Effects of integration time on rain rate distributions for microwave link design based on measurement in Malaysia

Abstract

The demand for radio frequency spectrum is rapid since the most desirable frequency spectrum is congested; hence 5G and satellite communications are moving forward to the frequency band utilization above 10 GHz. Frequency higher than 10 GHz is subjected to impairment by rain. ITU-R has established rain attenuation prediction methods deduced from the measured rainfall rate with an integration time of 1-minute or less. However, recently, significant discrepancies in ITU-R prediction are found in the measurements of rain attenuation at mmWave bands for short-length propagation links. All researchers used rain intensity from 1- min integration time measurement, as not less than 1-minute data are unavailable. Therefore, this project aims to consider rain rate less than 1-minute integration time, investigate the effects of less than 1-minute integration time on rain rate distribution, and compare rain attenuation predictions using measured rain intensities with different integration times. A real-time rain gauge with a resolution of 10-secs integration time is installed in the International Islamic University Malaysia (IIUM) Gombak. A one-year measured rain rate data with integration times of 10-secs, 20-secs, 30-secs, 1- minute, and 2-minutes are utilized to analyze the effects of integration times on rain intensity distributions and rain attenuation predictions. From the analysis, it is found that at 0.01% probability, rain rates are 123 mm/hr and 191 mm/hr with 1-min and 10-secs integration times, respectively. At 0.1% and 0.001% probabilities, the differences increase to 80% and above. The rain attenuation measured at 26 GHz, 38 GHz, and 73 GHz terrestrial links with 300 m lengths and 12 GHz earth-to-satellite links in Malaysia are compared with those predicted by data from 5 integration times. Predicted attenuation with 10-secs is closer to measurement than 1-min integration time for all three terrestrial links and two satellite links. However, 30-sec integration time data was found close to the measurement for one satellite link. Hence mm-wave short paths in 5G, lower integration time-based rain rate measurement will provide more accurate prediction for path loss and high reliability in the tropical climate.