Page 66 - 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

precisely quantifying the impact of such a difference
is a non-trivial task, especially considering the
substantially dissimilar meteorological conditions
between Greece (more convective rain) and the UK
(more stratiform rain). More details regarding the
impact of the stratiform and convective type of
precipitation on the site diversity gain can be found
in [14], [15] and [16].
In order to better explain the impact the elevation
angle has on the site diversity gain considering also
the type of precipitation more experimental data in
various climatic regions and in different separation
distances are required [8], [17], [18]. In [19] an
investigation of the factors that affect the site
Fig. 7 - Measured annual joint complementary distribution of diversity gain has been conducted and it has shown
excess attenuation for Greece and the UK that the dependence of the elevation angle on the
diversity gain should in any case not be particularly
pronounced.
As can be observed in figures 5-8, the effectiveness
and practical value of a site diversity scheme
becomes apparent at time exceedance probabilities
less than <0.1%; above that value a dual antenna
scheme could provide a solid 3 dB gain as
mentioned in [20].

4. CONCLUSION
In this paper the results from the first two years of
the ALPHASAT Ka-band site-diversity experiment
in Greece and the UK are presented yielding
interesting observations regarding both the small
and the large scale site diversity scenarios (as can
Fig. 8 - Measured annual joint complementary distribution of be seen in Fig. 8). The deployment of receivers at
excess attenuation between Greece and the UK in comparison two sites per region enables the study and
with the independent joint distributions
development of new site diversity techniques,
A significant observation can be made in Fig. 7; it is based on the temporal and spatial distribution of
apparent that the measured annual joint statistics.
complementary distribution of excess attenuation
for both experiments in Greece and the UK share a The campaign is still ongoing and future work has
very similar behavior and their lines almost overlap; already been planned; ultimately, the processed
this is an outstanding result that, despite potentially time series should provide statistical evidence for
being a random effect, has to be noted. Finally, in modeling in-excess attenuation, total attenuation
Fig. 8 the results for the measured annual joint and scintillation, providing feedback that could be
complementary distribution of excess attenuation used by standardization bodies (e.g. ITU-R Study
between Greece and the UK are presented; these Group 3 – Propagation) in order to revise their
results are presented considering the application of recommendations (e.g. ITU-R P.618-12 [7], ITU-R
the smart gateway diversity concept in feeder links P.1815-1[21], and ITU-R P.1853-1 [22]) and
[13]. experimental databases as far as long and short-
term statistics of atmospheric channels are
There is a notable discrepancy in elevation angles concerned.
across the two regions potentially influencing the
derived results to some extent; the UK receivers
operate at an elevation angle of approximately 26º
while the Greek ones around 46º. However,

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