Regional variability of Specific rain attenuation in mm wave region for Indian Sub-tropical climate

Abstract

The radio signal in mm wave region is affected by rain characteristics such as rain rate, rain drop size distribution, spatial and temporal structure apart from polarization of signal. Thus, rain causes attenuation of radio signal in the mm wave region (30 GHz to 300 GHz), which becomes important as fade margin for the design of reliable communication. The rain drop size distribution (RDSD), which varies for different climatic conditions at the same rain rate, plays very important role for attenuation of radio signals in mm wave region. The tropical region such as India, Malaysia, Brazil, Nigeria, South Africa and Singapore follows log-normal rain drop size distribution. In this paper, various lognormal RDSD models of Indian Climate based on rain drop size spectra measurement at Dehradun, Kharagpur, Shillong, Ahmedabad, Hassan and Trivandrum have been discussed in respect of rain drop size spectra and compared with lognormal RDSD models of other tropical countries. Further, the specific rain attenuation model developed from different RDSD models of Indian tropical climate is described, which shows the regional variability in the specific attenuation at mm wave region due to variation in the rain characteristics. It is observed that specific rain attenuation at 100 GHz decreases less compared to 60 GHz with the increase of rain rate. The specific rain attenuation at 100 GHz is less compared to 60 GHz beyond the rain rate of 30 mm/hr depending upon the locations due to different RDSD characteristics in the Indian tropical region.