Search

The article describes the evolution of an innovative legal interoperability laboratory within the National School of Public Administration and Local Government in Athens, Greece. While critically analysing its general scope, objectives and structure, the knowledge management perspective of an interoperable legal informatics solution for handling big open legal data is brought into focus. In the context of the laboratory, the use of Legislation Editing Open Software (LEOS), a legal informatics tool that has been developed as a European Union ISA2 solution, is highlighted. Different aspects of and lessons learned from the training of public administrators are discussed while assessing this operations support system for potential use as a web-based authoring tool by the Hellenic public service. The evaluation of both the laboratory and the tool was conducted based on expert surveys, and possible upgrades are discussed to make the training of public administration more efficient. [ABSTRACT FROM AUTHOR]

The article describes the creation of an innovative legal interoperability laboratory from scratch at the National School of Public Administration and Local Government in Athens. Its scope and objectives are critically analyzed and its modules described. The problem-based learning method has been applied to a synchronous and asynchronous distance learning educational environment. In particular, in the context of the laboratory, the use of LEOS (Legislation Editing Open Software), a legal informatics tool that has been developed as a European Union ISA2 solution, is highlighted. Moreover, the relation of the laboratory to existing open interoperability courses and the wider European Interoperability Framework are presented along with the tool being assessed for potential use as an authoring tool by the Hellenic public administration. Both the laboratory and the course have been thoroughly evaluated and the results of this evaluation are presented and discussed, in view of plans for the design of additional related interoperability courses and laboratories.

The deviations of the microwave signal transmitting point of Global Navigation Satellite Systems (GNSS) satellites with respect to the corresponding center-of-mass were and still are significant bias sources for GNSS-based terrestrial reference frames (TRF). Satellite phase center offsets (PCOs) and variations (PVs) are usually derived from GNSS observations from the tracking network of the International GNSS Service (IGS). Because of the strong correlation between the scale of the TRF and the satellite PCOs in the z-direction (z-PCOs), a no-net-scale (NNT) condition relative to, for instance, the International Terrestrial Reference Frame (ITRF) is commonly applied. One approach for estimating transmitter phase centers without constraining the scale is to consider space-based GNSS observations. Within this study, we estimate the satellite PCOs of the Global Positioning System (GPS) based on zero-difference ionosphere-free observations from six low Earth orbiters (LEOs) and ground networks with different numbers of stations. The six LEOs are different in their orbits, GPS receiver equipment, and tracking characteristics. We jointly estimate orbits, station coordinates, and GPS satellite PCOs in an integrated processing. The horizontal offsets are shown to significantly benefit from the LEOs onboard observations by reducing the correlation between these offsets and the GPS satellite orbit and attitude. Without applying a no-net-scale condition to the ground network, the GPS z-PCOs are estimated. By adding six LEOs, the correlation coefficients between the GPS z-PCOs and the scale is reduced significantly (about from 0.85 to 0.3), consequently, the precision of estimation is improved. When including the six LEOs, the GPS z-PCOs estimated without applying NNS are very stable. The estimated GPS z-PCOs have a −231 mm difference in average to the values in igs14 _ 2134.atx and the corresponding scale to IGS14 reference frame is +1.89 part per billion. The estimated GPS z-PCOs agree with previous studies based on Swarm satellites and Galileo. The improvement due to different numbers of LEOs and the impact of LEO z-PCO errors on the estimation are discussed. [ABSTRACT FROM AUTHOR]

The accessibility and reuse of legal data is paramount for promoting transparency, accountability and, ultimately, trust towards governance institutions. The aggregation of structured and semi-structured legal data inevitably leads to the big data realm and a series of challenges for the generation, handling, and analysis of large datasets. When it comes to data generation, LEOS represents a legal informatics tool that is maturing quickly. Now in its third release, it effectively supports the drafting of legal documents using Akoma Ntoso compatible schemes. However, the tool, originally developed for cooperative legislative drafting, can be repurposed to draft parliamentary control documents. This is achieved through the use of actor-oriented software components, referred to as software agents, which enable system interoperability by interlinking the text editing system with parliamentary control datasets. A validated corpus of written questions from the Hellenic Parliament is used to evaluate the feasibility of the endeavour, and the feasibility of using it as an authoring tool for written parliamentary questions and generation of standardised, open, legislative data. Systemic integration not only proves the tool's versatility, but also opens up new grounds in interoperability between formerly unrelated legal systems and data sources. [ABSTRACT FROM AUTHOR]

The GPS satellite transmitter antenna phase center offsets (PCOs) can be estimated in a global adjustment by constraining the ground station coordinates to the current International Terrestrial Reference Frame (ITRF). Therefore, the derived PCO values rest on the terrestrial scale parameter of the frame. Consequently, the PCO values transfer this scale to any subsequent GNSS solution. A method to derive scale-independent PCOs without introducing the terrestrial scale of the frame is the prerequisite to derive an independent GNSS scale factor that can contribute to the datum definition of the next ITRF realization. By fixing the Galileo satellite transmitter antenna PCOs to the ground calibrated values from the released metadata, the GPS satellite PCOs in the z-direction (z-PCO) and a GNSS-based terrestrial scale parameter can be determined in GPS + Galileo processing. An alternative method is based on the gravitational constraint on low earth orbiters (LEOs) in the integrated processing of GPS and LEOs. We determine the GPS z-PCO and the GNSS-based scale using both methods by including the current constellation of Galileo and the three LEOs of the Swarm mission. For the first time, direct comparison and cross-check of the two methods are performed. They provide mean GPS z-PCO corrections of - 186 ± 25 mm and - 221 ± 37 mm with respect to the IGS values and + 1.55 ± 0.22 ppb (parts per billion) and + 1.72 ± 0.31 in the terrestrial scale with respect to the IGS14 reference frame. The results of both methods agree with each other with only small differences. Due to the larger number of Galileo observations, the Galileo-PCO-fixed method leads to more precise and stable results. In the joint processing of GPS + Galileo + Swarm in which both methods are applied, the constraint on Galileo dominates the results. We discuss and analyze how fixing either the Galileo transmitter antenna z-PCO or the Swarm receiver antenna z-PCO in the combined GPS + Galileo + Swarm processing propagates to the respective freely estimated z-PCO of Swarm and Galileo. [ABSTRACT FROM AUTHOR]

The precise orbit determination (POD) of Global Navigation Satellite System (GNSS) satellites and low Earth orbiters (LEOs) are usually performed independently. It is a potential way to improve the GNSS orbits by integrating LEOs onboard observations into the processing, especially for the developing GNSS, e.g., Galileo with a sparse sensor station network and Beidou with a regional distributed operating network. In recent years, few studies combined the processing of ground- and space-based GNSS observations. The integrated POD of GPS satellites and seven LEOs, including GRACE-A/B, OSTM/Jason-2, Jason-3 and, Swarm-A/B/C, is discussed in this study. GPS code and phase observations obtained by onboard GPS receivers of LEOs and ground-based receivers of the International GNSS Service (IGS) tracking network are used together in one least-squares adjustment. The POD solutions of the integrated processing with different subsets of LEOs and ground stations are analyzed in detail. The derived GPS satellite orbits are validated by comparing with the official IGS products and internal comparison based on the differences of overlapping orbits and satellite positions at the day-boundary epoch. The differences between the GPS satellite orbits derived based on a 26-station network and the official IGS products decrease from 37.5 to 23.9 mm ( 34 % improvement) in 1D-mean RMS when adding seven LEOs. Both the number of the space-based observations and the LEO orbit geometry affect the GPS satellite orbits derived in the integrated processing. In this study, the latter one is proved to be more critical. By including three LEOs in three different orbital planes, the GPS satellite orbits improve more than from adding seven well-selected additional stations to the network. Experiments with a ten-station and regional network show an improvement of the GPS satellite orbits from about 25 cm to less than five centimeters in 1D-mean RMS after integrating the seven LEOs. [ABSTRACT FROM AUTHOR]

The mega-launch of low Earth orbit satellites (LEOs) represents a critical opportunity to integrate navigation and communication (NavCom), but first, challenges related to signal design must be overcome. This article proposes a novel signal scheme named CE-OFDM-PM. Via research on the in-band or adjacent band, it was found that the proposed signal scheme was suitable for S-band and had a wide normalized power spectrum density (PSD), high peak-to-side lobe ratio (PSR), and multiple peaks in autocorrelation. In an analysis of the simulation performance evaluation in navigation and communication, it is found that the proposed signal scheme has the potential for high accuracy, a code tracking accuracy of up to 0.85 m, a small mutual influence between the proposed signal scheme and other schemes, excellent anti-interference properties, and a better performance at both short and long distances in terms of its anti-multipath capability. Furthermore, the proposed signal scheme shows the ability to communicate between satellites and the ground and is outstanding in terms of its bit error rate (BER), CNR, and energy per bit to noise power spectral density ratio (Eb/N0). From the technical, theoretical, and application perspectives, our proposed signal scheme has potential as an alternative scheme in future BDS, PNTs, and even 5G/B5G.

The accessibility and reuse of legal data is paramount for promoting transparency, accountability and, ultimately, trust towards governance institutions. The aggregation of structured and semi-structured legal data inevitably leads to the big data realm and a series of challenges for the generation, handling, and analysis of large datasets. When it comes to data generation, LEOS represents a legal informatics tool that is maturing quickly. Now in its third release, it effectively supports the drafting of legal documents using Akoma Ntoso compatible schemes. However, the tool, originally developed for cooperative legislative drafting, can be repurposed to draft parliamentary control documents. This is achieved through the use of actor-oriented software components, referred to as software agents, which enable system interoperability by interlinking the text editing system with parliamentary control datasets. A validated corpus of written questions from the Hellenic Parliament is used to evaluate the feasibility of the endeavour, and the feasibility of using it as an authoring tool for written parliamentary questions and generation of standardised, open, legislative data. Systemic integration not only proves the tool’s versatility, but also opens up new grounds in interoperability between formerly unrelated legal systems and data sources.

Orbital maneuvers are usually performed as needed for low earth orbiters to maintain a predefined trajectory or formation-flying configuration. To avoid unexpected discontinuities and to connect pre- and post-maneuver arcs with a minimal set of parameters, a maneuver has to be considered in the routine GPS-based orbit determinations. We propose a maneuver handling method in a reduced-dynamic scheme. With the proper thrust modeling and numerical integration strategy, the effects caused by orbital maneuver can be largely eliminated. The performance for both single-satellite precise orbit determination (POD) and inter-satellite precise baseline determination (PBD) is demonstrated using selected data sets from the Gravity Recovery and Climate Experiment (GRACE) mission. For the POD results, the orbit determination residuals indicate that the orbit with maneuver modeling is well fit to the GPS observations. The external orbit validation shows that the GRACE-B orbits obtained from our approach match the DLR reference orbits better than 3 cm (3D RMS), which is comparable to the result of the maneuver-free GRACE-A satellite. For the PBD results, on average 87 % of double-difference phase ambiguities can be resolved to integers and an RMS of the K-band ranging system residuals of better than 0.7 mm can be achieved, even though the orbital maneuver was performed on the spacecraft. Furthermore, the actual maneuver performance derived from the POD and PBD results provides rigorous feedback on the thruster system, which is not only beneficial for current maneuver assessment but also for future maneuver plans. [ABSTRACT FROM AUTHOR]

The combination of GPS measurements and high-fidelity dynamic models via a Kalman filter/smoother, known as the reduced dynamic technique, allows 3D positioning of Low Earth Orbiters to the sub-decimeter level. Such accuracies can only be achieved if the GPS data are nearly continuous, post-processed and a dual-frequency receiver is utilized. The focus of this study is to quantitatively analyze the degradations in position accuracy in the presence of various limitations or constraints, which can be brought on by mission hardware limitations, for example, on micro- or nanosatellites. The constraints explored in this study are as follows: the use of single-frequency data only; real-time processing; limited dynamic modeling due to computing capabilities; and non-continuous GPS receiver operation due to power limits. The experiments are conducted with 6-h data arcs for 7 separate days using data from the CHAllenging Mini-Satellite Payload. A 3D root mean square (rms) error of 15 cm is observed in the best-case solution, in which dual-frequency data are post-processed with all available data. Various levels of accuracy degradations are observed as constraints are placed on this best-case solution. The 3D rms error of the post-processed, single-frequency solution is 68 cm and 1.3 m for the real-time, dual-frequency solution. In very challenging environments, for example, with the receiver on for only 10 min of a 90-min orbit, the 3D rms increases to 350 m. [ABSTRACT FROM AUTHOR]

The mega-launch of low Earth orbit satellites (LEOs) represents a critical opportunity to integrate navigation and communication (NavCom), but first, challenges related to signal design must be overcome. This article proposes a novel signal scheme named CE-OFDM-PM. Via research on the in-band or adjacent band, it was found that the proposed signal scheme was suitable for S-band and had a wide normalized power spectrum density (PSD), high peak-to-side lobe ratio (PSR), and multiple peaks in autocorrelation. In an analysis of the simulation performance evaluation in navigation and communication, it is found that the proposed signal scheme has the potential for high accuracy, a code tracking accuracy of up to 0.85 m, a small mutual influence between the proposed signal scheme and other schemes, excellent anti-interference properties, and a better performance at both short and long distances in terms of its anti-multipath capability. Furthermore, the proposed signal scheme shows the ability to communicate between satellites and the ground and is outstanding in terms of its bit error rate (BER), CNR, and energy per bit to noise power spectral density ratio (Eb/N0). From the technical, theoretical, and application perspectives, our proposed signal scheme has potential as an alternative scheme in future BDS, PNTs, and even 5G/B5G. [ABSTRACT FROM AUTHOR]

Low earth orbit satellite (LEOS) systems promise to provide global communication. A LEOS system consists of a large number of satellites in low orbits. A satellite has a limited life of approximately five to eight years. Therefore, frequent satellite replenishments are required, and the LEOS systems will be facing annual replenishment costs in the range of several hundred million dollars. This paper considers static satellite launch policies for LEOS systems. The satellite launch problem is formulated and a solution method based on dynamic programming is proposed. Lexicographic ordering is used to reduce the search space of the dynamic program to a moderate size. An algorithm for calculating optimal static policies is used to demonstrate the potentially significant economic impact of satellite launch policies on system maintenance costs. [ABSTRACT FROM AUTHOR]

Several future operators of the mobile handheld telephone (P-service) satellite communications systems are gearing up for system implementation to compete for the mobile handheld telephone market of the future. While these companies are proceeding with system realization, they are also looking for partners to finance these huge satellite projects. Potential partners or bulk users are administrations of national communication systems and operators of national communication satellites. These future partners ask themselves which P-service satellite communication system they should choose. There is not an easy answer because P-service satellite systems come in many varieties. There are the low altitude earth orbiting satellites (LEOs), the medium altitude earth orbiting satellites (MEOs), and the geosynchronous altitude earth orbiting satellites (GEOs). Each system has a different type of satellite repeater: digital regenerative, transparent digital, and the bent-pipe. And each satellite system uses its own modulation/multiple access system. The fact that satellites circle the earth at different altitudes has an impact on speech quality, and, because systems vary in satellite as well as constellation complexity, there are different price tags attached. All systems display ingenious features and will eventually work. Mobile users will decide which system will best serve their purposes. This article attempts to compare six P-service satellite systems and find a method for system selection. By use of self-established system criteria, it is possible to arrive at a P-service system selection. By weighing the system criteria, the sensitivity of system selection can be tested. The results or the selection of a particular system should not be considered a recommendation; rather, the process of selection should be used as a possible guideline. [ABSTRACT FROM AUTHOR]