This article proposes a discussion on the strengths, weaknesses, opportunities, and threats related to the deployment of QUIC end-to-end from a satellite-operator point-of-view. The deployment of QUIC is an opportunity for improving the quality of experience when exploiting satellite broadband accesses. Indeed, the fast establishment of secured connections reduces the transmission time of short files. Moreover, removing transport-layer performance-enhancing proxies reduces the cost of network infrastructures and improves the integration of satellite systems. However, the congestion and flow controls at end points are not always suitable for satellite communications due to the intrinsic high bandwidth-delay product. Further acceptance of QUIC in satellite systems would be guaranteed if its performance in specific use cases were increased. Based on an emulated platform and on open-source software, this paper proposes values of performance metrics as one piece of the puzzle. The final performance objective requires consensus among the different actors. The objective should at least provide acceptable performance for satellite operators to allow QUIC traffic but reasonable enough to keep QUIC deployable on the Internet.
Free-space radio-frequency (RF) communication links for intersatellite or satellite-to-ground communications are getting increasingly constraint by the insufficient spectrum availability and limited data rate of RF technology. With the advent of large satellite mega-constellation networks for global communications coverage, this limitation of classical RF communication becomes even more critical. Therefore, the establishment of point-to-point free-space optical link technology (FSO) in space will become of paramount importance in future systems, where the application will be for data-relays links, or for mega-constellations inter-satellite links, as well as for direct data downlinks, or from deep-space probes to ground. Further advantages of optical FSO—besides spectrum availability—is its increased power efficiency, higher data rates, avoidance of interference, and inherent protection against interception. When, however, these optical communication links have to pass through Earth's atmosphere, attenuation and scattering effects do influence the signal transmission. In this publication, we investigate the effects of atmospheric attenuation, including the effects of molecular absorption as well as aerosol scattering and absorption, for typical wavelength regions used for FSO, dependent on the link geometries. Based on transmission-simulation databases, we show useful spectral ranges and their specific attenuation strength. Free spectral transmission windows dependent on atmospheric quality and elevation angle are identified for reliable and efficient use of the optical transmission technology in space applications.
VHF data exchange system (VDES) is an emerging maritime communications standard that is meant to provide ship-to-shore, shore-to-ship, and ship-to-ship information services. VDES also includes a satellite component to extend the service coverage also to the high sea. Ships can receive important information via VDES and access this service via satellite when they are far from the shore. This paper uses data taken during a measurement campaign to develop an ON-OFF model for the VDE-SAT downlink channel taking the multipath effects caused by sea reflections into account. This model has been used to evaluate the impact of packet-level forward error correction (FEC) schemes (i.e., ideal codes, RaptorQ codes, and 2-Dimension Reed-Solomon codes) to further protect transmissions from deep fading events and to evaluate the impact at the transport level considering the possibility to adopt the transmission control protocol (TCP) for a file map delivery service.
The aim of the scientific community, towards the investigation of solutions able to favor a futuristic human settlement on Mars, also concerns ad hoc communication systems and wireless networks to be deployed over the “Red planet.” However, the state-of-the-art appears to be missing of realistic and replicable models for understanding the radio propagation over precise Martian locations. This means that performing solid simulations, rather than roughly approximated ones, is really a tough task. Thus, this paper describes the design of a 3D ray-tracing simulator based on high-resolution digital elevation models (DEMs) for the evaluation of Martian large-scale and small-scale phenomena in the S and EHF bands. First, by taking advantage of the Cole–Cole equations, we computed the complex permittivity of the JSC Mars-1 Martian regolith simulant. Then, we developed a 3D tile-based structure of the Gale crater, thanks to its DEM, and finally, we implemented a ray-tracing algorithm for outdoor environments able to trace the line of sight (LOS), the first and second reflections of a radio frequency (RF) signal between a transmitter (TX) and a receiver (RX) over the 3D structure. The results focus on estimating path losses, shadowing values, outage probability, and on the parametrization of multipath channels for selected areas and subareas, presenting heavily different morphological features, of the Gale crater. Moreover, some brief considerations about dust storms and atmosphere harmful effects on propagation will be drawn.
There has been growing interest within the satellite navigation community in the possibility of delivering positioning and timing services from existing or emerging constellations of Low-Earth Orbit communication satellites. At the same time, the international maritime community has been investigating the potential use of communication signals transmitted from shore-based stations for positioning—a concept commonly referred to as ‘ranging mode’, or R-Mode. The driving force for these developments is the desire to reduce the reliance on traditional Global Navigation Satellite Systems (GNSS). One of the technologies being considered for use in R-Mode is the evolution of the Automatic Identification System (AIS) known as the Very High Frequency Data Exchange System (VDES). VDES has a terrestrial and a satellite component. The feasibility of using terrestrial VDES transmissions for ranging was studied in a previous publication by the authors. This paper builds on the previous study and extends its results to the satellite component of VDES. Statistical bounds on the ranging error are derived for all downlink waveforms currently being considered for use in satellite VDES and for several custom-designed transmission formats. The analysis supports the feasibility of using both the existing and custom waveforms in ranging applications and points to related trade-offs that will need to be considered in the design of satellite VDES R-Mode systems.
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