Tropospheric scintillation can become a significant impairment in satellite communication systems, especially in those with low fade-margin. Moreover, fast amplitude fluctuations due to scintillation are even larger when rain is present on the propagation path. Few studies of scintillation during rain have been reported and the statistical characterization is still not totally clear. This paper presents experimental results on the relationship between scintillation and rain attenuation obtained from slant-path attenuation measurements at 50 GHz. The study is focused on the probability density function (PDF) of various scintillation parameters. It is shown that scintillation intensity, measured as the standard deviation of the amplitude fluctuations, increases with rain attenuation; in the range 1-10 dB this relationship can be expressed by power-law or linear equations. The PDFs of scintillation intensity conditioned to a given rain attenuation level are lognormal, while the overall long-term PDF is well fitted by a generalized extreme value (GEV) distribution. The short-term PDFs of amplitude conditioned to a given intensity are normal, although skewness effects are observed for the strongest intensities. A procedure is given to derive numerically the overall PDF of scintillation amplitude using a combination of conditional PDFs and local statistics of rain attenuation.

Detailed measurements of the rain phenomena can be obtained from modern equipment that provides experimental drop size distributions (DSDs), which can be used to analyze the effects of past rain events or to predict their influence on colocated radio links. In this letter, the use of experimental DSDs to predict rain effects on millimeter-wave propagation is discussed from a practical point of view, taking advantage of the availability of measurements from various instruments. The derived results show that predictions can be calculated with reasonable accuracy, provided that some practical considerations are taken into account.

SUMMARYSatellite systems and high-altitude platform systems working in Ka and V bands require the application of adaptive techniques in order to mitigate link degradations caused by atmospheric impairments such as those due to cloud cover. Among these techniques, resource sharing system techniques and site diversity need information on the spatial distribution of impairments caused by cloud cover, including the probability of simultaneous occurrence of adverse conditions in various regions.A study has been performed in Spain, within the framework of COST Action 280, to investigate the large-scale spatial distribution of cloud cover using synoptic meteorological data. Cloud cover distribution for individual sites and the spatial correlation properties for pairs of sites have been investigated. The geographical distributions of the values obtained from the statistical analysis have been represented in maps of contour lines using standard mapping procedures. Correlation parameters are expected to decrease with distance; however, the maps derived taking a given site as reference reveal a significant influence of climatic and geographic factors such as weather fronts, orography or the proximity to the sea. The statistics and maps obtained can be useful to optimize power sharing in multi-beam satellite systems, as suggested in this paper.

Rain attenuation in millimeter-wave links depends on the Drop Size Distributions (DSD) of the raindrops. Empirical models disregard this dependence and estimate the specific attenuation using only the integrated rainfall rate (R (mm/h)). This approach is valid for lower frequencies but it progressively losses accuracy as the frequency of interest becomes higher within the millimeter-wave range. Both the characterization of rainfall phenomena and the prediction of rain attenuation can be improved with the knowledge of DSD, which, in turn, depend on the type of rain event (stratiform or convective) and the R. In this paper, long-term DSD measurements from a vertical Doppler radar (MRR-2) and a laser optical disdrometer (Thies Laser disdrometer) are used to obtain, classify and compare the statistics of DSD in Madrid in periods of more than ten years. The process to obtain the DSD from these advanced instruments is analyzed in detail, providing recommendations about the calibration of the radar data and the most appropriate particle filtering to apply on the Laser disdrometer data.

This study is based on the results of a slant-path Ka-band propagation experiment carried out in Madrid, Spain, regarding rain attenuation, which is the main propagation impairment in this frequency band. The experimental and statistical results correspond to seven complete years of measurements, a period large enough to accomplish a comprehensive analysis in order to characterize the variability of rain rate and attenuation. It is shown that year-to-year variability is significant in temperate climates as Madrid's. The aforementioned significance is also apparent with regards to seasonal, monthly, worst-month and hourly variability concerning rain attenuation, which are also discussed and related when possible to the variability of the rain phenomena, either represented by the total amounts of rainfall in the different periods or by rain rate statistics.Report of COST Action 255 [4], or the more recent National Technical University of Athens model [5], or the Synthetic Storm Technique (SST) [6], in addition to the global models for rain rate included in ITU-R Rec. P. 837-6 [7]. Procedures to predict worst-month statistics from average-year predictions or measurements are described in ITU-R Rec. P. 841-4 [8].Thus, the variability of propagation phenomena is not well-addressed in propagation models. Regulatory documents, such as [9,10], partially deal with this subject, which is of growing interest, as shown for example in [11]. Studies on the variability of the propagation measurements from experimental results are very scarce, being [12][13][14] some of the few examples that can be found in the literature. Another approach is the simulation of propagation results starting from long-term rain rate data that are converted into attenuation data using the SST. The variability of the resulting propagation results can be analyzed as was performed, for example, in [15,16]. The variability of rain rate statistics has also been addressed in a few papers [17][18][19][20][21].In this paper, the variability of rain rate and rain attenuation is assessed, making use of the results of a long-term propagation experiment carried out in Madrid, Spain. The Ka-band beacon of the Eutelsat Hot Bird 13A satellite (previously known as Hot Bird 6) has been continuously measured since June 2006 to the first days of July 2013, when the beacon was switched off as part of the process of reconfiguring the satellite to a different orbital position. The period of measurements includes seven complete years, which allows a comprehensive characterization of the propagation channel. The minimum number of years of measurements needed to take into account the natural variability of the rain phenomena and their effects on propagation has been discussed for a long time. A study of long-term rain rate data [17] concludes that seven is the minimum number of years for which most of the averages (of individual distributions) fall within the 5-95% confidence limits of the long-term (49 years) distribution. According to this study, longer periods, such as 1...