Evaluation of Diversity and Power Control Techniques for Satellite Communication Systems in Tropical and Equatorial Rain Climates

Satellite communication systems operating at frequencies above 10 GHz in tropical climates are subjected to many fade occurrences due to heavy rain. Service providers need to consider the use of appropriate forward error correction codes, the choice of modulations, diversity techniques, and the range of uplink/downlink power controls to use during severe rain fade periods in the overall design of their communications networks. The probable duration of a rain fade at a given level, what time of day it is likely to occur, how frequently it happens, and when it might next return are all important aspects that will contribute to customer perceptions. This paper presents the performances of annual and seasonal site-diversity and time-diversity measurements. Statistics of fade duration and fade slope variations are provided to give the detailed insight necessary for the design of very small aperture terminal (VSAT) systems, in particular, in choosing an economical link margin and a suitable adaptive power control subsystem. Furthermore, the variations in the received clear-sky level of the satellite beacon show evidence of a diurnal variation that has a period of a solar day due to the atmospheric thermal tide. There is also evidence for annual periodicity in absorption levels through the atmosphere on top of the diurnal tidal effect, again suspected to be due to a longer period atmospheric tide. In rain-fade countermeasure design (now more commonly referred to as fade mitigation techniques) for Ku/Ka-band systems in the tropics, the compensation for signal impairment due to tropospheric/atmospheric thermal tide should also be included in the fade countermeasure algorithm.