Armin Dammann, Stephan Sand

Barcelona, March 9-10, 2005

NEWCOMDLR Research Topics and Activities

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31 Research Institutes and

Scientific/Technical

Facilities at

8 Sites

4 Branches

German-DutchWind Tunnels (DNW)

European Transonic

Wind Tunnel (ETW)

Total Staff: 5000

German Aerospace Center (DLR)The national aerospace research center and space agency

Institute of Communications and NavigationActivities and Research in Communications

Research Activities in Satellite Communications• Signal design of the satellite navigation system

Galileo• Optical free space communications

(inter satellite links)• Broadband satellite services to aircraft for wireless

access technologies

Research Activities in Terrestrial Communications• DoCoMo Euro-Labs research collaboration• Combination of communications and navigation• EU projects:

• 4MORE (4G MC-CDMA Multiple Antenna Systemon Chip for Radio Enhancements)

• WINNER (Wireless World Initiative New Radio)• NEWCOM (Network of Excellence in Wireless Communications)

DLR Research Center Oberpfaffenhofen• Institute of Radio Frequency Technology and

Radar Systems• Institute of Communications and Navigation• Institute of Methods of Remote Sensing• Institute of Optoelectronics• Institute of Physics of the Atmosphere• Institute of Robotics and Mechatronics • German Space Operation Center• German Remote Sensing Data Center

Total Staff in Oberpfaffenhofen: 1000

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Institute of Communications and NavigationDepartment of Communications Systems

Topics of the Mobile Radio Transmission Group

• Multicarrier Transmission Systems– Multiple access (MC-CDMA)– Detection for MC-CDMA and related schemes– Channel estimation– Multicellular environments– Multiple Antenna Techniques (Cyclic Delay Diversity, Doppler Diversity, …)

• Combination of Communications and Navigation– Performance improvements of 4G mobile radio systems using GALILEO– Navigation by means of 4G systems

• Involvement in EU-projects NEWCOM, WINNER and 4MORE

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Institute of Communications and NavigationDepartment of Communications Systems

Possibilities of Cooperation

• Joint publications• Meetings, Seminars, Colloquia, Talks• Exchange of researchers

– Undergraduate• Diploma/Master theses at DLR• Internships at DLR

– Graduate, Postgraduate, …• Visit as guest scientists at DLR

– Visit of DLR research staff at NEWCOM partner institutions

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OFDMModulation

CyclicPrefix

TN1

Front end of a generic OFDM Transmitter

Doppler Diversity Extension

( )s k

T 1( )Ns k

1( )s k

0 ( )s k

1 ( )k

T 1( )N k

0 ( )kOFDMModulation

T

1NT

1N

Front end of a generic OFDM Transmitter

Cyclic Delay Diversity Extension

CyclicPrefix

CyclicPrefix

CyclicPrefix

( )s k

T

cyc1N

cyc1

T 1( )Ns k

1( )s k

0 ( )s k

Coding Design for OFDM and MIMO SystemsPerformance of Differential Modulation in OFDM Systems with CDD and DoD

• Cyclic Delay Diversity (CDD) and Doppler Diversity (DoD) schemes offer additional diversity in frequency resp. time direction

• This means contemporarily a decorrelation of the subcarriers in frequency and/or time. TX antenna diversity techniques above can be viewed as “channel transformation”

• Differential modulation schemes, however, suffer from a decorrelation of the channel fading

CDD Transmitter DoD Transmitter

CDD shifts TX signals (cyclically) in time. This decreases fading correlation in frequency direction

DoD shifts TX signals in frequency.This decreases fading correlation in frequency direction

Cyclic shift of timedomain OFDM symbol

Spectral shift of time domainsignal by complex valuedexponential functions.

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Coding Design for OFDM and MIMO SystemsPerformance of Differential Modulation in OFDM Systems with CDD and DoD

1 TX antenna

Influence of CDD on a 12-tap Rayleigh fading channel(snapshots of the channel transfer function)

2 TX antenna CDD

Key questions:• The modulation and diversity strategy

e.g. increase frequency domain diversity only while differential modulation is done in time direction or vice versa.

• Find optimum tradeoff between additional diversity and differential modulation performance

Frequency selectivity increases increased frequency diversity diff. mod. suffers, when done in frequency direction

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Turbo Processing in MC-CDMAand Related Systems

The Topic• Detection of users in MC-CDMA or related systems with a-priori information• Exploit soft-out decoding results of outer channel coding schemes• View MC-CDMA as (serial) concatenation of a Walsh-Hadamard code and an

outer channel code.• Investigate the convergence behavior

Key Questions:• The shape of extrinsic information transfer (EXIT) charts with respect to

– Symbol mapping – User load– Rotation of spreading sequences– Different multipath fading channels

• Proper channel codes for turbo processing• Detection/Decoding procedure for outer turbo codes

– Include WH-Decoding in turbo decoding iterations or …– … doing turbo decoding as an inner iteration process, while an outer iteration process

includes WH-Decoding

Activities in that topic are currently running at DLR