Nowadays, mobile phone antennas can be found almost everywhere. We can see many of them in urban regions and also in very remote areas. Where the service provider is lacking a sufficient cable network, point-to-point radio systems are normally used to connect one antenna to the next or to the a nearby access point of the telephone network. The network of radio links has become very dense in the last years, especially in urban areas. But this kind of transmission is only possible if there is direct line of sight between the sender and the receiver. As soon as it starts to rain, the signal strength is lowered because the rain drops hamper the propagation of the electromagnetic waves. This attenuation of the signal depends on the intensity of the rainfall and can be measured at the receiver. By means of a widely accepted empirical relationship it is possible to estimate the average rain rate along the link from the attenuation measurements at the receiver. An urban area of about 150km2 in Greater Zurich is subject to this thesis. Measurements from 23 microwave links are provided by a local network operator and reference data from 13 rain gauges, two disdrometers and a weather radar were available. A total of 128 calibrations were conducted to estimate the parameters for the empirical relationship and two different types of the necessary pre-processing of the data were compared to each other. It could be shown that 50 per cent of the predictions made by means of a constant parameter set, are afflicted with a mean error of less than 1.2mm/h. Differences in the drop size distribution of rain events and the quality of the received signal were identified as important influence factors for reliable model predictions.