LEO-Augmented GNSS Based on Communication Navigation Integrated Signal

Low Earth Orbit (LEO) is of great benefit for the positioning performance of Global Navigation Satellite System (GNSS). To realize the system of LEO-augmented GNSS, three methods to integrate communication and navigation signal for LEO communication system with the least influence on the communication performance are analyzed. The analysis adopts the parameters of IRIDIUM signal as restrictions. This paper gives quantitative comparison of these methods considering CN0(carrier noise power spectral density rate) margin, pseudorange accuracy, Doppler accuracy, and communication loss. For method 1, a low-power navigation signal is added to the communication signal. For method 2, the navigation signal is launched in one or more frames. For method 3, the navigation signal is launched in the frequency band separated to the communication signal. The result shows that the pseudorange accuracy of method 2 is far below method 1 and method 3. However, the difference of Doppler accuracy among the three methods can be emitted. Detailed analysis shows that method 1 is practicable when the communication and navigation signal power rate is 15 dB. It achieves the balance of pseudorange accuracy and bit error rate (BER) performance under this condition. Comprehensive comparison of these methods is given in the last. The result shows that the CN0 margin of the navigation signal for method 3 can be 13.04 dB higher than method 1, based on the accuracy threshold considered in this paper. Methods 1 and 3 have the advantage of high accuracy and high CN0 margin respectively. However, method 3 causes high communication capacity loss. Considering that the main disadvantage of GNSS signals is low CN0, method 3 is a good choice for the LEO-augmented GNSS system. Methods 1 and 3 can be combined to realize both high accuracy and high CN0 margin if possible.

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Improving DGNSS Performance through the Use of Network RTK Corrections

Remote Sensing ◽

10.3390/rs13091621 ◽

2021 ◽

Vol 13 (9) ◽

pp. 1621

Author(s):

Duojie Weng ◽

Shengyue Ji ◽

Yangwei Lu ◽

Wu Chen ◽

Zhihua Li

Keyword(s):

Carrier Phase ◽

Local Area ◽

Satellite System ◽

High Accuracy ◽

Single Frequency ◽

Baseline Length ◽

Low Latitude ◽

Phase Measurements ◽

Network Rtk ◽

Global Navigation Satellite

The differential global navigation satellite system (DGNSS) is an enhancement system that is widely used to improve the accuracy of single-frequency receivers. However, distance-dependent errors are not considered in conventional DGNSS, and DGNSS accuracy decreases when baseline length increases. In network real-time kinematic (RTK) positioning, distance-dependent errors are accurately modelled to enable ambiguity resolution on the user side, and standard Radio Technical Commission for Maritime Services (RTCM) formats have also been developed to describe the spatial characteristics of distance-dependent errors. However, the network RTK service was mainly developed for carrier-phase measurements on professional user receivers. The purpose of this study was to modify the local-area DGNSS through the use of network RTK corrections. Distance-dependent errors can be reduced, and accuracy for a longer baseline length can be improved. The results in the low-latitude areas showed that the accuracy of the modified DGNSS could be improved by more than 50% for a 17.9 km baseline during solar active years. The method in this paper extends the use of available network RTK corrections with high accuracy to normal local-area DGNSS applications.

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From GPS Receiver to GNSS Reflectometry Payload Development for the Triton Satellite Mission

Remote Sensing ◽

10.3390/rs13050999 ◽

2021 ◽

Vol 13 (5) ◽

pp. 999

Author(s):

Yung-Fu Tsai ◽

Wen-Hao Yeh ◽

Jyh-Ching Juang ◽

Dian-Syuan Yang ◽

Chen-Tsung Lin

Keyword(s):

Satellite System ◽

Low Earth Orbit ◽

Export Control ◽

Navigation Systems ◽

Gps Receiver ◽

Design Development ◽

Satellite Mission ◽

Essential Components ◽

Gnss Reflectometry ◽

Global Navigation Satellite

The global positioning system (GPS) receiver has been one of the most important navigation systems for more than two decades. Although the GPS system was originally designed for near-Earth navigation, currently it is widely used in highly dynamic environments (such as low Earth orbit (LEO)). A space-capable GPS receiver (GPSR) is capable of providing timing and navigation information for spacecraft to determine the orbit and synchronize the onboard timing; therefore, it is one of the essential components of modern spacecraft. However, a space-grade GPSR is technology-sensitive and under export control. In order to overcome export control, the National Space Organization (NSPO) in Taiwan completed the development of a self-reliant space-grade GPSR in 2014. The NSPO GPSR, built in-house, has passed its qualification tests and is ready to fly onboard the Triton satellite. In addition to providing navigation, the GPS/global navigation satellite system (GNSS) is facilitated to many remote sensing missions, such as GNSS radio occultation (GNSS-RO) and GNSS reflectometry (GNSS-R). Based on the design of the NSPO GPSR, the NSPO is actively engaged in the development of the Triton program (a GNSS reflectometry mission). In a GNSS-R mission, the reflected signals are processed to form delay Doppler maps (DDMs) so that various properties (including ocean surface roughness, vegetation, soil moisture, and so on) can be retrieved. This paper describes not only the development of the NSPO GPSR but also the design, development, and special features of the Triton’s GNSS-R mission. Moreover, in order to verify the NSPO GNSS-R receiver, ground/flight tests are deemed essential. Then, data analyses of the airborne GNSS-R tests are presented in this paper.

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Opportunistic In-Flight INS Alignment Using LEO Satellites and a Rotatory IMU Platform

Aerospace ◽

10.3390/aerospace8100280 ◽

2021 ◽

Vol 8 (10) ◽

pp. 280

Author(s):

Farzan Farhangian ◽

Hamza Benzerrouk ◽

Rene Landry

Keyword(s):

Kalman Filter ◽

State Space Model ◽

Flight Test ◽

Satellite System ◽

Low Earth Orbit ◽

Measurement Unit ◽

Starting Point ◽

Leo Satellites ◽

Positioning Method ◽

Global Navigation Satellite

With the emergence of numerous low Earth orbit (LEO) satellite constellations such as Iridium-Next, Globalstar, Orbcomm, Starlink, and OneWeb, the idea of considering their downlink signals as a source of pseudorange and pseudorange rate measurements has become incredibly attractive to the community. LEO satellites could be a reliable alternative for environments or situations in which the global navigation satellite system (GNSS) is blocked or inaccessible. In this article, we present a novel in-flight alignment method for a strapdown inertial navigation system (SINS) using Doppler shift measurements obtained from single or multi-constellation LEO satellites and a rotation technique applied on the inertial measurement unit (IMU). Firstly, a regular Doppler positioning algorithm based on the extended Kalman filter (EKF) calculates states of the receiver. This system is considered as a slave block. In parallel, a master INS estimates the position, velocity, and attitude of the system. Secondly, the linearized state space model of the INS errors is formulated. The alignment model accounts for obtaining the errors of the INS by a Kalman filter. The measurements of this system are the difference in the outputs from the master and slave systems. Thirdly, as the observability rank of the system is not sufficient for estimating all the parameters, a discrete dual-axis IMU rotation sequence was simulated. By increasing the observability rank of the system, all the states were estimated. Two experiments were performed with different overhead satellites and numbers of constellations: one for a ground vehicle and another for a small flight vehicle. Finally, the results showed a significant improvement compared to stand-alone INS and the regular Doppler positioning method. The error of the ground test reached around 26 m. This error for the flight test was demonstrated in different time intervals from the starting point of the trajectory. The proposed method showed a 180% accuracy improvement compared to the Doppler positioning method for up to 4.5 min after blocking the GNSS.

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Detecting Targets above the Earth’s Surface Using GNSS-R Delay Doppler Maps: Results from TDS-1

Remote Sensing ◽

10.3390/rs11192327 ◽

2019 ◽

Vol 11 (19) ◽

pp. 2327 ◽

Cited By ~ 2

Author(s):

Changjiang Hu ◽

Craig Benson ◽

Hyuk Park ◽

Adriano Camps ◽

Li Qiao ◽

...

Keyword(s):

Specular Reflection ◽

Satellite System ◽

Low Earth Orbit ◽

Earth Orbit ◽

Navigation Satellite ◽

Reflection Point ◽

Leo Satellites ◽

Gnss Reflectometry ◽

Global Navigation Satellite ◽

Remotely Sense

Global Navigation Satellite System (GNSS) reflected signals can be used to remotely sense the Earth’s surface, known as GNSS reflectometry (GNSS-R). The GNSS-R technique has been applied to numerous areas, such as the retrieval of wind speed, and the detection of Earth surface objects. This work proposes a new application of GNSS-R, namely to detect objects above the Earth’s surface, such as low Earth orbit (LEO) satellites. To discuss its feasibility, 14 delay Doppler maps (DDMs) are first presented which contain unusually bright reflected signals as delays shorter than the specular reflection point over the Earth’s surface. Then, seven possible causes of these anomalies are analysed, reaching the conclusion that the anomalies are likely due to the signals being reflected from objects above the Earth’s surface. Next, the positions of the objects are calculated using the delay and Doppler information, and an appropriate geometry assumption. After that, suspect satellite objects are searched in the satellite database from Union of Concerned Scientists (UCS). Finally, three objects have been found to match the delay and Doppler conditions. In the absence of other reasons for these anomalies, GNSS-R could potentially be used to detect some objects above the Earth’s surface.

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Variability and Performance of Short to Long-Range Single Baseline RTK GNSS Positioning in Indonesia

E3S Web of Conferences ◽

10.1051/e3sconf/20199401012 ◽

2019 ◽

Vol 94 ◽

pp. 01012 ◽

Cited By ~ 1

Author(s):

Irwan Gumilar ◽

Brian Bramanto ◽

Fuad F. Rahman ◽

I Made D. A. Hermawan

Keyword(s):

Long Range ◽

High Frequency ◽

Carrier Phase ◽

Satellite System ◽

High Accuracy ◽

Gnss Positioning ◽

And Performance ◽

Gnss Network ◽

Single Baseline ◽

Global Navigation Satellite

As the modernized Global Navigation Satellite System (GNSS) method, Real Time Kinematic (RTK) ensures high accuracy of position (within several centimeters). This method uses Ultra High Frequency (UHF) radio to transmit the correction data, however, due to gain and power issues, Networked Transport of RTCM via Internet Protocol (RTCM) is used to transmit the correction data for a longer baseline. This Research aims to investigate the performance of short to long-range single baseline RTK GNSS (Up to 80 KM) by applying modified LAMBDA method to resolve the ambiguity in carrier phase. The RTK solution then compared with the differential GNSS network solution. The results indicate that the differences are within RTK accuracy up to 80 km are several centimeter for horizontal solution and three times higher for vertical solution.

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Ionospheric corrections tailored to the Galileo High Accuracy Service

Journal of Geodesy ◽

10.1007/s00190-021-01581-x ◽

2021 ◽

Vol 95 (12) ◽

Author(s):

A. Rovira-Garcia ◽

C. C. Timoté ◽

J. M. Juan ◽

J. Sanz ◽

G. González-Casado ◽

...

Keyword(s):

Satellite Orbit ◽

Satellite System ◽

High Accuracy ◽

Integer Ambiguity ◽

Electron Content ◽

Confidence Bounds ◽

Total Electron ◽

Phase Measurements ◽

Model Geometry ◽

Global Navigation Satellite

AbstractThe Galileo High Accuracy Service (HAS) is a new capability of the European Global Navigation Satellite System that is currently under development. The Galileo HAS will start providing satellite orbit and clock corrections (i.e. non-dispersive effects) and soon it will also correct dispersive effects such as inter-frequency biases and, in its full capability, ionospheric delay. We analyse here an ionospheric correction system based on the fast precise point positioning (Fast-PPP) and its potential application to the Galileo HAS. The aim of this contribution is to present some recent upgrades to the Fast-PPP model, with the emphasis on the model geometry and the data used. The results show the benefits of integer ambiguity resolution to obtain unambiguous carrier phase measurements as input to compute the Fast-PPP model. Seven permanent stations are used to assess the errors of the Fast-PPP ionospheric corrections, with baseline distances ranging from 100 to 1000 km from the reference receivers used to compute the Fast-PPP corrections. The 99% of the GPS and Galileo errors in well-sounded areas and in mid-latitude stations are below one total electron content unit. In addition, large errors are bounded by the error prediction of the Fast-PPP model, in the form of the variance of the estimation of the ionospheric corrections. Therefore, we conclude that Fast-PPP is able to provide ionospheric corrections with the required ionospheric accuracy, and realistic confidence bounds, for the Galileo HAS.

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A Novel Signal Design and Performance Analysis in NavCom Based on LEO Constellation

Sensors ◽

10.3390/s21248235 ◽

2021 ◽

Vol 21 (24) ◽

pp. 8235

Author(s):

Jing Ji ◽

Yuting Liu ◽

Wei Chen ◽

Di Wu ◽

Hongyang Lu ◽

...

Keyword(s):

Mutual Influence ◽

Density Ratio ◽

Side Lobe ◽

Low Earth Orbit ◽

Noise Power ◽

Signal Design ◽

Tracking Accuracy ◽

Alternative Scheme ◽

Simulation Performance ◽

Noise Power Spectral Density

The mega-launch of low Earth orbit satellites (LEOs) represents a critical opportunity to integrate navigation and communication (NavCom), but first, challenges related to signal design must be overcome. This article proposes a novel signal scheme named CE-OFDM-PM. Via research on the in-band or adjacent band, it was found that the proposed signal scheme was suitable for S-band and had a wide normalized power spectrum density (PSD), high peak-to-side lobe ratio (PSR), and multiple peaks in autocorrelation. In an analysis of the simulation performance evaluation in navigation and communication, it is found that the proposed signal scheme has the potential for high accuracy, a code tracking accuracy of up to 0.85 m, a small mutual influence between the proposed signal scheme and other schemes, excellent anti-interference properties, and a better performance at both short and long distances in terms of its anti-multipath capability. Furthermore, the proposed signal scheme shows the ability to communicate between satellites and the ground and is outstanding in terms of its bit error rate (BER), CNR, and energy per bit to noise power spectral density ratio (Eb/N0). From the technical, theoretical, and application perspectives, our proposed signal scheme has potential as an alternative scheme in future BDS, PNTs, and even 5G/B5G.

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Satellite Availability and Service Performance Evaluation for Next-Generation GNSS, RNSS and LEO Augmentation Constellation

Remote Sensing ◽

10.3390/rs13183698 ◽

2021 ◽

Vol 13 (18) ◽

pp. 3698

Author(s):

Haomeng Cui ◽

Shoujian Zhang

Keyword(s):

Satellite System ◽

Low Earth Orbit ◽

Global Navigation Satellite Systems ◽

Navigation Satellite ◽

Next Generation ◽

Satellite Systems ◽

Satellite Visibility ◽

Under Construction ◽

Global Navigation Satellite ◽

Average Position

Positioning accuracy is affected by the combined effect of user range errors and the geometric distribution of satellites. Dilution of precision (DOP) is defined as the geometric strength of visible satellites. DOP is calculated based on the satellite broadcast or precise ephemerides. However, because the modernization program of next-generation navigation satellite systems is still under construction, there is a lack of real ephemerides to assess the performance of next-generation constellations. Without requiring real ephemerides, we describe a method to estimate satellite visibility and DOP. The improvement of four next-generation Global Navigation Satellite Systems (four-GNSS-NG), compared to the navigation constellations that are currently in operation (four-GNSS), is statistically analyzed. The augmentation of the full constellation the Quasi-Zenith Satellite System (7-QZSS) and the Navigation with Indian Constellation (11-NavIC) for regional users and the low Earth orbit (LEO) constellation enhancing four-GNSS performance are also analyzed based on this method. The results indicate that the average number visible satellites of the four-GNSS-NG will reach 44.86, and the average geometry DOP (GDOP) will be 1.19, which is an improvement of 17.3% and 7.8%, respectively. With the augmentation of the 120-satellite mixed-orbit LEO constellation, the multi-GNSS visible satellites will increase by 5 to 8 at all latitudes, while the GDOP will be reduced by 6.2% on average. Adding 7-QZSS and 11-NavIC to the four-GNSS-NG, 37.51 to 71.58 satellites are available on global scales. The average position DOP (PDOP), horizontal DOP (HDOP), vertical DOP (VDOP), and time DOP (TDOP) are reduced to 0.82, 0.46, 0.67 and 0.44, respectively.

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High-Accuracy Optical Frequency Atomic Clock

Physics and High Technology ◽

10.3938/phit.30.005 ◽

2021 ◽

Vol 30 (3) ◽

pp. 2-7

Author(s):

Myoung-Sun HEO ◽

Dai-Hyuk YU ◽

Won-Kyu LEE

Keyword(s):

Atomic Clock ◽

Satellite System ◽

High Accuracy ◽

Optical Frequency ◽

Atomic Clocks ◽

Navigation Satellite ◽

Fundamental Constants ◽

Quantum Metrology ◽

Order Of Magnitude ◽

Global Navigation Satellite

Frequencies have been the most accurately measured physical quantity since the second was defined in 1967 based on the microwave atomic transition of a Cs atom. Recently, atomic clocks using optical frequency transitions have shown an order of magnitude better accuracy than microwave clocks. Thanks to their high accuracy and resolution, atomic clocks have become a new tool for investigations involving fundamental science and technology, such as the search for dark matter, gravitational wave detection, the temporal variation of fundamental constants, relativistic geodesy, quantum metrology, and the advanced Global Navigation Satellite System (GNSS). In addition, a redefinition of the second based on the optical frequency is expected. In this paper, we review the principles and applications of optical clocks.

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Three-dimensional morphology of equatorial plasma bubbles deduced from measurements onboard CHAMP

Annales Geophysicae ◽

10.5194/angeo-33-129-2015 ◽

2015 ◽

Vol 33 (1) ◽

pp. 129-135 ◽

Cited By ~ 6

Author(s):

J. Park ◽

H. Lühr ◽

M. Noja

Keyword(s):

Three Dimensional ◽

Satellite System ◽

Low Earth Orbit ◽

Electron Content ◽

Total Electron ◽

Plasma Bubbles ◽

Equatorial Plasma Bubbles ◽

Global Navigation Satellite ◽

Plasma Depletion

Abstract. Total electron content (TEC) between Low-Earth-Orbit (LEO) satellites and the Global Navigation Satellite System (GNSS) satellites can be used to constrain the three-dimensional morphology of equatorial plasma bubbles (EPBs). In this study we investigate TEC measured onboard the Challenging Minisatellite Payload (CHAMP) from 2001 to 2005. We only use TEC data obtained when CHAMP passed through EPBs: that is, when in situ plasma density measurements at CHAMP altitude also show EPB signatures. The observed TEC gradient along the CHAMP track is strongest when the corresponding GNSS satellite is located equatorward and westward of CHAMP with elevation angles of about 40–60°. These elevation and azimuth angles are in agreement with the angles expected from the morphology of the plasma depletion shell proposed by Kil et al.(2009).

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