Satellite Terminals Research Articles

Estimation of direction and zero errors of satellite laser terminals in low-light conditions based on machine learning

In the assembly, launch, and on-orbit operation of satellite optical communication terminals, small deviations are difficult to avoid, which can lead to pointing errors and challenges to the establishment of optical communication links. To estimate the pointing errors of on-orbit satellite terminals, a calibration algorithm is developed based on lunar surface imagery. First, a feature extraction algorithm for low-light images is employed to process consecutive frames of low-light images to obtain a lunar surface feature map. Then, by combining the feature map and error estimation model, predictions of direction errors and zero errors were achieved. The ground validation results demonstrate the effectiveness and feasibility of the proposed on-orbit error estimation algorithm under low-signal-to-noise-ratio conditions.

Novel Resource Allocation Technique for DVB - RCS Compliant Satellite Terminals

Novel Resource Allocation Technique for DVB - RCS Compliant Satellite Terminals

Energy Efficiency for Faster-than-Nyquist Data Transmission Using Processing Algorithms with Decision Feedback

One of the ways to increase the volume of transmitted information is to increase the bit rate above the Nyquist barrier. However, an increase in bit rate in the case of FTN (Faster-Than-Nyquist) signals leads to an increase in energy costs for receiving information on channels with limited bandwidth, for example, in Digital Video Broadcasting satellite systems like DVB-S2/S2X. It is possible to minimize energy losses by using the processing algorithm “maximum likelihood sequence estimation”. However, the computational complexity of this algorithm is extremely high, which limits its use, especially in terrestrial mobile satellite terminals. We propose a new bit-by-bit decision feedback algorithm with maximum likelihood ratio estimation of subsequent symbols in the observation interval. This algorithm provides minimal energy costs comparable to the method “maximum likelihood sequence estimation” at speeds 2–3 times higher than the Nyquist barrier. At the same time, the complexity is two orders of magnitude less. It is shown by simulation for a channel with additive noise that energy losses in relation to the potential bit error rate (BER) are less than 4.5 dB. In the presence of Rayleigh fading, the application of the proposed algorithm makes it possible to provide the processing of FTN signals for double bit rates in urban areas with energy costs equal to 12 dB when using an equalizer. We give numerical estimations of the increase in computational complexity for the proposed processing algorithm. It is shown that an increase in the bit rate by 1.5 times leads to an increase in the computational complexity by more than an order of magnitude. The same conclusion can be reformulated in another form: for the proposed algorithm, each decibel of energy gain is achieved by increasing the number of computational operations by 1.5×105. It is experimentally shown that additional energy losses due to non-ideal phase and timing synchronization are no more than 1 dB when the proposed algorithm is applied in a fading channel. The energy costs in fading channels relative to a stationary channel for twice the Nyquist rate are equal to 13.8 dB when using an equalizer.

Novel Resource Allocation Technique for DVB-RCS Compliant Satellite Terminals

Satellite communication is advantageous for several reasons such as broad coverage, small installation time of remote user sites, and network services in inhospitable terrains, where installing terrestrial infrastructure is costly. With the advent of broadband multimedia satellites such as Ku and Ka band satellites, multimedia services to the satellite terminals are gaining momentum. Digital Video Broadcast Return Channel via Satellite (DVB-RCS) is an open standard developed by ETSI which has further standardized, commercialized and solved the problem of inter-operability of Ku Band satellite terminals. Satellite bandwidth is scarce therefore treated as precious resource. In the present paper, authors aim to develop and realize the resource allocation techniques in return link channel for DVB-RCS compliant satellite terminals. The paper provides method for giving preference to real time application in terms of early processing of allocation request generated against the real time traffic to reduce delay and also provides method to avoid parallel connection arises due to transmission of terminal on more than one frequency at a time. Authors have realised DVB-RCS resource allocation technique and have given simulation results.

Synthesis of Antenna Array Radiation Pattern at Large Scanning Angles Using Genetic Algorithm

At present, in most modern communication systems, for example, in modern satellite terminals, the use of scanning beam antennas, i. e. antenna arrays is assumed. At the same time, at large scanning angles, the side lobe level (SLL) increases strongly and decrease in the gain is observed. In this regard, the problem of finding a procedure for synthesizing an amplitude-phase distribution (APD) with low SLL and high gain (G) at large scanning angles comes up. One of the ways to reduce SLL and compensate for the decrease in G is to synthesize the optimal APD (in terms of the maximum G and minimum SLL) using optimization algorithms. At the same time, taking into account the characteristics of the radiation pattern of the array emitters requires numerical electrodynamic calculation. The goal of this paper is to develop a procedure for the synthesis of APD with low SLL for linear and rectangular antenna arrays at various, including large, scanning angles and compensation for G reduction using a genetic algorithm and numerical electrodynamic calculation. The methods for studying the characteristics of antenna radiators are numerical electrodynamic modeling by the finite element method (FEM) in Ansys HFSS computer-aided design system and optimization of the APD for a given radiation pattern(RP) by a random search method using partial diagrams of antenna elements. The novelty is the combination of accurate numerical electrodynamic calculation of the RP of antenna elements and optimization search for APD for the synthesis of the required RP using partial diagrams. As a result, a procedure for APD synthesis of linear and uniform rectangular equidistant (for example, 8- and 64-element) antenna arrays has been developed, taking into account the exact electrodynamic characteristics of antenna elements and their mutual resistance. Radiation patterns were obtained taking into account the effect of neighboring elements, with the help of which, using a genetic algorithm, APDs on emitters were found at different scanning angles. The change in SLL and G of the antenna array is analyzed at different scanning angles using different APDs. The proposed algorithm allows to synthesize APD for a RP with low SLL and high G at scanning angles up to 40° for linear antenna array and up to 80° in the case of a uniform rectangular antenna array. The results of this work are relevant in the problems of radiation pattern synthesis, since the proposed solution provides a significant gain in the radiation pattern synthesis rate of APD of linear and rectangular antenna arrays, especially for systems with a large number of antenna elements. At the same time, it is possible to maintain a high G at large scanning angles, and achieve a significant reduction of SLL.

Multi-Objective Robust Beamforming for Integrated Satellite and Aerial Networks Supporting Heterogeneous Services

An integrated satellite and aerial network (ISAN) is considered a promising candidate to provide seamless connectivity for future wireless communication systems. In this paper, we propose a multi-objective based robust beamforming (BF) scheme for an ISAN to support heterogeneous services with high flexibility, where the satellite network serves various heterogeneous satellite terminals through multicast non-orthogonal multiple access (MC-NOMA), while the aerial network offers services to many internet of things devices using layered division multiplexing (LDM). Specifically, we first formulate a multi-objective optimization problem (MOOP) to achieve a good trade-off between sum rate maximization and total transmit power minimization. To tackle this mathematically intractable problem, we exploit the weighted Tchebycheff approach to transform the MOOP into a single-objective problem. Since only the angular information based channel state information is available, we exploit the angular discretization method and sequential convex approximation to design a robust BF algorithm to obtain the Pareto optimal solutions. Finally, simulation results demonstrated that our proposed scheme can achieve a optimal trade-off between multiple performance metrics with high spectrum and energy efficiency, so as to support heterogeneous services in the ISAN and fill the gap of only single type of serivce in the existing ISAN works.

Inter-terminal transportation for an offshore port integrating an inland container depot

Offshore ports, which are located on islands or away from the hinterland, are usually connected with the hinterland via bridges for truck transportation. With the rapid growth of port throughput, the bridges are likely to become a bottleneck restricting the development of port business. Inland container depots (ICD) have been introduced as satellite terminals to address congestion issues on bridges by allowing a proportion of drayage trucks to pick up and drop off containers at the ICD instead of going to the container terminals of the offshore ports. Containers are transported between the ICD and container terminals by inter-terminal transportation (ITT) trucks owned by port authorities. The ICD is expected to mitigate the bridge congestion by transferring the travel demands of drayage trucks in peak hours to the travel demands of ITT trucks in off-peak hours. We propose a methodology for analyzing the influence of ICDs on port efficiency. An integer linear programming model is developed to optimize the movements of containers, drayage trucks and ITT trucks in an offshore port area with the objective of minimizing the costs of drayage trucks and ITT trucks and the penalty for late delivery of containers. Two model transformation approaches are proposed to reduce the solution space of the model for improving the computational efficiency of the algorithm. The influence of ICDs on port efficiency is evaluated through a real-world case study using the proposed methodology. The results provide insights for port authorities to make strategic decisions.

Aerial Edge Computing: A Survey

In the beyond 5G/6G era, Aerial Edge Computing (AEC) is expected to be used as significant components in Internet of Things. AEC brings flexible deployment with Line-of-Sight communication links for task offloading and computing services. In this paper, we present a comprehensive survey of the AEC technology. Firstly, we introduce a three-layer architecture of AEC, which includes the satellite, UAVs and ground terminals. Secondly, we illustrate challenges in AEC, and summarize recent studies in terms of AEC performance metrics that include energy efficiency, latency and operation cost to address challenges in AEC. Further, we introduce the advanced technologies applied in AEC management, e.g., Artificial Intelligence (AI) and the distributed optimization. Finally, the applications and the open issues with AEC are summarized and classified in the study.

Research on Resource Allocation Algorithm for Satellite Uplink to Provide Differentiated QoS Support

Broadband satellite systems are built to serve different user groups ranging from enterprise and military users to common personal users, with various kinds of services calling for dissimilar quality of service (QoS). Obviously, the satellite systems are expected to distinguish the specific type of an incoming service request as well as the importance of its owner in order to perform an efficient assignment of valuable resources. In this article, the uplink resource management challenge in a multifrequency-time-division multiple access satellite system is addressed where provisioning the discriminated QoS is of vital importance. Having taken both user priority and service type into account, a differentiated QoS support principle conforming to the digital video broadcast - second generation DVB interactive satellite system (DVB-RCS2) standard is put forward, based on which the uplink timeslot assignment problem is formulated.The NP-hardness of the problem is proved, and a differentiated QoS resource allocation scheme is designed, decoupling the problem into the coarse-level of resource allocation and fine-level of timeslot assignment. The former stage involves the constant rate assignment, bandwidth adjustment, QoS degradation and user scheduling, among which the subproblem of user scheduling is an integer nonlinear program. To tackle the issue, the problem is first innovatively converted to an integer linear program, and is then modeled as the multiple-choice multiple knapsack (MCMK) problem. Furthermore, an MCMK algorithm is presented to give the optimal solution to the user scheduling problem, after which the timeslot assignment is investigated in the second phase to generate the terminal burst time plan table for return channel satellite terminals.

Cyber-Physical Attack Using High Power RF in Havana, Cuba

Abstract: Global communications have relied heavily on fiber-optic cables. Satellite communications have become the norm for areas that are not highly populated or easily reached by conventional wires. The availability and use of satellite communications systems have had a limited market; with this limitation, the need for open development of each vendor's software never gained traction. This led to weaknesses not being discovered until a flaw was made public in a systems breach that affected the end users. Wireless communications that rely on microwaves lead to the use of malware to provide an override to normal operations of the equipment. As the issue of Stuxnet would allow for the override of the safety settings of satellite terminals, the malware could even be deployed remotely through a system update. The weaponization of such systems is now a point of concern. Previous studies have shown that naval satellite communications systems can be a weapon by removing the software power limitations McKay, R. W 2021 [15]. As satellite systems on ships can be larger due to being fixed, transmission power generation may be more significant. This study considers the land-based mobile systems deployed against any target and quickly dismantled and removed. Can land-based mobile satellite communication systems affected by Stuxnet or manually altered yield the same power output, and at what range will it affect human tissue? This is believed to be the case with the ongoing investigation. The survey results showed that mobile equipment could be dangerous to human tissue at distances easily achieved by mobile terminals, especially if the target is a fixed location like a building with large glass windows that R.F. power can penetrate easily

Increasing the gain of an antenna array based on Fabry-Perot cavities at high scanning angles

An approach for increasing the gain of an antenna array based on Fabry-Perot cavities with mechanoelectrical scanning in the 60-90o angle sector by using a radio-absorbing material on the shading subarray is described. Simulation and analysis of the directional characteristics of the antenna array based on Fabry-Perot cavities with a radio-absorbing material have been performed, and the characteristics have been compared with those of the antenna array without an absorber. Conclusions on the applicability of the proposed configuration of the antenna array based on Fabry-Perot cavities in mobile satellite terminals are made. Keywords: antenna array, Fabry-Perot cavity, wide-angle scanning, radio absorber.

Увеличение коэффициента усиления антенной решетки на основе резонаторов Фабри-Перо в области сканирования больших углов

An approach for increasing the gain of an antenna array based on Fabry-Perot cavities with mechanoelectrical scanning in the 60-90° angle sector by using a radio-absorbing material on the shading subarray is described. Simulation and analysis of the directional characteristics of the antenna array based on Fabry-Perot cavities with the use of radio absorbing material have been performed, the characteristics have been compared with the antenna array without an absorber. Conclusions on the applicability of the proposed configuration of the antenna array based on Fabry-Perot cavities in mobile satellite terminals are made.

A Feasibility Study on Opportunistic Rainfall Measurement From Satellite TV Broadcasts

Rainfall precipitation maps are usually derived based on the measurements collected by classical weather devices, such as rain gauges and weather stations. This article aims to show the benefits obtained by opportunistic rainfall measurements based on signal strength measurements provided by commercial-grade satellite terminals (e.g., used in TV broadcasting). To assess not only the feasibility of this approach, with significant advantages in terms of capital and operational expenditure, but also improvements in terms of accuracy, we focus on a case study for agricultural applications using a Gaussian-modeled synthetic rain over a specific, real-world test area.

Deep Learning Forecasting and Statistical Modeling for Q/V-Band LEO Satellite Channels

As the number of satellite networks increases, the radio spectrum is becoming more congested, prompting the need to explore higher frequencies. However, it is more difficult to operate at higher frequencies due to severe impairments caused by varying atmospheric conditions. Hence, radio channel forecasting is crucial for operators to adjust and maintain the link’s quality. This paper presents a practical approach for Q/V-band modeling for low Earth orbit satellite channels based on tools from machine learning and statistical modeling. The developed Q/V-band LEO satellite channel model is composed of; (i) forecasting method using model-based deep learning, intended for real-time operation of satellite terminals, and (ii) statistical channel simulator that generates a time-series path-loss random process, intended for system design and research. Both approaches capitalize on real-measurements obtained from Al-phaSat’s Q/V-band transmitter at different geographic latitudes. The results show that model-based deep learning can outperform simple statistical and deep learning methods by at least 50%. Moreover, the model is capable of incorporating varying rain and elevation angle profiles.

Stand-Alone, Affordable IoT Satellite Terminals and Their Opportunistic Use for Rain Monitoring

Internet of Things (IoT) communication via satellite is an important emerging technology, which is essential for a variety of applications such as agriculture, financial technology, and homeland security in rural or isolated areas. In this article, we deal with two-way low cost, stand-alone IoT satellite terminals communicating over geostationary satellites at Ku-band frequencies, already deployed in isolated areas in Africa and South America. On top of their designated use for specific IoT applications, we suggest using such terminals for opportunistic rain monitoring, based on the two-way link quality measurements that are being regularly collected for network management purposes. The local <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$E_{s}/N_{0}$</tex> measurements are transmitted to the cloud, where their transformation to rain-intensity estimates is carried out. We present preliminary results using real measurements, showing good agreement with direct rainfall measurements recorded by a rain gauge. Enabling this feature in two-way communication of IoT satellite terminals is beneficial, as it will provide the ability to monitor the rain in areas where designated weather monitoring equipment is sparse, helping to improve local weather-based applications in such areas, and to better track the climate change globally.

A Dual Ka/Q-Band Reflectarray

Introduction. Duplex satellite communication is commonly arranged using two spaced frequency bands, with one band receiving and the other band transmitting signals to a satellite. The main task of a communications satellite antenna system consists in providing an identical coverage area across all involved frequency bands, which is often a challenging task for conventional parabolic reflector antennas. Reflectarrays allow an independent control of the reradiated wave phase in spaced frequency bands, which can be used to create efficient multi-band antenna systems for modern communication satellites.Aim. To develop a Ka/Q-frequency range phase-correcting element and to create on its basis a dual-band reflectarray for operation with orthogonal circular polarizations and identical gains in a given sector of angles in significantly spaced frequency ranges.Materials and methods. Numerical studies were carried out using the finite element analysis method. Radiation patterns were measured using the near field scanning method.Results. A single-layer dual-band phase-correcting reflectarray element was developed for operation with orthogonal circular polarizations with low losses and a weak dependence of the relative position of the elements on the phase characteristic. On the basis of the proposed element, a reflectarray consisting of 24 465 two-frequency elements was synthesized and manufactured. The developed prototype of a single-layer dual-band reflectarray demonstrated good characteristics, with the efficiency reaching 56 and 36 % in the Ka- and Q-frequency ranges, respectively, and an almost identical minimum gain in the ±0.75° angle sector.Conclusion. The research results confirm the potential of the developed reflectarray to successfully replace conventional parabolic reflectors installed both on modern communication satellites and as part of ground-based satellite terminals in the millimeter wavelength range.

Performance of Spectrum Sharing in Hybrid Satellite Terrestrial Network with Opportunistic Relay Selection

In this paper, we consider the uplink of a hybrid satellite-terrestrial spectrum sharing system, in which satellite terminal communicates with satellite through terrestrial relay-assisted transmission. To accommodate expanding networks within limited spectrum, spectrum sharing is considered a promising candidate. For the system in which satellite terminals and terrestrial terminals share spectrum, we propose opportunistic relay selected spectrum sharing method based on decoding and forwarding protocol. Selecting the optimal relay station is aimed at minimizing the outage probability of the satellite terminal and maximizing the throughput of the system. Due to spectrum sharing policy and imperfections in the RF front end, we also consider the effects of cochannel interference (CCI) and hardware impairments (HIs). The satellite link is modeled as Shadowed-Rician fading, and the terrestrial link uses Nakagami-m fading. In addition, we deduce the closed-form analytical expressions of the satellite terminal outage probability, deduce the asymptotic expressions under the condition of high signal-to-noise ratio, and analyze their achievable diversity orders. Numerical and simulation results validate the performance gain of opportunistic relay selection compared to partial relay selection. Monte Carlo simulations confirm the correctness of the theoretical analysis and illustrate the effects of CCI and HIs on the system.

User Grouping in Multiuser Satellite MIMO Downlink With Fairness Consideration

In this letter, a multi-user satellite MIMO downlink including a multi-beam GEO satellite and multiple user terminals (UTs) is considered. In order to make every UT get the service fairly, all UTs need to be divided into multiple groups so that UTs in the same group can be served simultaneously, and different groups can be served sequentially in different time slots. The user grouping problem is investigated in this letter with the objective of maximizing the average channel capacity per time slot, and a genetic based user grouping (GBUG) algorithm is proposed. Simulations show that the average channel capacity obtained by GBUG is larger than that of the existing algorithms in the ZF and MMSE precoding system.

Can You Hear Me Now? [Turnstile

Reports on the deliverance of Starlink Terminals by the US Agency for International Development (USAID) to the Government of Ukraine through a public/private partnership with SpaceX. The Starlink satellite terminals will enable unlimited, unthrottled data connectivity from anywhere in Ukraine. Starlink provides Internet service by connecting from small ground terminals to fast-moving satellites in low-Earth orbits.

Asymmetric Differential Routing for low orbit satellite constellations

Low Earth Orbit (LEO) constellations create a network that includes the satellites (as routing nodes) connected by Inter-Satellite Links (ISLs) while the satellite terminals are dynamically connected to one or more satellites. The combination of transient, high-rate changes with high latency presents a unique challenge for designing a routing protocol that can provide guaranteed bandwidth, and support the frequent changes without packet drops. Current works focus on end-to-end routing between multiple gateways and terminals and do not provide guaranteed service.This paper addresses the problem of routing traffic from a source terminal to a destination terminal on a LEO constellation using Asymmetric Differential Routing (ADR) to plan ‘semi-fixed’ routes. ADR keeps most of the planned route fixed and only minor (differential) adjustments are required to account for handovers. Using ADR, a terminal and a gateway (GW) communicate using a fixed route with a time complexity of O(1) to account for handovers.