Abstract:
The strong impact of rain on satellite-based telecommunication systems makes the prediction of rain
induced propagation impairments (such as attenuation and interference) using the cumulative
distribution of the point rainfall intensity a subject of continuous research interest. Tropical rainfall
has interesting characteristics, which are quite distinct from those of temperate rainfall; and therefore
have dire consequences on the quality of signal at Super High Frequencies (SHF). For the prediction
of interference, many models and techniques have been used for determining interference due to
hydrometeor (raindrop) scatter between independent microwave stations. The present study employs
the modified version of the three dimensional (3D) rain cell model to estimate microwave
interference due to rain scattering. It uses as input three elevation angles, 55° (over the Atlantic
Ocean Region), 23° (over Indian Ocean Region) and 42.5° (NIGCOMSAT -1 geostationary satellite)
in the analysis of transmission loss. The transmission loss and effective transmission loss statistics
are computed at frequencies ranging between 4 - 35 GHz used for satellite and terrestrial
communication. However, in computing the transmission loss and the effective transmission loss,
both horizontally and vertically polarized radio signals are assumed to pass through the rain medium.
Results are presented for thunderstorm rainfall type which is prevalent in the tropical region. Results
are also presented for the variation of transmission loss particularly for the Ku (11/14 GHz) and Ka
(20/30 GHz) frequency bands. Also, the estimation of the statistics of the transmission loss are
computed for varying distances from the terrestrial system (TS) antenna to the common volume (CV)
formed by the intersection of the antenna beams for all the look angles. The study also considered the
transmission loss effects at two path length configurations; short (:S 50km) and long (> 50km) ,
varying antenna gains and varying percentage time unavailabilities (outage time) for vertical and
horizontal polarizations. The results obtained were then used to predict the severity of rain scattering
resulting in intersystem interference, particularly at frequencies ranging from 4 - 35 GHz currently
in use by most communication satellite systems.
