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International audience; In this paper, we present a methodology to compare frequency scaling techniques of rain attenuation. This methodology consists in obtaining rain attenuation from beacon measurements, selecting a subset of events, and applying metrics on the obtained time series. Are also discussed methodologies to separate the contributions of clouds and rain to attenuation, as well as a method to identify events affected by noise. The relevance of the approaches is evaluated on a database of satellite beacon attenuation: Italsat beacon measurements from Spino d'Adda (7 years).

Contributions to the GSAT 14 Ka-band propagation campaign, designed and carried out by ISRO, has been conducted by ONERA in Shillong (25.6750°N, 91.9136°E), and CNES in Hassan, India since 2015. Two beacon Earth stations operating at 20.2 GHz, and 30.5 GHz, a profiling radiometer, and a rain gauge are available at the experiment site. Two beacon receivers at 20.2 GHz and 30.5 GHz measure the received signal strength with a 10-Hz sampling rate. In the present paper, rain rate and copolar attenuation data have been analysed. Details of the instruments and methodology of the data analysis have been described. A case study in terms of time series variation of rain rate, and copolar attenuation has been shown. The complementary cumulative distribution function (CCDF) of rain rate and copolar attenuation for the total study period has been calculated and compared with ITU-R model. A high year to year variability has been observed. The experimental CCDF shows good matches with Rec. ITU-R P.618-13 above 0.1 % of time exceedance over Shillong. The comparison of 30.5 GHz copolar attenuation data with ITU-R frequency scaling model shows a good match. Difference has been observed between experimental data and ITU-R model over Hassan.

International audience; Ce papier présente l'utilisation d'un simulateur atmosphérique reposant sur un modèle de prévision météorologique à haute résolution pour reproduire des statistiques d'atténuations due à la pluie pluriannuelles en bande Ka en Guyane française. Les résultats obtenus à l'aide de ce modèle sont comparés d'une part aux données expérimentales disponibles dans cette région et d'autre part aux modèles de prévision de l'UIT.

International audience; In 2019, new methods to synthesize time series of single-site and multi-site tropospheric impairments on Earth-space paths have been adopted by ITU-R Study Group 3 in Recommendation ITU-R P.1853-2. However, these methods are only applicable in the case of a Geostationary Earth Orbit (GEO). As the deployment of multimedia services from Low-Earth Orbit (LEO) or Medium Earth Orbit (MEO) satellites constellations is gathering momentum worldwide, the access to simple attenuation and tropospheric scintillation time series synthesizers for Non-Geostationary Earth Orbit (NGEO) applications appears to become critical. This paper presents an adaptation of the recommendation ITU-R P.1853-2 to a NGEO link in single site configuration using elevation-dependent parameters to parameterize the statistical distribution of attenuation for time series generation.

International audience; Les nouvelles bandes de fréquences pour les systèmes de télécommunications par satellite L. Castanet (ONERA) Comment le satellite peut-il rester un complément des solutions terrestres afin de fournir un accès global aux infrastructures de communications et ainsi éviter les zones blanches et résorber la fracture numérique ? Historique Le premier satellite artificiel, Spoutnik, a été lancé par l'URSS en 1957 et a été suivi par un certain nombre d'envois de satellites expérimentaux au début des années soixante. Les premiers services commerciaux de télécommunications par satellite sont apparus à la fin de cette décennie sous l'égide de l'opérateur Intelsat. A cette époque, le satellite était considéré comme un moyen alternatif aux liaisons par câbles sous-marins ou aux liaisons par faisceaux hertziens. Ces premiers systèmes utilisaient un satellite en orbite géostationnaire de quelques dizaines de kilogrammes et quelques dizaines de Watts de puissance embarquée et se caractérisaient par une durée de vie très courte (moins de deux ans), une fable capacité (moins de 500 canaux téléphoniques) et un coût d'opération par canal qui serait aujourd'hui considéré comme exorbitant. Ils permettaient d'acheminer des communications intercontinentales en point à point. Depuis cette époque, les progrès techniques ont permis d'allonger la durée de vie des satellites pour atteindre 15 ans aujourd'hui, avec des satellites dépassant les 10 tonnes pour des puissances électriques de 20 kW. Ces satellites permettent de desservir de larges zones de couverture, avec une capacité de diffusion à des centaines de milliers d'utilisateurs en même temps.

International audience; Since 2009, ONERA has been running a Ka-band propagation experiment in Toulouse (south of France). A rain gauge, a microwave profiling radiometer and a beacon receiver able to record the 19.7 GHz signal from Hot Bird 6 satellite and the 20.2 GHz signal from Astra-3B satellite have been deployed. This paper gathers nine years of results from the still ongoing experiment. The annual, monthly and seasonal complementary cumulative distribution functions of rain attenuation are presented. A comparison is made with the annual rain attenuation prediction method of Recommendation ITU-R P.618-13 and its dispersion given by Recommendation ITU-R P.678-3. Fade slope and fade duration statistics are studied for different attenuation thresholds.

International audience; A propagation experiment funded by ESA with support from CNES has been deployed in Svalbard (Northern Norway, 80° latitude North) in order to study propagation impairments at Ka-band caused by the troposphere at high latitudes and low elevation angles in representative conditions for GEO satcoms systems in the Artic region. In this context, a NASA Glenn Research Centre beacon receiver, operated by KSAT in Norway, measures the signal from the THOR7 satellite at a 2.65° elevation angle since March 2016. ONERA processes and analyses the data since the beginning of the experiment. At this stage 2 years of propagation data from the satellite have been gathered. An Atmospheric Numerical Simulator relying on the high resolution meteorological model (WRF-ARW) is used to generate 3D states of the atmosphere during a concurrent period to the experiment at high spatial & temporal resolutions. Propagation calculations based upon those outputs are then conducted to derive simulated attenuation time series between the beacon receiver and THOR7. Results show a fairly good statistical agreement between the measured and simulated attenuation time series whereas the simulated statistics seem to underestimate the overall attenuation for all percentages of time.

International audience; ONERA, the French Aerospace Lab, and CNES, the French Space Agency, are currently running a Ka-band propagation experiment at the Guiana Space Centre (CSG) in Kourou (French Guiana). A rain gauge and a beacon receiver able to record the 20.2 GHz beacon signal of the Amazonas 3 satellite have been deployed. The equipment is operational since January 1, 2017 and the duration of the experiment has been set to 3 years. This letter addresses some results of the first year of measurements (from January 2017 to December 2017). The annual and monthly Complementary Cumulative Distribution Functions of rainfall rate and rain attenuation are presented as well as a comparison with the rain attenuation prediction method recommended in ITU-R P.618-13.

International audience; Maritime environment, and in particular the sea clutter, has a significant impact on the detection efficiency. Therefore the physical properties of the radar sea clutter must be well mastered. In this paper, we focus on sea clutter data acquired during an experiment called MARLENE, which was held in the Mediterranean Sea region of Toulon, France, in 2014. The aim of this experiment was to characterize the sea environment influence on radar propagation and backscattering for Refractivity From Clutter (RFC) and radar Doppler detection. Three coastal radars, MARSIG (WTD 71), MEMPHIS (FHR) and MEDYCIS (ONERA) were used to acquire sea clutter measurements simultaneously. During the radar measurements, the in-situ oceanic and meteorological conditions were characterized on board of the RV PLANET meteorological ship deployed by WTD 71 and by WAVEWATCH III and SWAN wave models. The paper gives an overview of the MARLENE experiment, presents the radar data and the first results on sea clutter reflectivity and Doppler.

International audience; Since April 2011, ONERA has been operating in Toulouse, France, a beacon receiver able to receive the 20.199 GHz beacon signal of ASTRA 3B. From June 2013 to December 2013, ONERA and CNES successively deployed in the South of France four more beacon receivers in order to characterize the space-time behaviour of the propagation channel at Ka-band. This Site Diversity configuration is of great interest for the development of future high data rate satellite services as it efficiently mitigates severe tropospheric propagation impairments, in particular rain attenuation which is the major issue. The ONERA-CNES Ka-band site diversity experiment consists of three beacon receivers deployed in the area of Toulouse with site separation between 16 and 26 km, and two additional beacon receivers at 140 km and 300 km from Toulouse. This paper aims at providing a complete description of the experimental set-up and the statistical results of the campaign from July 2013 to December 2014. The Complementary Cumulative Distribution Functions (CCDF) of rain attenuation on each site and the Joint Distributions for several pairs of radio links are illustrated. Some comparisons of the measured Diversity Gain with two state-of-the-art prediction models are also presented.

Tropospheric phenomena such as clouds and mainly rain cause higher attenuation at 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 (satellite Anik F2); Aveiro, Portugal; Madrid, Spain; and Toulouse, France (satellite HotBird 6 in the last three cases) and have been running since 2004 in Aveiro, 2006 in Ottawa and Madrid, and 2008 in Toulouse. After a brief introduction of the experiments, rain rate and excess attenuation results are discussed, first for a common two-year measurement period and later for the whole database available. Seasonal attenuation statistics for Madrid, Ottawa and Aveiro are compared. Finally, fade duration and fade slope statistics derived at three locations are presented and discussed.

L'objectif de ce travail de recherche est d'analyser l'intérêt de concevoir et d'introduire des techniques de compensation des affaiblissements de propagation pour améliorer les performances des systèmes de télécommunications par satellite fonctionnant aux fréquences supérieures à 20 GHz et fournir une disponibilité de service suffisante du point de vue de l'utilisateur. Pour atteindre cet objectif, une nouvelle méthodologie est développée afin d'optimiser la conception de ces techniques de compensation en prenant en compte la dynamique du canal de propagation grâce à l'introduction de séries temporelles de propagation. Dans un premier temps, un recensement des caractéristiques du canal de propagation dans les bandes de fréquence Ka et V est réalisé. En particulier, les propriétés statistiques de la dynamique du canal dans ces bandes de fréquences sont décrites : vitesses de variation, durée des affaiblissements et similitude en fréquence. Ensuite, un état de l'art des techniques de compensation des affaiblissements adaptées aux systèmes de télécommunication par satellite est réalisé : d'une part par un recensement des méthodes envisageables et d'autre part par l'étude de l'implémentation de ces techniques au niveau de terminaux utilisateurs. L'influence sur les couches réseau est étudiée, de même que sur les différents types de service. La mise en place de ces techniques est alors étudiée via la conception et la mise au point d'une boucle de contrôle qui doit assurer trois fonctions différentes : la détection de l'état du canal, la prédiction temps réel de l'évolution de son état au cours du temps et la décision de lancer ou non une technique de compensation. L'architecture d'une boucle de contrôle de FMT incluant une méthode de compensation de la scintillation est proposée, résultat d'un processus d'optimisation des différents paramètres internes de la boucle. Enfin, l'influence du canal de propagation en bande Ka est étudiée sur l'interface-air du concept de système GEOCAST. Après avoir défini les techniques de compensation utilisables pour GEOCAST, des prédictions sont réalisées à l'aide de modèles statistiques conventionnels de manière à estimer la disponibilité due au canal de propagation. Les performances du système sont alors évaluées en terme de disponibilité, de nombre de commutations entre états du système ou de capacité, à travers l'introduction de séries temporelles de propagation mesurées lors de la campagne Olympus. The objective of this research activity is to analyse the interest of designing and implementing Fade Mitigation Techniques to improve the performances of satellite communications systems operating at frequency above 20 GHz and to provide the range seryice availability required by the end-user. To reach this objective, a new methodology is developed in order to optimise the design of FMT taking into account the dynamics of the propagation channel thanks to the introduction of propagation time series. First of all, an overview of the characteristics of the propagation channel forSatCom services planned to operate at Ka and V bands is given. in particular. the statistical properties of the propagation channel dynamics in these frequency bands are described : distributions of fade and interfade duration. fade slope, and frequency scaling. Afterwards, an overview of adaptive Fade Mitigation Techniques (FMT) suitable for high frequency band GEO satellite communication systems is carried out 1 firstly an overview of the basic principles of F MT and afterwards operational issues for systems deployed at these frequencies. Access and network characteristics as well as type of services are addressed too. Then, the interest is focused on the practical implementation of Fade t\/litigation Techniques. Outlines are given concerning the design of a FMT control loop and the three main functions to be carried out are described : detection, prediction and decision functions. Finally, a FMT control loop architecture including a scintillation controller is proposed, as the result of an optimisation process. Finally, the last part aims at studying the influence of the Ka-band propagation channel on the air interface of a Ka-band satellite system : called GEOCAST. After having defined FMT suitable for GEOCAST, predictions are performed with conventional statistical models in order to estimate channel availability. Then, the performances of the system are studied (in term of link availability or number of switches and system capacity) through the introduction of propagation time series.