SC 4.2: Multi-frequency Multi-constellation GNSS

Chair: Jianghui Geng (China)
Vice-Chair: Panagiotis Psimoulis (UK)
Secretary: Kunlun Zhang (China)

Terms of Reference

The GNSS has witnessed rapid development in recent years, providing increasingly refined PNT services worldwide. The construction of multi-constellations and the utilization of multi-frequency have expanded the spatial coverage, catering to the diverse application requirements across various scenarios and levels. These applications encompass autonomous driving, instantaneous high-precision positioning, precise time andfrequency transfer, as well as meteorological disaster monitoring and early warning, highlighting the immense potential of GNSS. Furthermore, GNSS chips integrated into consumer devices are progressively supporting multi-system and multi-frequency carrier phase observations, presenting extensive prospects for application. However, these advancements have also introduced new technological challenges.For instance, GNSS positioning performance is vulnerable to fragility, the issue of ambiguity resolution remains persistently challenging, and consumer device data often suffers from significant degradation. SC 4.2 aims to facilitate research activities and focuses on addressing multi-level application issues, including high-precision global time and frequency transfer, valid and reliable ambiguity resolution, high-accuracy positioning in consumer devices, and precise monitoring of meteorological disasters. SC 4.2 will coordinate various activities to provide both theoretical and practical solutions for engineering and scientific applications, thereby bridging the gaps in the application domain.

Objectives

The main objective of SC 4.2 is to facilitate collaborative research on innovative and diverse applications within the evolving landscape of GNSS, characterized by multiple systems and frequencies. It aims to promote the dissemination and translation of scientific research accomplishments and foster close cooperation among researchers, international organizations, and industry stakeholders.

Program of Activities

• Identify and investigate theoretical, methodological, and technological issues arising from the development of multi-constellation and multi-frequency systems;
• Promote and facilitate close collaboration among researchers, fostering knowledge exchange and cooperation;
• Organize international conferences and workshops to provide platforms for sharing research findings and advancements;
• Promote interdisciplinary scientific research and encourage the application of engineering solutions in various domains.

WG 4.2.1: Precise GNSS time and frequency transfer

Chair: Jiang Guo (Belgium)
Vice-Chair: Giulio Tagliaferro (France)

Terms of Reference

In the realm of precise time transfer, GNSS has played a pivotal role, enabling synchronization across the globe with remarkable accuracy. The commonly employed methods such as Common-View (CV) and Two-Way Time Transfer (TWTT) have been instrumental in achieving this, yet they come with certain limitations. CV and TWTT have significantly contributed to global time transfer, primarily by utilizing shared satellite observations. However, they heavily rely on a limited set of common-view satellites, which restricts their applicability in wide regions with obstructed satellite visibility. Precise Point Positioning Ambiguity Resolution (PPP-AR) holds the key to independent global time transfer, free from the constraints of common-view satellites. By resolving ambiguities in GNSS signals, we empower precise time transfer without the need for synchronized satellite observations. This breakthrough enables us to disseminate time information seamlessly across the world, enhancing the accessibility and accuracy of time transfer. This WG will mainly work on the technique details of PPP-AR; it is dedicated to verifying the effects of related GNSS error sources to PPP-AR time and frequency transfer.

Objectives

• Combining multi-constellation GNSS (GPS/GLONASS/Galileo/BDS-3) as well asmulti-frequency signals (L5/E6/B1C/B2a) for PPP-AR time /frequency transfer. To harness their combined capabilities to improve the reliability and availability oftime transfer service.
• Decreasing the effects of multipath errors on short- and medium-term (tens of minutes to several hours) frequency stability by generating multipath mitigating or orrecting products.
• Mitigating the long-term (more than one day) frequency stability limitations inherent in GNSS-based time and frequency transfer. Analyse the factors that aredeteriorating the long-term stability of GNSS time links from the aspects of the errorof precise satellite orbit and clock products, troposphere delay and the receiver-end hase hardware bias.
• Working for the method to precisely align the integer daily boundaries between the time links of two adjacent days originating from the discontinuities of satellite clock products. Most importantly, trying to mitigate the fractional day boundaries which cannot be aligned directly like integer ones.

Members

• Jiang Guo (Belgium); Chair
• Giulio Tagliaferro (France); Vice-Chair
• Frédéric Meynadier (France)
• Antoine Baudiquez (France)
• Pascale Defraigne (Belgium)
• Elisa Pinat (Belgium)
• Bin Jian (Canada)
• Xiaolong Mi (China)
• Ahmed Elmaghraby (Germany)

WG 4.2.2: Advances and unification of PPP-AR

Chair: Marcus Franz Wareyka-Glaner (Austria)
Vice-Chair: Tomasz Hadaś (Poland)

Terms of Reference

GNSS enable a worldwide positioning and navigation service independent of time, location, and weather. Nowadays, multiple GNSS transmit various signals on 3+ frequencies, enabling innovative developments and techniques. Over the past decades, the principle of Precise Point Positioning (PPP) has proven itself as a substantial GNSS method. PPP is an absolute positioning method using complex observation models and relying on precise satellite orbits, clocks, and biases. Various analysis centers and agencies publicly provide such satellite products in real-time and post-processing with slightly different computation strategies. This circumstance provides some challenges for the PPP user because consistency is essential. Nowadays, multiple PPP software packages, mostly publicly available, offer innovative approaches. Discussing and linking these advantages should benefit the whole PPP community. Typically, PPP achieves accuracies similar to relative positioning methods like Real-Time Kinematic (RTK) and offers several benefits in comparison (e.g., global corrections). However, the convergence time of PPP is still an issue limiting its application in real-time and time-critical applications. It must be reduced to way below one minute (“instantaneous convergence”) to make PPP completely competitive with relative positioning methods. PPP with integer ambiguity fixing (PPP-AR) has proven to effectively reduce or even eliminate the convergence time. In particular, approaches besides the ionosphere-free linear combination based on 2+ frequencies are currently heavily investigated. Fully utilizing all current GNSS constellations and their signals on 3+ frequencies for PPP and ambiguity resolution is an ongoing topic.

Objectives

• To discuss effective methods for reducing the convergence time of PPP;
• To give a recommendation for defining PPP convergence and coordinate accuracy;
• To create an overview and comparison of satellite products and software packages enabling PPP-AR;
• To define test cases to compare different PPP algorithms and software packages;
• To disseminate the major findings through journal papers and conference proceedings.

Members

• Marcus Franz Wareyka-Glaner (Austria); Chair
• Tomasz Hadaś (Poland); Vice-Chair
• Salih Alcay (Türkiye)
• Berkay Bahadur (Türkiye)
• Thomasz Hadas (Poland)
• Kamil Kazmiersky (Poland)
• Pan Li (China)
• Massarweh Lotfi (Netherlands)
• Naser Naciri (USA)
• Sermet Ötgütcü (Türkiye)
• Yuanxin Pan (Switzerland)
• Guorui Xiao (China)
• Qiyuan Zhang (China)

WG 4.2.3: Mass-market high-precision GNSS and applications

Chair: Guangcai Li (China)
Vice-Chair: Himanshu Sharma (Germany)

Terms of Reference

Mass-market GNSS chips embedded into consumer devices, such as smartphones, now offer broad support for multi-frequency and multi-constellation high-precision carrier phase observations. This advancement is opening up opportunities for them to be effectively utilized in high-precision positioning applications. Since Google announced the availability of GNSS raw measurements in the Android N operating system in 2016, there has been a proliferation of research on mass-market GNSS signal quality, positioning algorithms and applications. This emerging trend gives a glimpse ofthe potential for centimeter positioning using mass-market GNSS data. The achievement of such high-precision positioning will significantly improve the user navigation experience and facilitate the emergence of new location-based applications such asassisted driving and semi-professional tasks, and even become a favorable complement to geodetic grade receivers in geosciences applications. Nonetheless, attaining precise positioning in mass-market GNSS devices like smartphones remains a substantial challenge. These obstacles encompass severe multipath errors, frequent cycle slips,emerging phase biases, unknown antenna phase center offsets and variations, amongothers. Consequently, this WG is committed to confronting these issues and delving into their prospective applications in navigation, positioning, and selected geosciencesfields.

Objectives

• To perform a thorough assessment of the quality of mass-market/smartphone GNSS signals, and identify and investigate anomalies present in the observation data;
• To develop innovative methods and techniques for mass-market/smartphone GNSSmultipath mitigation;
• To estimate and calibrate the Phase Center Offset (PCO) and Phase Center Variation (PCV) parameters of mass-market/smartphone GNSS antennas;
• To devise robust ambiguity resolution methods and verification techniques tailored to the challenges posed by mass-market/smartphone GNSS data;
• To explore and implement the integration of mass-market GNSS data with inertial and visual sensors to enhance the availability and reliability of positioning solutions;
• To investigate and unlock the potential of mass-market GNSS applications across various domains, including navigation, positioning, meteorology and geological disaster monitoring.

Members

• Guangcai Li (China); Chair
• Himanshu Sharma (Germany); Vice-Chair
• Umberto Robustelli (Italy)
• Paolo Dabove (Italy)
• Francesco Darugna (Germany)
• Anja Hesselbarth (Germany)
• Changsheng Cai (China)
• Weikai Miao (China)
• Robert Odolinski (New Zealand)
• Xianlu Tao (China)
• Marcin Uradzinski (Poland)
• Lambert Wanninger (Germany)
• Chenyu Xue (UK)
• Farzaneh Zangenehnejad (Canada)
• Yuanxin Pan (Switzerland)
• Martin Hakansson (Sweden)
• Roland Hohensinn (Switzerland)
• Zhetao Zhang (China)
• Zengke Li (China)

WG 4.2.4: Quality Control and Integrity Monitoring of Precise Positioning

Chair: Krzysztof Nowel (Poland)
Vice-Chair: Ahmed El-Mowafy (Australia)

Terms of Reference

GNSS are the prime source of precise position information for a variety of applications including intelligent transport systems, autonomous driving, precision agriculture, civil aviation drones, marine and deformation monitoring. For such applications, theposition information needs to be highly reliable; even small errors may have serious consequences like the loss of human lives, liability, and damage to infrastructure. Any positioning platform, either based on standalone- or augmented-GNSS, is subject to a series of vulnerabilities, e.g. signal faults, interference, satellite orbital and clock biases, carrier phase cycle slips and wrong integer ambiguity resolution. All these can dramatically deteriorate the reliability and disruption of the positioning andtiming solutions. As such, it is crucial to have proper quality control mechanisms in place for the timely detection of hazardous threats and faults. In addition, monitoring the integrity of the system is an essential part of this quality control procedure, to ensure that the resulting positioning errors are bounded by protection levels that are determined according to the application’s allowable risk probability. The components of a quality control and integrity monitoring procedure will vary depending on the positioning sensors in use, the positioning method, and the performance requirements. This will in turn raise the need for thorough research into factors contributing to the quality of a positioning platform as well as their interactions, so as to enable the development of optimal application-dependent quality control and integrity monitoring procedures.

Objectives

• To derive optimal statistical testing regimes, capable of detection and exclusion of multiple alternative fault hypotheses using the underlying positioning models;
• To develop integrity monitoring algorithms for precise positioning methods using carrier phase measurements such as RTK and PPP;
• To consider new elements in integrity monitoring of the augmented-GNSS positioning, for example, the involvement of LEO satellites;
• To disseminate the developed algorithms and numerical results through journal papers and conference proceedings.

Members

• Krzysztof Nowel (Poland); Chair
• Ahmed El-Mowafy (Australia); Vice-Chair
• Kan Wang (China)
• Amir Khodabandeh (Australia)
• Nobuaki Kobu (Japan)
• Ivandro Klein (Brazil)
• Ling Yang (China)
• Artur Fischer (Poland)
• Anja Hesselbarth (Germany)
• Safoora Zaminpardaz (Australia)
• Sandra Verhagen (Netherlands)
• Yang Gao (Canada)

WG 4.2.5: Multi-GNSS for Natural Hazards and Disaster Resiliency

Chair: Xiaoming Wang (China)
Vice-Chair: Haobo Li (Australia)

Terms of Reference

Climate change is resulting in heightened intensity and frequency of hazardous weather and climate extremes such as severe storm, drought, tropical cyclone, and flood. Numerous challenges, e.g., major gaps in the observing networks, continue to impede the provision of sound observations, effective early warning systems, as well as comprehensive climate and weather services. It is therefore imperative to improve our understanding of weather and climate systems and the ability to reduce detrimental impacts on current and future generations. With the rapid development of multi-frequency multi-constellation GNSS andthe explosion in new data streams and information, this WG focuses on improving the analysis of climate change process and the monitoring of weather and climate extremes by fully harnessing the potential and capabilities of the next-generationspace/air/ground-based GNSS atmospheric sounding techniques, thereby constructing weather- and climate-resilient communities.

Objectives

• Collect multi-GNSS observations through international collaborations to create along-term and homogeneous GNSS climate dataset.
• Enhance the performance of near real-time and real-time processing of multi-GNSS products suitable for rapid-update NWP and weather nowcasting.
• Assess the qualitative and quantitative contributions of multi-GNSS products to climate modeling; develop robust methods for the monitoring of climate changefingerprints, atmospheric circulation, e.g., atmospheric river, and the detection ofclimate extremes, e.g., ENSO and drought.
• Evaluate the qualitative and quantitative contributions of multi-GNSS products to NWP systems; enrich the data assimilation techniques to improve weather forecastsand the acquisition of atmospheric parameters and background fields; investigate miscellaneous statistical methods, e.g., AI-empowered models, for the nowcasting of weather extremes using multi-GNSS atmospheric products.
• Encourage the transfer of knowledge and expertise, the dissemination of data,software, and techniques regarding the aforementioned issues; stimulate cross-sectional collaboration for articulating climate action plans, facilitating risk-informed decision-making, and supporting sustainable development goals.

Members

• Xiaoming Wang (China); Chair
• Haobo Li (Australia); Vice-Chair
• Florian Zus (Germany)
• Weixing Zhang (China)
• Hong Liang (China)
• Zhi-Weng Chua (Australia)
• Peng Yuan (Germany)
• Longjiang Li (China)
• Minghua Wang (China)
• Zohreh Adavi (Austria)
• Hongxing Zhang (China)
• Shilpa Manandhar (Singapore)
• Nabila Sofia Eryan Putri (Indonesia)
• Li Li (China)
• Shijie Fan (China)
• Manhong Tu (China)