Jean-Luc Issler

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.

U-SBAS: A universal multi-SBAS standard to ensure compatibility, interoperability and interchangeability

Several regional augmentation GNSS systems (like SBAS) are already fully operational and other are under development with new frequencies and signals on the way. Therefore, it becomes imperative to guarantee for all GNSS users the compatibility, interoperability and interchangeability between all these systems. The goal is to ensure that the users multi-mode receiver can choose and mix signals from different GNSS and SBAS systems to achieve more availability, accuracy and robustness. Attaining that objective will require agreements on frequency plans and signal designs, as well as other details including means to ensure interoperability of system times and geodetic reference systems. This paper suggests a Universal-SBAS (U-SBAS) standard, compatible with all the existing and planned regional GNSS systems (and their evolutions) in the world, like IRNSS, QZSS, PCW, BEIDOU-1, WAAS, EGNOS, SDCM, GAGAN, MSAS. The proposed worldwide multimodal U-SBAS standard carries additional channels (signals and messages) to cover the non-aeronautical specific Safety-of-Life (SoL) services, and also High Precision Positioning Services (HPPS), Position Velocity Time (PVT), authentication services, safety services, scientific application services, High Precision Timing Services (HPTS), etc. U-SBAS is designed to be fully interoperable with the current SBAS standards and to allow significant performance and service improvements in operational, scientific and/or security areas. Finally usage examples of the proposed standard are given for different types of applications such as science, aviation, precise point positioning, timing, security, robust positioning, maritime and reflectometry.

Toward centimetric positioning thanks to L- and S-Band GNSS and to meta-GNSS signals

RDSS downlink bands, usually with a paired uplink, could be used, like RNSS bands, for satellite navigation. The eventual need for additional Galileo frequencies and signals in S-band or C-band in addition to those currently used is not only about improving the pseudoranging or timing performance, but primarily about introducing new services. Another very important field recently studied to improve accuracy worldwide, is Integer Ambiguity Resolution on Undifferenced Phase which could allow very precise positioning accuracies close to a few cm in real time when permanent phase tracking is maintained on at least two carrier frequencies at the same time. Since cycle slip could occur on a carrier at a given dates, at least 3-carrier tracking is required to ensure robustness for such PPP techniques. In this paper, this last concept of integer ambiguity resolution together with the introduction of new signals/services at S-Band will be studied. The new functions/services specifically provided by a satellite navigation signal at S-band could be also complementary to already existing LEO mobile telecommunication constellations. In this paper it is shown how S-band GNSS signals in addition to the actual L-band signals could also improve the robustness and accuracy, by easing significantly the Integer Ambiguity Resolution on Undifferenced Phase process, combining two fundamental concepts. The first concept introduced in the paper is based on the following finding: if a GNSS system has two signals transmitted at two carrier frequencies that are multiple one of the other, then the wide lane carrier phase ambiguity resolution can be eased a lot. The second concept is the one of “Meta-GNSS signals”. The basic idea consists of processing two different GNSS signals transmitted at different carrier frequencies as a single signal thanks to an AltBOC processing. As it is shown in the paper, these two concepts combined together could therefore allow a robust quasi-centimetric “absolute” positioning, worldwide, thanks to a possible new Galileo signal added at S-band frequencies. The paper details these two concepts and their related area of research, and presents preliminary possible Sband signal designs accordingly.

Galileo E1 OS/SoL acquisition, tracking and data demodulation performances for civil aviation

This article presents a methodology related to the computation of civil aviation acquisition, tracking and data demodulation thresholds adapted to the case of Galileo E1 OS/SoL signal. These thresholds are compared against worst case link budgets representing operational scenarios. It is shown that these thresholds provide a positive margin although these theoretical results would probably require a deeper analysis and confirmation through extensive testing.

Influence of external magnetic fields on the inductive properties of rapid single-flux-quantum digital circuits

A method has been developped to take into account the presence of a local external magnetic field in Superconducting Quantum Interference Devices (SQUIDs) loops composing Rapid Single-Flux-Quantum (RSFQ) circuits, through modifications of circuit inductances. A good agreement is observed between analytical formulas and simulations performed by time-domain softwares. The agreement with the first experiments is still only qualitative at this stage.

Laser communication experiments between Sota and Meo optical ground station

Optical transmissions between earth and space have been identified as key technologies for future high data rate transmissions between satellites and ground. CNES is investigating the use of optics both for High data rate direct to Earth transfer from observation satellites in LEO, and for future telecommunications applications using optics for the high capacity Gateway link.

Characterization of an On-Chip Magnetic Shielding Technique for Improving SFQ Circuit Performance

An on-chip magnetic shielding technique was characterized on several DC-SQUIDs to prepare the next generation of complex digital RSFQ circuits designed by the FLUXONICS foundry. The maximal frequency of operation of a toggle flip-flop cell was used as a criteria to validate the concept. It goes from a simulated value of 52 GHz (46 ± 2 GHz experimentally), for a McCumber parameter βc = 1 with JC = 1 kA/cm2 in the absence of external magnetic field, down to 29 GHz in the presence of an external field of 88 μT. The shielding technique consists of surrounding a circuit by one or several superconducting niobium loops with the same layers as for the SFQ circuit. The loops are connected to the ground plane with vias. It is shown experimentally that the local magnetic field is reduced by a factor of 4 for the best shielded configuration, which limits the reduction of the maximal frequency of operation in presence of external magnetic field.