Assessment of Rain Attenuation for Terrestrial Communication Links in Kaduna State, Nigeria

Abstract

Designing satellite and terrestrial communication links requires accurate predictions of rain rate and rain attenuation because rain-fade and its dynamic fluctuations have consistently been detrimental to received signals, especially in tropical regions known to be prone to heavy rainfall. Nigeria's rain is characterized by heavy rainfall, frequent rainfall occurrences and a greater abundance of large raindrops when compared to temperate regions. Research on prediction of rain attenuation has become a necessity in the study area, as the study of rain attenuation prediction in Kaduna State is minimal (if available). Also, research and forecast by NIMET indicated that the northwestern region of Nigeria is expected to face a significant rainfall event in the coming days, which could lead to flooding and hazardous conditions (signal attenuation) that requires preparedness and mitigation efforts by authorities and resident. This study looks into the effect of rain-induced attenuation on microwave and millimeter wave propagation for terrestrial communication links in Kaduna State, Nigeria. 36 years (1986-2022) daily rainfall (mm) data was obtained from the Nigerian Meteorological Agency (NIMET) Abuja. The rainfall accumulation (mm) was converted to 1 minute rain rate (mm/h) using the Chebil rain rate model, while rain attenuation values were computed using the ITU-R P. 530-17 rain attenuation model. The analysis shows that Kaduna State has a rainfall rate of 106.12mm/hr at 0.01% of time exceedance. For the rain attenuation analysis, higher attenuation values were recorded at higher frequencies. At 25 GHz and 20 km path length, values of 103 dB and 127 dB were predicted for vertical and horizontal polarisations respectively, while 165 dB and 188 dB were predicted for vertical and horizontal polarizations respectively at 40 GHz. Hence, the findings show that the attenuation become higher at horizontal polarisation than at vertical polarisation.