Ambiguity Resolution Research Articles

Tight Integration Kinematic PPP-AR Using GPS/Galileo/QZSS Overlapping Frequency Signals and Its Performance in High-Shade Environments

Several global navigation satellite systems (GNSS) broadcast overlapping frequencies to enhance interoperability, allowing tight integration with only one reference satellite for every system with the same frequency. The key to realizing tight integration is estimating and utilizing differential intersystem biases, which allows the integer characteristic of the differenced ambiguity of two satellites from different systems to be retrieved. In this study, a detailed algorithm flow of a tight integration kinematic uncalibrated phase delay (UPD)-based PPP ambiguity resolution (PPP-AR) method, which includes multiple parts, is introduced. Subsequently, PPP-AR numerical experiments were conducted in a high-shade observation environment to determine the performance. In comparison with traditional methods, our results indicate that the average success fix rate improves from 83% to 100% after using the tight integration method in an environment where only three satellites are observed for each system. Moreover, for fewer than nine satellites, the tight integration method can still consistently maintain a fixed state. However, for comparison, the traditional loose integration method could no longer be implemented.

GIVE: A Tightly Coupled RTK-Inertial–Visual State Estimator for Robust and Precise Positioning

Continuous and reliable high-precision positioning in a wide area is an important task for autonomous driving. In this paper, we present GIVE, a nonlinear optimization-based GNSS-inertial-visual (GIV) state estimator that tightly fuses multi-GNSS raw carrier phase and pseudorange observations with inertial and visual information to address the problem of continuous and reliable centimeter-level positioning in urban canyons where GNSS signal may be intermittent or even outage. The primary contribution of this work is the investigation of the high-precision carrier phase observations in terms of continuity and ambiguity resolution (AR) in GIV fusion. In particular, first we propose a carrier phase-enhanced bundle adjustment (CPBA) method for accurate and drift-free GIV state estimation, in which the continuously tracked carrier phase arcs are used to establish the ambiguity constraints of current and historical states which have common-view satellites. The common-view ambiguity constraints are jointly optimized with IMU pre-integration constraints and visual reprojection constraints under the factor graph framework. Furthermore, we develop a marginalization-based carrier phase ambiguity propagation (AP) method to leverage the continuity of the carrier phase and achieve an optimal estimation of the float ambiguity, which is essential for the correct AR of the carrier phase. An integer AR module, in combination with the proposed CPBA, enables the centimeter-level positioning accuracy of the GIV framework. We extensively evaluate the proposed method in both public datasets and challenging datasets collected in deep urban environments. Statistics show that the GIVE can provide smooth centimeter-level positioning results in open-sky conditions. Two challenging urban driving tests demonstrate the GIVE can achieve continuous centimeter to decimeter-level positioning accuracy and obtain 86.5-94.1% 2D positioning availability (<10 cm) and more than 94% 3D positioning availability (<30 cm) in deep urban environments.

Enhanced Spatial Spoofing Detection With and Without Direction of Arrival Estimation

Spoofing, the transmission of false (GNSS) signals, threatens receivers. The first step in dealing with spoofers is to detect the attack. Once a spoofing attack is detected, spatial detection methods using an array of antennas can additionally mitigate spoofing through spatial nulling. This article presents a spatial spoofing detection approach using the estimated (ASVs) from (DOA) estimation. Further, the method is compared to blind detection and post-DOA estimation methods. Simulation results show that the approach is comparable to the current state-of-the-art if the same a priori information is used. However, superior performance is achieved if the attitude of the antenna array is known. The presented approach represents an alternative method for spatial spoofing detection that leverages the DOA estimates but remains in the ASV domain. Therefore, it benefits from noise modeling and ambiguity resolution.

Two High-Precision Ultrashort Baseline Location Methods Based on Phase Difference

In this paper, two ultra-short baseline location methods for underwater broadband signal are proposed. In order to improve the positioning accuracy of acoustic positioning, the coarse time delay is measured by parabolic interpolation of cross-correlation results. According to the coarse time delay, the ambiguity number of the phase at the cross-correlation peak is solved and the ambiguity is solved twice, so as to obtain the high-precision time delay difference and improve the positioning accuracy. This method is suitable for the case without near body multipath. Aiming at the near body multipath problem, its influence on ambiguity resolution and positioning accuracy is analyzed. Based on the coarse time delay, adjusting time delay and the Fourier transform of cross-power spectrum phase joint method is proposed to further improve the accuracy of coarse time delay, so as to improve the accuracy of ambiguity resolution. On this basis, the location information feedback and real-time attitude information are used to estimate the coarse time delay difference, and the ambiguity number is further constrained to further improve the accuracy of ambiguity resolution. In order to reduce the influence of multipath on the phase and improve the positioning accuracy, a Kaiser window is added to the source and the phase difference is changed to the phase difference at the first point of threshold. Numerical simulation and field test demonstrate that the first algorithm proposed in this paper improves the positioning accuracy and the accuracy of ambiguity resolution. The second algorithm improves the accuracy of ambiguity resolution and positioning accuracy in the presence of near body multipath.

Carrier Assisted Robust Unambiguous Positioning Technique for Subcarrier Modulated Signals in GNSS

Various subcarrier modulations bring wider Gabor bandwidths and higher-precision ranging and positioning potential to the new generation of Global Navigation Satellite System (GNSS) signals. However, they may also introduce intolerable ambiguity problems for signal tracking, ranging, and positioning. In order to take advantage of high-precision subcarriers in subcarrier modulated signals for unambiguous ranging and positioning, we propose a Carrier Assisted Robust Unambiguous Positioning Technique (CARUPT), which consists of a Carrier Assisted Kalman filter (CA-Kalman) module and an Observation Cycle-slip Detection (OCD) module. The CA-Kalman module utilizes the undifferenced code and subcarrier observations and time-differenced carrier observations derived from two-dimensional tracking to resolve subcarrier ambiguities in the position domain. The OCD module includes a carrier-involved Subcarrier Cycle-slip Detector (SCD) and a high-order difference-based Carrier Cycle-slip Detector (CCD) so as to avoid the impact of subcarrier and carrier cycle slips on the robust resolution of subcarrier ambiguities. In this paper, performances in theory, simulation, and real data experiments comprehensively demonstrate that compared with existing techniques, the CARUPT can resolve subcarrier ambiguities with faster convergence speed, higher accuracy, and robustness, deriving the most reliable unambiguous positioning results.

Low-Cost Inertial Aiding for Deep-Urban Tightly Coupled Multi-Antenna Precise GNSS

<h3>Summary</h3> A vehicular pose estimation technique is presented that tightly couples multi-antenna carrier-phase differential GNSS (CDGNSS) with a low-cost MEMS inertial sensor and vehicle dynamic constraints. This work is the first to explore the use of consumer-grade inertial sensors for tightly coupled urban CDGNSS, and first to explore the tightly coupled combination of multi-antenna CDGNSS and inertial sensing (of any quality) for urban navigation. An unscented linearization permits ambiguity resolution using traditional integer least-squares while both implicitly enforcing known-baseline-length constraints and exploiting the multi-baseline problem’s inter-baseline correlations. A novel false fix detection and recovery technique is developed to mitigate the effect of conditioning the filter state on incorrect integers. When evaluated on the publicly available TEX-CUP urban positioning data set, the proposed technique achieves, with consumer- and industrial-grade inertial sensors, respectively, a 96.6% and 97.5% integer fix availability, and a 12.0-cm and 10.1-cm overall (fix and float) 95th percentile horizontal positioning error.

Алгоритм обработки сигналов в фазовых пеленгаторах с двумя линейными антенными решетками, расположенными под углом друг к другу

The article suggests an algorithm of processing the signals in two-coordinated phase radio finders. The aerial systems of this finders consist of two linear aerials with any number of phasemetric bases in each. The correlations for calculating the probability of ambiguity resolution of phase measurements and the standard error of the calculation results are obtained and checked by modeling the finder operation on computers. The use of the mentioned above algorithm simplifies the signal processing in comparison with the known ones.

Mixed QZSS/GPS/Galileo RTK positioning with a trade-off between ionosphere-weighting and ionosphere-fixed models: an ambiguity resolution method for Japan

Mixed QZSS/GPS/Galileo RTK positioning with a trade-off between ionosphere-weighting and ionosphere-fixed models: an ambiguity resolution method for Japan

High‐Precision Positioning Simulation and Experimental Research of Special Operation Vehicles Based on Network RTK

In terms of driverless systems, high‐precision positioning technology is one among the critical aspects of driverless cars to achieve driverlessness. This study analyzed the working principles of GNSS (global navigation satellite system) and SINS (strapdown inertial navigation system) and elaborated the principles of the least square method and LAMBDA algorithm in the integer ambiguity resolution. Based on the network RTK positioning technology and the abovementioned theory, the unmanned automatic work vehicle was used as the research object, and the fusion positioning algorithm of the BDS/GPS system and inertial sensor was used to propose a high‐precision positioning technology for the unmanned automatic work vehicle. The combined navigation system model was studied and constructed. Relevant verification was carried out through simulation and experiment. The results were as follows: the pitch angle error was less than 0.1°, the roll angle error was less than 0.05°, the speed error was less than 0.2 m/s, and the position error was less than 2.1 m. The outcomes indicate that an integrated navigation and positioning algorithm for driverless vehicles can significantly enhance the localisation accuracy and reliability of navigation. The research results are of engineering value and practical application for the development of unmanned automatic special vehicle positioning systems.

Radar Interferometric Phase Ambiguity Resolution Using Viterbi Algorithm for High-Precision Space Target Positioning

Radar Interferometric Phase Ambiguity Resolution Using Viterbi Algorithm for High-Precision Space Target Positioning

Realizing rapid re-convergence in multi-GNSS real-time satellite clock offset estimation with dual-thread integer ambiguity resolution

Realizing rapid re-convergence in multi-GNSS real-time satellite clock offset estimation with dual-thread integer ambiguity resolution

Ambiguity-Fixing in Frequency-Varying Carrier Phase Measurements: Global Navigation Satellite System and Terrestrial Examples

<h3>Abstract</h3> Carrier phase signals are considered among the key observations in global navigation satellite systems (GNSSs) and several other high-precision interferometric measurement systems. However, these ultra-precise measurements are not fully exploited when the integerness of their inherent ambiguities is discarded during the estimation process. Provided that the integer-estimable functions of their phase ambiguities are properly identified, integer ambiguity resolution (IAR) can be utilized to benefit their parameter solutions. For the GNSS code division multiple access systems with transmitters that broadcast carrier phase signals on identical frequencies, these integer-estimable functions have been characterized and are well-known as double differenced ambiguities. However, this is not the case with “frequency-varying” carrier phase signals that are broadcast by GLONASS satellites, Low-Earth-Orbiting communication satellites, or cellular long-term evolution (LTE) transmitters. This study aims to present full-rank models that can be used to identify integer-estimable ambiguity functions, thereby bringing the observation equations of frequency-varying carrier phase measurements into an IAR-applicable form. Our analytical results are supported by several numerical examples, including GNSS and terrestrial-based IAR as well as a new set of “inter-frequency” integer ambiguities that this study discovers in Galileo multi-frequency carrier phase signals.

BDS/QZSS integrated PPPAR time–frequency transfer

Based on BeiDou navigation satellite system (BDS), the Quasi-Zenith satellite system (QZSS) was added to assist in studying the precise point positioning (PPP) time and frequency transfer effect. Ambiguity resolution (AR) is the key to the rapid conversion of the PPP method. Therefore, this paper also used the ionospheric-free combination and the observable-specific signal bias (OSB) product of Wuhan University to test the time–frequency transfer effect of BDS ambiguity-fixed. In this way, BDS PPP, BDS + QZSS PPP, BDS PPP-AR, and global positioning system (GPS) PPP methods were formed. Six stations located in Japan and Australia were selected for experiments. Conclusion: BDS can reach the same level as GPS; when the cut-off angle is greater than 15°, adding QZSS could improve the success rate, accuracy, and frequency stability of the solution of time links effectively; the ambiguity fixed strategy can improve the time transfer accuracy but not the short-term frequency stability.

PPP-ARISEN: an open-source precise point positioning software with ambiguity resolution for interdisciplinary research of seismology, geodesy and geodynamics

PPP-ARISEN: an open-source precise point positioning software with ambiguity resolution for interdisciplinary research of seismology, geodesy and geodynamics

Processing Referentially Ambiguous Pronouns by Adult Learners of English as a Foreign Language

Introduction: Processing ambiguous pronouns by L1 speakers of English has been the subject of a great bulk of research. Only a few studies, however, have investigated the ambiguity resolution of pronouns by people for whom English is a second or foreign language. In this study, the researchers employed a picture selection task to explore how adult Iranian EFL learners treated ambiguous pronouns.&#x0D; Methodology: The materials were 20 experimental items in four different conditions (i.e., manipulation of neither noun phrases [NP1] nor NP2, NP1 manipulation, both NPs manipulation and NP2 manipulation) plus 30 filler items. The principal purpose of this study was to investigate whether the manipulation of NPs by attaching extra content/semantic information to them had any impact on their accessibility and how the participants associated ambiguous pronouns with NPs when attempting to choose an antecedent.&#x0D; Results: The results confirmed the idea that increasing the length of an NP is an important mechanism employed by EFL learners in the process of ambiguity resolution of pronouns. The results also indicated that the NP length mechanism was a better predictor of accessibility in comparison with other mechanisms, such as the primacy effect, the subject rule, and the grammatical role.&#x0D; Conclusion: The findings demonstrated that when an NP carries extra-linguistic information compared to other NPs, it might have a better chance of being selected as the referent of an ambiguous pronoun.

Using Various Analysis Center Products to Assess the Time-Frequency Transfer Performance of GPS/Galileo/BDS PPPAR Methods

Numerous organizations and Analysis Centers (AC) currently offer various Ambiguity Resolution (AR) products using various methodologies. However, there are no associated studies on their use for time-frequency transfer. This paper examines 16 Multi-GNSS Experiment (MGEX) stations with external high-precision atomic clocks to constitute 15 international time comparison links, and uses AR products data from CNES, SGG, CODE, and PRIDE laboratories, using three ambiguity-fixed strategies, to thoroughly evaluate the effects of various strategies and AR products for high-precision time-frequency transfer. We reach the following results by using the IGS final clock product as a reference and comparing it to ambiguity-float. With various ambiguity-fixed procedures, the time stability Standard Deviation (STD) of time transfer is increased for a single GPS, and the improvement ranges from 10 to 40%. The frequency stability has barely improved; up to 40%, the most notable improvement comes from FCB with GRM products. The time stability STD of combinations has improved after the addition of the Galileo system compared to the single GPS, and the improvement ranges from 2 to 9%. Most strategies have been improved, while a few techniques have been weakened with the GEC (GPS + Galileo + BDS) combination. We feel that the stability has not significantly increased with the systems’ increase in terms of short-term stability after comparing multiple groups of linkages.

Inherent Limitations of Smartphone GNSS Positioning and Effective Methods to Increase the Accuracy Utilizing Dual-Frequency Measurements

Xiaomi Mi8 with a Broadcom BCM47755 chip, an Android smartphone that supports multi-constellation (GPS, GLONASS, Galileo, BeiDou, and QZSS) and dual-frequency (L1/E1 and L5/E5), was launched in May 2018. Unlike previously released smartphones, it was technically expected to provide robust precise positioning with a fast ambiguity resolution, which led many researchers to be overly optimistic about the applicability of high-accuracy techniques such as real-time kinematic (RTK) systems and precise point positioning (PPP) of smartphones. The global navigation satellite system (GNSS) raw measurement quality of Android smartphones is, however, inherently far lower than that of general GNSS receivers due to their structure, which accordingly makes it difficult for them to be realized. Considering inherent limitations of smartphones such as low-quality antenna, frequent cycle slips, and the duty cycle, a practical strategy including L5 measurements, pseudo-range corrections for L5, and a weighting method is proposed in this paper. The results show that the proposed methods of L5 differential GNSS (DGNSS) and Doppler-based filtering can guarantee a positioning accuracy of 1.75 m horizontally and 4.56 m vertically in an Android device, which is comparable to the performance of commercial low-cost receivers.

Adaptive Kalman filter based on integer ambiguity validation in moving base RTK

In high-precision dynamic positioning, it is necessary to ensure the positioning accuracy and reliability of the navigation system, especially for safety–critical applications, such as intelligent vehicle navigation. In the face of a complex observation environment, when the global navigation satellite system (GNSS) uses carrier phase observations for high-precision relative positioning, ambiguity resolution will be affected, and it is difficult to estimate all ambiguities. In addition, when the GNSS signal quality and measurement noise level are difficult to predict in an environment with many occlusions, the received satellite observations are prone to very large errors, resulting in apparent deviations in the positioning solution. However, traditional positioning algorithms assume that the measurement noise is constant, which is unrealistic. This will cause incorrect ambiguity resolution, lead to meter-level positioning errors, reduce the reliability of the system, and increase the integrity risk of the system. We proposed an innovative adaptive Kalman filter based on integer ambiguity validation (IAVAKF) to improve the efficiency of ambiguity resolution (AR) and positioning accuracy. The partial ambiguity resolution (PAR) method is applied to solve the integer ambiguities. Then, the accuracy of the fixed ambiguity is verified by the ambiguity success rate. Taking the ambiguity success rate as a dynamic adjustment factor, the measurement noise matrix and variance–covariance matrix of the state estimation is adaptively adjusted at each time interval in the Kalman filter to provide a smoothing effect for filtering. The optimal Kalman filter gain matrix is obtained to improve positioning accuracy and reliability. As a result, the static and dynamic vehicle experiments show that the positioning accuracy of the proposed IAVAKF is improved by 26% compared with the KF. Through the IAVAKF, a more realistic PL can be obtained and applied to evaluate the integrity of the navigation system in the position domain. It can reduce the false alarm rate by 2.45% and 1.85% in the horizontal and vertical directions, respectively.

Production and Comprehension of Prosodic Boundary Marking in Persons With Unilateral Brain Lesions.

Persons with unilateral brain damage in the right hemisphere (RH) or left hemisphere (LH) show limitations in processing linguistic prosody, with yet inconclusive results on their ability to process prosodically marked structural boundaries for syntactic ambiguity resolution. We aimed at systematically investigating production and comprehension of three prosodic cues (f 0 range, final lengthening, and pause) at structural boundaries in coordinate sequences in participants with right hemisphere brain damage (RHDP) and participants with left hemisphere brain damage (LHDP). Twenty RHDP and 15 LHDP participated in our study. Comprehension experiment: Participants and a control group listened to coordinate name sequences with internal grouping by a prosodically marked structural boundary (grouped condition, e.g., "(Gabi und Leni) # und Nina") or without internal grouping (ungrouped condition, e.g., "Gabi und Leni und Nina") and had to identify the target condition. The strength and combinations of prosodic cues in the stimuli were manipulated. Production experiment: Participants were asked to produce coordinate sequences in the two conditions (grouped, ungrouped) in two different tasks: a Reading Aloud and a Repetition experiment. Accuracy of participants' productions was subsequently assessed in a rating study and productions were analyzed with respect to use of prosodic cues. In the Comprehension experiment, RHDP and LHDP had overall lower identification accuracies than unimpaired control participants and LHDP were found to have particular problems with boundary identification when the pause cue was reduced. In production, LHDP and RHDP employed all three prosodic cues for boundary marking, but struggled to clearly mark prosodic boundaries in 28% of all productions. Both groups showed better performance in reading aloud than in repetition. LHDP relied more on using f 0 range and pause duration to prosodically mark structural boundaries, whereas RHDP employed final lengthening more vigorously than LHDP in reading aloud. We conclude that processing of linguistic prosody is affected in RHDP and LHDP, but not completely impaired. Therefore, prosody can serve as a relevant communicative resource. However, it should also be considered as a target area for assessment and treatment in both groups. https://doi.org/10.23641/asha.21637505.

Precise orbit determination and baseline consistency assessment for Swarm constellation

Precise orbit determination (POD) and precise baseline determination (PBD) of Swarm satellites with 4 years of data are investigated. Ambiguity resolution (AR) plays a crucial role in achieving the best orbit accuracy. Swarm POD and PBD based on single difference (SD) AR and traditional double difference (DD) AR methods are explored separately. Swarm antenna phase center variation (PCV) corrections are developed to further improve the orbit determination accuracy. The code multipath of C1C, C1W and C2W observations is first evaluated and clear variations in code noise related to different receiver settings are observed. Carrier phase residuals of different time periods and different loop tracking settings of receiver are studied to explore the effect of ionospheric scintillation on POD. The reduction of residuals in the polar and geomagnetic equator regions confirms the positive impact of the updated carrier tracking loops (TLs) on POD performance. The SD AR orbits and orbits with float ambiguity (FA) are compared with the Swarm precise science orbits (PSOs). An average improvement of 27 %, 4 % and 16 % is gained in along-track, cross-track and radial directions by fixing the ambiguity to integer. For Swarm-A/B and Swarm-B/C formations, specific days are selected to perform the DD AR-based POD during which the average distance of the formation satellites is less than 5000 km. Satellite laser ranging (SLR) observations are employed to validate the performance of FA, SD AR and DD AR orbits. The consistency between the SD AR orbits and SLR data is at a level of 10 mm which shows an improvement of 25 % when comparing with the FA results. An SLR residuals reduction of 15 % is also achieved by the DD AR solution for the selected days. Precise relative navigation is also an essential aspect for spacecraft formation flying missions. The closure error method is proposed to evaluate the baseline precision in three dimensions. A baseline precision of 1–3 mm for Swarm-A/C formation and 3–5 mm for Swarm-A/B and Swarm-B/C satellite pairs is verified by both the consistency check and closure error method.