Modélisation des assemblages de ballons pressurisés stratosphériques

Long duration super-pressure balloon design and manufacturing is a great challenge for the CNES in scientific ballooning. They are made of 50 µm thick polymer films (PET/PA/PET) which are joined with 23 µm thick adhesive PET bands. To date, during flight missions, a real problem appears: some balloons explode prematurely. This is why this study deals with the mechanical behaviour of the stratospheric pressurized balloons and particularly with the assembly of the constitutive materials. Firstly, a nanoindentation test campaign makes it possible to identify the elastic properties of the materials directly in the assembly at two different temperatures. Then, we simulate a nominal assembly in two approaches: 2D and 3D. More particularly, we present an example concerning a defect of the junction in 3D approach using the submodeling technique. Finally, we use the factorial design method at two levels and finite-element models to study the influence of the various conception parameters on the mechanical behaviour of the assembly

Optimized GSE Packet Scheduling over DVB-S2

International audienceThe evolution of satellite communication towards packet-based communication and the adoption of modern physical layer techniques, such as Adaptive Coding and Modulation, raise new issues, brought by this variability, for scheduling algorithms. This paper addresses the problem of GSE packets scheduling over DVB-S2 with QoS support by adopting a utility-based scheduling strategy. Utility functions are considered as a mean to encompass parameters from several layers into a single scheduling process. By making use of a first-order approximation, a low complexity scheduling algorithm is derived from the utility functions optimization problem, adaptable to a wide range of functions. The algorithm determines the characteristics of the next BBFrame to be send, and which GSE packets it should contain. We focus particularly on delay as a joint metric to represent QoS requirements, and assess the performance of our algorithm and the relevance of our assumptions using comparative simulations

Rule-based Packet Scheduling for DVB-S2 Through Generic Stream Encapsulation

International audienceIn this paper, we consider the problem of IP packet scheduling over a GSE/DVB-S2 satellite link. Scheduling flows with QoS requirements has been widely addressed in the mobile field, especially in LTE and WiMAX, with emphasis on fairness, efficiency and dynamic adaptation to transmission conditions. We focus on the well-known empirical scheduling rules known as PF, M-LWDF and EXP-PF for both QoS and MODCOD scheduling, and present how they were adapted to GSE/DVB-S2 encapsulation. Some of the challenging issues yielded by DVB-S2 are tackled, such as joint scheduling of both QoS and MODCODs, concatenation of numerous user packets into one BBFrame and fairness issues introduced by the scheduling algorithm, especially when dealing with various transmission scenarios. We show the potential of our scheduling algorithm using several simulations

Effect of residual channel estimation errors in random access methods for satellite communications

International audienceIn recent random access methods used for satellite communications, collisions between packets are not considered as destructive. In fact, to deal with the collision problem, successive interference cancellation is performed at the receiver. Generally, it is assumed that the receiver has perfect knowledge of the interference. In practice, the interference term is affected by the transmission channel parameters, i.e., channel attenuation, timing offsets, frequency offsets and phase shifts, and needs to be accurately estimated and canceled to avoid performance degradation. In this paper, we study the performance of an enhanced channel estimation technique combining estimation using an autocorrelation based method and the Expectation-Maximization algorithm integrated in a joint estimation and decoding scheme. We evaluate the effect of residual estimation errors after successive interference cancellation. To validate our experimental results, we compare them to the Cramer-Rao lower bounds for the estimation of channel parameters in case of superimposed signals