Page 62 - ITU Journal: Volume 2, No. 1 - Special issue - Propagation modelling for advanced future radio systems - Challenges for a congested radio spectrum

ITU Journal: ICT Discoveries, Vol. 2(1), December 2019

availability and performance. Of course the two single and joint statistics in Greece and UK, as well
stations need to be interconnected through a high as a brief, nonetheless rigorous discussion is given.
capacity network to enable dynamic rerouting of Finally, section 4 concludes the paper and presents
the data traffic whenever a gateway switch occurs. ideas for future work.
Such an approach is quite practical for satellite
networks characterized by one or a few beams since 2. ALPHASAT PROPAGATION CAMPAIGN
a second gateway greatly improves the availability IN GREECE AND THE UK
at an acceptable cost increase and allows the use of
smaller gateways to meet a particular availability. In July 2013 the ALPHASAT satellite (commercial
name Inmarsat-4A F4) has been developed and
The demand for a site diversity performance launched to 25.0ºE providing, among others,
assessment before actual system deployment payloads for experimental purposes under the
necessitates the development of accurate supervision and coordination of the European
prediction models [1], [2]. However, reliable long- Space Agency (ESA). The so-called Aldo Paraboni
term measurements which could be used either for Technology Demonstration Payload 5 (TDP#5),
the design and modeling of site diversity (i.e. testing named after Professor Aldo Paraboni of Politecnico
existing models [6], [7]) or the development of new di Milano, who was principal investigator of this
prediction models (for regions where data is not project but passed away in 2011 provides two
available), are sparse, particularly at high frequency coherent beacons at Ka- (19.701 GHz) and Q-band
bands such as Ka and Q/V bands. (39.402 GHz). The transmitted beacons have been
The novelty of this paper is that it evaluates and utilized by many research groups around Europe to
compares the statistical performance of the site conduct propagation experiment campaigns,
diversity technique based on 2-year measurements ultimately to enhance available propagation data
at two vastly different climatic regions within and allow the development of new models and
Europe, Greece (Southern Mediterranean climate) techniques. As already stated in the introduction,
and Southern England (North Atlantic climate). both NTUA and RAL Space are members of the
Greece is well known for its Mediterranean climate relevant ESA consortium ASALASCA [8].
with irregular, whilst intense, rainfalls (convective Table 1 – Experimental campaign receivers’ sites
precipitation) mainly during winter, as well as for
Elev.
its long and hot summers; in particular Greece has Locations Longitude, Altitude Azimuth Angle
Latitude
a.m.s.l.*
Angle
been known to suffer from heavy storms and rain
commonly originating from the west because of its Greece, 37.975 N
o
unique location and terrain morphology. On the Athens NTUA 23.785 E 0.21 km 178.03 o 45.97
o
o
other hand, the United Kingdom is characterized by Campus
frequent showers throughout the entire year Greece, 37.723 N
o
o
(stratiform precipitation) with small temperature Lavrion 24.048 E 0.02 km 178.44 o 46.26
o
fluctuations between different seasons. For both
UK,
o
regions the measurement data was aquired using Chilbolton 51.15 N 0.1 km 147.45 o 26.40
o
1.43 W
o
the Alphasat SCIEX Ka band beacon signal in the
framework of the European Space Agency (ESA) UK, 51.57 N 0,1 km 147.77 o 26.07
o
o
o
ASALASCA propagation experiment [8]. RAL Space, Chilton 1.29 W
who led the ASALASCA consortium, is responsible *above mean sea level
for the site diversity experiment in England while 2.1 Receivers’ details
the Radio and Satellite Communications Group at
the National Technical University of Athens (NTUA), The ongoing experimental campaign described in
also member of the ASALASCA consortium, is this paper takes place at four sites in total, two in
responsible for the experimental campaign in Greece (Athens and Lavrion, about 36.5 km apart)
Greece. and two in the UK (Chilbolton, Chilton, 47.8 km
apart); such a configuration enables the study of site
The remainder of this paper continues as follows: In
section 2 the experimental campaigns (the diversity schemes in small and large scale distances.
architecture of the receivers, the preprocessing The Ka-band beacon signal transmitted by
technique and the ancillary measurements) are ALPHASAT is a constant power continuous wave
briefly described. In section 3 the experimental (CW) (unmodulated signal) at 19.701 GHz. The
ground terminals receive and measure the beacon
46 © International Telecommunication Union, 2019