Russian Global Navigation Satellite System Research Articles

Acquisition of Positional Accuracy with Comparative Analysis of GPS and EGNOS in Urban Constituency

Over the years, precise positioning has been the ultimate goal for Satellite Navigation Systems. The American Global Navigation Satellite System deliver the position and time information intended for various sectors such as vehicle tracking, oil exploration, atmospheric studies, astronomical telescope pointing, airport and harbor security tracking etc. Corresponding technological competitors such as Russian Global Navigation Satellite System (GLONASS), European Union’s GALILEO, China’s BeiDou and Japanese Quasi Zenith Satellite System (QZSS) are few other versions of Satellite based Augmentation Systems. Nevertheless, stern security measures, geographical statistics and stimulation of diverse Electronic Gadgets at indoor/outdoor surroundings make it critical to acquire data about any vicinity with seamless accessibility, accuracy and integrity with satellite links. In this paper, positional accuracy has been tested with analysis of EGNOS, EDAS and simple GPS receiver models at Rome City, Italy. To support results, various real time experiments/tests has been performed with GPS Receiver SIRF Demo software. The test was conducted on-board a car by installing a laptop equipped with GPS Receiver plus supportive SBAS (EGNOS particularly) through three diverse bus routes of locality and outcomes of few tested samples inside the Rome City center are specified to check the availability of desired satellite signals. Subsequently, comparative analysis has been executed between the simple GPS data received and GPS + EGNOS data collected during daytime traffic. The strength of test signals reveals accuracy of EGNOS in open terrain area with less congestion. Furthermore, Asian and European Advanced GPS systems are compared in terms of performance as well as feasibility of authentic, accurate and swift satellite navigation systems.

Improving solar radiation pressure modeling for GLONASS satellites

The Russian Global Navigation Satellite System (GLONASS) satellites have a stretched body shape and take a specific attitude mode inside the eclipse. Based on previous studies, the new Empirical CODE orbit model (ECOM2) performs better than the classical ECOM model if a satellite has elongated shape or does not maintain yaw-steering mode, and the use of an a priori box-wing (BW) model improves the orbits significantly when employing the ECOM model. However, we find that the ECOM model performs better than the ECOM2 model for GLONASS satellites outside eclipse seasons, while it performs two times worse in eclipse seasons. The use of the conventional box-wing model results in very little improvement. By assessing the ECOM Y _{0} estimates, we conclude that there are potential radiators on the -x surface of GLONASS satellites causing orbit perturbations also inside the eclipse. The higher-order Fourier terms of the ECOM2 model can compensate for such effects better than the ECOM model. Based on this finding, we first confirm that GLONASS-K satellites take a similar attitude mode as GLONASS-M satellites inside the eclipse. Then, we adjust optical parameters of GLONASS satellites as part of precise orbit determination (POD) considering the potential radiator and thermal radiation effects. Finally, the adjusted parameters are introduced into a new box-wing model and jointly used with the ECOM and ECOM2 model, respectively. Results show that the amplitude and the dependency of the empirical parameters on the beta angle are greatly reduced for both ECOM and ECOM2 models. Rather than the conventional box-wing model, the new box-wing model reduces the orbit misclosure between two consecutive arcs for both GLONASS-M and GLONASS-K satellites. In particular, the improvement in GLONASS-M satellites is more than 30% for the ECOM model during eclipse seasons. Further evaluation from 24-h predicted orbits demonstrates that the improvement during eclipse seasons is mainly in along- and cross-track directions. Finally, we validate GLONASS satellite orbits using Satellite Laser Ranging (SLR) observations. The use of the new box-wing model reduces the spurious pattern of the SLR residuals as a function of beta and Delta u significantly, and the linear dependency of the SLR residuals on the elongation drops from as large as -0.760 mm/deg to almost zero for both ECOM and ECOM2 models. In general, GLONASS-M satellites benefit more from the new a priori box-wing model and the BW+ECOM model results in the best SLR residuals, with an improvement of about 50% and 20%, respectively, for the mean and standard deviation (STD) values with respect to the orbit products without a priori model.

Refining GPS/GLONASS Satellite Clock Offset Estimation in the Presence of Pseudo-Range Inter-Channel Biases

Because of the frequency division multiple access (FDMA) technique, Russian global navigation satellite system (GLONASS) observations suffer from pseudo-range inter-channel biases (ICBs), which adversely affect satellite clock offset estimation. In this study, the GLONASS pseudo-range ICB is treated in four different ways: as ignorable parameters (ICB-NONE), polynomial functions of frequency (ICB-FPOL), frequency-specific parameters (ICB-RF), and satellite-specific parameters (ICB-RS). Data from 110 international global navigation satellite system (GNSS) service stations were chosen to obtain the ICBs and were used for satellite clock offset estimation. The ICBs from the different schemes varied from −20 ns to 80 ns. The ICB-RS model yielded the best results, improving the clock offset accuracy from 300 ps to about 100 ps; it could improve the GLONASS precise point positioning (PPP) accuracy and the converging time by approximately 50% and 30%, respectively. Along similar lines, we introduced the GPS-ICB parameters in the process of GPS satellite clock estimation and GPS/GLONASS PPP, as ICBs may exist for GPS because of different chip shape distortions among GPS satellites. This possibility was found to be the case. Further, the GPS-ICB magnitude ranged from −2 ns to 2 ns, and the estimated satellite clock offsets could improve the accuracy of the GPS and combined GPS/GLONASS PPP by 10%; it also accelerated the converging time by more than 15% thanks to the GPS-ICB calibration.

Time and frequency characterization of GLONASS and Galileo on-board clocks

As the core component of navigational satellites, the on-board atomic clock is of key importance for guaranteeing the stable operation of global satellite navigation systems (GNSSs). As GNSSs are modernized, the clocks of several satellites have been changed to support long-term in-orbit operation. Analysis of the performance of on-board clocks is therefore crucial for supporting the positioning, navigation and timing of the satellite navigation system. Most studies involving stability analysis have not paid much attention to performance variation as a consequence of clocks being changed. This motivated our study, in which we analyzed the time domain characterization of on-board clocks from January 2016 to October 2018 to detect the variation. With respect to frequency domain characterization, conventional methods for noise analysis are easily affected by frequent fluctuations and local discontinuities as the averaging time increases. Hence, we propose the lag 1 autocorrelation function method based on overlapping samples to identify the noise of satellite clocks. We find that the time domain stability of the Galileo clock is of the magnitude of 10–13, 10–14 and 10–15 at averaging times of 100 s, 1000 s and 1 d, respectively, which is one order of magnitude better than that of the Russian global navigation satellite system (GLONASS). Moreover, the stability of the passive hydrogen masers on board Galileo shows a certain improvement due to the frequency modulation. The overall performance of the GLONASS cesium atomic clock and the Galileo rubidium atomic frequency standard is stable without any obvious aging in recent years. In terms of the frequency domain characterization, GLONASS clocks are mainly affected by flicker phase modulation noise, white frequency modulation noise and flicker frequency modulation noise, whereas the Galileo clocks are mainly affected by three kinds of frequency modulation noise.

Refinement of GLONASS Phase Inter-Frequency Biases and Their Applications on Single-Epoch Ambiguity Fixing

Carrier-phase inter-frequency bias (IFB) exists in GLObal NAvigation Satellite System (GLONASS) baselines when receivers of different brands are used. Those biases need to be calibrated in GLONASS data processing to derive precise fixed solutions. Consequently, the accuracy of the IFB calibration affects ambiguity fixing, and low-accuracy IFB values in the calibration will degrade the positioning results. Hitherto, at least two IFB rate value sets for various receiver brands have been given in previous studies. Some of the differences between the value sets exceed 2 mm/FN (frequency number) and the effects of those differences on ambiguity fixing have not been investigated until now. This study showed that ambiguity fixing in GLONASS single-epoch positioning is very sensitive to the accuracy of the IFB rates. Even errors of millimetres can seriously lower the empirical success rate. The short baselines from the Global Navigation Satellite System (GNSS, which includes Russian GLONASS) networks of the International GNSS Service and the Regional Reference Frame Sub-Commission for Europe were employed to obtain more accurate IFB rate estimates with the proposed two-dimensional particle filtering. Afterwards, the IFB estimates were statistically refined by the least-squares method. Experiments showed that when the refined IFB rates were used in the IFB calibration, the empirical success rates of ambiguity fixing in GLONASS single-epoch positioning were largely improved compared with the values given before, improvements such as 20·6% for a Septentrio and Leica receiver combination.

Global Ionosphere Estimation Based on Data Fusion From Multisource: Multi‐GNSS, IRI Model, and Satellite Altimetry

AbstractTraditionally, the ionosphere determination just uses American Global Positioning System and Russian GLObal NAvigation Satellite System dual‐frequency data and has a low precision particularly on oceans. With the rapid development of Chinese BeiDou and European Galileo systems, they are playing an increasingly important role for modeling global ionosphere. Meanwhile, satellite altimetry provides valuable and precise ionosphere delay over the oceans. Through introducing priori ionosphere values from an advanced empirical ionosphere model, combining the advantages of Global Navigation Satellite System (GNSS) and satellite altimetry technologies, the precision of global ionosphere estimation can be further improved. To assess the improvement, we collect satellite altimetry data from Jason‐2/3 and more than 300 global GNSS stations, the data are processed in 2014 and 2018 when the Sun is in a high and a low activity conditions. The results suggest that the ionosphere determination based on multitechnique fusion in a solar‐geomagnetic reference frame is well suitable to represent the ionosphere and its structure. The determined ionosphere achieves a better global consistency, and its formal accuracy is significantly reduced. By comparing with the International GNSS Service products, evaluating by satellite altimetry measurements, and independently validating with ionosonde techniques, it is proved that the ionosphere results are further improved through employing additional available data, especially for the ionosphere over the oceans.

Evaluation of carrier-phase precise time and frequency transfer using different analysis centre products for GNSSs

The carrier-phase (CP) technique, based on the global navigation satellite system (GNSS), has proved to be a useful spatial tool for remote and precise time transfer. In this study, we analysed the performance of CP time and frequency transfer with different GNSSs, using a satellite orbit and clock products collected from three analysis centres (ACs): CODE, WHU, and GFZ. From the time and frequency transfer experiments with six international time links, we concluded that the CP technique, based on different GNSSs, can all achieve a sub-nanosecond level accuracy for time and frequency transfer. Statistical analysis of the experiments shows that the global positioning system (GPS) solution can obtain the mean root mean square (RMS) of the six time links: 0.321 ns for cod (satellite products of CODE), 0.347 ns for whn (satellite products of WHU), and 0.288 ns for gbm (satellite products of GFZ). For Russian global navigation satellite system (GLONASS) solutions, the mean RMS is 0.306 ns for cod, 0.371 ns for whn, and 0.298 ns for gbm. In terms of emerging GNSSs, the Galileo can achieve a mean RMS of 0.293 ns for cod, 0.356 ns for whn, 0.295 ns for gbm, and the BeiDou navigation satellite system (BDS) can achieve a mean RMS of 0.294 ns for cod, 0.333 ns for whn, and 0.303 ns for gbm. The mean RMS is 0.288 ns for GPS, 0.298 ns for GLONASS, 0.295 ns for Galileo, and 0.303 ns for BDS. Regarding the three ACs, cod and gbm solutions show better performance than whn solutions. With respect to the frequency stability of CP technique by different GNSSs, Galileo and BDS are comparable to GPS at different averaging time intervals, while GLONASS is significantly worse than GPS.

A Fast Parallel GPS Acquisition Algorithm Based on Hybrid GPU and Multi-core CPU

Over the last decade, to improve the necessary accuracy and reliability of the existing global positioning system (GPS), incorporation with new constellations such as European Galileo navigation system and the update of the Russian Global Navigation Satellite System (GLONASS) attract a lot of attentions. In software integrations, the most important challenge is the calculation load which should be solved using suitable techniques. The parallel nature of this application causes graphic processing unit (GPU) and multi-core platform as a low cost and effective solution for the implementation of a software receiver. In this paper, in order to accelerate GPS acquisition, a hybrid parallel algorithm based on GPU and multi-core CPU is designed and implemented on two systems with GT630 and GT630M GPU. Experimental results show that the proposed algorithm is 2.2 times faster than sequential algorithm in one-core implementation and 4 times faster in quad core. On the other hand, the proposed parallel acquisition algorithm on GPU-based 2-core is 15% faster than acquisition on 4-core without GPU, which shows the effective role of GPU in parallelism of this application.

Robust adaptive joint tracking of GNSS signal code phases in urban canyons

Despite rapid developments in global navigation satellite system (GNSS), positioning in urban canyons is a big challenge for civil receivers. Low accessibility to the sky, multipath, weak signal and blocking incidents are the major problems of positioning in these environments. This study proposes a robust adaptive joint tracking architecture to improve the tracking and positioning results of the receiver. In this architecture beside the conventional tracking architecture, one adaptive tracking method works to aid the computation of the code phase error in weak channels. To increase the availability of the satellites above the receiver, global positioning system and Russian GLobal NAvigation satellite system integration is utilised. Different tests in static mode including blocking, multipath and weak-signal scenarios and a dynamic test in an urban environment are included. Experimental results show that the joint adaptive receiver could find the position with more than 31 and 14% improvements in RMS error rather than conventional receiver during the static multipath and dynamic tests, respectively. How the proposed method solves the fault propagation problem of vector tracking is also shown using a simulated scenario.

Jamming Mitigation using an Improved Fuzzy Weighted Least Square Method in Combined GPS and GLONASS Receiver

One of the important concerns in Global Positioning System (GPS) is interference and jamming attack. Different methods have been proposed to mitigate GPS jamming such as antenna array and digital signal filtering. In this paper, the integration of GPS with Russian Global Navigation Satellite System (GLONASS) is utilized to overcome this issue. Increasing the number of visible satellites is a significant benefit of this combined system. We also introduce an improved Fuzzy-Weighted Least-Square (FWLS) method to weight the information according to its transmitter system reliability and satellite properties. The experimental comparison between the proposed method and an improved Wavelet-Packet-Transform (WPT)-based anti-jammer shows that though the accuracy of WPT-based method is more than FWLS method, the FWLS has significantly less computation complexity and more reliability.

The Impact of Estimating High-Resolution Tropospheric Gradients on Multi-GNSS Precise Positioning

Benefits from the modernized US Global Positioning System (GPS), the revitalized Russian GLObal NAvigation Satellite System (GLONASS), and the newly-developed Chinese BeiDou Navigation Satellite System (BDS) and European Galileo, multi-constellation Global Navigation Satellite System (GNSS) has emerged as a powerful tool not only in positioning, navigation, and timing (PNT), but also in remote sensing of the atmosphere and ionosphere. Both precise positioning and the derivation of atmospheric parameters can benefit from multi-GNSS observations. In this contribution, extensive evaluations are conducted with multi-GNSS datasets collected from 134 globally-distributed ground stations of the International GNSS Service (IGS) Multi-GNSS Experiment (MGEX) network in July 2016. The datasets are processed in six different constellation combinations, i.e., GPS-, GLONASS-, BDS-only, GPS + GLONASS, GPS + BDS, and GPS + GLONASS + BDS + Galileo precise point positioning (PPP). Tropospheric gradients are estimated with eight different temporal resolutions, from 1 h to 24 h, to investigate the impact of estimating high-resolution gradients on position estimates. The standard deviation (STD) is used as an indicator of positioning repeatability. The results show that estimating tropospheric gradients with high temporal resolution can achieve better positioning performance than the traditional strategy in which tropospheric gradients are estimated on a daily basis. Moreover, the impact of estimating tropospheric gradients with different temporal resolutions at various elevation cutoff angles (from 3° to 20°) is investigated. It can be observed that with increasing elevation cutoff angles, the improvement in positioning repeatability is decreased.

Reliable Urban Canyon Navigation Solution in GPS and GLONASS Integrated Receiver Using Improved Fuzzy Weighted Least-Square Method

Global Positioning System encounters many problems in urban canyons and hard environments because of obstacles that decrease the number of visible satellites in receiver view. So, integration with other satellite-based navigation systems such as Russian Global Navigation Satellite System is utilized in new receivers. Least square as the popular and usual method typically used for navigation solution associates all satellite information with the same weights. However, the satellite impacts in reliability and accuracy of the receiver outputs are different in real condition and can be weighted by intelligent factors. In this paper, an improved fuzzy-weighted least square method is proposed which weights the satellite based on the satellite effect on dilution of precision, elevation angle and a defined constellation factor. Experimental results show that the proposed method can calculate 2D position more reliable and accurate than other popular weighted least square methods. This improvement is more than 57.23 % in a defined figure of merit.

COMPARATIVE MULTIOBJECTIVE ANALYSIS OF COMPLICATED TECHNICAL AND SOCIAL SYSTEMS IN TERMS OF ECONOMICS AND MANAGEMENT

The article is devoted to the comparative multiobjective analysis of complicated technical and social systems in terms of economics and management. The difficulty of carrying out such comparison is determined by multidimensionality of the target application, diversity and qualitative variety of separate system elements, dissimilarity of technological conditions, under which they are created, and analogues used for the comparison. It is not about choosing the one “best” solution out of several alternatives, how it is required having the traditional optimization task setting, but about the comparison of home object to its analogues. Usually the purpose of such comparison consists in the assessment of its comparative objective efficiency. However, the object compared is the product of the respective technological chain. The resources used to create the object and analogues compared are always different as well as technologies used to transform resources to end products. It is the reason for the new problem to assess the management quality of own object creation as compared to the analogues. Objectives. The purpose is the development of effective approaches to the management quality assessment of complicated technical and social systems creation. Four multiobjective tasks of integral assessment are considered to solve the stated problem: objective efficiency assessment, assessment of all kinds of resources used, applied technology assessment and finally three-objective task to assess the management quality of object creation with assessed objective efficiency by using stated resources and technologies. The last task implies achievement of the highest objective efficiency with the use of less resource and less sophisticated technology that points at the higher management level. The stated task pertains to the class of multiobjective decision making where alternatives are distinguished by partial criteria and depend on the range of uncertain factors. Methods. The methodology of solving this problem relies on the use of confident judgment method that allows making decision simply and on a reasonable basis taking into account only natural judgments. The stated method does not use artificial procedures, intended to formalize the task by means of searching the unique appropriate way to consider uncertainty, but takes into account the whole variety of such ways. Indeed the method allows identifying the rating of the required solution that represents the rate of uncertainty consideration ways whereby this solution is the best compared to other ones. Results. Test approval of the proposed method application are illustrated through the management quality comparative analysis while creation of Global Navigation Satellite Systems (GNSS). Russian Global Navigation Satellite System (GLONASS) is compared to similar systems of the USA (GPS), Europe (Galileo) and China (Kompas/Beidou). Conclusions and Relevance. The proposed approach has powerful capabilities and can be used in complex comparison to the existing analogues of complicated technical and social systems both being created and already in place. The method gives the possibility to acquire useful information about the quality and the efficiency of such systems and to elaborate recommendations regarding further development.

Assessment of the Contribution of BeiDou GEO, IGSO, and MEO Satellites to PPP in Asia-Pacific Region.

In contrast to the US Global Positioning System (GPS), the Russian Global Navigation Satellite System (GLONASS) and the European Galileo, the developing Chinese BeiDou satellite navigation system (BDS) consists of not only Medium Earth Orbit (MEO), but also Geostationary Orbit (GEO) as well as Inclined Geosynchronous Orbit (IGSO) satellites. In this study, the Precise Point Positioning (PPP) and PPP with Integer Ambiguity Resolution (IAR) are obtained. The contributions of these three different types of BDS satellites to PPP in Asia–Pacific region are assessed using data from selected 20 sites over more than four weeks. By using various PPP cases with different satellite combinations, in general, the largest contribution of BDS IGSO among the three kinds of BDS satellites to the reduction of convergence time and the improvement of positioning accuracy, particularly in the east direction, is identified. These PPP cases include static BDS only solutions and static/kinematic ambiguity-float and -fixed PPP with the combination of GPS and BDS. The statistical results demonstrate that the inclusion of BDS GEO and MEO satellites can improve the observation condition and result in better PPP performance as well. When combined with GPS, the contribution of BDS to the reduction of convergence time is, however, not as significant as that of GLONASS. As far as the positioning accuracy is concerned, GLONASS improves the accuracy in vertical component more than BDS does, whereas similar improvement in horizontal component can be achieved by inclusion of BDS IGSO and MEO as GLONASS.

Use of GLONASS for studying the ionosphere

Results of using the Russian Global Navigation Satellite System (GLONASS) to measure absolute values of the ionosphere’s total electron content (TEC) are presented. Specific features of configurations and differences in parameters of GLONASS and GPS are given, and their impact on TEC evaluation is analyzed. The statistical analysis is also carried out for comparing the TEC measurement data obtained from the GPS and GLONASS observations; a high correlation between measurements of both systems is shown. Investigations have revealed that the use of both systems allows of extending the possibilities of their employment for studying the ionosphere’s structure and dynamics. To restore the diurnal behavior of TEC of the ionosphere above the observation station, the phase measurements are proposed to be taken as input data. Their advantage over the group measurements is not only their high accuracy but the fact that they are less subject to the multipath effect. The technique for processing the phase observations implemented for GLONASS is an essential part of the system for monitoring of the ionosphere over the European part of p]Russia, which is under development at the West Department of Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation.

A Fast GLONASS FDMA Acquisition Algorithm Using Multi-Satellite Search Strategy

Integration of US global positioning system with other existing global navigation satellite system such as recently-augmented Russian Global Navigation Satellite System (GLONASS) suffers calculation time cost in software platforms. Acquisition stage as the first part of a software receiver is a challenging part for increasing the speed. In this paper, a rapid GLONASS acquisition algorithm is proposed using multi-satellite search strategy. The proposed algorithm divides satellites in multi-groups and generates a local replica for them. Analyzing of the received signal and this replica correlation will show whether this group has in-view satellites or not. Simulations on real data base created using an AAA GLONASS receiver prove the positive effect of this algorithm in speeding up the receiver acquisition to about 2.32 with least misdetection probability.

Space Weather Observations by GNSS Radio Occultation: From FORMOSAT-3/COSMIC to FORMOSAT-7/COSMIC-2.

The joint Taiwan-United States FORMOSAT-3/COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) mission, hereafter called COSMIC, is the first satellite constellation dedicated to remotely sense Earth's atmosphere and ionosphere using a technique called Global Positioning System (GPS) radio occultation (RO). The occultations yield abundant information about neutral atmospheric temperature and moisture as well as space weather estimates of slant total electron content, electron density profiles, and an amplitude scintillation index, S4. With the success of COSMIC, the United States and Taiwan are moving forward with a follow-on RO mission named FORMOSAT-7/COSMIC-2 (COSMIC-2), which will ultimately place 12 satellites in orbit with two launches in 2016 and 2019. COSMIC-2 satellites will carry an advanced Global Navigation Satellite System (GNSS) RO receiver that will track both GPS and Russian Global Navigation Satellite System signals, with capability for eventually tracking other GNSS signals from the Chinese BeiDou and European Galileo system, as well as secondary space weather payloads to measure low-latitude plasma drifts and scintillation at multiple frequencies. COSMIC-2 will provide 4–6 times (10–15X in the low latitudes) the number of atmospheric and ionospheric observations that were tracked with COSMIC and will also improve the quality of the observations. In this article we focus on COSMIC/COSMIC-2 measurements of key ionospheric parameters.

Ionospheric hole made by the 2012 North Korean rocket observed with a dense GNSS array in Japan

A dense array of Global Navigation Satellite System (GNSS) receivers is useful to study ionospheric disturbances. Here we report observations by a Japanese GNSS array of an ionospheric hole, i.e., localized electron depletion, made by water vapor molecules in the exhaust plume of the second-stage engine of the Unha-3 rocket launched from North Korea, on 12 December 2012. The Russian GNSS was used for the first time to observe such an ionospheric hole. The hole emerged ~6 min after the launch above the middle of the Yellow Sea, and its size and depth suggest that the Unha-3 is slightly less powerful than the 2009 Taepodong-2 missile, also from North Korea. Smaller-scale electron depletion signatures appeared ~10 min after the launch above the southern East China Sea, which is possibly caused by the exhaust plume of the third-stage engine.

Rapid and Precise GLONASS GDOP Approximation using Neural Networks

Russian global navigation satellite system (GLONASS) provides civilian and military users three-dimensional position determination and navigation services as same as US global positioning system. Geometric dilution of precision (GDOP) provides a simple interpretation of positioning precision. Usual method for GLONASS GDOP calculation is matrix inversion. However this process imposes a huge calculation load on receiver, especially when large number of visible satellites exists. To overcome this problem, artificial neural network is used. Different configurations and training methods are simulated on a data base obtained by a GLONASS receiver. Then navigation precision and execution times are explored and compared. Results show that recurrent neural network has 0.00024 RMS error, which is the best against other focused tools including feed forward back propagation and radial basis function neural network with usual training and with genetic algorithm adopted weights and biases.

Performance Analysis of GPS/GLONASS Precise Point Positioning

Precise Point Positioning (PPP) with Global Positioning Systems (GPS) has attracted the attention of many researchers over the past decade. Recently, the Russian global navigation satellite system (GLONASS) has been modernized and restored to near full constellation status, which has made it more attractive for positioning and navigation. Having two healthy systems, namely GPS and GLONASS provides a combination of both constellations, which in turn promises to improve the availability, positioning accuracy, and reliability of PPP solutions. This study investigates the effect of combining GPS and GLONASS dual-frequency measurements on the static PPP solution and its sensitivity to different processing strategies. Many data sets from five globally distributed International GNSS Service (IGS) tracking stations were processed using the Bernese GPS software package. The addition of GLONASS constellation improved the satellite visibility and geometry by more than 60%, and 40%, respectively, and improves the positioning convergence by up to 41%, 38%, and 19% in east, north, and up directions, respectively.