Géraldine Artaud

First results of wavefront sensing on SOTA

For satellite to ground laser links, atmospheric turbulence is a major cause of impairments. The induced phase perturbations along the propagation path cause beam scintillation in the receiver plane and they can also severely compromise the coupling of the flux into a receiver of limited size. To address these impairments, dedicated mitigation strategies must be developed. This requires accurate understanding of the perturbation origin. Beam propagation models have demonstrated their ability to reproduce statistical characteristics of optical perturbations on a satellite to ground laser link for elevations as low as 20°. For smaller elevations, measurements performed on stars illustrated the limits of analytical approaches and the interest for end-to-end models. We report here the first propagation channel measurements performed on a LEO microsatellite with a Shack-Hartmann wavefront sensor (WFS). The laser beam at 976 nm provided by SOTA optical terminal have been analyzed with a Shack- Hartmann wavefront sensor located at Coudé focus of the French ground station (1,55 m MéO telescope) in July 2015. Wavefront characteristics and scintillation patterns recorded with the WFS are analyzed and compared to atmospheric turbulence perturbations model fed with in situ measurements of atmospheric parameters retrieved from GDIMM.

A new GNSS multi constellation simulator: NAVYS

With the multiplication of navigation systems (GPS, GALILEO, GLONASS, QZSS, …) and the large variety of signals to be received, GNSS constellation simulators need to be more and more flexible. In the scope of its navigation activities, the CNES has expressed the need for a simulator that, in addition to allow the test of a large variety of receivers, satisfies a twofold objective: the emulation of a propagation channel representative of degraded environments, typically indoor or urban and high level of flexibility to generated new type of signals in order to assess the performances of future GNSS systems. For that purpose, Thales Alenia Space and Elta are currently developing a highly flexible and modular GNSS constellation simulator under CNES contract. In this development, they take benefit of their experience inherited from the realization of a flexible NSGU modulator that can handle a large diversity of modulations and can cope with most of the current and future GNSS systems. These modulations comprise BOC, BPSK, ALTBOC, CBOC, TMBOC, on selectable frequency bands. This paper describes the GNSS multi constellation simulator (NAVYS) design and architecture, includes validation test results and presents the status of the development of this equipment.

Development of a flexible real time GNSS software receiver

With the multiplication of navigation systems (GPS, GALILEO, GLONASS, QZSS, …) the variety of radio navigation signals to be received increases greatly and involves 8 frequency bands and about 20 different signals. The paper presents an innovative receiver architecture resting on a full flexibility concept, allowing any tracking channel to be allocated to any kind of signal. The resulting software defined receiver stands for a high sensitivity and high accuracy receiver coping with very large dynamic, making the concept adapted to any kind of mission.

Field test performance assessment of GNSS/INS ultra-tight coupling scheme targeted to mass-market applications

This article describes field test results of hybridization between MEMS inertial measurement unit (IMU) and GPS L1 C/A signal using an ultra-tight coupling (UTC) architecture. A software receiver is used to post-process raw GPS signal and IMU measurement recorded during the field tests. Both indoor and outdoor environments are explored and UTC with MEMS is compared to UTC with high-grade IMU and vectorized GNSS standalone positioning.

Laboratory GNSS receiver test bench

With the multiplication of GNSS and the increasing complexity of the new GNSS applications, such as Location-Based Services applications, it will be essential in the coming years to have access to receivers test benches providing a series of test procedures being reproducible and standardized, enabling localization performance assessment. GNSS receiver test benches have to fulfill a twofold need: first, to provide a standardized methodology to enable comparison, in various controlled conditions, of different products that seem to have similar performance specifications on paper. And secondly, to provide a platform to test the functions of receivers in conditions closed to the real targeted environment.