Global Navigation Satellite System System Research Articles

A SINS‐aided two‐step fast acquisition method for GNSS signal based on compressive sensing

SummaryThe Global navigation satellite system (GNSS) multi‐mode compatible and multi‐frequency information not only improves information redundancy but also eliminates errors such as ionospheric delays to improve positioning performance. However, multi‐mode and multi‐frequency observation information increases the hardware overhead and computational complexity, especially the signal acquisition. In this contribution, according to the strong complementarity between GNSS and Strapdown inertial navigation system (SINS) and the sparsity of the GNSS signal spreading code in the autocorrelation domain, a SINS‐aided fast acquisition method for GNSS signals based on Compressive sensing (CS) is proposed. First, the inertia information of SINS narrows the Doppler frequency search range; then, the CS is applied to measure compressively the GNSS signal in two steps, ie, the first step is to narrow down the code phase search range, and the second step is to determine the code phase of the half chip accuracy. Finally, the proposed method and the other two typical acquisition methods are compared by the detection probability and the Mean acquisition time (MAT). Theoretical analysis and experimental results show that the proposed method can not only reduce the number of correlators and computational complexity but also improve the detection probability and reduce the MAT.

TRANSLATING AERIAL IMAGES INTO STREET-MAP-LIKE REPRESENTATIONS FOR VISUAL SELF-LOCALIZATION OF UAVS

Abstract. Unmanned aerial vehicles (UAVs) rely on global navigation satellite systems (GNSS) like the Global Positioning System (GPS) for navigation but GNSS signals can be easily jammed. Therefore, we propose a visual localization method that uses a camera and data from Open Street Maps in order to replace GNSS. First, the aerial imagery from the onboard camera is translated into a map-like representation. Then we match it with a reference map to infer the vehicle’s position. An experiment over a typical sized mission area shows localization accuracy close to commercial GPS. Compared to previous methods ours is applicable to a broader range of scenarios. It can incorporate multiple types of landmarks like roads and buildings and it outputs absolute positions with higher frequency and confidence and can be used at altitudes typical for commercial UAVs. Our results show that the proposed method can serve as a backup to GNSS systems where suitable landmarks are available.

Overview of Microstrip Patch Antenna for GNSS communication System

Microstrip patch antenna are playing very important role in all wireless global navigation satellite communication system. It uses L band, X band, C band, Ku band, Ka band for global navigation satellite system (GNSS) communication application. L band frequency range is 1-2GHz so it can be used in lower frequency range communication. With the increasing need for communication and the emergence of many other systems, it is important to design compact size antennas to cover a wide frequency range. The design of an efficient wideband small size antenna, for recent wireless applications, is a major challenge. Patch antennas have found extensive applications in wireless communication system. In this paper microstrip patch antenna discussed and detail studied of GNSS system application.

A novel adaptive beamforming algorithm against impulsive noise with alpha-stable process for satellite navigation signal acquisition

Adaptive beamforming is an effective spatial filtering technique for overcoming the vulnerability to interference of global navigation satellite system (GNSS) receivers. Although beamforming-based satellite system has the capability of nulling electronic interference sources, the distortions to GNSS receiver induced by impulsive noises are always neglected. This paper addresses the satellite navigation signal acquisition problem in the presence of impulsive noises with alpha-stable noise using the maximum correntropy criterion in framework of the GNSS system. In addition, in order to decrease the number of active elements for avoiding overmuch energy consumption, a sparse regularization is introduced to the constraints of the novel criterion. From the analysis, the novel constraint sparse maximum correntropy (CSMC) beamforming technique that can achieve robustness against impulsive noises which uses less power is developed in this manuscript for satellite signal acquisition. The proposed CSMC, maintains the robustness against impulsive outliers and achieve better performance in conjunction with less power consumption. A mean square analysis of the CSMC algorithm is presented to verify the validity of our theory. Simulation results demonstrate the superiority of the proposed methods over other previously developed beamforming techniques in GNSS.

BeiDou Augmented Navigation from Low Earth Orbit Satellites.

Currently, the Global Navigation Satellite System (GNSS) mainly uses the satellites in Medium Earth Orbit (MEO) to provide position, navigation, and timing (PNT) service. The weak navigation signals limit its usage in deep attenuation environments, and make it easy to interference and counterfeit by jammers or spoofers. Moreover, being far away to the Earth results in relatively slow motion of the satellites in the sky and geometric change, making long time needed for achieved centimeter positioning accuracy. By using the satellites in Lower Earth Orbit (LEO) as the navigation satellites, these disadvantages can be addressed. In this contribution, the advantages of navigation from LEO constellation has been investigated and analyzed theoretically. The space segment of global Chinese BeiDou Navigation Satellite System consisting of three GEO, three IGSO, and 24 MEO satellites has been simulated with a LEO constellation with 120 satellites in 10 orbit planes with inclination of 55 degrees in a nearly circular orbit (eccentricity about 0.000001) at an approximate altitude of 975 km. With simulated data, the performance of LEO constellation to augment the global Chinese BeiDou Navigation Satellite System (BeiDou-3) has been assessed, as one of the example to show the promising of using LEO as navigation system. The results demonstrate that the satellite visibility and position dilution of precision have been significantly improved, particularly in mid-latitude region of Asia-Pacific region, once the LEO data were combined with BeiDou-3 for navigation. Most importantly, the convergence time for Precise Point Positioning (PPP) can be shorted from about 30 min to 1 min, which is essential and promising for real-time PPP application. Considering there are a plenty of commercial LEO communication constellation with hundreds or thousands of satellites, navigation from LEO will be an economic and promising way to change the heavily relay on GNSS systems.

Identifying GNSS market in Indonesia before and the future

Global Navigation Satellite System (GNSS) is one of the best finding of the twenty century world technologies. It is satellite base positioning and timing system. A millimeter accuracy of 4D positions can be provided by this GNSS system, allowed us to measure the geodynamic with millimeter per year signal only, measure small deformation and even the change of pole of earth rotation. Not to mention the GNSS for navigation and transportation system, it helps a lot in such traffic management, tracking, controlling, etc. GNSS market has contributed huge amount of dollars in world’s economy. Japan and America are two country of among others for biggest GNSS market so far. As for Indonesia, it is only part of 4% of Asia market in the early 2000. With such similar characteristic between Indonesia and Japan, especially relating to fast growing nation and the ring of fire, in this case market of GNSS in the future can be promising in Indonesia. This paper will highlight the GNSS market in Indonesia before and the future. We found that within ten to fifteen years the GNSS market in Indonesia will be the biggest around South East Asia and probably in Asia Pacific.

The ionosphere prediction service prototype for GNSS users

The effect of the Earth’s ionosphere represents the single largest contribution to the Global Navigation Satellite System (GNSS) error budget and abnormal ionospheric conditions can impose serious degradation on GNSS system functionality, including integrity, accuracy and availability. With the growing reliance on GNSS for many modern life applications, actionable ionospheric forecasts can contribute to the understanding and mitigation of the impact of the ionosphere on our technology based society. In this context, the Ionosphere Prediction Service (IPS) project was set up to design and develop a prototype platform to translate the forecast of the ionospheric effects into a service customized for specific GNSS user communities. To achieve this overarching aim, four different product groups dealing with solar activity, ionospheric activity, GNSS receiver performance and service performance have been developed and integrated into a service chain, which is made available through a web based platform. This paper provides an overview of the IPS project describing its overall architecture, products and web based platform.

Study the capabilities of RTK Multi GNSS under forest canopy in regions of Indonesia

For more than two decade, the position on the earth can be precisely determined “real-time” in the order of few centimeters by Real Time Kinematic (RTK) GNSS (Global Navigation Satellite Systems) Method. Nevertheless, few limitations are still recognized such as degradation of accuracy against limited satellite visibilities (e.g. heavy satellite obstructions from forest canopy). It usually takes time to resolve the ambiguities or even in many occasion resulted in failure. Fortunately since recent years to the future seems more satellite systems beside GPS and GLONASS are being launched such as BEIDOU, GALILEO, QZSS, etc. It means that more satellite will be existed above the sky. The term GNSS has changed into Multi GNSS. This Multi GNSS is theoretically adding the value to previous GNSS System like GPS; problems of limited satellite visibilities (e.g. under forest canopy) to the position accuracy perhaps will reduce. Within this paper we try to do study the capabilities of RTK Multi GNSS under forest canopy in Indonesia. We observed by RTK in the forest areas which have canopy of 40 to 90 percent. As conclusion we found improvement in positioning result of even area of very limited satellite visibilities.

Characterization of GNSS observations from a Nexus 9 Android tablet

Global navigation satellite system (GNSS) raw data were made available in the application programming interface (API) starting from version 7.0 of the Android operating system. This opens possibilities for precise positioning with Android devices, as externally generated GNSS corrections can now be included in the positioning estimation in a convenient way. The Nexus 9 tablet is a good candidate for an early assessment of the raw GNSS observables and the corresponding derived precise positions, as it also supports many of the optional features and observation types presented by the API, including carrier phase observations which play an important role in many precise positioning techniques. It is known from the previous studies that poor handling of multipath in smartphones and tablets is a big challenge when it comes to precise GNSS positioning with these kinds of devices. Hence, this study assesses the raw GNSS observations and the calculated precise positions of the Nexus 9 tablet in two experimental setups with different multipath impacts. In addition, various biases of the observations are determined, some of which is not present on high-grade geodetic receivers. The analysis is done for GPS and GLONASS, which are supported by the Nexus 9 tablet. The study shows that multipath plays an important role for the expected accuracy of the calculated precise positions, both due to the induced error on the measurements, and due to loss of lock of the GNSS signals, which significantly affects precise positioning from carrier-phase measurements. Position accuracy ranges from just below 1 m to a few decimeters between the experimental setups with moderate and low levels of multipath respectively, for positioning based on carrier-phase observations. It is, furthermore, demonstrated that consideration of code inter-system biases and code inter-frequency biases of the Nexus 9 tablet are crucial for differential GNSS with multiple GNSS systems and when GLONASS observations are used in the positioning solutions. Besides these expected biases, also other less expected behaviors were discovered in the Nexus 9 GNSS observations, including various drifts for the code and phase observations. This study also proposes some strategies to handle these.

Multiantenna GNSS and Inertial Sensors/Odometer Coupling for Robust Vehicular Navigation

Location information is one of the most vital information required to achieve intelligence and context-awareness for Internet of Things applications such as driverless cars. However, related security and privacy threats are a major holdback. With increasing focus on the use global navigation satellite system (GNSS) for autonomous navigation and related applications, it is important to provide robust navigation solutions. Radio frequency interference, either intentional or unintentional, has a direct impact on GNSS navigation performance related to observability and accuracy. In terms of security, spoofing is the major issue of concern. This paper focuses on multiantenna GNSS and inertial navigation system (INS)-odometer integration to improve robustness, security, and privacy of navigation solutions. Multiantenna GNSS provides robustness against different interference sources and integration with INS provides continuous navigation solutions during short-term signal outages. Performance of the proposed architecture is evaluated using different user scenarios in the presence of spoofing and interference signals in real vehicular environments.

The adjusted optical properties for Galileo/BeiDou-2/QZS-1 satellites and initial results on BeiDou-3e and QZS-2 satellites

Solar Radiation Pressure (SRP) is the dominant non-gravitational perturbation for GNSS (Global Navigation Satellite System) satellites. In the absence of precise surface models, the Empirical CODE Orbit Models (ECOM, ECOM2) are widely used in GNSS satellite orbit determination. Based on previous studies, the use of an a priori box-wing model enhances the ECOM model, especially if the spacecraft is a stretched body satellite. However, so far not all the GNSS system providers have published their metadata. To ensure a precise use of the a priori box-wing model, we estimate the optical parameters of all the Galileo, BeiDou-2, and QZS-1 (Quasi Zenith Satellite System) satellites based on the physical processes from SRP to acceleration. Validation using orbit prediction proves that the adjusted parameters of Galileo and QZS-1 satellites exhibit almost the same performance as the corresponding published and “best guess” values. Whereas, the estimated parameters of BeiDou-2 satellites demonstrate an improvement of more than 60% over the initial “guess” values. The resulting optical parameters of all the satellites are introduced into an a priori box-wing model, which is jointly used with ECOM and ECOM2 model in the orbit determination. Results show that the pure ECOM2 model exhibits better performance than the pure ECOM model for Galileo, BeiDou-2 GEO and QZS-1 orbits. Combined with the a priori box-wing model the ECOM model (ECOM+BW) results in the best Galileo, BeiDou-2 GEO and QZS-1 orbits. The standard deviation (STD) of satellite laser ranging residuals reduce by about 20% and 5% with respect to the pure ECOM2 model for Galileo and BeiDou-2 GEO orbits, while the reductions are about 40% and 60% for QZS-1 orbits in yaw-steering and orbit-normal mode respectively. BeiDou-2 IGSO and MEO satellite orbits do not benefit much from the a priori box-wing model. In summary, we suggest setting up a unified SRP model of ECOM+BW for Galileo, QZS-1, and BeiDou-2 orbits based on the adjusted metadata. In addition, we estimate the optical parameters of BeiDou-3e and QZS-2 satellites using a limited number of tracking stations. Results regarding the unified SRP model indicate the same advantages, the STD of satellite laser ranging residuals reduces by about 30% and 20% for QZS-2 and BeiDou-3e orbits respectively over orbit products without a priori model. The estimation procedure is effective and easy to apply to the new emerging satellites in the future.

Factor Graph-Assisted Distributed Cooperative Positioning Algorithm in the GNSS System.

The development of smart cities calls for improved accuracy in navigation and positioning services; due to the effects of satellite orbit error, ionospheric error, poor quality of navigation signals and so on, it is difficult for existing navigation technology to achieve further improvements in positioning accuracy. Distributed cooperative positioning technology can further improve the accuracy of navigation and positioning with existing GNSS (Global Navigation Satellite System) systems. However, the measured range error and the positioning error of the cooperative nodes exhibit larger reductions in positioning accuracy. In response to this question, this paper proposed a factor graph-aided distributed cooperative positioning algorithm. It establishes the confidence function of factor graphs theory with the ranging error and the positioning error of the coordinated nodes and then fuses the positioning information of the coordinated nodes by the confidence function. It can avoid the influence of positioning error and ranging error and improve the positioning accuracy of cooperative nodes. In the simulation part, the proposed algorithm is compared with a mainly coordinated positioning algorithm from four aspects: the measured range error, positioning error, convergence speed, and mutation error. The simulation results show that the proposed algorithm leads to a 30–60% improvement in positioning accuracy compared with other algorithms under the same measured range error and positioning error. The convergence rate and mutation error elimination times are only to of the other algorithms.

Performance analysis of GNSS units in manned helicopter operations

Global Navigation Satellite System (GNSS) receivers make use of the United States' Global Positioning System (GPS), Russia's Global Navigation Satellite System (GLONASS), Europe's Galileo, China's Beidou, and Japan's Quasi-Zenith Satellite System constellations to determine the geolocation of the receiver based on the location of satellites and measurements of the distance and travel time of the GNSS signals. GNSS signals are dependent on line of sight to satellites with reflections or obstructions resulting in errors in the estimated position [1]. GNSS systems, while having their origin in military applications [2], have been adopted for many civilian uses from recreational navigation [3] to automated vehicle location systems [4]. While the GPS Standard Positioning Service without any correction sources establishes a 30 m range error limit for civilian use, GPS receivers typically perform better than this standard with errors primarily from atmospheric interference [5]. This is further improved in mobile devices by assisted GPS, WiFi, and cellular positioning when available [6].

Integration of terrestrial laser scanning and soil sensors for deformation and hydrothermal monitoring of frost mounds

In this geomorphological research, terrestrial laser scanning (TLS) and a global navigation satellite system (GNSS) were employed to monitor the evolution of surface deformation in two frost mounds located in the Qinghai-Tibet engineering corridor (QTEC). The QTEC is classified as a critical engineering and transportation corridor and is connected to both inland China and the Tibetan Plateau.The engineering infrastructures over the QTEC are distributed around two slopes. A high-accuracy FARO Focus3D X130 3D laser scanner, nine Trimble 5700 GNSS systems and a DJI Inspire 1 unmanned aerial vehicle (UAV) system were used to generate a 3D surface model for the slopes. The deployment of the GNSS datum points (GDPs), GNSS control points (GCPs), a reference sphere set and a set of rectangular white–black cardboards used as registration reference targets (RRTs) enhanced the capacity for data collection, registration and pre-processing of the TLS point cloud. The mapping changes of the slopes based on the TLS data were used to examine the 3D surface topography dynamics during different time periods. Soil temperature and moisture sensors were also adopted to monitor the water and heat exchange for one of the slopes, which can reveal the effects of the hydrothermal process on slope deformation during freeze-thaw cycles. This occurred mainly because the phase transitions initiated slope deformation due to water and heat transfer. The two slopes exhibited mainly thaw slumping during thawing periods and frost heaving during the freezing period, but the frost heaving was dominant after several freeze-thaw cycles. The implementation of TLS and hydrothermal measurement technologies allow for a better understanding and assessment of hazards related to slopes adjacent to engineering and transportation corridors, and this will provide guidance for the future of highway and high-speed railway design and construction along the QTEC.

Modeling African equatorial ionosphere using ordinary Kriging interpolation technique for GNSS applications

The ability to model the ionosphere accurately for single frequency users in satellite applications has gained some appreciable usage, most especially during quiet conditions in a mild (middle latitudes) ionosphere. However, solving the problem of ionosphere for single frequency user of Global Navigation Satellite Systems (GNSS) in equatorial ionization anomaly (EIA) region is of a great concern for space scientists and engineers. Several methodologies have been used to develop models that describe global or regional maps for ionosphere errors in order to mitigate the effect of the errors on GNSS systems. Global or regional ionosphere Maps have been known to be an efficient tool to monitor the delay introduced by the ionosphere in the satellite signals. This research uses the conventional Planar fit and ordinary Kriging methodologies to assess a regional map for ionosphere correction in equatorial African sector. The result obtained is an indication that modified Kriging methodology describes the EIA ionosphere corrections better compared with ordinary Kriging and Planar fit methodologies.

GLONASS: Revisão teórica e estado da arte

O GPS (Global Positioning System) e o GLONASS (GLObal NAvigation Satellite System) começaram a ser desenvolvidos ainda no início da década de setenta e são, atualmente, os principais sistemas GNSS (Global Navigation Satellite System) com constelação completa disponível. Apesar de os dois sistemas terem obtido constelações completas em períodos próximos, o GLONASS passou por um longo período de degradação, causada principalmente pela falta de investimentos e lançamentos para substituição de satélites mais antigos. Com isso o uso de dados combinados GPS/GLONASS acabou se tornando inviável já no final da década de noventa, devido à instabilidade do GLONASS. Porém, o sistema passou por um processo de modernização e restabelecimento a partir de 2001, obtendo novamente constelação completa de 24 satélites e cobertura global em 2011. A partir dessa nova realidade, novos estudos se fizeram necessário. Nesse sentido o presente trabalho buscou fazer uma revisão dos principais conceitos relacionados ao sistema, bem como do seu histórico, estrutura, além do seu processo de modernização e algumas perspectivas futuras.

Initial Assessment of Precise Point Positioning with LEO Enhanced Global Navigation Satellite Systems (LeGNSS)

The main challenge of precise point positioning (PPP) applications is the long convergence time of typically a half hour, or even more, to achieve centimeter accuracy. Even when the multi-constellation is involved and ambiguity resolution is implemented, it still requires about ten minutes. It is becoming a hot spot to incorporate the low Earth orbit (LEO) satellite constellation for enhancing the Global Navigation Satellite System (GNSS), named here as LEO-enhanced GNSS (LeGNSS). In this system, the LEO satellites cannot only receive GNSS signals, but also serve as GNSS satellites by transmitting similar navigation signals to the ground users, but with higher signal strength and much faster geometric change due to their low altitude. As a result, the convergence time of PPP is expected to be shortened to a few minutes, or even seconds. Simulation software is developed to simulate GNSS and LEO observations for ground stations taking into account tropospheric delay, satellite clock errors, observation noises, as well as other error sources. Then the number of visible satellites, the geometry dilution of precision (GDOP), and the convergence time of the kinematic mode of PPP are evaluated on a global scale compared to those of GNSS systems. The simulation results show that LeGNSS can decrease the PPP convergence to 5 min. If there are more LEO satellites included in the LeGNSS, it is expected that the initialization of PPP can be further shortened.

Special Issue on Application of GNSS for Mitigating Natural Disaster

The Global Navigation Satellite System (GNSS) has been utilized in a variety of research fields within the geosciences. This research has been further developed for application to hazard monitoring and natural disaster mitigation. Some developments have even been implemented in society in countermeasures against natural disasters. The Geospatial Information Authority of Japan (GSI), for example, has established a nationwide GNSS network called GEONET. The data from GEONET are used extensively among researchers and practitioners, not only for basic research but also for the development of methods and systems that can mitigate disasters. This special volume is a collection of articles that discuss how such methods and systems are now being developed and/or planned to both clarify the mechanisms behind natural hazards and mitigate the damage they may cause. The volume consists of 13 papers covering a wide range of natural phenomena, such as earthquakes, crustal movements, tsunamis, ionospheric disturbances, and volcanic eruptions. Some papers help us to understand how natural hazards behave, which should be the first step toward disaster mitigation. On the other hand, other articles report direct efforts made toward providing early warnings of impending disasters. Disaster mitigation systems may require real-time (and even kinematic with high-rate data sampling) processing and dissemination of data. Moreover, some applications involve data collection from coastal waters and the open sea. Now that the density of GNSS stations has approached saturation on land, the scarcity of data collected offshore will have to be rectified through the development of GNSS systems in the ocean. We do hope that this volume will be a step in the further progress of utilizing GNSS for disaster monitoring and mitigation in the future to make society safer and more secure.

Positioning stability improvement with inter-system biases on multi-GNSS PPP

Abstract The availability of multiple signals from different Global Navigation Satellite System (GNSS) constellations provides opportunities for improving positioning accuracy and initial convergence time. With dual-frequency observations from the four constellations (GPS, GLONASS, Galileo, and BeiDou), it is possible to investigate combined GNSS precise point positioning (PPP) accuracy and stability. The differences between GNSS systems result in inter-system biases (ISBs). We consider several ISB values such as GPS-GLONASS, GPS-Galileo, and GPS-BeiDou. These biases are compliant with key parameters defined in the multi-GNSS PPP processing. In this study, we present a unified PPP method that sets ISB values as fixed or constant. A comprehensive analysis that includes satellite visibility, position dilution of precision, position accuracy is performed to evaluate a unified PPP method with constrained cut-off elevation angles. Compared to the conventional PPP solutions, our approach shows more stable positioning at a constrained cut-off elevation angle of 50 degrees.

Tightly-Coupled GNSS/Vision Using a Sky-Pointing Camera for Vehicle Navigation in Urban Areas.

This paper presents a method of fusing the ego-motion of a robot or a land vehicle estimated from an upward-facing camera with Global Navigation Satellite System (GNSS) signals for navigation purposes in urban environments. A sky-pointing camera is mounted on the top of a car and synchronized with a GNSS receiver. The advantages of this configuration are two-fold: firstly, for the GNSS signals, the upward-facing camera will be used to classify the acquired images into sky and non-sky (also known as segmentation). A satellite falling into the non-sky areas (e.g., buildings, trees) will be rejected and not considered for the final position solution computation. Secondly, the sky-pointing camera (with a field of view of about 90 degrees) is helpful for urban area ego-motion estimation in the sense that it does not see most of the moving objects (e.g., pedestrians, cars) and thus is able to estimate the ego-motion with fewer outliers than is typical with a forward-facing camera. The GNSS and visual information systems are tightly-coupled in a Kalman filter for the final position solution. Experimental results demonstrate the ability of the system to provide satisfactory navigation solutions and better accuracy than the GNSS-only and the loosely-coupled GNSS/vision, 20 percent and 82 percent (in the worst case) respectively, in a deep urban canyon, even in conditions with fewer than four GNSS satellites.