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1 © NOKIA
Key technologies for future wireless systems
Dr. Kari PehkonenWorkshop on Future Wireless Communication
Systems and Algorithms12.8.2002
2 © NOKIA
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
3 © NOKIA
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
4 © NOKIA
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.)
5 © NOKIA
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
6 © NOKIA
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
7 © NOKIA
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)
8 © NOKIA
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
9 © NOKIA
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
10 © NOKIA
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
11 © NOKIA
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 +⋅
12 © NOKIA
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
13 © NOKIA
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 ?
14 © NOKIA
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 !
15 © NOKIA
IP Backbone
Evolved Network
EvolvedUMTS
EvolvedWLAN
EvolvedFixed
ALL IPServices
4G RAN ?
DVB-T ?
16 © NOKIA
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
17 © NOKIA
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 !
18 © NOKIA
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
19 © NOKIA
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
20 © NOKIA