 degradation can have several causes. These include reduced microwave link performance, interference, and synchronisation-related problems. The most common reason for degradation in microwave links is varying and unpre- dictable propagation conditions. Earlier in this chapter, conditions such as fading (flat, multipath and k-fading), layering, ducting, attenuation due to rain, etc., were discussed. However, when the signal fades and stays that way, it is essential to look for the cause(s) and remedy the situation. The quality of microwave links is measured in terms of error performance and availability. When the quality targets have been checked and redefined, the process of data collection starts. This data generally includes planning data (topology, hop lengths, planned link budget calculations, frequency plans etc ) and link performance data that should contain the performance data at the time of link commissioning and during the problem period. Also, data collected during different periods of the year and at different times of the day would be of help. Mobile call statistics during the fading and non-fading phases would enable a better understanding of the correlation, if any, between call drops and fading. Analysis of the data should begin with recalculation of the link budgets SO as to confirm that there were no errors in the initial design. The data of these links monitored at the time of commissioning and during the optimisation phase should be analysed against the backdrop of the design data in the master plans (made before the network launch). One such example of link data calculated and monitored during the optimisation phase is shown in Figure 3.27. The unavailability figures of the four links in a region are calculated and the worst case is analysed by using the data recorder for a period of 24-hours. Once it has been detected that the received level is below the desired level, path profile analysis should be done again in case the path lengths are more than a few kilometres. Also, error performance 