LEO Communication Constellation Design Using Street of Coverage (SOC) Technique

In order to network small satellite constellations for Earth observation and communication, several limitations must be addressed, including distributed topology management, slow down-link data-rates, and single point-to-point communication. Since distributed satellite constellations exacerbate the severity of these limitations, thorough analysis of a constellation's network performance is required to ensure that task objectives are achievable. In this paper, we designed network topologies using Satellite Toolkit (STK) for two low Earth orbit (LEO) Earth observing small satellite constellations: a sun-synchronous repeating ground track constellation and a flower (an elliptical repeating ground track) constellation. Both constellations include six sink satellites that provide a high speed down-link relay point to a ground station. We compared the constellations' inter-satellite links and down-links with respect to network metrics including access window time, drop-ratio, and throughput. We evaluated these network metrics using the Network Simulator (ns-2). Though previous works have proposed sun-synchronous and flower small satellite constellations for Earth observation, these constellations have not been analyzed for these network metrics. Results show that the sun-synchronous constellation with a repeating ground track outperforms the flower constellation with respect to more access time, lower drop-ratio, and higher throughput. Additionally, our simulations determined the optimum media access control slot time and packet transmission intervals for long distance satellite links. Further, our method of designing satellite constellation topologies in STK and exporting them to ns-2 can be used for future studies on any desired constellation network performance evaluations.

Recent deployments of satellite constellations have taken an increased interest in Low Earth Orbit (LEO) owing to the advantages of lower path loss, lower latency in terms of the propagation delay and coverage of concentrated pockets of area. Due to the nature of these orbits, antennas on the ground station with the ability to scan over wide angles is necessitated. Phased array antennas are the ideal candidates in such a scenario owing to their low cost, low profile and wide-angle scanning performance. In this paper, a phased array antenna is designed and presented to operate around the n261 band of 5GNRFR2 and the 28 GHz Ka-band with an azimuthal beamscanning range of 50° on either side of the boresight. There is also a symmetric elevation scan around boresight of +/-25° attained without the use of phase shifters. The antenna element consists of a multilayer series aperture coupled antenna fed by a meander line. It offers good performance in terms of beamscanning cost as the phase shifter requirement is reduced, owing to the use of frequency scanning in elevation and phase scanning only in the azimuth, drastically reducing the cost. The phased array has a good total efficiency around 80%. The antenna has been designed and its performance validated by full wave simulations in the solver CST Studio Suite.

A low earth orbit (LEO) observation satellite offers a shorter distance to the target area, low cost, and low communication latency. The low orbit translates to high orbital speed and results in short observation and communication contact periods. Swarms of multiple satellites offer extended coverage and spatial resolution for applications such as earth observation and monitoring. LEO communication satellite constellations create a network that includes hundreds to tens of thousands of satellites with onboard processing capabilities (as routing nodes) connected by Inter-Satellite Links (ISL) that provide continuous coverage of the earth. The LEO constellations aim to provide end-to-end routing between multiple gateways and terminals. This paper assumes the LEO constellation satellite payload includes sensors and processing capabilities. We explore the problem of managing an autonomous LEO virtual satellite swarm that will provide continuous and adjustable coverage. We preset a novel virtual swarm: a subset of the constellation satellites is dynamically assigned to the swarm when they cover the target area. The virtual swarm algorithm provides distributed data synchronization among the swarm virtual satellites and a distributed dynamic assignment of physical satellites to the virtual swarm satellites.

Today most operational Earth observing satellites reside in low Earth orbits (LEO) at less than 1,000 km altitude, and in geostationary Earth orbits (GEO) at ~35,800 km altitude. These orbits have been the venues of choice for observations, albeit for very different reasons. LEO provides high spatial resolution with low temporal resolution while GEO provides for low spatial resolution, but high temporal resolution. NOAA utilizes both venues for their environmental satellites. The NOAA Polar-orbiting Operational Environmental Satellites (POES) reside in LEO Sun synchronous orbits at approximately 830 km in altitude, as do the Defense Meteorological Satellite Program (DMSP) satellites of the Department of Defense. In the near future the POES and DMSP satellites will be merged into a new satellite system referred to as the National Polar-orbiting Operational Environmental Satellite System (NPOESS). The NOAA Geostationary Operational Environmental Satellite (GOES) system, as the name specifies, resides at the other preferred observational venue of GEO. The Jet Propulsion Laboratory (JPL), under contract to NOAA, has been studying the characteristics of medium Earth orbits (MEO), at altitudes between 1000 and 35,800 km, as an observation venue to answer the question as to whether MEO might capture the attributes of the two traditional venues. This on-going study initially focused on determining the optimal altitude for MEO observations, through numerous trade studies involving altitude, instrument complexity, coverage, radiation environment, data temporality, revisit time, data rates, downlink requirements and other parameters including cost and launch complexity. Once the optimal altitude of 10,400 km had been determined the study proceeded to explore single through multiple MEO satellite constellation performance capabilities using two instrument types, a visible through infrared (IR) imager and IR sounder as the satellites’ payload. The MEO performance capabilities were compared to comparable LEO and GEO satellite constellation capabilities. This portion of the study concluded that indeed for global coverage a constellation of satellites operating in the MEO venue could capture the attributes of those operating in the LEO and GEO venues. Three 8-satellite constellations configurations - Walker, ICO, and Equatorial-Polar (EP) - then were studied to develop more constellation coverage statistics including robustness to individual satellite failure. That study phase concluded that the EP constellation was superior to both the ICO and Walker configurations. The study is presently examining if, and to what extent, the equatorial portion of the EP constellation might provide substantive supplemental data to that collected by the NPOESS and GOES satellite constellations.

Any robust communication system can be defined as one that can provide ubiquitous connectivity with lower latency periods. Since 1990, Low Earth Orbit (LEO) satellite constellations have proven to be plausible and efficient alternatives to high altitude GEO satellites in delivering seamless voice and data communication services. This is due to some of their important advantages over geo- stationary such as low power requirement, efficient utilization of frequency spectrum and, low propagation delays pertaining to the satellite’s closer proximity to the ground station. On the downside, the difference in the mobility speed of a LEO satellite and a user on earth is so high that the user can be considered constant, unless he/she is on a fast-moving vehicle. This calls for strategical user handover mechanisms between LEOs to avoid call drops, as usually the service time for a user tend to be higher than the coverage time of a typical non-stationary LEO. Consequently, it is admissible to claim that the quality of service provided by such a network is limited by the performance of LEO handoff algorithms (generally based on parameters like Probability of call blocking/call termination, Throughput, Delay in transmission). In this paper, we will discuss the LEO handoff algorithms developed over the years and particularly delve into the most commendable satellite handover techniques exploiting the property of satellite diversity, that fall with Acceptable Forced termination of existing calls and dropping of new calls.

The Global Navigation Satellite System (GNSS) is strongly dependent on the choice of the satellite constellation. At the present time, the GNSS space segment is made by the following satellite constellations: GPS, GLONASS and a set of geostationary satellites. In a medium-long term future, a new GNSS could substitute the existing satellite navigation system, or, in any way, there will be an overlapping and an integration between the current system and the next one.Alenia Aerospazio, is studying, since 1990, the possibility to identify new navigation satellite constellations able to verify the Required Navigation Performance (RNP) for all users. Particular attention has been focused on airspace users, due to the fact that the accuracy requirements during the aircraft landing phases are very stringent, and the existing GPS system is not able to guarantee the desired RNP.In this paper a new satellite constellation with 75 satellites in Low Earth Orbit (LEO) at a common altitude of 2700 Km, and a common inclination of about 66°, has been identified. It is able to comply with the RNP (i.e. accuracy, availability, continuity, and integrity) up to CAT I landing.The transition phase between the co-existence of the current GNSS space segment and the evolving LEO constellation is discussed and analysed in this paper, outlining the advantages, with respect to the previous system, coming from the progressive implementation, in a step-wise fashion, of this LEO space segment, until its completion.KeywordsGlobal Navigation Satellite SystemGlobal Navigation Satellite SystemOrbital PlaneTime PercentageSatellite ConstellationThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

This paper presents a theoretical analysis of the potential risk posed by artificial debris clouds in low Earth orbit (LEO) from mega-constellations, modeled after current communication constellations such as Starlink and OneWeb with 750 satellites each. The analysis examines three different constellation designs: a low-altitude LEO, a high-altitude LEO, and a medium Earth orbit (MEO) constellation, which will be positioned using the Walker-Delta design. The study is based on physics-based digital mission engineering and a Monte Carlo simulation framework. The simulation involves debris generated from a single breakup of one randomly selected satellite per run, but does not consider cascading debris events. This debris cloud is propagated for 1 week and how it interacts with the mega-constellation is recorded. The results show an average of 705.65 potential conjunctions within the LEO constellation, with 14.40% of those being considered catastrophic, and an average of 165.5 conjunctions in the MEO constellation, with 0.72% considered catastrophic.

Digital connectivity has become the foundation of prosperity and an essential need for functioning societies. Despite this dependence, limitation on Internet access remains a prevalent issue, largely hinging on socioeconomic and geographic factors. A promising solution to attain global access equality is based on integrated terrestrial-satellite networks that rely on low Earth orbit (LEO) mega constellations. While the benefits of LEO constellations complement the shortcomings of terrestrial networks, their incorporation impacts the network design, adding complexity and challenges. This article presents a systematic analysis of next generation LEO mega satellite constellations, outlining opportunities by virtue of the many benefits these constellations can provide and highlighting the major challenges. Furthermore, it provides a synopsis of analytic models and underscores modern simulation approaches for next generation mega satellite constellations. This article provides network designers with the necessary insights into satellite network performance.

Growing interest in the commercialization of space (NewSpace) is leading to increased acceptance of commercial off-the-shelf (COTS) electronics and thus enabling use in space of the latest technologies developed for terrestrial applications. This opens new capabilities for applications in space missions. RF communication via satellites has been established for decades; traditionally used for military applications, it is becoming increasingly important for commercial users. Today, global connectivity and access to the Internet has never been so important, and the demand for worldwide connectivity increases significantly each year. Space-based Internet access is especially important for areas with poor terrestrial infrastructure, such as Africa and Antarctica. There are already geostationary-Earth orbit (GEO)-stationary-located satellites available such as <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Inmarsat</i> or low-Earth orbit (LEO) satellite constellations like Iridium, which provide almost-global access to the Internet, but they are either very expensive or have low data rates and long latencies, so they are not very attractive. New solutions with high data rates, low latencies, and affordable fees are currently in development, such as StarLink, with its giga constellation <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref> , <xref ref-type="bibr" rid="ref2" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[2]</xref> , and Amazon’s Project Kuiper <xref ref-type="bibr" rid="ref3" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[3]</xref> , <xref ref-type="bibr" rid="ref4" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[4]</xref> , <xref ref-type="bibr" rid="ref5" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[5]</xref> . So it is true: there really has been a change in the market with the NewSpace Era. With NewSpace, or in other words, the commercialization of space, traditional space missions with high-quality assurance requirements, very long design and manufacturing times, and extraordinary costs may become obsolete at a certain point, at least when it comes to commercial services like satellite-based Internet access. To decrease the lead time and costs of such missions, satellite designers and manufacturers need to rely on commercially available electronics, namely, COTS devices, which are usually much cheaper and have better performance and shorter lead times compared to space-qualified parts. In terms of performance, COTS devices have great benefits over space-qualified parts simply because the design, development, and qualification processes for space parts are very complex and take years before they are qualified and available for the market. It is likely that state-of-the-art space-qualified parts are 10 years behind what we currently have available for terrestrial applications, such as for the automotive or industrial markets <xref ref-type="bibr" rid="ref6" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[6]</xref> . One obvious reason is certainly that electronic parts manufacturers develop products for certain markets, and space is yet not one of the biggest or most attractive markets. But this has already started changing and big players such as Texas Instruments and Analog Devices are moving forward with the NewSpace wave and establishing ever-more products for commercial space applications. Truly, using state-of-the art electronics is not only of interest for the space-based Internet, there are also other space-related applications that can clearly benefit from using the latest technologies.

Air Quality (AQ) monitoring in Belgium has hitherto been relying mostly on in-situ measurements of surface concentration, with geographical gaps between observations filled in with numerical modelling ingesting (proxies for) bottom-up emission estimates.&amp;#160; &amp;#160;However, a new generation of satellite sounders on sun-synchronous Low Earth Orbits (LEO) &amp;#8211; like the Copernicus Sentinel-5(p) series &amp;#8211; performs now daily global mapping of atmospheric composition down to the 3-km scale. Soon this daily global mapping will be complemented with geostationary instruments (GEO, e.g. Sentinel-4) observing the diurnal cycle in trace gas concentrations, although over the limited geographical area accessible from a geostationary viewpoint. This new constellation of satellite sounders is built to support detailed monitoring of AQ on the different relevant scales: from point-like emissions to intercontinental transport, and from city-level to international regulations established by public authorities to manage AQ in their area of responsibility. Nevertheless, uptake of these new satellite AQ data by the various Belgian stakeholders is not guaranteed.&amp;#160; Indeed, to realize the full complementary impact of this constellation of LEO and GEO satellites, i.e. to make their observations fit-for-purpose for air quality applications at the different scales, several challenges need to be addressed. These include (1) the need to enhance to sub-city scales the resolution of satellite data to make them better suited for the monitoring of e.g. the impact of the Low Emission Zones enforced in several European cities, (2) to characterize the non-trivial relation between the column amount of the pollutant measured by a satellite and the near-surface concentrations measured by in-situ networks, and (3) to determine how the different LEO and GEO vantage points lead to a different perception of atmospheric and surface details and how we can benefit from - or correct for - these differences.Work on these challenges is taking place in the dedicated Belgian federal research project LEGO-BEL-AQ (2020-2023, https://lego-bel-aq.aeronomie.be/index.php) funded by BELSPO, with a particular focus on AQ in Belgium.&amp;#160; In this contribution, we demonstrate that a combination of temporal aggregation, careful data selection, and horizontal oversampling can produce a meaningful increase in horizontal resolution in S5P tropospheric NO2 column maps, revealing policy-relevant features in the NO2 distribution over Belgium&amp;#8217;s major cities. Comparisons between our high-resolution S5P NO2 maps and the near-surface in-situ observations as procured by the Belgian authorities, reveal high correlation when considering longer time scales (seasonal and annual), allowing a pragmatic conversion from tropospheric columns to near-surface concentrations over the complete Belgian domain, and consequently also a confrontation to WHO annual thresholds at the level of individual Belgian municipalities.Acknowledgements This work has been supported by the BELSPO BRAIN-be 2.0 project LEGO-BEL-AQ (https://lego-bel-aq.aeronomie.be)

The demand for high-speed, low-latency connectivity is driving the rapid deployment of Low Earth Orbit (LEO) satellite constellations (LEOs). The LEOs are becoming integral to global Internet infrastructure to support the increasing need for broadband Internet access for social, economic, and governmental functions. LEOs can significantly reduce the digital divide by reaching underserved regions if utilised effectively. However, the cybersecurity threat landscape expanded by these systems remains a critical concern, with other significant interests—including digital inclusivity, digital autonomy, and data protection—posing obstacles to their effective deployment. Cybersecurity is fundamentally defined as the “security of cyberspace,” which includes the complex web of connections and relationships among entities accessible through a generalized telecommunications network.

An ubiquitous network for multimedia personal communications (Personal Communications Network (PCN)) with small, individual low-cost terminals is one of the most ambitious worldwide projects for the 21st century that are being pursued nowadays. In the development of such PCN, Geostationary, Medium, and Low Earth Orbiting (GEO, MEO, LEO) satellite constellations will play a fundamental role to provide worldwide coverage for most services required by the end-user. The characteristics of efficiency and flexibility inherently required by that scenario suggest, amidst other possibilities, to take into special consideration a radio interface based on code division multiple access (CDMA) to ensure, in addition to the features mentioned above, a sufficient grade of power and spectral efficiency of the relevant satellite radio link. The aim of this paper is a review of the current status of those issues in the field of satellite CDMA transmission systems design that, in our opinion, appear fundamental to the successful operation of an efficient PCN. In particular, we survey the techniques for multiplexing, coding and transmission of direct-sequence spread spectrum (DS/SS) signals, and we touch upon the techniques for the minimization of the self-noise effect, and the related topics of power-control and multiuser detection. We also shortly address in this respect some technological aspects related to an efficient modem design via digital signal processing techniques. The final part of the paper deals more specifically with some typical issues of satellite transmission, namely the minimization of the detrimental effects of the nonlinear satellite transponder and of multipath propagation; the applicability of diversity reception to a multisatellite network is also addressed as possible means of performance boost.

In recent years, low earth orbit (LEO) satellite constellation systems have been developed rapidly. However, the scarcity of satellite spectrum resources has become one of the major obstacles to this trend. LEO satellite constellation communication systems sharing the spectrum of incumbent geostationary earth orbit (GEO) satellite system is a feasible way to alleviate spectrum scarcity. Therefore, it has practical significance to study the optimization of satellite resources allocation (RA) in a spectrum sharing scenario. This paper focuses on the RA problem that LEO satellites share a GEO high throughput satellite’s spectrum in a beam-hopping (BH) manner. The GEO satellite system is served as the primary system and the LEO satellite constellation system is served as the secondary system whose frequency bands and transmitting power are strictly limited. Compared with conventional multibeam satellites, BH satellites have the advantage of flexibility in the time dimension. Therefore, we make full use of the flexibility of LEO BH satellites to realize the matching of traffic demand and traffic supply. The RA problem is decomposed into three sub-problems, namely, frequency band selection (FBS) problem, illuminated cell selection (ICS) problem, and transmitting power allocation (TPA) problem. We solve each sub-problem in order and finally form a complete RA scheme. The performance evaluation of the proposed RA scheme is carried out in real-time and simulation results show that the LEO BH satellite paired with the RA scheme we proposed has good adaptability to the uneven distribution of traffic demand in the spectrum sharing scenario.

Low Earth Orbit (LEO) constellations have recently gained tremendous attention in the navigational field due to their larger constellation size, faster geometry variations, and higher signal power levels than Global Navigation Satellite Systems (GNSS), making them favourable for Position, Navigation, and Timing (PNT) purposes. Satellite signals are heavily attenuated from the atmospheric layers, especially from the ionosphere. Ionospheric delays are, however, expected to be smaller in signals from LEO satellites than GNSS due to their lower orbital altitudes and higher carrier frequency. Nevertheless, unlike for GNSS, there are currently no standardized models for correcting the ionospheric errors in LEO signals. In this paper, we derive a new model called Interpolated and Averaged Memory Model (IAMM) starting from existing International GNSS Service (IGS) data and based on the observation that ionospheric effects repeat every 11 years. Our IAMM model can be used for ionospheric corrections for signals from any satellite constellation, including LEO. This model is constructed based on averaging multiple ionospheric data and reflecting the electron content inside the ionosphere. The IAMM model’s primary advantage is its ability to be used both online and offline without needing real-time input parameters, thus making it easy to store in a device’s memory. We compare this model with two benchmark models, the Klobuchar and International Reference Ionosphere (IRI) models, by utilizing GNSS measurement data from 24 scenarios acquired in several European countries using both professional GNSS receivers and Android smartphones. The model’s behaviour is also evaluated on LEO signals using simulated data (as measurement data based on LEO signals are still not available in the open-access community; we show a significant reduction in ionospheric delays in LEO signals compared to GNSS. Finally, we highlight the remaining open challenges toward viable ionospheric-delay models in an LEO-PNT context.

Global Navigation Satellite Systems (GNSSs) are by far the most widespread technology for Position Navigation and Timing (PNT). They have been traditionally deployed exploiting Medium Earth Orbit (MEO) or Geostationary Earth Orbit (GEO) satellite constellations. To meet future demands and overcome MEO and GEO limitations, GNSSs based on Low Earth Orbit (LEO) constellations have been investigated as a radical system change. Although characterized by a higher Doppler effect, a PNT service supplied by means of LEO satellites can provide received signals that are about 30 dB stronger. Moreover, existing LEO constellations and the forthcoming mega-constellations, which are designed for broadband internet coverage, can be exploited to provide a piggybacked PNT service. With this cost-effective solution, a secondary PNT service might be subject to an economical use of resources, which may result in substantial bandwidth limitations. At the same time, the introduction of meta-signals in the GNSS literature has brought a new receiver signal processing strategy, particularly effective in terms of available bandwidth exploitation. It allows to increase the positioning accuracy exploiting a wideband processing approach, which might be challenging under severe Doppler conditions. A narrowband implementation of the meta-signal concept, namely Virtual Wideband (VWB) can tolerate harsh Doppler conditions while also reducing the processed bandwidth. It is thus more effective when addressing a secondary PNT service, where a limited frequency occupation might be an essential requirement. The aim of this work is to show the applicability of a VWB receiver architecture on signals provided by a piggybacked PNT service, hosted on a broadband LEO constellation. We demonstrate the capability of this implementation to bear high Doppler conditions while empowering the potential of LEO PNT.