The Olympus-1 satellite carries four distinct payloads for experimental utilization and research in the field of satellite communications: (1) the Direct Broadcasting Service (DBS) payload; (2) the Specialized Services Payload; (3) the 20/30 GHz Advanced Communications Payload; and (4) the Propagation Payload. Experimental utilization of the first three payloads involves ground transmissions to the satellite and hence sharing of available satellite time among experimenters. This is coordinated through the Olympus Utilization Program

Brussaard, Gert

English

NASA Technical Reports Server

N89-11090
OPEX - Oiympus Propaqation EXperiment
by Gert Brussaard, Dr. Ir.
European Space Technology Centre
Noordwijk, the Netherlands
The Olympus propaqation mission
The Olympus-i satellite carries four distinct payloads for
experimental utilisation and research in the field of satellite
communications:
m
m
the Direct Broadcasting Service (DBS) Payload
the Specialised Services Payload
the 20/30 GHz Advanced Communications Payload
the Propagation Payload.
Experimental utilisation of the first three payloads involves
ground transmissions to the satellite and hence sharing of
available satellite time among experimenters. This is coordinated
through the Olympus Utilisation Programme.
The Beacon Payload consists of three microwave transmitters that
produce three unmodulated CW (Continuous-Wave) signals through
three individual horn antennas. The beacon signals are designated
B0, B1 and B2, respectively. B0 is at 12.5 GHz and provides i0
dBW of radiated power (EIRP) over the entire visible earth The
horn antennas for B1 and B2 are designed to cover W. Europe with
an EIRP of 24 dBW. High EIRP, and hence high flux density on the
ground allow the use of relatively small earth stations, with
antenna diameters ranging from 1 to 6 meters. The beacon
frequencies are all derived from a common oscillator through
multiplication chains. This allows coherent detection of all
three beacons, providing possibilities for special experiments
and several alternatives for earth station design. An interesting
feature of the coverage of the 20 and 30 GHz (BI and B2) beacons
is that reception from the U.S. and Canadian East coast is not
excluded, albeit with reduced signal power and stability (see
Proceedings of NAPEX XI).
The Propagation Payload allows reception on ground by ,all
participants simultaneously and is available continuously. Its
utilisation therefore is not a matter of scheduling. Instead, the
high level of interest in utilising this payload shown by many
research institutes has led to a programme of intensive
cooperation in preparing for the propagation experiments with
Olympus. This voluntary cooperation project is coordinated by
ESA/ESTEC under the acronym OPEX (Olympus Propagation
EXperiment).
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rate inter-satellite communication technology and the second is to
investigate personal satellite communication systems. The onboard system
has 40 cm dish antenna and is installed on a gimbal platform of ETS-VI. A
solid state power amplifier of 0.5 w output power is under development for
the transponder. A possible user spacecraft for inter-satellite link is
Japanese Experimental Module of the Space Station. Personal
communication terminals with 30 cm-class antennas can communicate each
other at the data rate of about 16 kbps. Ground stations with antenns of
various sizes will also be prepared for experiments to demonstrate a
personal communications concept.
(3) Optical inter-satellite communications
CRL develops experimental optical communication system with telescope
of 75 mm diameter which has gimbal mirror beam pointing/tracking
mechanism. The onboard system has fundamental optical communication
functions with laser diode transmitter of wavelength 0.83 micron, laser
beam point-ahead mechanism, receiver of wavelength 0.51 micron,
modulation/demodulation subsystem, and so on. Various basic experiments
simulating inter-satellite link are planned. In the experiments two
optical ground staions are used, one is a fixed station with ].5 m
telescope and the other is a transportable station.
139
History of European cooperation
In the period July 1976 - October 1977 the NASA satellite ATS-6
was placed at 35 deg E longitude and the European scientific
community was given the opportunity to carry out propagation
experiments using the beacon facilities of the satellite. These
included the so-called millimeter-wave (MMW) experiment using
stable on-board beacons at 20 and 30 GHz and the COMSAT
experiment using a transponder arrangement allowing 13 and 18 GHz
uplink measurements. Unfortunately, these experiments could only
be carried out during certain hours of the day (or rather, the
night). The rather complicated arrangements that were necessary
for participation included dissemination of schedules, loan of
transmit equipment and centralised processing of the uplink
measurements. ESA was asked to coordinate the European
participation in the experiments and represent experimenters vis
avis NASA and COMSAT. This led to the establishment of a
European experimenters group which met regularly during the
project and published its collective results in an ESA Special
Publication (ref. i).
Another activity of European cooperation in propagation research
was initiated in the framework of the COST (COoperation
Scientifique et Technique) project of the European Commission.
From 1972 to 1977, in "Action COST 25/4" results of propagation
experiments above i0 GHz obtained in 13 different countries were
collectively analysed in order to obtain better understanding of
the variations of propagation effects with climate (ref. 2). In
this project mainly analysed results of individual experiments were
put together and compared. It was realised that a higher level of
collective analysis would be possible, if statistics obtained
from measurements were put into a common data base and made
available for collective analysis. This was carried out in the
subsequent action COST 205 (1978-1984), where 11/14/18 GHz
propagation data obtained with the ESA satellite OTS and the
Italian satellite SIRIO were collated and analysed (ref. 3). This
required a higher level of cooperation, including agreements on
standard formats for presenting the various statistics
obtained.
The OTS experiments themselves were coordinated by ESA and
Eutelsat together. The habit of convening the coordination
meetings of experimenters at the different participating
institutes across Europe, which was established in the COST 25/4
project and since then followed by many other COST projects, has
led to an intensive exchange of information which has proven to
be indispensible for cooperation "at working level". Collective
European results of the satellite propagation experiments have
been made available to the International Telecommunications Union
(ITU) and form a major part of the data bank of CCIR Study Group
5 on Earth-Satellite propagation statistics.
141
Orqanisation of OPEX
Thus in the previous 15 years an active European community of
researchers in the field of radio propagation was established.
When in the late seventies plans for a large satellite carrying a
number of experimental telecommunications payloads were taking
shape, this community was called upon to input their requirements
for a propagationexperiment. ESA specifications were drawn up in
consultation with prospective experimenters. Soon it became clear
that there was wide interest in such experiments and a need
existed for regular information exchange in the preparatory
stages. Starting as early as 1980 regular meetings of interested
parties (researchers and industry) were held. Based on the
experience from the COST projects the general opininon was that
collective development of specifications for earth station
hardware as well as procedures for data acquisition,
preprocessing and analysis would be very beneficial for
experimenters and greatly enhance the results to be obtained. In
1984 this work was started by the establishments of three working
groups:
W.G. 1 - Earth station requirements.
Chairman: Mr. S.K. Barton (UK)
W.G. 2 - Data acquisition and preprocessing
Chairman: Mr. F. Zelders (NL)
W.G. 3 - Data analysis
Chairman: Prof. A. Paraboni (I)
The overall objective of the preparatory stage of theOPEX project
thus established was to arrive at a level of standardization that
allows direct comparison of results of experiments without the
usual uncertainties regarding equipment quality and compatibility
of data analysis procedures. Detailed discussions were held in
the working groups of all aspects of the experiments and the
results envisaged. The work of these groups resulted in the
issuing of three handbooks, specifying quality objectives and
defining interfaces for data acquisition, preprocessing and
analysis, respectively.
Participation in the OPEX meetings has been very encouraging and
a good measure of the high level of interest. Attendance to the
meeting is at a constant level of some 40 people from all ESA
member states. The possibility to carry out experiments from the
N. American continent has generated interest also from U.S.
experimenters and resulted in regular contact with the NAPEX
group. The table on next page lists the organisations that are
actively involved in the OPEX work.
142
Table of participants in OPEX
Organisation Location
Technical University Graz
ASSA
BTMC
Newtech
E.B.U.
U.C.L./Lab. de Telecomm.
C.R.C./Radio Prop. Lab.
FTZ
Dornier System
Graz, Austria
Vienna, Austria
Antwerpen, Belgium
Antwerpen, Belgium
Brussels, Belgium
Louvain-la-Neuve, Belgium
Ottawa, Canada
Darmstadt, W.Germany
Friedrichshafen, W.Germany
Inst. Fuer Rundfunktechnik Muenchen, W.Germany
DFVLR
P. and T./Radio Comms.
ElektronikCentralen
T.U.D./Electromagn. Inst.
ETSI Telecomunicacion
ETSI Telecomunicacion
CNET
I .R.A.M.
Eutelsat
March Microwave
Univ. Bradford
Signal Processors
Rutherford Appleton Lab.
Univ. Essex
CSR
BTRL
Portsmouth Polyt.
BAe
Politecnico di Milano
CNR / PSN
Fond. Ugo Bordoni
SeleniaSpazio
Telespazio
CSELT
Telecomm. Research Est.
ELAB
NIVR
Technical Univ. Delft
Technical Univ. Eindhoven
APT
Dr, Neherlab. PTT
Universidade Aveiro
Swedish Telecom Radio
Oberpfaffenhofen, W.German
Copenhagen, Denmark
Copenhagen, Denmark
Copenhagen, Denmark
Barcelona, Spain
Madrid, Spain
Paris, France
Grenoble, France
Paris, France
Braintree, U.K.
Bradford, U.K.
Cambridge, U.K.
Chilton, U.K.
Colchester, U.K.
Ilkley, U.K.
Martlesham, u.k.
Portsmouth, U.K.
Stevenage, U.K.
Milano, Italy
Roma, Italy
Roma, Italy
Roma, Italy
Roma, Italy
Torino, Italy
Kjeller, Norway
Trondheim, Norway
Delft, Netherlands
Delft, Netherlands
Eindhoven, Netherlands
Huizen, Netherlands
Leidschendam, Netherlands
Aveiro, Portugal
Farsta, Sweden
Helsinki Univ. of Technol. Espoo, Finland
Virginia Tech Blacksburg, U.S.A.
JPL Pasadena, U.S.A.
NASA Washington, U.S.A.
143
Results
Major results of discussions of beacon receiver design have been
in the area of standardization of output specifications of
receivers and a thorough discussion of calibration principles.
For the output interface of the receiver hardware a digital
output has been recommended presenting i00 samples/second of I
and Q channels of the receiver. Principles of oversampling of
signals in the presence of noise have been discussed and resulted
in some novel design ideas for digital beacon receivers. A
digital receiver has been developed by Signal Processors Ltd in
Cambridge, U.K., based on frequency feed-forward control, using
digital signal processing techniques in software.
In the areas of preprocessing and analysis of data the OPEX
Handbooks produced by the Working Groups have been the basis for
the specification of a software system, the development of which
is now taking place under contract to ESA by Siemens Austria
(Vienna) and CSR Ltd. (Ilkley, U.K.). This processing system is
intended to become the European reference system for the
treatment of propagation data. CSR have already delivered a
complete Olympus propagation station, including a data
acquisition and processing system, to the German Post Office
Research Centre FTZ.
It has been emphasized as a result of the studies by the OPEX
group, that for an accurate measurement of fading an independent
measurement of total attenuation under conditions of clear sky or
light rain by means of radiometers is indispensable. The
development of a low-cost 20/30 GHz dual-frequency radiometer for
this purpose is being pursued under contract to ESA by Farran Ltd
(Ireland). The instrument which has been named Atmospheric Water
Radiometer (AWR) will have a variety of other applications
(remote sensing, meteorology) by virtue of its capability to
measure total atmospheric water vapour content and liquid water
content separately through a well-proven inversion process.
In the area of scientific analysis a major decision facilitating
a comparison of results among experimenters concerned the
treatment of crosspolar data. As the polarisation orientation at
the groundstation is dependent on its location, crosspolarisation
results cannot be compared directly. The common analysis
specified as a standard is in terms of the tilt angle of the
principal axes of the medium itself and the differential
attenuation along these axes.
To facilitate an exchange of calibrated time-series data on a
bilateral basis, a specification of a standard file format for
the storage of "events" has been made. This "standard event tape"
(which, physically, most likely will be an optical disk) at the
same time serves as the "reference" interface between the data
acquisition and preprocessing system and the data analysis
system.
144
Anticipating a large amount of statistical information to result
from propagation research in the nineties, ESA also started, in
collaboration with Intelsat, the development of an intelligent
data base management system for the production of propagation
predictions and the evaluation of prediction methods that use
large-scale statistics of propagation and meteorological data. A
contract to study the feasibility of a DBMS using modern software
techniques is carried out by Bradford University under contract
with ESA and Intelsat.
Propagation measurements using millimeter waves will be possible
in a few years in Europe with the Italsat satellite (40/50 GHz).
Looking ever further ahead, ESA has now started the development
of a small, light-weight 45/90/135 GHz beacon payload by letting
a contract to assess feasibility and critical technology for such
an instrument to Contraves Italiana (Rome).
Conclusion
The OPEX project was started as a voluntary coordination activity
under ESA guidance. Its success is marked by industrial
activities now taking place in Europe to implement the
recommendations of the European experimenters. As a result there
exists now a very positive outlook for an unprecedented level of
cooperation and exchange of information in the area of
propagation research. Large-scale pooling of results appears to
be the only way to make progress in the development of global
prediction methods that can be used effectively in the planning
of new satellite communication systems.
Marking the conclusion of the preparatory phase of the OPEX
project will be the llth OPEX meeting mid June in Copenhagen,
where status of user preparations and current research are
reviewed, as well as progress in the software development
contract on data processing.
A symposium on the utilisation of Olympus, covering all planned
experiments with the four payloads, will be organised by ESA in
collaboration with the Austrian Solar and Space Agency (ASSA)
next year April in Vienna, hopefully marking the sucessful launch
of the satellite.
References
I. G. Brussaard and B. Battrick (editors), "ATS-6 propagation
experiments in Europe", ESA SP-131, October 1977
2. F. Fedi (editor), "The Eurocop-COST 25/4 project on
radiopropagation above i0 GHz", Alta Frequenza, April 1979
3. F. Fedi (editor), "Special Issue on the COST 205 project on
Earth-Satellite radio propagation above i0 GHz", Alta
Frequenza, May/June 1985
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OPEX: (Olympus Propagation EXperiment)

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