Receiver Independent Exchange Research Articles

Exploring GNSS Crowdsourcing Feasibility: Combinations of Measurements for Modeling Smartphone and Higher End GNSS Receiver Performance.

GNSS receiver data crowdsourcing is of interest for multiple applications, e.g., weather monitoring. The bottleneck in this technology is the quality of the GNSS receivers. Therefore, we lay out in an introductory manner the steps to estimate the performance of an arbitrary GNSS receiver via the measurement errors related to its instrumentation. Specifically, we do not need to know the position of the receiver antenna, which allows also for the assessment of smartphone GNSS receivers having integrated antennas. Moreover, the method is independent of atmospheric errors so that no ionospheric or tropospheric correction services provided by base stations are needed. Error models for performance evaluation can be calculated from receiver RINEX (receiver independent exchange format)data using only ephemeris corrections. For the results, we present the quality of different receiver grades through parametrized error models that are likely to be helpful in stochastic modeling, e.g., for Kalman filters, and in assessing GNSS receiver qualities for crowdsourcing applications. Currently, the typical positioning precision for the latest smartphone receivers is around the decimeter level, while for a professional-grade receiver, it is within a few millimeters.

Improving GLONASS orbit quality by re-estimating satellite antenna offsets

Earlier studies performed at the Center for Orbit Determination in Europe (CODE) analysis center have revealed conspicuous signatures for certain GLONASS satellites when comparing their orbits with Satellite Laser Ranging (SLR) measurements. In this study we show that this phenomenon can be significantly reduced when using horizontal satellite antenna offsets that differ from the nominal values used by the International GNSS Service (IGS) for specific intervals and satellites.Analysis of multi-year time series shows instantaneous changes in the satellite antenna offset parameters of several centimeters in the X- and Y-component whereas the Z-component is not affected. In some cases the offsets do not agree with the nominal values during the entire lifetime of the satellite. The magnitude of the deviation may vary between 5 and 15 cm. Using these re-estimated satellite antenna offsets in the orbit determination the residuals with respect to the Satellite Laser Ranging (SLR) measurements are significantly reduced whereas the orbit misclosures for one-day arcs are too noisy to detect a positive or negative impact.It is difficult to reconstruct from the available information what actually caused the observed changes. However, changes in the carrier-to-noise density reported in the observation files in Receiver INdependent EXchange format (RINEX) by several IGS stations suggest an issue with the satellite antennas.

Variability of VTEC Gradient and TEC Rate Index Over Kisumu, Kenya During Selected Quiet and Storm Days of 2013 and 2014

Vertical Total electron content (VTEC) gradient or rate of change of TEC (ROT) and total electron content (TEC) rate index or rate of change of TEC index (ROTI) can directly be estimated from receiver independent exchange (RINEX) data and can be used to estimate presence and intensity of ionospheric irregularities. In this paper we present results of the variation of ROT and ROTI over Kisumu, Kenya (Geomagnetic coordinates: 9.64°S, 108.59°E; Geographic coordinates: 0.02°S, 34.6°E) for both selected quiet and disturbed conditions between 1^st January 2013 and 31^st December 2014 using data derived from NovAtel GSV4004B SCINDA-GPS receiver at Kisumu as a step in establishing ionospheric irregularities over Kisumu, Kenya during a high solar activity period of solar cycle 24. ROT was calculated from filtered average daily VTEC data within intervals of 120 seconds while ROTI was computed over 4 minutes window from ROT. ROT and corresponding ROTI for the selected quiet and storm days were plotted against universal time (UT). The presence and intensity of irregularities on the selected quiet and storm days of the years 2013 and 2014 were determined by checking ROT fluctuations and the corresponding ROTI values from the plots. The obtained results showed increased fluctuation of ROT corresponding with large ROTI values after sunset. The selected storm days of the years 2013 and 2014 had higher ROTI values than the selected quiet days of the years 2013 and 2014. The higher ROTI values during the selected storm days may be attributed to the impact of geomagnetic storms brought about by several competing dynamics including Prompt penetration electric field (PPEF), disturbance dynamo electric field (DDEF) and reduction in electron density due to increased recombination rates. The high ROTI values after sunset were a manifestation of post-sunset plasma irregularities. The obtained results also showed a diurnal trend for ROT and ROTI where ROT increased steadily from 0.00UT to around 12:00UT before falling and having an increased fluctuation between 18:00UT and 20:00UT. This corresponded well with low ROTI values between 0:00UT and 16:00UT followed by high ROTI values between 18:00UT and 20:00UT. The diurnal variability of ROT might have resulted from variation of TEC and which was attributed to changes in the intensity of incoming solar radiation.

NavIC receiver clock offsets estimation with common view master clock method

The current manuscript proposes a new methodology for receiver clock offset estimation in IRNSS (Indian Regional Navigation Satellite System) which is also known as NavIC (Navigation Indian Constellation). This new methodology has been designed by clubbing the master clock concept with the traditional common view time transfer method and therefore it has been named as Common View Master Clock Method (CVMCM). The proposed methodology is intended to share the reference time uniformly and precisely across all the receiver clocks of IRNSS. The IRNSS receivers equipped at IRIMS (IRNSS Range and Integrity Monitoring Stations) acquire IRNSS satellite signals and generate code and carrier phase measurements on L5 and S frequencies. For ease of convenience, this range measurements and broadcast navigation messages are converted to standard RINEX (Receiver Independent Exchange) format in the form of RINEX observation files and RINEX navigation files respectively. As IRNWT1 (IRNSS Network Time Facility Bangalore) has been directly fetched to IRIMS Bangalore we have chosen IRIMS Bangalore as the master (reference) station. This is followed by time offset estimation of all IRIMS with respect to IRIMS Bangalore using the CVMCM method. This proposed methodology reduces all the error sources in IRNSS signals and produces very accurate time offsets results for all IRIMS. This helps in maintaining IRNSS reference time very precisely across all IRIMS with a proper time steering, thereby revamping the process of time synchronization in NavIC. Analyses were performed which establishes the stability and credibility of our results. In the process, it also corrects almost all the error sources in NavIC signals.

A case study of the application of GPS to lunar laser ranging timing systems

Abstract The Hartebeesthoek Radio Astronomy Observatory is currently building a Lunar Laser Ranging station. This geodetic technique requires a good timing system to measure a round trip of laser photons from the telescope to the Moon and back to the telescope. We test the newly acquired timing system using examples of the Global Positioning System applications. Data in Receiver Independent Exchange Format was processed using GAMIT/GLOBK software. The results were compared against those derived from the Global Positioning System receivers that were integrated with a frequency standard from a hydrogen maser and a standard internal quartz. The results indicate that (i) the rubidium clock operates optimally and the clock drifted to within error margins of sub-centimetre level during the period of 2.5 seconds, (ii) the selected site for the permanent installation of the timing antenna has minimal multipath effect and (iii) we observed no improvement in Global Positioning System products derived from receivers that were integrated with different frequency standards.

The impact of GPS receiver modifications and ionospheric activity on Swarm baseline determination

The European Space Agency (ESA) Swarm mission is a satellite constellation launched on 22 November 2013 aiming at observing the Earth geomagnetic field and its temporal variations. The three identical satellites are equipped with high-precision dual-frequency Global Positioning System (GPS) receivers, which make the constellation an ideal test bed for baseline determination. From October 2014 to August 2016, a number of GPS receiver modifications and a new GPS Receiver Independent Exchange Format (RINEX) converter were implemented. Moreover, the on-board GPS receiver performance has been influenced by the ionospheric scintillations.The impact of these factors is assessed for baseline determination of the pendulum formation flying Swarm-A and -C satellites. In total 30 months of data - from 15 July 2014 to the end of 2016 - is analyzed. The assessment includes analysis of observation residuals, success rate of GPS carrier phase ambiguity fixing, a consistency check between the so-called kinematic and reduced-dynamic baseline solution, and validations of orbits by comparing with Satellite Laser Ranging (SLR) observations. External baseline solutions from The German Space Operations Center (GSOC) and Astronomisches Institut - Universität Bern (AIUB) are also included in the comparison.Results indicate that the GPS receiver modifications and RINEX converter changes are effective to improve the baseline determination. This research eventually shows a consistency level of 9.3/4.9/3.0 mm between kinematic and reduced-dynamic baselines in the radial/along-track/cross-track directions. On average 98.3% of the epochs have kinematic solutions. Consistency between TU Delft and external reduced-dynamic baseline solutions is at a level of 1 mm level in all directions.

AN ALGORITHM FOR NETWORK REAL TIME KINEMATIC PROCESSING

Abstract. NRTK1 is an efficient method to achieve precise real time positioning from GNSS measurements. In this paper we attempt to improve NRTK algorithm by introducing a new strategy. In this strategy a precise relocation of master station observations is performed using Sagnac effect. After processing the double differences, the tropospheric and ionospheric errors of each baseline can be estimated separately. The next step is interpolation of these errors for the atmospheric errors mitigation of desired baseline. Linear and kriging interpolation methods are implemented in this study. In the new strategy the RINEX2 data of the master station is re-located and is converted to the desired virtual observations. Then the interpolated corrections are applied to the virtual observations. The results are compared by the classical method of VRS generation. 1 Network Real Time Kinematic 2 Receiver Independent Exchange Format

English

The paper describes determination of GPS receiver position using Bancroft algorithm. The position is determined by obtaining pseudo ranges from seven different GPS satellites. The measured ranges do not represent the true ranges as the signal coming from a GPS satellite will be affected by various errors like Ephemeris error; Propagation error in the form of Ionospheric and Tropospheric delays; Satellite and Receiver clock biases with respect to GPS Time (GPST); Multipath error etc. Most of these errors can be estimated accurately and can be accounted for. In this paper some standard mitigation techniques have been applied for the estimation of GPS errors and user position is then determined using Bancroft algorithm technique after making appropriate corrections. GPS data of Chitrakut station available in RINEX (Receiver Independent Exchange) format have been used for this purpose u j u j u j j ct z z y y x x 2 2 2

Performance of the High Sensitivity Open Source Multi-GNSS Assisted GNSS Reference Server.

AbstractThe Open Source GNSS Reference Server (OSGRS) exploits the GNSS Reference Interface Protocol (GRIP) to provide assistance data to GPS receivers. Assistance can be in terms of signal acquisition and in the processing of the measurement data. The data transfer protocol is based on Extensible Mark-up Language (XML) schema. The first version of the OSGRS required a direct hardware connection to a GPS device to acquire the data necessary to generate the appropriate assistance. Scenarios of interest for the OSGRS users are weak signal strength indoors, obstructed outdoors or heavy multipath environments.This paper describes an improved version of OSGRS that provides alternative assistance support from a number of Global Navigation Satellite Systems (GNSS). The underlying protocol to transfer GNSS assistance data from global casters is the Networked Transport of RTCM (Radio Technical Commission for Maritime Services) over Internet Protocol (NTRIP), and/or the RINEX (Receiver Independent Exchange) format. This expands the assistance and support model of the OSGRS to globally available GNSS data servers connected via internet casters. A variety of formats and versions of RINEX and RTCM streams become available, which strengthens the assistance provisioning capability of the OSGRS platform.The prime motivation for this work was to enhance the system architecture of the OSGRS to take advantage of globally available GNSS data sources. Open source software architectures and assistance models provide acquisition and data processing assistance for GNSS receivers operating in weak signal environments. This paper describes test scenarios to benchmark the OSGRSv2 performance against other Assisted-GNSS solutions. Benchmarking devices include the SPOT satellite messenger, MS-Based & MS-Assisted GNSS, HSGNSS (SiRFstar-III) and Wireless Sensor Networks Assisted-GNSS. Benchmarked parameters include the number of tracked satellites, the Time to Fix First (TTFF), navigation availability and accuracy.Three different configurations of Multi-GNSS assistance servers were used, namely Cloud-Client-Server, the Demilitarized Zone (DMZ) Client-Server and PC-Client-Server; with respect to the connectivity location of client and server. The impact on the performance based on server and/or client initiation, hardware capability, network latency, processing delay and computation times with their storage, scalability, processing and load sharing capabilities, were analysed.The performance of the OSGRS is compared against commercial GNSS, Assisted-GNSS and WSN-enabled GNSS devices. The OSGRS system demonstrated lower TTFF and higher availability.

Analysis of the TXDOT RTN and OPUS-RS from the Geoid Slope Validation Survey of 2011: Case Study for Texas

AbstractAs part of the Geoid Slope Validation Survey of 2011 (GSVS11), the global positioning system (GPS) was used in a variety of ways to determine the geodetic coordinates of nearly 400 passive geodetic control marks. The Texas DOT (TXDOT) real-time network (RTN) was one of the GPS positioning tools used. Both 6- and 180-s occupations were performed with the TXDOT RTN, as well as static 20-min occupations [processed using the National Geodetic Survey (NGS) Online Positioning User Service, Rapid-Static (OPUS-RS) tool], and 48+h occupations were adjusted as a network (using the NGS OPUS-Projects tool). Although the original 20-min occupations processed by OPUS-RS had an unforeseen systematic error (invalidating their use in this comparison), a direct comparison between OPUS-RS and the other techniques was still possible by subdividing the OPUS-Projects 48+h receiver independent exchange format (RINEX) files on 218 points into more than 30,000 individual 20-min segments. A comparison between all technique...

Estimation Of Global Positioning System Measurement Errors For GAGAN Applications

The Global Positioning System (GPS) has been in use for providing positioning, navigation and timing (PNT) services in many parts of the world. There are several errors that affect the positional accuracy of GPS. Prominent among them are ephemeris errors, satellite and receiver clock errors, multipath errors, signal propagation errors such as ionospheric delay, tropospheric delay, and instrumental biases of the satellite and receiver. In this paper, prominent estimation techniques to characterize various GPS measurement errors are reviewed. The GPS data in the Receiver INdependent EXchange (RINEX) format obtained from a Dual frequency GPS receiver is used in this analysis. Among all the errors, ionospheric delay is found to be the most dominant. However, these delay measurements are affected by the satellite and receiver instrumental biases. The instrumental biases exist as the signals at the two GPS frequencies experience different delays inside the satellite and receiver hardware. For estimation of the instrumental biases Extended Kalman filter(EKF) technique is adopted. The user equivalent range error (UERE) obtained due to all the error sources is of the order of few metres. After accounting for various errors, the estimation accuracy is significantly improved.The positional accuracy of the GPS Aided GEO Augmented Navigation (GAGAN) system is basically dependent on ranging errors and the satellite constellation geometry(1). The lineof-sight ionospheric measurements derived from the Global Positioning System (GPS) observables are corrupted by the instrumental biases present in both the GPS satellites and the receivers. The instrumental bias and Total Electron Content (TEC) results (Hyderabad GAGAN station (78.47°E, 17.45°N)) obtained using theExtended Kalman filter technique are presented in this paper. In this work the main focus is towards development of an improved error free approach for aircraft navigation. The existing navigation solutions are based on iterative algorithms and require an initial estimate of the receiver position for computing the navigation solution which is not possible in all conditions. Accurate, reliable and cost effective navigation solution algorithms that suit the Indian geographic area and area of application are proposed in this work. A non-iterative point solution approach algorithm computes the navigation solution based on the available satellite positions and pseudorange measurements(3). The improvement in GPS system has given a feasibility of automated operation of satellite based augmenting system in aircraft navigation can augment GAGAN and improves the positional accuracy of the user. In this paper a communication approach , high, accurate processing using EKF scheme is proposed for GPS aided geo augmented navigation (GAGAN) application. The effectiveness of the proposed approach for higher performance is evaluated under variable conditions.

Real-time GPS Ionospheric TEC Estimation over South Korea

Ionosphere is one of the largest error sources when the navigational signals produced by Global Positioning System (GPS) satellites are transmitted. Therefore it is very important to estimate total electron contents (TEC) in ionosphere precisely for navigation, precise positioning and some other applications. When we provide ionospheric TEC values in real-time, its application can be expanded to other areas. In this study we have used data obtained from nine Global Navigation Satellite System (GNSS) reference stations which have been operated by Korea Astronomy and Space Science Institute (KASI) to detect ionospheric TEC over South Korea in real-time. We performed data processing that covers converting 1Hz raw data delivered from GNSS reference stations to Receiver INdependent Exchange (RINEX) format files at intervals of 5 minutes. We also analyzed the elevation angles of GPS satellites, vertical TEC (VTEC) values and their changes.

A New Window-Based Program for Quality Control of GPS Sensing Data

The main purpose of this study is to develop a new Windows-based program that calculates a quality control parameter that shows the quality of GPS observations using Global Positing Sensing (GPS) data in a Receiver INdependent Exchange (RINEX) format. This new program, Global Positing Sensing Quality Control) (GPSQC), allows general GPS users to easily and intuitively check the quality of GPS observations before post-processing, which will lead to the improvement of GPS positioning precision in diverse areas of GPS applications. The GPSQC is designed to control the multi-path, cycle slip, and ionospheric errors of L1 and L2 signals in GPS observations. The GPSQC was developed using C#.NET language for the Window series with Microsoft Graphical User Interfaces (MS GUIs). This program gives brief information for GPS observations, time series plots, graphs of quality control parameters, and a summary report in MS word, Excel and PDF formats. It can simply perform quality checking of GPS observations that is difficult for surveyors conducting field work. We expect that GPSQC can be used to improve the accuracy of positioning and to solve time-consuming problems due to data loss and large errors in GPS observations.

Imaging meso‐scale ionospheric structures

The accuracy and capacity to resolve meso‐scale structures of a four dimensional ionospheric imaging algorithm in the circumstance of data from dense networks of permanent GNSS ground receiver stations were investigated. Simulation studies were conducted in order to be able to assess the performance of the algorithm over the entire imaged region. The Multi‐instrument Data Assimilation Software (MIDAS) algorithm was used for this purpose. Simulated input data in Receiver Independent Exchange Format (RINEX) were produced by calculating slant Total Electron Content (sTEC) values for satellite to receiver raypaths through an artificially generated ionosphere. Modeling these signals including Differential Code Biases (DCBs) and noise had negligible impact on the output from the imaging algorithm when compared with modeled signals that included neither. Comparing the output from MIDAS using a range of grid definitions show that finer grids have improved capacity to resolve meso‐scale structures in the input model but over all are less accurate than coarser grids. The greatest errors occur in low‐data regions of the grid and where structures in the input have the greatest gradients in vertical Total Electron Content (vTEC). A good compromise between the conflicting needs of resolution and accuracy is given by a grid defined with 2° × 2° latitude by longitude local horizontal grid divisions.

The Compact Network RTK Method: An Effective Solution to Reduce GNSS Temporal and Spatial Decorrelation Error

This paper proposes a method that combines compact real-time kinematic (RTK) and reference station (RS) networking techniques, and shows that this approach can reduce both the temporal and spatial decorrelation error. The compact RTK method compatibility with all the conventional network RTK systems, i.e., Master-Auxiliary Concept (MAC), Virtual Reference Stations (VRS), and Flächen-Korrektur Parameter (FKP), is examined theoretically in this paper. To prove that the compact RTK approach is not only valid, but also helpful to the network RTK system, a field test was held using one hour of Receiver Independent Exchange Format (RINEX) data logged every second from Continuously Operating Reference Stations (CORS). No matter which network RTK method is applied, the Compact Network RTK approach resolves the ambiguity of the carrier phase in 10–40 s and determines position with 6–7 cm horizontal and 7–8 cm vertical error (95%) in a 100 by 100 km region. Moreover, the Compact Network RTK approach enables network RTK service providers to reduce the data-link bandwidth for correction messages to 5–700 bps (bit/s) down from several thousand bps, currently 9600 bps of GPRS/GSM, without a severe degradation of accuracy.

Space Weather and the Global Positioning System

Space Weather and the Global Positioning System

Performance Analysis of Korean WADGPS Algorithms with NDGPS Data

To provide more accurate and reliable positioning and timing services to Korean nationwide users, the Ministry of Maritime Affairs and Fisheries of Korea is implementing Korean NDGPS (Nationwide DGPS), which is operational partly. And it also has a plan to construct WADGPS (Wide Area Differential GPS) system using sites and equipments of the NDGPS reference stations. For that, Seoul National University GNSS Laboratory is implementing and testing prototypes of WRS (Wide-area Reference Station) and WMS (Wide-area Master Station). Until now, because there are not enough installed WRSs to be used for computing wide area correction information, we cannot test algorithms of WMS with the data processed actually in WRSs. Therefore to evaluate the performance of the algorithms, we made a MATLAB program which can process RINEX (Receiver INdependent Exchange) format data with WADGPS algorithm. Using that program which consists of WRS, WMS and USER modules, we processed the data collected at NDGPS reference stations, which are saved in RINEX format. In WRS module, we eliminate the atmospheric delay error from the pseudorange measurement, smooth the measurement by hatch filter and calculate pseudorange corrections for each satellite. WMS module collects the processed data from each reference stations to generate the wide area correction information including estimated satellite ephemeris errors, ionospheric delays at each grid point, UDRE (User Differential Range Error), GIVE (Grid Ionosphere Vertical Error) and so on. In USER part, we use the measurements of reference stations as those of users and estimate the corrected users' positions and protection levels (HPL, VPL). With the results of estimation, we analyzed the performance of the algorithms. We assured the estimated UDRE /GIVE values and the protection levels bound the corresponding errors effectively. In this research, we can expect the possible performance of WADGPS in Korea, and the developed modules will be useful to implementation and improvement of the algorithms.

Online GPS processing services: an initial study

There are a number of online Global Positioning System (GPS) processing services that provide GPS processing results to the user free of charge and with unlimited access. These services provide solutions for a user-submitted Receiver Independent Exchange Format (RINEX) file based on differential methods using reference stations or precise point positioning using precise GPS orbit and clock data. Different data sets varying in time and location were submitted to the online services and their results compared. Although the quality of results depends on many factors, in most cases the users can expect reliable online processing results for a 10-h data set made by a geodetic dual frequency receiver anywhere in the world.

Time transfer to TAI using geodetic receivers

The classical time transfer method used to realize International Atomic Time (TAI) is based on the common view technique, with GPS observations collected by C/A code receivers. The resulting clock offsets between the laboratory clock and GPS time are obtained from a fixed procedure defined by the Consultative Committee for Time and Frequency (CCTF). A similar procedure can be applied to the Receiver INdependent EXchange (RINEX) observation files produced by geodetic receivers driven by a stable external frequency. If the link between the receiver clock and the external clock is stable and precisely determined, the geodetic receivers can then be used for time transfer to TAI. In that case, we propose some modifications to the CCTF procedure to adapt it for the links between geodetic receivers, in order to take advantage of the P codes available on L1 and L2. This new procedure forms the ionosphere-free combination of the P1 and P2 codes as given by the 30 s RINEX observation files, the standard of the International GPS Service. The procedure is tested using the Ashtech Z-XII3T geodetic receivers and the results are compared with those obtained with the classical CCTF procedure based on the C/A code by computing the fractional frequency stability (Allan deviation) of the time links. Over short baselines, the two techniques are equivalent, while the new technique provides a factor 2 improvement for a transatlantic time link. For time links between a time receiver and a geodetic receiver, the differential satellite delays (P1-C/A or P2-C/A) must additionally be introduced. We show here that these biases do not, however, alter the long-term (>3 days) stability of the time transfer results. The corrections associated with tidal station displacement are also investigated, and the results indicate that they do not significantly improve the results at the present level of precision.

A new plotting program for Windows-based TEQC users

In a 1999 issue of GPS Solutions (Vol. 3, No. 1) Estey and Meertens describe a multi-purpose software toolkit for GPS and GLONASS data called TEQC (pronounced "tek"). The program's name reflects its three main functions: translating, editing, and quality checking. TEQC can be used on many different computer platforms, including Windows-based personal computers. This amazingly capable program can be used for converting native binary files from a wide variety of GPS receivers into the standard Receiver Independent Exchange Format (RINEX). It can also be used for editing and quality-controlling existing RINEX files. And it can be used for generating plot files of several different quantities normally associated with satellite observations. This article describes a new C/C++ program which gives Windows-based TEQC users increased flexibility for viewing and printing TEQC plot files. The user can now specify a start and stop time for each plot, a subset of satellites to be plotted, labels for the x- and y-axes, and a title to appear at the top of each plot. The new software converts the original "Compact Format" plot files output by TEQC into PostScript files, which can then be viewed or printed. An additional benefit of PostScript files is that they can be used to provide high-quality, high-resolution graphics for document publishing.