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A special issue of Remote Sensing (ISSN 2072-4292). This special issue belongs to the section "Engineering Remote Sensing".

Deadline for manuscript submissions: closed (15 September 2023) | Viewed by 22215

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Special Issue Editors

Prof. Mohammad Zahidul Hasan Bhuiyan

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Guest Editor

Finnish Geospatial Research Institute, Vuorimiehentie 5, 02150 Espoo, Finland
Interests: Global Navigation Satellite System; Multi-GNSS Receiver Design and algorithm development; Resilient PNT

Prof. Dr. Elena Simona Lohan

E-Mail Website
Guest Editor

Tampere University (TAU), P.O.Box 553, FIN-33101 Tampere, Finland
Interests: wireless localization; tracking and navigation; signal processing for wireless communications; wearable computing
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Special Issue Information

Dear Colleagues,

Global navigation satellite systems (GNSS) are evolving quickly towards offering precise position, navigation, and timing (PNT) services via modernized signals and new frequencies. In addition, there are more and more satellites being launched from different global and regional constellations, helping to improve navigation performance by allowing the user–receiver to utilize multi-GNSS and multi-frequency diversity. This Special Issue will address novel GNSS technologies that exploit these new signals and new features, for example, Galileo Open Service Navigation Message Authentication (OSNMA), which is in its public observation phase, Galileo High Accuracy Service (HAS), which is in its test and experimentation phase, or other correction services, for example, the wide area differential correction for BeDiou Satellite Navigation system (BDS).

This Special Issue will investigate different techniques and solutions that can improve receiver performance through advanced algorithms at signal processing and navigation layers and/or in conjunction with different state-of-the-art sensors adopted in different user case scenarios in road, air, and maritime transport modes.

This Special Issue invites contributions on the following topics (but is not strictly limited to these subject areas):

Advances in multi-frequency multi-constellation (MFMC) GNSS signal processing;
Resilient and robust position, navigation, and timing (PNT);
Advances in precise point positioning (PPP);
Advances in real-time kinematic (RTK) positioning;
Advances in signal processing techniques for high-precision applications addressing the requirements for autonomous navigation in all transport mode;
GNSS vulnerability detection, characterization, and mitigation in challenging environments;
Sensor fusion for robust high-precision applications;
Cloud-based solutions for PNT;
Alternative or dedicated PNT with low earth orbit (LEO) satellites;
Sensor fusion with signals of opportunity (SoOP) for robust and accurate PNT.

Prof. Mohammad Zahidul Hasan Bhuiyan
Prof. Dr. Elena Simona Lohan
Guest Editors

Manuscript Submission Information

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Keywords

global navigation satellite systems (GNSSs)
position, navigation, timing (PNT)
resilient PNT
sensors
autonomous navigation
real-time kinematic (RTK) positioning

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Published Papers (10 papers)

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25 pages, 6383 KiB

Open AccessArticle

GNSS Spoofing Detection Using Q Channel Energy

by Jiaqi Wang, Xiaomei Tang, Pengcheng Ma, Jian Wu, Chunjiang Ma and Guangfu Sun

Remote Sens. 2023, 15(22), 5337; https://doi.org/10.3390/rs15225337 - 13 Nov 2023

Cited by 4 | Viewed by 1185

Abstract

Spoofing interference poses a significant challenge to the Global Navigation Satellite System (GNSS). To effectively combat intermediate spoofing signals, this paper presents an enhanced spoofing detection method based on abnormal energy of the quadrature (Q) channel correlators. The detailed principle of this detection method is introduced based on the received signal model under spoofing attack. The normalization parameter used in this method was the estimation of the noise floor. The performance of the proposed Q energy detector is validated through simulations, the Texas Spoofing Test Battery dataset and field tests. The results demonstrate that the proposed detector significantly enhances detection performance compared to signal quality monitoring methods, particularly in overpowered scenarios and dynamic scenarios. By increasing the detection probability in the presence of spoofing signals and decreasing the false alarm probability in the absence of spoofing signals, the proposed detector can better meet the requirements of practical applications. Full article

(This article belongs to the Special Issue Advancement of GNSS Signal Processing and Navigation)

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28 pages, 5876 KiB

Open AccessArticle

A Novel Single Differencing Measurement for Multipath Detection

by Matthew Alcock and Paul Blunt

Remote Sens. 2023, 15(22), 5312; https://doi.org/10.3390/rs15225312 - 10 Nov 2023

Cited by 2 | Viewed by 1480

Abstract

Increased global dependence on Global Navigation Satellite Systems (GNSSs) has resulted in a high demand for greater precision and reliable measurements from GNSS receivers. The multipath problem is the single largest source of errors in modernised GNSSs. Double differencing techniques, such as Code Minus Carrier (CMC) have been shown to accurately detect and measure multipath, allowing for corrections to be made via Ground Base Augmentation Systems (GBAS), for example. However, these techniques require at least two receivers and the protection provided is not extended to stand-alone receivers. This paper introduces a new single differencing technique for the accurate detection of multipath in standalone GNSS receivers receiving modernised Binary Offset Carrier (BOC)-modulated signals. Similarities to CMC are drawn before the novel measurement, Code minus Subcarrier, (CMS) is characterised statistically and a threshold for multipath detection is determined. The effectiveness and sensitivity of this novel measurement as a multipath detection technique are analysed through simulation and multipath error envelope analysis. It will be shown that multipath echos capable of inducing a psuedorange error larger than the threshold are detectable at any amplitude. The method is finally verified using simulated fixed offset multipath, confirming that when code and subcarrier early–late spacings are optimal, all ranges of multipath delays, even as small as 21 meters, are detectable. This novel method of multipath detection requires no additional complex correlators than already exist in the chosen tracking algorithm, thus, providing excellent detection with minimum complexity added to the receiver structure. Full article

(This article belongs to the Special Issue Advancement of GNSS Signal Processing and Navigation)

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15 pages, 1885 KiB

Open AccessCommunication

Anti-Jamming GNSS Antenna Array Receiver with Reduced Phase Distortions Using a Robust Phase Compensation Technique

by Song Li, Feixue Wang, Xiaomei Tang, Shaojie Ni and Honglei Lin

Remote Sens. 2023, 15(17), 4344; https://doi.org/10.3390/rs15174344 - 3 Sep 2023

Cited by 7 | Viewed by 1616

Abstract

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. Full article

(This article belongs to the Special Issue Advancement of GNSS Signal Processing and Navigation)

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20 pages, 3650 KiB

Open AccessArticle

Evaluation and Analysis of the Accuracy of Open-Source Software and Online Services for PPP Processing in Static Mode

by Jesus René Vázquez-Ontiveros, Jorge Padilla-Velazco, J. Ramon Gaxiola-Camacho and Guadalupe Esteban Vázquez-Becerra

Remote Sens. 2023, 15(8), 2034; https://doi.org/10.3390/rs15082034 - 12 Apr 2023

Cited by 7 | Viewed by 4000

Abstract

It has been proven that precise point positioning (PPP) is a well-established technique to obtain high-precision positioning in the order between centimeters and millimeters. In this context, different studies have been carried out to evaluate the performance of PPP in static mode as a possible alternative to the relative method. However, only a few studies have evaluated the performance of a large number of different open-source software programs and have focused extensively on online free PPP services. Therefore, in this paper, a comprehensive comparison of processing in static mode between different open-source software and the online free PPP services is developed. For the evaluation, different GNSS observation files collected at 45 International GNSS Service (IGS) stations distributed worldwide were processed in static PPP mode. Within this frame of reference, ten open-source PPP software and five online free PPP services were studied. The results from the processing strategy demonstrate that it is possible to obtain precision in the order of millimeters with both open-source software and online PPP services. In addition, online PPP services experienced better performance than some other specialized PPP software. In summary, the results show that the daily solutions for the E (East), N (North), and U (Up) components estimated by the ten open-source software and by the five online free PPP services can reach millimeter precision for some stations. Among the open-source software, the PRIDE-PPPAR presented the best performance with a Root Mean Square Error (RMSE) of 5.52, 5.40, and 6.79 mm in the E, N, and U components, respectively. Alternatively, in the case of the online free PPP services, the APPS and CSRS-PPP produced the most accurate results, with RMSE values less than 12 mm for the three components. Finally, the open-source software and online free PPP services experienced similar positioning performance in the horizontal and vertical components, demonstrating that both can be implemented in static mode without compromising the accuracy of the measurement. Full article

(This article belongs to the Special Issue Advancement of GNSS Signal Processing and Navigation)

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25 pages, 6498 KiB

Open AccessArticle

Carrier Characteristic Bias Estimation between GNSS Signals and Its Calibration in High-Precision Joint Positioning

by Yao Guo, Yongnan Rao, Xue Wang, Decai Zou, Huihui Shi and Ning Ji

Remote Sens. 2023, 15(4), 1051; https://doi.org/10.3390/rs15041051 - 15 Feb 2023

Viewed by 1782

Abstract

A distinctive feature of modern Global Navigation Satellite System (GNSS) signals is that they transmit multiple signal components at the same carrier frequencies. The idea of joints across the signal channels from the same carrier frequency and even across different frequencies has been presented in many studies for tracking purposes. Carrier joint tracking is required on the premise that the frequency and phase relationship between signals are nominal values, and the bias of carrier characteristics between signals is drowned in noise as the signal reaches the ground, which requires high-gain receiving equipment to restore the original signal. The space signal-quality monitoring and evaluation system built by the National Timing Center of the Chinese Academy of Sciences is based on a 40 m dish antenna, which can automatically track a single satellite and achieve a high-fidelity reception of navigation signals to a certain extent, realizing fine signal quality monitoring (SQM) of GNSS satellites. Based on this platform, we discuss four types of time distributions of the combined signals among different signal components and provide a method to estimate the carrier characteristic bias between GNSS signals. We derived the correction method of carrier characteristic bias in the joint reception by the joint tracking mathematical model. Under the conditions of narrow correlation and unobstructed case, the carrier characteristic deviation does not vary significantly with the correlator interval and the satellite elevation angle. Based on the results of stability analysis, it is recommended that the receivers should update the carrier frequency bias correction number of the intra-frequency signal and carrier phase bias correction number of the intra-frequency signal monthly. The carrier phase deviation correction number of the inter-frequency signal is performed daily. The measured data from satellites show that the phase accumulation error of the joint tracking carrier loop can be eliminated to achieve long-term stable tracking after frequency bias correction. After the carrier phase bias correction, the joint positioning accuracy of the B2a and B2b signals was improved by 0.81%, and those of the B1C, L1C, E1C, and B2a signals were improved by 0.35%, 0.04%, 0.20%, and 0.11%, respectively. The positioning accuracy improvement effect of inter-frequency signals was greater than that of intra-frequency signals after carrier phase correction. Full article

(This article belongs to the Special Issue Advancement of GNSS Signal Processing and Navigation)

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19 pages, 8587 KiB

Open AccessArticle

Weak Signal Processing Method for Moving Target of GNSS-S Radar Based on Amplitude and Phase Self-Correction

by Wenning Gao, Fuzhan Yue, Zhenghuan Xia, Xin Liu, Chuang Zhang, Zongqiang Liu, Shichao Jin, Yao Zhang, Zhilong Zhao, Tao Zhang and Ying Zhang

Remote Sens. 2023, 15(4), 969; https://doi.org/10.3390/rs15040969 - 9 Feb 2023

Cited by 9 | Viewed by 2696

Abstract

Navigation satellite signals have the advantages of all-day, all-weather, and global coverage, and the use of navigation signals for the detection of moving targets has significant application prospects. However, the GNSS signal is very weak, and the signal power is greatly attenuated after being scattered by the target. In order to detect the echo signal, a long integration time is required. However, the movement of the target will cause the echo signal to produce unpredictable range migration and a Doppler frequency shift, which will weaken the cumulative effect of long-term integration. This paper proposes a weak signal processing method with amplitude and phase self-correction for moving target detection in the GNSS-S radar. First, the phase consistency of the echoes of a single GNSS satellite is realized by the block expansion compression and phase differential correction method to improve the coherent accumulation gain; then, multi-star joint accumulation is carried out after the signal amplitudes of multiple satellites are corrected by the improved keystone method, so as to obtain a stable echo signal track. This method can effectively improve the integral gain of the scattering signal of the moving target and realize target detection. The simulation results and field tests show that this method can effectively improve the SNR of the GNSS-S signal and can realize the detection of small moving targets such as cars with GNSS-S radar. Full article

(This article belongs to the Special Issue Advancement of GNSS Signal Processing and Navigation)

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22 pages, 7532 KiB

Open AccessArticle

Using Deep Learning to Map Ionospheric Total Electron Content over Brazil

by Andre Silva, Alison Moraes, Jonas Sousasantos, Marcos Maximo, Bruno Vani and Clodoaldo Faria, Jr.

Remote Sens. 2023, 15(2), 412; https://doi.org/10.3390/rs15020412 - 9 Jan 2023

Cited by 4 | Viewed by 2316

Abstract

The low-latitude ionosphere has an active behavior causing the total electron content (TEC) to vary spatially and temporally very dynamically. The solar activity and the geomagnetic field have a strong influence over the spatiotemporal distribution of TEC. These facts make it a challenge to attempt modeling the ionization response. Single frequency GNSS users are particularly vulnerable due to these ionospheric variations that cause degradation of positioning performance. Motivated by recent applications of machine learning, temporal series of TEC available in map formats were employed to build an independent TEC estimator model for low-latitude environments. A TEC dataset was applied along with geophysical indices of solar flux and magnetic activity to train a feedforward artificial neural network based on a multilayer perceptron (MLP) approach. The forecast for the next 24 h was made relying on TEC maps over the Brazilian region using data collected on the previous 5 days. The performance of this approach was evaluated and compared with real data. The accuracy of the model was evaluated taking into account seasonality, spatial coverage and dependence on solar flux and geomagnetic activity indices. The results of the analysis show that the developed model has a superior capacity describing the TEC behavior across Brazil, when compared to global ionosphere maps and the NeQuick G model. TEC predictions were applied in single point positioning. The achieved errors were 27% and 33% lower when compared to the results obtained using the NeQuick G and global ionosphere maps, respectively, showing success in estimating TEC with small recent datasets using MLP. Full article

(This article belongs to the Special Issue Advancement of GNSS Signal Processing and Navigation)

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11 pages, 626 KiB

Open AccessCommunication

DOA Estimation under GNSS Spoofing Attacks Using a Coprime Array: From a Sparse Reconstruction Viewpoint

by Yuqing Zhao, Feng Shen, Biqing Qi and Zhen Meng

Remote Sens. 2022, 14(23), 5944; https://doi.org/10.3390/rs14235944 - 24 Nov 2022

Cited by 1 | Viewed by 1734

Abstract

The antispoofing method using the direction-of-arrival (DOA) feature can effectively improve the application security of the global navigation satellite system (GNSS) receivers. In this paper, a sparse reconstruction approach based on a coprime array of antennas is proposed to provide reliable DOA estimation under a GNSS spoofing attack. Specifically, the self-coherence property of genuine satellite signals and spoofing was fully exploited to construct a denoised covariance matrix that enables DOA estimation before receiver despreading. Based on this, an equivalent uniform linear array (ULA) was generated from the constructed covariance matrix via virtual array interpolation. By applying the ideal of sparse reconstruction to an equivalent ULA signal, the preliminary DOA estimation results could be obtained without the need for a number of signals. Considering that the sparse estimation technique suffers from basis mismatch effects, we designed an optimization problem with respect to off-grid error to compensate the initial DOA such that the performance loss of DOA estimation could be reduced. Numerical examples demonstrated the advantages of the proposed method in terms of degrees-of-freedom (DOFs), resolution and accuracy. Full article

(This article belongs to the Special Issue Advancement of GNSS Signal Processing and Navigation)

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18 pages, 2890 KiB

Open AccessArticle

External Tropospheric Corrections by Using Kriging Interpolation for Improving PPP-RTK Positioning Solutions

by Chuanfeng Song, Hongyang Ma, Huizhong Zhu, Bo Wu and Nan Shen

Remote Sens. 2022, 14(15), 3747; https://doi.org/10.3390/rs14153747 - 4 Aug 2022

Cited by 5 | Viewed by 1980

Abstract

With the availability of satellite carrier-phase delay corrections provided by a reference network or the International GNSS Service (IGS), the integer ambiguity resolution for a single receiver can be successfully achieved, which is the so-called PPP-RTK concept. Although PPP-RTK can significantly shorten the convergence time, it is still worthwhile to further investigate fast and high-precision GNSS parameter estimation to improve efficiency and productivity. In order to fully exploit the potential of GNSS for positioning applications, we herein introduce external troposphere corrections as constrained pseudo observables to the undifferenced and uncombined PPP-RTK model. Since the uncertainties of the corrections are considered in the data processing, the PPP-RTK model with the weighted tropospheric corrections is referred to as the tropospheric-weighted model. Kriging interpolation is applied to generate the tropospheric corrections, as well as the corresponding variances. The quality of the tropospheric-weighted model is assessed by the positioning Root Mean Square (RMS) errors and the convergence time to reach a 10 cm accuracy. The 90% 3D convergence time of the kinematic positioning mode of the tropospheric-weighted model is 43.5 min with the ambiguity-float solution and 21.5 min with the ambiguity-fixed solution, which are shortened by 4.5 min and 5.5 min as compared to those of the standard PPP-RTK model, respectively. As for the static positioning mode, the 90% 3D convergence time of the tropospheric-weighted model for the ambiguity-float and -fixed solutions is 25.5 min and 15 min, while the 3D convergence time is 31.5 min and 18.5 min for the standard PPP-RTK model, respectively. The results also show that the tropospheric-weighted model can still work well in a 5 cm convergence threshold. Full article

(This article belongs to the Special Issue Advancement of GNSS Signal Processing and Navigation)

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13 pages, 5908 KiB

Open AccessTechnical Note

Blind Adaptive Beamforming for a Global Navigation Satellite System Array Receiver Based on Direction Lock Loop

by Jian Wu, Xiaomei Tang, Long Huang, Shaojie Ni and Feixue Wang

Remote Sens. 2023, 15(13), 3387; https://doi.org/10.3390/rs15133387 - 3 Jul 2023

Cited by 4 | Viewed by 1801

Abstract

The adaptive beamforming algorithm can realize interference suppression and navigation signal enhancement, and has been widely used. However, achieving high-precision real-time estimation of the direction of arrival (DOA) parameters of navigation signals in strong-interference scenarios with low complexity is still a challenge. In this paper, a blind adaptive beamforming algorithm for a Global Navigation Satellite System (GNSS) array receiver based on direction lock loop is proposed without using the prior information of the DOA parameter. The direction lock loop is used for DOA tracking and estimation after interference suppression, which uses the spatial correlation of the array beam pattern to construct a closed direction-tracking loop. The DOA estimation value is adjusted in real time based on the loop errors. A blind beamformer is constructed using the DOA estimation results to provide gain by forming a beam in the satellite direction. This method improves the accuracy and dynamic adaptability of DOA estimation while significantly reducing the computational complexity. The theoretical analysis and simulation results verify the effectiveness of the proposed algorithm. Full article

(This article belongs to the Special Issue Advancement of GNSS Signal Processing and Navigation)

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