Mass-market Receivers Research Articles

On the quality of tropospheric estimates from low-cost GNSS receiver data processing

The goal of this study is to verify whether the low-cost GNSS receivers may provide the tropospheric parameters with accuracy close to that of high-grade ones. In this way, we address a scientific question on the potential usability of low-cost receivers for climate monitoring. We assess zenith tropospheric delays (ZTD) and, for the first time, horizontal gradients derived from Precise Point Positioning with low-cost receivers. ZTD estimates are also validated against ERA5, which is the fifth generation reanalysis for the global climate and weather produced by the European Centre for Medium-Range Weather Forecasts. We proved that low-cost equipment has the potential to provide tropospheric estimates with comparable accuracy to high-grade receivers. We also reveal a high agreement between GNSS ZTDs and these of ERA5 reanalysis. Finally, we show that applying a surveying-grade antenna to a low-cost receiver may enhance the accuracy of the tropospheric estimates derived from mass-market receivers.

A Novel GNSS Single-Frequency PPP Approach to Estimate the Ionospheric TEC and Satellite Pseudorange Observable-Specific Signal Bias

As the significant error sources influencing the Global Navigation Satellite System (GNSS) positioning, navigation, and timing (PNT) services, ionospheric delay and satellite hardware delay should be properly calibrated. Particularly, the pseudorange observable-specific signal bias (OSB) is convenient and can be directly corrected in the raw pseudorange measurement. In this work, we present a novel single-frequency ionospheric-free-half precise point positioning (PPP) (SFPPP2) approach for ionospheric studies, in which the ionospheric vertical total electron content (VTEC) and satellite OSB are isolated from the slant ionospheric observables by means of the ionospheric multilayer mapping function (MF). The computation and parameterization methods of the ionospheric VTEC and satellite pseudorange OSB are present. To validate the effectiveness and reliability of the novel method, we investigate and compare the performance of the single-frequency ionospheric-float PPP (SFPPP1), SFPPP2, and dual-frequency ionospheric-float PPP (DFPPP1) solutions for ionosphere sensing. The analytical results indicate that the novel approach can extract the slant ionospheric observables with the accuracy of submeters. The accuracy of the estimated ionospheric VTEC by the single-frequency PPP approaches is in the submeter level, which exhibits a slightly worse accuracy than that from the dual-frequency PPP solution. The estimated ionospheric VTEC accuracy is improved with the multilayer MF compared with the single-layer MF. The estimated BeiDou Navigation Satellite System (BDS) pseudorange OSB with the proposed SFPPP2 approach is stable, reliable, and of the high accuracy, and the rms’s with respect to Chinese Academy of Sciences (CAS) product for C2I and C6I signals with single-layer and multilayer MFs are 0.40, 0.41, 0.60, and 0.63 ns, respectively. The proposed PPP approach can retrieve the VTEC and satellite pseudorange OSB by mass-market receivers for the GNSS users.

Eyjafjallajökull Volcanic Ash 2010 Effects on GPS Positioning Performance in the Adriatic Sea Region

The Eyjafjallajökull volcanic ash crisis in 2010 temporarily suspended European air traffic operations, as the 39-day eruption caused widely dispersed ashes to enter the lower atmosphere. In this paper, we assessed the effects of this event on the ionosphere layer and, consequently, on GPS positioning. We collected and analysed the data from four IGS stations, nearest to the volcano, for the month of April 2010. We recorded Vertical Total Electron Content (VTEC) time series, analysed their dynamics, and compared them with the GPS positioning errors of a commercial-grade, un-aided, single-frequency GPS receiver (simulating the response of a mass-market GPS receiver). The geomagnetic indices during the time period show little geomagnetic disturbance, especially during the volcanic event. Our results show an enhancement in ionosphere error by up to 15% during the volcanic ash event and an enhanced variance in GPS position components errors. This study reveals the potential impact of the charged volcanic ash on single-frequency, unaided GPS positioning accuracy in the Adriatic Sea region and establishes a foundation for studying similar events in future.

Impact of Galileo-to-GPS-Time-Offset accuracy on multi-GNSS positioning and timing

The combined use of multi-GNSS systems in positioning, navigation and timing requires taking into account the variable time offset between the individual system times. This offset can be determined at the user level as an additional unknown in the position-velocity-time (PVT) solution when a sufficient number of satellites is visible. However, a known value of the inter-system bias can also be injected in the PVT algorithm. We investigate in which situation determining the Galileo-to-GPS-Time-Offset (GGTO) or fixing this parameter to a known value provides the best PVT solution and quantify the impact of a biased fixed GGTO value on the PVT solutions. Our results indicate that the recommendation on fixing or determining the GGTO, as well as the impact of a biased fixed GGTO value, heavily depends on the receiver noise level. In high visibility conditions, fixing the GGTO provides a similar or better solution than determining the GGTO if the accuracy of the fixed GGTO is better than 2 ns for a high precision receiver and 7 ns for a smartphone. Furthermore, an extreme bias of 20 ns on the fixed GGTO with respect to the true value induces an increase in the position or timing errors lower than 50% for a smartphone, while up to 150% for a high precision receiver. As a consequence, fixing the GGTO should be preferred in mass-market receivers, while determining the GGTO should be preferred in high precision receivers. The study also shows that there is no significant correlation between the superiority of determining or fixing the GGTO and either the dilution of precision or the number of visible satellites.

HDDM Hardware Evaluation for Robust Interference Mitigation.

Interference can significantly degrade the performance of global navigation satellite system (GNSS) receivers. Therefore, mitigation methods are required to ensure reliable operations. However, as there are different types of interference, robust, multi-purpose mitigation algorithms are needed. This paper describes the most popular state-of-the-art interference mitigation techniques. The high-rate DFT-based data manipulator (HDDM) is proposed as a possible solution to overcome their limitations. This paper presents a hardware implementation of the HDDM algorithm. The hardware HDDM module is integrated in three different receivers equipped with analog radio-frequency (RF) front-ends supporting signals with different dynamic range. The resource utilization and power consumption is evaluated for the three cases. The algorithm is compared to a low-end mass-market receiver and a high-end professional receiver with basic and sophisticated interference mitigation capabilities, respectively. Different type of interference are used to compare the mitigation capabilities of the receivers under test. Results of the HDDM hardware implementation achieve the similar or improved performance to the state of the art. With more complex interferences, like frequency hopping or pulsed, the HDDM shows even better performance.

GNSS Positioning Using Mobile Devices with the Android Operating System

The access and the use of the global navigation satellite system (GNSS) pseudo-range and carrier-phase measurements mobile devices as smartphones and tablets with an Android operating system has transformed the concept of accurate positioning with mobile devices. In this work, the comparison of positioning performances obtained with a smartphone and an external mass-market GNSS receiver both in real-time and post-processing is made. Particular attention is also paid to accuracy and precision of positioning results, also analyzing the possibility of estimating the phase ambiguities as integer values (fixed positioning) that it is still challenging for mass-market devices. The precisions and accuracies obtained with the mass-market receiver were about 5 cm and 1 cm both for real-time and post-processing solutions, respectively, while those obtained with a smartphone were slightly worse (few meters in some cases) due to the noise of its measurements.

GLONASS ambiguity resolution

A new integer-estimable GLONASS FDMA model is studied and analysed. The model is generally applicable, and it shows a close resemblance with the well-known CDMA models. The analyses provide insights into the performance characteristics of the model and concern a variety of different ambiguity-resolution critical applications. This will be done for geometry-free, geometry-fixed and several geometry-based formulations. Next to the analyses of the model’s instantaneous ambiguity-resolved positioning and attitude determination capabilities, we show the ease with which the model can be combined with existing CDMA models. We thereby present the instantaneous ambiguity-resolution performances of integrated L1 GPS + GLONASS, both for high-grade geodetic and mass-market receivers. We also consider the potential of the single-frequency combined model for mixed-receiver processing, particularly for the case the between-receiver GLONASS pseudorange data are biased. In all cases, the speed of successful ambiguity resolution is studied as well as the precision with which positioning is determined. Software routines for constructing the model are also provided.

The usability of GNSS mass-market receivers for cadastral surveys considering RTK and NRTK techniques

Abstract Nowadays many positioning techniques and methods are applied to the cadastral surveys. Starting from last decade, GPS/GNSS positioning had become one of the most used methodology thanks to the rapid development of satellite-based positioning and to the appearance of GNSS mass-market receivers and antennas. Methods based on these instruments are more affordable than the conventional ones even if their use for precise positioning is not so intuitive. This study is aimed to evaluate the use of single-frequency GPS/GNSS mass-market receivers for cadastral surveys, considering both single-base Real-Time Kinematic (RTK) and Network Real-Time Kinematic (NRTK) methodologies. Furthermore, a particular tool for predicting and estimating the occurrence of false fix of the phase ambiguities has been considered, in order to improve the accuracy and precision of the solutions. Considering the single-base positioning, the research results showed the difference of a few centimetres between the reference coordinates and the estimated ones if the distance between master and rover is less than 3 km, while considering the network positioning and the Virtual Reference Station correction, the difference are about a couple of centimetres for East and North component, and about 5 cm for the Up.

Distributed least-squares estimation applied to GNSS networks

In view of the recent proliferation of low-cost mass-market receivers, the number of network receivers and GNSS users will be growing rapidly, demanding an efficient way of data processing in terms of computational power and capacity. One way of improving the computational capacity is to decentralize the underlying data processing and distribute the task of the computer center across individual network receivers. In this invited contribution we review the problem of distributed estimation and present an algorithm for distributed least-squares estimation using the alternating direction method of multipliers. Applying the algorithm to a network of GNSS receivers, we show how the distributed data processing of individual receivers can deliver parameter solutions comparable to their centralized network-derived counterparts. With distributed estimation techniques, GNSS single-receiver users can therefore obtain high-precision solutions without the need of having a centralized computing center.

Multi-GNSS PPP-RTK: From Large- to Small-Scale Networks

Precise point positioning (PPP) and its integer ambiguity resolution-enabled variant, PPP-RTK (real-time kinematic), can benefit enormously from the integration of multiple global navigation satellite systems (GNSS). In such a multi-GNSS landscape, the positioning convergence time is expected to be reduced considerably as compared to the one obtained by a single-GNSS setup. It is therefore the goal of the present contribution to provide numerical insights into the role taken by the multi-GNSS integration in delivering fast and high-precision positioning solutions (sub-decimeter and centimeter levels) using PPP-RTK. To that end, we employ the Curtin PPP-RTK platform and process data-sets of GPS, BeiDou Navigation Satellite System (BDS) and Galileo in stand-alone and combined forms. The data-sets are collected by various receiver types, ranging from high-end multi-frequency geodetic receivers to low-cost single-frequency mass-market receivers. The corresponding stations form a large-scale (Australia-wide) network as well as a small-scale network with inter-station distances less than 30 km. In case of the Australia-wide GPS-only ambiguity-float setup, 90% of the horizontal positioning errors (kinematic mode) are shown to become less than five centimeters after 103 min. The stated required time is reduced to 66 min for the corresponding GPS + BDS + Galieo setup. The time is further reduced to 15 min by applying single-receiver ambiguity resolution. The outcomes are supported by the positioning results of the small-scale network.

Positioning Performance Assessment of Geodetic, Automotive, and Smartphone GNSS Receivers in Standardized Road Scenarios

Intelligent transport system applications use the global navigation satellite systems (GNSSs) to deliver the information on position, velocity, and time. With the expected deployment of critical road services, GNSS-based positioning terminals will have to be sufficiently accurate and their service will have to be available under any environmental condition. As the answer to the absence of standards and certification procedures of positioning terminals in road transport services, the European COST Action SaPPART was launched and the European norm EN 16803-1 was accepted. They provide the methodology and the guidelines for the terminal performance assessment. Section I presents the data collection methodology based on European norm EN 16803-1 with the definition of performance metrics and classification, operational scenarios, standardized GNSS environments, and field test guidelines. It is followed by the description of the measurement setup, including the trajectories, experimental vehicle with a reference trajectory system, and 17 tested GNSS receivers. The performance assessment of geodetic, automotive, and smartphone GNSS receivers was carried out through the extensive data collection campaign in Nantes, France. The campaign covered four types of environments: clear-sky, rural, peri-urban, and urban. The presented results focus on the basic performance features of accuracy, availability, and the classification of positioning terminals according to SaPPART methodology. The final conclusion is that for achieving a sub-meter accuracy at 95% confidence level in mixed road scenarios, a hybrid multi-sensor positioning approach is required for the majority of mass-market receivers.

Artificial neural network for detecting incorrectly fixed phase ambiguities for L1 mass-market receivers

One of the main challenges in global navigation satellite systems (GNSS) network real-time kinematic positioning is phase ambiguity estimation. We describe methods that predict false fixing (FF) of phase ambiguities in mass-market receivers. In this work, FF is defined to occur when the differences between 3D coordinates estimated in real-time differ by more than 20 cm with respect to the reference coordinates. Phase ambiguity FF events occur for many reasons, such as wrong estimation of phase ambiguities by the network software, noise in the corrections, and the environment of the rover. Moreover, one of the main reasons for phase ambiguity FF is the high level of noise and the low redundancy of observation by receivers that track L1 frequencies only. We develop and analyze a specific tool utilizing an artificial neural network that, when trained, tested, and refined specifically for GNSS mass-market receivers, can predict and detect FF. This tool comprises three inputs for all epochs, the Horizontal Dilution of Precision index, the latency of the differential correction, and the number of satellites with fixed phase ambiguities seen by the rover. It provides as output an index consisting of values 0 or 1, i.e., 0 for no FF and 1 for FF. A description of the training and validating phases is provided. The results of tests show that the algorithm has a 99.7% probability of detecting phase ambiguity FF in these cases.

GPS & GLONASS mass-market receivers: positioning performances and peculiarities.

Over the last twenty years, positioning with low cost Global Navigation Satellite System (GNSS) sensors have rapidly developed around the world at both a commercial and academic research level. For many years these instruments have only acquired the GPS constellation but are now able to track the Global’naja Navigacionnaja Sputnikovaja Sistema (GLONASS) constellation. This characteristic is very interesting, especially if used in hard-urban environments or in hard conditions where satellite visibility is low. The goal of this research is to investigate the contribution of the GLONASS constellation for mass-market receivers in order to analyse the performance in real time (Network Real Time Kinematic—NRTK positioning) with post-processing approaches. Under these conditions, it is possible to confirm that mass-market sensors could be a valid alternative to a more expensive receiver for a large number of surveying applications, but with low cost hardware the contribution of the GLONASS constellation for fixing ambiguities is useless, if not dangerous.

Performance of low-cost GNSS receiver for landslides monitoring: test and results

Italy is deeply afflicted by geo-hydrological risk, where a predominant part of its area is under risk.Recently, advanced research and sensors have played an important role in realizing automatic systems for landslide monitoring and to alerting. The cost of these systems, considering all parts, limits their use and the cost of each sensor influences the investment. Geodetic global navigation satellite system (GNSS) receivers, which are commonly used to realize these activities, are an appropriate example; however, their costs are quite high.The aim of this research was to test the actual performance of a mass-market GNSS receiver, with the purpose of verifying if such type of sensors can be used for landslide monitoring. In particular, the benefits due to the coupling between mass-market receivers and products offered by a network of GNSS permanent stations (e.g. Virtual RINEX) have been investigated.To verify the capability of these sensors to detect a deformation, under the minimum deformation detectable point of view, a special slide was built, in order to conduct a dedicated test. The support was moved both in horizontal and vertical directions with high precision, with purpose to detect correctly a three-dimensional movement.Tests were carried out considering the dependence of some factors: the most important are the acquisition time and the distance from the GNSS reference station. Interesting is the use of virtual reference station based on GNSS network, as a reference station: the performance achieved using Virtual RINEX for the control of movements and deformations are analysed. The accuracy and precision of movement determination were evaluated and compared, for each test, considering the different factors. The tests and results are described in this contribution.

Multiple Gate Delay Tracking Structures for GNSS Signals and Their Evaluation with Simulink, SystemC, and VHDL

Accurate delay tracking in multipath environments is one of the prerequisites of modern GNSS receivers. Several solutions have been proposed in the literature, both feedback and feedforward. However, this topic is still under active research focus, especially for mass‐market receivers, where selection of lowcomplexity, nonpatented methods is preferred. Among the most encountered delay tracking structures implemented in today′s receivers, we have the narrow correlator and the double‐delta correlators. Both are heavily covered by various patents. The purpose of this paper is to introduce a new, generic structure, called multiple gate delay (MGD) structure, which covers also the patented correlators but offers much more flexibility in the design process. We show how the design parameters of such a structure can be optimized, we argue the performance of this structure via detailed simulation results based on various simulators, such as Matlab/Simulink‐based tool, GRANADA, and we test the implementation feasibility of MGD structures on actual devices, via SystemC and FPGA prototyping. One of the main advantages of the proposed structure is its high degree of flexibility, which allows the designer to choose among, to the authors′ knowledge, nonpatented solutions with delay tracking accuracy comparable with that of the current state‐of‐art trackers.