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Key technologies for future wireless systems

Dr. Kari PehkonenWorkshop on Future Wireless Communication

Systems and Algorithms12.8.2002

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4G trends and drivers • Many definitions for the term 4G exist. Nokia’s view:

❑ 3G evolution is based on the combination of existing technologies like cellular as main interface and Wireless LAN for hot-spot usage

❑ 4G (a.k.a. ”Systems Beyond 3G” or ”Systems beyond IMT-2000”) is a research topic for new air interfaces and systems to be considered after 2010

• Radio performance and higher throughput/lower delaysidentified as major drivers for 4G

❑ Streaming and fast download (instant gratification) of medium size entertainment material (MP3, good resolution video clips, 3D)

➘ System needs to serve at least up to 2020 and user interfaces will develop radically

❑ Large size down-loads (e.g. mail-box synch.)

• Transport and last hop transmission for very high throughput are also issues but need to be developed for 3G evolution already

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Mobile Radio Systems Generations

80’s80’s 90’s90’s 00’s00’s 10’s10’s

Analog voice telephony

1G

2GDigital voice, mobile data

2G EvolutionPacket data, always connected

3GMultimedia Messaging, Multiple services

3G EvolutionCost efficient IP based network, higher data rates

4GRadio performance seems to bethe main driver for new generation

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4G radio research positioning• 3G will go towards 10/100 Mbps (wide/local area) (with WLAN

providing the 100 Mb/s hot spot capability) – 4G should be clearly better

❑ Up to 100 Mbps/1 Gbps carrier bit rates in wide/local area deployments

❑ Bandwidth up to 100 MHz

• Clear cellular capacity improvements over 3G (best effort packet)

❑ Multicellular efficiency of e.g. WCDMA+HSDPA up to 0.5-1.0 bits/s/Hz❑ 4G

➘ Single cell efficiency up to 5-10 bits/s/Hz➘ Multicell efficiency >> 1 bits/s/Hz

• Adaptability to different radio environments❑ Parametrized solution yielding optimal or close to optimal performance

in different radio conditions (wide area, local area)

• Efficient support of services with wide variety of QoSrequirements (RT, non-RT, etc.)

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Constant evolution of radio towards higher data rates and better mobility

Mob

ility

Vehicular

Pedestrian

Stationary

Data Rate (Mbps)0.1 1 10 100 1000

WLAN802.11b

Adaptive

modulation

WC

DM

A Rel 4

Divers

ity

tech

nique

s

1xEV-DV

Cdm

a2000 1X, EDG

E = Evolved 2G

WLAN802.11a

HL/2

Evolved 3G 4Gresearch target

Mult

icarri

er ?

1xEV-DO

WCDMARel.5

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Why 100 Mbps/1 Gbps ?• Absolute numbers are not that important but target setting is !• 3G will go towards 10/100 Mbps (wide/local area) – 4G should

be clearly better• No application may need that high bit rates but the system may

need it in order to ❑ Serve many high bit rate users simultaneously❑ Maximize throughput/capacity❑ Minimize latencies

• There may be an optimum bandwidth which will maximize the spectral efficiency of a wireless system

❑ Research target must be set high to “capture” that optimum

• Short distance radio bit rates will go towards 1 Gbps and users expect wide area coverage service level to be fairly close

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Where are the capacity limits ?• Simple analysis of cellular capacity limit based on “Nilsson, O. Fundamental

limits and possibilities for future telecommunications. IEEE Communications Magazine, vol. 39 no. 5, May 2001, 164-167 pp”.

❑ Bandwidth = 100 MHz❑ Carrier frequency = 2 GHz❑ Density of mobile terminals = 1000 per km2

• Although analysis is idealistic very high capacities per cell seem to be possible

• Additional (possible) capacity increase by MIMO solutions not included !

1.75

1.80

1.85

1.90

1.95

2.00

2.05

2.10

2.15

2.20

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Terminal power (W)

Cap

acity

(Gbp

s)

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DS CDMA vs. TDMA capacity

• Does a cross over point really exist where DS-CDMA is no longer the right choice?

• From [3] Verdu shows the spectrum efficiency for CDMA with increasing Eb/N0

-2 0 2 4 6 8 10 12 140

0.5

1

1.5

2

2.5

3

3.5

4

Eb/N 0

Spec

tral e

ffici

ency

(bps

/Hz)

Blue- CDMA optimum detection

Black – CDMA RAKE detection

Green - TDMA with reuse 4

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Role of Multicarrier• Hypothetical single carrier TDMA system

❑ R=1/2 channel code ❑ Symboling rate of 50 Million per second ❑ 4 bits per modulated symbol

• Typical cellular channel has 2 us of memory ❑ 2 us channel memory = 100 symbols of memory❑ Optimal (ML) equalization requires 16100 operations per decoded symbol

(ouch!) ❑ Single carrier (GSM style) TDMA is computationally intractable

• Conclusion: A parallel bank of single channel equalizers spanning few number of symbols is less complex than a one equalizer over manysymbols

Data Stream

Serial to P

arallel

Parallel to S

erial

Data Out

Communication Channel

Filter bank Filter bank

• Multicarrier systems create parallel streams of data such that each independent data stream sends a fraction of the overall required data rate

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MIMO• What is MIMO?

❑ Multiple transmit and receive antennas

❑ Spatial multiplexing is a type of MIMO that creates multiple simultaenous radio channels between the base station and mobile station

❑ Placing multiple antennas on a ”terminal” becomes easier the higher the carrier frequency

h11

h12

h13h14

h21

h24 h23

h22

h31

h34

h33

h32

hN1

hN4

hN3

hN2

y = Hx + n

Tx1

Tx2

Tx3

TxN

Rx1

Rx2

Rx3

RxN

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4G Targets and Multiantennas The ultimateultimate bound for achievable spectral efficiency and

data rate• NTx and NRx are the number of transmit and receive antennas • SNR(NTx, NRx) is the signal-to-noise-ratio with given number of

antennas• Capacity in bps/Hz

• If either NTx or NRx equals 1 ⇒ capacity increases logarithmically (=slowly) when SNR increases

• If NTx and NRx both are larger than 1, capacity increases much faster

( ) ( )( )RxTxRxTx NNSNRNNC ,1log,Min~ 2 +⋅

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4G Targets and Multiantennas

Conclusion: 1 to 10 bps/Hz at reasonable SNR can only be achieved with MIMO

0 5 10 15 20 250

5

10

15

20

25

30Same number of Tx & Rx antennas

SNR [dB]

Cha

nnel

cap

acity

[bits

/dim

ensi

on]

1x1

2x2

4x4

8x8

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Current likely direction for 4G radio

• Key technology conclusions❑ Multicarrier is needed to

contain receiver complexity and allow flexibility in use of available spectrum

❑ Spatial multiplexing (MIMO) will play an important role in 4G

• One key question❑ Is spreading useful in

achieving up to 10 bps/Hz ?

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Future network evolution• Different layers of the network have different innovation cycles

❑ Development of radio interfaces, network solutions, and service machineries should not be artificially tied together

• 3G Networks will evolve gradually to ❑ Optimize service delivery❑ Integrate different access technologies

• Graceful evolution of the 3G systems can provide viable path to 4G networks; i.e., 4G radio interface could be plugged-in to the evolved 3G network

❑ Hot spot access technologies (e.g., 802.11) can be integrated into the 3G networks (with loosely or more tightly coupled service provision)

❑ Solutions to further improve the performance and flexibility of the 3G architecture are already investigated in relevant standardization bodies

• 4G is associated with a new wide area radio technology – improvements of the end-user experience in the network and service layers are continuouseffort that is not tied to any “generations”

New networks and applications do not have to wait 4G radio !On the other hand, 4G radio do not necessary need new network !New networks and applications do not have to wait 4G radio !

On the other hand, 4G radio do not necessary need new network !

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IP Backbone

Evolved Network

EvolvedUMTS

EvolvedWLAN

EvolvedFixed

ALL IPServices

4G RAN ?

DVB-T ?

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4G and spectrum• Spectrum is a scarce resource and needs long term planning• Topics requiring careful consideration

❑ Frequency range➘ Preferably under 5-6 GHz

❑ Paired/unpaired band➘ Unpaired bands are easier to find

❑ Dedicated/shared bands➘ Capability of spectrum sharing would be beneficial

❑ Minimum width of a frequency block➘ Spectrum efficiency important

❑ Number of bands➘ Should be minimized

❑ Global harmonization➘ Globally common bands should be sought after as much as possible

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WRC-2003 agenda item 1.22: "to consider progress of the ITU studies concerning future development of IMT-2000 and systems beyond IMT-

2000, .…" Draft WRC-2006 agenda item 2.16: "to review the requirements for future development of IMT-2000 and systems beyond IMT-2000, .…"

4G spectrum: next steps

• At WRC-2003 we should get a proper agenda item agreed to the WRC-2006.

• In the meantime international view needs to be shaped positive towards identifying new spectrum for systems beyond IMT-2000 in WRC-2006

• Somebody needs to justify the need !

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4G Timetable

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012

WRC03 WRC06

Possible Spectrum AvailabilitySpectrum

Research

Standardisation

System Development

System Integration

Initial System Deployment

1st Release

Research &standardization

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Conclusions• 3G will continue to evolve after initial deployment• Evolution towards IP-based core networks with multi-radio access, integrated

3G and WLAN will offer data rates from 10 to 100 Mbps• In parallel, a revolution may happen within 10-15 years• One key driver for 4G systems: high data rates everywhere -> hyperavailability

of all media• Unused spectrum does not exist - long term planning necessary to make

spectrum available❑ WRC-2006 expected to consider requirements and identification of

spectrum for 4G systems• Possible 4G solutions and system will compete with evolved 3G => research

targets must be set high❑ Peak data rates of 100 Mbps/1 Gbps in wide/local area access

• Target is for initial standards to be ready around 2010, subject to the outcome of WRC-2006

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