Opportunity for Intern Student - Data Communications Engineering: CLOSED

Participation in a Study for the European Space Agency
International space agencies currently plan high data rate space research missions with bandwidth requirements up to 400 MHz. Satellites for these missions may carry telescopes and/or other passive instruments to measure phenomena such as the Earth’s magnetosphere and solar flares. Moreover, satellites belonging to the international human exploration initiative, that will first target the Moon and later Mars, will need a frequency allocation which is not restricted to near earth or deep space missions only, so that the same communications equipment can be used at Moon and Mars orbits.

Until recently, 8 450-8 500 MHz was the only band below the 37-38 GHz band that was available on a primary basis in the Space Research Service (SRS) to transmit moderate to high-rate data directly from Earth-orbiting satellites to earth stations. Since this band will not meet the requirements of future high rate space research missions, a new allocation in the band 25.5-27 GHz was obtained at the ITU Word Radiocommunications Conference in 2003 (WRC-03).

Such new allocation has formally entered into force on 1 January 2005. Given that no additional indicators are attached to this allocation, the 25.5-27.0 GHz band can be used by both near earth and deep space missions, thus fulfilling the requirements of human exploration as well.

The missions not part of the human exploration initiative will be limited in number with an estimated three to five satellites per year worldwide, and will generally be in an equatorial orbit with some at geo-stationary altitudes and others at the L1 or L2 libration points.

SRS systems have been designed to support a data rate of up to 400 Mb/s on the space-to-Earth link from GSO orbit using moderate sized ground station antennas. However,in order to support the same data rate from Moon distance (or further), the Earth station antenna gain has to be at least 20 dB higher than the antenna supporting geo-stationary missions, i.e. 75 dBi. This is commensurate with a 35-m class antenna like existing DSA antennas. Supporting missions to Lagrangian points and human exploration missions to farther away distances will be possible by reducing the data rate accordingly, increasing the transmitted power or using cryogenic cooled Low Noise Amplifiers (LNAs).

Both ESA and NASA are considering the 25.5-27.0 GHz band and among these the JWST joint NASA/ESA mission.

Objectives of the feasibility study
The overall objective of the feasibility study are:
To perform a detailed analysis of the mission requirements.
• To verify the feasibility of the introduction of the new frequency band into the existing ESA Deep Space Ground Stations (DSGS) by taking into account all the electrical/mechanical limitations of the existing configurations. The work shall not be limited to the ground station Front-End but it shall take into account also Back-End and data communication aspects
• To perform feasibility analysis of the ESA DSGS modifications required accommodating the new 26 GHz band (reception). The output of this feasibility analysis shall be the definition of the budgetary effort and time needed to finally implement the upgrade
• The feasibility analysis shall take into account all the elements of the ESA DSGSs:
o Optical antenna layout: modifications required to the antenna reflectors in order to accommodate an additional frequency band
o Dichroic/multi-frequency feed feasibility: Frequency Selective Surface (FSS) to separate the different frequency bands to simplify the feed design and multi-frequency feed to overcome possible difficulties with FSS design
o LNA: evaluate the possibility to extend the 32 GHz LNA coverage or to have a dedicated design for the 26 GHz band
o Down-converters: wide bandwidth and high Intermediate Frequency (IF) required
o Intermediate frequency demodulators: to deal with higher IF and bandwidth
o Telemetry processors.

Study Team
Callisto will undertake the study on the use of 25.5-27 Ghz band in ESA ground station with a number of partners, which are identified below. Callisto will lead the project and be responsible for the organisation and management of the project.

In addition to Callisto the project team is as follows:
• University of Pavia (UNIPV), which will be responsible for the antenna optical design analysis, the dichroics design analysis and the feed preliminary analysis for PDR.
• ERA Technology Limited, which will be responsible for the feed detailed design analysis for the CDR.
• Zelinda Limited, which will be responsible for the demodulator design analysis.
• Makalumedia GmbH, which will be responsible for data communication design analysis.

UNIPV, ERA, Zelinda and Makalumedia will be sub-contractors to Callisto.

Callisto will be responsible for coordinating the design effort of the project team and for organising the design reviews. Callisto will also be responsible mission analysis and requirements consolidation, LNA design analysis, downconverter design analysis, System analysis and cost analysis.

Task of Analysis of Ground Station Reception Chain
A critical part of the work which will be undertaken by Callisto will be to perform an analysis of the ground station reception chain to determine the requirements for filtering and other key specifications. This will require the following activities to be undertaken for which Callisto is interested in employing and Intern Student to support:

1. Research planned/potential use of 20-30 GHz spectrum for applications other than for SRS for all DSA locations in order to determine K band filtering requirements in terms of external RFI rejection.
2. Undertake Matlab/Simulink analysis of the effects of reception chain filtering in amplitude and phase on high data rate modulation signals using various bandwidth efficient modulations schemes.
3. Conduct an apportionment analysis of all critical K band receive chain performance parameters in order to derive preliminary sub-system level parameters.
4. Analyse station interfaces for K band reception equipment at subsystem level.

Some additional background information on points 1 and 2 are given below:

Research into Future Use of the 20-30 GHz Spectrum
In order to determine the input filter requirements consideration needs to be given to the potential from interference generated internal to the ground station (in particular the TX signals) as well as potential external RFI. The analysis of internal interference is relatively straight forward as the frequencies and levels of transmission signals are known, however high order harmonics should not be forgotten. Consideration of external interference is a somewhat different matter and some research will have to be done in this area into current or planned radio frequency uses in bands adjacent to our band of interest, and this research will have to consider the different locations of DSA1 and DSA2 as separate cases due to the different RF regulatory regimes between Australia and Europe. It should be noted that today terrestrial or satellite applications above 20 GHz are very few. However, it will not stay this way as demand grows for emerging wireless technologies for data communications and for digital TV services.

Wideband Communications Simulations
One of the main aspects to consider as far as the analysis of the receive chain after the LNA are the type of signals which will be received, which are characterised by having high data rates and consequently a large modulation bandwidth. In this respect we can immediately focus on modulation schemes which are foreseen for the new services in the 25.5-27 GHz band. In particular, the new recommendations for bandwidth efficient modulation for data rates above 2 Mbps agreed by the CCSDS. A brief background to these recommendations is given below:

Concerned about spectral occupancy for high data rate services for satellite communications links, the SFCG and the CCSDS has been working for some time to produce recommendations for modulations schemes which are bandwidth efficient and power efficient. The main concern of the CCSDS has been for producing recommendations for services using data rates above 2 Mbps in Space Research missions and Earth Exploration missions. Prior to the publication of the new recommendations in this area [RD3] Space Agencies have been traditionally using unfiltered BPSK, QPSK as well at PCM/PM/SP-L for these high rates services.

The starting point for the CCSDS in 1996 was the publication by the SFCG of a spectral mask for emissions for services of greater than 2 Mbps. Thereafter, a number of CCSDS members have conducted studies and research into various modulation schemes which would meet the SFCG spectral mask. The results of these studies have lead to the identification of a number of modulations schemes which will meet the Bandwidth Efficient spectral emissions requirement, and at the same time offer good communications performance. The bandwidth efficient modulation schemes now recommended by CCSDS, depending on the type of service are as follows:

For Space Research, Space-to-Earth, Category A (non-Deep Space)
FQPSK-B
GMSK (BT=0.25)
SRRC pre filtered (=0.5) OQPSK
6 pole Butterworth shaped OQPSK
For Space Research, Space-to-Earth, Category B (Deep Space)
GMSK (BT=0.5)
Trellis OQPSK
For Earth Exploration Satellites, Space-to-Earth
SRRC filtered 4D 8 PSK Trellis Coded.

In order to establish system and subsystem specifications for the complete receive chains, we intend to carryout some simulation activities using Matlab/Simulink. The objective of these simulations will be to establish working values for the amplitude and phase distortion, including phase noise, which can be allowed in the downlink chain without producing significant levels of degradation on the wideband modulation signals. We consider that is necessary because of the very wideband signals and very high data rates which will be carried by the receive chains and the need of anti-alias filtering at the input to digitisation in the demodulator. In this respect Callisto is fortunate to have already developed a number of Simulink models based on bandwidth efficient modulations schemes. These models will be enhanced and re-used in the course of the activity.

Qualifications and Other Requirements
The Internship would be suitable for a student who has followed a higher level degree engineering course with specialisation in digital communications. The student should have knowledge of modern modulation schemes widely used for data communication (BPSK, QPSK, GMSK). Some knowledge of satellite communications system would also be an advantage. It would be a distinct advantage if the student were familiar with Mathlab/Simulink in the simulation of communications systems. It is essential that the student is able to work in the English language.

The activity is scheduled to run from June to September 2006. The work will be based in Callisto’s offices in Labastide d’Anjou (near Toulouse) France.

Posted: April 18, 2006 • Category: Job Training Offers

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