GPS World

Tag: Wuhan University

  • Adaptive model shields real-time positioning from ionospheric chaos

    Adaptive model shields real-time positioning from ionospheric chaos

    For users relying on centimeter-level accuracy — such as surveyors, engineers and autonomous systems — ionospheric disturbances can mean system downtime and significant losses. Traditional network real-time kinematic (NRTK) positioning methods assume smooth ionospheric conditions and thus fail during active solar periods.

    To meet these challenges, a research team from Wuhan University and Guangzhou Hi-Target Navigation Tech Co. Ltd. developed an NRTK positioning model capable of maintaining centimeter-level accuracy under intense ionospheric disturbances.

    This approach could serve as the foundation for next-generation, self-correcting navigation systems that operate reliably under any atmospheric condition.

    The study (DOI: 10.1186/s43020-025-00179-4), published in Satellite Navigation on Oct. 6, introduces a dual-optimization framework that integrates real-time ionospheric indices with adaptive functional and stochastic models. By learning from disturbance patterns and automatically recalibrating user-side algorithms, the system dramatically enhances GNSS reliability during the ongoing solar cycle peak — offering a key safeguard for positioning technologies in low-latitude regions most vulnerable to ionospheric turbulence.

    The innovation centers on leveraging the rate of the total electron content index (ROTI), a key indicator of ionospheric activity, to dynamically adjust both ionospheric residual estimation and observation weighting. When the system detects disturbances, it automatically reduces the influence of affected satellites and refines error models in real time.

    Using data from Hong Kong’s Continuously Operating Reference Station (CORS) network — one of Asia’s most active low-latitude regions — the researchers found that ROTI showed a strong positive correlation (0.91) with ionospheric interpolation errors and a negative correlation (–0.9) with signal-fixing rates.

    Compared to conventional NRTK methods, their adaptive “Method B” improved horizontal and vertical positioning accuracy by 37.6% and 41.6%, respectively. Moreover, it achieved a stable 84% average fixing rate, even during equinoctial months when ionospheric scintillation is strongest. The results reveal not just a technical upgrade but a practical solution for real-time navigation across regions frequently affected by solar-induced ionospheric noise.

    “Our method essentially teaches GNSS systems to think smarter under stress,” said Xiaodong Ren, senior researcher at Wuhan University and lead author of the study. “By allowing the model to ‘sense’ and adapt to space-weather disturbances in real time, we’ve moved beyond static correction systems toward intelligent positioning. This is crucial not only for maintaining accuracy but also for ensuring resilience as solar activity intensifies.”

    He added that this approach could serve as the foundation for next-generation, self-correcting navigation systems that operate reliably under any atmospheric condition.

    This adaptive NRTK framework marks a significant leap forward for industries that depend on precise, real-time location data — from autonomous driving and drone surveying to precision agriculture and infrastructure monitoring, Ren said. By integrating live ionospheric monitoring into everyday positioning workflows, it ensures continuous accuracy even when solar storms strike.

    Future developments may combine the model with artificial intelligence and multi-constellation GNSS networks to further enhance forecasting and resilience. As Earth moves through one of its most active solar cycles, Ren said, such innovations will be essential to keeping navigation, communication and automation systems firmly on course.

  • New satellite orbit determination method could boost navigation precision for future mega-constellations

    New satellite orbit determination method could boost navigation precision for future mega-constellations

    The rotation-corrected integrated POD method holds significant promise for global navigation augmentation, autonomous LEO-based navigation systems, and real-time positioning services.

    Modern satellite constellations such as OneWeb, Starlink and CENTISPACE promise global communications and navigation capabilities using low-Earth orbit (LEO) constellations. However, their precise orbit determination (POD) requires dense ground station networks — costly and often limited by geopolitical or geographical constraints.

    Inter-satellite links (ISLs) help reduce ground dependence but suffer from “rotational unobservability,” where the entire constellation drifts in orientation due to the lack of an absolute spatial reference. Existing fixes often require additional infrastructure or high-quality GNSS products, which increase latency and operational complexity.

    Because of these challenges, a more autonomous, low-latency approach that leverages existing onboard capabilities is needed to ensure reliable, high-accuracy orbits for mega-constellations.

    Wuhan University researchers have developed and validated a rotation-corrected integrated POD method that fuses ISL measurements with onboard BeiDou-3 (BDS-3) GNSS observations. Published (DOI: 10.1186/s43020-025-00175-8) in Satellite Navigation on Aug. 4, the study demonstrates how the technique simultaneously estimates the orbits of LEO and BDS-3 medium-Earth-orbit (MEO) satellites, corrects systematic rotation using BDS-3 broadcast ephemerides, and achieves centimeter-level precision.

    The approach significantly reduces reliance on ground stations, making it well-suited for real-time applications in large-scale LEO constellations, the researchers said.

    The team simulated a 66-satellite LEO constellation equipped with ISLs and onboard BDS-3 receivers, alongside 24 real BDS-3 MEO satellites. Two processing strategies were tested: using BDS-3 data from all LEOs, and from only a subset. In both cases, ISL and GNSS data were jointly processed to form a unified high–low constellation.

    Due to internal-only measurements, the initial solutions exhibited significant systematic rotation — up to 40 cm cross-track error for LEOs and over 1 meter for MEOs.

    This innovation could become a cornerstone technology for integrating LEO constellations with existing GNSS systems to enhance global navigation and timing performance.

    The researchers derived rotation angles between the integrated POD coordinate frame and the BeiDou Coordinate System implied in broadcast ephemerides, then applied a Helmert transformation to correct the orbits. After correction, LEO along-track and cross-track errors dropped from 22.7 cm and 39.3 cm to 1.3 cm and 4.2 cm, respectively. MEO errors fell from over 1.2 m to about 13 cm.

    Even when only 36 of 66 LEOs carried GNSS receivers, ISL connectivity propagated the correction across the constellation with minimal accuracy loss. Tests also examined the influence of predicted Earth rotation parameters and residual errors in broadcast ephemerides.

    “This method tackles one of the most stubborn issues in autonomous constellation orbit determination — systematic rotation caused by the lack of absolute spatial reference,” said Kecai Jiang, corresponding author of the study. “By harnessing readily available BDS-3 broadcast ephemerides and inter-satellite measurements, we can deliver centimeter-level precision without waiting for post-processed GNSS products or building extensive ground networks. This approach is not only efficient but also scalable, paving the way for real-time, high-accuracy navigation services in future mega-constellations.”

    The rotation-corrected integrated POD method holds significant promise for global navigation augmentation, autonomous LEO-based navigation systems, and real-time positioning services. By dramatically reducing reliance on ground infrastructure, it enables resilient operations in remote or geopolitically constrained regions. Its scalability makes it suitable for next-generation satellite constellations supporting broadband internet, disaster response, and precision agriculture, the researchers said.

    Moreover, the ability to achieve near-uniform accuracy across all satellites — even when only part of the constellation carries GNSS receivers — lowers hardware requirements and operational costs. This innovation could become a cornerstone technology for integrating LEO constellations with existing GNSS systems to enhance global navigation and timing performance.

  • PPP GNSS delivers real-time positioning with centimeter accuracy

    PPP GNSS delivers real-time positioning with centimeter accuracy

    Precise Point Positioning (PPP) has long held promise as a standalone, high-accuracy positioning technique, but its slow convergence and complexity in ambiguity resolution have limited widespread use. Over the past decade, GNSS modernization (GPS, Galileo and BeiDou) has introduced multi-frequency, high-precision signals, enhancements that expand opportunities for precise positioning.

    Yet challenges remain, especially in environments with obstructed views or fast-changing motion. High-fidelity corrections and real-time performance are critical for sectors like smart transportation, robotics and disaster response.

    Further in-depth research is needed to refine PPP solutions and meet the demands of real-world, dynamic applications.

    A collaborative research team from Wuhan University and affiliated institutions has published a major study in the July 2025 issue of Satellite Navigation. The team developed and validated an enhanced PPP and PPP-RTK framework using next-generation GNSS signals and satellite augmentation services.

    The study evaluated the performance of BDS-3’s PPP-B2b and Galileo’s HAS services across a variety of experimental settings, revealing dramatic improvements in positioning accuracy, convergence time, and reliability.

    These breakthroughs offer a practical roadmap for deploying real-time high-precision navigation at global scale.

    The researchers constructed an integrated precise point positioning with real-time kinematic (PPP-RTK) system incorporating real-time atmospheric corrections, observable-specific bias (OSB) products, and multi-constellation satellite data. Through extensive global experiments, they demonstrated that a combined GPS/Galileo/BeiDou configuration reduced static convergence time to under 5 minutes while achieving horizontal accuracy below 2 cm. In dynamic tests — including a real-world vehicular trial in Wuhan — PPP-RTK achieved sub-5 cm accuracy with instant or near-instant convergence, even under rapidly changing observation environments.

    These systems proved especially effective when paired with atmospheric modeling techniques like Kriging and distance interpolation. With fix rates exceeding 98%, the results underscore PPP-RTK’s readiness for mission-critical applications in rapidly changing environments.

    Additionally, the study evaluated augmentation services: the BeiDou PPP-B2b and Galileo High Accuracy Service (HAS). Both were found to significantly accelerate convergence (to under 15 minutes and 100 seconds, respectively) and deliver decimeter-level accuracy in kinematic scenarios.

    “This study marks a turning point in the quest for real-time, high-accuracy positioning,” said Xiaodong Ren, lead author and professor at Wuhan University. “By merging advanced GNSS signals, atmospheric corrections, and real-world testing, we’ve demonstrated that PPP-RTK can deliver fast, stable and highly accurate results — even in the most demanding environments. These capabilities are essential for the next generation of autonomous systems, from self-driving cars to drones and beyond.”

    The ability to achieve centimeter-level positioning accuracy quickly and without reliance on dense base station networks opens doors for a wide range of smart technologies, Xiaodong said. PPP-RTK has the potential to reshape industries such as precision agriculture, surveying, transportation logistics, and unmanned systems.

    This study provides a robust framework and empirical validation for real-world adoption of high-precision GNSS applications, according to the authors. “As satellite constellations and augmentation services continue to evolve, PPP-RTK is poised to become the foundation of global positioning solutions — reliable, scalable, and ready for deployment in tomorrow’s connected world,” Xiaodong said.

    DOI: 10.1186/s43020-025-00169-6

  • GNSS Research Center offers new version of PRIDE software

    GNSS Research Center offers new version of PRIDE software

    PRIDE logoThe latest version of the open-source PRIDE PPP-AR software is now available for GNSS researchers, students and professionals.

    “Based on the feedback of global users in the past two years, we have been improving the software to enhance its robustness and make it easy to use,” said Jianghui Geng, GNSS geodesy professor at the GNSS Research Center, Wuhan University.

    PRIDE PPP-AR V2.2 fully supports GPS, GLONASS, Galileo, BDS-2 and 3, and QZSS precise point positioning (PPP), as well as undifferenced ambiguity resolution (AR) for GPS, Galileo and BDS-2 and 3.

    Version 2.2 features improved high-precision GNSS data-processing capabilities. It supports kinematic positioning for mobile platforms such as aerial photogrammetry and ship-borne gravimetry.

    Other features include the following:

    • high-rate data up to 50 Hz can also be processed
    • the second-order ionospheric delays can be corrected
    • VMF3 for troposphere modeling is available
    • multi-day processing is allowed
    • satellite attitude quaternions are supported.

    Versions are available for the Linux, Windows and Mac operating systems to facilitate researchers and class teaching.

    The project is fully supported by the National Science Foundation of China (No. 42025401) and under the auspices of IAG Sub-Commission 4.4 “GNSS Integrity and Quality Control.” Direct questions to [email protected].

    An online training course will be held Sept. 19-23 through UNVACO.