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Stochastic models play a crucial role in global navigation satellite systems (GNSS) data processing. Many studies contribute to the stochastic modeling of GNSS observation noise, whereas few studies focus on the stochastic modeling of process noise. This paper proposes a method that is able to jointly estimate the variances of observation noise and process noise. The method is flexible since it is based on the least-squares variance component estimation (LS-VCE), enabling users to estimate the variance components that they are specifically interested in. We apply the proposed method to estimate the variances for the dual-frequency GNSS observation noise and for the process noise of the receiver code bias (RCB). We also investigate the impact of the stochastic model upon parameter estimation, ambiguity resolution, and positioning. The results show that the precision of GNSS observations differs in systems and frequencies. Among the dual-frequency GPS, Galileo, and BDS code observations, the precision of the BDS B3 observations is highest (better than 0.2 m). The precision of the BDS phase observations is better than two millimeters, which is also higher than that of the GPS and Galileo observations. For all three systems, the RCB process noise ranges from 0.5 millimeters to 1 millimeter, with a data sampling rate of 30 s. An improper stochastic model of the observation noise results in an unreliable ambiguity dilution of precision (ADOP) and position dilution of precision (PDOP), thus adversely affecting the assessment of the ambiguity resolution and positioning performance. An inappropriate stochastic model of RCB process noise disturbs the estimation of the receiver clock and the ionosphere delays and is thus harmful for timing and ionosphere retrieval applications.

Over the past two decades, we have witnessed the astounding development of Global Navigation Satellite Systems (GNSS). Celestial navigation has gradually been declining, displaced by the availability of these new, accurate, and easy-to-use electronic systems. Nonetheless, according to the International Convention on Standards of Training, Certification and Watchkeeping (STCW), deck officers onboard merchant ships must have been trained in the observance of celestial bodies to plot the ship’s position and to calibrate compass error. It is a real challenge in the current context to which lecturers in nautical astronomy can respond through innovation in their teaching methods. A new approach to training students in celestial navigation at the Nautical College of the University of the Basque Country is discussed in this paper. It has already achieved promising results in comparison with the traditional teaching methodology, and is both efficient and effective. The adoption of institutional measures is also proposed to ensure that the competence acquired in the training phase is at all times present throughout professional practice.

A single-receiver integer ambiguity resolution-enabled precise point positioning (PPP-RTK) user experiences a long convergence time when the rather weak single-constellation dual-frequency ionosphere-float model is used. Nowadays, the rapid development of Global Navigation Satellite Systems (GNSS) provides a multitude of available satellites and frequencies that can serve in improving the user's model strength and, therefore, its ambiguity resolution and positioning capabilities. In this study, we provide insight into and analyze the global impact of a multi-GNSS (GPS, Galileo, BeiDou-3) multi-frequency integration on the expected ambiguity resolution and positioning performance of the ionosphere-float uncombined PPP-RTK user model, and demonstrate whether it is the increased number of satellites or frequencies, or a combination thereof, that speeds up ambiguity-resolved positioning. Moreover, we explore the capabilities of both full (FAR) and partial (PAR) ambiguity resolution, considering the full ambiguity information content with the LAMBDA method, and investigate whether PAR is an efficient solution to the multi-dimensional ambiguity case. The performance of our solutions is assessed in terms of the ambiguity success rate (ASR), the number of epochs (TTFA) to achieve both an ASR criterion and a horizontal positioning precision better than 10 cm, as well as the gain in precision improvement. Based on multi-system multi-frequency simulated data from nine globally distributed stations and a large number of kinematic solutions over a day, we found that the increase in number of frequencies enhances the ambiguity resolution performance, with PAR achieving a TTFA reduction of 70% when five instead of two Galileo frequencies are used, while the ambiguity-float solution is only slightly improved. Further, our numerical results demonstrated that the increase in number of satellites leads to an improvement in both the positioning and ambiguity resolution performance, due to the improved geometry strength. It is shown that the GPS+Galileo+BeiDou solutions can achieve a TTFA of 6.5 and 4.5 min (at 90%) on a global scale when two and three frequencies are used, respectively, without any a priori information on the ionospheric delays. Finally, we analyzed the sensitivity of the PPP-RTK user's performance to changes in the precision of the measurements. [ABSTRACT FROM AUTHOR]

Taking space-time datum of Global Navigation Satellite Systems as a clue, this paper starts from the basic principle of GNSS (Global Navigation Satellite Systems) and it’s technical realization including space-time relation, orbit and distance measurement, precise timing and time synchronization, expounds the fundamental contribution of Chinese Academy of Sciences (CAS) in precisely measuring and basic supporting for space-time datum which is the most indispensable for BDS (China’s GNSS). [ABSTRACT FROM AUTHOR]

We study the problems of serviceability of contemporary high-precision terminals of global navigation satellite systems under the conditions of jamming and spoofing interferences. The application of digital antenna arrays with algorithms of space-time signal processing of the signals can be regarded as a solution of the problem of low interference resistance. We describe well-known, most studied, and currently applied algorithms of space-time signal processing. We also formulate the causes that do not enable one to use well-known algorithms in high-precision terminals of satellite systems of global navigation. We propose an algorithm of space-time signal processing based on a space-time filter of finite length with a theoretically justified requirement of Hermitian symmetry for the matrix impulse response. The proposed algorithm guarantees the absence of distortions of signals under any signal and interference conditions. In this case, the impulse response of the space-time filter is computed according to the criterion of optimal suppression of the interference. The characteristics of the proposed space-time filter and other algorithms of space-time signal processing are investigated. For this purpose, we apply the method of mathematical simulation with random search of numerous parameters of signals and interferences (directions to signals, directions to numerous interferences, and to their reflections, remoteness of the reflectors of interferences, the phases of reflections, and the levels of interferences and reflections, etc.). The results of simulations are presented in the form of the distribution functions of the signal-to-interference ratios at the output of the algorithms of space-time signal processing and the distribution functions of the phase and signal-time biases. The obtained dependences substantiate the absence of the phase and signal-time biases in the space-time filter for any signal and interference conditions with interference multipath. It is shown that the space-time filter guarantees a higher interference resistance than the compensating algorithms of space-time signal processing. [ABSTRACT FROM AUTHOR]

In this article, the problem of detecting and excluding faulty global navigation satellite systems (GNSSs) measurements at the receiver end is formulated as a parameterized quadratic programming (PQP) problem. Compared to the existing fault detection and exclusion (FDE) methods, which mostly rely on exhaustive search, the PQP method is computationally efficient for finding the outliers even when the number of outliers is moderate or large. In the context of multiconstellation GNSS where the probability of multiple simultaneous faults is increased, the PQP method is ideal for the task of fault exclusion since the computation time does not increase with the number of fault hypotheses. It is noted that this article addresses the computational load due to the exclusion function only. The integrity risk bound and continuity risk bound are of fundamental importance to assess the performance of FDE algorithms for safety-critical applications. With the aim to benefit safety-critical applications, the PQP method is integrated with the integrity risk bound and the continuity risk bound derived for FDE using Chi-squared receiver autonomous integrity monitoring (RAIM). It is emphasized that the integration of the PQP method and the integrity and continuity risk bounds do not make the PQP method a practical integrity monitoring method. This is because the computation of the integrity risk bound is still combinatorial and the resulting integrity risk bound is rather conversative. Instead, the integration allows for the opportunity to refine the PQP method so that it can be considered a practical integrity monitoring method. In particular, improvements to reduce the computational load for the Chi-squared RAIM FDE integrity risk bound calculation can readily be applied to the integrity risk bound calculation for the PQP method. Also, further research on PQP parameter tuning can be pursued to tighten the integrity risk bound. [ABSTRACT FROM AUTHOR]

In the process of composing a double-differenced positioning model, it is difficult to separate different frequency signals between code division multiple access (CDMA) systems, the single-difference ambiguity of the pivot satellite and phase differential inter-system biases (PDISBs). Hence it is difficult to calibrate in advance the bias between systems in order to build an inter-system model which only needs one pivot satellite. Based on analysis of the stability of PDISB parameters for non-overlapping frequency CDMA systems, this study adopts a particle filter to estimate the fractional part of the PDISBs (F-PDISBs) between the systems and proposes a particle filter-based inter-system positioning model. Results show that the F-PDISBs and code DISBs for the baselines with the same receiver types and some with different receiver types are rather stable over time and for these baselines it is feasible to use a particle filter to estimate the F-PDISB parameters in the initial stage. Having attained the F-PDISBs, the inter-system model can be constructed to improve positioning accuracy in complex operational environments. [ABSTRACT FROM AUTHOR]

The paper deals with Personal Navigation Systems based on sensors commonly found in small devices such as smartphones and wearables. This research field has recently received broad interest within the scientific community thanks to many novel applications, which span from health and entertainment up to human navigation, rescue operations in dangerous environments, goods delivering, and others. The proposed approach features an outdoor navigation system obtained via an event-triggered multi-rate size-varying Kalman filter, which exploits the complementary properties of both a ground-based positioning system and an on-board navigation system, namely a Global Navigation Satellite System and a Pedestrian Dead Reckoning algorithm based only on inertial measurements. The data fusion method is designed to exploit real-time estimates of heading and step length, provided by the PDR, with the position obtained from GNSS. The presented solution can be used to recognize how the time-varying features of the user gait evolve, and to remove systematic errors due to wrong calibration of the sensors or to environmental noises. The proposed implementation can also work at each step with reduced information from the sensors, thus covering both the case of missing data (e.g., poor satellite coverage), and the situation of different sampling rates for each source. This latter scenario can be enforced to strongly decrease the use of GNSS and so to improve the efficiency for future implementations in low-energy devices. Experimental results show both the accuracy of the basic algorithm and possible applications of the extended features. [ABSTRACT FROM AUTHOR]

We investigate the influence of the perturbed (by a solar X-ray flare) ionospheric D-region on the global navigation satellite systems (GNSS) and synthetic aperture radar (SAR) signals. We calculate a signal delay in the D-region based on the low ionospheric monitoring by very-low-frequency (VLF) radio waves. The results show that the ionospheric delay in the perturbed D-region can be important and, therefore, should be taken into account in modeling the ionospheric influence on the GNSS and SAR signal propagation and in calculations relevant for space geodesy. This conclusion is significant because numerous existing models ignore the impact of this ionospheric part on the GNSS and SAR signals due to its small electron density which is true only in quiet conditions and can result in significant errors in space geodesy during intensive ionospheric disturbances. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of the autocorrelations of monitor test statistics on navigation integrity and continuity. General analytical methods are rigorously developed to evaluate the actual integrity risk and false alert probability over the exposure interval. Prior to this work, the probabilities computed based on one-sample test have been widely applied in aviation navigation. However, it will be shown that using the one-sample probability may lead to overly optimistic results, because the actual risk can be significantly higher, especially for false alert. The new methods are applied to an example problem of advanced receiver autonomous integrity monitoring. To quantify integrity, a simple but conservative upper bound is derived. As for continuity, both analytical and experimental results show that the actual false alert probability is two orders of magnitude higher than previously thought, due to the time-correlation effects. A feasible solution to mitigate this impact is provided, without degrading navigation availability. [ABSTRACT FROM AUTHOR]

Currently, Global Navigation Satellite Systems (GNSS) are developing at a fairly rapid pace. Over the last years US GPS and Russian GLONASS were modernizing, whilst new systems like European Galileo and Chinese BDS are launched. The modernizations of the existing and the deployment of new GNSS made a whole range of new signals available to the users, and create a new concept ? multi-GNSS. Ionospheric delay is one of the major error sources in multi-GNSS observations. At present, GNSS users usually eliminate the influence of ionospheric delay of the first order items by dual-frequency ionosphere-free combinations. But there is still residual ionospheric delay error of higher orders. In this paper we present four different processing scenarios to exclude the higher orders ionospheric delay effects on multi-GNSS Precise Point Positioning (PPP) performance, including: "only GPS" and "GPS+GLONASS+Galileo+BDS" - without/with eliminating ionospheric delay error of higher orders. Dataset collected from one GNSS station BOR1 (Borowiec, Poland) over almost two years provided by multi-GNSS experiment (MGEX) were used for dual-frequency PPP tests with one- and quadconstellation signals. For the second pair of scenarios were used a IONosphere map EXchange format (IONEX) that supports the exchange of 2- and 3-dimensional TEC maps given in a geographic grid. Numeric experiments show that, the results of different pairs of scenarios differ at the submillimeter level. The results also show that the multi-GNSS processing are better than those based on "only GPS". [ABSTRACT FROM AUTHOR]

This paper introduces modern projects and solutions of space systems for military and civilian Communication, Navigation and Surveillance (CNS) at sea, on the ground and in the air. Deploying new CNS technologies and techniques, military mobile assets, such as ships, land vehicles and aircrafts, including their personnel, will be connected, controlled and managed in more tactical, reliable and safe ways. The new satellite communication and navigation transponders onboard Geostationary Earth Orbit (GEO) satellites will able to provide connection and control of all military vehicles and personnel, enhance traffic control and management, improve safety and security of movements, and augment collision avoidance, especially for navy and air forces assets. The integrated CNS components for military applications described in this paper are solutions that provide reliable Mobile Satellite Communications (MSC), Digital Video Broadcasting-Return Channel via Satellite (DVB-RCS) and augmentation of Global Navigation Satellite Systems (GNSS). Separately, modern satellite CNS applications for the navy, ground and air forces with their technical concepts and advantages are discussed. [ABSTRACT FROM AUTHOR]

The Spanish Mediterranean area is periodically affected by torrential rainfall events during autumn. In September 2012, one of these episodes took place with up to 50 mm of rain in a 1-hour period and with more than 300 mm in 12 hours. This study shows the spatial and temporal variability of the atmospheric integrated water vapour (IWV) observed using delays in Global Navigation Satellite System (GNSS) signals and associated rainfall during this severe weather event. This experiment focuses on the relationship between the variations of IWV values in GNSS stations and meteorological variables such as atmospheric pressure and precipitation. This study was carried out on the Mediterranean coast of Spain during a heavy rainfall episode. The results show a mean increase in IWV of around 30 kg/m2 occurring prior to heavy precipitation. They further revealed an increase of up to a 100% in IWV values in several GNSS stations available in the study area. Fluctuations in IWV fields correlate well with approaching frontal rainfall and a combined rise in IWV and a drop in atmospheric pressure may well be used as a pre-cursor to heavy precipitation.

Modern infrastructure heavily relies on various location-based services using global navigation satellite systems (GNSSs) such as the U.S. global positioning system for access to positioning, navigation, and timing information. Location information enables guidance in many applications, including finding the location of vehicles for public safety emergency E-911 services. Nevertheless, GNSS signals can be jammed or manipulated by radio frequency spoofers, so receivers may produce unreliable location data. With increasing reliance on infrastructure and public services on location awareness, location data should be properly validated. This paper presents an approach of validating GNSS data using magnetic field fingerprint maps, which are not sensitive to potential spoofers. It first captures unique or rare geomagnetic profiles (referred to as fingerprints), including all location-dependent fluctuations and anomalies from both natural and man-made sources (referred to as landmarks), on a traveling vehicle. It then tracks their alignment with the GNSS data. A two-tier fingerprint matching localization framework has also been proposed to identify target landmarks by captured fingerprints. [ABSTRACT FROM AUTHOR]

Fugro is operating a global GNSS infrastructure for the delivery of high-accuracy multi-constellation Precise Point Positioning (PPP) service, named G4. Precise orbit and clock for all global satellite navigation systems are estimated in real-time and broadcast to the users using geostationary satellites. End-users with a G4-enabled receiver are able to obtain sub-decimeter positioning accuracy in real-time. The system has been tailored for offshore applications where a nearby GNSS station is not always readily available. G4 offers seamless integration of GPS, GLONASS, Galileo and BeiDou in the navigation solution, therefore allowing the user to obtain a reliable and accurate position even in challenging environments, especially in presence of interference, scintillation or partial sky visibility. In addition, carrier-phase integer-ambiguity resolution (IAR) is supported, for those users requiring the highest possible navigation accuracy. This paper presents the G4 system architecture and current performance. The benefits of multi-constellation Precise Point Positioning (PPP) are shown in terms of increased availability, robustness and accuracy.

An uninterrupted information about the user’s position can be obtained generally from satellite navigation system (SNS). At the time of this writing (January 2017) currently two global SNSs, GPS and GLONASS, are fully operational, two next, also global, Galileo and BeiDou are under construction. In each SNS the accuracy of the user’s position is affected by the three main factors: accuracy of each satellite position, accuracy of pseudorange measurement and satellite geometry. The user’s position error is a function of both the pseudorange error called UERE (User Equivalent Range Error) and user/satellite geometry expressed by right Dilution Of Precision (DOP) coefficient. This error is decomposed into two types of errors: the signal in space ranging error called URE (User Range Error) and the user equipment error UEE. The detailed analyses of URE, UEE, UERE and DOP coefficients, and the changes of DOP coefficients in different days are presented in this paper.

The paper considers the introduction of the newest methods of topographic surveying into the educational and scientific process, using global navigation satellite systems (GNSS) at the Faculty of Geography of Moscow State University. It describes the designation and use of the current reference geodetic training network for the training of students within the program of topographic practice. The basic concepts and purpose of the equipment of the geodetic class of the user segment of GNSS, both the basic location (reference stations) and mobile complexes are disclosed. The technique of measuring and processing the accumulated data after field fixation (in static or kinematic modes) of geographic objects and phenomena using GNSS has been given. A constantly operating network of reference stations of the faculty has been described. A full-scale example of using the GNSS complex by students of the faculty of the study area is given, the collected materials have been used for subsequent modeling (relief restoration) based on the results of field measurements. Within the framework of the perspective development of the network of GNSS reference stations of the Moscow State University, the scheme of their location in the meridian direction on an ongoing basis has been shown, which will substantially expand the territorial coverage of the use of mobile GNSS complexes in geographic studies. Within the framework of the program of preservation of monuments of Russia’s cultural heritage, an example has been shown of the joint use of groundbased laser scanning techniques and a mobile GNSS complex conducted by students and teachers of leading Moscow universities and representatives of GFK Firm LLC. The result is the fixation of the geometric characteristics of the object in 1 cm steps in real coordinates, which makes it possible to carry out the necessary modeling, visualize the object in perspective form, carry out the necessary measurements, build sections, etc. The prospects for using unmanned aerial vehicles (UAVs) equipped with a digital camera and a GNSS complex have been discussed, with a view to largescale monitoring of the underlying surface.

The solar terminator is a moving boundary between day-side and night-side regions on the Earth, which is a substantial source of perturbations in the ionosphere. In the vicinity of the solar terminator, essential parameters like S4 index measurements are widely analyzed in order to monitor and predict perturbations in the ionosphere. The utilization of the scintillation index S4 is a well-accepted approach to describe the amplitude/intensity fluctuation of a received signal, predominantly caused by small-scale irregularities of the ionospheric plasma. We report on the longitudinal daily and seasonal occurrence of GNSS signal scintillations, using the data derived from the GNSS stations in Bahir Dar, Ethiopia, Lomé, Togo and Dakar, Senegal. The observed seasonal climatology of GNSS signal scintillations in equatorial Africa is adequately explained by the alignment of the solar terminator and local geomagnetic declination line. It should be pointed out that the strongest scintillations are most frequently observed during the time when the solar terminator is best aligned with the geomagnetic declination line. At all three stations, the comparison of computational and observational results indicated that the scintillation activity culminated around equinoxes in the years 2014, 2015 and 2016. Comparatively, the western equatorial Africa sector has the most intense, longest-lasting, and highest scintillation occurrence rate in equinoctial seasons in all three years. For the first time, we show that the seasonal variation of the scintillation peaks changes systematically from west to east at equatorial GNSS stations over Africa. A detailed analysis of the solar day–night terminator azimuth at ionospheric heights including the time equation shows that the scintillation intensity has a maximum if the azimuth of the terminator coincides with the declination line of the geomagnetic field. Due to the remarkable change of the declination by about 10° at the considered GNSS stations, the distance between scintillation peaks increases by 46 days when moving westward from the Bahir Dar to the Dakar GNSS station. The observations agree quite well with the computational results, thus confirming Tsunoda’s theory.

Radio frequency fingerprinting (RFF) methods are becoming more and more popular in the context of identifying genuine transmitters and distinguishing them from malicious or non-authorized transmitters, such as spoofers and jammers. RFF approaches have been studied to a moderate-to-great extent in the context of non-GNSS transmitters, such as WiFi, IoT, or cellular transmitters, but they have not yet been addressed much in the context of GNSS transmitters. In addition, the few RFF-related works in GNSS context are based on post-correlation or navigation data and no author has yet addressed the RFF problem in GNSS with pre-correlation data. Moreover, RFF methods in any of the three domains (pre-correlation, post-correlation, or navigation) are still hard to be found in the context of GNSS. The goal of this paper was two-fold: first, to provide a comprehensive survey of the RFF methods applicable in the GNSS context; and secondly, to propose a novel RFF methodology for spoofing detection, with a focus on GNSS pre-correlation data, but also applicable in a wider context. In order to support our proposed methodology, we qualitatively investigated the capability of different methods to be used in the context of pre-correlation sampled GNSS data, and we present a simulation-based example, under ideal noise conditions, of how the feature down selection can be done. We are also pointing out which of the transmitter features are likely to play the biggest roles in the RFF in GNSS, and which features are likely to fail in helping RFF-based spoofing detection.

Estimability and S -systems are important concepts when dealing with rank-defect models. In this contribution, we generalize the concept of estimability to integer estimability and determine the necessary and sufficient conditions that need to be satisfied for parameter functions to be integer estimable. This is then worked out and applied to the integer estimability analysis of GNSS observation equations. We hereby consider both network ambiguity resolution and single-receiver PPP-RTK ambiguity resolution. In our analyses, use is made of graph theory and properties of the ambiguity incidence matrices of the bipartite and connected network graphs. [ABSTRACT FROM AUTHOR]

Recently, several global navigation satellite systems (GNSS) emerged following the transformative technology impact of the first GNSS—U.S. global positioning system (GPS). The power level of GNSS signals as measured at earth’s surface is below the noise floor and is consequently vulnerable against interference. Spoofers are smart GNSS-like interferers, which mislead the receivers into generating false position and time information. While many spoofing mitigation techniques exist, spoofers are continually evolving, producing a cycle of new spoofing attacks and counter-measures against them. Thus, upgradability of receivers becomes an important advantage for maintaining their immunity against spoofing. Software-defined radio implementations of a GPS receiver address such flexibility but are challenged by demanding computational requirements of both GNSS signal processing and spoofing mitigation. Therefore, this paper reviews reported SDRs in the context of instrumentation capabilities for both conventional and spoofing mitigation modes. This separation is necessitated by significantly increased computational loads when in spoofing domain. This is demonstrated by a case study budget analysis. [ABSTRACT FROM AUTHOR]

The Minimal Detectable Bias (MDB) is an important diagnostic tool in data quality control. The MDB is traditionally computed for the case of testing the null hypothesis against a single alternative hypothesis. In the actual practice of statistical testing and data quality control, however, multiple alternative hypotheses are considered. We show that this has two important consequences for one's interpretation and use of the popular MDB. First, we demonstrate that care should be exercised in using the single-hypothesis-based MDB for the multiple hypotheses case. Second, we show that for identification purposes, not the MDB, but the Minimal Identifiable Bias (MIB) should be used as the proper diagnostic tool. We analyse the circumstances that drive the differences between the MDBs and MIBs, show how they can be computed using Monte Carlo simulation and illustrate by means of examples the significant differences that one can experience between detectability and identifiability. [ABSTRACT FROM AUTHOR]

This paper proposes low-complexity measures to be deployed on most aircraft to enable the management of Global Navigation Satellite Systems (GNSS) interference, and in particularly of jamming and spoofing threats, in order to reach the Flightpath2050 safety and security targets. It is known that, if there is a jamming interference and GNSS navigation is lost, a disruption will be caused, requiring the likely intervention of Air Traffic Control. Also, the presence of a spoofing signal is a serious security threat with a potentially catastrophic impact on the safety of the aircraft and on any other ground infrastructure. Through our jamming and spoofing detection and localization stages, based on minimal additional infrastructure, we will reduce the time required to detect and localize an interfering source and, therefore, the time required to mitigate it and restore the nominal traffic operations. Our solutions will also improve the safety of the Air Traffic Management system. Moreover, the deployment of our solution, with its capability of localizing an interfering device, could be a deterrent to any agent interested in intentionally generating a jamming or spoofing signal, and so will reduce the likelihood of this type of interference events. [ABSTRACT FROM AUTHOR]

Mid-latitude ionospheric scintillation has been studied in very poor proportion as compared to the equatorial and high latitude ionospheric scintillation. Mid-latitude ionospheric scintillations are often associated with either day time photo-ionization or due to the storm enhanced density. Using the phase screen model and the wave propagation theory in random media, we have identified the orientation of the ionospheric irregularities over Weihai with the local geomagnetic field. Amplitude and phase scintillation data observed using global positioning system (GPS) scintillation receiver deployed at the mid-latitude observation station Weihai, have been used along with K-index derived from the horizontal magnetic field component of the local magnetometer. The proposed model uses the scintillation indices relationship with the local K-index. We identified the scintillation dependence over local K-index during geomagnetic quiet and disturbed condition. This dependence coefficient is used on the real scintillation data for modeling. The presented scintillation model has been validated by comparing it to the real observations. The co-relation coefficient is more than 90% during the disturbed as well as quiet geomagnetic conditions. [ABSTRACT FROM AUTHOR]

In this work, we present an antenna array-based algorithm to detect GNSS repeater and/or spoofing attacks with an experimental validation. With an array receiver capable of measuring the impinging ranging signals direction of arrival in terms of azimuth and elevation, it is possible to estimate the antenna platforms attitude. The fact that this information is computed (w.r.t. a reference frame) during the position calculation is used. We propose an algorithm aiming to find the relation between both representations. This mapping defines the receiver's attitude in terms of pitch, roll and yaw angle. The residual of this mapping is used to construct a quality metric for the mapping. If a threshold is undershot, spoofing/repeating is indicated. The performance is demonstrated using software simulations. To show the capabilities under realistic conditions, a test platform is described. It consists of a real-time array receiver and a sampling device enabling post-processing. A maritime measurement campaign including two vessels—one acting as receiver and the other acting as transmitter—is portrayed. Finally, the real-time and post-processing performance of the algorithm is evaluated. [ABSTRACT FROM AUTHOR]

In this work, we present mitigation algorithms to protect GNSS receivers against malicious interference. Maritime applications with an antenna array-based receiver are considered as a use case. A two-stage mitigation algorithm, that tackles multipath and radio frequency interference (RFI), caused by personal privacy devices (PPD) or additive white Gaussian noise (AWGN) interferers is presented. Our approach consists of a pre-whitening step, followed by a space-time adaptive principle component analysis (PCA) beamformer that uses a dimensionality reduction (i.e. compression) method based on Canonical Components (CC) with a bank of signal-matched correlators. The algorithms are capable of suppressing strong RFI and separating highly correlated and even coherent multipath signals, thus achieving a reliable time delay and, therefore, pseudorange estimation performance. Finally, we evaluate and compare the proposed algorithms not only via numerical simulations but also with real data collected from a measurement campaign performed at DLR's maritime jamming testbed in the Baltic sea. A complete description of the test platform and the scenarios is provided. [ABSTRACT FROM AUTHOR]

Intentional jammers broadcasting chirp-style signals present a major threat to the operation of the global navigation satellite systems (GNSS) receivers. The time–frequency (TF) domain method based on the subspace projection technique is a common countermeasure against jamming. However, it is sensitive to inaccuracies in the instantaneous frequency (IF) estimates when dealing with jammers with rapidly changing frequency characteristics. In this paper, an approach for chirp-style jamming signal suppression in GNSS receivers using an adaptive-partitioned subspace projection is developed, which is insensitive to IF estimation errors. We first propose to choose the TF observation window length based on the jammer sweep rate and displace the IF estimates by a spectral bin to handle the resolution errors in the IF estimates. This operation ensures that the instantaneous phase (IP) estimation errors approximately stay constant for the interval that the jammer IF varies linearly upward. Owing to this property, the received data vector is partitioned into adaptive block sizes based on the jammer chirp rate estimates, which reflect the varying IF characteristics. The received signal is then projected onto the jammer orthogonal subspace constructed from the IF estimates according to the adaptive projection blocks. Simulation results indicate the effectiveness of the proposed technique for suppressing chirp-style jammers when compared with other techniques reported in the literature. The proposed approach provides an improvement by up to 11 dB in terms of the correlator signal-to-noise power ratio of the processed signal. [ABSTRACT FROM AUTHOR]

Abstract Global sea level rise due to an increasingly warmer climate has begun to induce hazards, adversely affecting the lives and properties of people residing in low-lying coastal regions and islands. Therefore, it is important to monitor and understand variations in coastal sea level covering offshore regions. Signal-to-noise ratio (SNR) data of Global Navigation Satellite System (GNSS) have been successfully used to robustly derive sea level heights (SLHs). In Taiwan, there are a number of continuously operating GNSS stations, not originally installed for sea level monitoring. They were established in harbors or near coastal regions for monitoring land motion. This study utilizes existing SNR data from three GNSS stations (Kaohsiung, Suao, and TaiCOAST) in Taiwan to compute SLHs with two methods, namely, Lomb–Scargle Periodogram (LSP)-only, and LSP aided with tidal harmonic analysis developed in this study. The results of both methods are compared with co-located or nearby tide gauge records. Due to the poor quality of SNR data, the worst accuracy of SLHs derived from traditional LSP-only method exceeds 1 m at the TaiCOAST station. With our procedure, the standard deviations (STDs) of difference between GNSS-derived SLHs and tide gauge records in Kaohsiung and Suao stations decreased to 10 cm and the results show excellent agreement with tide gauge derived relative sea level records, with STD of differences of 7 cm and correlation coefficient of 0.96. In addition, the absolute GNSS-R sea level trend in Kaohsiung during 2006–2011 agrees well with that derived from satellite altimetry. We conclude that the coastal GNSS stations in Taiwan have the potential of monitoring absolute coastal sea level change accurately when our proposed methodology is used. [ABSTRACT FROM AUTHOR]

Forecasting the ionospheric space weather is crucial for improving the accuracy of the global navigation satellite systems (GNSS). Nonetheless, comprehending the nonhomogeneous ionospheric variability under space earth environmental conditions is a major challenge, and so is developing an accurate ionospheric forecasting model. The complex spatial and temporal variations in the ionospheric region are the results of the solar and interplanetary activities, in addition to the magnetosphere, mesosphere, thermosphere, stratosphere, troposphere, and lithosphere processes. Thus, this calls for an urgent need to develop a suitable ionospheric forecasting algorithm to capture the ionospheric perturbations. Total electron content (TEC) is the key parameter derived from GNSS receivers to represent the status of the ionosphere. This paper introduces a novel ionospheric forecasting algorithm based on the fusion of principal component analysis and artificial neural networks (PCA–NN) methods to forecast the ionospheric TEC values. Solar index (F10.7), geomagnetic index (Ap index), and 20-year TEC data (1997–2016) over a Japan Grid Point (34.95 °N and 134.05 °E) were used to apply artificial intelligence methodologies. The experimental results underscore the reliability of the proposed algorithm in forecasting the ionospheric time delay effects. [ABSTRACT FROM AUTHOR]

Global Navigation Satellite Systems give opportunities for atmospheric parameters analysis in behalf of solving many atmosphere monitoring tasks. The authors of this article demonstrated possibility of slant tropospheric delays determination with using precise point positioning method – PPP. The atmospheric parameters, retrieved from GNSS observations, including zenith tropospheric delays, horizontal gradients, and slant tropospheric delays, are analyzed and evaluated. It was obtained slant tropospheric delays, along the satellite path, for each satellite, at a certain elevation angle and azimuth, at each time, instead of obtaining a single zenith tropospheric delay composed of all visible satellites at one time. The results obtained proved that suggested method was correct. [ABSTRACT FROM AUTHOR]

Absolute distance determination in the open air with an uncertainty of a few tenths of a millimetre is increasingly required in many applications that involve high precision geodetic metrology. No matter the technique used to measure, the resulting distances must be proven consistent with the unit of length (SI-metre) as realized in the outdoor facilities traditionally used in length metrology, which are also known as calibration baselines of reference. The current calibration baselines of reference have distances in the range of 10 to 1000 m, but at present there is no solution on the market to provide distances with submillimetric precision in that range. Consequently, new techniques such as multi-wave interferometry, two-wave laser telemeters or laser trackers are being developed. A possible alternative to those sophisticated and expensive techniques is the use of widely used Global Navigation Satellite Systems (GNSS) in order to provide a GNSS-Based Distance Meter (GBDM). The use of a GBDM as a potential technique for length metrology has been thoroughly analysed in several European research projects by using the state-of-the-art geodetic software, such as Bernese 5.2, but no definite conclusions have been drawn and some metrological questions are considered still open. In this paper, we describe a dedicated approach to build up a submillimetric GBDM able to be applied in the current calibration baselines of reference, as well as possible methods to cope with the multipath error of the GNSS signals which is the major limitation for the practical uptaking of the technique in metrology. The accuracy of the proposed approach has been tested following the length metrology standards in four experiments carried out in the Universitat Politècnica de València (UPV). The results demonstrate that the proposed GBDM can provide an accuracy of a few tenths of a millimetre in the current calibration baselines of reference.

In order to improve the throughput performance in VANET, a channel access mechanism based on equally al-location (EA) of protocol sequence was proposed. For highway scenery, the proposed mechanism re-planed the mapping of traffic channel allocation of IEEE 802.11p to competition zone. In addition, the frame structure was also redesigned according to the characteristic of user irrepressible protocol sequence. A few bits of data were used to find out the number of nodes in the competition zone. Cyclic polling allocation was proposed to allocate the protocol sequences under average meaning. The theoretical throughput expression is derived and proved to be correct by simulation. It is also verified that the throughput of EA is more superior to classical met in a sparser distributed network or a higher PHY data rate. Equally importantly, EA can also keep relative low net overhead and available fairness about channel access of the nodes.

The tectonics and geodynamics of the Calabria region are presented in this study. These are inferred by precise computation of Global Navigation Satellite Systems (GNSS) permanent station velocities in a stable Eurasian reference framework. This allowed computation of the coordinates, variance and covariance matrixes, and horizontal and vertical velocities of the 36 permanent sites analyzed, together with the strain rates, and using different techniques. Interesting geodynamic phenomena are presented, including compressional, and deformational fields in the Tyrrhenian coastal sites of Calabria, extensional trends of the Ionian coastal sites, and sliding movement of the Crotone Basin. Conversely, on the northern Tyrrhenian side of the network near the Cilento Park area, the usual extensional tectonic perpendicular to the Apennine chain is observed. The large-scale pattern of the GNSS height velocities is shown, which is characterized by general interesting geodynamic vertical effects that appear to be due to geophysical movement and anthropic activity. Finally, the strain-rate fields computed through three different techniques are compared.

This paper describes a dataset of continuous GNSS positioning solutions referring to slope movements in the Ca’ Lita landslide (Northern Apennines, Italy). The dataset covers the period from 24 March 2016 to 17 July 2019 and includes time-series of the daily position of three GNSS rovers located in different parts of the landslide: head zone, upper track zone, and lower track zone. Two different types of continuous GNSS arrays have been used: one is based on high-end Leica geodetic receivers, and the other is based on low-cost effective Emlid receivers. Displacements captured in the dataset are up to more than a hundred meters and are characterized by prolonged phases of slow movement and moderately rapid acceleration phases. The data presented in this contribution were used to underline slope processes and validate displacements retrieved by the application of digital image correlation to a stack of a satellite images.

This is a data descriptor paper for a set of raw GNSS signals collected via roof antennas and Spectracom simulator for general-purpose uses. We give one example of possible data use in the context of Radio Frequency Fingerprinting (RFF) studies for signal-type identification based on front-end hardware characteristics at transmitter or receiver side. Examples are given in this paper of achievable classification accuracy of six of the collected signal classes. The RFF is one of the state-of-the-art, promising methods to identify GNSS transmitters and receivers, and can find future applicability in anti-spoofing and anti-jamming solutions for example. The uses of the provided raw data are not limited to RFF studies, but can extend to uses such as testing GNSS acquisition and tracking, antenna array experiments, and so forth.

The paper discusses the ASG EUPOS services. There is presented an assessment of the possibility of using this system selected sites in hydrography and off-shore navigation tasks. Presented and analyzed the experiments were carried out in the port of Gdynia and on the Gulf of Gda?sk. The results obtaining in the work confirm the possibility of the position accuracy guaranteed by ASG EUPOS services. The obtained accuracy greatly exceeds the needs and requirements of coastal navigation and underwater mining and exploration of sea bottom.

Over the last decade the Global Positioning System has become a global, multifunctional tool which provides services that are an integral part of U.S. national security as well as the security of other highly developed countries. Economic development, transport security as well as homeland security are important elements of the global economic infrastructure. In 2000 the United States acknowledged the growing significance of GPS for civilian users and stopped intentionally degrading accuracy for non-military signals that are known as “Selective Availability”. Since then, commercial applications of satellite systems have been proliferating even more rapidly, and therefore, their importance in everyday life has greatly increased. Currently, services that depend on information obtained from the Global Positioning System are the driving force behind economic growth, economic development and the improvement in life safety. This economic development would not be possible without the financial and political support of the US government to maintain the operation of the GPS system. Therefore it is important to have knowledge about the intentions of the US government how system GPS will be developed in the future. Decisions taken in the last 3 months are the subject of this article.

In this article the question of the direction of use of jig-time and navigation providing the motor transport in the field of steering of transportation process is considered. The solution of transport tasks demand existence of jig-time and navigation providing (JTNP) based on use of the global navigation satellite systems (GNSS), geographical information systems (GIS), means and technologies of telematics.