GNSS Receiver Performance Research Articles

Cascaded multiplier-free implementation of adaptive anti-jamming filter based on GNSS receiver

Evaluating the computational complexity is critical for assessing the time-domain anti-jamming performance of GNSS receivers. The multiplier is the core component that contributes to the computational complexity in time-domain anti-jamming. However, current algorithms aimed at reducing the complexity of time-domain anti-jamming typically concentrate on shortening the filter length, which fails to address the high computational complexity introduced by the use of multipliers. This paper introduces a cascaded multiplier-free approach for implementing time-domain anti-jamming in navigation receivers. We propose a numerical power decomposition technique based on optimal Canonical Signed Digit coding and coefficient decomposition. By substituting the multiplier with minimal adder and shift operations, the computational complexity of the anti-jamming filter with a high quantization bit-width can be considerably decreased. An optimization strategy is presented, and the low-complexity multiplier-free technique is applied to the time-domain anti-jamming filter. Compared to the traditional Canonical Signed Digit multiplier-free technique, our method can reduce the components required for a 12-bit quantization anti-interference filter by one adder, 20 shift operations, and five coded word lengths, while maintaining a pseudo-range measurement deviation below 0.27 ns.

THE APPLICABILITY OF LOW-COST MULTI-FREQUENCY MULTI-GNSS RECEIVERS FOR GEODETIC CONTROL SURVEYING

Abstract. In geodetic surveys, survey-grade receivers are conventionally used due to their accuracy. However, expensive survey-grade receivers deter users from performing geodetic surveys utilizing the technology. Considerably, multi-system and multi-frequency low-cost GNSS receivers are available today, which can already provide good positioning accuracy output. This paper evaluates the performance of low-cost GNSS receivers in single-point positioning, relative positioning, and network solutions compared to survey-grade GNSS receivers. The study used a survey-grade antenna to test the u-blox C099-F9P evaluation kit equipped with the ZED-F9P module, a low-cost GNSS receiver. Simultaneously, the survey-grade GNSS receiver utilizes the same antenna using a GPS splitter to ensure simultaneous observation. Based on the results, the low-cost GNSS receiver is comparable to the survey-grade GNSS receiver for single and relative positioning. For single-point positioning, the low-cost GNSS receiver achieved 1- and 1.5-meter accuracy in horizontal and vertical components at a 95% confidence level, respectively. In relative positioning, it achieved an accuracy of 1 millimeter on average at a 95% confidence level. The network solution utilizes four (4) Active Geodetic Stations of the National Mapping and Resource Information Authority within the National Capital Region, used as reference stations. The low-cost GNSS receiver achieved an average accuracy of 8 millimeters. In summary, the ublox C099-F9P low-cost GNSS receiver achieved better than 1:100,000 or first-order survey accuracy stipulated in DAO 2007-29 surveying standards. Results show that the u-blox C099-F9P is possible for geodetic and other land surveying applications, even for high-accuracy requirements surveys.

The positioning performance of low-cost GNSS receivers in the Precise Point Positioning method

The positioning performance of low-cost GNSS receivers in the Precise Point Positioning method

Static and kinematic PPP-AR performance of low-cost GNSS receiver in monitoring displacements

Recently, low-cost GNSS receivers have played a significant role in displacement monitoring studies due to the increasing availability of mass-market applications. In this work, the performance of static and kinematic PPP-AR using a low-cost u-blox ZED-F9P GNSS receiver in monitoring displacements is investigated by comparing it with a geodetic-grade GNSS receiver using a displacement simulation apparatus. The capability to determine the horizontal displacement direction is also investigated for both receivers. The results showed that one-sigma horizontal / vertical RMSEs computed from the true displacements and computed displacements are 1.4 / 5.6 mm and 2.6 / 8.4 mm for the geodetic and u-blox receivers, respectively, using 24-h data with static GPS + GLONASS PPP-AR. It is found that GLONASS contribution to GPS-only static PPP is more evident for the u-blox receiver compared with the geodetic one. RMSEs are found to be higher as observation times are decreased. The post-processed kinematic test results showed that minimum 10 / 20 and 20 / 30 mm horizontal / vertical dynamic displacements can be visually detected as an offset from the daily time series for the geodetic and u-blox receivers, respectively.

Enhancing GNSS receiver performance with software-defined vector carrier tracking for rocket launching

It is well-known that the use of Vector Tracking Loops (VTL) in GNSS receivers can result in improved tracking performance and sensitivity, faster acquisition, and improved interference robustness. However, despite the availability of software-defined radio (SDR) GNSS receivers in practical applications, there is currently no open-source implementation of Vector Tracking techniques able to operate in real-time. This work introduces a VTL algorithm applied to track the Doppler shift and its rate, using the open-source GNSS-SDR framework. This leads to a novel real-time SDR GNSS VTL receiver capable to work with different COTS front-ends. The proposed implementation was tested in a challenging non-conventional, high dynamics positioning scenario to obtain the position and velocity vectors of a rotation-stabilized guided rocket. The scenario was simulated with a GNSS RF signal generator, captured with a COTS front-end and processed by GNSS-SDR. Results show that the algorithm and its proposed implementation are able to provide full tracking, even under demanding accelerations. The positioning performance is measured using standard metrics, and we provide a fully automated reproducibility path. The source code is released under the General Public License v3.0, and will contribute to GNSS-SDR's open-source code base.

Performance evaluation of single and double-frequency low-cost GNSS receivers in static relative mode

The advancement of low-cost GNSS receivers with modern built-up characteristics has opened a new window to investigate the performance of various low-cost receivers with an outlook on their performance and suitability for varied geodetic purposes. The main objective of this study is to evaluate the positioning performance of single and double-frequency GNSS receivers in combination with geodetic antennas in static relative mode regarding Mexican regulations. The recorded observations were processed by a static relative method including the CORS station from the National Institute of Statistics and Geography in Mexico (INEGI). The results of the survey conducted at a distance of 4 and 33 km from CORS station show similar accuracy for all low-cost receivers. For low-cost GNSS receivers NEO-M8T, NEO-6T, and ZED-F9P the solutions that were obtained reached mm in horizontal precision using a geodetic grade antenna. Similarly, the ZED-F9P model was proved at a long distance from the CORS station and presents high precision. Regarding the vertical component, in all cases where the GGM10 model was included, the vertical component is not allowed to use for topography or geodetic works, however, the horizontal component where mm precision was achieved is allowed for different highly precision survey works.

Feasibility analysis of the performance of low-cost GNSS receivers in monitoring dynamic motion

The development of low-cost GNSS receivers broadens their applications, such as deformation monitoring, which have been performed routinely by survey-grade GNSS receivers. To evaluate the performance of low-cost GNSS receivers, we assessed the precision of low-cost multi-GNSS receivers in monitoring dynamic motion and developed methods of using a closely-spaced dual low-cost GNSS receivers’ system to enhance their performance. In this study, both the survey-grade and low-cost GNSS receiver/antennas were mounted on a circular rotating device executing controlled periodic rotation. It was shown that the precision of the low-cost GNSS receivers could be enhanced to the level of 2–4 mm, by using multi-GNSS observations and limiting the noise level based on error modelling and filtering of the closely–spaced low-cost GNSS receivers. Finally, from the experiments and a real bridge monitoring application, it was proved that low-cost GNSS receivers could accurately define modal frequencies of ∼0.362 Hz and ∼1.680 Hz, respectively.

Effect of Continuous Wave Interference on GNSS Receivers

The positioning performance of GNSS receivers is strongly influenced by radio interferences, especially continuous wave interference (CWI). Recent studies have modeled the effects of the interference and have shown that the effect of the interference is strongest where the frequency offset between CWI interference and the GNSS signal is a multiple of 1KHz. However, these studies have not yet modeled the effect of phase offset between CWI interference and signal which has a significant impact on the positioning performance. In this paper, we present the effect of CWI interference on positioning performance considering the role of both frequency and phase offset. In addition, theoretical and simulation results also show that CWI noise does not significantly affect the signal with some specific values of phase offset.

Low Computational-Complexity vector tracking for Low-Cost GNSS receivers

Estimating the position, velocity, and time of GNSS receivers is based on tracking loops and extracting navigation satellite information. There are two methods for navigation satellites signal tracking: Scalar Tracking Loop (STL) and Vector Tracking Loop (VTL). The inexpensive GNSS receivers usually use STL approach, but VTL approach has advantages such as weak signal tracking, better capability against signal interference, faster tracking after temporary signal outages. Hence, using this method for tracking can improve the performance of GNSS receiver. The main drawback of the VTL method is its high computational volume. In this paper, three techniques have been proposed to reduce the computational load of this tracking method that enables the implementation of the VTL method on inexpensive receivers. The results with real data and simulations show that if these three techniques are used simultaneously, the computational load is reduced by more than 90% and on the one hand; the performance of the tracking loops shows no significant reduction compared to the standard VTL. Therefore, the simultaneous use of these three techniques to implement the VTL method can be very effective on low-cost and low-dynamic receivers. Two techniques of the three proposed techniques can also be used to implement the VTL on all types of GNSS receivers.

Feasibility Analysis of the Performance of Low-Cost Gnss Receivers in Monitoring Dynamic Motion

Feasibility Analysis of the Performance of Low-Cost Gnss Receivers in Monitoring Dynamic Motion

Assessing the positioning performance of GNSS receivers under different geomagnetic storm conditions

GNSS signals are affected when solar activity causes sudden variations in the density of the ionosphere. Few studies concentrate on positioning performance of IGS stations using different GNSS receivers under different geomagnetic storm conditions. This paper for the first time presents IF and UC PPP positioning performance of stations with different receivers during the quiet, moderate, intense, and super storms period. Firstly, a comprehensive investigation of geomagnetic storms effects on the occurrence of GPS cycle-slip and PPP positioning performance have been presented. Secondly, the influences of geomagnetic storms on the occurrence of cycle-slip and IF PPP positioning performance for stations using receivers provided by ‘JAVAD’, ‘LEICA’, and ‘TRIMBLE’ manufacturers have been comprehensively studied. Finally, this study investigates the geomagnetic storms effects on IF PPP positioning performance of stations using receiver types ‘JAVAD TRE_G3TH DELTA’, ‘JAVAD TRE_3 DELTA’, ‘LEICA GR25’, and ‘TRIMBLE NETR9’ by analysing observed data collected at mid-latitude region.

A probabilistic model for on-line estimation of the GNSS carrier-to-noise ratio

This article is dedicated to the estimation of the GNSS signal carrier-to-noise ratio using the in-phase component of the signals as observations. In a GNSS receiver, it is the statistic of the correlation provided by the code tracking loop that is used to estimate the carrier-to-noise ratio. In fact, carrier-to-noise estimation is used to monitor the performance of GNSS receivers and the quality of the received signals. In this article, we aim at high rate carrier-to-noise estimation, namely the code repetition rate (e.g. 1ms for GPS C/A), in order to maximize the time resolution of carrier-to-noise observations. We show that in a 1-bit quantization receiver, the in-phase component of the signal can provide a direct observation of the signal amplitude, and therefore of the carrier-to-noise ratio. However, the model that links the 1ms rate observations of the in-phase component with the signal amplitude is non-linear. The non-linear expression that links the maximum value of the in-phase correlation component to the signal amplitude is derived. In order to estimate the time varying amplitudes of the signals, we propose an Extended Kalman Filter to reverse the non-linear expression with the noisy observations of correlation provided by the tracking loop. The proposed model and filter inversion method are assessed on synthetic and real data, while investigating the effect of the cross-correlation contribution of the visible satellites on the estimations. We show using real data that, for a 1-bit quantization receiver, the proposed estimator can achieve the same accuracy as a widely known commercial GNSS receiver with a much higher data rate. We also show that the proposed approach can cope with abrupt changes in the observations compared to a classical C/N0 estimate.

Feasibility of Consumer Grade GNSS Receivers for the Integration in Multi-Sensor-Systems.

Various GNSS applications require low-cost, small-scale, lightweight and power-saving GNSS devices and require high precision in terms of low noise for carrier phase and code observations. Applications vary from navigation approaches to positioning in geo-monitoring units up to integration in multi-sensor-systems. For highest precision, only GNSS receivers are suitable that provide access to raw data such as carrier phase, code ranges, Doppler and signal strength. A system integration is only possible if the overall noise level is known and quantified at the level of the original observations. A benchmark analysis based on a zero baseline is proposed to quantify the stochastic properties. The performance of the consumer grade GNSS receiver is determined and evaluated against geodetic GNSS receivers to better understand the utilization of consumer grade receivers. Results indicate high similarity to the geodetic receiver, even though technical limitations are present. Various stochastic techniques report normally distributed carrier-phase noise of 2 mm and code-range noise of 0.5–0.8 m. This is confirmed by studying the modified Allan standard deviation and code-minus-carrier combinations. Derived parameters serve as important indicators for the integration of GNSS receivers into multi-sensor-systems.

Evaluation method for the performance of GNSS receiver influenced by GEO SAR signal

Evaluation method for the performance of GNSS receiver influenced by GEO SAR signal

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.

Benefits and Limitations of the Record and Replay Approach for GNSS Receiver Performance Assessment in Harsh Scenarios

Global navigation satellite systems play a significant role in the development of intelligent transport systems, where the estimation of the vehicle’s position is a key element. However, in strongly constrained environments such as city centers, the definition of quality metrics and the assessment of positioning performances are challenges to be addressed. Due to the variability of different urban scenarios, the modeling of the dynamics as well as the architecture of the positioning platform, which might embed other sensors and aiding means to the GNSS unit, make it hard to define unambiguous positioning metrics. Performance assessment through analytical models and simulators can be ineffective in terms of cost, complexity, and general validity and scalability of the results. This paper shows how a record and replay approach can be an efficient solution to grant fidelity to a realistic scenario. This work discusses advantages and disadvantages with emphasis on the case study of harsh scenarios. Such an approach requires proper data collections that allow the replay phase to test the GNSS-based positioning terminals. This paper presents the results obtained on a set of field tests related to different scenarios, selected as representative for the key performance indicators assessment.

Research on multi-constellation GNSS compatible acquisition strategy based on GPU high-performance operation

With the continuous development of satellite navigation, how to make full use of the compatibility and interoperability among the four constellations deserves our deep thinking. Signal acquisition is a critical technology that affects the performance of GNSS receivers. However, its implementation has high requirements on both resource consumption and processing time. In recent years, graphics processing unit (GPU) technology with a large number of parallel processing units is gradually applied to the navigation field. In this paper, a multi-constellation-compatible capture strategy based on GPU is proposed. Compared with the traditional GNSS signal processing, the design has better flexibility and portability, and the acquisition parameters of the system can be configured flexibly through the interface. The experimental results show that the proposed scheme makes full use of the powerful parallel processing capability of GPU, which greatly reduces the acquisition time and improves the efficiency of signal processing, with the increase of data processing. In addition, as the amount of signal processing data increases, the advantages of the CPU high-performance computing platform will be more obvious.

Assessment Method of Multipath Mitigation Performance for GNSS Antenna with Receiver Algorithms

Multipath is one of the most important sources of positioning error in GNSS. Well-designed antennas can mitigate multipath signals and enhance the performance of GNSS receivers. This paper concentrates on methods to assess multipath mitigation performance for GNSS antennas. We propose a model to describe multipath environment in GNSS ground stations. The model analyzes effects caused by inclined reflective surfaces and multipath mitigating algorithms in receivers. A method to assess multipath mitigation performance is put forward by analyzing pseudorange code phase errors caused by multipath signals after signal processing. Based on the model and method, principles in site selection for GNSS antenna are introduced to minimize effects caused by multipath.

Increase of Carrier-to-Noise Ratio in GPS Receivers Caused by Continuous-Wave Interference

The increased use of personal private devices (PPDs) is drawing greater attention to the effects of continuous-wave interference (CWI) on the performance of global positioning system (GPS) receivers. The effective carrier-to-noise density ratio (C/N0), an essential index of GNSS receiver performance, is studied in this paper. Receiver tracking performance deteriorates in the presence of interference. Hence, the effective C/N0, which measures tracking performance, decreases. However, simulations and bench tests have shown that the effective C/N0 may increase in the presence of CWI. The reason is that a sinusoidal signal is induced by the CWI in the correlator and may be tracked by the carrier tracking loop. Thus, the effective carrier power depends on the power of the signal induced by the CWI, and the effective C/N0 increases with the power of the CWI. The filtering of the CWI in the carrier tracking loop correlator and its effect on the phase locked loop (PLL) tracking performance are analyzed. A mathematical model of the effect of the CWI on the effective C/N0 is derived. Simulation results show that the proposed model is more accurate than existing models, especially when the jam-to-signal ratio (JSR) is greater than 30 dBc.

Pre-Despreading Authenticity Verification for GPS L1 C/A Signals

The performance of GNSS receivers can be highly affected by structural interference signals such as spoofing and meaconing. The structure and power level of these signals are very similar to those of the authentic GNSS signals and as such they cannot be easily detected in the received signal set. This paper proposes a low complexity authenticity verification technique that takes advantage of the GPS signal structure in order to detect the presence of undesired structural interferences in the received signal samples. The proposed technique operates on the raw signal samples and can detect the overpowered GPS spectrum prior to signal de-spreading. This method does not need any information regarding the AGC gain and operates on digitized signal samples only. The simulation results and real data processing verify the desired performance of the proposed method even when the received signal strength (RSS) of the spoofing and authentic signals are very close to each other. Copyright © 2014 Institute of Navigation.