GLONASS Satellites Research Articles

Evolution of orbit and clock quality for real-time multi-GNSS solutions

High-quality satellite orbits and clocks are necessary for multi-GNSS precise point positioning and timing. In undifferenced GNSS solutions, the quality of orbit and clock products significantly influences the resulting position accuracy; therefore, for precise positioning in real time, the corrections for orbits and clocks are generated and distributed to users. In this research, we assess the quality and the availability of real-time CNES orbits and clocks for GPS, GLONASS, Galileo, and BeiDou-2 separated by satellite blocks and types, as well as the product quality changes over time. We calculate the signal-in-space ranging error (SISRE) as the main orbit and clock quality indicator. Moreover, we employ independent orbit validation based on satellite laser ranging. We found that the most accurate orbits are currently available for GPS. However, Galileo utmost stable atomic clocks compensate for systematic errors in Galileo orbits. As a result, the SISRE for Galileo is lower than that for GPS, equaling 1.6 and 2.3 cm for Galileo and GPS, respectively. The GLONASS satellites, despite the high quality of their orbits, are characterized by poor quality of clocks, and together with BeiDou-2 in medium and geosynchronous inclined orbits, are characterized by SISRE of 4–6 cm. BeiDou-2 in geostationary orbits is characterized by large orbital errors and the lowest availability of real-time orbit and clock corrections due to a large number of satellite maneuvers. The quality of GNSS orbit and clock corrections changes over time and depends on satellite type, block, orbit characteristics, onboard atomic clock, and the sun elevation above the orbital plane.

Alternative navigation systems use for satellite positioning in Russia

The article provides a comparative analysis of the joint application and accuracy of determining the locations by GLONASS, Galileo, BeiDou satellites, obtained from the navigation messages and available forecasting algorithms.Nowadays the high-precision satellite definitions are based not only on the two-frequency measurement mode use, but also on the information inclusion from various existing satellite systems in processing [1,2]. Practical experiments performed in 2016 at latitude B=47° and presented in [3], confirmed the advantages of the GPS and GLONASS satellite systems’ joint use. To date, alternative GNSSs have appeared - the European “Galileo” and the Chinese “BeiDou”, the capabilities’ studies of which are not given due attention to. Therefore, we will try to compare the location determination accuracy by GLONASS, Galileo, BeiDou satellites received by the navigation messages, by comparing them with the exact data provided by the International GNSS Service (IGS), as well as with the available GNSS prediction algorithms available on the satellite observation equipment manufacturer Trimble site.

Investigation of real-time carrier phase time transfer using current multi-constellations

Real-time precise point positioning (RTPPP) time transfer has grown up to be a research hotspot. With the operation of IGS real-time products, multi-GNSS RTPPP time transfer has become possible. In our work, CLK93 products are applied for RTPPP time transfer, and the availability and accuracy of real-time products is evaluated over a testing period of 31 days. Then, GPS, Galileo, GLONASS and multi-GNSS RTPPP time transfer are studied and analyzed by performing a 31-day processing with 28 time-links. The results show that the availability of GPS, GLONASS and Galileo are approximately 98%, 99% and 99%, respectively. The mean root mean square (RMS) values of Radial (R), Along (A) and Cross (C) direction for GPS, GLONASS and Galileo satellites are (0.025, 0.035, 0.027) m, (0.025, 0.073, 0.048) m and (0.029, 0.040, 0.035) m, respectively. The mean standard deviation (STD) values of GPS, GLONASS and Galileo satellites are (0.12, 0.38, 0.09) ns. Furthermore, Galileo RTPPP time transfer solutions perform better than GLONASS, and GPS RTPPP show performs best performance among the single-GNSS. Multi-GNSS RTPPP outperforms that of single-GNSS. The mean daily STD values of the difference between GPS, Galileo, GLONASS and multi-GNSS RTPPP solutions and IGS final products are (0.093, 0.103, 0.133, 0.083) ns, respectively. 15360 s stability is (3.87E−15, 4.56E−15, 8.61E−15, 3.73E−15) for GPS, Galileo, GLONASS and multi-GNSS RTPPP solutions at PT11-PTBB.

Multi-constellation GNSS interferometric reflectometry with mass-market sensors as a solution for soil moisture monitoring

Abstract. Per capita arable land is decreasing due to the rapidly increasing population, and fresh water is becoming scarce and more expensive. Therefore, farmers should continue to use technology and innovative solutions to improve efficiency, save input costs, and optimise environmental resources (such as water). In the case study presented in this paper, the Global Navigation Satellite System interferometric reflectometry (GNSS-IR) technique was used to monitor soil moisture during 66 d, from 3 December 2018 to 6 February 2019, in the installations of the Cajamar Centre of Experiences, Paiporta, Valencia, Spain. Two main objectives were pursued. The first was the extension of the technique to a multi-constellation solution using GPS, GLONASS, and GALILEO satellites, and the second was to test whether mass-market sensors could be used for this technique. Both objectives were achieved. At the same time that the GNSS observations were made, soil samples taken at 5 cm depth were used for soil moisture determination to establish a reference data set. Based on a comparison with that reference data set, all GNSS solutions, including the three constellations and the two sensors (geodetic and mass market), were highly correlated, with a correlation coefficient between 0.7 and 0.85.

The Research Into the Integrity Parameter in Air Transport Using GLONASS Data

Abstract The article presents the results of the integrity parameter of the GLONASS satellite positioning system in civil aviation. As a source material for the research the authors used observation and navigation data of the GLONASS system from the onboard GNSS receiver mounted on the Cessna 172. In the research, the authors used a model to determine the aircraft position based on the single-frequency SPP code method for GLONASS L1-C/A observations. The numerical calculations were conducted in the RTKLIB software, in the RTKPOST library. The obtained results are interesting from the point of using an application of the GLONASS system in aviation and the possible implementation of the single-frequency GLONASS code observations in the SPP model in order to determine the aircraft position. On the basis of the obtained results it was found that the GLONASS integrity performance data can be used in a procedure of non-precision approach to landing NPA GNSS.

Investigation of Inter-Frequency Signal Delays on Board Glonass Navigation Satellites

The problem of inter-frequency signal delays estimation of GLONASS system navigation satellites is considered. Such signal delays in the radio-frequency channel of navigation satellites are a source of instrumental error of pseudorange measuring. A method for estimating the inter-frequency signal delays is proposed, based on the calculation of the first differences of pseudorange measurements on navigation satellites, the relative angular position of which differs by no more than 1°. An experiment on estimating the inter-frequency signal delays based on the developed method was performed. The experiment is based on the use of calibrated navigation user equipment to separate errors caused by signal delays in the receiver and the navigation satellite. Furthermore, to minimize the influence of the Earth’s ionospheric layer, only those measurements that are obtained at a low value of the total electron content (TEC) are included in the processing. Pseudorange measurements from the signals of navigation satellites of the GLONASS and GPS systems were used as the initial data. The estimation results for all GLONASS orbit group satellites were compared with the form values provided as part of the navigation frame. The results of experimental studies were analyzed and the standard deviations of the delays of GLONASS orbit group were obtained. To confirm the adequacy of the results, the internal convergence of the results was verified and the error of the developed method for estimating the inter-frequency delays of navigation satellites was determined.

Technical and economic feasibility of the on-board location system application for the aircraft and satellite communication system

The paper considers the joint application of the Iridium satellite communications system as well as the GLONASS and GPS satellite navigation systems that corresponds to the CNS/ATM concept. The originality of the proposed detection method is in constant communication between an object and a control center. The method can be applied to both manned and unmanned aircrafts. In any case, a control center can quickly respond to deviations of the trajectory of an object, or to an operation of accelerometers at critical overloads. The paper examines the advantages of introducing the Iridium satellite radio navigation system into the aviation sector to monitor aircrafts in both manned and unmanned aircrafts. Technical and economic advantages are given on the example of various search and rescue operations.

Calculation of the Ephemeris and Clock Corrections of GLONASS and GPS Navigation Space Vehicles in Ultra-Rapid Regime on the Basis of Measurement Data

An algorithm and program for calculation in ultra-rapid regime of the ephemeris and time information of GLONASS and GPS navigation space vehicles are developed. The results presented here were obtained at the Main Metrological Center of the State Time and Frequency Service and Determination of the Parameters of the Earth’s Rotation at the All-Russia Research Institute of Physicotechnical and Radio Measurements (VNIIFTRI). Calculations of the ephemeris and time information are performed on the basis of the data of code and phase measurements at two carrier frequencies. The measurement data are presented in the form of hourly RINEX files of observations and files of navigation messages from tracking stations in the network of the IGS international service of global navigation satellite systems (International GNSS Service). Results of test calculations of the ephemeris and clock corrections of GLONASS and GPS navigation satellites in ultra-rapid regime are presented. An analysis of the precision of the results as compared to a posteriori (final) data from other data processing and analysis centers is presented.

Impact analysis of arc length in multi-GNSS ultra-rapid orbit determination based on the one-step method

With the development of near real-time and real-time high-precision global navigation satellite system (GNSS) applications, users’ requirements for the accuracy and stability of ultra-rapid orbits have increased, especially for multi-constellation orbits. Generally, several factors affect the accuracy and stability of multi-GNSS ultra-rapid orbit determination; however, this study is focused only on analyzing the orbit arc length of ultra-rapid orbits of the GPS, GLONASS, BeiDou-2, and Galileo satellites based on the one-step method. To realize nearly ideal conditions in the process of analysis, one full year’s rapid orbit products during 2018 provided by the GeoForschungsZentrum multi-GNSS experiment analysis center were used as fitted observed orbits and also as a reference orbit for comparison to the predicted orbit. In terms of residual analysis of orbit difference and stability analysis of Helmert transformation parameters, the numerical results showed that the optimal orbit arc lengths of quad-constellation medium earth orbit (MEO) satellites for 6 h and 3 h predicted ultra-rapid orbits based on the one-step method were in the range of 44–45 h and 41–44 h, respectively. Overall, for both 6 h and 3 h predictions, when only considering the impact of the orbit arc length on the accuracy and stability of the orbit itself, 44 h can be considered as the overlapping optimal orbit arc length of quad-constellation MEO satellitesʼ ultra-rapid orbits generated by the one-step method. In addition, these ranges of orbit arc length can contribute to the multi-GNSS ultra-rapid orbit determination.

Total Electron Content Measurements in the Ionosphere Disturbed by High-Power High-Frequency Waves by the Methods of Incoherent Scattering of Radio Waves and Radio Sounding by Glonass Satellite Signal

We present the results of comparing the total electron content measurements based on GLONASS satellite signals and the EISCAT UHF incoherent scatter radar (Tromso, Norway) during modification of the high-latitude ionosphere in the magnetic zenith direction by high-frequency radio waves of the EISCAT/Heating facility (Tromso, Norway). The measurements were performed during two experiment campaigns in October 2013 and in October 2018. In general, the total electron content variations obtained from the radar data in the altitude range 100–400 km were consistent with the total electron content variations from the GLONASS satellites. The efficiency of using GLONASS satellites for observations of high-latitude phenomena was shown. The anomalous increase in the total electron content by 4 TECU obtained from the incoherent scatter radar when the ionosphere was heated in the region close to the magnetic zenith is considered. The GLONASS satellite data show the total electron content reduction in the same region. To explain the disagreement between measurements by these two methods, the effect of smallscale electron-density irregularities arising in the region modified by high-power HF radio waves is considered. It is shown that when the electron density in artificial irregularities exceeds the background density of the medium by 2 ・ 10−3 times in relative units, scattering by irregularities with spatial scales of the order of 16 cm becomes predominant in the reflected signal.

Estimating the Adequate Observation Times of a Single GNSS Receiver by Utilizing Online Processing Services

Global Navigation Satellite Systems (GNSS) have witnessed rapid developments in the field of online post-processing services and the abundance of continuously operating reference stations (CORS), which reflected on facilitating the tasks of surveyors, engineers and geoscientists. However, the sufficient time for observations to achieve a certain level of accuracy is still one of the main concerns for researchers and specialists. In this study, the geometry of a short-sides triangle has been employed to estimate the sufficient observing times of GNSS receivers throughout the online processing services. The short-sides triangle vertices were observed for 24 hours and partitioned into shorter periods of time, then GPS and GLONASS have been processed as well as GPS alone after filtering out the GLONASS observables. Datasets have been processed using online post-processing services, i.e. AUSPOS and CSRS-PPP. A number of propagation error models have been applied to investigate the station accuracy behaviour. the results have revealed that RMS errors of 1 cm can be achieved after two hours for horizontal component and three hours for the vertical component. Furthermore, including GLONASS satellites is playing a role to enhance accuracy especially in short observation times.

Estimation of precise orbits and clock corrections of GLONASS and GPS navigation satellites in ultra-rapid regime based on observation data

The article presents the results on development of an algorithm and a program for calculation in ultra-rapid regime of ephemeris-time information for GLONASS and GPS navigation satellites, achieved by now in the Main metrological center of the state service of time and frequency and determination of earth rotation parameters of VNIIFTRI. Calculation of ephemeris-time information is carried out by data of code and phase measurements at two carrier frequencies. The measurement data are presented in the form of hourly RINEX observation files and navigation message files from tracking stations involved in the IGS (International GNSS Service) network. Results of test calculations of ephemeris and clock corrections of GLONASS and GPS navigation satellites are presented. The analysis of the accuracy of the obtained results compared to the aposteriori data of other analysis centers is given.

Analysis of noise immunity of GLONASS and GPS positioning receivers

The article describes the method of comparative analysis of noise immunity of GLONASS and GPS satellite positioning receivers based on a broadband noise oscillator which allows us to compare multivendor positioning receivers on a real-time basis. Besides, the suggested method enables to assess the capacity of a robust positioning signal produced by GLONASS and GPS systems to resist the noise. The method is charecterized by the clarity of obtained results and allows to choose products of the best quality among the commercially available models of positioning receivers.

A Study Interfrequency Onboard Delays of Signals Navigation Satellites GLONASS

The problem of interfrequency signal delays estimation of GLONASS system navigation satellite is considered Such delays in the radio-frequency massage of navigation satellites are the source of the instrumental error of pseudorange measurements. The estimation method of interfrequency signal delays is proposed, based on the calculation of first differences of pseudorange measurements on navigation satellites, the relative position of which differs by no more than 1°. The experiment on estimation of inter-frequency delays signal on the basis of the developed method was conducted. The experiment is based on the use of calibrated navigation receiver to separate errors caused by signal delays in the receiver and navigation satellite. Also, to minimize the effects of the Earth's ionosphere layer navigation signal delay, only those measurements taken at a low Total Electronic Concentration TEC are included in the processing. Pseudorange measurements using GLONASS and GPS navigation satellites signals were used as the main source data. The results of the estimation for all GLONASS orbital group satellites were compared with the form values provided in the navigation massage. The results of experimental research have been analyzed and the values of standard deviation of GLONASS orbital group delays have been obtained. To confirm the adequacy of the results was checked for internal convergence of the results and determined the error of the developed method for assessing the interfrequency delays of navigation spacecraft.

Real-Time Estimation and Calibration of GLONASS Inter-Frequency Phase and Code Bias

The frequency division multiple access (FDMA) strategy used in GLONASS causes inter-frequency phase bias (IFPB) and inter-frequency code bias (IFCB) between receivers from different manufacturers. The existence of IFPB and IFCB significantly increases the difficulties of fixing GLONASS ambiguity and limits the accuracy and reliability of GLONASS positioning. Moreover, the initial value of IFPB and IFCB may be unavailable or unreliable with the increasing number of receivers from different manufacturers in recent years. In this study, a real-time and reliable calibration algorithm of IFPB and IFCB based on multi-GNSS assistance is proposed by providing a fixed solution. Real-time IFPB rate and IFCB can be obtained using this algorithm without the initial IFPB and IFCB. The IFPB rate for all GLONASS satellites and IFCB for each GLONASS satellite are estimated due to different characteristics of IFPB and IFCB. IFPB calibration can be divided into constant and real-time IFPB calibrations to meet the different positioning requirements. Results show that constant IFPB rate has only 2 mm difference from the mean value of real-time IFPB rate. The IFPB rate and IFCB estimated by this algorithm have excellent stability, and the change in reference satellite cannot affect the results of IFPB rate and the stability of IFCB. The centimetre-level positioning results can be obtained using two calibration methods, and the positioning results with real-time calibration method are 10%–20% better than those with the constant calibration method. Under satellite-deprived environments, the improvements of multi-GNSS positioning accuracy with constant inter-frequency bias calibration gradually increase as the satellite cut-off elevation angle increases compared with GPS/BDS, which can reach up to 0·9 cm in the vertical direction.

Low Computational Complexity in Low-Cost GNSS Receivers

One of the key issues in low-cost GNSS receivers is the computational complexity. One of the computational components of the GNSS receivers is the satellite positioning calculations. The main focus of this paper is to reduce the computational burden of this stage of processing. In this paper, four different models to fit the GPS and GLONASS satellites orbit are investigated. These models are compared with each other in terms of their computational load and accuracy, and the models have good accuracy and less computational load are selected. Among these four methods, the Hermite model and the Chebyshev model are superior to other methods for determining orbits of GPS and GLONASS satellites, respectively. In order to evaluate the performance of these models, two different data including ground stations data and measured data by GNSS receivers are used. The results show that these two models can improve the computational burden by about 90% compared to conventional methods like the Runge–Kutta and the Keplerian parameters that used in GNSS receivers.

Simulation of Navigation Receiver for Ultra-Small Satellite

Currently, ultra-small satellite aresubjectstostringentrequirementsintermsoftheaccuracyof determining the position of the satellite in orbit, while the satellite is the subject to restrictions on mass, size and power consumption. The aim of this work is to simulate of navigation receiver operation for the ultra-small satellite with restrictions on energy consumption and computational resources.The operating conditions are considered and the requirements to the onboard navigation receiver for the ultra-small satellite are determined. The navigation receiver operation at the initial stage, performance testing, error detection, analysis of the reliability of the solution of the navigation-time determination problem are described.The structure of the design ballistics problems for orbit prediction of ultra-small spacecraft and navigation satellites, radio visibility intervals for GLONASS and GPS systems, parameters of navigation signals have been developed.The motion relative to the satellite systems GPS and GLONASS for a preliminary orbit of СubeBel-1 have been simulated. The Doppler dynamics of the GPS satellite signals in the receiver without restrictions on the relative speed for one day has been calculated. Radio visibility intervals for GPS and GLONASS satellites were calculated and optimal conditions for the cold start of the navigation receiver with a relative speed limit (Vr < 500 m/s) for 1 hour of operation both in separate and in joint operation on both systems were determined.To test the verification methods of the experimental data of the СubeBel-1 satellite, the operation of the navigation receiver of the Nsight satellite was studied according to the received telemetry from the beginning of its flight until the moment it entered stable operation.It is shown that the telemetry data of the navigation receiver at the testing stage had a significant error. After software correction, the navigation receiver worked steadily throughout the week of observation, the error of longitude and latitude measurements did not exceed 0.2 degrees.

Galileo and GLONASS group delay variations

Similar to the antenna phase center corrections for phase measurements, group delay variations (GDV) of satellite and receiving GNSS antennas affect code pseudorange measurements. They are frequency-dependent and vary with the direction of signal transmission and reception. We present the first GDV estimates for all five Galileo and three GLONASS frequency bands based on terrestrial observations. As compared to GPS, the orbit properties of Galileo and GLONASS simplify this approach, because a single reference station can observe each Galileo and GLONASS satellite in its entire elevation angle range during one orbit repeat period. The homogenous results of three receiver antenna models for identical satellite types and a comparison to GPS Block IIF indicate mainly receiver antenna-specific GDV. They amount to 35 and 28 cm peak-to-peak for Galileo and GLONASS frequency bands E1 and G1, respectively, depending on the receiver antenna type. We show their effect on linear combinations where the code observable is used for precise applications and validate our GDV estimations by improving the height component in single-frequency precise point positioning.

EDAS (EGNOS Data Access Service) Differential GNSS Corrections: A Reliable Free-of-Charge Alternative for Precision Farming in Europe

Abstract EDAS (EGNOS Data Access Service) is the EGNOS internet broadcast service, which provides free of charge access to the data collected and generated by the EGNOS infrastructure. EDAS disseminates over the Internet, both in real time and via an FTP archive, the raw data of the GPS, GLONASS (no commitment on GLONASS data is provided (1)) and EGNOS GEO satellites collected by the receivers located at the EGNOS reference stations, which are mainly distributed over Europe and North Africa. The EDAS services offer several types of GNSS data in various protocols and formats, such as DGNSS corrections. This paper reports on the results of some in-field tests conducted by ESSP and Topcon Agriculture to confirm the suitability of EDAS DGNSS corrections for precision farming in Europe. The European Commission (EC) is the owner of EGNOS system (including EDAS) and has delegated the exploitation of EGNOS to the European GNSS Agency (GSA). EDAS service provision is performed by ESSP, as EGNOS Services Provider, under contract with the GSA, the EGNOS program manager. In the ENC 2018 article “EDAS (EGNOS Data Access Service): Differential GPS corrections performance test with state-of-the-art precision agriculture system”, ESSP and Topcon Agriculture presented the results of the first in-field test conducted in a dynamic and real-life environment in the summer of 2017. The test results indicated that the EDAS DGNSS corrections could enable a reliable pass-to-pass accuracy performance for a wide range of precision agriculture applications and become an attractive solution for cereal farms, when the farm is located in the vicinity of an EGNOS reference station. In particular, Topcon Agriculture acknowledged that the observed performance was sufficient to support the following precision agriculture applications: spraying and spreading of any crop type, tilling and harvesting of cereal. Then, ESSP and Topcon Agriculture engaged in additional testing activities to further characterise the EDAS DGPS performance in different scenarios (i.e. at various European locations and with a variety of distances between the designated farm and the target EGNOS reference station). In each test, multiple runs with the rover tractors have been performed over the reference patterns predefined in the Topcon guidance systems. Data recorded during the tests has been analysed in detail, looking at the key performance indicators (e.g. cross track error and pass-to-pass performance) that characterize the EDAS DGPS performance for precision agriculture applications. Different techniques for the computation of the pass-to-pass accuracy performance have been used, including a procedure to measure live in the field and a post-processing alternative. The diversity of scenarios available allows drawing conclusions on the applicability of EDAS DGPS corrections (in terms of maximum distance from the target EGNOS station) for precision agriculture and also understanding the impact of operationally relevant aspects such as the quality of the mobile internet coverage (highly variable across Europe). The EDAS system and its architecture, the main types of data disseminated through EDAS services and the online information available to the EDAS users are introduced in this paper. In particular, the EDAS Ntrip service is described in detail, since it provides the differential corrections to the GPS and GLONASS satellites at the EGNOS reference stations in RTCM format, which are the basis for the present study. The article also reports on the results of the latest tests, which have been performed using Topcon receivers, vehicles and auto-steering systems. In all cases, two different Topcon guidance systems on board tractors were running simultaneously to assess the EDAS DGPS positioning performance with respect to a the reference provided by a top-performing RTK-based Topcon solution. The objective of this paper is to draw conclusions on the use of EDAS DGPS corrections as a reliable free-of-charge alternative for precision farming in Europe (especially for cereal farms), based on the available performance results from the testing campaign and the feedback from the involved precision agriculture experts.

Combined precise orbit determination of GPS and GLONASS with ambiguity resolution

Precise orbit products of Global Navigation Satellite Systems (GNSS) are an essential precondition for precise positioning. Ambiguity resolution (AR) can enhance the orbit accuracy in precise orbit determination (POD). To improve the quality of orbits, we propose a method of combined POD for GPS and GLONASS with AR. Firstly, GLONASS wide-lane and narrow-lane fractional cycle biases (FCBs) are daily estimated. Then, by applying the estimated FCBs, GLONASS and GPS double-differenced wide-lane and narrow-lane ambiguities are successfully resolved, even for the baselines of up to several thousand kilometers. Finally, the ambiguity-resolved solutions are achieved by introducing the constraints of the resolved ambiguities into the real-valued solutions. To prove the contribution of the AR to GPS and GLONASS POD, a network including 141 sites is processed over 2018. The results show that the receiver types and firmware versions seriously affect the stability of the daily wide-lane FCBs. The fluctuation of the inter-system biases between two adjacent days is obviously larger than a half narrow-lane wavelength, causing an irregular change of the daily narrow-lane FCBs. After FCB calibration, the success rate of GLONASS can reach up to 90% over the whole year, which is at the same level compared with that of GPS. The improvements of GLONASS and GPS orbits after AR are confirmed by the orbit comparison with the International GNSS Service final products, the orbit misclosures at day boundaries and satellite laser ranging residuals. Due to some other issues, such as the GLONASS frequency-division multiple access and the high noise of observations, the improvement of GLONASS orbit is still less obvious than that of GPS orbit.