Ana Benarroch

Spatial distribution of cloud cover

Satellite 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. Copyright

Attenuation Measurements and Propagation Modeling in the W-Band

The frequency range that extends from 70 to 115 GHz presents low gaseous attenuation and offers the possibility of implementing radio links with capabilities of transporting more than 1 Gb/s over distances up to a few kilometers. A better knowledge of the propagation characteristics of the atmosphere at these frequencies can benefit future technological advances, providing better performance in terms of the use of radio resources. Unfortunately, the number of propagation results communicated for this band is very small. In this paper, propagation in this frequency range is analyzed on the basis of two-year experimental measurements carried out in Madrid, Spain, on a commercial link working at 75 and 85 GHz. Rain attenuation is the most relevant propagation effect in the W-band. Attenuation measurements are processed to remove wet antenna effects, leaving only the path attenuation time series. Statistics obtained from these time series are compared with a number of model predictions that use rain information of various types as input data, assessing in this way their precision and usefulness.

Experimental assessment of slant-path rain attenuation variability in the Ka-band

Summary 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 Madrids. 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. Copyright

Slant path attenuation measurements at 50 GHz in Spain

A one-year campaign of slant path attenuation measurements has been carried out in Madrid using the ITALSAT satellite beacon at 50 GHz. The experimental cumulative distributions of rainfall rate and rain attenuation are presented. The first one is compared with the ITU-R (International Telecommunication Union-Radiocommunication) maps while measured attenuation values are compared with several prediction models. Finally, the relationship between average year and worst month is investigated.

Joint results of long-term earth-space propagation experiments at 20-GHz in Canada and Europe

Propagation effects such as rain or clouds attenuation cause deeper fades in the Ka-band than at lower frequencies. In this collaborative paper, the main results of four long-term Ka-band propagation campaigns are presented. The experiments are carried out in Ottawa, Canada; Aveiro, Portugal; Madrid, Spain; and Toulouse, France. Attenuation statistics are derived from satellite beacon data collected over 6 years at Aveiro, 5 years at Ottawa and Madrid and 2 years at Toulouse. Multi-year measurements allow the production of more stable statistics reflecting the long-term behavior of propagation phenomena and to investigate its year-to-year variability. The beacon signal data was monitored and collected on a continuous basis over the whole measurement period. After a brief introduction of the experiments, rain rate and excess attenuation results are discussed, first for a common measurement period and later for the whole database available. Seasonal attenuation statistics for Ottawa and Aveiro are compared. Finally, fade duration and fade slope statistics derived at three locations are presented and discussed.

Joint Statistics of Rain Attenuation at 20 GHz in Madrid and Aveiro

Rain attenuation is the most severe propagation impairment affecting radiowave signals in the Ka-band. The use of these frequencies for satellite communication systems is facilitated by the implementation of fade mitigation techniques (FMTs). Spatial correlation of rain rate and rain attenuation for distances of several hundred kilometers has been rarely characterized in experiments, however it is relevant for site diversity studies, with distances in this range, and for the design and operation of multibeam satellite systems with shared on-board radio resources. In this letter, experimental results regarding joint statistics of rain and rain attenuation are presented for Madrid, Spain, and Aveiro, Portugal, located 420 km apart. These results have been achieved from two years of simultaneous measurements of the Eutelsat HB-6 Ka-band beacon at 19.7 GHz. It is shown that high-attenuation events are independent, whereas there is some correlation for low-attenuation levels.

Dynamic characteristics of fading on a 50 GHz slant path

The dynamic characteristics of fading due to atmospheric propagation are of interest for the optimization of the link quality and availability of satellite systems and high altitude platform systems working in Ka and V band. More effort is needed in fade dynamics characterization in a wide range of climates, especially in high frequencies, where few measurements and studies are available nowadays. A study has been performed in the Universidad Politecnica de Madrid, Spain, to analyze fade dynamic characteristics using one year of experimental measurements on a 50 GHz slant path. Statistics of fade duration, interfade duration and fade slope are presented and analyzed. In general, the ITU-R model of fade dynamics, which includes the estimation of both fade duration and fade slope, provides acceptable results.

Spatial properties of cloud cover and rainfall rate based on data from spanish sites

Accurate information on the spatial properties of both cloud cover and rainfall rate is needed for the development of specific Propagation Impairment Mitigation Techniques (PIMTs) required for satellite telecommunication and high-altitude platforms (HAP) systems. A statistical study of both phenomena has been performed in Spain in the framework of COST Action 280. Cloud cover distribution for individual sites and correlation characteristics for pairs of sites, for both cloud cover and rainfall rate, have been investigated. The geographical distributions of the values obtained from the statistical analysis have been represented in maps of contour lines. The maps derived from correlation statistics 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 seaboard.

Ka-band propagation characterization: Madrid experiment

The use of the Ka-band (30/20 GHz) for broadcasting applications is envisaged for the future, in order to fulfill the needs for higher and higher data rates. A propagation experiment is being carried out in Madrid, Spain, with the objective of characterizing the propagation channel in the downlink sub-band. Propagation results can be related to meteorological data obtained from co-located instruments. Rain attenuation is the main propagation impairment in this band. Its effects are analyzed in detail.

Large‐scale correlation of rainfall rate based on data from Spanish sites

SUMMARY Modern and future satellite systems working in the Ka and Q/V bands often require the application of site diversity to mitigate the degradations caused by rain. Satellite systems operating in these bands may make use of multi-beam techniques to provide high-capacity services. To achieve an efficient performance in both techniques, precise information is necessary on the occurrence of simultaneous rain fades in various links under a given satellite coverage. This is attained through the knowledge of the spatial characteristics of rainfall rate over the area of interest. The availability of a large database of rain gauge data from about 50 sites in Spain has allowed the undertaking of a study on the large-scale spatial distribution of rainfall rate. Joint distributions and correlation parameters have been investigated for pairs of sites, and experimental results have been compared with predictions based on the ITU-R site diversity model, obtaining the best results when stratiform rainfall is dominant in both sites. Some statistical dependence has been found even for distances above 700 km. The values obtained from the statistical analysis have been represented taking a given site as reference in maps of contour lines using standard mapping procedures. Correlation parameters are expected to decrease with distance; however, the contour maps 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 are useful to optimise both power sharing in multi-beam satellite systems and the application of site diversity. Copyright