Page 61 - 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

ALPHASAT SITE DIVERSITY EXPERIMENTS IN GREECE AND THE UK AT KA BAND:
COMPARISON OF 2-YEARS’ RESULTS

Apostolos Z. Papafragkakis , Spiros Ventouras , Charilaos I. Kourogiorgas , Athanasios D. Panagopoulos 4
2
3
1
1 School of Electrical & Computer Engineering, National Technical University of Athens, Athens, Greece
2 STFC Rutherford Appleton Laboratory, RAL SPACE, Harwell, UK
3 School of Electrical & Computer Engineering, National Technical University of Athens, Athens, Greece
4 School of Electrical & Computer Engineering, National Technical University of Athens, Athens, Greece

Abstract –Satellite communications have already started to employ mmWave bands such as the Ka-band
(20/30GHz) for broadcasting and broadband services; Ka-band is used either for backhauling (feeder links)
or direct-to-user services. To enhance the propagation modeling and assist in the development of advanced
satellite radio systems, two site diversity experiments are simultaneously conducted in Greece and in the UK
using the satellite beacon transmitted by ALPHASAT. In this paper, the two years of collected experimental
data are presented and evaluated in terms of first-order statistics. Considering the different climate of the
two experiment locations, one in the Southern Mediterranean Sea (Greece) and one in the Northern Atlantic
Sea (UK), a comparison between the two respective Ka-band long-term radio diversity channels is also
performed. Several conclusions for the diversity system design are drawn that can be particularly significant
towards the application of a smart gateway diversity concept in feeder links.

Keywords – ALPHASAT, exceedance probability, excess attenuation, joint statistics, Ka Band, satellite
comunications, site diversity

achieved by merely using a fade margin; more
1. INTRODUCTION advanced Fading Mitigation Techniques (FMTs)
have to be utilized.
In modern satellite communication systems the
reliable design and system performance are A typical feeder link FMT is uplink power control,
constrained by the radio propagation effects, the providing a few more dB of extra fade margin at the
interference and the noise, phenomena inherently expense of bulkier gateway RF front-ends [4].
present in every radio system. Currently, fixed However, even such a technique might not be
satellite services using GEO satellites commonly sufficient to provide the required availability level
employ [1] Ku (12/14GHz) and Ka (20/30GHz) for the feeder links, particularly when the Q/V-
bands. These frequency bands are used for both bands are considered. At such frequencies rain
direct-to-user (DTU) and broadcasting applications, effects can severely impair the signal and depending
as well as for feeder links and satellite backhaul on the rain intensity and the elevation angle, can
networks [2], [3]. New, data-rate intensive satellite potentially cause attenuation in excess of 15 to 20
applications have evolved and led to the adoption of dB for a non-negligible percentage of time
higher frequency bands (such as Ka-band) for both throughout the year.
fixed and mobile satellite networks. Despite the fact Site Diversity (SD) is a well-known strategy to
that the use of higher frequency bands bears many mitigate the impact of fading events in satellite
advantages (namely greater bandwidth and less feeder links by exploiting the temporal and spatial
interference), the signal propagation can be variability of the radio channel [1], [2], [5]. A
significantly affected by the various atmospheric gateway is complemented by a backup station
phenomena (i.e. rain, clouds, gases, the melting within the same feeder beam at a suitable
layer and tropospheric turbulence).
separation distance depending on the regional
In order to meet the elevated system performance meteorological characteristics. Considering a
requirements imposed by the new services and properly configured station arrangement, the two
applications, feeder links design must provide a locations should encounter severe radio
very high link availability, typically in the order of propagation impairments at different times; in this
99.9% or higher [1], [3]. Maintaining such a high case, switching to the site experiencing the least
link availability is a non-trivial task and cannot be fading should considerably improve system

© International Telecommunication Union, 2019 45