Internet par satellite | EPFL Graph Search

alt=Antenne internet satellite portable|vignette|Antenne internet satellite portable Internet par satellite est à la fois une méthode d'accès au réseau Internet et un mode de large diffusion via une transmission satellitaire à destination du grand public ou des entreprises. Principes techniques Le foyer ou le véhicule est équipé d'une antenne de réception satellite (exemple : antenne parabolique) disposant à la fois d'un dispositif de réception (liaison descendante) et d'un système d'émission intégré (liaison montante). L'antenne est reliée à un récepteur spécial ou démodulateur-modem. Celui-ci est connecté à un ou plusieurs ordinateurs (via cordons Ethernet, USB ou par une liaison sans fil de type Wi-Fi). Il est nécessaire de souscrire un abonnement pour l'accès au service auprès d'un opérateur, sur le principe de l'ADSL. Le débit alloué par l'opérateur peut aller jusqu'à 20 Mb/s et est donc supérieur à la plupart des accès xDSL. Selon l'ARCEP, l'éligibilité théorique

Civil war hinders crop production and threatens food security in Syria

Xi Li, Li Mi

Assessing the impact of violent conflict on Syrian agriculture is challenging given data limitations and attributability issues. Using satellite data at 30 m spatial resolution, we found that the extent of productive cropland showed greater interannual variability and spatial heterogeneity after the start of the civil war in 2011. Using changes in satellite-based night-time light as a proxy for war impact intensity, we also found that cropland close to severely impacted urban settlements faced greater disruption. Fixed-effects models revealed the relationship between productive cropland and precipitation for the pre-war period, whereas a counterfactual scenario constructed for the period 2012-2019 showed substantial variation at the regional level. While the ongoing conflict promoted cropland cultivation in safer zones, cropland reduction took place in the country's northwest and southeast regions. Our study demonstrated the combined utility of daytime and night-time satellite data to assess food insecurity in extreme environments and can help guide distribution of food and aid in Syria. Conflicts are known to disrupt agriculture, food supply chains and the economy at large. Mapping and quantifying such disruptions, although key for aid planning, remains a challenge in war zones. This study uses daytime and night-time satellite data from Syria over 1998-2019 to assess the link between war-induced impacts on infrastructure and urban areas with cropland dynamics.

NATURE PORTFOLIO2022

Uncooperative Rendezvous in Space: Design of an Electronic Architecture for High Performance Avionic with Multi Sensor Input and Intensive Data Rate.

Michaël Yannick Juillard

Active Debris Removal missions consist of sending a satellite in space and removing one or more debris from their current orbit. A key challenge is to obtain information about the uncooperative target. By gathering the velocity, position, and rotation of the desired object, the satellite is able to plan its trajectory and define the sequence of approach. It requires the use of a variety of sensors with often a high data rate. For this task, a dedicated payload computer is envisioned with the responsibility of processing the information from the various rendezvous sensors. This component has the goal to provide meaningful information to the main satellite computer about the targeted debris. The focus of this work is on the data processing, the number of elements, and the electrical energy with constraints due to internal communication.First, an avionic testbench was built at the EPFL Space Center to assess early hardware and software architectures. The goal is to enable Hardware-In-the-Loop testing while developing the payload computer. A communication data bus has been implemented between the Platform and the Payload On-Board Computer. Emphasis was placed on the reliability of the high-level protocol and multiple concepts for improvement were analyzed.In a second phase, the testbench has been extended to support other data buses. The aim was to develop a reliable and efficient backup or fall-back data bus in case of failure in the main link. Four data buses have been tested with extensive analyses on their resilience to error and the efficiency of their data exchange.In parallel, extensive work has been performed to develop a simulation and optimization tool. Its goal is to support the design of payload avionic architectures for ADR missions by providing trade-offs and analyses. In the first iteration, a simulator has been created with instances of various high-level elements modeled.The second iteration introduced the additional dimension of optimization. It is trying to determine the best set of instruments and algorithms to use. With this capability, numerous analyses have been conducted on the influence of various parameters linked to the general optimizer behavior. It allows us to better understand the strength and limitations of the tool.The third step regarding the tool was to start its verification. The task has been to develop an Hardware-In-the-Loop architecture to compare its behavior with the results of the optimizer. The implementation of various mock-up algorithms enables the verification of their models in the tool. These analyses guarantee the feasibility of the outputted solution.The last part was dedicated to the creation and analysis of a realistic payload avionic architecture. The goal was to test the capability of the tool with hardware elements inspired by actual components. This work has shown the procedure to efficiently use the tool in the design phase of a mission.In conclusion, the work on the communication between the Payload and the Platform On-Board Computer has brought valuable lessons and experiences to the projects. They can now be used for the establishment of the high-level protocol into ClearSpace-1 flight software. In addition, the optimizer created allows tackling the design of complex payload avionic architecture where mass saving and processing resources are crucial. It is an essential point to develop a highly efficient payload computer for an Active Debris Removal satellite.

EPFL2022

Reputation-based Wi-Fi Deployment - Protocols and Security Analysis

Naouel Ben Salem, Jean-Pierre Hubaux

In recent years, wireless Internet service providers (WISPs) have established thousands of WiFi hot spots in cafes, hotels and airports in order to offer to travelling Internet users access to email, web or other Internet service. However, two major problems still slow down the deployment of this kind of networks: the lack of a seamless roaming scheme and the variable quality of service experienced by the users. This paper provides a response to these two problems: We present a solution that, on the one hand, allows a mobile node to connect to a foreign WISP in a secure way while preserving its anonymity and, on the other hand, encourages the WISPs to provide the users with good QoS. We analyse the robustness of our solution against various attacks and we prove by means of simulations that our reputation model indeed encourages the WISPs to behave correctly.

2004

Uncooperative Rendezvous in Space: Design of an Electronic Architecture for High Performance Avionic with Multi Sensor Input and Intensive Data Rate.

Michaël Yannick Juillard

EPFL2022