Ger man Aerospace Center Gothenburg, 11-12 April, 2007 High Spectral Efficient and Flexible Next Generation Mobile Communications Simon Plass, Stephan

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


2G & 3Gbands

4GCand.band

Cand.band

Candidateband

Shared by 4G

II


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

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Thank you!

Documents

Ger man Aerospace Center Gothenburg, 11-12 April, 2007 High Spectral Efficient and Flexible Next Generation Mobile Communications Simon Plass, Stephan