Satellite-based Navigation Systems Research Articles

Exploring ionospheric dynamics: a comprehensive analysis of GNSS TEC estimations during the solar phases using linear function model

Abstract The modeling and forecasting of Total Electron Content (TEC) play a major role in influencing signals from satellite-based navigation systems and impact the performance of diverse satellite-dependent technologies. The intensity of solar ionizing radiation and the state of geomagnetic field activity influence the Global Navigation Satellite System (GNSS)-TEC. This paper uses a Linear TEC Function (LTF) climatology model to understand ionospheric behavior under solar and geomagnetic activities that cause variations in the electron distribution of the ionosphere medium. The LTF model integrates representations of solar EUV photon (MgII) and geomagnetic (SYMH) activities, incorporating solar-modulated oscillations (periodic variations) at four seasonal cycles and a linear trend. The LTF model examined the time series of GPS-TEC at a location (geographic 34.95° N, 134.05° E) with a time resolution of 1 h, from 1997 to 2016, covering solar cycles 23 and 24. The Root Mean Square Deviation (RMSD) and correlation coefficient between the GNSS-TEC and model TEC (LTF) was 5.30 TECU and 95 %. The results indicate that solar components, as well as annual and semi-annual variations, have a significant impact on the daily average TEC. Solar activity appears to be the predominant determining factor of TEC during the solar phases of cycles 23 and 24. In contrast, periodic influences primarily outline TEC during periods characterized by minimal solar activity. The geomagnetic component presents an increased influence, particularly during storm periods. The model demonstrates superior performance in Total TEC modeling compared to other state-of-the-art approaches.

Overall integrated navigation based on satellite and lidar in the standardized tall spindle apple orchards

Overall navigation in orchards is essential for autonomous production activities, however, most navigation studies, in orchards, focus on in-row scenes, and few of them pay attention to the headland transition or the overall navigation. This paper proposes an integrated navigation method based on satellite and lidar for overall orchards scenes, where the lidar was mainly used for in-row navigation and chassis position (CP) obtaining, whilst the satellite was utilized for headland transition as well as the assistant for in-row integrated navigation. Two overall integrated navigation modes were investigated: CMD-INT, which integrates the command signals from the lidar-based and satellite-based navigation systems, and BIAS-FUS, which combines the information of bias from the two navigation systems. The CP was used to detect the headland of the tree rows and achieve overall navigation integration. A position-ratio-based path planning method was also proposed, which enabled the chassis to maintain a proper constant offset from one side of the orchard. The refined pure pursuit algorithm was adopted for path tracking with good adaptivity on both the path curvature and tracking velocity. Both simulation and field tests with ten group parameters configuration in total were conducted to verify the performance of the system. The BIAS-FUS mode outperformed the CMD-INT mode, and the findings for the simulation experiments were consistent with that of the field tests. In the simulation experiments, the maximum value (Max), mean value (Mean), and root mean square error (RMSE) for the in-row process decreased by 0.0054 m, 0.0053 m, and 0.0062 m, respectively. Additionally, the corresponding heading deviation decreased by 0.3027°, 0.0050°, and 0.0256°, respectively. In the field tests, the Mean of the heading and lateral deviation for the in-row tracking process decreased by 0.3823°, and −0.0072 m respectively, and the corresponding deviations for the transition tracking process decreased by 2.8903°, and 0.0164 m respectively. Aiming at the standardized tall spindle apple orchards, this work contributes to an available overall integrated navigation method.

Machine learning approach for ionospheric scintillation prediction on ROTI parameter over the African Region during solar cycle 24

Scintillation is a dynamic phenomenon of the earth's ionosphere that adversely affects satellite-based communication and navigation systems. It is characterized by rapid fluctuations in phase and amplitude of trans-ionospheric radio waves, posing immense risks to systems that operate at radio frequencies, such as the Global Positioning System (GPS). In this regard, harnessing modern technology and state-of-the-art datasets to predict their occurrence is crucial for mitigating their effects. This paper presents a neural network approach to predict ionospheric scintillation using datasets obtained from distributed geodetic receivers in the African region. The motivation for this work is to develop a model backed by an extensive database for scintillation prediction over the region. Eleven years of data from the stations were obtained for magnetically quiet days and the Rate of TEC index (ROTI) was computed as a proxy for scintillation. The model development was backed by data from the ascending to the maximum phases of solar cycle 24 while the years in the descending phase were used for model validation and prediction. Using the solar flux (F10.7 cm), elevation and critical frequency (FoF2) as physical model parameters, the model achieved a prediction accuracy of about 70 %. A control experiment using the wavelet features increased the model's accuracy to about 91 % during the testing phase with an 86 % prediction accuracy. The model was extensively evaluated using metrics such as the Root Mean Square Error (RMSE), statistics from the Residuals and the Wavelet Coherence Analysis (WCA) technique. The standard deviation was used alongside the RMSE to gauge dispersion and ascertain model stability. The developed model demonstrated the ability to reconstruct the ROTI with low errors.

Implementasi Matriks Augmented dan Metode Eliminasi Gauss-Jordan untuk Menyelesaikan Masalah GPS (Studi Kasus: Menentukan Posisi Pejalan Kaki yang Tersesat)

The Global Positioning System (GPS) is a satellite-based navigation system that enables users to determine their position and time anywhere near the Earth's surface. GPS calculates distance by knowing how long it takes for a radio signal to move from one point to another. Linear algebra, especially augmented matrices and the Gauss-Jordan elimination method, can be applied to solve GPS problems in the case study of a pedestrian lost in the desert. The position of a lost pedestrian in a desert will be determined based on satellite position and time data. The calculation results indicate that the position of the lost pedestrian is in the Bilma desert area, Agadez district, Niger, with coordinates at a longitude of 11.41199 and a latitude of 18.549.

A machine-learning approach to estimate satellite-based position errors

Abstract Satellite-based navigation systems are widely used in transportation. GNSS signal’s strength or quality can easily be degraded by local environments. As a result, the position accuracy of satellite-based navigation systems decreases. In this paper, a novel approach for estimating the positioning error is proposed using ML/DL technique. For learning the relationship between position errors and increased data from GNSS receivers without any prior experience, neural networks have become the machine learning option of choice in the past few years. Signal degradation is best measured by dilution of precision, elevation angles, and carrier-to-noise ratios. To estimate the position error of satellite-based navigation systems, neural networks are trained in this paper. This paper applies a long-short-term memory (LSTM) network to model the temporal correlation of position error measurements. Therefore, neural networks are capable of learning the trend of position errors through training.

Overview and Progress of GNSS Anti-multipath Antenna Designs

This article provides a comprehensive review of recent applications of GNSS anti-multipath antenna. Emphasis is placed on the role of anti-multipath antenna in GNSS. A brief summary of the current anti-multipath antenna in satellite-based navigation systems is provided and also the GNSS anti-multipath antenna plays a key role is emphasised, which will help in getting a better understanding of the requirements on the various performance parameters of a GNSS antenna. In addition, we review GNSS anti-multipath antenna design strategies and specific design examples that highlight the application of various types of GNSS anti-multipath antenna. Ultimately, this articles seeks to demonstrate the value of GNSS anti-multipath antenna design insights for antenna engineering and look toward promising new research directions for GNSS antenna research.

Polar Cap Patches Scaling Properties: Insights from Swarm Data

Among the effects of space weather, the degradation of air traffic communications and satellite-based navigation systems are the most notable. For this reason, it is of uttermost importance to understand the nature and origin of ionospheric irregularities that are at the base of the observed communication outages. Here we focus on polar cap patches (PCPs) that constitute a special class of ionospheric irregularities observed at very high latitudes in the F region. To this purpose we use the so-called PCP flag, a Swarm Level 2 product, that allows for identifying PCPs. We relate the presence of PCPs to the values of the first- and second-order scaling exponents and intermittency estimated from Swarm A electron density fluctuations and to the values of the Rate Of change of electron Density Index (RODI) for two different levels of geomagnetic activity, over a time span of approximately 3.5 years starting on 16 July 2014. Our findings show that values of RODI, first- and second-order scaling exponents and intermittency corresponding to measurements taken inside PCPs differ from those corresponding to measurements taken outside PCPs. Additionally, the values of the first- and second-order scaling exponents and of intermittency indicate that PCPs are in a turbulent state. Investigation of the coincidence of loss of lock (LoL) events with PCPs displayed that approximately 57.4% of LoLs in the Northern hemisphere and 45.7% in the Southern hemisphere occur in coincidence of PCPs when disturbed geomagnetic activity is considered. During quiet geomagnetic conditions these percentages decrease to 51.4% in the Northern hemisphere and to 20.1% in the Southern hemisphere.

Preliminary performance analysis of BeiDou-2/GPS navigation systems over the low latitude region

Abstract On a regional or worldwide scale, satellite-based navigation systems can offer three-dimensional Position, Velocity, and Timing (PVT) services to an indefinite number of users. BeiDou-2 is China’s regional navigation satellite system that encompasses the Asia-Pacific region. BeiDou-2’s space section comprises GEO, MEO, and IGSO satellites, making it unique among the navigation systems. This research focuses on key aspects, including satellite visibility and signal strength, as a function of the elevation angle across the low latitude region (Indian region). In addition, the results were compared with those obtained using the GPS. The data is acquired from a GNSS receiver located at the Hyderabad station (latitude:17°24′28″, longitude:78°31′04″). The results show that BeiDou-2 satellites have better visibility than GPS satellites at all elevation angles. However, visibility is low at high elevations; therefore, multiple systems are required to obtain user information. As the elevation angle increases, the carrier-to-noise density ratio (C/No) also increases. Additionally, the standard deviation (STD) was calculated and compared to that of the GPS. Despite the average signal strength of GPS satellites remaining high throughout the elevation range, the STD of BeiDou-2 satellites was found to be low. These results indicate that further work is needed to improve the interoperability of multiple navigation systems and to provide more accurate location information to Indian users.

Ionospheric Effect on Global Navigation Satellite System Performance - A Review

Satellite-based Communication, Navigation, Surveillance and Air Traffic Management (CNS/ATM) systems have been adopted by the international aviation community to meet the challenges of continuously rising global air traffic. Global Navigation Satellite System (GNSS) has been prescribed for the provision of navigation services to the air traffic. Performance of GNSS depends upon many factors including refraction and scintillation effects of ionosphere on the satellite signals. Severity of this effect depends largely upon the geographical location of the navigation receiver, the time of the day, the month of the year and the year on the 11-year solar cycle. This paper studies ionosphere mechanism and discusses its effect on the performance of GNSS. The paper also predicts the performance during solar cycle maximum expected in 2013-2014 [Jensen, Anna B.O., Mitchell, Cathryn 2011]. It touches upon the preparations going on to face the adverse effects of increased solar activity during the cycle maximum and recommends coordination/cooperation between various relevant organizations/institutions in the processes of data collection and development of a model.

Development and experimental evaluation of visual-acoustic navigation for safe maneuvering of unmanned surface vehicles in harbor and waterway areas

Ship maneuvering in narrow harbor environments requires accurate navigation data to operate safely. Since Global Navigation Satellite Systems (GNSS) can be unreliable and inaccurate in such environments, other aiding techniques should be used for increased redundancy and reliability. To this end, we present a GNSS-free sensor suite consisting of visual, acoustic, and inertial sensors that can be used to navigate small vehicles in a harbor environment. The proposed method is aided by two navigation systems: a doppler velocity log (DVL) for low-drift velocity aiding and a visual fiducial system to estimate the drift-free position and attitude of a camera onboard the vehicle with respect to easily identifiable tags at the dockside. The visual and acoustic measurements are fused with inertial data using an error-state Kalman filter for robust state estimation. To benchmark the performance, we employ an unmanned surface vehicle equipped with a dual-antenna real-time kinematic GNSS receiver for accurate positioning and heading. The benefits of supplementing landmark-based navigation with acoustic measurements are demonstrated by conducting adverse scenarios that include noisy measurements and sensor dropouts in the harbor environment. As a result, the proposed visual-acoustic system can supplement satellite-based navigation systems for safety-critical harbor maneuvering.

Evaluation of different satellite navigation methods for the Moon in the future exploration age

Numerous lunar missions are planned for the next decade and the current deep space tracking system could not be sufficient to support all of them, since it has inherent limits in terms of complexity, availability, costs and user capacity. Consequently, new semi-autonomous or autonomous navigation systems are under study for the Moon, using satellites deployed in lunar orbit.In this work, a general and modular architecture for a satellite based navigation system, compatible with the state-of-the-art recommendations, is defined and three different localization methods, exploiting One-Way and Two-Way ranging, are proposed. The Two-Way ranging is proposed with two different implementation techniques: Earth based and user based round trip delay. These solutions were evaluated for two types of constellations that are, at the moment, the most promising for a future lunar navigation system, the Halo and ELFO constellations, by the use of the Cramer–Rao Lower Bound. Moreover, models for measurement errors affecting the lunar navigation system are proposed.The results show that Two-Way localization has slightly better accuracy and availability w.r.t. the One-Way localization, but it has also some limits in terms of capacity and latency. In the author’s opinion, the two methods might coexist for different user requirements and services in a future lunar navigation system.

Ionospheric scintillation characteristics from GPS observations over Malaysian region after the 2011 Valentine’s day solar flare

Abstract Ionospheric scintillations due to plasma irregularities can severely affect the modern dynamic and technological systems whose operations rely on satellite-based navigation systems. We investigate the occurrence of ionospheric scintillation in the equatorial and low latitude region over Malaysia after the 2011 Valentine’s Day solar flare. A network of three Global Ionospheric Scintillation and Total Electron Content Monitor (GISTM) GSV4004B receivers with increasing latitudes from the magnetic equator were used to monitor ionospheric TEC, rate of change of TEC index (ROTI), and amplitude (S4) as well as phase (σ φ) scintillation indices. The results show a simultaneous sudden rise in S4 and σ φ along with a significant depletion of TEC at all three locations. However, the largest enhancement of scintillation indices accompanying a substantial TEC depletion is observed at the farthest low latitude station (UNIMAS) from the equator with values around 0.5, 0.3 rad, and 1 TECU, respectively. The corresponding values at the near-equatorial station (Langkawi; 0.4, 0.2 rad, and 3 TECU) and intermediate station (UKM; 0.45, 0.3 rad, and 5 TECU) are examined along with ROTI variations, confirming the simultaneous occurrence of kilometer-scale and sub kilometer scale irregularities during 17 and 18 February 2011. The radiation effects of the solar flare on the ionosphere were prominently recognized at the local nighttime hours (around 14:00 to 17:00 UT) coinciding with the equatorial prereversal enhancement (PRE) time to seed the equatorial plasma bubbles (EPBs) enhancement that resulted in ionospheric irregularities over the low latitudes. The significant TEC depletion seen in the signals from selected GPS satellites (PRNs 11, 19, 23, and 32) suggests plausible degradation in the performance of GPS-based services over the Malaysian region. The study provides an effective understanding of the post-flare ionospheric irregularities during an episode of minor geomagnetic storm period and aligns with the efforts for mitigating the scintillation effects in space-based radio services over low latitudes.

Autonomous Cooperative Guidance Strategies for Unmanned Aerial Vehicles During On-Board Emergency

This paper presents autonomous guidance strategies for both solo and group of unmanned aerial vehicles (UAVs), to be used when emergency conditions are encountered during mission. Fixed-wing UAVs equipped with batteries that serve as on-board power source are considered. They are also equipped with inertial and supervisory satellite-based navigation system. An emergency condition where limited available on-board power along with nonavailability of both ground command link and satellite-based navigation information is considered. We proposed two guidance strategies, look-lock-land and inject-contribute-exit for single- and multiple-UAV missions. An optimization model is developed to arrive at the maximum area that can be covered by spiral trajectory without violating on-board power constraints. In addition, we also proved that spiral trajectory acts like a circular highway for multiple-UAV missions. Algorithms to achieve look-lock-land, inject-contribute-exit and to compute Inertial Navigation Systems (INS) error correction factor are discussed. The performance of the proposed autonomous emergency guidance strategies is demonstrated on a sea-based oil-well-monitoring mission.

Equatorial Plasma Bubbles: A Review

The equatorial plasma bubble (EPB) phenomenon is an important component of space weather as the ionospheric irregularities that develop within EPBs can have major detrimental effects on the operation of satellite-based communication and navigation systems. Although the name suggests that EPBs occur in the equatorial ionosphere, the nature of the plasma instability that gives rise to EPBs is such that the bubbles may extend over a large part of the global ionosphere between geomagnetic latitudes of approximately ±15°. The scientific challenge continues to be to understand the day-to-day variability in the occurrence and characteristics of EPBs, such as their latitudinal extent and the development of irregularities within EPBs. In this paper, basic theoretical aspects of the plasma processes involved in the generation of EPBs, associated ionospheric irregularities, and observations of their characteristics using different techniques will be reviewed. Special focus will be given to observations of scintillations produced by the scattering of VHF and higher frequency radio waves while they propagate through ionospheric irregularities associated with EPBs, as these observations have revealed new information about the non-linear development of Rayleigh–Taylor instability in equatorial ionospheric plasma, which is the genesis of EPBs.

Cold atom inertial sensors for navigation applications

Quantum sensors based on atom interferometers can provide measurements of inertial quantities with unprecedented accuracy and precision. It has been suggested that this sea change in sensing could provide an inertial navigation capability that is comparable with current satellite based navigation systems. However, the accuracy of sensor measurements is not the only factor that limits the accuracy of inertial navigation systems. In this paper, we explore the fundamental limits to inertial navigation, and explain how quantum inertial sensors could be used to alleviate some of the problems encountered in current classical inertial navigation systems, but not to solve the fundamental instability inherent in inertial navigation methods.

Wireless muometric navigation system

While satellite-based global navigation systems have become essential tools in our daily lives, their effectiveness is often hampered by the fact that the signals cannot be accessed in underground, indoor, or underwater environments. Recently, a novel navigation system has been invented to address this issue by utilizing the characteristics of the ubiquitous and highly penetrative cosmic-ray muons. This technique, muometric navigation, does not require active signal generation and enables positioning in the aforementioned environments within a reference coordinate defined by the three-dimensional positions of multiple detectors. In its first phase of development, these reference detectors had to be connected to the receivers via a wired configuration to guarantee precise time synchronization. This work describes more versatile, wireless muometric navigation system (MuWNS), which was designed in conjunction with a cost-effective, crystal-oscillator-based grandmaster clock and a performance evaluation is reported for shallow underground/indoor, deep underground and undersea environments. It was confirmed that MuWNS offers a navigation quality almost equivalent to aboveground GPS-based handheld navigation by determining the distance between the reference frame and the receivers within a precision range between 1 and 10 m.

A Comprehensive Evaluation of Possible RNSS Signals in the S-Band for the KPS.

Recently, the Korean government has announced a plan to develop a satellite-based navigation system called the Korean Positioning System (KPS). When designing a new Radio Navigation Satellite Service (RNSS) signal, the use of the S-band has emerged as an alternative to avoiding signal congestion in the L-bands, and South Korea is considering using the S-band with the L-bands. Therefore, this study proposed possible S-band signal candidates and evaluated their performance, such as the radio frequency (RF) compatibility, spectral efficiency, ranging performance, and receiver complexity. Several figures-of-merit (FoMs) were introduced for quantitative performance evaluation for each candidate. Each FoM was calculated using an analytical equation by considering the signal design parameters, such as the center frequency, modulation scheme, and chip rate. The results showed that the outstanding candidate signal was different depending on the signal performance of interest and the reception environments. Therefore, we discuss and summarize the signal performance analysis results considering the whole FoMs together. Under the assumptions given in this paper, the binary phase shift keying (BPSK)(1), sine-phased binary offset carrier (BOCs)(5,2), and BPSK signals were superior for the spectral efficiency, ranging performance, and receiver complexity, respectively.

AMSS in Europe

Nowadays, technology is developing rapidly, therefore satellite and aviation systems need to keep pace with modern trends and new technology. The paper is focused on satellite systems and aviation systems. Based on analysis of the issues it is possible to take measures against problems that may arise in the future. There is a need for satellite-based navigation system that can solve the problems of the existing systems and make the existing systems better and more efficient by providing great convenience to the airspace users for the safe, efficient, comfortable and economical realisation of flights in the future. The paper contains information about Air Communication and Navigation Systems and discusses the state of current aviation and satellite systems.

Investigation of the impact of Ionospheric Scintillation on GNSS Performance over East Africa

In recent decades, the reliance on Global Navigation Satellite System (GNSS) applications is gaining ground in the East African region. This region lies within the low geomagnetic latitudes where signal scintillation events due to ionospheric irregularities are frequent. Signal scintillation events pose a considerable challenge to the carrier tracking loop of a Global Positioning System (GPS) receiver’s phase locked loop (PLL) and can result in cycle slips or even a total loss-of-lock. The cycle slips can degrade and disrupt satellite-based navigation systems, leading to significant positioning errors. In this study, data from the International GNSS Service (IGS) and SCIntillation Network and Decision Aid (SCINDA) for the year 2011 was used to statistically analyse the effects of ionospheric scintillation on satellite-based navigation over the East African region. Results obtained show that signal scintillation events follow a seasonal pattern with a higher percentage occurrence of amplitude scintillation events over phase scintillation events. Using the method of phase combinations, cycle slips were identified on GPS L-band signals. It was observed that the frequency of occurrence of cycle slips is higher on L2-frequency than on L1-frequency of the L-band. Furthermore, results showed that the presence of signal scintillation events in signal ray paths increased the errors in GPS receiver position measurement by up to about 10 m. This can compromise the reliability and accuracy of GPS applications in navigation.

Complexity and Limitations of GNSS Signal Reception in Highly Obstructed Enviroments

Multipath (MP) and/or Non Line-Of-Sight (NLOS) reception remains a potential vulnerability to satellite-based positioning and navigation systems in high multipath environments, such as an urban canyon. In such an environment, satellite signals are reflected, scattered or faded, and sometimes completely blocked by roofs and walls of high-rise buildings, fly-over bridges, complex road structures, etc. making positioning and navigation information inaccurate, unreliable, and largely unavailable. The magnitude of the positioning error depends on the satellite visibility, geometric distribution of satellites in the sky, and received signal quality and characteristics. The quality of the received signal (i.e. its statistical characteristics) can significantly vary in different environments and these variations can reflect in signal strength or power, range measurements (i.e. path delay and phase difference), and frequency, all of which distort the correlation curve between the received signal and receiver-generated replicas, resulting in range errors of tens of meters. Therefore, in order to meet stringent requirements defined for the Standard Positioning Service (SPS), the characterization of distortions that could significantly affect a Global Navigation Satellite System (GNSS) signal is essentially important. The scope of this paper is to detect possible imperfections/deviations in the GNSS signal characteristics that can occur due to MP or NLOS reception and analyze its effects. For this purpose, analysis of fading patterns in received signal strength (i.e. Carrier-to-Noise Ratio and strength fluctuations) is carried out in both clear LOS and high MP environment and then its impact on satellite lock state (i.e. tracking) is assessed. Furthermore, phase fluctuations and range residuals are computed to analyze the effects of path delays. The results show that significant variations can occur in GNSS signal characteristics in the MP environment that may result in loss of lock event and inaccurate/faulty range measurements.