Time Diversity and Linear Combining Gain Obtainable During Rain at Ka Band in the Alphasat Slant Path in Spino D'Adda

The purpose of this paper is to show how time diversity and linear combining techniques - (a) selection diversity, (b) equal-gain combining and (c) maximal-ratio combining- can be used, with great advantage, in two distinct ranges of rain attenuation, to reduce both the probability of exceeding a given value of rain attenuation (i.e., a link design based on constant and assigned power margin) , and the rain attenuation exceeded for a given probability (i.e., a link design based on constant and assigned outage probability), in the ALPAHSAT slant path (elevation 35.5°) in Spino d'Adda, where both the 19.7 GHz and 39.4 GHz beacons are received. Technology issues, some of which are discussed in the literature, are beyond the purpose of this paper. The main conclusions are: a) As expected, the instantaneous time-diversity gain can be large when the delay time is large and rain attenuation is large; b)Equal-gain and maximal-ratio combining can add up to 3 dB to the selection diversity gain when the time-diversity gain is very small; c) Equal-gain and maximal-ratio combining reduce the fraction of time of rain attenuation in an average year to a value less than the probability of exceeding 3 dB in the link without diversity.