me and location. Although for planning calculations rainfall rates mentioned by the ITU standards are used (Figures 3.48 to 3.50), it is always beneficial to use the data collected from previous years. Researches have proved that the accuracy of the prediction increases with larger amounts of collected data. Error reduction can vary from 0.001 % to 10% when collected data varies from 10 years to 1 year. The attenuation due to rainfall is not only dependent upon the rain rate but also upon factors such as the drop size distribution, terminal velocity, canting angle and properties of water. The drop size distribution is further dependent upon the drop shape, precipitation type and atmospheric temperatures. Precipitation is dependent upon the type of clouds. The canting angle is the angle that the raindrops make with the vertical. The terminal fall velocity of the raindrops is dependent upon the air pressure, humidity and temperature. Dielectric properties depend upon temperature and frequency. For l > 1 mm, the dielectric properties are due to the polar nature but for l 1 mm the dielectric properties depend upon the resonant absorption of the molecules. Based on long-term statistics of the rain rate, the attenuation due to rain can be calculated using the following steps: 1. Find the rain rate exceeded for 0.01% of the time (see Table 3.12) or the graphs given in ITU-R PN837 (Figures 3.48 to 3.50). 2. Calculate specific attenuation YR (dB/km) based on frequency, polarization and the rain rate. The specific attenuation can be calculated using the following equation: YR=kRa (3.47)* where k and a are frequency dependent constants whose values are given in Table 3.13. 3. Calculate the effective path length deff: (3.48)* where do = 0.015R0.01 This is valid for R0.01 < 100 mm/h. For a rain rate greater than 100 mm/h, the value of 100 mm/h should be used instead of R0.01. 4. Calculate the attenuation due to rain (Arain). The product of YR and deff give the attenuation due to rain. The path attenuation exceeded for 0.01 % 