Site: German Aerospace Research Establishment (DLR)
D-8031 Oberpfaffenhofen
Germany

Date Visited: June 24, 1992

Report Author: P. Hager

ATTENDEES

NASA/NSF:

M. DeHaemer
P. Hager
R. Jennings

HOSTS:

Dr. Friedrich Kuhne

Dr. Roland Bucklein

Dr. Arno Schroth

Barbara Backhaus

BACKGROUND

The primary task of DLR is to establish a scientific-technical basis for the development and utilization of future aircraft and spacecraft. In the past few years the application of energy technology has been established as a further key activity of DLR.

DLR's scientific-technical experience lies in the institutes of its five scientific research departments: Flight Mechanics/Guidance and Control, Fluid Mechanics, Materials and Structures, Telecommunications Technology and Remote Sensing, and Energy. Its expertise is also used in the construction and operation of large-scale test and simulation facilities, as well as space support installations.

The Department for Telecommunications Technology and Remote Sensing was the primary focus of interest. This department is organized into four institutes: the Institute for Telecommunications, the Institute for Radio Frequency Technology, the Institute for Opto-electronics, and the Institute for Atmospheric Physics. The Institute for Communications Technology, the Institute for Radio Frequency Technology, and elements of the Remote Sensing Division were visited.

DLR has three primary areas of responsibility:

1. Industrial applications
2. Training of scientists
3. Scientific and technical advice to German Government

Total DLR manpower is 4,400. The staff at Oberpfaffenhofen numbers 1,139, with 70 working on satellite communications.

Primary sources of funding are the German government Ministry of Technology, Ministry of Defense, and state governments. DLR also received DM 428 million in contract funding from ESA. DLR is operating under a budget which is frozen at 1991 levels. Inflation is thus causing manpower reductions.

The scientific and technical facilities at the research center at Oberpfaffenhofen include the German Space Operations Center (GSOC), the Crew Operations and Astronauts Office, Central Data Processing, Flight Operations and Wind Tunnels, Applied Data Technology, the Remote Sensing Data Center (DFD), as well as the libraries of the DLR. Facilities include a Cray Y-MP supercomputer. Some simulation models presently run on the Cray are to be converted to operation on work stations.

The Space Vehicles, Space Applications and Space Mission Operations sectors of DLR play important roles in the national astronautics programs and Germany's contribution to large-scale European projects such as Ariane 5, COLUMBUS, and HERMES.

DLR's role in DFS-KOPERNIKUS includes the initial positioning of the satellites and support to German Telecom on orbit control and communications experiments at 30/20 GHz.

RESEARCH AND DEVELOPMENT ACTIVITIES

DLR claims significant expertise and performs significant research in many areas of interest to the panel. These include the following:

1. Mobile satellite and high frequency (20 to 60 GHz) channel modelling, probing and simulation. This work entails monitoring the OLYMPUS satellite at 30 GHz.
2. Modulation and coding. These efforts include coded phase modulation, multistage and concatenated coding, soft-output algorithms, and high speed receivers. They are looking at incoherent laser modulation for ISLs such as SILEX. DLR is concentrating on the transmission channels and transmission methods. DLR's high-speed receiver work involves speeds above that available from standard DSP chips which forces them to consider sub-optimal coding methods.
3. Joint source and channel coding (speech, audio, images).
4. Spread spectrum techniques. Here emphasis is on applications in mobile satellite systems.
5. Multiple access techniques. Packet communications are emphasized.
6. Adaptive error control.
7. Network protocols and simulation techniques for packet communications. Applications to dedicated, mobile systems are a major focus.
8. Heterodyne and homodyne coherent optical free space communications.

DLR conducts two types of research: internal projects and projects entailing external cooperation, with a wide variety of German and foreign partners.

1991/1992 Internal Research Projects

1. Channel probing for 30/20 GHz satellite links.
2. Coded modulation. Efforts are focussed on hybrid 8/4-PSK (Phased Shift Keyed) and Coded-Octal-PSK and multistage demodulation realized with DSPs.
3. Spread Spectrum Multiple Access.
4. Joint image and transmission coding for deep space projects. Twenty-year-old technology is being updated.
5. Modem and receiver design. Designs are based on TMS 320C25 signal processing chips.
6. Multiple access channel models, information theory aspects, coding, and combined data and voice networks
7. Concatenated coding with block and convolutional codes (SOVA). Concatenated coding is used for very high transmission rates, e.g., 500 Mbits/sec.
8. 565 Mbits/sec free space optical heterodyne differential PSK (DPSK) link.
9. 500 Mbits/sec PSK homodyne system for ISLs. Experiments have been conducted at 1.064 mm, 3.5 dB above the shot noise limit, which achieved detection at 20 photons/bit and a bit error rate (BER) of 10(superscript -10).

1991/1992 Projects with External Cooperation

1. 30/20 GHz communications with channel probing, experimental modems, and TDMA. This project involves the OLYMPUS and DFS-KOPERNIKUS satellites, and is performed in cooperation with the Swiss and German PTTs, and Marconi.
2. SATCOM (military). In cooperation with Dornier.
3. DBA for both terrestrial and satellite transmission. This work entails channel encoding for DAB. In cooperation with EUREKA (Bosch and CCETT).
4. SATPHONE (passenger telephone for aircraft - satellite links). DLR hopes to double capacity over Inmarsat. In cooperation with German Ministry of Research and the Technical University of Berlin.
5. PROMETHEUS. This is directed at vehicle communications at 60 Ghz for short distance communications and frequency reuse. In cooperation with EUREKA (Mercedes and universities).
6. DRIVE. Packet communications to mobile users is the focus here. In cooperation with SEL, Alcatel, and Marconi under the RACE program.
7. RACE II. The objective is a universal mobile telephone system. In cooperation with EC (industries).
8. Research in coherent receiver design. The receiver is being built by ANT using a DLR concept. In cooperation with Solacos (Dornier and BMFT [MOD]).

Key Technologies

Microstrip Antennas. DLR has developed design and analysis techniques which demonstrate the capability to develop microstrip antenna designs for new applications. Work has focused on the 9 and 10 GHz band, but most results should be amenable to scaling to higher frequencies such as Ka-band. Electromagnetically- coupled square and circular patch microstrip antennas have been designed, built, and analyzed. Units include 8 x 8 arrays and 3 x 8 arrays. Facilities used include a small anechoic chamber (Splitt and Davidovitz 1990).

Laser Transmission Coding and Modulation. DLR has a newly installed Free Space Optical Test Facility. The system has just been established with little research results to date. Research could find applicability to optical ISLs from either GEO-GEO or GEO-LEO. Laser transmitter and receiver were installed on a roof-top range with a reflecting mirror about five meters apart. As soon as the system is calibrated the reflecting mirrors will be relocated to a distance of several hundred meters. The stated research objectives were to investigate advanced modulation techniques for laser communications focussed on countering atmospheric effects. Investigations are planned for heterodyne, homodyne PSK and DPSK modulations schemes with data rates up to 560 Mbits/sec. No papers are yet available.

Land-Mobile Satellite Communications Channel Modeling. DLR has conducted extensive propagation experiments using a mobile vehicle covering several locations in northern Europe, at elevation angles of 13, 18, 21, 24, 34, and 43 degrees. Data were gathered for both open highway and urban environments. Detailed models for propagation effects have been implemented. These models are now being used to support development of advanced modulation and coding techniques for new land-mobile satellite communications applications (Lutz, Cygan, Dippold, Dolainsky and Papke 1991).

Monitoring OLYMPUS Beacons at 19 - 20 GHz. DLR has ongoing research monitoring OLYMPUS downlink beacons signal attenuation through the atmospheric channel while simultaneously collecting Doppler radar data at approx. 5 GHz. This simultaneous monitoring of the channel and satellite transmission receive level enables the correlation of temperature, humidity, and atmospheric pressure data with transmission path propagation impairments such as fades and phase shifts. The empirical data derived from these experiments is used to create models. DLR then employs the channel models to simulate propagation environment and evaluate designs for mitigation techniques (Hornbostel and Schroth 1992).

Radar Data Derived From Monitoring of Downlink Beacons. Radar data derived from monitoring of downlink beacons is used to develop characteristic electromagnetic signatures for targets such as clouds. These methods also apply to man-made objects and thus have applications in synthetic aperture radar.

Modulation and Coding Techniques. Development of new modulation and coding techniques for improved transmission performance is covered in several references (Hagenauer and Lutz 1987; Cygan and Offer 1991; Hornbostel and Schroth 1992; Lutz et al. 1991; Hagenauer et al. 1987).

SUMMARY

DLR satellite communications programs are concentrated in those basic (enabling) research areas with limited work with direct, immediate application to the commercial telecommunications industry. Work is of high quality. Some work under direct contract to ESA or private firms may have more immediate application. DLR has demonstrated significant capabilities in the enabling research areas similar to, but smaller than, those found at MITRE Bedford.