Effect of multipath fading on millimetre wave propagation: a field study

Analysis of clear air fading encountered on millimetric wave and infrared radio links are presented. The analysis is based on data obtained during a four-year field study in the city of Riyadh, Saudi Arabia. The region can be considered as a typical arid climate where the rate of evaporation is higher than the rate of precipitation. Maximum rain rate is of the order of 30 mm/h for 0.001% of the year. A brief description of the experimental setup is presented, together with the results of measuring clear air fading experienced by the radio links. Statistical characterisation of fading is given for both the millimetric wave links operating near 40 GHz and the infrared radio link at a wavelength of 0.88 μm. It is shown that fading is dominated by multipath, having a Rayleigh amplitude distribution and an occurrence factor similar to the microwave band. Fades were highly correlated for the two links sharing the same path and separated in frequency by 1%. Multipath fading was also measured on the infrared link. Even at the short hop length at 0.75 km, the occurrence factor was about 1%. Time duration of fades are also analysed, and fade durations were essentially exponentially distributed. Small fades, however, have normal duration distribution