Optimal Computation Resource Allocation Scheme for LEO Satellite Networks

Gravity field recovery of inter-satellite links between Beidou navigation satellite system (BDS) and LEO based on geodesy and time reference in space (GETRIS)

As small satellites become more capable through miniaturized electronics and on-board processing, constellations of low-cost satellites lunched in Low-Earth Orbit (LEO) become feasible. The increase in the number of LEO satellites drives the need for frequency coexistence between the LEO constellation systems with the already existing geostationary (GSO) satellite networks. In this context, it is crucial to design the communication links paying special attention to interference analysis. This is particularly true when the LEO satellite constellation exploit inter-satellite communication links (ISL). In this paper, a radio frequency interference analysis based on simulation of the dynamic satellite constellation is presented and the design parameters of the inter-satellite links are analyzed. The results suggest that carefully choosing the design parameters of the intersatellite links, spectrum coexistence of LEO and GSO networks may be possible.

The increasing demand for ultra-low-latency and high-throughput communication necessitates network architectures capable of ensuring reliable real-time connectivity. To address this requirement, integrated architectures combining terrestrial networks (TN) and non-terrestrial networks (NTN)—particularly hierarchical multi-layer satellite systems composed of geostationary Earth orbit (GEO), medium Earth orbit (MEO), and low Earth orbit (LEO) satellites—have attracted considerable attention. Such hierarchical systems offer global coverage, low latency, and high capacity. However, their highly dynamic topology, fast-moving satellites, and fluctuating link quality pose significant challenges to establishing efficient end-to-end routing paths. Traditional routing methods based on static paths or centralized control lack the adaptability required for such environments. To address these challenges, this paper introduces a neural hierarchical reinforcement learning (HRL)-based routing algorithm for satellite networks. The framework exploits the layered structure of GEO, MEO, and LEO satellites, enabling gateway-assisted routing and adaptive path selection. Control responsibilities are distributed across orbital layers: the GEO layer allocates hop-count budgets, the MEO layer selects feasible LEO paths, and the LEO layer forwards data packets. When inter-satellite links are unavailable, terrestrial gateways provide alternative routes. Routing decisions further account for satellite-to-satellite and satellite-to-ground link quality, with an end-to-end delay-based reward function capturing transmission, processing, and propagation effects. Simulation results show that the proposed neural hierarchical framework, supported by integrated terrestrial and non-terrestrial networking, achieves faster convergence, greater route stability, and better adaptability than conventional routing algorithms and HRL approaches.

Precise orbit and Earth parameter determination supported by LEO satellites, inter-satellite links and synchronized clocks of a future GNSS

The improvement of BDS Observation Geometry with LEO constellations in Orbit Determination

Line-of-sight communications links between satellites allow data to be transmitted directly from one satellite to another. The different types of links which can be implemented between satellites in geostationary orbit (GSO) and low Earth orbit (LEO), are illustrated. There are two main classes, interorbit links between LEO and GSO satellites, and intersatellite links (ISLs) between satellites which are both in GSO or LEO orbit. This paper is primarily concerned with ISLs between GSO satellites for military communications.

In this paper, we propose a double-edge-assisted computation offloading and resource allocation scheme tailored for space-air-marine integrated networks (SAMINs). Specifically, we consider a scenario where both unmanned aerial vehicles (UAVs) and a low earth orbit (LEO) satellite are equipped with edge servers, providing computing services for maritime autonomous surface ships (MASSs). Partial computation workloads of MASSs can be offloaded to both UAVs and the LEO satellite, concurrently, for processing via a multi-access approach. To minimize the energy consumption of SAMINs under latency constraints, we formulate an optimization problem and propose energy efficient algorithms to jointly optimize offloading mode, offloading volume, and computing resource allocation of the LEO satellite and the UAVs, respectively. We further exploit an alternating optimization (AO) method and a layered approach to decompose the original problem to attain the optimal solutions. Finally, we conduct simulations to validate the effectiveness and efficiency of the proposed scheme in comparison with benchmark algorithms.

Currently many efforts are undertaken to develop and install communication networks based on low earth orbit (LEO) and intermediate circular orbit (ICO) satellites. However, many problems are to be solved until the final operation of such networks. This paper deals with basic design problems of LEO/ICO‐based networks. In the first part, estimates for the necessary number of satellites, orbits and number of communication channels per satellite are derived. Since the latter is a crucial quantity, the number of communication links and channels per link are derived with a more elaborate model in the second part of the paper. This includes the radio links from the satellites to mobile users and to gateways, as well as intersatellite links and terrestrial lines. We introduce a formal model for LEO/ICO‐based networks and propose a method for the evaluation of link capacities, given the network topology and the traffic requirements. As an example, two constellations are investigated in detail. One of these constellations is the IRIDIUM system proposed by Motorola.

Non-Terrestrial Networks (NTNs) will constitute a cornerstone of the next-to-come Sixth-Generation (6G) technology. Specifically, Low-Earth Orbit (LEO) satellite constellations play a crucial role, either as a stand-alone networking solution or as a complement to terrestrial networks, in providing network access and services anywhere and anytime with lower latency than geostationary satellites. However, LEO’s narrow coverage areas and mobility will likely cause service interruptions whenever the link between the NTN platform and NTN-Gateway (GW) (i.e., the feeder link) becomes unavailable. The Third Generation Partnership Project (3GPP) has defined a set of feeder link switch over procedures, which may lead to a long procedure duration and, hence, long service interruptions, especially in the case of NTN-GWs located far from each other. To cope with the mentioned issues, this paper proposes a novel feeder link switch over procedure, which exploits inter-satellite links (ISLs) to implement, through a chain of LEO satellites, virtual visibility between a LEO satellite and an NTN-GW that are not in direct sight. This aims at reducing the time of feeder link switch over and avoiding service disruptions. The advantages of the proposed ISL-aided feeder link switch over procedure over the one defined by 3GPP are assessed via simulative campaigns.

Inter-satellite link technologies and applications in Low Earth Orbit satellite networks

Recently, more research attention has been focused on LEO (Low Earth Orbit) satellite networks connected to ISL (Inter Satellite Link). If terrestrial and LEO satellite networks are seamlessly interconnected by TCP/IP protocols, a global network that covers the whole earth can be integrated into the Internet. However, handover and rerouting issues in LEO satellite networks cause delay variance, and the delay variance can degrade performance of TCP, originally designed for wired networks, because of unnecessary retransmission. In this paper, we propose a method for avoiding the unnecessary retransmission by using the TTL (Time To Live) field in IP headers. Our simulation results show how our mechanism is effectively avoiding unnecessary retransmissions. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(1): 64–71, 2005; Published online in Wiley InterScience (www.interscience.wiley. com). DOI 10.1002/ecja.10205

Machine learning (ML) frameworks are investigated for use in simultaneous tracking and navigation (STAN) with low Earth orbit (LEO) satellites. STAN is a navigation paradigm that utilizes specialized LEO receivers to extract navigation observables (e.g., pseudorange and Doppler) from LEO satellite signals. Two neural network architectures are compared: Feed Forward Neural Network (FFNN) and Recurrent Neural Network (RNN). Additionally, two ML-based orbit determination frameworks are compared: ephemeris propagation and residual error propagation. The objective of the comparison is to select an approach with the lowest open-loop propagation error as well as computational cost. Based on simulation results, a nonlinear autoregressive neural network with exogenous inputs (NARX) embedded within the residual error modeling framework is selected as the best ML approach among the compared candidates. Experimental results are presented demonstrating a ground vehicle navigating for a total of 258 seconds, while receiving signals from two Orbcomm LEO satellites. Global navigation satellite system (GNSS) signals were artificially cut off for the last 30 seconds, during which the vehicle traversed a trajectory of 871 m. Two navigation frameworks are compared to estimate the vehicle’s trajectory: (i) LEO signal-aided inertial navigation system (INS) STAN framework using Simplified General Perturbation (SGP4) as its propagator and (ii) the proposed LEO signal-aided INS STAN framework using ML as its propagator. The STAN with SGP4 achieved a three-dimensional (3-D) position root-mean squared error (RMSE) of 30 m. In contrast, the proposed STAN with SGP4+NARX framework achieved a 3-D position RMSE of 3.6 m.

The European Space Agency's satellite ARTEMIS will support data links between spacecraft in low earth orbit, ARTEMIS in geostationary orbit and ground stations in Europe. The links between spacecraft in low earth orbit and ARTEMIS will operate at S-band (2 GHz), Ka-band (25 GHz) or optical wavelength (800 nm). This paper addresses the S-band and Ka-band links, which both operate via a steerable 2.85 m diameter reflector antenna on ARTEMIS. The link design has been performed to minimize the signal degradations, and has led to rather demanding requirements on the flatness of the amplitude and group delay distortion versus frequency, on the phase noise and on the linearity of the payload. The measured values for these parameters are presented. In S-band, the antenna pointing is performed in open loop according to a preloaded table, while in Ka-band a closed loop pointing system is implemented and open loop pointing is back-up. The design, test and operation of the antenna pointing system are presented. The European Space Agency (ESA) participates in the Satellite Network Interoperability Panel (SNTP) together with NASA and NASD A. SNTP has established a set of interoperability parameters making it possible for low earth spacecraft from the three agencies to operate through the relay satellites of NASA, NASDA and ESA. ARTEMIS will be the first ESA satellite to offer data relay services, and its performances are compared to the interoperability parameters established by SNIP. Inter Orbit Links Spacecraft in low earth orbit (LEO) are restricted in their ability to communicate with the ground, because of the limited time a spacecraft in LEO is visible from a single ground station. ARTEMIS, located in the geostationary orbit, will significantly increase the communication time between the spacecraft in LEO and a single ground station. This is illustrated in Fig. 1. When a spacecraft is flying over the cross hatched areas in Fig. 1 at 300km altitude, no contact is possible via ARTEMIS. This area is slightly increased for a spacecraft at 1000km altitude as marked by the contour. Spacecraft can maintain contact to ground via ARTEMIS, when they are over SouthAmerica, eastern part of North-America, the Atlantic, Europe, Africa, most of Asia, the Indian Ocean and the polar regions The data relay function is provided by communication links between the ground and ARTEMIS named feeder links and links between ARTEMIS and the LEO spacecraft named inter orbit links (IOL). The feeder link operates at 20 GHz from ARTEMIS to ground (i.e. return feeder link) and at 30 GHz from ground to ARTEMIS (i.e. forward feeder link). The IOL can operate in three different bands namely S-Band (i.e 2.025 to 2.110 GHz for the forward IOL from ARTEMIS to LEO spacecraft and Copyright © 1997 by J. Sandberg. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission.

According to previous studies, the UDLs (user data links) or ISLs (intersatellite links) switch and failure can result in the packet reordering in Low Earth Orbit (LEO) satellite networks. The packet reordering can severely deteriorate the performance of transmission in LEO satellite networks, especially at very high levels of packet reordering. In order to improve the TCP (Transmission Control Protocol) performance in LEO satellite networks, this paper proposes a modified TCP variant named TCP-D-SACK, which is based on the TCP-SACK. Our results indicate that the new TCP variant can improve the throughput.

Global navigation satellite systems (GNSS) are widely used in low Earth orbit (LEO) satellite navigation; however, their availability is poor for users in medium Earth orbits (MEO), and high Earth orbits (HEO). With the increasing demand for navigation from MEO and HEO users, the inadequate coverage of GNSS has emerged. Inter-satellite links (ISLs) are used for ranging and communication between navigation satellites and can also serve space users that are outside the navigation constellation. This paper aims to summarize their application method and analyze their service performance. The mathematical model of visibility is proposed and then the availability of time division ISLs is analyzed based on global grid points. The BeiDou navigation constellation is used as an example for numerical simulation. Simulation results show that the availability can be enhanced by scheduling more satellites and larger beams, while the presence of more users lowers the availability. The availability of navigation signals will be strengthened when combined with the signals from the ISLs. ISLs can improve the space service volume (SSV) of navigation constellations, and are therefore a promising method for navigation in MEO/HEO spacecraft.