ger man aerospace center gothenburg, 11-12 april, 2007 high spectral efficient and flexible next...
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Ger manAerospace Center
Gothenburg, 11-12 April, 2007
High Spectral Efficient and Flexible Next Generation Mobile Communications
Simon Plass, Stephan Sand, Mikael Sternad, andArne Svensson
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Motivation
What are the requirements and challenges for next generation communications systems?
How can these technical challenges be solved?
Remark: The focus is on the physical layer (PHY) in this presentation
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Evolution of Mobile Communications
Analog systems1G
GSM2G
UMTS3G
???4G
Digital systems
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4GGMC
Scenarios
0,1 1 10 100 Mbit/s
mobility
high speed/wide area
medium speed/within a city
walking speed/within a limited areas
portable/indoor
2GTDMAFDMA
3GCDMA
WLAN (IEEE 802.11)OFDM
data rate
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Main Requirements for 4G
Efficient use of the valuable spectrum
Flat IP architecture for low operational expenditure and less capital expenditure
Flexible spectrum allocation and sharing has to be included
New services based on real time applications, e.g., gaming or new trends of Web 2.0
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Cyclicprefix
IFFTCyclicprefix
IFFT
Basic Transmission Technique:Generalized Multi Carrier (GMC)
Robust to multi-path environments Efficient use of the available spectrum Flexible allocation of user data to sub-carriers Includes all OFDM based transmission techniques such as OFDMA,
MC-CDMA, SS-MC-MA, IFDMA, etc.
Data symbolsSpace-Time-
FrequencyPrecoding
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Advanced Techniques for the PHY
Adaptive functionalities at the transmitter and receiver exploiting channel state information and user demands
Transmitter:
• Adaptive bit-interleaved coded modulation (BICM)
• Adaptive Space-time-frequency (STF) precoding
Coding Mod
Adaptive BICM
Predicted CSI
Cyclicprefix
IFFTCyclicprefix
IFFTData symbols
adaptiveSpace-Time-
FrequencyPrecoding
Predicted MIMO-CSI
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Advanced Techniques for the PHY
Receiver:
• Iterative channel estimation, demodulation, and decoding
• Improve bit estimates by toggle until regeneration brings optimality (TURBO) principle
Decod -1 DemodSTF
Decod
ChannelEstimation
CSIPrediction
SISO CSI
MIMO CSI
Inverse OFDMconverted signals
sink
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Technical Highlights for 4G Systems
Spectrum Flexibility
Inter-cell Interference Handling
Relaying Concepts
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Spectrum Flexibility – Spectrum Assignment Concepts
Definition of new spectrum assignment at the World Radiocommunications Conference (WRC) in Oct/Nov 2007
900 MHz 2.6 GHz 3.4 GHz 5 GHz
2G & 3Gbands
4G Candidate bandCand.band
I
900 MHz 2.6 GHz 3.4 GHz 5 GHz
2G & 3Gbands
4GCand.band
Cand.band
Candidateband
Shared by 4G
II
900 MHz 2.6 GHz 3.4 GHz 5 GHz
2G & 3Gbands
Shared by 4G
Candidateband
Cand.band
Cand.band
Candidateband
Shared by 4G
Narrowband 4G
III
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Spectrum Flexibility – Spectrum Sharing Mechanisms
Sharing and Co-existence (spectrum sharing with fixed satellite systems (FSS))
• Use of geographical ‚exclusion zones‘
• Use of directional antennas and beamforming to avoid LOS transmissions towards FSS ground stations
Flexible Spectrum Usage
• Long-term spectrum assignment
• Short-term spectrum assignment
• Resource partitioning
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Inter-cell Interference Problem
Goal: High overall spectral efficiency in combination with high flexibility for packet data traffic
Method: Frequency reuse of one and generalized multi-carrier system
Result: Inter-cell interference problem at the cell borders
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Inter-cell Interference Handling
Difficulties:
• Fast and tight inter-cell coordination is required for maximal gains in interference avoidance
• Complication with packet-switched channel-aware scheduled transmission
Possible approaches:
• For high loads, allocate low SINR user to a separated frequency pool with frequency reuse of three, the others with reuse of one
• For low loads, dynamic frequency assignment and/or coordinated beamforming can be used of the lower fraction of low SINR users
• Inter-cell interference cancellation schemes at the receiver, if resources at receiver available
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Conclusions
We have shown:
The needs of next generation communications systems The underlying transmission technique GMC The adaptive components of the PHY The need of spectrum flexibility and its mechanisms The need of inter-cell interference handling and possible
approaches