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In the field of navigation and positioning, the inertial navigation system (INS)/global navigation satellite system (GNSS) integrated navigation system is known for providing stable and high-precision navigation services for vehicles. However, in extreme scenarios where GNSS navigation data are completely interrupted, the positioning accuracy of these integrated systems declines sharply. While there has been considerable research into using neural networks to replace the GNSS signal output during such interruptions, these approaches often lack targeted modeling of sensor information, resulting in poor navigation stability. In this study, we propose an integrated navigation system assisted by a novel neural network: an inverted-Transformer (iTransformer) and the application of a frequency-enhanced channel attention mechanism (FECAM) to enhance its performance, called an INS/FECAM-iTransformer integrated navigation system. The key advantage of this system lies in its ability to simultaneously extract features from both the time and frequency domains and capture the variable correlations among multi-channel measurements, thereby enhancing the modeling capabilities for sensor data. In the experimental part, a public dataset and a private dataset are used for testing. The best experimental results show that compared to a pure INS inertial navigation system, the position error of the INS/FECAM-iTransformer integrated navigation system reduces by up to 99.9%. Compared to the INS/LSTM (long short-term memory) and INS/GRU (gated recurrent unit) integrated navigation systems, the position error of the proposed method decreases by up to 82.4% and 78.2%, respectively. The proposed approach offers significantly higher navigation accuracy and stability. [ABSTRACT FROM AUTHOR]

A novel probe fed right hand circularly polarized (RHCP) shared aperture antenna with concentric configuration is designed for L5 and S-bands NavIC receiver application. The structure consists of a square loop-type patch antenna for the L5 band, serves as the top radiator, and a concentrically truncated corner patch antenna for the S-band is embedded in the non-radiating portion of the L5 band antenna. The square loop is orthogonally fed with electromagnetically coupled strips with equal power and quadrature phased shift through symmetric vias. These vias are connected to the feeding network, which consists of a Wilkinson power divider that is designed on opposite sides of the ground to mitigate spurious radiations. Furthermore, the S-band antenna, placed inside the L5 band substrate, achieves CP by corner truncation. This technique increases the aperture reuse efficiency and improves the isolation between both radiators. The overall profile of the antenna is 75×75×8mm3 and exhibits a wide impedance bandwidth of 25.5% for the L5 band and 6.5% for the S-band, with an isolation of better than 20dB for both bands. The axial ratio bandwidth achieved is 25.5% and 4.1% for the L5 and S bands, respectively, with boresight gain of 3.57 dBiC and 4.8 dBiC in the L5 band and S-band, respectively. The proposed antenna is based on a shared aperture technique, which has different feeding ports for both bands; thus, it improves the G/T performance and noise figure of the overall system. These characteristics make the proposed antenna suitable for use in NavIC application. [ABSTRACT FROM AUTHOR]

CubeSats hold promise for various applications, but their viability in demanding missions such as future low Earth orbiting position, navigation, and timing (LEO-PNT) systems hinges on higher orbital accuracy and reliable attitude information. To address these challenges, we present an array-aided combined precise orbit and attitude determination model with an optimal solution. In the estimation process, multi- and affine-constrained models are used to precisely determine the attitude, and then, highly precise observations for an antenna array are reconstructed based on fixed ambiguities and a decorrelation step. Validations confirm the significance of integer ambiguities in the model, highlighting the cost-effectiveness of this model compared with star trackers for attitude determination. The reconstructed observations outperform the original observations, leading to improved orbital components, with the three-dimensional root mean square (RMS) equal to 4.1 cm. The observation residuals are smoother, with an RMS of 6 mm, half of that obtained via a single antenna. The developed models offer great potential for CubeSats, advancing their orbit and attitude determination capabilities. [ABSTRACT FROM AUTHOR]

The Moon is the closest celestial body to the Earth. Its rich unique resources are an important supplement to the Earth's resources and have a profound impact on the sustainable development of human society. As large-scale exploration missions gradually progress, demands for communication, navigation, surveying and other services of lunar-space probes have significantly increased. Constellation navigation and orbit determination technology will become an indispensable part of future lunar exploration infrastructure. This article systematically analyzes the current status of lunar relay navigation satellite networks at home and abroad, summarizes the technical principles of single-satellite and constellation navigation and orbit determination, discusses the technical difficulties in lunar navigation constellation orbit determination and navigation, and analyzes possible solutions. Finally, the development trend of research on high-precision orbit determination and navigation methods for lunar navigation constellations is proposed. [ABSTRACT FROM AUTHOR]

The system time of the four major navigation satellite systems is mainly maintained by multiple high-performance atomic clocks at ground stations. This operational mode relies heavily on the support of ground stations. To enhance the high-precision autonomous timing capability of next-generation navigation satellites, it is necessary to autonomously generate a comprehensive space-based time scale on orbit and make long-term, high-precision predictions for the clock error of this time scale. In order to solve these two problems, this paper proposed a two-level satellite timing system, and used multiple time-keeping node satellites to generate a more stable space-based time scale. Then this paper used the sparse sampling Long Short-Term Memory (LSTM) algorithm to improve the accuracy of clock error long-term prediction on space-based time scale. After simulation, at sampling times of 300 s, 8.64 × 104 s, and 1 × 106 s, the frequency stabilities of the spaceborne timescale reach 1.35 × 10–15, 3.37 × 10–16, and 2.81 × 10–16, respectively. When applying the improved clock error prediction algorithm, the ten-day prediction error is 3.16 × 10–10 s. Compared with those of the continuous sampling LSTM, Kalman filter, polynomial and quadratic polynomial models, the corresponding prediction accuracies are 1.72, 1.56, 1.83 and 1.36 times greater, respectively. [ABSTRACT FROM AUTHOR]

Some agriculture machinery like the transplanter, needs to operate by following the crop-free ridges. In order to improve working efficiency and quality, some autonomous navigation systems were developed and applied to ridge-following machinery. At present, agricultural navigation systems are mainly the satellite navigation system and the machine vision system. The satellite navigation system is difficult to apply to the machinery that needs to work by following the ridge because it cannot distinguish the shape of the navigated ridge and guide the machinery working along the ridge. In this study, 697 cloudy ridge images and 235 sunny ridge images were taken in the field, and these images were used as the dataset. Moreover, a machine vision navigation method based on the color of ridges was proposed. Firstly, the regions of interest (ROI) in the ridge image were extracted according to the reaction time and the forward speed of the machine. Then, a gray reconstruction method was used to enlarge the color difference between the ridge and the furrow. The optimal threshold for the gray image segmenting was calculated real-timely by using the threshold segmentation method. Then, based on the contour detection method, the ridge contour which was not surrounded by holes was extracted. Finally, the approximate quadrilateral method was proposed to recognize the ridge center line as the navigation line. The method proposed in this study was verified by four types of ridges with different colors and textures. The experimental results showed that the recognition success rates of the light ridge, the dark ridge, the film-covered ridge, and the sunny ridge were 100%, 97.5%, 100%, and 98.7%, respectively. The recognition success rate of the proposed method was at least 8% higher than that of the existing ridge-furrow recognition methods. The results indicate that this method can effectively realize navigation line recognition. This method can provide technical support for the autonomous navigation of agricultural machinery, such as transplanters, seeders, etc., operating on the ridge without crops. [ABSTRACT FROM AUTHOR]

Aiming to establish a long-term presence on the Moon, interest in new and robust communication and navigation capabilities on the lunar surface is greater than ever before. In response, lunar navigation systems (LNS) have been conceptualized and put into action by space agencies. While we expect these services to be fully functional before the late 2020s, many missions are set to begin surface exploration before the initiation of these services. To meet the immediate needs of early missions, our group proposed a small-start technology demonstration mission called the Lunar Navigation CubeSat (LunaCube). The mission aims to demonstrate a LNS transmitter and store-and-forward radio in the vicinity of the Moon and to provide lunar positioning services to lunar surface assets. The project was initiated with funding support from the Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT) and completed preliminary design and detailed design in 2021 and 2022 respectively. As a result of the design study, the satellites consist of a 6U-size structure, a 50W-class deployed solar panel, a X-band transponder, three-axis attitude control using a star tracker, sun sensors, gyro, reaction wheels, and reaction control system thruster, as well as orbit control using a water-based resistojet. The total wet mass is less than 14 kg. • A dual-satellite lunar navigation system, called LunaCube, is proposed. • LunaCube can provide 50 m user positioning accuracy relative to a reference station. • MDPO algorithm is used to reduce the size and numbers of the navigation satellites. • The system consists of two 6U CubeSats, each with a total wet mass of under 14 kg. [ABSTRACT FROM AUTHOR]

In recent years, the number of expected missions to the Moon has increased significantly. With limited terrestrial-based infrastructure to support this number of missions, as well as restricted visibility over intended mission areas, there is a need for space navigation system autonomy. Autonomous on-board navigation systems in the lunar environment have been the subject of study by a number of authors. Suggested systems include optical navigation, high-sensitivity Global Navigation Satellite System (GNSS) receivers, and navigation-linked formation flying. This paper studies the interoperable nature and fusion of proposed autonomous navigation systems that are independent of Earth infrastructure, given challenges in distance and visibility. This capability is critically important for safe and resilient mission architectures. The proposed elliptical frozen orbits of lunar navigation satellite systems will be of special interest, investigating the derivation of orbit determination by non-terrestrial sources utilizing celestial observations and inter-satellite links. Potential orbit determination performances around 100 m are demonstrated, highlighting the potential of the approach for future lunar navigation infrastructure. [ABSTRACT FROM AUTHOR]

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

This paper describes a concept for local GNSS (Global Navigation Satellite System) augmentation derived from the established Ground Based Augmentation System (GBAS) in civil aviation. The aim of this concept is to provide reliable and accurate GNSS measurements for integration into a redundant, safe and reliable integrated navigation architecture tailored to serve Urban Air Mobility (UAM). The proposed concept for local GNSS augmentation addresses the specific challenges of UAM, in particular for take-off and landing operations, and ensures safe separation between UAM vehicles en route between vertiports. By using less expensive hardware compared to the traditional GBAS, the concept aims to make the integration into future urban airspace easier and more cost-effective, both in terms of ground infrastructure demands and on-board navigation hardware. In addition to the high-level system concept and considerations, we present an initial nominal performance assessment of local augmentation using lower-cost airborne and ground hardware. This assessment is based on actual UAV (Unmanned Aerial Vehicle) flight trials conducted in different urban scenarios, as well as long-term rooftop measurements. [ABSTRACT FROM AUTHOR]

To realize the societal need for greener, safer, and smarter mobility, ambitious technical challenges need to be addressed. With this aim, the H2020-EUSPA project ESRIUM investigates various aspects of highly accurate, reliable, and assured EGNSS localization information for road vehicles with a particular focus on automated vehicles. To analyze the achievable accuracy, reliability, and availability of multi-frequency and multi-GNSS mass-market receivers, we have conducted test drives under different GNSS reception conditions. In the tests, special focus was placed on using the Galileo Open Service Navigation Message Authentication (OSNMA) service, offering an additional feature for assured PVT (position, velocity, and time) information with respect to spoofing. We analyzed the performance of three Septentrio Mosaic-X5 receivers operated with different OSNMA settings. It could be shown that strict use of OSNMA provides very good positioning accuracy as long as sufficient suitable satellites are available. However, the overall performance suffers from a reduced satellite number and is therefore limited. The performance of a receiver using authenticated Galileo with GPS signals (final status of Galileo OSNMA) is very good for a mass-market receiver: 92.55% of the solutions had a 2D position error below 20 cm during 8.5 h of driving through different environments. [ABSTRACT FROM AUTHOR]

The General Lighthouse Authorities (GLA) R&D Directorate has, for some time, advocated that alternate position navigation and timing (PNT) systems should be established to offset critical dependency on Global Navigation Satellite Systems (GNSS), both in the maritime world and across wider industry. The maritime world already has a number of viable systems that may provide a ship's navigator with position-fixing information independent of GNSS. A promising option is radar. Depending on size, merchant vessels are required to fit radar operating in the X-band (9 GHz) and, optionally S-band (3 GHz). The radar return from the shoreline provides a unique and identifiable fingerprint that depends on the location of the vessel. GRAD has developed a number of different processes that can convert a series of images from the ship's radar into a series of output position-fixes, independent of having access to satellite (GNSS) positioning. This report describes the methods we investigated and presents the results from a number of ship trials. [ABSTRACT FROM AUTHOR]

To support the increasing number of planned lunar missions, a collaborative international initiative is underway to conceptualise and establish a lunar satellite constellation for communication and navigation. In this context, the goal of the current paper is to analyse what the obtainable performance is for a lunar lander that executes state estimation employing one-way ranging signals from such a Lunar Navigation Service (LNS). In particular, a small-sized optimised navigation constellation is considered as the main source of measurements, which, coupled with an accelerometer and an altimeter, is used to estimate the lander absolute trajectory during the main braking phase. The guidance is extracted on board by interpolation of a ground-optimised trajectory, followed by a reference-tracking regulator. Two alternative control tuning cases are presented, one targeting high performance, the other targeting low propellant mass. Nominal performance and associated sensitivity analyses assessed the feasibility of supporting such a critical phase with a reduced LNS constellation, reaching final control errors below 500 m , with the better performing one going down to 56 m. Among the two proposed alternatives, the one targeting low fuel expenditure has proven, however, to also be more robust against time and state uncertainty, providing much larger success rates. [ABSTRACT FROM AUTHOR]

Low Earth orbit (LEO) satellites have high signal strength and faster geometry changes over short periods, offering unique advantages in navigation augmentation. Integrating LEO satellites into the navigation system can help augment the performance of the global satellite navigation system and break the dilemma of the existing navigation system with limited services in challenging environments. Constellation design is the key before establishing a complete LEO navigation augmentation platform. Therefore, in this study, two LEO navigation augmentation constellations, Polar/Walker (S1) and Walker/Walker (S2) with different inclinations, are designed and optimized using the non-dominated sorting genetic algorithm III (NSGA-III). The global average geometric dilution of precision (GDOP) of BDS-3 is reduced from 1.56 to 0.92 and 0.95, and the average visible satellite number is improved from 11.74 to 27.83 and 25.72 with the navigation augmentation of the optimized constellations. To further validate the navigation augmentation effect of two LEO constellations on BDS-3 precision point positioning (PPP), nine stations at different latitudes were selected for LEO augmented BDS-3 PPP simulation experiments. The results show that after adding S1 and S2 constellations to BDS-3, respectively, the convergence times of the nine stations are reduced by 35.5%∼96.5% and 43.7%∼96.2%, and the positioning accuracy is improved by 5.7%∼71.9% and 24.2%∼69.5%, respectively. Overall, each S1 and S2 constellations can significantly improve the global service performance and PPP performance of BDS-3. [ABSTRACT FROM AUTHOR]

While Galileo approaches Full Operational Capability and is close to completion of the deployed satellite constellation, a portfolio of new Galileo service features is under development and validation. The Galileo Open Service (OS) is planned to be enhanced with the provision of Navigation Message Authentication (NMA). In November 2020, the Galileo satellites started broadcasting OSNMA test data for an internal preparation phase of seven months duration. The objective of this test period was to determine and select the OSNMA test signal configuration for a subsequent 'Public Observation phase.' The paper presents the main outcomes of the preparation phase for a set of defined OSNMA performance parameters. Airbus is supporting the Galileo service provider, the European Union Agency for the Space Programme (EUSPA), both in Galileo service definition and in planning and execution of OSNMA test activities, which have been performed during this preparation phase. [ABSTRACT FROM AUTHOR]

Aim of publication is to introduce reader with general need and current situation of development of air traffic management systems and evaluation of actual operating network of aviation electronic support systems. The theme of the contribution is actual because there is currently an increase in the volume of the air traffic, which places increased demands on the safety level of air transport. Attempting to find new answers related to insufficient navigation systems has led aviation authorities to develop progressive systems based on cooperation with satellite navigation systems. Solution for capacity limited airports is development of system GBAS – Ground Based Augmentation System. The main purpose of publication is to present drafts of possible rationalization of navigation infrastructure of M.R. Stefanik airport. The effort to use the maximum potential of airspace consisted in the search for new concepts and trends in air traffic management based on the development of the technical pillar and new ways of managing the entire ATM system. [ABSTRACT FROM AUTHOR]

Copyright of Journal of South China University of Technology (Natural Science Edition) is the property of South China University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper realizes the evaluation and optimal decision of the spoofing effect on the global navigation satellite system (GNSS) under navigation countermeasures based on the game perspective, to overcome the limitations of current relevant research findings and maintain the secure application of the GNSS and maximize its defensive benefit during countering. An evaluation system based on the perspective of the game between spoofing strategies and defense measures is created to build the benefit matrix, which can solve the limitation in building a benefit matrix (the vital element in a game) that conforms to the confrontation‐oriented GNSS spoofing properties. Based on the built benefit matrix, a method integrating the grey expert‐based system with the hybrid evolutionary method is developed to realize quantifying the matrix and further make the optimal decision stably, which can solve the uncertainties of qualitative indices during quantifying and no global optimal solution for benefit equations deduced from the quantified matrix. Finally, based on various judgment principles, simulation and testing results verify the effectiveness of the obtained results and the superiority of the proposed method by comparing the results solved by the method in this paper with the results obtained by other decision‐making processing methods. [ABSTRACT FROM AUTHOR]

This paper introduces an adaptive Convolutional Neural Network (CNN)-based Unscented Kalman Filter for the pose estimation of uncooperative spacecraft. The validation is carried out at Stanford's robotic Testbed for Rendezvous and Optical Navigation on the Satellite Hardware-In-the-loop Rendezvous Trajectories (SHIRT) dataset, which simulates vision-based rendezvous trajectories of a servicer spacecraft to PRISMA's Tango spacecraft. The proposed navigation system is stress-tested on synthetic as well as realistic lab imagery by simulating space-like illumination conditions on-ground. The validation is performed at different levels of the navigation system by first training and testing the adopted CNN on SPEED+, Stanford's spacecraft pose estimation dataset with specific emphasis on domain shift between a synthetic domain and an Hardware-In-the-Loop domain. A novel data augmentation scheme based on light randomization is proposed to improve the CNN robustness under adverse viewing conditions, reaching centimeter-level and 10 degree-level pose errors in 80% of the SPEED+ lab images. Next, the entire navigation system is tested on the SHIRT dataset. Results indicate that the inclusion of a new scheme to adaptively scale the heatmaps-based measurement error covariance based on filter innovations improves filter robustness by returning centimeter-level position errors and moderate attitude accuracies, suggesting that a proper representation of the measurements uncertainty combined with an adaptive measurement error covariance is key in improving the navigation robustness. [ABSTRACT FROM AUTHOR]

Aiming to reduce the impact that the measurement uncertainty of nonlinear system brings to filtering accuracy, a novel sparse grid quadrature filter (SGQF) algorithm based on the double‐state chi‐square test is proposed. And the strap‐down inertial navigation system (SINS)/global navigation satellite system (GNSS) integrated navigation system is used to verify the algorithm. A discrete‐time system model with uncertain measurement is constructed, then the system state through the SGQF algorithm is estimated. To determine the uncertainty of the measurement, the double‐state chi‐square test is introduced. By comparing the results of the state recursor, the chi‐square test value is obtained and it is used to update the measurement noise. Further, the system state and error covariance are re‐estimated. So far a robust sparse grid filter algorithm with statistical adjustment of the measurement noise is obtained. The proposed algorithm can overcome the influence of error statistical characteristic amplification on system filtering accuracy. Taking the SINS/GNSS integrated navigation system as the application object, off‐line simulation experiments and online flight tests verify the robustness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

To acquire an accurate location on the occasions, such as in an indoor, tunnel, and valley, where satellite navigation signals fail. The paper designs a pedestrian navigation system by using the zero velocity update procedure technology (ZUPT) and Kalman filter to reduce the location error. The measurement noise characteristic (mean and variance) of the micro electro mechanical systems gyros is unknown and time variant, but in traditional studies, it is usually thought and calculated as a constant. So the optimality of the error estimation of the Kalman filter cannot be reached. To address this question, this paper proposes the improved Sage–Husa Adaptive Kalman Filter (SHAKF) based on the index fading memory factor to realise the state estimation of the Kalman filter and navigation error correction. The advantage of improved SHAKF is it can accurately estimate the state vector when the measurement noise is unknown and time variant. To verify the validity of novel navigation methods, walking experiments under outdoor environments and indoor environments are carried out. The results of actual walking experiments demonstrate that the proposed method can effectively reduce the pedestrian location error compared with the traditional ZUPT method. The mean location error is reduced by more than 10%, and the variance of the location error is reduced by more than 5%. [ABSTRACT FROM AUTHOR]

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This article investigates a novel Bluetooth odometer (BOD)-aided smartphone-based vehicular navigation system for satellite-denied environments. First, a wheel-mounted BOD is designed to measure rotational speed and send data to smartphones by Bluetooth transmission. Second, a nonlinear smartphone-based microelectromechanical system (MEMS) inertial measurement unit (IMU)/BOD error model is derived to solve the problem of azimuth divergence. Then, a position delay time model is proposed to compensate for the delay time of Bluetooth transmission. An Android app is developed to receive the BOD data from Bluetooth transmission, and the proposed BOD smartphone-based vehicular navigation algorithm provides positioning information in real time. In field tests, positioning accuracy reaches 0.38%D by using the proposed MEMS-IMU/BOD model. The designed scheme can be used as a low-cost and convenient solution for smartphone-based civilian vehicular autonomous navigation systems without changing the habits of drivers. [ABSTRACT FROM AUTHOR]

Due to the cost of inertial navigation and visual navigation equipment and lake of satellite navigation signals, they cannot be used in large‐scale underground mining environment. To solve this problem, this study proposes a large‐scale underground 3D real‐time positioning method with seam height assistance. This method uses the ultra wide band positioning base station as the core and is combined with seam height information to build a factor graph confidence transfer model to realise 3D positioning. The simulation results show that the proposed real‐time method is superior to the existing algorithms in positioning accuracy and can meet the needs of large‐scale underground users. [ABSTRACT FROM AUTHOR]

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the rapid development of large urban agglomerations and the increasing complexity of urban roads, the high-precision positioning of vehicles has become the cornerstone for the application of vehicle core technologies such as automatic driving. The real-time positioning accuracy of satellite navigation is easily affected by urban canyons, and its stability is poor; thus, how to use the information of the internet of vehicles to achieve satellite navigation fusion has become a difficult problem of multivehicle cooperative positioning. Aiming at this problem, this paper proposes a multivehicle 3D cooperative positioning algorithm based on information geometric probability fusion of GNSS/wireless station navigation (MVCP-GW), which creatively converts various navigation source information into an information geometric probability model, unifies navigation information time–frequency parameters, and reduces the impact of sudden error. Combined with the Kullback–Leibler algorithm (KLA) fusion method, it breaks off the shackles of the probabilistic two-dimensional model and achieves multivehicle three-dimensional cooperative positioning. Compared with the existing cooperative positioning algorithms in the performance of accuracy stability, applicability, obstruction scenarios, and physical verification, the simulation results and physical verification show that the MVCP-GW algorithm can effectively improve real-time vehicle positioning and the stability of vehicle positioning, as well as resist the impact of obstructed environments. [ABSTRACT FROM AUTHOR]

A description of a new method of autonomous navigation for determining the orbits and orientation of artificial Earth satellites is presented. The method is based on the sighting of selected stars by optoelectronic devices, from which the virtual zenith angles of the stars are calculated. We consider various orbits to which these measurements are applied, as well as solutions to the problems of navigation and orientation of artificial Earth satellites for navigation satellites of the GLONASS system. The possibility of synchronization of spacecraft time scales based on the reception of pulsar signals is described. [ABSTRACT FROM AUTHOR]

In view of the strict compatibility constraint requirements of C-band satellite navigation signals, continuous phase modulation based on prolate spheroidal wave functions (CPM-PSWF) is exploratorily applied to C-band navigation. After analyzing the influence of key parameters on the power spectrum characteristics of CPM-PSWF signal, four CPM-PSWF sub-families are initially screened as candidate navigation igneous for C-band, and their navigation performance indicators are also evaluated. On the basis of weighing the spectrum compatibility of the C-band signal and various navigation performance indicators, it is proposed to use the CPM-PSWF signal with "QM2PSWF (10) C=6" and h=0. 5 as the C-band navigation signal of the BeiDou system. The research shows that compared with the current C-band non-CPM-PSWF candidate navigation signal, the proposed CPM-PSWF signal spectrum leakage is less, the out-of-band attenuation is faster, and the code tracking accuracy and anti-multi-path performance are more competitive. [ABSTRACT FROM AUTHOR]

Due to the functional limitations of a single UAV, UAV clusters have become an important part of smart cities, and the relative positioning between UAVs is the core difficulty in UAV cluster applications. Existing UAVs can be equipped with satellite navigation, radio navigation, and other positioning equipment, but in complex environments, such as urban canyons, various navigation sources cannot achieve full positioning information due to occlusion, interference, and other factors, and existing positioning fusion methods cannot meet the requirements of these environments. Therefore, demand exists for the real-time positioning of UAV clusters. Aiming to solve the above problems, this paper proposes multisource fusion UAV cluster cooperative positioning using information geometry (UCP-IG), which converts various types of navigation source information into information geometric probability models and reduces the impact of accidental errors, and proposes the Kullback–Leibler divergence minimization (KLM) fusion method to achieve rapid fusion on geometric manifolds and creatively solve the problem of difficult fusion caused by different positioning information formats and parameters. The method proposed in this paper is compared with the main synergistic methods, such as LS and neural networks, in an ideal scenario, a mutation error scenario, and a random motion scenario. The simulation results show that by using UAV cluster movement, the method proposed in this paper can effectively suppress mutation errors and achieve fast positioning. [ABSTRACT FROM AUTHOR]

Absolute navigation using the downlink communication signals of massive low Earth orbit (LEO) constellations augmented by data from an inertial navigation system (INS) is considered. Lack of atomic clocks on-board LEO satellites requires the use of Doppler shift as a navigation observable. Furthermore, footprint limits of downlink signals’ beams necessitate the use of a tightly coupled INS/radio-navigation filter in order to compensate for the fact that it is not possible to measure carrier Doppler shift simultaneously from eight or more satellites. The navigation solution error is shown for a simulation, which demonstrates the feasibility of combining measurements from LEO constellations and INS data to enable global navigation satellite systems-like navigation capabilities. Additional simulations study how navigation solution error is affected by IMU quality, signal availability, downlink spot beam steering protocol, and constellation characteristics. [ABSTRACT FROM AUTHOR]

In the fields of positioning and navigation, the integrated inertial navigation system (INS)/global navigation satellite systems (GNSS) are frequently employed. Currently, high-precision INS typically utilizes fiber optic gyroscopes (FOGs) and quartz flexural accelerometers (QFAs) rather than MEMS sensors. But when GNSS signals are not available, the errors of high-precision INS also disperse rapidly, similar to MEMS-INS when GNSS signals would be unavailable for a long time, leading to a serious degradation of the navigation accuracy. This paper presents a new AI-assisted method for the integrated high-precision INS/GNSS navigation system. The position increments during GNSS outage are predicted by the convolutional neural network-gated recurrent unit (CNN-GRU). In the process, the CNN is utilized to quickly extract the multi-dimensional sequence features, and GRU is used to model the time series. In addition, a new real-time training strategy is proposed for practical application scenarios, where the duration of the GNSS outage time and the motion state information of the vehicle are taken into account in the training strategy. The real road test results verify that the proposed algorithm has the advantages of high prediction accuracy and high training efficiency. [ABSTRACT FROM AUTHOR]

Global navigation satellite system (GNSS) plays a crucial role in many fields, such as aerospace and transportation. Integrity is the measure of trust used in GNSS positioning especially in safety-critical applications. Advanced receiver autonomous integrity monitoring (ARAIM), taking full advantage of multi-constellation GNSS, shows huge potential to provide vertical navigation in civil aviation en route navigation and terminal approaches. However, the multi-constellation ARAIM also greatly exposes computational complexity and potential performance hazards in fault modes determination and fault-tolerant positioning. From the perspective of integrity risk control, rather than the pursuit of better positioning accuracy blindly for safety-critical applications, the concept of constellation dynamic selection is proposed and implemented in ARAIM and the performance analysis is discussed in this paper. Only the best two constellations which have the best vertical geometry performance are involved in ARAIM calculation anytime anywhere. The proposed method shows superiority in both integrity availability and computational complexity in both simulations and actual GNSS signal experiments. While the computational complexity is less than 10% of that using four constellations, 100% availability under LPV-200 criteria can be achieved in worldwide coverage experiment. The proposed method also overcomes the shortcomings of ARAIM with two fixed constellations and shows good robustness under depleted scenarios. Furthermore, the statistics results from observation stations proved the applicability and generality of the proposed method under current developing GNSS constellations. [ABSTRACT FROM AUTHOR]

Frequency-hopping binary offset carrier modulation improves the anti-interference performance and mitigates the autocorrelation function (ACF) ambiguity problem of binary offset carrier modulation. To save payload resources and make high-power amplifiers on satellites operate at the nonlinear saturation region, there is further demand for finding an efficient constant-envelope frequency-hopping binary offset carrier multiplexing technique to combine several signal components. Thus, we propose a dual-sideband constant-envelope multiplexing modulation, named asymmetric constant-envelope frequency-hopping binary offset carrier multiplexing (ACE-FHBOC), which is also a multicarrier constant-envelope multiplexing modulation. ACE-FHBOC provides higher design flexibility in the number of subcarrier frequencies than ACE-BOC while maintaining the same flexibility of signal design as ACE-BOC in the number of signal components and power ratio among components. We first establish the theory and give implementation methods of ACE-FHBOC. Then, we develop a software-defined receiver to simulate and analyze the performance for several specific ACE-FHBOC and ACE-BOC signals. The results show that the recommended ACE-FHBOC signals have lower ACF ambiguity, better anti-narrowband interference, and multipath performance than ACE-BOC under the same conditions. With these advantages, ACE-FHBOC is a promising solution for the signal design of new generation global navigation satellite systems. [ABSTRACT FROM AUTHOR]

At present, the research on the tracking performance of navigation receivers is based on the conditions of single-frequency interference, however, the space electromagnetic environment is complicated, and so it is necessary to study the effect of the navigation receiver under multifrequency interference. Through the analysis of the blocking interference mechanism of the navigation receiver and the mathematical model of the tracking loop, the effect model under in-band and out-of-band multifrequency interference is established, when the satellite tracking is missing. The Beidou navigation receiver is used as the experiment object to build a multifrequency interference effect experiment platform, and the carrier-to-noise ratio (C/N0) threshold is used as the criterion for the satellite tracking missing, Finally, the model is verified with the experimental data, the error of the model under tri-frequency out-of-band interference exceeds 3 dB. For reducing the model error, the corrected model is proposed, and the corrected model errors are less than 1 dB. The model is helpful to predict the satellite signal status in the navigation receiver under complex electromagnetic environments. [ABSTRACT FROM AUTHOR]

An integrated navigation algorithm based on a multiple fading factors Kalman filter (MFKF) is proposed to solve the problems that the Kalman filtering (KF) algorithm easily brings about diffusion when the model becomes a mismatched or noisy, and the MFKF accuracy is reduced when the fading factor is overused. Based on the innovation covariance theory, the algorithm designs an improved basis for judging filtering anomalies and makes the timing of the introduction of the fading factor more reasonable by switching the filtering state. Different from the traditional basis of filter abnormality judgment, the improved judgment basis adopts a recursive way to continuously update the estimated value of the innovation covariance to improve the estimation accuracy of the innovation covariance, and an empirical reserve factor for the judgment basis is introduced to adapt to practical engineering applications. By establishing an inertial navigation system (INS)/global navigation satellite system (GNSS) integrated navigation model, the results show that the average positioning accuracy of the proposed algorithm is improved by 26.52% and 7.48%, respectively, compared with the KF and MFKF, and shows better robustness and self-adaptability. [ABSTRACT FROM AUTHOR]

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The velocity and acceleration of geostationary transfer orbit (GTO) satellites change dramatically and periodically, and the operating area extends from hundreds of kilometers to 36,000 km above the Earth's surface. This leads to the limitation of navigation methods of GTO satellites, the complexity of perturbation components and the increase of sensor measurement noise. Therefore, in this paper, a celestial navigation system/Beidou navigation system (CNS/BDS) integrated navigation method based on the adaptive spherical simplex unscented transformation federated Kalman filter (ASSUT-FF) algorithm is designed for GTO satellite high-precision autonomous navigation, considering the integrated navigation method and filtering algorithm. A Beidou observation model based on the relative pseudorange/pseudorange rate is established. Even when the GTO satellite moves to the high orbit region, it can still use BDS navigation information to determine the orbit. In addition, the designed adaptive algorithm can still ensure the filter stability in a complex space environment. The CNS/BDS integrated navigation method based on the ASSUT-FF algorithm proposed in this paper can realize continuous and high-precision autonomous navigation of GTO satellites. The simulation results show that the orbit determination accuracy of the proposed navigation method is 96.23% and 84.06% higher than that of the single celestial navigation method and the traditional Beidou geometric positioning correction celestial navigation method, respectively. The performance test results of the adaptive algorithm also show that the ASUT-FF algorithm has good robustness. [ABSTRACT FROM AUTHOR]

In satellite positioning systems, optimizing navigation satellite constellation and reducing the observation residuals are usually adopted to improve positioning precision and accuracy of the receiver. This paper presents a method to improve positioning precision by using multi-frequency navigation signals. The observation data of CAPS and GPS system are used to simulate the experiment. When the number of downlink frequencies is different, the root mean square of positioning error, improvement percentage, and standard deviation are calculated, respectively. When the number of descending frequencies is k, the root mean square of positioning error in three-dimensional space is 1/ k of that in single frequency. The theoretical derivation and experiment show that the precision of satellite positioning can be effectively improved by using multi-frequency navigation signals. The research work can provide theoretical support and data reference for the future research of satellite positioning. [ABSTRACT FROM AUTHOR]

Camera-based visual navigation has great potential for various applications, especially in satellite-signal-degenerated environments. However, the lack of integrity protection has constrained its utilization in safety-critical applications. Integrity characterizes the quality of the information that a navigation system delivers. Integrity frameworks have been developed over decades for satellite navigation, and continue to play an essential role in safety-critical applications like civil aviation. Nevertheless, there are several challenges to quantify the risks associated with visual navigation. Over the last few years, several approaches to tackle these challenges have been investigated. These developments are the first steps toward a reliable visual positioning framework with integrity monitoring capabilities. In this paper, we review the current status, particular challenges, and development trends in visual positioning integrity monitoring. In addition, we propose a preliminary framework so that the future developments on visual navigation integrity can benefit from a systematic approach. [ABSTRACT FROM AUTHOR]

Herein, the application of optical quantum standards (quantum sensors) based on cold atoms in satellite navigation is discussed. The advantages of placing quantum sensors based on cold atoms in space are also discussed. It has been established that to improve the accuracy of measurements using quantum sensors, their operation in zero-gravity or microgravity on specific platforms must be studied. The main platforms that provide microgravity conditions are reviewed in this article, and a test platform for falling along a parabolic trajectory in the form of a slide of various shapes with a moving trolley is proposed. Four different slide configurations have been described in detail, with a computer simulation for each of them. A comparative analysis of the characteristics of the slides has been performed, their advantages and disadvantages have been identified, and the most effective configuration has been found. Furthermore, a method for improving microgravity quality is proposed, and it will be considered in the future. [ABSTRACT FROM AUTHOR]

The collaborative exchange of information between members of a cluster can provide additional observations to improve the reliability of navigation. To address the problems of poor geometric configurations of satellites and low positioning accuracy of satellite navigation systems in complex environments, this paper proposes a collaborationaugmented navigation method with optimisation of the geometric dilution of precision for a clustered aircraft. A collaboration-augmented navigation model is established in which the differences between the characteristics of satellite pseudorange measurements and collaborative information measurements are taken into consideration to overcome heteroscedasticity. Then, an optimal collaboration-augmented navigation algorithm is proposed on the basis of geometric configuration analysis. In this method, all visible satellites are projected onto the current horizontal plane, and in accordance with the satellite distribution, a satellite reference ring is constructed to determine the optimal collaborative area for an aircraft. Then, a collaborative aircraft selection is made to select an optimal aircraft to assist the satellite navigation system for configuration optimisation. Finally, the algorithm performance is simulated and verified by simulation, and the in- fluence of the equivalent ranging error on the effectiveness of geometric configuration optimisation is analysed, indicating the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

With the continuous development of positioning technology in today's world, the accuracy requirements for navigation and positioning are also getting higher and higher. Global Positioning and Navigation System (GPS) can provide high-precision long-term navigation and positioning information. However, it has a strong dependence on the external environment, which means that it is easily disturbed by environmental changes and affects the accuracy of navigation and positioning and even leads to positioning failure. The inertial navigation system (INS) is an autonomous navigation system. It uses sensors to measure the specific force and angular velocity of the carrier for positioning and navigation, which means that it is less affected by the environment. However, the inertial navigation device will produce a certain initial error due to the restriction of the manufacturing level, and the error will increase with time, so the inertial navigation method is not suitable for long-term navigation. Therefore, it is of great practical significance to realize satellite/inertial navigation integrated navigation by combining the respective advantages of satellite navigation and inertial navigation methods and avoiding their respective disadvantages. This paper is aimed at studying the satellite/inertial navigation integrated navigation method based on the improved Kalman filter algorithm. The satellite inertial navigation integrated navigation experiment is carried out based on the improved Kalman filter algorithm. In the experiment, the noise reduction experiment of the designed satellite inertial navigation system was carried out by using the filtering noise reduction function of the improved Kalman filter algorithm, and the conclusion was drawn after the experiment. The navigation accuracy of the satellite inertial navigation system is improved by a total of 2 m after the improved Kalman filter algorithm is used to filter the noise reduction. [ABSTRACT FROM AUTHOR]

Currently, BeiDou Navigation Satellite System (BDS) has been a mature satellite navigation system. However, the transmission rate of the navigation signal is low. A novel Navigation and Communication Integrated (NCI) signal had been proposed in our previous work, its transmission rate was improved compared with the traditional navigation signal. In addition, an optimization algorithm was proposed to avoid cross-correlation interference between the navigation signal and the communication signal. Based on the above theoretical system, this paper gives a specific design for the BDS. The communication signal used in BDS is selected basing on the optimization algorithm, and the original BDS signal is used as the navigation signal. In addition, the error correction coding and interleaving technique in BDS are applied to the NCI signal to further improve the compatibility between the signal and BDS. The simulation results verify the superiority of the optimization algorithm. It illustrates each communication signal selected is suitable for the navigation signal of each satellite in BDS. [ABSTRACT FROM AUTHOR]

The availability of orbit information with high precision and low latency is a key requirement for many Earth‐observation missions, predominantly in the field of radio occultation. Traditionally, precise orbit determination solutions of low‐Earth orbit (LEO) satellites are obtained offline on ground after downloading GNSS measurements and auxiliary spacecraft data to the processing center. The latency of this processing depends on the frequency of LEO downlink contacts and the availability of precise GNSS orbit and clock products required for the orbit determination process. These dependencies can be removed by computing the precise orbit determination solution on board the satellite using GNSS broadcast ephemerides. In this study, both real data and simulated measurements from a representative LEO satellite are processed in a flight‐proven Kalman‐filter algorithm. The paper studies the use of GPS, Galileo and BeiDou‐3 for real‐time orbit determination in different combinations with simulated measurements. Results show that use of dual‐frequency observations and broadcast ephemerides of Galileo and BeiDou‐3 leads to a significant reduction of 3D rms orbit errors compared to GPS‐only processing. An onboard navigation accuracy of about one decimeter can be achieved without external augmentation data, which opens up new prospects for conducting relevant parts of the science data processing in future space missions directly on board a LEO satellite. [ABSTRACT FROM AUTHOR]

The olfactory navigation hypothesis proposed to explain homing pigeon navigation predicts that birds learn the association of wind directions and wind-borne odours at home, and once displaced, determine the home direction on the basis of local environmental odours at the release site. This hypothesis was proposed on the basis of two kinds of empirical observations: (i) pigeons develop navigational abilities only if exposed to winds at the home loft, (ii) anosmic pigeons displaced to unfamiliar sites are unable to home. Soon after the discovery of the role of olfaction in pigeon navigation about 50 years ago, olfactory navigation became a subject of hot scientific debate. Until the beginning of the GPS era, the large body of evidence in support of olfactory navigation in pigeons, swifts and starlings consisted mainly of vanishing bearings and homing performance data. The use of GPS, allowing the observation of the pigeons' behaviour en route provided further compelling evidence of the role of olfactory cues in pigeon navigation. The development of wildlife telemetry in the past two decades produced strong evidence about the use of olfactory cues, also in navigation of some species of wild birds. Wild birds artificially displaced both during migration, or during incubation showed impaired capacities to compensate displacements only if deprived of their sense of smell. Contrariwise, satellite telemetry failed to find any empirical validation for the existence of a navigational map based on magnetic cues in the tested species. In spite of the fact that the nature of the olfactory map in wild birds has not yet been elucidated, the development and miniaturisation of satellite technology will hopefully allow us in the near future to investigate in detail the features of the olfactory map found in some wild species, and to clarify the sensory basis of navigation in free-ranging small passerines. [ABSTRACT FROM AUTHOR]

A numerical analysis is conducted for assessing the feasibility on the use of Global Navigation Satellite System (GNSS) receivers for Korea Positioning System (KPS) satellites in space service volume (SSV). KPS is planned to provide a navigation and timing service by constructing seven satellites over the Korean Peninsula, which will orbit above the GNSS constellation in SSV. The major problems caused by such orbital characteristics include reduced satellite visibility due to poor geometric diversity and weak signals, causing an increase in the user range error (URE). To address these constraints, this study considers multi‐GNSS and 1‐st side‐lobe signal utilization scenarios. More specifically, the GNSS satellite visibility, geometric dilution of precision, carrier‐to‐noise ratio, URE, and navigation error for KPS satellites in SSV are analysed through a numerical simulation. A trade‐off between visibility and received signal power as well as their effects on positioning accuracy is analysed to describe the utility of side‐lobe signals. Finally, based on numerical analysis of the simulation results, this verifies the applicability of GNSS SSV for KPS satellites through multi‐GNSS and side‐lobe utilization scenarios. [ABSTRACT FROM AUTHOR]

Short Message Communication (SMC) is a featured service of BeiDou Navigation Satellite System (BDS). After its successful deployment in 2003, Regional Short Message Communication (RSMC) service has been continuously serving China and its neighboring countries and regions, especially in life safety scenarios. In this paper, the architecture of the Global Short Message Communication (GSMC) system is proposed based on the medium earth orbit (MEO) constellation and the crosslinks of the global BeiDou navigation system (BDS-3). Three subtypes of GSMC service, i.e. positioning report, emergency search and rescue (SAR) and regular SMC are designed in accordance with the technical characteristic of integration of navigation and communication in BDS-3, which supports future wide applications of GSMC. The performance of the designed GSMC system is analyzed by numerical calculations. As BDS-3 was officially announced completion on July 31, 2020, GSMC has been providing initial service. First test results of the in orbit GSMC payloads are also presented in the paper to verify the designed capabilities. Preliminary results also show that the requirements of Global Maritime Distress and Safety System (GMDSS) can also be fulfilled. [ABSTRACT FROM AUTHOR]

As unmanned aerial vehicles (UAVs) use global navigation satellite systems for positioning, the openness and weak security of satellite navigation signals make these systems easily falsifiable. By leveraging these characteristics, we propose a path following identification algorithm to gain control of UAVs using navigation spoofing as a countermeasure against illegal activities. Our contribution is threefold. First, we redefine the UAV kinematics model by treating the spoofing signal as wind. Subsequently, the relation between the spoofing signal and UAV heading angle is identified based on a path following algorithm, and the relation accuracy is experimentally verified. Finally, we propose the spoofing sparse A* search (SSAS) algorithm, whose effectiveness is verified by simulations of a UAV directed to a designated area while avoiding obstacles and forbidden areas. • Navigation spoofing can prevent illegal activities performed using UAVs. • The UAV kinematics model under navigation spoofing is established. • Spoofing signals are used to identify path following parameters. • The spoofing sparse A* search can lure the non-cooperative UAV to a designated area. • Flight test and simulation results verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]