EVALUATION OF THE FEASIBILITY OF SATELLITE SYSTEMS DESIGN IN THE 10–100 GHZ FREQUENCY RANGE

We have presented a picture of the total attenuation to be considered in satellite communication and broadcasting systems in the 10–100 GHz frequency range. Although the findings and methodology are of general interest, the numerical results apply to the Italian (mid-latitude) sites of Fucino and Gera Lario and to slant paths of elevation angles 33° and 32° respectively. The rain attenuation probability distributionP(A), of exceeding the value A(dB) at a given carrier frequency in an average year, has been estimated by the synthetic storm technique and an associated formula, presently derived, which links Ato frequency for fixed probabilities. The extra fading due to water vapour, clouds, oxygen and scintillations is estimated by applying the ITU-R formulae. After studying how the received carrier power PR changes as a function of frequency for fixed antenna dimensions and transmitted carrier power PT, we have carried out an exercise to show what first order values of PT we need in an ideal QPSK modulation scheme, with a standard uncoded stream of 64 kbit/s, in a complete earth–satellite–earth connection, with regenerative or transparent transponders, for a given maximum bit error rate tolerated by users. After this analysis we have drawn the following conclusions: (a) the results depend very much on the outage probability and on the site; (b) there are two windows at high outage probabilities, e.g. 1%, the first in the 20–50 GHz frequency range and the second beyond 70 GHz; (c) in the frequency range 50–70 GHz any significant service availability level cannot be achieved because of the very large fading due to oxygen; (d) the transmitted power can show sharp minima which depend significantly on the outage probability and on the site; (e) service availability levels better than 99·99% of the year cannot be achieved at frequencies of 30 GHz and above, with ground station antennae of 25 cm or less aperture diameter.