Ka-band return link for UAVs using adaptive spreading factor for DSSS in a DVB-RCS2 context

This paper evaluates the potential performances of a Direct Sequence Spread Spectrum (DSSS) satellite communication for Unmanned Aerial Vehicles (UAVs) in Ka-band using low directional antenna. The need to comply with the interference templates established by ITU enforces a bound to the signal power emitted toward adjacent satellites and greatly limits the accessible data rate. That prevents the UAVs communications to use a dedicated repeater for the return link. Instead, simultaneous transmission with return link communications in accordance to DVB-RCS2 standard is investigated. The proposed system is thus based on simultaneous transmission of narrow-band carriers (DVB-RCS2 primary system) and spread spectrum carriers (secondary system dedicated to UAVs). Mutual interferences are evaluated, it is shown that secondary transmissions do not affect primary systems availability, but conversely DVB-RCS2 carriers forces the secondary systems to use a high spreading factor, typically between 28 and 214 which can be updated as the number of primary active carriers changes within the beam. A compromise between secondary burst length and speed of adaptation for spreading factor is also discussed. Typically, if the targeted Packet Error Rate (PER) of the secondary link is 10e-5 and modulation is QPSK with a code rate 1/3, SNIR has to be held over 0 dB. This objective is reached with a spreading factor switching from 2e10 to 2e14 as the number of active primary carriers changes with a maximum bandwidth occupation of 90%, resulting in a data rate varying between 8 kbps and 34 kbps for the secondary system and a SNIR maintained between 1.5 dB and 4.5 dB

Influence of bottom trawling on sediment resuspension in the 'Grande-Vasière' area (Bay of Biscay, France)

Sea trials were performed on two zones with different fishing efforts on the continental shelf of the Bay of Biscay ('Grande-VasiSre' area of muddy sand) in order to assess particulate matter resuspension and seabed disturbances (i.e., penetration, reworking, grain size changes) induced by different types of trawls. Optical and acoustic measurements made in the water column indicate a significant trawling-induced resuspension mainly due to the scraping action of doors. It manifests as a highly dynamic turbid plume confined near the seabed, where suspended sediment concentrations can reach 200 mg l(-1). Concentration levels measured behind an "alternative" configuration (trawls with jumper doors instead of classical doors penetrating the sediment) are significantly lower (around 10-20 mg l(-1)), which indicates a potential limiting impact regarding the seabed. Grain size analyses of the surficial sediment led to highlight a potential reworking influence of bottom trawling. On the intensively trawled zone, this reworking manifests as an upward coarsening trend in the first 5 cm of the cores. A significant decrease in mud content (30 %) has been also witnessed on this zone between 1967 and 2014, which suggests an influence on the seabed evolution. The geometric analysis of bottom tracks (4-5-cm depth, 20-cm width) observed with a benthic video sledge was used to compute an experimental trawling-induced erosion rate of 0.13 kg m(-2). This erosion rate was combined with fishing effort data, in order to estimate trawling-induced erosion fluxes which were then compared to natural erosion fluxes over the Grande-VasiSre at monthly, seasonal and annual scales. Winter storms control the annual resuspended load and trawling contribution to annual resuspension is in the order of 1 %. However, results show that trawling resuspension can become dominant during the fishing high season (i.e., until several times the natural one in summer). In addition, the contribution of trawling-induced resuspension is shown to increase with water depth, because of the rapid decay of wave effects. Finally, the seasonal evolution of the respective contributions for erosion (mainly trawling and waves) could be mapped for the whole study area

L'ordinaire des sciences et techniques. Cultures populaires, cultures informelles (5)

International audienceLa présente édition de la Lucarne matérialise la poursuite d’un travail engagé depuis 2013. Comme pour la précédente livraison, il a été réalisé dans le cadre d’un atelier collaboratif d’histoire socioculturelle. L’atelier lui-même est animé par un collectif formé des enseignant∙e∙s et auditeur∙rice∙s des formations du CNAM dédiées à la médiation socioculturelle des sciences et techniques. Certificat de compétences, Licence professionnelle ou Magister s’attèlent ainsi à la réflexion, à la conception et à la réalisation de dispositifs pour la médiation des sciences et techniques en société par le design culturel. C’est dans ce cadre de réalisation pédagogique que sont rassemblés ces textes et documents pour lesquels sont proposés de courtes analyses sur leur fonction de support de diffusion massive dans l’espace public d’une culture populaire et ordinaire des sciences et techniques. Tous ont été rédigés dans le cadre d’un exercice exigé pour la validation d’un enseignement. Si le résultat final peut s’avérer inégalement satisfaisant à l’aune des critères de leurs commanditaires, tous les textes apportent cependant un regard jugé pertinent sur un des aspects des manifestations des sciences et techniques dans leurs rapports à la société au travers de la production et de la consommation culturelle de masse. Quelques-uns ont été un peu remaniés pour la présente édition. Retrouvez-les tous, ainsi que d’autres non publiés dans ce volume, sur le site de la Lucarne : http://ateliercst.hypotheses.org/Avec les contributions de Philippe Cholet, Christophe Thomas, Julie Piskor, Prisca Cez, Karine Guillon, Jessica Signahode, Antonella Cavanna, Claire Robin, Daphné Debilly, Claire Combettes, Fabienne Thomas, Annie Dumont, Alexandre Couturas, Mirielle Rineau, Jan-Philippe Dubroca, Cyndie Dupoux, Laurent Marche, Carole Zagouri, Mario Vocale, Julie Daviet-Draye, Marie Berlingue, Gisele Butterlin, Laurène Legrand, Ludivine Cavé, Frederic Pitout, Delphine Blanchard, Charlotte Joguet, Alexandre Ben Othman, Roxane Bibard, Victoire Chabert, Morgane Petit, Ariane Rudelle, Tanit Halfon, Marie Danielle et Meryem Hameg