolutionHSPA evolutionHSDPAHSDPA

2004 2006 20082002

Studies Spec’s

LTELTE LTELTE--AdvancedAdvanced

Requirements

WCDMAWCDMA

2005 2007


Wireless vs Wireline

Wireless seems simple…

∇×H

∇⋅D = ρ

∇⋅B = 0

∇×E = - ∂B∂t

= J + ∂D∂t

…so what’s the problem?


Radio Channels and Packet Data

Radio channel quality varies...– ...distance to base station– ... random variations in the

environment

Traffic pattern varies...– ...user behavior– ...server load

Adapt to and exploit channel and traffic variations!


Rate Control

Reliable reception requires a certain Eb/N0

How to control Eb?– Eb = P•T

Cha

nnel

Q

ualit

y

TxP

ower

Dat

a R

ate

Power Control

Dat

a R

ate

Cha

nnel

Q

ualit

y

TxP

ower

Rate Control

Rate control more efficient than power control!

Varying instantaneous data rate acceptable for packet-data services– Rapid – tracks fast fading


Rate Control

Data rate controlled through...

...different channel coding rates– Advantageous channel conditions high code rate– Code rates from 1/3 to ~1

...different modulation schemes– Advantageous channel conditions higher-order modulation

...different multi-antenna schemes

QPSK 16QAM 64QAM


Shared-Channel Transmission

Dedicated channel– User resources assigned at ”call

setup”– Independent of instantaneous traffic

situation

Shared channel– Dynamic sharing of common

resource– Adapts to instantaneous traffic

situation


Channel-dependent Scheduling

Scheduling determines at each time instant…– …to whom to assign the shared channel– …which data rate to use

Basic idea: transmit at fading peaks– May lead to large variations in data rate between users– Tradeoff: fairness vs cell throughput

Cha

nnel

Qua

lity User #1

User #2

User #3

Time#1 #3 #2 #3 #1

Effective channel variations seen by the base station



Round Robin (RR)– Cyclically assign the channel to users without taking channel

conditions into account– Simple but poor performance

Max C/I– Assign the channel to the user with the best channel quality– High system throughput but not fair

Proportional Fair (PF)– Assign the channel to the user with the best relative channel

quality– High throughput, fair

Rad

io L

ink

Qua

lity

Time

Rad

io L

ink

Qua

lity

Time

Rad

io L

ink

Qua

lity

Time


data1data2data3data4

TimeFrequency

User #1 scheduled

User #2 scheduled

1 ms

180 kHz

Time-frequency fading, user #1

Time-frequency fading, user #2


HSPA – channel-dependent scheduling in time-domain only

LTE – channel-dependent scheduling in time and frequency domains


Channel Quality Indication

Scheduling and rate control adapts to channel variations

Problem: need channel knowledge at the base station

Solution: terminals transmit channel-quality reports to base station

Reporting rate configurable– HSPA – reports as often as every 2 ms– LTE – reports as often as every 1 ms


Hybrid ARQ with Soft Combining

Retransmsision of erroneously received packets– Fast no disturbance of TCP behavior

Soft combining of multiple transmission attempts– Soft combining improved performance

NAK

ACK

NACK

ACK

ACK

+ +

Transmitter

Receiver

P1,1 P1,2 P2,1 P2,2 P3,1

P1,1 P1,1 P2,1 P2,2 P3,1

P1,2 P2,2


R=3/4

redundancy version 1

Initial transmission

Transmitted bits

Bits input to decoder

Resulting code rate

Accumulated energy

Eb

CRC insertion,Turbo coding

Data

Puncturing to• generate different redundancy versions

• match the number of coded bits to the channel


R=3/8

First retransmission

2Eb


R=1/4

Second retransmission

3Eb

Hybrid ARQ with Soft Combining

Incremental redundancy

R=1/4

Third retransmission


4Eb


Basic Principles – Summary

Shared channel transmission

Channel-dependent scheduling

Rate control

Hybrid-ARQ with soft combining


Summary

Adapt to and exploit– variations in radio channel quality– variations in the traffic pattern

…instead of combating them!

Traffic pattern is time varying

Radio channel quality is time varying

Work in 3GPP


History

NMT, ...NMT, ...Analog, speechAnalog, speech

1980 1990 2000 2010

GSM, ...GSM, ...Digital, speech and lowDigital, speech and low--rate datarate data

HighHigh--speed data speed data (up to ~20 Mbps)(up to ~20 Mbps)

WCDMA/HSPAWCDMA/HSPA

20 MHz

5 MHz

200 kHz

HighHigh--speed data speed data (up to 300 Mbps)(up to 300 Mbps)

LTELTE

30 kHz

Research and standardization




””4G4G””

3G Evolution

R99 Rel4 Rel5 Rel6 Rel7 Rel8

LTELTE

HSPAHSPAWCDMAWCDMA HSPA evolutionHSPA evolutionHSDPAHSDPA

HSPA evolution– gradually improved performance at a low additional cost

in 5MHz spectrum allocation

LTE– significantly improved performance in a wide range of spectrum allocations– further evolved into IMT-Advanced

LTE AdvancedLTE Advanced

Rel10

1999 2002 2005 2007 2008


PCG(Project coordination

group)

TSG GERAN(GSM EDGE

Radio Access Network)

TSG RAN(Radio Access Network)

WG2Radio Layer 2 &

Layer 3 RR

WG1Radio Layer 1

WG3Iub, Iuc, Iur &

UTRAN GSM Req.

WG4Radio Performance& Protocol Aspects.

WG2Protocol aspects

WG1Radio Aspects

WG3Terminal testing

TSG SA(Services &

System Aspects)

WG2Architecture

WG1Services

WG3Security

WG4Codec

TSG CT(Core Network &

Terminals)

WG3Interworking withExternal Networks

WG1MM/CC/SM (Iu)

WG4MAP/GTP/BCH/SS

WG5OSA

Open Services Access

WG5Mobile Terminal

Conformance Test

WG5Telecom

Management

WG6Smart Card

Application Aspects

3GPP

International organization– Vendors and operators co-operate– Develop specifications for GSM, WCDMA/HSPA, LTE


Standardization – a Flying Circus?

RAN1 meetings held ~8 times a year– Meetings run from Monday to Friday– Held in various countries in Europe, North America, and Asia

Meeting schedule 2007– January 15-19, Sorrento, Italy– February 12-16, St Louis, USA– March 26-30, St Juliens, Malta– April 17-20, Beijing, China– May 7-11, Kobe, Japan– June 25-29, Orlando, USA– August 20-24, Athens, Greece– October 8-12, Shanghai China– November 5-9, Seoul Korea


Typical RAN1 Meeting

Approx 200 delegates attending and ~550 documents submitted...Number of Contributions per Agenda Item

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Broadband Wireless Access – HSPA and LTE - 3G, 4G · PDF fileBroadband Wireless Access – HSPA and LTE Dr Stefan Parkvall Senior Specialist, Adaptive Radio Access ... but many basic

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