Development of high-speed and high-efficiency downlink transmitter with GaN-HEMT amplifier and pre-distortion technique for nano/small satellite

A high-speed downlink telecommunication system is required to meet various applications for small satellites such as earth observation. The purpose of this research is to develop a high-data-rate (typically over 300Mbps) communication system. Generally, the operation at nonlinear region provides high efficiency for a RF power amplifier. However the amplitude-phase modulated signal, which is an efficient scheme in term of frequency band, requires high linearity. In order to amplify amplitude-phase modulated signal for high data rate, a 2W X Band GaN-HEMT power amplifier and digital pre-distortion technique were developed. In this paper measurements and simulations of the system are presented

Prophylactic clip closure for mucosal defects is associated with reduced adverse events after colorectal endoscopic submucosal dissection: a propensity-score matching analysis

博士（医学）乙日本医科大学202

Performance Analysis of Ultra-Wideband Channel for Short-Range Monopulse Radar at Ka-Band

High-range resolution is inherently provided with Ka-band ultra-wideband (UWB) vehicular radars. The authors have developed a prototype UWB monopulse radar equipped with a two-element receiving antenna array and reported its measurement results. In this paper, a more detailed verification using these measurements is presented. The measurements were analyzed employing matched filtering and eigendecomposition, and then multipath components were extracted to examine the behavior of received UWB monopulse signals. Next, conventional direction finding algorithms based on narrowband assumption were evaluated using the extracted multipath components, resulting in acceptable angle-of-arrival (AOA) from the UWB monopulse signal regardless of wideband signals. Performance degradation due to a number of averaging the received monopulses was also examined to design suitable radar's waveforms

300 Mbps Downlink Communications from 50kg Class Small Satellites

Recently small satellites start playing important roles in earth observation missions. It, however, is true that small satellites have drawbacks of sensor resolutions and down link data rate. As a solution to the latter drawback, we have developed novel communications system for 320Mbps down link with 16QAM for small satellites with 50kg class. We developed a new GaN HEMT X-band amplifier with high efficiency and small distortion, digital filter and pre-distortion processing with relatively low clock frequency in FPGAs, and small X-band on-board antennas. As ground segments, we are developing a compact S/X dual band ground antenna station and a high performance demodulator with turbo equalizer/decoder based on CCSDS high rate telemetry standard. These technologies will be demonstrated in 2014 by Japanese Hodoyoshi-4 satellite with 50 kg mass

Premiers résultats d'analyse de front d'onde avec SOTA

International audienceFor 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.La turbulence atmosphérique est la principale cause de dégradation des liens laser sol satellite. Les perturbations de phase induites le long du cana de propagation conduisent à de la scintillation dans le plan du récepteur et peuvent sévèrement compromettre le couplage du flux dans un récepteur de petite dimension. Pour résoudre ces problèmes, différentes stratégies dédiées doivent être développées. Cela nécessite une compréhension précise de l'origine des perturbations. Les modèles de propagation de faisceau ont démontré leur capacité à reproduire les caractéristiques statistiques des perturbations optiques affectant un lien laser satellite sol pour des élévations descendant à 20°. Pour des élévations plus petites des mesures réalisées sur étoiles ont démontrées toutefois les limites de ces approches analytiques et l'intérêt de modèles de type Monte-Carlo. Nous faisons état ici des premières mesures sur un canal de propagation établi avec un microsatellite LEO grâce à un analyseur de Shack Hartmann. Le faisceau laser à 976nm est fourni par le terminal optique SOTA et analysé grâce à un Shack Hartmann situé au foyer coudé d'une station française (télescope MéO de 1.55m) en juillet 2015. Les caractéristiques du front d'onde et les structures de scintillation enregistrées avec l'analyseur sont analysées et comparées aux modèles de perturbation de la turbulence atmosphérique alimentés par les mesures in situ des paramètres atmosphériques tels que fournis par un GDIMM

Prophylactic clip closure for mucosal defects is associated with reduced adverse events after colorectal endoscopic submucosal dissection: a propensity-score matching analysis

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