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GNSS spoofing has become a significant security vulnerability threatening remote sensing systems. Hardware fingerprint-based GNSS receiver identification is one of the solutions to address this security issue. However, existing research has not provided a solution for distinguishing GNSS receivers of the same specification. This paper first theoretically proves that the CSACs (Chip-Scale Atomic Clocks) used in GNSS receivers have unique hardware noise and then proposes a fingerprinting scheme based on this hardware noise. Experiments based on the neural network method demonstrate that this fingerprint achieved an identification accuracy of 94.60% for commercial GNSS receivers of the same specification and performed excellently in anomaly detection, confirming the robustness of the fingerprinting method. This method shows a new real-time GNSS security monitoring method based on CSACs and can be easily used with any commercial GNSS receivers. [ABSTRACT FROM AUTHOR]

Evaluating the computational complexity is critical for assessing the time-domain anti-jamming performance of GNSS receivers. The multiplier is the core component that contributes to the computational complexity in time-domain anti-jamming. However, current algorithms aimed at reducing the complexity of time-domain anti-jamming typically concentrate on shortening the filter length, which fails to address the high computational complexity introduced by the use of multipliers. This paper introduces a cascaded multiplier-free approach for implementing time-domain anti-jamming in navigation receivers. We propose a numerical power decomposition technique based on optimal Canonical Signed Digit coding and coefficient decomposition. By substituting the multiplier with minimal adder and shift operations, the computational complexity of the anti-jamming filter with a high quantization bit-width can be considerably decreased. An optimization strategy is presented, and the low-complexity multiplier-free technique is applied to the time-domain anti-jamming filter. Compared to the traditional Canonical Signed Digit multiplier-free technique, our method can reduce the components required for a 12-bit quantization anti-interference filter by one adder, 20 shift operations, and five coded word lengths, while maintaining a pseudo-range measurement deviation below 0.27 ns. [ABSTRACT FROM AUTHOR]

In order to solve the problem of converting a large amount of original GNSS receiver observation data into RINEX format files independent of the receiver during satellite positioning measurement in railway line engineering plane control networks, this paper used the C # language for secondary development of the program. The GNSS receiver observation data of Trimble Company was taken as the research object, and the syntax rules of the batch processing file of the GNSS receiver original observation data which provided by the company decoding program Convert To RINEX were analyzed. Then, the batch processing file calling method of the program was used to develop the Trimble GNSS observation data batch processor. After engineering verification, this batch of processor software could conveniently and quickly convert the massive raw data of Trimble GNSS receivers into RINEX format files independent of the receivers, and can be applied to various large-scale satellite measurement projects such as railway line engineering plane control network satellite positioning measurement. [ABSTRACT FROM AUTHOR]

The article presents the results of experimental studies of the accuracy of measuring navigation parameters by a receiver of global navigation satellite systems (GNSS receiver) equipped with an antenna array. The use of ring antenna arrays in GNSS receivers is substantiated. The main advantage of such antenna arrays is their invariance to the direction of the main lobe of the radiation pattern in the azimuthal plane. However, ring antenna arrays have some disadvantages. The use of the minimum required number of radiators in such antenna arrays to form a beam of a given width leads to a simultaneous increase in the level of side lobes. However, when using ring antenna arrays in GNSS receivers, this drawback can be neglected, since the level of side lobes significantly affects the quality of navigation signal reception only with powerful signal re- reflections. The structure of the hardware- software complex for research is given and the principle of its operation is described. Its main parts are a 24-channel beam- forming GNSS receiver and an 8-element ring antenna array. The software and hardware complex allows the study of various configurations of antenna arrays – two, four and eight elements. The technique of carrying out the experiment is given. A eature of the technique is the use of differences in measured pseudoranges using a single antenna and various configurations of antenna arrays. The results of measurements of code and phase pseudorange are presented.

• We propose spaceborne snapshot GNSS receivers to estimate thermospheric density. • We show that these receivers (<0.1 mW) have a position accuracy 100 superior to TLEs. • We show (T_s ∼ 8 hrs) a relative density accuracy like from TLEs or geodetic receivers. • This improves the time update rate of density values from TLEs by a factor of 9. This paper proposes a novel concept of using highly efficient Snapshot Global Navigation Satellite Systems (GNSS) receivers to provide precise position fixes of single or multiple satellites in Low-Earth Orbit (LEO) to improve upper atmospheric modeling and thus contribute to superior space situational awareness (SSA). While tracking of LEO satellites and the use of onboard GNSS receivers for drag measurements and upper atmosphere modeling are well-established techniques, the expected advent of snapshot GNSS receivers for spaceborne scientific applications will allow massive improvements on the GNSS sensor's Size, Weight, Power and Cost (SWaP-C). With chip-size dimensions of 4x4 mm2, a mass of less than 5 gr, an average power level below 0.1 mW, snapshot receiver technology is expected to provide position fixes in space with an accuracy of ∼19 m (3D r.m.s.), which will surpass the accuracy of Two-Line Elements (TLE) provided by the US Joint Space Operations Center (JSpOC) by at least two orders of magnitude. Equally important to their SWaP-C benefits, Snapshot GNSS receivers will allow mission and spacecraft designers to trade onboard-processing requirements versus payload downlink requirements, leading to either minimum onboard processing or a minimum amount of downlinked data. In this research, we establish the concept and architectural overview of using snapshot GNSS receivers for SSA, including the role of using them in a Distributed Space System (DSS), and detail their characterization and performance in terms of the required GNSS hardware and the impact of these payload on the power budget, the link budget and the OnBoard Data Handling (OBDH) budget of a satellite. It will be shown that these receivers lend themselves especially to their use on femto-, pico- and nano-satellites, although integrated snapshot modules may be flown as auxiliary payloads on micro- or mini-satellites as well. While this work focuses on the implications of the use of snapshot GNSS receivers on spacecraft design for the use of upper atmosphere modeling and SSA, their use may open up other science applications which avoid the need for expensive high-grade GNSS receivers. [ABSTRACT FROM AUTHOR]

Multipath propagation is a major source of error in global navigation satellite systems (GNSSs), especially in urban environments. This is because conventional GNSS receivers can provide biased range estimates that lead to positioning errors. In this paper, an Extended Kalman Filter (EKF)-based solution that relies on a multi-correlator structure is proposed to replace the conventional delay locked loop (DLL). The underlying signal model incorporates the radio propagation channel between the satellite and receiver and thus inherently accounts for reflected signal replicas. The algorithm was evaluated with simulations and hardware emulations and a measurement campaign was conducted in road traffic with different multipath environments. Our results revealed that the proposed EKF was very effective against multipath-associated error. [ABSTRACT FROM AUTHOR]

GNSS spoofing has become a significant security vulnerability threatening remote sensing systems. Hardware fingerprint-based GNSS receiver identification is one of the solutions to address this security issue. However, existing research has not provided a solution for distinguishing GNSS receivers of the same specification. This paper first theoretically proves that the CSACs (Chip-Scale Atomic Clocks) used in GNSS receivers have unique hardware noise and then proposes a fingerprinting scheme based on this hardware noise. Experiments based on the neural network method demonstrate that this fingerprint achieved an identification accuracy of 94.60% for commercial GNSS receivers of the same specification and performed excellently in anomaly detection, confirming the robustness of the fingerprinting method. This method shows a new real-time GNSS security monitoring method based on CSACs and can be easily used with any commercial GNSS receivers.

Air pollution is a significant problem in big cities due to the rapid increase of anthropogenic activities and severe traffic congestion. Therefore, real-time and micro tools for air monitoring are urgently necessary for fast and better policy decision-making. The current city air monitoring tool is typically static and serves a macro area. This study introduces technology development to integrate the air quality sensor with the satellite-based navigation receiver. This study used a carbon dioxide (CO2) MH-Z19C sensor and real-time kinematic global navigation satellite system (RTK GNSS) U-Blox F9P with GNSS Trimble NetR9 receiver. The field air quality monitoring (CO2 observed in ppm) and the movement velocity (vehicle speed observed in km/h) were recorded on two main roads of Jakarta by using a survey vehicle. The study compares the observation results of the non-integrated system (NIS) and integrated technology system (IS). The two systems generated the CSV database (CO2 and vehicle speed); however, IS generated the automatic synchronized and error-free data output. The statistical regression analysis of CSV data (CO2 and vehicle speed) between the NIS and IS reported significant results, which means both are reliable. Still, the NIS did not require manual synchronization, with some possibility of error. The R square values show a significant gap (speed 0.99 over CO2 0.144), indicating that IS needs further development as the CO2 data varies due to technicality. The finding presents that integrating the CO2 sensor and GNSS receiver generates a more effective time synchronization process and a reliable error removal technique in developing the CSV data. This finding is a significant reference in developing the integrated satellite-based receiver system with external environmental sensors.

Antenna arrays with adaptive filtering can protect the integrity and functionality of global navigation satellite system (GNSS) receivers against interference. However, a major problem with existing adaptive array processing algorithms is that they cause phase distortions and introduce bias errors into the carrier phase measurement, limiting high-precision applications. In this paper, a robust phase compensation technique is proposed to reduce the phase distortion. First, a phase bias detection method is developed to trigger the phase compensation technique. Then, the phase bias is estimated using a robust estimation method and compensated for in the GNSS receiver. The proposed technique operates in real time and causes no processing delay, while requiring only a minor modification to existing GNSS receivers. This technique is applied to the power inversion adaptive antenna, and can also be extended to a wide variety of adaptive antennas. The simulation experiments verify the applicability of the proposed technique and also confirm its superiority over existing techniques. [ABSTRACT FROM AUTHOR]

This paper presents the performance analysis of CentiSpace low earth orbit (LEO) experiment satellites. Distinguishing them from other LEO navigation augmentation systems, the co-time and co-frequency (CCST) self-interference suppression technique is employed in CentiSpace to mitigate significant self-interference caused by augmentation signals. Consequently, CentiSpace exhibits the capability of receiving navigation signals from the Global Navigation Satellite System (GNSS) while simultaneously broadcasting augmentation signals within the same frequency bands, thus ensuring excellent compatibility for GNSS receivers. CentiSpace is a pioneering LEO navigation system to successfully complete in-orbit verification of this technique. Leveraging the on-board experiment data, this study analyzes the performance of space-borne GNSS receivers equipped with self-interference suppression and evaluates the quality of navigation augmentation signals. The results show that CentiSpace space-borne GNSS receivers are capable of covering more than 90% visible GNSS satellites and the precision of self-orbit determination is at the centimeter level. Furthermore, the quality of augmentation signals meets the requirements outlined in the BDS interface control documents. These findings underscore the potential of the CentiSpace LEO augmentation system for the establishment of global integrity monitoring and GNSS signal augmentation. Moreover, these results contribute to subsequent research on LEO augmentation techniques. [ABSTRACT FROM AUTHOR]

Abstract Non‐stationary interferences are parts of the global navigation satellite system (GNSS) threats; this paper focusses on the impact of intermittent interferences on the baseband processing of the array GNSS receiver. We call the jitters of channel response caused by distributed intermittent interferences as channel scintillations. The inevitability of the channel scintillations under intermittent interferences was illustrated first. Then, the characteristics of channel scintillations were analysed through theory analysis and simulations. Finally, the impact of channel scintillations on the receiver baseband processing was assessed. The results show that though the intermittent interferences power can be suppressed completely by the anti‐jamming filter, the phase lock loop may lose lock due to channel scintillations.

Due to the low received power of Global Navigation Satellite Signals (GNSS), the performance of GNSS receivers can be disrupted by anthropogenic radio frequency interferences, with intentional jamming and spoofing activities being among the most critical threats. It is reported in the literature that modern, GNSS-equipped Android smartphones are generally resistant to simplistic spoofing, and many recent contributions support such a biased belief. In this paper, we present the results of a test campaign designed to further stress the resilience of such devices to simplistic spoofing attacks and highlight their actual vulnerability. We then propose an effective spoofing detection technique, that exploits the spatial and temporal correlation of the counterfeit signals by leveraging the statistical analysis of raw GNSS measurements. By not requiring access to the low signal processing level of the GNSS receiver, the proposed solution applies to any device embedding a GNSS receiver that provides raw GNSS measurements, such as current Android smartphones. Vulnerability analysis and validation of the proposed technique were conducted in a controlled environment by transmitting realistic, counterfeit Global Positioning System L1/CA navigation signals to a variety of Android smartphones embedding also different GNSS chipsets. We show that, under proper conditions, the devices were vulnerable to the attacks and that the effects were visible through their raw measurements, i.e., Carrier-to-noise ratio $(C/N_{0})$ , pseudo-range measurements, and position estimates. In particular, the study demonstrates that cross-correlation between the $C/N_{0}$ time series provided by each device for different GNSS satellites increases under spoofing conditions, thus constituting an effective metric to detect the attack within a few seconds.

The High Energy Rapid Modular Ensemble of Satellites (HERMES) is a constellation of 3U nano-satellites for high energy astrophysics. The HERMES nano-satellites' components have been designed, verified, and tested to detect and localize energetic astrophysical transients, such as short gamma-ray bursts (GRBs), which are the electromagnetic counterparts of gravitational wave events, thanks to novel miniaturized detectors sensitive to X-rays and gamma-rays. The space segment is composed of a constellation of CubeSats in low-Earth orbit (LEO), ensuring an accurate transient localization in a field of view of several steradians exploiting the triangulation technique. To achieve this goal, guaranteeing a solid support to future multi-messenger astrophysics, HERMES shall determine its attitude and orbital states with stringent requirements. The scientific measurements bind the attitude knowledge within 1 deg ( 1 σ a ) and the orbital position knowledge within 10 m ( 1 σ o ). These performances shall be reached considering the mass, volume, power, and computation constraints of a 3U nano-satellite platform. Thus, an effective sensor architecture for full-attitude determination was developed for the HERMES nano-satellites. The paper describes the hardware typologies and specifications, the configuration on the spacecraft, and the software elements to process the sensors' data to estimate the full-attitude and orbital states in such a complex nano-satellite mission. The aim of this study was to fully characterize the proposed sensor architecture, highlighting the available attitude and orbit determination performance and discussing the calibration and determination functions to be implemented on-board. The presented results derived from model-in-the-loop (MIL) and hardware-in-the-loop (HIL) verification and testing activities and can serve as useful resources and a benchmark for future nano-satellite missions. [ABSTRACT FROM AUTHOR]

Tracking ambiguity and multipath are two serious threats in processing binary offset carrier (BOC) signals that are widely used in global navigation satellite systems (GNSS). Three-loop tracking methods, such as dual binary phase-shift keying tracking (DBT), use a delay lock loop (DLL), a phase lock loop (PLL), and a subcarrier PLL (SPLL) to track the code, carrier, and subcarrier, respectively, thus solving the tracking ambiguity problem. However, the multipath remains an important factor in the ranging performance deterioration of these tracking methods. Using the offset correlator (OC) technique in the SPLL can effectively mitigate subcarrier multipath errors, but it substantially raises thermal noise errors. To solve this contradiction, this paper proposes a prompt-assisted-offset correlator (PAOC) technique that combines the prompt and offset correlators in a complementary way to mitigate multipath for BOC signals. Compared with the original OC technique, the PAOC technique has less thermal noise performance loss. Moreover, this paper discovers and quantifies the interaction between carrier and subcarrier multipath errors by analyzing the coupling effect between SPLL and PLL. Most multipath mitigation methods for BOC signals ignore the carrier multipath in the PLL, so their subcarrier multipath performance is not optimal. Thus, this paper further proposes applying the PAOC technique in both PLL and SPLL to mitigate carrier and subcarrier multipath errors simultaneously. Theoretical analysis and experimental results demonstrate that the proposed method can significantly improve the multipath performance with small noise performance loss. [ABSTRACT FROM AUTHOR]

Non‐stationary interferences are parts of the global navigation satellite system (GNSS) threats; this paper focusses on the impact of intermittent interferences on the baseband processing of the array GNSS receiver. We call the jitters of channel response caused by distributed intermittent interferences as channel scintillations. The inevitability of the channel scintillations under intermittent interferences was illustrated first. Then, the characteristics of channel scintillations were analysed through theory analysis and simulations. Finally, the impact of channel scintillations on the receiver baseband processing was assessed. The results show that though the intermittent interferences power can be suppressed completely by the anti‐jamming filter, the phase lock loop may lose lock due to channel scintillations. [ABSTRACT FROM AUTHOR]

The accuracy and real-time performance of the speed measurement method were important factors influencing the accuracy of the seeding spacing monitoring. In this study, three different speed measurement methods (including GNSS (Global Navigation Satellite System) receiver speed measurement, radar speed measurement, and encoder measurement rotation speed) were used to compare and analyze the monitoring results of seeding spacing. The same monitoring system was used to calculate the seeding spacing under three different speed measurement methods. The encoder directly measured the rotation speed of the seeding disc instead of the traditional method of measuring the rotation speed of the driving wheel. The monitoring results of uniform-speed and variable-speed seeding field tests showed that the three speed measurement methods have extremely high correlations, with a correlation coefficient R > 0.95. There was small difference among the three speed measurement methods, and they all met the needs of field seeding operations. After comprehensively considering the use cost and installation complexity, it was recommended to use GNSS receiver speed measurement to monitor the speed of the seeding operation and the real-time seeding spacing. [ABSTRACT FROM AUTHOR]

An adaptive digital phase-locked loop (DPLL) continually adjusts the noise bandwidth of the loop filter in global navigation satellite system (GNSS) receivers to track signals by measuring the signal-to-noise ratio and/or dynamic stress. Such DPLLs have a relatively large amount of computational complexity compared with the conventional DPLL. A table-based adaptive DPLL is proposed that adjusts the noise bandwidth value by extracting it from the pre-generated table without additional calculations. The values of the noise bandwidth table are computed in an optimal manner in consideration of the thermal noise, oscillator phase noise, and dynamic stress error. The calculation method of the proper integration time to maintain the stability of the loop filter is presented. Additionally, the simulation is configured using the trajectory analysis results from the Moon exploration mission and shows that the proposed algorithm operates stably in harsh environments, while a conventional fixed bandwidth loop cannot. The proposed algorithm has a similar phase jitter performance to the existing adaptive DPLL algorithms and has an execution time that is approximately 2.4–5.4 times faster. It is verified that the proposed algorithm is computationally efficient while maintaining jitter performance. [ABSTRACT FROM AUTHOR]

Antenna arrays with adaptive filtering can protect the integrity and functionality of global navigation satellite system (GNSS) receivers against interference. However, a major problem with existing adaptive array processing algorithms is that they cause phase distortions and introduce bias errors into the carrier phase measurement, limiting high-precision applications. In this paper, a robust phase compensation technique is proposed to reduce the phase distortion. First, a phase bias detection method is developed to trigger the phase compensation technique. Then, the phase bias is estimated using a robust estimation method and compensated for in the GNSS receiver. The proposed technique operates in real time and causes no processing delay, while requiring only a minor modification to existing GNSS receivers. This technique is applied to the power inversion adaptive antenna, and can also be extended to a wide variety of adaptive antennas. The simulation experiments verify the applicability of the proposed technique and also confirm its superiority over existing techniques.

This paper proposes a reconfigurable dual-band bandpass filter with independently tunable center frequencies that is intended to be integrated into reconfigurable multiband global navigation satellite system receivers. The center frequencies can be adjusted within the range of 1160-1280 MHz and 1530-1630 MHz for the two passbands, respectively. To achieve the design goal, the input and output feed lines are shared by a pair of quarter-wave uniform impedance resonators and a stub-loaded stepped impedance resonator with terminal-loaded varactor bias circuits. The electric length of the transmission lines is changed by using bias voltage to control the varactor diodes, thereby changing the operating frequencies of the dual-band filter’s two passbands, and the independent reconfigurability of the two passbands is realized. The insertion loss is less than 1.5 dB and the return loss is better than 26 dB in all tuning ranges. The proposed dual-band reconfigurable filter demonstrates the flexibility of controlling the passband independently to be compatible with multistandard signals, which can accommodate the deployment of new GNSS standard specifications.

The Earth's gravity field and upper atmosphere are very important scientific information and their mechanical models can be obtained by inversion of the satellite precision orbit. It would be ideal to develop a constellation of satellites distributed with different orbits to measure atmospheric drag and gravity. Based on this idea, Tsinghua University developed a microsatellite Q-Sat for measuring the gravity field and the density of the upper atmosphere. Low-cost, high-precision measurements can greatly improve the cost effectiveness of scientific missions. In this paper, a spatial modification method for GNSS receivers based on commercial off-the-shelf was proposed. The base module of the receiver is a ground-based general-purpose device, and this modification method allows for the space-batch modification of industrial-grade devices. The modified receiver was successfully applied to the Q-Sat and a large amount of continuous on-orbit data were obtained. Data analysis results show that the receiver can simultaneously receive GPS-L1\L2 and BD1\BD2 multifrequency navigation satellite signals in the highly dynamic spatial environment. To reduce the precision orbit determination error, the GNSS observations were corrected by antenna center modelling, and the long-term orbit determination accuracy is stabilized at the centimeter level. The commercial off-the-shelf based GNSS receiver modification method and precision orbit determination strategy can provide a reference for low-cost and high-precision microsatellites. • There are four highlights in this paper. • Low-cost, high-precision GNSS receiver modification and testing method based on COTS. • Supporting GPS and BDS precision orbit determination. • Antenna center model modification significantly improving the POD accuracy. • Centimeter-level orbiting accuracy supporting microsatellite science missions. [ABSTRACT FROM AUTHOR]

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• Ionospheric effects of AGWs of volcano explosion over near-equatorial site using 205 MHz VHF Radar. • A bottom-side ESF irregularity echo with a plume-like structure noticed. • Quasi-periodic oscillations in TEC and amplitude scintillations were observed. • Concurrent observations by AWS network, GNSS receiver, and Swarm satellite confirms the findings. • This work offers valuable insight into lower atmosphere-Ionosphere coupling. The response of the Tonga volcanic eruption on the ionospheric F-region over the near-equatorial sector has been studied using the 205 MHz VHF radar at Cochin, Kerala, India. The Tonga eruption, a massive underwater volcanic event that occurred at Hunga Tonga-Hunga Ha'apai in the Pacific Ocean, started on 14th December 2021 and ended with a giant explosion on 15th January 2022. The internal gravity waves (IGWs) generated due to the eruption reverberated over the globe. The effect reached the ionosphere, creating spread-F irregularities. The activity was observed with the help of the 205 MHz VHF radar and other supporting instruments such as automatic weather station (AWS), Global Navigation Satellite System (GNSS) receiver, and Swarm Charlie (Swarm C) satellite. Enhanced surface pressure of 2 hPa was recorded at Cochin and adjoining areas due to the direct (i.e., wave along the shorter great circle path) gravity wave (GW) on 15th January. The shorter great circle path wave required 10 h 50 min to reach the Indian near-equatorial sector whereas, its antipodal counterpart wave (wave along the longer great circle path) reached Kerala on 16th January first as enhanced (0.54 hPa) and subsequently as reduced (0.8 hPa) surface pressure fluctuations. After the transit of IGWs on 15th January, a bottom-side F-region irregularity echo with a plume-like structure lasting for ∼ 4.5 h occurred between 276 km and 550 km. Multi-constellation (GPS, GLONASS, and GALILEO) observations and Swarm C satellite data over the Indian equatorial ionization anomaly (EIA) sector showed quasi-periodic oscillations in the total electron content (TEC) and amplitude scintillations resulting from the IGWs of Tonga explosion. [ABSTRACT FROM AUTHOR]

Global navigation satellite system (GNSS) array antenna receivers are effective for suppressing wideband jamming. However, its anti-jamming performance decreases sharply when the number of wideband interference surpasses the number of array elements. Since a large number of jammers are often used in navigation countermeasures, it is crucial to keep array antenna receivers available in such conditions. Aiming at this issue, two main tasks were performed in this research and are presented in this paper: Firstly, the direction sensitivity of the sup-freedom anti-jamming performance is revealed and an anti-jamming method for array antenna receivers based on antenna rotation is proposed. Secondly, in order to determine the optimal rotation angle rapidly, a variable-step iteration algorithm based on gradient descent is proposed. Theoretical analysis and simulation show the effectiveness of the proposed anti-jamming method and the efficiency of the implementation algorithm. In a typical airborne scenario with a maximum azimuth difference of 90°, the anti-jamming ability of the proposed method improved by 21~26 dB and 5~10 dB for arrays adopting the PI (power inversion) and MVDR (minimum variance distortionless response) algorithms, respectively. The iterative efficiency improved by 78.35–99.63% in comparison with a traversal of 0.1° search resolution. The proposed method and algorithm are not limited to airborne scenarios and they might be influential to anti-jamming algorithms in the data domain. [ABSTRACT FROM AUTHOR]

This study focuses on evaluating the positioning accuracy of smartphones in a deciduous forest environment compared to various levels of Global Navigation Satellite System (GNSS) devices. In a mixed coniferous forest with 90% broad-leaved forest (deciduous season), the accuracy of 57 test points was evaluated according to different openness levels under the forest. Taking the coordinates obtained by survey-grade GNSS devices in RTK (Real-time Kinematic) mode as standard, the accuracy of the single-point positioning (SPP) mode and precise-point positioning (PPP) mode obtained by three smartphones (one single frequency and two dual frequency), one survey-grade receiver and one recreational-grade receiver are compared. It can be found that there was a significant positive correlation between canopy openness and carrier-to-noise density(C/N0) (p < 0.05). Meanwhile, the C/N0 of survey-grade devices is significantly higher than that of smartphones. The results show that the positioning accuracy of dual-frequency smartphones under forests is better than that of single-frequency smartphones. Furthermore, the positioning accuracy of the smartphone corrected by PPP mode is better than that of the recreational-grade GNSS receiver and can achieve an accuracy of about 2.5 m in the horizontal direction, which can be used for forestry stakeout, reset and determination of forest area boundaries in environments with high openness (R > 0.7). However, in an environment with low openness (R < 0.7) and relatively complex forest area positioning, survey-grade GNSS devices are still required to cooperate with the PPP or real-time differential positioning method to obtain accurate sub-meter-level positioning data. [ABSTRACT FROM AUTHOR]

This paper presents the performance analysis of CentiSpace low earth orbit (LEO) experiment satellites. Distinguishing them from other LEO navigation augmentation systems, the co-time and co-frequency (CCST) self-interference suppression technique is employed in CentiSpace to mitigate significant self-interference caused by augmentation signals. Consequently, CentiSpace exhibits the capability of receiving navigation signals from the Global Navigation Satellite System (GNSS) while simultaneously broadcasting augmentation signals within the same frequency bands, thus ensuring excellent compatibility for GNSS receivers. CentiSpace is a pioneering LEO navigation system to successfully complete in-orbit verification of this technique. Leveraging the on-board experiment data, this study analyzes the performance of space-borne GNSS receivers equipped with self-interference suppression and evaluates the quality of navigation augmentation signals. The results show that CentiSpace space-borne GNSS receivers are capable of covering more than 90% visible GNSS satellites and the precision of self-orbit determination is at the centimeter level. Furthermore, the quality of augmentation signals meets the requirements outlined in the BDS interface control documents. These findings underscore the potential of the CentiSpace LEO augmentation system for the establishment of global integrity monitoring and GNSS signal augmentation. Moreover, these results contribute to subsequent research on LEO augmentation techniques.

As one of the most common types of interference, pulse interference and its suppression methods have been widely studied, in which the blanking method consumes less hardware resources and it is more commonly used in the Global Navigation Satellite System (GNSS) receivers. Previous studies used carrier-to-noise ratio (CNR) as an indicator to evaluate the performance of the receiver after pulse suppression. However, CNR is not the most important parameter that should be measured. The main function of the GNSS receiver is to measure the distance between the satellite and the receiver. How the pulse interference with different periods and duty cycle affects the ranging performance of the navigation receiver after blanking has not been fully studied. This paper focuses on the influence of the blanking method on the code tracking performance. Through derivation and simulation, it can be found that the ranging accuracy of the delay locked loop may not be deteriorated sometimes when the blanking operation plays a role of narrow correlation and the frequency of the pulse interference is close to the pseudo code. However, the blanking algorithm will cause large code tracking deviation, which will seriously affect the ranging performance of the receiver.

More than half of the incidents reported to EMSA relate to nautical events such as collision, groundings and contacts. Knowledge of accurate and high-integrity positioning is therefore not only a need for future automated shipping but a base for today’s safe navigation. Examples on accidents include Ever Given in the Suez Canal and HNoMS Helge Ingstad in Norway. A Network-RTK (NRTK) service can be used as an augmentation technique to improve performance of shipborne GNSS receivers for future positioning of manned and unmanned vessels in restricted areas, such as port areas, fairways, and inland water ways. NRTK service providers generate RTK corrections based on the observations of networks of GNSS reference stations which enables the users to determine their position with centimeter accuracy in real-time using a shipborne GNSS receiver. Selection of appropriate communication channels for dissemination of NRTK corrections data is the key to a secure positioning (localization) service. In PrePare-Ships project, the modern maritime communication system VDES (VHF Data Exchange System) is proposed to distribute SWEPOS (NRTK in Sweden) correction data to shipborne positioning modules. VDES is a very reliable technique and it is compatible with most onboard functionalities. In order to minimize the impact on the overall VDES data capacity in a local area, NRTK correction data shall only occupy a single VDES slot with a net capacity of 650 bytes. Update rates may vary but are preferably at 1Hz. However, NRTK correction data size changes instantly, depending on the number of visible GNSS satellites, and the data rate can therefore sometimes reach in excess of 1000 byte/s. In this study, a smart technique is proposed to reduce size of NRTK correction data to instantly adapt with the VDES requirements by choosing a combination of specific signals, satellites or even constellations such that the data rate is not more than 650 byte/s, and at the same time it achieves optimal positioning performance with the accuracy required by the PrePare-Ships project application.

GNSS signals are affected when solar activity causes sudden variations in the density of the ionosphere. Few studies concentrate on positioning performance of IGS stations using different GNSS receivers under different geomagnetic storm conditions. This paper for the first time presents IF and UC PPP positioning performance of stations with different receivers during the quiet, moderate, intense, and super storms period. Firstly, a comprehensive investigation of geomagnetic storms effects on the occurrence of GPS cycle-slip and PPP positioning performance have been presented. Secondly, the influences of geomagnetic storms on the occurrence of cycle-slip and IF PPP positioning performance for stations using receivers provided by 'JAVAD', 'LEICA', and 'TRIMBLE' manufacturers have been comprehensively studied. Finally, this study investigates the geomagnetic storms effects on IF PPP positioning performance of stations using receiver types 'JAVAD TRE_G3TH DELTA', 'JAVAD TRE_3 DELTA', 'LEICA GR25', and 'TRIMBLE NETR9' by analysing observed data collected at mid-latitude region. [ABSTRACT FROM AUTHOR]

A well-designed carrier tracking loop in a receiver of the Global Navigation Satellite System (GNSS) is the premise of accurate positioning and navigation in an aircraft-based surveying and mapping system. To deal with the problems of Doppler estimation in high-dynamic maneuvers, the interest on maximum-likelihood estimation (MLE) is increasing among the academic community. Levenberg-Marquardt (LM) method is usually regarded as an effective and promising approach to obtain the solution of MLE, but the computation of Hessian matrix loads a great burden on the algorithm. Besides, a poor performance on convergency in final iterations is the common failing of LM implementations. To solve these problems, an LM method based on Gauss-Newton and a Quasi-Newton (QN) method based on Hessian approximation are derived, making the computation cost of Hessian decline from O(N) to O(1). Then, on the basis of these two methods, a closed carrier loop with adaptive LM-QN algorithm is further proposed which can switch between LM and QN adaptively according to a damping parameter. Besides, an ideal LM with super-linear convergence (SLM) is constructed and proved as a reference of the convergence analysis. Finally, through the analyses and experiments using aircraft data, the improvements on computation cost and convergence are verified. Compared with scalar tracking and vector tracking, results indicate a magnitude increase in the precision of LM-QN loop, even though more computation counts are needed by LM-QN. [ABSTRACT FROM AUTHOR]