Results of 2 year measurements on a 18 GHz radio link: rain unavailability considerations for radio relay systems at low and high capacity

The use of radio frequencies for transmission and reception of digital signals above 10 GHz is practically limited by the effect of rain. The water drops adsorb and diffuse the radio signal, producing an attenuation that increases with rain intensity and depth of the rain cell. The system becomes unavailable when this attenuation equals its FFM, (flat fade margin) producing BER ⩾10^-3, for 10 consecutive seconds at least. Since rain phenomena usually last more than 10 seconds, it´s important to obtain the relationship between the rain fallen and the unavailability expected, in order to correctly design the radio links. A comparison is done between the values expected from two largely used prediction methods and the measured values