Rain attenuation prediction based on raindrop size distribution measurement in Malaysia

Abstract

Attenuation due to rain at frequencies above 10 GHz in temperate climates and above 7 GHz in tropical ones is a critical factor for both terrestrial and satellite link system designers. Knowledge of the rain drop size distribution (DSD) is essential for an accurate estimate of the attenuation experienced by electromagnetic waves traveling through the rain. Large uncertainties remain in the variability of DSDs and their dependence on rainfall types and climatological regimes. Such uncertainties are much more critical in the equatorial region, where there are only limited experimental results of DSD data. In this study, a two-year measurement of DSD, using a 2D video distrometer (2DVD) installed for the first time in UTM Johor Malaysia, has been used. The 2DVD is an advanced instrument that not only can measure large ranges of DSD but also can capture the raindrop shape, axial ratio, oscillation mode and drop fall velocity, so it can provide a higher accuracy of estimations than any other instrument. A millimeter wave (mmwave) link operating at 38 GHz and a meteorological station installed at the same location, as well as earlier DSD data from Kuala Lumpur, are used to validate the findings. Based on the statistical analysis of the measured data samples, DSD parameters are computed using T-Matrix calculations. Specific attenuation of mmwave signals is presented for vertical and horizontal polarisations. Satisfactory results are achieved in comparison with other prediction models. Further, the study separates stratiform and convective rain types using the characteristics of the main DSD parameters. Seasonal variations are studied to elucidate characteristics of DSD in the Asian monsoon region. It is found that DSDs are affected by diurnal convective cycles and seasonal variations in precipitation characteristics. The implications of the variations on specific attenuation are presented. The results of this study will be helpful for the proper design and allocation of the wireless communication system to achieve the expected quality of service (QoS) in Malaysia.