Rain integration time and percentage probability of rain in Indian subcontinent for satellite communications

The study of rain statistics, including average and extreme conditions, plays a significant role in predicting link availability and in calculating required tradeoff margins for the designing of a ground to space RF link. In this paper the cumulative distribution of average rainfall measured for 15 years is used in order to obtain probabilities of exceedance of rainfall rates using cumulative time statistics and empirical models for the Indian subcontinent. The results are compared with the rain rates extracted from the ITU-R model for the locations under study. The calculated rainfall rates suggest significant variances in the climatic features such as probability of heavy rain and number of rainy days in a year. The analysis shows that the ITU-R model underestimates the rainfall intensity rates by 32.6%, 26.2% and 40.7%, 19% at higher and lower percentage of time when compared with measured rain rate data from Indian Metrological department. It is shown that the discrepancy between the empirical model and ITU-R model at higher percentage of time results in a 15 to 5 dB difference in predicted signal attenuation depending on the region, percentage of time and frequency. Adaptive Power Control is proposed as a means to improve the link availability during period of higher intensity rainfall.