Space Link Research Articles

The Performance of Satellite-Based Links for Measurement-Device-Independent Quantum Key Distribution.

Measurement-device-independent quantum key distribution (MDI-QKD) protocol has high practical value. Satellite-based links are useful to build long-distance quantum communication network. The model of satellite-based links for MDI-QKD was proposed but it lacks practicality. This work further analyzes the performance of it. First, MDI-QKD and satellite-based links model are introduced. Then considering the operation of the satellite the performance of their combination is studied under different weather conditions. The results may provide important references for combination of optical-fiber-based links on the ground and satellite-based links in space, which is helpful for large-scale quantum communication network.

A satellite-based quantum key distribution using decoy-state protocol

An ideal QKD implementation that provides the promising unconditional security using single photon laser source is not practically easy, also sending these photons over a fiber channel affects the maximum distance of link up to few hundreds of kilometers because of the receiver’s detectors losses. Therefore, the achievement of a global quantum network is not easy, and the need to use LEO satellites [1,2] for establishing quantum links makes the job easier as quantum free space link provides much less losses to the link than fiber links. Nowadays, a quantum communication link can be established by satellites through free space. in this paper, we propose an implementation [3] of a satellite-based quantum key distribution using decoy-state protocol [4], we then compare this protocol with the BB-84 protocol [3] against security and the key length of the generated shared key.

Cost-Efficient Hybrid WDM-MDM-Ro-FSO System for Broadband Services in Hospitals

The expansion of high-speed communication needs due to explosive growth of subscribers each year has led the researchers to design the next generation communication systems which can cope with the current growing demand. Millimeter waves, operated within the range of 30 GHz to 300 GHz, can become potential carrier for delivering large amount of data. However, in hospital scenarios, these radio waves are subjected to strict regulations due to direct impact on patients’ health as well as high interference with other medical devices which again imposes critical challenge on patients. Thus, it is a challenge for the researchers to provide communication/broadband services for transmission of such sensitive biomedical sensor data in hospitals locations. Radio over Free space (Ro-FSO) systems may become the attractive solution to deliver millimeter waves over free space link with high speed. Further, to expand the capacity of Ro-FSO systems, mode division multiplexing (MDM) plays a vital role in addition to wavelength division multiplexing (WDM) scheme. In this work, we have demonstrated the MDM-WDM scheme to deliver four channels with each one having the capacity of 10 Gbps up-converted to 40 GHz over FSO link which is suitable for providing broadband and communication services within the hospital premises. Moreover, the proposed WDM-MDM-Ro-FSO link is evaluated under different fog conditions.

Quantum Keyless Private Communication Versus Quantum Key Distribution for Space Links

We study information theoretical security for space links between a satellite and a ground-station. Quantum key distribution (QKD) is a well established method for information theoretical secure communication, giving the eavesdropper unlimited access to the channel and technological resources only limited by the laws of quantum physics. But QKD for space links is extremely challenging, the achieved key rates are extremely low, and day-time operating impossible. However, eavesdropping on a channel in free-space without being noticed seems complicated, given the constraints imposed by orbital mechanics. If we also exclude eavesdropper's presence in a given area around the emitter and receiver, we can guarantee that he has only access to a fraction of the optical signal. In this setting, quantum keyless private (direct) communication based on the wiretap channel model is a valid alternative to provide information theoretical security. Like for QKD, we assume the legitimate users to be limited by state-of-the-art technology, while the potential eavesdropper is only limited by physical laws: physical measurement (Helstrom detector) and quantum electrodynamics (Holevo bound). Nevertheless, we demonstrate information theoretical secure communication rates (positive keyless private capacity) over a classical-quantum wiretap channel using on-off-keying of coherent states. We present numerical results for a setting equivalent to the recent experiments with the Micius satellite and compare them to the fundamental limit for the secret key rate of QKD. We obtain much higher rates compared with QKD with exclusion area of less than 13 meters for Low Earth Orbit (LEO) satellites. Moreover, we show that the wiretap channel quantum keyless privacy is much less sensitive to noise and signal dynamics and daytime operation is possible.

A Survey of Rain Fade Models for Earth–Space Telecommunication Links—Taxonomy, Methods, and Comparative Study

Satellite communication is a promising transmission technique to implement 5G and beyond networks. Attenuation due to rain begins at a frequency of 10 GHz in temperate regions. However, some research indicates that such attenuation effects start from 5–7 GHz, especially in tropical regions. Therefore, modeling rain attenuation is significant for propagating electromagnetic waves to achieve the required quality of service. In this survey, different slant link rain attenuation prediction models have been examined, classified, and analyzed, and various features like improvements, drawbacks, and particular aspects of these models have been tabulated. This survey provides various techniques for obtaining input data sets, including rain height, efficient trajectory length measurement techniques, and rainfall rate conversion procedures. No survey of the Earth–space link models for rain attenuation is available to the best of our knowledge. In this study, 23 rain attenuation models have been investigated. For easy readability and conciseness, the details of each model have not been included. The comparative analysis will assist in propagation modeling and planning the link budget of slant links.

Estimation of cloud attenuation over some coastal cities for satellite space links in South Africa

One of the vital constraints on satellite space link systems operating at higher frequencies is attenuation due to clouds. This paper presents a 5-year estimation of cloud attenuation in the millimeter-wave propagation over two coastal cities in the Republic of South Africa. The results show that some salient features of clouds observed were monthly and location dependent. The observed average cloud value ranges between 16% and 55.6%, the relative humidity recorded between 65.4% and 84.2%, while the rainfall amount is between 5.43 and 79.66 mm over the study locations. The specific attenuation coefficient and cloud attenuation increases as the frequency increases over the studied locations. Furthermore, about 1 dB and above was observed at frequencies from 60 GHz and above. The study reveals the impact of liquid water content (LWC) in the clouds, which has a more significant effect on radio signals. The differences in the attenuation observed may be due to the impact of LWC and other salient features observed over the locations.

Analysis of performance and robustness against jitter of various search methods for acquiring optical links in space.

We discuss various methods for acquiring optical links in space using a dedicated acquisition sensor. Statistical models are developed and simple analytical equations derived that compare the performance between a single- and dual-spiral scan approach as well as between sequential and parallel acquisition of link chains. Simple derived analytical equations allow relating essential search parameters such as track width, variance of the uncertainty distribution, capture radius, and scan speed to the probabilities of acquiring the links within a specific time. We also assess the probability of failing to acquire a link due to beam jitter and derive a simple analytical model that allows determining the maximum tolerable jitter for a given beam overlap and required probability of success. All results are validated by Monte Carlo simulations and applied to the concrete example of the GRACE FO mission.

Intrinsic in-plane nodal chain and generalized quaternion charge protected nodal link in photonics

Nodal lines are degeneracies formed by crossing bands in three-dimensional momentum space. Interestingly, these degenerate lines can chain together via touching points and manifest as nodal chains. These nodal chains are usually embedded in two orthogonal planes and protected by the corresponding mirror symmetries. Here, we propose and demonstrate an in-plane nodal chain in photonics, where all chained nodal lines coexist in a single mirror plane instead of two orthogonal ones. The chain point is stabilized by the intrinsic symmetry that is specific to electromagnetic waves at the Г point of zero frequency. By adding another mirror plane, we find a nodal ring that is constructed by two higher bands and links with the in-plane nodal chain. The nodal link in momentum space exhibits non-Abelian characteristics on a C2T - invariant plane, where admissible transitions of the nodal link structure are determined by generalized quaternion charges. Through near-field scanning measurements of bi-anisotropic metamaterials, we experimentally mapped out the in-plane nodal chain and nodal link in such systems.

ANALYSIS OF INFORMATION PREFERENCES OF AGRICULTURAL SCIENTISTS IN SIBERIA

The article presents the results of a survey of employees of 32 scientific organizations ofagricultural profile in Siberia in order to study their information needs. The assessment of significance for scholars of the library as an indispensable social institution in the system of scholarly communication and the Siberian Scientific Agricultural Library of the branch of SPSL SB RAS as a critical link in a single information space of the agricultural science of Siberia. Promising directions of development of the resource base and service of SibNSHB as a branch academic library for improving the quality of information support for scientific research on agricultural issues are identified.

Mathematical modelling of biology processes based on the table of prime links in the solid torus up to 4 crossings

The motivation to study links in lens spaces can be justified in recent applications to theoretical physics and biology. In this paper, we give a short outline of practical significance and implementation proposals of such links, the study of which begins with the study of links in the solid torus, since a punctured disk diagram of a link in the lens space can be considered as a punctured disk diagram in the solid torus provided with the additional slide move. However, links in the solid torus find their applications themselves as well. In this paper, we propose a method to represent knotted proteins as links in the solid torus. Such a method is based on the existence of correspondence between knotoids and knots in the solid torus using a double branched cover. To this end, the table of links in solid torus is necessary. Therefore, we classify all prime links in the solid torus up to 4 crossings. One of possible future applications of the constructed table is an analysis of the database LinkProt that collects information about protein chains and complexes that form links. Also, our table can be used to construct table of prime links in lens spaces.

PROZORRO: ВИКЛИКИ ДЛЯ ДІДЖИТАЛІЗАЦІЇ ДЕРЖАВНИХ ВИДАТКІВ В УКРАЇНІ

The article analyzes the impact of the electronic public procurement system Prozorro on the work in the public sector of the economy of Ukraine, considers the structure and dynamics of the public procurement market. The object of the study is the structure of the market and analysis of its volume, the number of procedures and bidders, and the amount of savings through the electronic public procurement system Prozorro. Public procurement is an important link in the fiscal space to stimulate national production, economic and government growth. It is noted that as a result of the functioning of the public procurement system, the state satisfies public needs in goods, jobs and services. The article considers the directions of the impact of digitalization on the transparency and effectiveness of public consumption policy. In particular, in the conditions of digitalization the development, possibilities of application of the electronic system of public procurement Prozorro are investigated and the service of financial accounting Prozorro as an effective way of centralization of public procurement is analyzed. Public spending and services, including the public procurement system, are an important part of the fiscal environment to stimulate national production, development and economic growth in any country in the world. The strategic task for Ukraine and the world is the rational use of resources (public funds) for public purposes. Lobbying, non-transparency in the field of public consumption causes vulnerability of all state institutions, slows down socio-economic development and distorts the competitive business environment. Budgets will show deficits at any level of tax revenue if government spending remains a poor tool for government intervention. The development of modern technologies has an increasing impact on all spheres of human activity, and its manifestation – digitalization turns it into a society of network interactions, transforms the structure and format of work, employment and entrepreneurship. It is digitalization in the context of globalization that implies innovative opportunities and tools for the implementation of public expenditure policy at a qualitatively new level, thereby accelerating the process of managing budget revenues and expenditures, reducing administrative burdens and increasing transparency.

The Radiation Effect on Low Noise Amplifier Implemented in the Space-Aerial–Terrestrial Integrated 5G Networks

This paper provides the details of a study on the effects of electron irradiation on two Low Noise Amplifiers (LNA), the Gallium-Arsenide (GaAs) pseudomorphic high electron mobility transistor (pHEMT) based and the Silicon-Germanium (SiGe) Heterojunction Bipolar Transistor (HBT)-based. Previous studies have shown that the properties of GaAs and SiGe HBT's are very tolerant of gamma, neutron, and proton irradiation without additional radiation hardening. Nowadays, commercials on the shelves (COTS) LNAs have been used in CubeSat space communication systems which may be connected to other communication networks for the implementation of the space-aerial- terrestrial integrated 5G network (SATIN) systems projects, for satellites, launched into Low and Medium Earth Orbits. Previous studies suggest that the electron radiation in space may degrade the LNAs' performance and might even lead to its failure. Located at the front end of the communication receiver system, this paper conducted such investigation to evaluate the performance under the radiation of the GaAs and SiGe LNAs considering the physics of the technology of each LNA, respectively. The results indicate that both SiGe and GaAs technologies are affected after electron irradiation. As a result, this degradation of the LNAs' performance affected the communications system performance of the inter-satellite radio link. After the assessment of the quality performance of the communication link at the system level, it has been found that the inter-satellite space link will be at risk under high space radiation dose and the link BER degrades proportionally to the radiation dose level.

Optimum Synthesis of Four-Bar Mechanism by Using Relative Angle Method: A Comparative Performance Study

In this paper, the dimensional synthesis of the four-bar mechanism for path generation is formulated using the relative angle motion analysis and the link geometry parameterization with Cartesian coordinates. The Optimum Dimensional Synthesis using Relative Angles and the Cartesian space link Parameterization (ODSRA+CP) is stated as an optimization problem, and the solution is given by the differential evolution variant DE/best/1/bin. This study investigates the behavior and performance of such formulation and performs a comparative empirical study with the well-known synthesis method based on vector-loop equation motion analysis where different modifications in the metaheuristic algorithms are established in the literature to improve the obtained solution. Five study cases of dimensional synthesis for path generation with and without prescribed timing are solved and analyzed. The empirical results show that the way of stating the optimization problem in the ODSRA+CP significantly improves the search process for finding promising solutions in the optimizer without requiring algorithm modifications. Therefore, it is confirmed that the optimizer search process in the optimal synthesis of mechanisms is not the only way of improving the obtained solutions, but also the optimization problem formulation has a significant influence on the search for better solutions.

A Legendrian Turaev torsion via generating families

We introduce a Legendrian invariant built out of the Turaev torsion of generating families. This invariant is defined for a certain class of Legendrian submanifolds of 1-jet spaces, which we call of Euler type. We use our invariant to study mesh Legendrians: a family of 2-dimensional Euler type Legendrian links whose linking pattern is determined by a bicolored trivalent ribbon graph. The Turaev torsion of mesh Legendrians is related to a certain monodromy of handle slides, which we compute in terms of the combinatorics of the graph. As an application, we exhibit pairs of Legendrian links in the 1-jet space of any orientable closed surface which are formally equivalent, cannot be distinguished by any natural Legendrian invariant, yet are not Legendrian isotopic. These examples appeared in a different guise in the work of the second author with J. Klein on pictures for $K_3$ and the higher Reidemeister torsion of circle bundles.

An Improvement to Precipitation Inversion Model Using Oblique Earth–Space Link Based on the Melting Layer Attenuation

Based on the power-law relation between rain intensity and corresponding specific attenuation, precipitation inversion by oblique earth–space link (OEL) has become a supplement to conventional method. However, the attenuation caused by melting layer has a significant effect on its performance. According to the microphysics, thermodynamics, and scattering properties of melting hydrometeors, a melting layer model is introduced to improve OEL inversion approach. Meanwhile, the observations by a microrain radar (MRR) located at Nanjing Reference Climatological Station (NRCS) are used and plenty of numerical simulations are also performed, which aim to validate the melting layer model. The choice of raindrop size distribution (DSD) determines the simulated values of radar reflectivity factor (RRF) and path-integrated attenuation (PIA). The gamma distribution gives the results of simulated RRF that are consistent with MRR observations. Considering the nonspherical shape of melting hydrometeors, its effects on attenuation calculation are discussed based on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T$ </tex-math></inline-formula> -matrix, which indicates the error due to hydrometeor shape is negligible below Ka-band. The values of PIA derived from our melting layer model show good agreements with MRR observations. In the simulation experiment, we found the average multiplier of melting layer attenuation is a function of rain intensity and frequency. The relation is established by using the nonlinear least-squares method. According to the multiplier, a novel model is proposed to estimate the melting layer attenuation. Compared with other existing attenuation models, it shows a similar performance in different frequency bands. Moreover, we introduce an equivalent multiplier into OEL rainfall inversion model, which demonstrates the obvious enhancement of effectiveness and robustness of improved model in the validation experiment.

2D optical wireless broadcasting system enabled by a liquid crystal on silicon and rotated-splitting-SLM algorithm.

In this paper, a 2D optical wireless broadcasting system with low path loss is proposed and experimentally demonstrated based on a commercial liquid crystal on silicon (LCoS) device and rotated-splitting-SLM algorithm. The low path loss is realized by our designed pair of fiber collimators with large beam waist, which can significantly reduce the coupling loss. By using the proposed system and algorithm, a 60-Gb/s PAM-4 signal is successfully broadcasted over 2-km standard single mode fiber and 14 m free space link with 16 dB path loss for up to four mobile users. The experimental results reveal that the LCoS based on the proposed rotated-splitting-SLM method can be used for multi-user broadcasting in the high-speed in-building dynamic networks.

Delay aware energy-efficient opportunistic node selection in restricted routing

Mobile sink can implicitly provide uniform energy consumption across sensor networks and load-balanced data delivery by alleviating the sensor data disruptions and hotspot problems. Advertisement of mobile sink's current position in ring routing introduces control packet overhead in terms of energy consumption and leads to shorter network lifetime. In order to minimize this overhead, we have exploited the functionality of ring nodes rather than anchor nodes for the advertisement of mobile sink's current position and forwarding the aggregated data towards mobile sink. In this paper, we propose a novel, distributed, Delay Aware and Energy-Efficient Opportunistic Node Selection in Restricted Routing (DA-EEORR) protocol, suitable for delay-sensitive applications. Based on asynchronous working-sleeping cycle of sensor nodes, our proposed scheme utilizes the concept of opportunistic connection random graph in ring routing for selection of next-hop using optimal link and path connectivity in restricted search space. Our simulation results reveal that proposed scheme outperforms the existing benchmarks i.e., hierarchical mobile sink routing schemes in terms of control packet overhead, network lifetime, energy consumption and packet delivery ratio.

Evaluating Processing Choices for the Geodetic Estimation of Earth Orientation Parameters With Numerical Models of Global Geophysical Fluids

AbstractDifferent Earth orientation parameter (EOP) time series are publicly available that typically arise from the combination of individual space geodetic technique solutions. The applied processing strategies and choices lead to systematically differing signal and noise characteristics particularly at the shortest periods between 2 and 8 days. We investigate the consequences of typical choices by introducing new experimental EOP solutions obtained from combinations at either normal equation level processed by Deutsches Geodätisches Forschungsinstitut at the Technical University of Munich (DGFI‐TUM) and Federal Agency for Cartography and Geodesy (BKG), or observation level processed by European Space Agency (ESA). All those experiments contribute to an effort initiated by ESA to develop an independent capacity for routine EOP processing and prediction in Europe. Results are benchmarked against geophysical model‐based effective angular momentum functions processed by Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences (ESMGFZ). We find, that a multitechnique combination at normal equation level that explicitly aligns a priori station coordinates to the ITRF2014 frequently outperforms the current International Earth Rotation and Reference Systems Service (IERS) standard solution 14C04. A multi‐Global Navigation Satellite System (GNSS)‐only solution already provides very competitive accuracies for the equatorial components. Quite similar results are also obtained from a short combination at observation level experiment using multi‐GNSS solutions and SLR from Sentinel‐3A and Sentinel‐3B to realize space links. For ΔUT1, however, very long baseline interferometry (VLBI) information is known to be critically important so that experiments combining only GNSS and possibly SLR at observation level perform worse than combinations of all techniques at normal equation level. The low noise floor and smooth spectra obtained from the multi‐GNSS solution nevertheless illustrates the potential of this most rigorous combination approach so that further efforts to include in particular VLBI are strongly recommended.

End-to-End Simulations of Coded Transmissions in Space Links Affected by Solar Scintillation

In this article, coded space communication links impaired by solar scintillation are investigated followed by a comprehensive end-to-end approach. With respect to baseband analyses, this allows for a more realistic modeling of actual communication links in these scenarios, though at the cost of longer simulation times and higher minimum values of the error rates assessable. The effect of solar scintillation on both signal amplitude and phase is studied, by considering the potential use of noncoherent demodulation to withstand phase synchronization impairments. This article allows optimizing some receiver parameters, such as the phase-locked loop bandwidth, in a way to face critical contingency scenarios as well.

On Combining Attenuation Statistics of Different Tropospheric Effects Affecting EHF Earth–Space Links

On Combining Attenuation Statistics of Different Tropospheric Effects Affecting EHF Earth–Space Links