Welcome to the Fall 2025 issue of NAVIGATION. In this issue, we have articles on GNSS integrity and interference detection, issues related to low Earth orbit and geosynchronous navigation satellites, and studies of navigation in the cislunar and lunar environments. Plus, a number of other articles on state-of-the-art developments in positioning and navigation.
ION promotes the research of journal authors in a variety of ways including video abstracts hosted on the ION website. The latest video abstracts are documented below. You can find the video abstract for any recently published article under the article’s supplemental menu item on the journal’s website. ION also engages with the PNT community, through its social media platforms, including Facebook, LinkedIn, and Instagram (@ionavigation).
VIDEO ABSTRACTS
Video Abstracts allow authors to present their research in their own words. This multimedia format communicates the background and context of authors’ research in a quick and easy way, elevating research from simple print delivery.
Video for “Doppler Positioning Using Multi-Constellation LEO Satellite Broadband Signals as Signals of Opportunity”
By Amir Allahvirdi-Zadeh, Ahmed El-Mowafy, and Kan Wang (https://navi.ion.org/content/72/2/navi.691/tab-supplemental)
Abstract: This paper investigates the potential of signals of opportunity for positioning using broadband low Earth orbit constellations. We developed analytical absolute and differential models based on Doppler-shift observations from multi-constellation satellite bursts across various frequency ranges. Owing to the unavailability of multi-constellation broadband receivers, simulations were conducted with the application of two primary restrictions common for these satellites: a 30° elevation mask angle and a 15-s intermittency for observations. Signal attenuation factors were modeled, indicating that free space loss was the dominant factor whereas cloud and fog losses were minimal. The accuracy of absolute static positioning, considering the aforementioned broadband restrictions, reached 4.32 m. The kinematic receiver showed similar trends, with a degraded accuracy of 4.83 m. Tests in urban areas revealed significant accuracy degradation to approximately 10 m. However, the differential model significantly improved kinematic positioning accuracy, achieving promising sub-meter levels even with a limited number of satellites.
Article Citation: Allahvirdi-Zadeh, A., El-Mowafy, A., & Wang, K. (2025). Doppler positioning using multi-constellation LEO satellite broadband signals as signals of opportunity. NAVIGATION, 72(2). https://doi.org/10.33012/navi.691
Video for “Performance Evaluation of DFMC SBAS Messages Broadcast by the Japanese Quasi-Zenith Satellite System (QZSS) in Oslo, Norway”
By Toru Takahashi, Susumu Saito, Mitsunori Kitamura, and Takeyasu Sakai (https://navi.ion.org/content/72/2/navi.692/tab-supplemental)
Abstract: The main objective of this study was to evaluate the performance of a dual-frequency multi-constellation (DFMC) satellite-based augmentation system (SBAS) broadcast from the Japanese Quasi-Zenith Satellite System (QZSS) in the Arctic and high-latitude regions. We installed a global navigation satellite system (GNSS) antenna and receiver on the roof of the Kjemibygningen (chemistry building) at the University of Oslo, Norway, on February 24, 2021, and conducted experiments continuously until March 17, 2021.
We found that the QZSS-based DFMC SBAS achieved a system availability of 84.68% for localizer performance with vertical guidance when the horizontal and vertical alert limits were set to 40 and 50 m, respectively. This result is below the performance of QZSS-based DFMC SBAS in Japan. However, our analysis shows that adding three or more QZSS reference stations in Europe will enable DFMC SBAS from QZSS to reach 100% availability.
Article Citation: Takahashi, T., Saito, S., Kitamura, M., & Sakai, T. (2025). Performance evaluation of DFMC SBAS messages broadcast by the Japanese Quasi-Zenith Satellite System (QZSS) and received in Oslo, Norway. NAVIGATION, 72(2). https://doi.org/10.33012/navi.692
Video for “Thirty Years of Maintaining WGS 84 with GPS”
By William Konyk, Alex Smith, Bob Wong, and Andrew Tollefson (https://navi.ion.org/content/72/2/navi.693/tab-supplemental)
Abstract: With the release of a new International Terrestrial Reference Frame (ITRF) in April 2022, the National Geospatial-Intelligence Agency (NGA) began the process of aligning the World Geodetic System 1984 Terrestrial Reference Frame (WGS 84 TRF) to the latest ITRF realization. The resulting realization, WGS 84 (G2296), represents the seventh such update using Global Positioning System measurements in 30 years. This work outlines the historical development of WGS 84, documents a new technique adopted by NGA in 2021 to maintain alignment between WGS 84 and the latest ITRF, provides transformation parameters between recent WGS 84 TRF realizations, and assesses the accuracy of WGS 84 TRF relative to the ITRF. We demonstrate that for high-accuracy users, the two frames have empirically remained within 3 cm of each other over the past decade.
Article Citation: Konyk, W., Smith, A., Wong, B., & Tollefson, A. (2025). Thirty years of maintaining WGS 84 with GPS. NAVIGATION, 72(2). https://doi.org/10.33012/navi.693
Video for “Comprehensive Analysis of Acquisition Time for a Multi-Constellation and Multi-Frequency GNSS Receiver at GEO Altitude”
By Young-Jin Song, Ki-Ho Kwon, and Jong-Hoon Won (https://navi.ion.org/content/72/2/navi.694/tab-supplemental)
Abstract: The utilization of global navigation satellite systems (GNSSs) in the space service volume, such as the geostationary Earth orbit (GEO) altitude, has recently attracted significant interest owing to their potential advantages in performance and cost. Because the acquisition of the satellite signal represents a fundamental function of a GNSS receiver, the expected amount of time for successful acquisition, or mean acquisition time (MAT), as well as the acquisition performance itself, must be analyzed. Owing to the limited number of satellites and poor geometry at the GEO altitude, GNSS receivers often utilize signals originating from the sidelobes of the transmitting antenna pattern, which results in a weak signal power and a high Doppler shift. This paper presents a research methodology for a comprehensive analysis of acquisition time, with a particular focus on operations at the GEO altitude, considering the utilization of sidelobe signals. A generalized mathematical and probabilistic model is provided for the acquisition performance and MAT analysis of multi-constellation and multi-frequency signals. In particular, a realistic MAT model is proposed, based on a detailed computational performance analysis of the acquisition algorithm applied to an actual spaceborne receiver. A geometric simulation was conducted using the publicly available antenna patterns of the Global Positioning System (GPS), Galileo, and Quasi-Zenith Satellite System to incorporate orbital and signal characteristics into the determination of the search space. A method is proposed to modify the antenna patterns for other systems whose patterns are not publicly available, while preserving the sidelobe characteristics. Based on realistic scenarios and receiver parameters, acquisition-related analysis results for cold and warm starts, including the search space, dwell time, and MAT for GEO altitude receivers, are provided. The methods and results were verified through a Monte Carlo simulation configured via a software simulator and receiver pair.
Article Citation: Song, Y.-J., Kwon, K.-H., & Won, J.-H. (2025). Comprehensive analysis of acquisition time for a multi-constellation and multi-frequency GNSS receiver at GEO altitude. NAVIGATION, 72(2). https://doi.org/10.33012/navi.694
Video for “Candidate Design of New Service Signals in the NavIC L1 Frequency Band”
By Vijay Singh Bhadouria, Dhaval J. Upadhyay, Parimal J. Majithiya, and Subhash Chandra Bera (https://navi.ion.org/content/72/2/navi.695/tab-supplemental)
Abstract: Satellite navigation payloads use a constant-envelope composite signal to efficiently operate their high-power amplifiers in the saturation region. This composite signal consists of multiple signals that are multiplexed at the baseband level to support various services. The complexity of the signal multiplexing technique increases with multi-level signals. Here, we propose designing new service signals for Navigation with Indian Constellation (NavIC) in the L1 frequency band. The NavIC L1-band open civilian service signal is a multi-level design. We propose multiplexing new service signals to this multi-level signal at a single frequency and multiple frequencies without interfering with existing navigation service signals while maintaining backward compatibility. We present a novel concept for preserving the power spectral density criteria in the optimization framework to meet interoperability requirements and present an optimal power-sharing and modulation scheme. Results show that the single-frequency and multi-frequency methods for multiplexing new service signals both achieve maximum multiplexing efficiency.
Article Citation: Bhadouria, V. S., Upadhyay, D. J., Majithiya, P. J., & Bera, S. C. (2025). Candidate design of new service signals in the NavIC L1 frequency band. NAVIGATION, 72(2). https://doi.org/10.33012/navi.695
Video for “Wide-Sense CDF Overbounding for GNSS Integrity”
By Odile Maliet, Kin Mimouni, Julie Antic, and Sébastien Trilles (https://navi.ion.org/content/72/2/navi.697/tab-supplemental)
Abstract: The need for highly reliable positioning in safety-of-life applications has led to the development of global navigation satellite system (GNSS) augmentation systems such as satellite-based augmentation systems and advanced receiver autonomous integrity monitoring. These systems rely on a transfer of integrity from the range to the position domain through concepts such as cumulative distribution function (CDF) overbounding and the more recent two-step overbounding. Here, we propose a new approach, wide-sense CDF overbounding, which offers more flexibility and robustness than existing methods by accommodating biased distributions and relaxing stringent assumptions of symmetry and unimodality while retaining the original simplicity of CDF overbounding. This method combines CDF and paired overbounding, adjusting protection volumes with a formula to compensate for weaker assumptions. We perform numerical analyses using real GNSS data that demonstrate the enhanced flexibility of wide-sense CDF overbounding and show its potential to improve the robustness and performance of GNSS-based safety solutions in various applications.
Article Citation: Maliet, O., Mimouni, K., Antic, J., & Trilles, S. (2025). Wide-Sense CDF overbounding for GNSS integrity. NAVIGATION, 72(2). https://doi.org/10.33012/navi.697
Video for “Combinatorial Watermarking Under Limited SCER Adversarial Models”
By Jason Anderson, Sherman Lo, and Todd Walter (https://navi.ion.org/content/72/2/navi.696/tab-supplemental)
Abstract: Combinatorial watermarking can help establish trust in global navigation satellite system (GNSS) signals. In combinatorial watermarking, the GNSS provider elects to secretly invert a subset of ranging code chips and then later distributes those inversions to receivers. From these ranging code perturbations, receivers can use signal statistics to determine the authenticity of the signal. In previous work, we demonstrated how one can design combinatorial watermarking schemes and derive the distributions of receiver statistics to ensure low probabilities of missed detection and false alarm, assuming that an adversary does not attempt to estimate the watermarked chips and replay. In this work, we extend the analysis of combinatorial watermarking to adversaries capable of engaging in security code estimation and replay (SCER) attacks. We derive the distributions of our statistics for defense against SCER-capable adversaries. Provided a bound on the estimation capability of the SCER-capable adversary, one can use this work to design a combinatorial watermarking scheme that meets security requirements.
Article Citation: Anderson, J., Lo, S., & Walter, T. (2025). Combinatorial water-marking under limited SCER adversarial models. NAVIGATION, 72(2). https://doi.org/10.33012/navi.696
Video for “Identification of Authentic GNSS Signals in Time-Differenced Carrier-Phase Measurements with a Software-Defined Radio Receiver”
By Zhen Zhu, Sanjeev Gunawardena, Eric Vinande, and Jason Pontious (https://navi.ion.org/content/72/2/navi.698/tab-supplemental)
Abstract: The time-differenced carrier phase can be computed from measurements recorded by a multi-global navigation satellite system software-defined radio receiver such as PyChips, from which the user displacement and receiver clock drift can be solved. PyChips is able to simultaneously track authentic and inauthentic signals in separate channels, which makes it possible to observe both types of measurements with corresponding navigation data. A random sample consensus algorithm has been introduced to assess the consistency between the measurements and data. This algorithm successfully separated authentic channels from inauthentic channels when they are broadcast simultaneously.
Article Citation: Zhu, Z., Gunawardena, S., Vinande, E., & Pontious, J. (2025). Identification of authentic GNSS signals in time-differenced carrier-phase measurements with a software-defined radio receiver. NAVIGATION, 72(2). https://doi.org/10.33012/navi.698
Video for “Robust Interference Mitigation in GNSS Snapshot Receivers”
By Helena Calatrava, Adrià Gusi-Amigó, Floor Melman, and Pau Closas (https://navi.ion.org/content/72/2/navi.699/tab-supplemental)
Abstract: The robust interference mitigation (RIM) framework offers a promising solution to jamming attacks on global navigation satellite system (GNSS) receivers. By identifying interfered samples as outliers in the selected transform domain, RIM operates without relying on jamming waveform assumptions. This paper adapts RIM for GNSS snapshot architectures, assessing the impact of low-bit quantization on receiver performance under continuous wave (CW) and chirp interference. Using simulated data, snapshot RIM demonstrates significant improvements, achieving gains of 10, 20, and 35 dB in detected satellites for 2-, 4-, and 8-bit quantization in the presence of CW jamming. We also analyze the effect of quantization on the effective jammer-to-noise ratio, waveform distortion, and robust variance estimation. An experiment with realistic recordings shows that snapshot RIM achieves a 20-dB gain in the carrier-to-noise ratio over a professional receiver. Finally, a 24-h specifications test supports the feasibility of RIM integration in snapshot receivers with a maximum time-to-first-fix increase of 0.31 s.
Article Citation: Calatrava, H., Gusi-Amigó, A., Melman, F., & Closas, P. (2025). Robust interference mitigation in GNSS snapshot receivers. NAVIGATION, 72(2). https://doi.org/10.33012/navi.699
Video for “GNSS L5/E5a Code Properties in the Presence of a Blanker”
By Seunghwan Kim, Nicolas Gault, Yongrae Jo, Hyosang Yoon, Byungwoon Park, Axel Garcia-Pena, Christophe Macabiau, and Dennis M. Akos (https://navi.ion.org/content/72/2/navi.700/tab-supplemental)
Abstract: Modern global navigation satellite system L5/E5a code families offer improved correlation properties, with lower auto-correlation sidelobes and cross-correlations, compared with legacy Global Positioning System L1 coarse/acquisition (C/A) codes. However, these codes encounter unique L5/E5a interference environments, particularly those including interference due to pulses from distance-measuring equipment and tactical air navigation systems. In civil aviation, temporal blanking is the assumed countermeasure. In temporal blanking, incoming samples are set to zero when the peak envelope power exceeds a threshold, blanking the codes within the sampled signals and affecting their correlation with non-blanked replicas. Through extensive simulations, this study analyzes L5/E5a code properties under blanking duty cycle (bdc) values of 0%–75% over a 1-ms integration time. Results indicate reduced auto-correlation and cross-correlation protections, although these effects remain superior to those of L1 C/A codes until bdc reaches approximately 60%. Further increases in bdc to 75%, likely due to increasing air traffic, diminish these advantages. Additionally, simulations show that Doppler residuals have a minimal impact on L5/E5a correlation properties.
Article Citation: Kim, S., Gault, N., Jo, Y., Yoon, H., Park, B., Garcia-Pena, A., Macabiau, C., & Akos, D. M. (2025). GNSS L5/E5a code properties in the presence of a blanker. NAVIGATION, 72(2). https://doi.org/10.33012/navi.700
Video for “Ranging Performance Evaluation for Higher-Order Scalable Interplex” By Florian C. Beck, Christoph Enneking, Steffen Thölert, and Felix Antreich (https://navi.ion.org/content/72/2/navi.702/tab-supplemental)
Abstract: Scalable interplex represents a multiplexing technique that has been specifically designed to modify a signal constellation in order to adapt the transmitted signal to the characteristics of a high-power amplifier and thereby enhance the received power of the navigation signals. This paper builds upon existing knowledge regarding the trade-off between increased usable signal power and amplifier efficiency when scaling intermodulation (IM) terms, with a particular focus on the Galileo E1 signals and one potential additional signal candidate. The scalable interplex is optimized based on the achievable joint receiver efficiency. The aim of this study is to determine whether this signal constellation optimization also results in a reduction in code tracking jitter. The findings indicate that in numerous instances, the scalable interplex achieves a reduction in code tracking jitter by scaling specific IM terms in comparison with a constant-envelope six-channel interplex.
Article Citation: Beck, F. C., Enneking, C., Thölert, S., & Antreich, F. (2025). Ranging performance evaluation for higher-order scalable interplex. NAVIGATION, 72(2). https://doi.org/10.33012/navi.702
Video for “ATLAS: Orbit Determination and Time Transfer for a Lunar Radio Navigation System”
By Andrea Sesta, Daniele Durante, Giovanni Boscagli, Paolo Cappuccio, Mauro Di Benedetto, Ivan Di Stefano, Michael Plumaris, Paolo Racioppa, Luciano Iess, Pietro Giordano, Richard Swinden, and Javier Ventura-Traveset (https://navi.ion.org/content/72/2/navi.701/tab-supplemental)
Abstract: The ATLAS consortium has proposed a novel architecture to implement a lunar radio navigation system capable of providing position, navigation, and timing services to several lunar users. The system consists of a small constellation of four satellites in elliptical lunar frozen orbits, with the aposelene above the southern hemisphere. The architecture envisages a ground station network of small dish antennas to establish tracking via multiple spacecraft per aperture at the K-band using a scheme based on code division multiple access. Such a configuration implements the same-beam interferometry technique with spread-spectrum ranging and Doppler measurements. We describe the orbit determination and time synchronization of the satellite constellation, validating the concept in multiple scenarios and establishing the system performance. Numerical simulations show an orbital accuracy ranging from a few centimeters to 10 m, while the signal-in-space error degrades, reaching up to 20 m after 10 h (95th percentile) or 6 h (99th percentile).
Article Citation: Sesta, A., Durante, D., Boscagli, G., Cappuccio, P., Di Benedetto, M., di Stefano, I., Plumaris, M. K., Racioppa, P., Iess, L., Giordano, P., Swinden, R., Ventura-Traveset, J. (2025). ATLAS: Orbit determination and time transfer for a lunar radio navigation system. NAVIGATION, 72(2). https://doi.org/10.33012/navi.701
HOW TO CITE THIS ARTICLE
Langley, R. B. (2025). Navigator notes: Editorial highlights from the editor-in-chief. NAVIGATION, 72(3). https://doi.org/10.33012/navi.703
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
