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OPS-SAT is an ESA technology demonstration cubesat which includes a colour camera, a Software Defined Radio (SDR) receiver and a powerful ARM processor. One of the experiments executed there is FAPEC, a high-performance and versatile data compression software. Among others, it features image compression and linear prediction coding algorithms, suitable for multi-band and baseband radio-frequency (RF) samples, respectively. Since its deployment on-board OPS-SAT in late 2020, FAPEC has allowed for downloading a large set of Earth Observation images. Recently, thanks to ESA Open Space Innovation Platform funds, these two algorithms from FAPEC are being improved to get better compression ratios and speeds, add video compression capabilities, and higher quality levels in case of lossy compression. A smart lossy approach is being developed for radio-frequency data, identifying the time segments with signal presence and quantizing noise-only samples to further reduce the size. In order to identify the really useful files to be downloaded from the satellite, on-board data analysis capabilities are being developed as well. In this work we present in-orbit results, recent developments and preliminary results obtained with the new algorithms on real data.

This paper proposes a hybrid network architecture combining a cell-free Massive MIMO terrestrial layout with a low Earth orbit satellite segment jointly targeting the maximization of the minimum per-user rate in the coverage area. Towards this end, an optimization framework is proposed, alongside a greedy solution, that diverts the terrestrial users experiencing poor propagation conditions to the satellite segment. Simulation results show the substantial benefits this integrated approach brings along, very specially when the terrestrial segment operates single-antenna access points or is sparsely deployed., Grant numbers : TERESA - Hybrid TERrEstrial/Satellite Air Interface for 5G and Beyond (TEC2017-90093-C3-1-R).

This paper investigates a novel closed-form noniterative precoding technique for multicast multibeam satellite systems. Next-generation satellite systems will be benefited from the flexible use of the satellite resources especially its power flexible allocation among beams. Intending to obtain a low-computational complexity design, we revisit the well-known signal-to-leakage-and-noise ratio design for multicast transmission. Two alternatives are introduced considering both the physical meaning of the ratio and certain multicast channel vector mapping. We observe the benefits of these techniques in satellite flexible payloads. The proposed technique shows a substantial gain compared to the benchmark according to the numerical simulations. Intuitive insights on the precoding behaviour are also presented. This work is funded by Ministry of Science, Innovation and Universities, Spain, under project TERESA -TEC2017-90093-C3-1-R (AEI/FEDER, UE) and by Catalan government under the grant 2017-SGR-01479.

In this paper, the problem of cross-layer design of the link scheduling and flow control is studied in hybrid terrestrial-satellite wireless backhauling network. Considering network limitations and requirements, the target is to minimize the traffic delivery time by deciding the active backhauling links that can transmit simultaneously. Additionally, the proposed scheme provides a way to utilize the satellite links efficiently in order to provide the required link failure resiliency and traffic off-loading capability. Simulation results quantify the benefits of using the satellite links in cases of link failure and traffic congestion.

This paper considers a multigateway multibeam satellite system with multiple feeds per beam. In these systems, each gateway serves a set of beams (cluster) so that the overall data traffic is generated at different geographical areas. Full frequency reuse among beams is considered so that interference mitigation techniques are mandatory. Precisely, this paper aims at designing the precoding scheme which, in contrast to single gateway schemes, entails two main challenges. First, the precoding matrix shall be separated into feed groups assigned to each gateway. Second, complete channel state information (CSI) is required at each gateway, leading to a large communication overhead. In order to solve these problems, a design based on a regularized singular value block decomposition of the channel matrix is presented so that both intercluster (i.e., beams of different clusters) and intracluster (i.e., beams of the same cluster) interference is minimized. In addition, different gateway cooperative schemes are analyzed in order to keep the inter-gateway communication low. Furthermore, the impact of the feeder link interference (i.e., interference between different feeder links) is analyzed and it is shown both numerically and analytically that the system performance is reduced severely whenever this interference occurs even though precoding reverts this additional interference. Finally, multicast transmission is also considered. Numerical simulations are shown considering the latest fixed broadband communication standard DVB-S2X so that the quantized feedback effect is evaluated. The proposed precoding technique results to achieve a performance close to the single gateway operation even when the cooperation among gateways is low.