DefinePK

Abstract

Nowadays Telecommunications and broadcasting services are in a rapid phase of expansion. There is an increasing demand for the multimedia services such as high-speed internet, on demand digital TV services, video conferencing and tele-education etc., which need high-speed data rates to cope with the demand whilst guaranteeing a high quality of service[9][10]. The current microwave frequency spectrum allocated for telecommunication and broadcast services has become packed as the proposed broadband systems requires higher bandwidths. However, the attenuation due to atmospheric gases, clouds and rain increases significantly, for the frequencies above Ku- band. Though the attenuation is due to clouds and gases frequently, it is rain that causes the largest attenuation. In this paper three sophisticated models (ITU-R, DAH and SAM) have been explained to calculate rain attenuation. ITU-R model is the most widely accepted model by the international propagation community and is used for estimating long term statistics of rain attenuation at high frequencies in most of the regions. DAH stands for Dissanayake-Allnutt-Haidara Model. This is similar to and an extension of the ITU-R model. This model is also used at high frequencies. SAM stands for Simple Attenuation Model, which is suitable for tropical climate and heavy rainfall regions to calculate attenuation at point rainfall.