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Abstract The optimal design of Global Navigation Satellite System (GNSS) software receivers should enable the accurate estimation of the receiver's position, velocity, and time under various environmental conditions. The software receivers consist of three sections: acquisition, tracking, and navigation. This paper specifically centers on the acquisition sections of the Global Positioning System (GPS), Global Navigation Satellite System (GLONASS), BeiDou, and Galileo satellite navigation systems. The acquisition stage necessitates the prompt and precise transmission of the satellite list within the receiver's view, along with Doppler frequency estimation and phase code offset, to facilitate a seamless transition to the tracking stage with the utmost speed and accuracy. Conventional acquisition demonstrates commendable speed, but lacks accuracy, especially in environments with a low Carrier-to-Noise Ratio (CNR). Contrastingly, precise acquisition methods will impede the speed of the acquisition stage. In this paper, a novel acquisition method is proposed. By integrating concepts like resampling, two-stage acquisition, and fine-acquisition, this method enables the attainment of higher accuracy without compromising speed. The results demonstrate that the proposed method enhances accuracy by 7.275% compared to conventional methods and boosts speed by 76.97% compared to methods focused on accuracy improvement.

The optimal design of Global Navigation Satellite System (GNSS) software receivers should enable the accurate estimation of the receiver's position, velocity, and time under various environmental conditions. The software receivers consist of three sections: acquisition, tracking, and navigation. This paper specifically centers on the acquisition sections of the Global Positioning System (GPS), Global Navigation Satellite System (GLONASS), BeiDou, and Galileo satellite navigation systems. The acquisition stage necessitates the prompt and precise transmission of the satellite list within the receiver's view, along with Doppler frequency estimation and phase code offset, to facilitate a seamless transition to the tracking stage with the utmost speed and accuracy. Conventional acquisition demonstrates commendable speed, but lacks accuracy, especially in environments with a low Carrier-to-Noise Ratio (CNR). Contrastingly, precise acquisition methods will impede the speed of the acquisition stage. In this paper, a novel acquisition method is proposed. By integrating concepts like resampling, two-stage acquisition, and fine-acquisition, this method enables the attainment of higher accuracy without compromising speed. The results demonstrate that the proposed method enhances accuracy by 7.275% compared to conventional methods and boosts speed by 76.97% compared to methods focused on accuracy improvement. [ABSTRACT FROM AUTHOR]

• Significant ionospheric disturbances during the 2021 Typhoon Chanthu were observed by GPS and GLONASS. • The ionospheric disturbances following the Typhoon are accompanied and propagated with the "N"-type wave. • The propagation velocity and center frequency of ionospheric disturbances are within the range of gravity waves. Severe typhoons often result in substantial economic and human losses. Therefore, near-real-time monitoring and forecasting of severe typhoons have a significant importance. In this paper, characteristics of ionospheric disturbances during the 2021 Typhoon Chanthu are estimated and investigated from GPS and GLONASS measurements. We calculate high-precision de-trended and filtered ionospheric vertical total electron content (VTEC) data based on GPS and GLONASS data from intensive Global Navigation Satellite System (GNSS) observations at 30-second intervals in Taiwan. Based on the VTEC values, we analyze the characteristics of ionospheric disturbances caused by Typhoon Chanthu, such as the time of appearance of ionospheric disturbances, changes in the magnitude of these disturbances, alterations in two-dimensional disturbances, fluctuations in the speed of disturbance propagation, and shifts in the frequency spectrum. The results reveal that both GPS-TEC and GLONASS-TEC exhibit noticeable disturbances during the specified timeframe. These disturbances are accompanied by the occurrence of "N"-type anomalies in TEC. Notably, at the occurrence of the disturbance, the elevation angle of GPS PRN32 and GLONASS PRN1 satellites is approximately 50°-55°, and their respective distances from the typhoon eye are roughly 350 km and 150 km. The propagation velocity and center frequency of the ionospheric disturbances are located in the range of gravity waves. Specifically, the disturbances propagation speeds of GPS PRN32 and GLONASS PRN1 are approximately 129.36 m/s and 128.33 m/s, respectively, while the center frequencies are about 1.17 mHz and 1.43 mHz. The ionospheric perturbations observed by GPS and GLONASS exhibit certain similarities, which provide valuable insights into the relationship between typhoons and ionospheric disturbances. [ABSTRACT FROM AUTHOR]

K2 is a new generation of GLONASS satellites that provides code division multiple access (CDMA) signals in the L1, L2 and L3 frequency bands in addition to legacy L1 and L2 signals based on frequency division multiple access (FDMA) modulation. The first GLONASS-K2 satellite was launched in August 2023 and started signal transmission in early September 2023. Based on measurements with a 30-m high-gain antenna, spectral characteristics of the various signal components are described and relative power levels are identified. A 3 dB (L1) to 4 dB (L2) higher total power is determined for the CDMA signal compared to the legacy FDMA signal and an equal power of the open service and secured CDMA signal components is found. The ranging code of the L2 channel for service information, which has not been publicly disclosed so far, is identified as a Gold code sequence consistent with the data channel of the L1 open service CDMA signal. The high-gain antenna measurements are complemented by tracking data from terrestrial receivers that enable a first assessment of user performance. An up to 50% improvement in terms of noise and multipath performance is demonstrated for the new L1 and L2 CDMA signals in comparison with their legacy counterpart, but no obvious differences between the different binary phase-shift keying and binary offset carrier modulations of the data and pilot components of these signals could be identified for the test stations. Triple-frequency carrier phase observations from L1, L2, and L3 CDMA signals exhibit good consistency at the noise and multipath level, except for small variations that can be attributed to slightly different antenna phase patterns on the individual frequencies. Overall, the new CDMA signals are expected to notably improve and facilitate precise point positioning applications once fully deployed across the GLONASS constellation. [ABSTRACT FROM AUTHOR]

Against the background of the intensive development and implementation of satellite technologies for position determination, navigation, and time synchronization, one of the central threats to critical industries is the creation of intentional interference to the signals of global navigation satellite systems. It is shown that the use of small-sized antenna arrays in navigation systems consisting of satellite constellations of GPS, GLONASS, GALILEO, BEIDOU, QZSS, or their combinations makes it possible to detect and suppress interfering signals by forming zeros of the antenna array directional pattern in the directions of their arrival. The interfering signal suppression is supplemented with detection procedures while maintaining the ability of navigation by using from one to four satellite systems according to criteria of the required number of satellites in the line of sight and the permissible geometric factor. The process of suppressing the interfering signal from four directions is illustrated by three scenarios, the initial data for which are signals from 35 satellites in the line of sight collected in real-time from five systems. It has been shown that the use of five systems and 35 satellites ensures the suppression of the interfering signal. At the same time, 22 satellites are involved in solving the navigation problem, 13 satellites are below the detection threshold, and the geometric factor is 1.18. When using GPS, GLONASS, and 19 satellites, the interfering signal is suppressed. In this case, 10 satellites are involved in solving the navigation problem, 9 are below the detection threshold, and the geometric factor is 2.1. When using only GPS, the interfering signal suppression is also ensured. This time 7 satellites are involved in solving the navigation problem, 4 are below the detection threshold, and the geometric factor is 1.76. [ABSTRACT FROM AUTHOR]

The task of improving the GLONASS characteristics in the context of the modern competitive development of global satellite navigation systems is considered. The authors consider research and development related, firstly, to improving the signal-in-space ratio indicator in the operational mode by creating new technological cycles onboard a spacecraft (SC) and involving onboard hardware in these processes; and, secondly, with the formation of a reserve with the subsequent implementation of the functionality of orbital groupings (OGs) without downloading the ephemeris-temporal information and time-frequency corrections from the ground control complex. This article considers the main factors hindering the implementation of the currently set goals and also suggests ways to eliminate or compensate the influence of these factors by developing and implementing special information technologies using modern and promising onboard hardware placed onboard a GLONASS SC and its potential additions. [ABSTRACT FROM AUTHOR]

Introduction: Sports Global Navigation Satellite Systems' receivers have been providing athletes, coaches, and scientists with valuable information on movement for over two decades. As these receivers are specific measuring instruments, there is a need to determine their accuracy. This paper presents a relatively simple methodology for assessing sports receivers of this type regarding their elevation determination. Material and methods: The methodology was based on the Digital Terrain Model of Poland, a discrete representation of the topographic elevation of the land surface. Three wearable devices from different years of manufacture were selected for the preliminary study by calculating the Root Mean Square (RMS), mean elevation error, and Total Elevation Gain (TEG) measures. The testing was conducted on two sections of varying length and elevation differences. Results: During the first trial, an instrument from 2019 came closest to the actual elevation (RMS = 7.0 m; mean error = -6.5 m), while during the second trial, it was an instrument from 2014 (2.5, -1.6 m, respectively). All the receivers overestimated the TEG factor during both trials. Conclusions: The applied methodology allowed the receivers to be distinguished. Due to the preliminary, pilot nature of the study, it is subject to certain limitations and recommendations listed at the end of the article. [ABSTRACT FROM AUTHOR]

This research delves into Global Navigation Satellite Systems (GNSS) positioning accuracy, focusing on GPS, GLONASS, and their combined utility to evaluate GLONASS as an independent system in case GPS is down. The study spans three phases. First, data from stations located in Port Said, analyzed using relative positioning technique, GPS shows an average coordinate deviation of 0.32 millimeters for GPS-only scenarios, while GLONASS exhibits 1.045 millimeters for GLONASS-only scenarios. Merging both narrows this gap, especially in shorter baselines. Second, an extensive dataset over three years from eight Egyptian stations, using GPS and GLONASS as references, shows that GPS consistently provides better three-dimensional accuracy in most stations with close values. Finally, employing Precise Point Positioning (PPP) techniques, the study rigorously compares three processing software solutions (PPPH, PPP-ARISEN, PRIDE-PPPAR) with the same dataset. PRIDE-PPPAR closely aligns with BERNESE software accuracy, followed by PPP-ARISEN and PPPH. These findings suggest that GLONASS alone can be used for many applications, and open-source PPP software can be employed with acceptable accuracy.

An analysis is performed of the growth of scintillations of GLONASS and GPS satellite signals using the Septentrio GNSS receiver installed in the city of Apatity during a strong magnetic storm on March 23–24, 2023. Data from the ionosonde at the Lovozero station and data from the EISCAT radar in Tromsø are used to show that the growth of phase scintillations is due to an increase of the plasma density mainly in the E-layer of the ionosphere. The growth of phase scintillations is accompanied by the appearance of discrete aurora. [ABSTRACT FROM AUTHOR]

Velocity estimation has a key role in several applications; for instance, velocity estimation in navigation or in mobile mapping systems and GNSSs is currently a common way to achieve reliable and accurate velocity. Two approaches are mainly used to obtain velocity based on GNSS measurements, i.e., Doppler observations and carrier phases differenced in time (that is, TDCP). In a benign environment, Doppler-based velocity can be estimated accurately to within a few cm/s, while TDCP-based velocity can be estimated accurately to within a few mm/s. On the other hand, the TDCP technique is more prone to availability shortage and the presence of blunders. In this work, the two mentioned approaches are tested, using three devices of different grades: a high-grade geodetic receiver, a high-sensitivity receiver, and a GNSS chip mounted on a smartphone. The measurements of geodetic receivers are inherently cleaner, providing an accurate solution, while the remaining two receivers provide worse results. The case of smartphone GNSS chips can be particularly critical owing to the equipped antenna, which makes the measurements noisy and largely affected by blunders. The GNSSs are considered separately in order to assess the performance of the single systems. The analysis carried out in this research confirms the previous considerations about receiver grades and processing techniques. Additionally, the obtained results highlight the necessity of adopting a diagnostic approach to the measurements, such as RAIM-FDE, especially for low-grade receivers. [ABSTRACT FROM AUTHOR]

For users of Precise Point Positioning (PPP), Multi-GNSS Advanced Orbit and Clock Augmentation PPP signals provide corrective data. When using the PPP approach and/or PPP-Ambiguity Resolution (AR) method, the QZSS signal provides globally applicable error corrections on satellite orbit, clock offset, and code/phase biases. In addition, from FY2024, as a part of the MADOCA-PPP technology demonstration, wide-area ionospheric correction data will be provided for the Asia-Oceania region. A software estimator of precise satellite information developed by JAXA, Multi-GNSS Advanced Demonstration Tool for Orbit and Clock Analysis (MADOCA), allows u-blox CO99-ZED-F9P and MSJ 3008-GM4-QZS utilizing MADOCA-PPP to be used in GNSS applications that need sub-decimetre precision but don't have to be expensive. Errors caused by positioning satellites are computed by using observation data from domestic and overseas GNSS monitoring station networks such as IGS and MIRAI, and obtained correction data is transmitted from QZSS signal to provide highly precise positioning augmentation services that can be used in the Asia-Oceania Region. Users may utilize the PPP technique for high-precision locating by employing a GNSS receiver that supports the QZSS signals. This paper describes an experiment carried out with the static method to combine GPS, GLONASS, and QZSS signals in the project site (ISHI, USUD and MIZU stations in Japan). This paper examines the GPS/GLONASS/QZSS obtainable accuracy. These obtained results indicate that integrating GPS system with GLONASS and QZSS is favoured for surveying applications. It appears that integrating GPS/GLONASS/QZSS (MADOCA precise ephemeris file) static measurements in the study area between 0-4 millimetres accuracy can be guaranteed on all occasions. [ABSTRACT FROM AUTHOR]

Since the first receiver independent exchange format (RINEX) version was released in 1989, it has gone through several versions, making the existing software, such as TEQC, incompatible with certain later versions. This study proposes a new Python package named PyRINEX, which is developed to batch process the most generally used versions of RINEX files, namely 2.0 and 3.0. The proposed package can be used to manage and edit numerous RINEX files as well as perform a data quality check function. PyRINEX can be easily imported into any Python IDE similar to any other open-source Python package, it also makes secondary development easy for users. [ABSTRACT FROM AUTHOR]

Introduction: Sports Global Navigation Satellite Systems’ receivers have been providing athletes, coaches, and scientists with valuable information on movement for over two decades. As these receivers are specific measuring instruments, there is a need to determine their accuracy. This paper presents a relatively simple methodology for assessing sports receivers of this type regarding their elevation determination. Material and methods: The methodology was based on the Digital Terrain Model of Poland, a discrete representation of the topographic elevation of the land surface. Three wearable devices from different years of manufacture were selected for the preliminary study by calculating the Root Mean Square (RMS), mean elevation error, and Total Elevation Gain (TEG) measures. The testing was conducted on two sections of varying length and elevation differences. Results: During the first trial, an instrument from 2019 came closest to the actual elevation (RMS = 7.0 m; mean error = -6.5 m), while during the second trial, it was an instrument from 2014 (2.5, -1.6 m, respectively). All the receivers overestimated the TEG factor during both trials. Conclusions: The applied methodology allowed the receivers to be distinguished. Due to the preliminary, pilot nature of the study, it is subject to certain limitations and recommendations listed at the end of the article.

For users of Precise Point Positioning (PPP), Multi-GNSS Advanced Orbit and Clock Augmentation PPP signals provide corrective data. When using the PPP approach and/or PPP-Ambiguity Resolution (AR) method, the QZSS signal provides globally applicable error corrections on satellite orbit, clock offset, and code/phase biases. In addition, from FY2024, as a part of the MADOCA-PPP technology demonstration, wide-area ionospheric correction data will be provided for the Asia-Oceania region. A software estimator of precise satellite information developed by JAXA, Multi-GNSS Advanced Demonstration Tool for Orbit and Clock Analysis (MADOCA), allows u-blox CO99-ZED-F9P and MSJ 3008-GM4-QZS utilizing MADOCA-PPP to be used in GNSS applications that need sub-decimetre precision but don’t have to be expensive. Errors caused by positioning satellites are computed by using observation data from domestic and overseas GNSS monitoring station networks such as IGS and MIRAI, and obtained correction data is transmitted from QZSS signal to provide highly precise positioning augmentation services that can be used in the Asia-Oceania Region. Users may utilize the PPP technique for high-precision locating by employing a GNSS receiver that supports the QZSS signals. This paper describes an experiment carried out with the static method to combine GPS, GLONASS, and QZSS signals in the project site (ISHI, USUD and MIZU stations in Japan). This paper examines the GPS/GLONASS/QZSS obtainable accuracy. These obtained results indicate that integrating GPS system with GLONASS and QZSS is favoured for surveying applications. It appears that integrating GPS/GLONASS/QZSS (MADOCA precise ephemeris file) static measurements in the study area between 0–4 millimetres accuracy can be guaranteed on all occasions.

We have compared effects of geomagnetic disturbances during magnetic storms of various types (CME and CIR) and during an isolated substorm on scintillations of GLONASS and GPS signals, using a Septentrio PolaRx5 receiver installed in Apatity (Murmansk Region, Russia). We analyze observational data for 2021. The magnetic storms of November 3–4, 2021 and October 11–12, 2021 are examined in detail. The November 3–4, 2021 magnetic storm was one of the most powerful in recent years. The analysis shows that the scintillation phase index reaches its highest values during nighttime and evening substorms (σϕ≈1.5–1.8), accompanied by a negative bay in the magnetic field. During magnetic storms, positive bays in the magnetic field, associated with an increase in the eastward electrojet, lead, however, to quite comparable values of the phase scintillation index. An increase in phase scintillations during nighttime and evening disturbances correlates with an increase in the intensity of ULF waves (Pi3/Pc5 pulsations) and with the appearance of aurora arcs. This confirms the important role of ULF waves in forming the auroral arc and in developing ionospheric irregularities. The predominance of the green line in the spectrum of auroras indicates the contribution of disturbances in the ionospheric E layer to the scintillation increase. Pulsating auroras, associated with ionospheric disturbances in the D layer, do not lead to a noticeable increase in phase scintillations. Analysis of ionospheric critical frequencies according to ionosonde data from the Lovozero Hydrometeorological Station indicates the contribution of the sporadic Es layer of the ionosphere to jumps in phase scintillations. The difference between phase scintillation values on GLONASS and GPS satellites during individual disturbances can be as great as 1.5 times, which may be due to different orbits of the satellites. At the same time, the level of GLONASS/GPS scintillations at the L2 frequency is higher than at the L1 frequency. We did not find an increase in the amplitude index of scintillations during the events considered.

The paper presents the results of a study showing the accuracy of the determination of aircraft position coordinates based on the SPP (Single Point Positioning) solution in the GLONASS (Globalnaja Navigatsionnaya Sputnikovaya Sistema) system. For this purpose, the paper develops and implements an algorithm for the correction of position errors as parameters describing positioning accuracy. The proposed algorithm uses position error values determined for a single GNSS (Global Navigation Satellite Systems) receiver, which are joined in a linear combination to determine the positioning accuracy of the aircraft. The algorithm uses linear coefficients as an inverse function of the number of GLONASS satellites being tracked by the GNSS receiver. The developed algorithm was tested for GLONASS satellite data recorded by Topcon HiPer Pro and Javad Alpha geodetic receivers, during a flight test carried out with a Cessna 172 aircraft around the military airport in Dęblin. Navigation calculations were carried out using RTKLIB v.2.4.3 and Scilab v.6.0.0 software. On the basis of the tests carried out, it was found that for single Topcon HiPer Pro and Javad Alpha receivers, position errors were up to ±11.4 m. However, by using the position error correction algorithm for both receivers, GLONASS positioning accuracy is up to ±3.6 m. The developed algorithm reduces position errors by 60-80% for all BLh (B- Latitude, L- Longitude, h- ellipsoidal height) coordinates. The paper shows the possibility of testing and implementing the proposed mathematical algorithm for the SPP solution in a GPS (Global Positioning System) navigation system. In this case the position errors from the GPS SPP solution range from -0.9 m to +0.9 m for all BLh coordinates. The obtained results showed that application the GLONASS and GPS system in air transport is important. The algorithm used in this work can also be applied to other global GNSS navigation systems (e.g. Galileo (European Navigation Satellite system) or BeiDou (Chinese Navigation Satellite System)) in air transport and navigation.

The popularity of sports and recreational receivers of the global navigation satellite systems is steadily increasing and provides athletes, coaches, and scientists with a wealth of information on movement occurring both horizontally and vertically. Under mountainous conditions, considering the effort put in by the athlete as well as their safety, the elevation parameter appears to be particularly relevant. The aim of the study was to propose a methodology for assessing sports receivers in terms of their determination of the elevation component based on digital elevation models while paying attention to the appropriate measures for testing these devices. The methodology was applied for wrist-worn global navigation satellite systems' receivers used by the participants of an uphill running event. In terms of elevation determination, the most accurate three receivers (same model) were those supported by the barometric altimeter, in which the Root Mean Square result obtained ranged from 3.6 to 4.1 m. The majority of receivers underestimated the total elevation gain, the mean value of which was −3.8%, which does not appear to be affected by the reception of two global navigation satellite systems or the use of a barometric altimeter. The error characteristics were common within the group of receivers of a particular manufacturer. [ABSTRACT FROM AUTHOR]

GNSS is used to determine the point positions on the earth with high accuracy. The accuracy that can be achieved with GNSS depends on the satellite system, processing software, logging interval, observation time, etc. varies depending on the effects. In the study, the impact of the Aegean Sea Earthquake that occurred on November 30, 2020, on TUSAGA was investigated. For this purpose, 7 TUSAGA stations located in the earthquake-affected area were selected. The 24-hour RINEX data for these stations were obtained both 15 days before and after the earthquake. The 24-hour RINEX data of 7 TUSAGA were processed using the GAMIT/GLOBK, based on 14 IGS stations. Furthermore, the evaluations were repeated by dividing the 24-hour RINEX data into 2, 4, and 12-hour intervals. In the evaluation, the GPS+GLONASS+Galileo (MIX) satellite configuration was utilized. The daily solutions obtained to reveal the effect of the earthquake are divided into two parts as before/after the earthquake. For each of TUSAGA stations, pre- and post-earthquake coordinates and RMSE were calculated. With statistical tests, whether the changes in the points are significant or not, the amount and direction of the changes were determined with 95% statistical confidence. As a result, it was concluded that the changes before/after the earthquake were mostly in the MNTS, which is the closest to the earthquake base, the changes in the points generally decrease as you move away from the earthquake center, and the evaluation before/after the earthquake can be made more healthy as the observation time increases. In addition, 30-day coordinates were examined through time series, and only the graph of the change in MNTS was given since it was the closest station to the epicenter of the earthquake. [ABSTRACT FROM AUTHOR]

The precise point positioning (PPP) technique, which is still being developed, provides position accuracy at the centimetre (cm) level and is widely employed in scientific research. In the PPP technique, cm-level accuracy can be achieved by evaluating raw data obtained from a single Global Navigation Satellite Systems (GNSS) receiver using precise satellite orbit and clock correction data and other parameters. The majority of studies in the literature are based on 24-hour data obtained from the International GNSS Service (IGS) and similar stations. However, there are fewer articles in which analyzes based on short-term measurements are taken. In this study; the effect of GLONASS on the static PPP technique was investigated with independent short measurement times. For this purpose, measurements were made at 7 different test points on consecutive days using a single GNSS receiver. A 4-hour static measurement was made at each test point. The data obtained were processed in two different scenarios, only GPS and GPS + GLONASS using the Canadian Spatial Reference System – PPP (CSRS-PPP) and Trimble RTX online process software. The processes were completed at 4, 2, 1, and 0.5 h. As a result of the analysis, it has been observed that GLONASS improves the results by 76%, but negatively affects some solutions (24%). It was also observed that GLONASS drastically reduced the outlier values. With this study, it is aimed to show the accuracy that users who make short-term measurements with a single GNSS receiver can be achieved in the static PPP technique by using GPS + GLONASS systems, with repeated measurements. [ABSTRACT FROM AUTHOR]

To improve the efficiency of estimation of deriving OTLD parameters with higher accuracy and take full advantage of multi-GNSS data, we investigate the potential of using global ocean tide model predictions as prior constraint for GLONASS and combined GPS+GLONASS kinematic precise point positioning (PPP), analyzing one year of GPS and GLONASS data from 20 Crustal Movement Observation Network China (CMONC) sites distributed along China coast. Seven global ocean tide models predictions are employed as prior constraint in kinematic PPP. Compared with the results of GPS-only kinematic PPP with priori information constraint, the result shows that GPS+GLONASS and GLONASS can improve the accuracy of OTLD estimates more than 40% in three components over GPS. The comparison of the effect of OTLD estimates on long-period signals in position time series shows that the correction effect of the kinematic PPP with seven different priori information constraint estimates is all as same as the reference model in three components. [ABSTRACT FROM AUTHOR]

Integer ambiguity resolution considerable improves the performance of precise point positioning (PPP). With the popularity of multi-frequency observations, multi-frequency PPP ambiguity resolution (PPP-AR) for GPS, BDS and Galileo has been well studied, whereas there is a lack of research on GLONASS triple-frequency PPP-AR. Fortunately, GLONASS currently transmits CDMA signals on the third frequency of two GLONASS-K and four GLONASS-M + satellites, making it possible to investigate the triple-frequency PPP-AR. To fully exploit GLONASS triple-frequency observation, this study proposes a CDMA + FMDA combined multi-frequency PPP-AR model with the careful consideration of GLONASS phase inter-frequency clock bias (IFCB) errors. The characteristics of GLONASS IFCBs and EWL UPDs are also well investigated. To verify our proposed model, tracking data of 14 stations is used to estimate uncalibrated phase delay (UPD) and another 6 stations are selected as users to perform PPP-AR. A time- and satellite-dependent IFCB of about 0.2 ~ 0.5 m is identified for GLONASS-M + triple-frequency observations. After the removal of the IFCB, the EWL, WL and NL UPDs of GLONASS satellites show remarkable stabilities at several hours. About 99.9% EWL, 98.7% WL and 99.4% NL residuals are within 0.15 cycles, which shows comparable accuracy compared with GPS. Based on the precise UPD products, GLONASS triple-frequency PPP-AR can be achieved. Compared with PPP float estimates, GLONASS triple-frequency PPP-AR improves the convergence time and 1-hourly positioning errors in the E, N and U directions from 14.5 min and [4.6 20.7 39.9] mm to 11.5 min and [3.1 4.6 14.1] mm, with an improvement of about 20.7% and [32.6% 77.8% 64.7%], respectively. However, limited by the number of datasets under current conditions, GLONASS triple-frequency PPP-AR exhibits insignificant improvement compared with the dual-frequency solution. After integrating GPS triple-frequency observations, results indicate that GLONASS + GPS triple-frequency PPP-AR exhibits significantly better positioning performance than the dual-frequency solution. [ABSTRACT FROM AUTHOR]

Global Navigation Satellite Systems (GNSS) have many applications in surveying, geodesy, and everyday life, so the accuracy of observations is very important. To have accurate results, many errors should be corrected, including ionospheric errors. Estimating the Differential Code Bias (DCB) and Total Electron Content (TEC) is essential to reduce ionospheric errors. This study's main aim is to determine how the combination of GPS (Global Positioning System) and GLONASS (GLObal NAvigation Satellite System) observations affect the estimation of DCB of satellites (SDCB) and receivers (RDCB) under the effects of geomagnetic storms and seasonal changes. The MATLAB-based software GR_DCB (GPS and GLONASS DCB estimation) was developed to estimate the SDCB and RDCB based on GPS and GLONASS observations. The results were tested using data from the International GNSS Service (IGS) network from nine stations and compared to previous studies to assess the effectiveness of the developed code. The findings are consistent with IGS products and more precise than previous studies that relied solely on GPS observations. An analysis of the effects of the geomagnetic storm on DCB variance is considered for June 22–23, 2015. During the geomagnetic storm, all GPS and GLONASS stations exhibited a fall in RDCB, led by a modest increase in some stations. The SDCB had no observed change on storm days compared with quiet days. The seasonal change affected GPS and GLONASS stations RDCB. Winter, which has the highest RDCB mean values, is also the season when a deviation in RDCB is the greatest. Autumn and Summer had the lowest dispersion in RDCB over the season and the lowest RDCB values. [ABSTRACT FROM AUTHOR]

The aspects of monitoring the energy characteristics of radio navigation signals of the global navigation satellite system (GLONASS) have been considered. It has been noted that the power of the incoming radio navigation signal in the lower atmosphere depends on the parameters of the onboard antenna system of the navigation spacecraft, primarily, on the shape of the antenna amplitude pattern. The amplitude pattern of the onboard antenna of the spacecraft has a complex shape, and in order to compensate for changes in the power of the radio navigation signal due to the navigation spacecraft moving away from (or approaching) the signal user, the shape of the amplitude pattern should be axisymmetric, i.e., resembling a figure of revolution. Based on regular monitoring of the energy characteristics of the GLONASS radio navigation signals, the shapes of the amplitude patterns of the onboard antenna feed systems of the spacecraft from the orbital group have been evaluated. As a result, asymmetry in the amplitude patterns of some spacecraft has been detected. It has been shown that the asymmetry of the amplitude pattern leads to a dependence of the power of the incoming radio navigation signal on the spacecraft aspect angle, i.e., the position of the spacecraft emitting antenna system relative to the signal user. The probable cause of such asymmetry has been identified as the gradual aging of the active devices in the antenna feed path. The obtained results indicate the need for regular and prompt monitoring of the energy characteristics of radio navigation signals in the lower atmosphere. The observed effect of asymmetry in the amplitude patterns should be taken into account when developing spacecraft antenna feed systems. [ABSTRACT FROM AUTHOR]

Time is the basis of satellite navigation systems. In precision studies, it is additionally important to ensure accuracy at the highest possible level, up to sub-millimetres. For this purpose, corrections of the clocks of satellites and GNSS reference stations are made available. This type of data is made available in real time in a navigation dispatch with an interval of 10 min–2 h depending on the GNSS system, or in a precision orbit file (interval of 15 min) or in the form of clock correction files (30 s or 300 s). This paper analyses the long-term stability of the clocks of satellites of four GNSS systems. For this purpose, IGS reprocessing data from 1994 to 2020 were used and ADEV (Allan deviation) and three related variances were adopted. The study showed the different nature of the satellite correction for each GNSS system and the increase of the stability over time. [ABSTRACT FROM AUTHOR]

The European Commission (EC) originally proposed ideas for a European Galileo satellite navigation system in 1999. A four-phase development is planned, involving investment from both the public and commercial sectors. Galileo is intended for both public and government use; the system is administered and operated by civil administration. Galileo will consist of a constellation of 30 satellites, a number of globally situated ground stations, and a ground control and monitoring system - all of which are quite similar to the structure, format, and layout of GPS. This document discusses an experiment at the project site that used the static approach to integrate GPS, GLONASS, GALILEO, Beidou, and QZSS signals. This research analyses the possible precision of GPS-only and GPS/GLONASS/GALILEO/Beidou/QZSS. These results suggest that combining a GPS system with GALILEO, GLONASS Beidou, and QZSS is preferable for surveying purposes. Integrating GPS/GLONASS/GALILEO/Beidou/QZSS static measurements in the study region with 0-120 millimetre accuracy looks to be possible in three days. [ABSTRACT FROM AUTHOR]

The utilization of the global navigation satellite system (GNSS) is becoming an attractive approach for autonomous navigation of the geostationary orbit (GEO) satellites. As one of the global navigation systems, the feasibility of using GLONASS in high-orbit spacecraft has attracted attention. A receiver compatible with GLONASS has been mounted in the GEO satellites of TJS-2 and TJS-5 to demonstrate the ability to track signals and real-time orbit determination. In accordance with flight data, the GLONASS signal characteristics are analyzed, including the observation availability and distribution. When the side lobe signals are considered, the mean number of GLONASS satellites tracked increases from 1.8 to 5.8. The transmit power of each GLONASS satellite was estimated by using the C/N0 measurements. Based on the influence analysis results, we found that the side lobe signal transmit power plays an important role in increasing the number of observations. In particular, we investigate the characteristics, such as quantity, C/N0, and doppler, of the GLONASS antipodal satellite signals tracked simultaneously in the GEO case. We give the navigation performance assessment based on GLONASS-only flight data through comparisons with the precision reference orbits. For single-epoch least square solutions, the root mean squares (RMS) of position differences in radial, along-track, and cross-track is 157.0, 29.5, and 21.5 m, respectively. The navigation accuracy is significantly improved when using the real-time orbit determination method, and the RMS of position differences in radial, along-track, and cross-track is 5.19, 8.98, and 3.15 m, respectively. [ABSTRACT FROM AUTHOR]

The paper presents the results of estimation of the effects of September 5–12, 2017 solar flares on the regional disturbance of Earth's ionosphere according to data from a distributed network of GNSS stations located mostly in the Volga Federal District of the Russian Federation. The GNSS data processing software package we have developed is used to analyze recorded signal power and daily two-frequency phase measurements, as well as to calculate the total electron content and map the data. The results of the study show that during powerful solar flares X2.2 and X9.3 on September 6 the median value of the total electron content, calculated for the Volga Federal District, increased up to 0.25 TECU and 0.6 TECU respectively. At that time, the region of interest (40°–55° E) was sunlit. The prolonged magnetic storms on September 8 also generated noticeable ionospheric disturbances up to 0.2 TECU. At the same time, neither the solar flares nor the magnetic storms had a significant effect on the power characteristics of the recorded signals from navigation satellites in the region under study. The median carrier-to-noise ratio calculated for the region considered over the entire observation period did not differ from the values recorded under undisturbed ionospheric conditions and varied between 47–53 dBHz and 38–49 dBHz for frequencies L1 and L2 respectively.

The European Commission (EC) originally proposed ideas for a European Galileo satellite navigation system in 1999. A four-phase development is planned, involving investment from both the public and commercial sectors. Galileo is intended for both public and government use; the system is administered and operated by civil administration. Galileo will consist of a constellation of 30 satellites, a number of globally situated ground stations, and a ground control and monitoring system – all of which are quite similar to the structure, format, and layout of GPS. This document discusses an experiment at the project site that used the static approach to integrate GPS, GLONASS, GALILEO, Beidou, and QZSS signals. This research analyses the possible precision of GPS-only and GPS/GLONASS/GALILEO/Beidou/QZSS. These results suggest that combining a GPS system with GALILEO, GLONASS Beidou, and QZSS is preferable for surveying purposes. Integrating GPS/GLONASS/GALILEO/Beidou/QZSS static measurements in the study region with 0–120 millimetre accuracy looks to be possible in three days.

We seek to quantify and understand the residual signal in GPS and GLONASS estimates of ocean tide loading displacements (OTLDs) after removing state-of-the-art model estimates. To consider contributions over a broad spatial scale, we estimate OTLD over the Australian continent using ∼ 5.5 years of continuous GPS and GLONASS data from 360 sites. We compare these with modelled estimates, with a focus on the lunar semidiurnal M 2 and diurnal O 1 constituents. We observe spatially coherent patterns of residual OTLD in each of the east, north, and up coordinate components after the removal of tidal loading using elastic models. We subsequently assess the impact of including anelastic dispersion in the model and show a 0.2 mm reduction in range of the up component residuals at coastal sites. A similar reduction at all sites is observed in the east and north components. Of the seven ocean tide models used, we find that three recent models, FES2014b, GOT4.10c and TPXO9.v1, perform similarly, noting these comparisons are made in the CE frame. However, we show that the latter contains centre of mass (CoM) biases in amplitude up to 0.2 mm and 0.5 mm for M 2 and O 1 , respectively, due to the assimilated altimetry data having not been corrected for geocentre motion. We find OTLD estimates are sensitive to the chosen orbit and clock products used in our analysis, with differences of up to 0.5 mm in the east component between solutions using the JPL and either of ESA or CODE products (GPS-only). Our analysis shows that current GNSS estimates of OTLD over Australia are typically accurate to ∼ 0.2 mm at which point we are unable to explain spatially coherent residuals when compared to modelled quantities. These may depend on the appropriate treatment of the CoM variation, anelasticity and/or three-dimensional Earth structure. As such, we recommend great care is taken when interpreting OTLD at the level of 0.1 or 0.2 mm, even if it is regionally coherent. [ABSTRACT FROM AUTHOR]

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GPS, GLONASS, Galileo, BeiDou are used in global positioning studies, while IRNSS and QZSS are used regionally. Until recently, point positions were determined using GPS, GLONASS, and BeiDou satellite systems. Since 2020, the Galileo satellite system has also been used. The accuracy of point positioning with GNSS depends on the satellite system used, processing software, data collection time/interval, etc. In this study, the effect of the Galileo satellite system on point positioning was investigated depending on the data logging time. For this purpose, daily RINEX data of 7 selected TUSAGA stations between October 15, 2020, and November 13, 2020, were analyzed in 2, 4, and 12-hour increments using 14 IGS station RINEX data, and the solutions were evaluated with GAMIT/GLOBK according to GPS (G), GLONASS (R), Galileo (E), and GPS+GLONASS+Galileo (GRE). As a result of the evaluations, the approaches of other satellite combinations to the daily coordinates obtained using only GPS were analyzed. In the analyses conducted, it was concluded that the accuracy increases as the measurement time increases and that GRE, Galileo, and GLONASS satellite combinations provide the best approximation to GPS coordinates, respectively. [ABSTRACT FROM AUTHOR]

GLONASS has been transmitting the code division multiple access navigation signals on the third band L3 for six GLONASS-M + and three GLONASS-K satellites, in addition to the legacy frequency division multiple access signals on L1 and L2. However, the significant inconsistency between the phase bias of different ionospheric-free (IF) combinations for GLONASS-M + satellites, known as the phase inter-frequency clock bias (IFCB), hinders the utilization of GLONASS triple-frequency positioning. We discuss the coupling relationship between GLONASS IFCB and the phase center offset (PCO) and propose a new IFCB estimation model considering the PCO differences between L3 and L2. GLONASS triple-frequency observations from 151 globally distributed IGS stations are employed to validate the proposed IFCB estimation model. The results show that the mean root mean square (RMS) value of IFCB estimates decreases from 0.097 m to 0.028 m when considering PCO differences, suggesting the GLONASS IFCB is ignorable. Meanwhile, the L3 PCO estimates for GLONASS-M + satellites exhibit high stability and consistency, with standard deviations of 52, 113, and 13 mm, in x-, y-, and z-components, respectively. By correcting the estimated L3 PCO instead of the legacy IFCB, the GLONASS-only triple-frequency precise point positioning PPP achieves positioning accuracies of 1.8, 0.9, and 1.5 cm in east, north, and up components, with the improvement of 13%, 3%, and 33%, respectively. Moreover, the RMS value of L3 phase residuals reduces from 10.2 to 5.0 mm. Therefore, we recommend correcting the PCO on L3 for GLONASS-M + satellites and disregarding the IFCB for GLONASS triple-frequency positioning, which can significantly simplify the observation model and achieve higher accuracy. [ABSTRACT FROM AUTHOR]

The Global Navigation Satellite Systems (GNSS) can monitor earth deformation at different frequencies, including sub-diurnal, fortnightly and seasonal bands. In standard 24-h GNSS data processing, we correct ocean tide loading (OTL) displacements by conventional models. Errors in the OTL modeling may lead to incorrect geophysical interpretation of observed displacements due to residual sub-daily OTL signals propagated to longer periods. OTL models and propagated signals have been studied mainly using GPS data, which introduce systematic errors at K1 and K2 tidal periods. We analyze the OTL residual displacements of eight major diurnal and semidiurnal tides derived from the FES2014b ocean tide atlas, using GPS, Galileo and GLONASS observations, and comparing both kinematic and static estimation approaches. The static method appears to be the most reliable way to retrieve the OTL residuals from other error sources with lower formal uncertainty. For the K1, K2 and S2 tides, the agreement improves by up to 55% when using Galileo and/or GLONASS, compared to GPS. We implemented an optimal weighting strategy with downweighted GPS contribution to the observation of K1/K2 for improving the estimation of the residual OTL errors. Several spurious signals appear for GPS, Galileo and GLONASS at the fortnightly band resulting from the propagation of mismodeled OTL. Estimating residual tidal coefficients alongside the 24-h static station positions mitigates the spectral power of these signals. Additional spurious signals appear at harmonics of the Galileo and GLONASS constellation repeat periods of 10 and 8 sidereal days, respectively. These signals cannot be attributed to mismodeled OTL. [ABSTRACT FROM AUTHOR]

According to the frequency division multiple access (FDMA) technology of GLONASS, the receiver inter-frequency differential code bias (IFDCB) exists in the GLONASS dual-frequency geometry-free combination observable. This study specifically investigates the contribution of GLONASS data to global ionosphere mapping, especially considering the GLONASS receiver IFDCB. A "co-located GNSS stations" experiment shows that the GLONASS receiver IFDCB is distinguishable from the leveling error induced by the "carrier-to-code leveling" method, and the individual GLONASS receiver IFDCB for each satellite at one station should be considered. Based on this experiment, a modified ionospheric model for combined GPS and GLONASS global ionosphere mapping is proposed, in which the GLONASS satellite plus receiver DCB (SPRDCB) for each satellite-station link is directly estimated. The influence of the modified ionospheric model on the DCB estimation and the global ionospheric vertical total electron content (VTEC) map is comprehensively analyzed using data from the international GNSS service (IGS) network for day of year (DOY) 49–108, 2014. First, the modified ionospheric model can slightly improve the stability of the GPS satellite DCB. The GPS receiver DCB at most stations are higher than when only GPS data are used. Second, the neglect of the satellite-dependent part of the GLONASS receiver IFDCB may introduce an error of tens of TEC units (TECU) in the slant TEC (STEC) computation. Comparing to the conventional ionospheric model that ignores the GLONASS receiver IFDCB, the modified ionospheric model can significantly reduce the GLONASS residual errors. Third, the modified ionospheric model can improve the accuracy of the global ionosphere map (GIM) at most independent stations based on an external accuracy assessment test (or dSTEC test). We suggest considering the GLONASS receiver IFDCB in the combined GPS and GLONASS global ionosphere mapping, it will revise the inaccurate estimation induced by the conventional ionospheric model and result in reliable GIM and DCB products. [ABSTRACT FROM AUTHOR]

The use of the Precise Point Positioning (PPP) technique has become very advantageous with the development of GNSS positioning technology. It is possible to get highly accurate position information without the need of any reference station data using the PPP technique. However, there are various factors that affect the accuracy of PPP solutions, including the initial phase ambiguity solution type, which can be fixed or float, atmospheric effects, observation length, used satellite systems, and used precise products. The Canadian Spatial Reference System-Precise Point Positioning (CSRS-PPP) service, one of the online PPP services, was updated on October 20th, 2020, and upgraded to version 3, capable of the Ambiguity-Fixed (PPP-AR) solution. Prior to this date, the service had offered the Ambiguity-Float (PPP-Float) solution. In this study, it is aimed to investigate the effect of using different satellite systems (GPS, GPS&GLONASS), length of observation time, static/kinematic processing modes, and initial phase ambiguity solution types on PPP accuracy. The daily observation data of ANKR, ISTA, IZMI, MERS, and KRS1 IGS GNSS stations located within the borders of Türkiye, divided into different sub-sessions (1-hour, 2-hours, 4-hours, 8-hours, and 12-hours) were processed using CSRS-PPP web-based service as PPP-Float before the update and PPP-AR after the update. As a result of the comparison, the combined use of GPS & GLONASS satellite systems instead of using GPS satellites alone has increased horizontal and vertical accuracy in both static/kinematic PPP-Float and PPP-AR solutions. Considering the static solutions, horizontal and vertical position accuracies increase as the observation time increases in both ambiguity solution methods using different constellations. In the case of comparison of the ambiguity solution methods, it was found that the PPP-AR approach offered higher accuracy than the PPP-Float in all solution cases.

The current GLONASS system suffers from the inter-frequency code bias (IFCB) and the inter-frequency phase bias (IFPB) due to its employment of the frequency division multiple access (FDMA) technology. The IFCB affects the code observation's accuracy and further degrades the positioning accuracy, while the IFPB can be absorbed into the float ambiguity term. With increasing demand on precise point positioning (PPP) in mass market applications using low-cost single-frequency (SF) receivers, the impact of IFCB on SF-PPP with low-cost receivers need to be investigated. In this paper, we propose the use of the University of Calgary (UofC) model to estimate the IFCB in SF-PPP. The feasibility of the proposed approach is first verified using GNSS observations from the IGS stations. Comparing to the traditional SF-PPP model, the UofC model enables more stable IFCB estimations with 80.2% of the maximum changes less than 1.0 ns within one week. Then, the stability of IFCB in the low-cost SF receiver is analyzed with static data collected with u-blox M8T, and the STandard Deviation (STD) of IFCB for each satellite within 5 days is less than 1.5 ns when applying real-time orbit, clock and ionospheric corrections. Further, it's verified that the power off won't affect the IFCB's value significantly in the low-cost receiver. Finally, six different strategies are designed to evaluate the impact of the GLONASS IFCB on SF-PPP. Comparing to those strategies ignoring IFCB, the strategies considering IFCB in SF-PPP can improve the positioning accuracy in both static and kinematic tests. [ABSTRACT FROM AUTHOR]

With global warming, extreme weather such as floods and waterlogging occurs more frequently and seriously in recent years. During the flood, the surrounding environment of the GNSS (Global Navigation Satellite System) station will change as the volume of water increases. Considering the multipath error is directly relevant to the observation environment, thus, the influence of flood on the L4 combination observation (a geometry-free ionosphere-free linear combination of carrier phase) which is related to the multipath error of GPS (Global Positioning System) and GLONASS satellites is investigated in depth. In addition, the ground track repetition periods of GPS and GLONASS satellites are analyzed in the sky plot to illustrate the rationality of chosen reference day. Based on the results of the satellite sky plot, one and eight days are adopted to demonstrate the influence of flood on L4 combination observation for GPS and GLONASS satellites, respectively. Real data sets collected at the ZHNZ GNSS observation station during the flood from DOY (Day of Year) 193 to DOY 204, 2021 are used. Experimental results show that the flood has a significant impact on the L4 combination observation of GPS and GLONASS satellites, and the fluctuation of L4 under flood performs much larger than that of without flood. For GPS satellites, the maximum RMS (root mean square) increase rate of L4 under flood is approximately 186.67% on the G31 satellite. Even for the minimum RMS increase rate, it can reach approximately 23.52%, which is the G02 satellite. Moreover, the average RMS increase rate of GPS and GLONASS satellites can reach approximately 109.53% and 43.65%, respectively. In addition, the influence of rainfall and hardware device are also investigated, which can further demonstrate that the fluctuation of L4 is mainly caused by the flood but not by the rainfall and hardware device elements. Thus, based on the above results, the influence of flood on L4 observation should be taken into account during the applications of L4 used, such as the retrieval of soil moisture and vegetation water content based on GNSS L4 combination observations [ABSTRACT FROM AUTHOR]