1 © 2006 Nokia

3G long-term evolution

by Stanislav Noncheve-mail : stanislav.nonchev@tut.fi

2 © 2006 Nokia

Contents

Radio network evolutionHSPA conceptOFDM adopted in 3.9GScheduling techniques

3 © 2006 Nokia

3G long-term evolution – Roadmap

Radio Network EvolutionHSDPA conceptScheduling techniques

Starting point:

ExistingGSM/EDGE &

WCDMA/HSDPAinfrastructure

4 © 2006 Nokia

3G long-term evolution – Key requirements

High data rates / user througput

Improved spectrum efficiency

Significantly redused delay / latency

Packet – domain services only

(including e.g. VoIP)

Spectrum flexibility

5 © 2006 Nokia

3G LTE - Complementary radio technologiesM

obili

ty a

nd c

over

age

Vehicular

Pedestrian

Stationary

0.1 1 10 100 1000

WCDM

A Rel 4

3G Future

Evolution

Cdm

a2000 1X, EDG

E

Evolved 3G 4Gresearch target

1xEV-DO

WLAN802.11a,g

WLAN802.11b

WLAN802.11n

802.16(WiMax)

Flarion

UMTS-TDD(IP Wireless)

HSDPA

1xEV-DVData Rate (Mbps)

6 © 2006 Nokia

3G LTE – data rates

WCDMA384kbps DL384kbps ULRTT ~150msCS/PS

HSDPA14.4Mbps peak

RTT ~100msPS

HSUPA

5.7Mbps peakRTT ~50msPS

Towards 4G

2009/102007/82005/62003/4

UTRA evolution : WCDMA: 5MHz UTRA Long term evolution: Up 20 MHz BW

Approx. year of roll-out

New radio access technique

EUTRA100Mbps peak DL50Mbbps peak ULRTT ~10msPS only

3GPP Rel.99/4 Release 5 Release 6 Release 7-8 ?

2011/12

Latency improvementsCapacity enhancements

7 © 2006 Nokia

3G LTE – spectrum flexibility

• Operation in all cellular bands

- 2600 MHz, 2100 MHz, 1900 MHz, 1700 MHz, 900 MHz, 800 MHz, 450 MHz, etc

. . . as well as other frequency bands

• Efficient operation in differently-sized spectrum allocations

- Up to 20 MHz to enable very high data rates

- 5 MHz (or less) to enable migration of e.g. 2G spectrum

8 © 2006 Nokia

3G LTE – WCDMA Evolving to HSPA

What is HSPA ???HSPA – High Speed Packed AccessHSPA = HSDPA + HSUPA

9 © 2006 Nokia

3G LTE - HSDPA

Peak data rates increased to significantly higher than 2 Mbps; Theoretically exceeding 10 Mbps

Packet data throughput increased 50-100% compared to 3GPP release 4

Reduced delay from retransmissions.

Solutions• Adaptive modulation and coding - QPSK and 16-QAM

• Layer1 hybrid ARQ

• Short frame 2ms

Schedule in 3GPP• Part of Release 5

• Firstspecificationsversion completed 03/02

HSDPA

AMC

MIMO ?

Short Frame Size(TTI=2 ms)

Fast Packet Scheduling

H-ARQ

Potential features in Rel’6

Agreed features in Rel’5

10 © 2006 Nokia

3G LTE - HSDPA

• Shown code rates are examples since real values are given by transport block size as well as transmission and rate matching parameters.

• 16QAM with 15 multi-codes supports >10Mbit/s throughput. QPSK alone can support up to 5.3 Mbit/s (up to 7.2 Mbit/s by disabling coding).

• Theoretically up to 14.4 Mbit/s can be sustained but 3GPP hardware specifications do not support it (+ interference problems from e.g. synchronization channel).

QPSK

1/4

Modulation EffectiveCode rate

2/4

3/4

16

SF

16

16

16QAM2/4

3/4

16

16

1.2 Mbit/s

Data rate(10 codes)

2.4 Mbit/s

3.6 Mbit/s

4.8 Mbit/s

7.2 Mbit/s

1.8 Mbit/s

Data rate(15 codes)

3.6 Mbit/s

5.3 Mbit/s

7.2 Mbit/s

10.7 Mbit/s

600 kbit/s

Data rate(5 codes)

1.2 Mbit/s

1.8 Mbit/s

2.4 Mbit/s

3.6 Mbit/s

4/416 4.8 Mbit/s 7.2 Mbit/s2.4 Mbit/s

SF – spreading factor

11 © 2006 Nokia

3G LTE - HSUPA

Peak data rates increased to significantly higher than 2 Mbps; Theoretically exceeding 5.8 Mbps

Packet data throughput increased, through not quite high numbers expected as with HSDPA

Reduced delay from retransmissions.

Solutions• Layer1 hybrid ARQ

• Node B based scheduling for uplink

• Frame sizes 2 ms & 10 ms

Schedule in 3GPP• Part of Release 6

• Firstspecificationsversion completed 12/04

12 © 2006 Nokia

3G LTE - HSUPA

• Shown code rates are examples since real values are given by transport block size as well as transmission and rate matching parameters.

• Theoretically up to 5.76 Mbit/s can be sustained

BPSK

1/4

Modulation EffectiveCode rate

3/4

4/4

960 kbit/s

Data rate(2 codes)

1.44 Mbit/s

1.92 Mbit/s

1.92 Mbit/s

Data rate(4 codes)

2.88 Mbit/s

3.84 Mbit/s

480 kbit/s

Data rate(1 code)

720 kbit/s

950 kbit/s

2.88 Mbit/s

Data rate(6 codes)

4.32 Mbit/s

5.76 Mbit/s

13 © 2006 Nokia

Evolution to 3.9G and 4G

• The first discussions about the UTRAN (UMTS Radio Access Network) LTE -November 2004. Release 8 expected ???

• Raise the performance of WCDMA

• System performance requirements for 3.9G• Peak Data Rate up to 100 Mbps DL; 50 Mbps UL

• User Throughput• DL: 2 to 3 times to rel-6 HSDPA

• UL: 2 to 3 times to rel-6 HSUPA

• Spectrum Efficiency• DL: 3 to 4 times to rel-6 HSDPA (MIMO included)

• UL: 2 to 3 times to rel-6 HSUPA

• Mobility: Optimized up to 15 km/h, 120 km/h with high performance, cellular NW mobility supported up to 350 km/h.

14 © 2006 Nokia

OFDM for 3.9G ?

• The problems in high bit rate transmissin• Multi-path interference• Affected by impulse noise• ...

• OFDM can solve many problems that will appear in high-bitrate transmission system

• Multi-path ImmunityAchieved using cyclic-prefix > channel delay-spread

• Bandwidth (spectral) EfficiencyAchieved using sub-carrier orthogonality

• Narrowband interferenceAchieved using large number of subcarrier

• Inpulse NoiseAchieving using FFT demultiplaxing

• OFDM is adopted in 3.9G!

15 © 2006 Nokia

What is OFDM?

• OFDM – Orthogonal Frequency Division Multiplaxing• N sub-channel signals generated jointly to make sure they are orthogonal each other• In traditional FDM, signals are generated separately for each sub-carrier• So in case of frequency resource allocation, OFDM is very similar to conventional

FDM

OFDM can achieve large delay spread tolernce at high bit rate by:• Converting single bit stream into N paralel bit streams

• Symbol duration is increased, so relative delay spread decreases• Each parallel bit stream is modulated on one of N sub-carriers

• Adding a guard time to each OFDM symbol• Inter symbol interference (ISI) is avoided• Guard loss is made small (<1 dB) by choosing N large enough

16 © 2006 Nokia

OFDM cont

Total channel bandwidth

Transmitted frequency spectrum:

S/P IFFT CPM-QAM

Transmitter structure Receiver structure

S/P FFTCPRe-

moval

1 TapEqua-lizer

M-QAM

Pros• Flexible and efficient spectrum usage.• Well suited for both unicast and multicast• Robustness against narrowband interference• Excellent robustness in multipath environments

using Cyclic Prefix• Simple frequency domain equalizer based on FFT• Superior performance in MIMO applications (due to

narrow carriers)• Frequency diversity and scheduling can be easily

utilized

Cons• Severe High PAPR• Non-linear amplification destroys orthogonality

between sub-carriers• Sensitive to phase noise for low carrier

spacing• Sensitive to frequency, clock an phase offset• Requires overhead to Cyclic Prefix

17 © 2006 Nokia

OFDM cont.

• Guard time and cyclic prefix• Guard time

The guard time is chosen larger than the expected delay spread, such that multi-path components from one symbol can not interfere with the next symbol. The guard time could consist of no signal at all. However, in that case the problem of inter carrier interference (ICI) would arise. ICI is cross-talk between different sub-carriers, which mean that they are not orthogonal.

• Cyclic prefix (CP)

CP helps the signal to be protected against both ISI and ICI

CP ensures that delayed replicas of the OFDM symbol always have an integer number of cycles within the FFT interva. In this way, the orthogonality is preserved and no ICI is present in the received signal.

18 © 2006 Nokia

OFDM cont.Flexible and efficient communications systems - by applying OFDM in combination with multiple access schemes such as CDMA, TDMA or FDMA.

• In OFDM-CDMA each user is assigned with a subset of orthogonal codes, so the information symbols can be spread in either the time or frequency domain.

• In OFDM-TDMA each user occupies whole bandwidth, but differentiated by different time slots.

• OFDM-FDMA (OFDMA) scheme allocates to each user a unique group of sub-carriers, which is part of system bandwidth.

19 © 2006 Nokia

3G LTE – 4G ?

Next step after 3.9G is 4G

Research stage

Part of All – IP network

Data rates > 1 Gbps

Price/performance

20 © 2006 Nokia

Packet schedulerWhat is the task of Packet Scheduler ?

• The task of Packet Scheduler (PS) is to select a most suitable user to access the channel in order to optimise throughput, fairness, and delayperformances.

• Fast packet scheduler is the mechanism determining which user to transmit to in a given transmission time interval (TTI)

• It is a key element in the design of packet-data system as it to a large extent determines the overall behavior of the system.

21 © 2006 Nokia

Scheduling principle - HSDPA

• Fast scheduling is done directly in Node-B based on feedback information from UE and knowledge of current traffic state.

UE2

Channel quality(CQI, Ack/Nack, TPC)

Channel quality(CQI, Ack/Nack, TPC)

Data

Data

Users may be time and/or code multiplexed

New base station functions• HARQ retransmissions• Modulation/coding selection• Packet data scheduling (short TTI)

New base station functions• HARQ retransmissions• Modulation/coding selection• Packet data scheduling (short TTI)

UE1

0 20 40 60 80 100 120 140 160-202468

10121416

Time [number of TTIs]

QPSK1/4

QPSK2/4

QPSK3/4

16QAM2/4

16QAM3/4

Inst

anta

neou

s EsN

o [d

B]

22 © 2006 Nokia

UE2

Channel quality(CSI, Ack/Nack)

Channel quality(CSI, Ack/Nack)

Data

Data

UE1

Multi-user selection diversity(give shared channel to “best” users)

USER 1 Es/N0USER 2 Es/N0

Scheduled user

Packet scheduling can utilize information on the instantaneous channel

conditions for each user.

Scheduling

freqtime

23 © 2006 Nokia

HARQ

What is HARQ ?

• HARQ is a transmission scheme that combines an error detection/correction with a retransmission mechanism of the erroneous packet

• HARQ is based on Stop-And-Wait (SAW) protocol • Four types of HARQ schemes.

• Conventional ARQ • HARQ with Chase Combining• HARQ with full IR• HARQ with Partial IR

24 © 2006 Nokia

HARQ : Chase Combining

25 © 2006 Nokia

HARQ: Incremental Redundancy

26 © 2006 Nokia

Adaptive Modulation and Coding

AMC - adjusts modulation and coding rate according to the current radio channel conditions

Modulation schemes – QPSK, 16QAM, 64 QAM …• HSDPA – higher order modulation is 16 QAM• 3.9 G - higher order modulation is 64 QAM

Link Adaptation is performed my AMC• UEs is needed to conduct LA• CQI information

27 © 2006 Nokia

Blind Scheduling Methods• Round RobinThe priority is defined as:

i=1,..,Nwhere,

is the priority of user i at time instant t is the queuing time of user i since the last channel access.

• Average C/IThe priority is defined as:

i=1,..,Nwhere,

is the average channel quality of user i at time instant t

( ) ( )tQtP ii =

( )tPi

( )tQi

( ) ( )tCtP ii =

( )tCi

Scheduling techniques

28 © 2006 Nokia

Scheduling techniques (cont.)

• Fair ThroughputThe priority is defined as:

i=1,..,N

where,represents the average offered data rate for user i at time instant t

Intelligent Scheduling Methods• Maximum C/IThe priority is defined as:

i=1,..,Nwhere,

is the channel quality of user i at time instant t

( )( )tT

tPi

i1

=

( )tTi

( ) ( )tCtP ii =

( )tCi

29 © 2006 Nokia

Scheduling techniques (cont.)

• Proportional FairThe priority is defined as:

i=1,..,N

where,is the supportable data rate for user i at time instant t

• Fast Fair ThroughputThe priority is defined as:

i=1,..,N

where,is the average supportable data rate of user i

is the max. of the average supportable data rates taken over all users j

( )( )tTtRtP

i

ii

)(=

( )tRi

( )( )

{ }⎥⎥⎦

⎤

⎢⎢⎣

⎡=

)()(max)(

tRtR

tTtRtP

i

jj

i

ii

{ })(max tRjj

)(tRi

ii

ioldi

i Rt

Tt

T 111 , +⎟⎟⎠

⎞⎜⎜⎝

⎛−= 1/ ti is called the forgetting factor

30 © 2006 Nokia

Benefit of Node-B Based Scheduling

Enables to allow more high bit rate users with faster data rate control

31 © 2006 Nokia

Frequency Domain Scheduling

New scheduling schemes for beyond 3G

• Possible only with OFDMA

• Performed for a sub-band instead of a time slot

• Could be combined with TD scheduling schemes• De-coupled time - frequency domain schedulers

• Coupled time - frequency domain schedulers

32 © 2006 Nokia

Performance comparison of PS

Packet scheduling performance

33 © 2006 Nokia

Performance comparison of PS (cont.)

Packet scheduling performance

With different forgetting factors the Proportional Fair scheduler can perform as most of the other scheduling schemes !

34 © 2006 Nokia

Performance comparison of PS (cont.)

Scheduler Scheduling rate Serve order Radio resource fairness

Round Robin Slow Sequential order Same amount of average radio resources to all UEs

Fair Throughput Slow User with lowest average offered data

rate

Fair throughput among all users

Proportional Fair Fast User with highest relative

instantaneous channel quality

Same amount of average radio resources under certain assumptions

Fast-Fair Throughput Fast User with highest equalized relative

instantaneous channel quality

Fair throughput among all users under certain assumptions

35 © 2006 Nokia

For Further Information

WCDMA for UMTS : Radio Access for Third Generation Mobile Communicationsby Harry Holma, Antti Toskala

www.3gpp.org