mmWave vs FSO Propagation: First Results from an Experimental Testbed in Italy

Optical wireless links, namely Free-Space Optics (FSO), and mmWave links, appear to meet the high-capacity requirements for backhauling in the next-generation communications systems. However, wireless links at such high frequencies are susceptible to weather conditions. Specifically, FSO is severely affected by fog attenuation, while mmWaves struggle through the rain. Moreover, the theory predicts that the impact of rain on FSO is not as significant as on mmWaves, due to the forward scattering gain. Two mmWave links (at E- and D-band, respectively) and a near-IR FSO link have been deployed across an 800-m path in Milan, Italy, to study those effects. The experimental setup also includes weather sensors (disdrometers and visibilimeters) on either side of the path. Results collected during an 8-hour rainy event are presented here. FSO attenuation (in dB) is around 50% of mmWave attenuation at a peak rainfall rate of 20 mm/h.