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International audience; The SAGAIE network was deployed in West-Africa in 2013 to assess the feasibility of an equatorial for ASECNA SBAS by studying ionospheric scintillation. This study of the network’s measurements, taken between 2013 and 2016, analyzes the characteristics of the scintillation recorded by five receivers that cover Sub-Saharan West-Africa.

International audience; Through several studies, CNES, ONERA, NSC and NMA have sought to define a prediction model for ionospheric variations that can disturb e.g. GNSS-based systems. The studies have focused on the high-latitude region, with a particular focus on the auroral oval. A first model was proposed in 2014. The model was a simple empirical model driven by the Kp geomagnetic index, and where the main output was the instantaneous mean Rate-of-TEC Index (ROTI) value. The model was found to not be sufficiently reliable to be used as an operational prediction model. In 2019, an updated model is proposed, where the main inputs are now the solar wind parameters pressure (the solar wind pressure p) and B z (the z component of the solar wind magnetic field). Moreover, a distribution of predicted ROTI or σ φ index is provided instead of a mean value. Thus, the model allows estimating the percentage of time of occurrence for a level of ROTI (or σ φ) to be exceeded in the next 5 minutes or 1 hour, or the exceeded ROTI (or σ φ) for a corresponding percentage of time. This empirical approach is based on 10 years of GNSS/scintillation data collected by more than 15 GNSS stations in Norway.

International audience; Ionospheric scintillation is a threat for the availability of systems with high service disponibility such as GNSS services. Indeed, this phenomenon is characterized by an important fluctuation of the amplitude and phase of the signal in reception, that can lead to loss of lock and signal outages. Given the fact that scintillation is caused by small-scale irregularities of the ionospheric density (ranging from a few meters to tenth of kilometers), the phenomenon is usually localized, both temporally and spatially. Moreover, it has an important day-to-day variability. After decades of interest for that phenomenon, the forecasting of ionospheric scintillation is still in progress.

International audience; La présente communication décrit un ensemble de travaux effectués à l'ONERA en partenariat avec l'université Paul Sabatier et le CNES sur la propagation électromagnétique à travers l'ionosphère turbulente. Le problème direct de la propagation à travers l'ionosphère turbulente est tout d'abord traité par le développement de modèles basés sur une description statistique du milieu ionosphérique inhomogène. Puis à partir du formalisme asymptotique développé, des mesures GNSS sont inversées pour obtenir des paramètres décrivant le milieu. Cette approche a été testée sur la base de données SAGAIE en zone équatoriale. Enfin un modèle dédié à la prédiction de la scintillation ionosphérique à hautes latitudes, régressé sur une base de données norvégienne acquises sur un cycle solaire, est proposé.

International audience; The main objective of this study was to figure out a relationship between space weather environment phenomena (solar activity and geomagnetism) and ionospheric events that impact L-band satellite navigation systems (scintillations, electron content gradients) in the Nordic European area.

International audience; The HFPE technological experiment aims at consolidating a new concept of long range transmissions between ground and the Low Earth Orbit. This concept relies on over-the-horizon transionospheric links in the HF-band. To prepare this experiment, propagation modelling and measurements have been carried out. In particular, a HF link planning software, MSATIS, has been tested with respect to experimental data, and improved. One of the major improvements is a global prediction of the ionospheric foF2 and hmF2 characteristics based on IONEX data. For air interface optimization, multipath effects not addressed by MSATIS had also to be characterized. Ray launching has been used to identify typical short-term propagation channels representative of HFPE propagation conditions.

International audience; Multipaths (MP) are still one of the major error sources in Global Navigation Satellite Systems operating in challenging environments such as urban areas. This paper presents how diversity algorithms may improve the multipath mitigation performances. The diversity can either lie on the space domain (antenna diversity) or on the frequency domain (frequency band diversity). In bothcases, the algorithms principle consists in taking benefit from information redundancy given by multiple diverse channels.

The new SAGE / STAP multicorrelators algorithm was recently proposed proving very good performances in multipath mitigation compared to other techniques such as Narrow correlator or adaptive beamformers. In this paper, the performances of SAGE / STAP multicorrelators in realistic tracking situations are presented, and show very promising results meanwhile real world measurement.

In GNSS applications, multipath errors and jamming threats are still one of the major error sources or service unavailability in conventional receivers. Antenna array algorithms are introduced as a possible solution to both these threats. Nevertheless, the performances of such techniques are degraded when considering technological defects and especially mutual coupling. To face this limitation, a HIS based antenna array design is presented. This design aims at minimizing the array mutual coupling coefficients while not increasing the size of the array

In Global Navigation Satellites Systems (GNSS), multipaths (MP) are still one of the major error sources. The additional signal replica due to reflection will introduce a bias in conventional Delay Lock Loops (DLL) which will finally cause a strong positioning error. Several techniques, based on Maximum Likelihood estimation (ML), have been developed for multipaths mitigation/estimation such as the Narrow correlator spacing [1] or the Multipath Estimating Delay-Lock-Loop (MEDLL) [2] algorithm. These techniques try to discriminate the MP from the Line Of Sight Signal (LOSS) on the time and frequency domains and thus, short delay multipaths (

The use of antenna array for multipaths mitigation in Global Navigation Satellite Systems (GNSS) is considered in this paper. Theoretical studies have shown that using the spatial sampling in combination with time and frequency dimensions can significantly reduce the final position estimation error. However, the lack of practical considerations is still an issue. Technological defaults are usually not taken into account in numerical simulations, and these defaults can seriously degrade the performances of the processing as they modify the amplitude and phase responses of the array. Moreover, implemented algorithms usually result from a trade off between the accuracy and the complexity. This paper aims at presenting two new tools based on antenna arrays for studying the GNSS multipaths mitigation. The first one is a new implementation of the well known Space Alternating Generalized Expectation Maximization algorithm (SAGE). By filtering the multipaths on the space, time and frequency domains, SAGE algorithms can strongly reduce the time-delay estimation error. Nevertheless, SAGE implementation requires high memory and computation capacities, and real time SAGE processing is still not possible. Simulation results show that with the same level of performance, the new implementation of SAGE can reduce the size of the signal and consequently, the memory and computation load requirements. In order to validate the simulation results, CNES and ELTA are developing a new reconfigurable 2×2 array GNSS receiver. Thus, this paper exhibits also the architecture and the specifications of this new array dedicated to offline signal processing.

The potential of small antenna array (2x2 square) for multipaths (MP) mitigation in GNSS systems is considered in this paper. This study focuses on two different approaches. In the first one, we use antenna array algorithms in order to have a spatial discrimination of the incoming paths. Due to the low directivity of the array, conventional beamforming turns out to be inefficient. Thus, high resolution beamformers have been tested. In the second one, we compare this solution with an approach which uses the spatial sampling in combination with time and frequency dimensions. To discriminate the different incoming signals on the three domains, Space Alternating Generalized Expectation Maximisation (SAGE)algorithm, which is a low-complexity generalization of the Maximum Likelihood maximisation (ML) algorithm, has been considered. Monte Carlo simulations clearly show the superiority of SAGE. Nevertheless, SAGE implementation requires a high memory and computation capacities, and real time SAGE processing is still not possible. In order to reduce these requirements, we investigated a new implementation based on both the correlation properties of the code and the thermal noise. With the same level of performance, the new implementation of SAGE can strongly reduce the size of the signal and consequently, the memory and computation requirements. Thus, this is a promising method to take the advantages of SAGE with reasonable hardware requirements.