Broadband Wireless Access – HSPA and · PDF fileBroadband Wireless Access – HSPA...

© 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?


Mobile Broadband is Already Here!

Rapid subscriber growth Rapid traffic growth

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 previous cellular systems designed primarily for voice

Sept 2006 July 2008


HSPA and LTE = Mobile Broadband

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

LTELTE LTELTE--AdvancedAdvanced

R99 Rel4 Rel5 Rel6 Rel7 Rel8

HSPAHSPAWCDMAWCDMA HSPA evolutionHSPA evolutionHSDPAHSDPA

Rel10

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

Different systems – but many basic principles are similar!


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!

LTE – An Overview


LTE – Spectrum Flexibility

Operation in differently-sized spectrum allocations– From 1.4 MHz to 20 MHz

system bandwidth

Support for paired and unpaired spectrum allocations

UplinkDownlink

frequency

timeFDD

frequency

timeHalf-duplex FDD

(terminal-side only)

frequency

timeTDD


LTE – Basic Principles

Downlink – OFDMParallel transmission on large number of narrowband subcarriers

Uplink – DFTS-OFDMDFT-precoded OFDM

Benefits:– Avoid own-cell interference– Robust to time dispersion

Main drawback– Power-amplifier efficiency

Tx signal has single-carrier propertiesImproved power-amplifier efficiency– Improved battery life – Reduced PA cost– Critical for uplink

Equalizer needed Rx Complexity– Not critical for uplink

Cyclic-prefixinsertion

OFDM modulatorDFT precoder

DFT IFFTIFFT Cyclic-prefixinsertion



Shared-channel transmission– Packet-data only– No CS support

Channel-dependent scheduling– In time and frequency

Hybrid-ARQ with soft combining

data1data2data3data4


Multi-antenna support– Integral part of LTE– All terminals support at least 2 Rx antennas

TXTX

MultiMulti--layer transmissionlayer transmission((““MIMOMIMO””))

Reduced Tx powerICIC– Inter-Cell Interference Coordination– To improve cell-edge performance

MBSFN– Multicast-Broadcast Single-Frequency Network



LTE – Time-domain Structure

Frame structure type 1 for FDD (full and half duplex)

Frame structure type 2 for TDD– Similar to FS1...but with a special subframe for DL-to-UL switch

ULDL

One radio frame, Tframe = 10 ms

One subframe, Tsubframe = 1 ms

fULfDL

Subframe #0 #1 #2 #3 #4 #5 #6 #7 #8 #9

ULDL

DwPTS GP UpPTS

fDL/UL

(special subframe) (special subframe)


LTE – Physical Resources

Time domain structure:– 10 ms frame consisting of 10 subframes of length 1 ms– Each subframe consists of 2 slots of length 0.5 ms– Each slot consists of 7 OFDM symbols (6 symbols in case of extended CP)

Resource element (RE)– One subcarier during one OFDM symbol

Resource block (RB)– 12 subcarriers during one slot (180 kHz × 0.5 ms)

One subframe (1 ms)

One slot (0.5 ms)

One frame (10 ms)

One resource element

12 sub-carriers

TCP Tu


Segmentation, ARQ

Ciphering

Header Compr.

Hybrid ARQHybrid ARQ

MAC multiplexing

Antenna and resrouce mapping

Coding + RM

Data modulation

Antenna and resource mapping

Coding

ModulationAntenna and resource assignment

Modulationscheme

Sche

dule

r

Retransmission control

Priority handling, payload selection

Payload selection

RLC

PHY

PDCP

User #i User #j

Reassembly, ARQ

Deciphering

Header Compr.


MAC demultiplexing

Antenna and resrouce mapping

Coding + RM

Data modulation

Antenna and resource demapping

Decoding

Demodulation

RLC

PHY

PDCP

MAC

Red

unda

ncy

vers

ion

IP packet IP packet

SAE bearers

Radio Bearers

Logical Channels

Transport Channel

MAC

MAC

LTE – Protocol Architecture

Packet Data Convergence Protocol– Header compression to

reduce overhead– Ciphering for security

Radio Link Control– Segmentation/concatenation– RLC retransmissions– In-sequence delivery

Medium Access Control– Multiplexing of radio bearers– Hybrid-ARQ retransmissions

Physical Layer– Coding, Modulation– Multi-antenna processing– Resource mapping


SAE – Architecture

Core network evolved in parallel to LTE– EPC – Evolved Packet Core

Flat architecture, single RAN node, the eNodeB– Compare HSPA, which has an RNC

RNC RNC

to other Node Bs to other Node Bs

Dedicated channels

NodeBUE

PSTN Internet

Core Network

LTELTE HSPAHSPA

eNodeBUE

Internet

Core Network

S1 S1

X2


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


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– Number of transmission layers selected to match channel rank

QPSK 16QAM 64QAM


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 absolute 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


Hybrid-ARQ with Soft Combining

Retransmsision of erroneously received packets– Fast (8 ms roundtrip time) no disturbance of TCP behavior

Soft combining of multiple transmission attempts– Soft combining improved performance

Hybrid-ARQ retransmissions complemented by RLC retransmissions

Process transport block 3 Process transport block 5

Process #0Process #1

Process #2

1 12 3 5 14

Process transport block 2 Process transport block 4

Process transport block 1 Process transport block 1 Process transport block 1

Hybrid-ARQprotocol

To RLC for in-sequence delivery

Block 2

Process #7

Block 3 Block 4 Block 5 Block 1


R=1

redundancy version 1

Initial transmission

Transmitted bits

Bits input to decoder

Resulting code rate

Accumulated energy

Eb

CRC insertion,Turbo coding, rate 1/3

Data

Puncturing to• generate different redundancy versions

• match the number of coded bits to the channel


R=1/2

First retransmission

2Eb


R=1/3

Second retransmission

3Eb

Hybrid ARQ with Soft Combining

Incremental redundancy

R=1/3

Third retransmission


4Eb


Interaction with RLC

Why two retransmission mechanisms, RLC and hybrid-ARQ?– Answer: difference in feedback signaling

Hybrid ARQ [with soft combining]– Fast retransmission, feedback every 1 ms interval– Frequent feedback need low overhead, single bit– Single, uncoded bit errors in feedback (~10-3, too high for TCP)

RLC– Reliable feedback (sent in same manner as data)– Multi-bit feedback less frequent longer delay

Hybrid-ARQ and RLC complement each other

Segmentation, ARQARQ


MAC multiplexing

RLC

MAC


Multi-antenna transmission

Diversity for improved system peformance

Beam-forming for improved coverage(less cells to cover a given area)

SDMA for improved capacity(more users per cell)

Multi-layer transmisson (”MIMO”) for higher data rates in a given bandwidth

The multi-antenna technique to use depends on what to achieve

TX



One, two, or four antenna ports

Multiple antenna ports multiple time-frequency grids

Each antenna port defined by an associated reference signal

Single-antenna transmisson Multi-antenna transmisson

TX



Spatial Multiplexing – Multiple parallel data streams Higher data rates– One or two code words– Number of layers ≤ Number of antenna ports

Transmit Diversity (”open-loop”)– Transmission of same information from multiple antenna ports Diversity– One code word– Number of layers = Number of antenna ports

Layermapping Precoding

Up to four layers

RE mappingUp to four

antenna ports

RE mapping

One or two code words

Multi-antenna processing

TX


LTE – Example of Testbed Results20 MHz, 2x2 MIMO

Throughput– Max 154 Mbit/s– Mean 78 Mbit/s– Min 16 Mbit/s

Terminal speed – Max 45 km/h– Mean 16 km/h– Min 0 km/h

Distance– Max 710 m– Mean 360 m– Min 50 m

12

23

37

54

74

97

123

154

Ericsson Head OfficeEricsson Head Office

LTE Testbed2007


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

Shared-channel transmission Channel-dependent scheduling Rate adaptation Hybrid ARQ with soft combining

Basic Tools

TX


Work in 3GPP


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


3GPP Organization

PCGProject Coordination Group

TSG RAN

RAN WG1Radio L1

RAN WG2L2/L3

RAN WG3NW protocols

RAN WG4Core, Perf req.

RAN WG5MT conf. testing

WCDMA/HSPAand LTE

TSG GERAN

GERAN1Radio

GERAN2Protocol

GERAN3Testing

GSM/GPRS

TSG SA

SA1Services

SA2Architecture

SA3Security

SA4Codec

SA5Telecom Mgmt.

ServicesOverall System

TSG CT

CT1MM/CC/SM

CT3Interworking

External NWs

CT4MAP/GTP/BCH/SS

CT5Open Service Access

CT6Smart Card Apl.

Core Network


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

0

20

40

60

80

100

120

Appr

oval

of t

he a

gend

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of t

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of R

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Rel

ease

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Evol

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Fra

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Fina

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Dow

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sign

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Upl

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Con

trol S

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Map

ping

of v

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ourc

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to p

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Bit s

cram

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Fina

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Tim

ing

sync

hron

izat

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UL/

DL

Pow

er C

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Inte

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renc

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oord

inat

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RAC

H ti

min

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d pr

eam

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sequ

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sel

ectio

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Proc

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nlin

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Proc

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Cat

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ighe

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(FD

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Upl

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FAC

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Stud

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m o

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Standardization in Practice

Contribution driven

Decision by consensus– Coffee breaks important part of meetings (off-line)

Good relations important– Social relations across cultural borders– Mutual respect and co-operation

One week meetings Long meeting days


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