Swarm operations for unmanned vehicles are expanding across reconnaissance, logistics, and defense applications. Missions with tight inter-vehicle spacing-such as aerial refueling and close-formation flight-require centimeter-level relative positioning and navigation integrity. This paper presents a protection level (PL) computation method for carrier phase differential GNSS (CDGNSS) that operates with measurement-domain monitors. We derive the biases in the Kalman filter estimates caused by undetected faults with consideration of the recursive nature of the filters. The impacts of these biases on fixed-baseline solutions and ambiguity resolution are separately derived under the worst-case scenario. These impacts are then combined to compute the PL. The performance of the proposed method is assessed through simulations assuming the use of an ephemeris monitor. The computed PLs are compared with PLs computed using a Solution Separation (SS)-based method. The obtained results show that, for short baselines, the proposed method yields smaller PLs and a lower computational burden by avoiding parallel multi-subset filtering. Sensitivity analyses across inter-vehicle separations indicate that the performance degrades with increasing baseline distance, whereas the benefits are strongest at short separations. Given these characteristics the approach is well-suited to tightly spaced multi-vehicle operations.

This paper presents a Lie Group Extended Kalman Filter (LGEKF) for attitude estimation, formulated directly on the special orthogonal group SO(3), to preserve the geometric properties of 3D rotations. Unlike conventional methods that suffer from singularities or normalization issues, our approach leverages an exponential map to propagate rotations and fuses the Magnetometer, Accelerometer, Rate Gyroscope (MARG) sensor data while respecting the manifold structure of the SO(3). Using a dynamically challenging helical trajectory with realistic sensor noise and biases, we demonstrate that the LGEKF significantly outperforms the standard Extended Kalman Filter (EKF), reducing Root Mean Square (RMS) errors by 26.7% in yaw (0.44° vs. 0.60°), 99.48% in pitch (0.007° vs. 1.34°), and 99.84% in roll (0.008° vs. 5.15°). The covariance propagation of the filter remained stable even during aggressive maneuvers, reflecting its robustness in highly dynamic scenarios. The simulation results highlight the superiority of the LGEKF in drift mitigation and estimation efficiency, making it ideal for real-time applications in autonomous navigation vehicles in underwater environments and other Global Positioning System (GPS)-denied environments.

Regional navigation satellite systems (RNSS) consist of geosynchronous orbit for servicing positioning, navigation and timing regionally. This presents a challenging environment for precise orbit determination (OD) as their regional ground networks provide limited line-of-sight diversity and weaken the observation geometry. To address these limitations, this study focuses on Japan's Quasi-Zenith Satellite System (QZSS) as a representative RNSS and evaluates two practical improvement strategies: (i) augmenting the processing with GPS observations, and (ii) expanding the ground tracking network. Three network configurations are tested-an 11-station regional network (R11), a denser 20-station regional network (R20), and a 20-station global network (G20)-under both QZSS-only processing (J) and joint QZSS+GPS (GJ) processing. Orbit and clock solutions are evaluated against the product from the Multi-GNSS Experiment Project (MGEX) of the International GNSS Service (IGS) as a reference. Using R11-J (which is the most probable scenario and exhibits the largest QZSS 3D RMS in our scenarios) as the baseline, including GPS reduces the QZSS 3D RMS by about 70% and shows a clear geometric benefit. Without GPS, R20-J outperforms G20-J, which indicates that for RNSS the number of usable observations from a denser regional network dominates the advantage of global distribution. When GPS is incorporated, the overall optimum shifts to G20-GJ: adding GPS raises QZSS OD to the level achieved by R20-GJ, while the GPS orbits are substantially more accurate-the mean (over days) of the daily-median 3D RMS of GPS reaches ~6.7 cm, compared with ~23.1 cm under R20-GJ. The station-deployment choice is tightly coupled to the processing strategy. If stand-alone independence is required, densifying the regional network to ~20 stations is a more effective option; if GPS augmentation is acceptable, a globally distributed 20-station network is recommended for maximum overall performance.

This study evaluates the performance of Global Navigation Satellites System, Reflectometry (GNSS-R)-based tide estimation techniques in coastal environments such as the Korean coastline, where the spatial and temporal variability of the sea level is large. GNSS-R estimates sea surface heights by analyzing multipath interference patterns in the signal-to-noise ratio (SNR) of GNSS signals. To enable the retrieval of sea level estimates with higher spatial and temporal resolution, several signal processing methods were applied, including a time-dependent phase model, optimal sliding-window spectral analysis, and multi-frequency consistency checking. The methods were tested at two coastal GNSS stations in the United States: CALC in Louisiana, which experienced Hurricane Harvey in 2017, and AT01 in Alaska, which was affected by a storm surge in 2019. GNSS-R-derived sea level estimates were compared with tide gauge observations at each site. At CALC, correlation coefficients reached 0.99 during the full period and 0.97 during the hurricane, with mean differences of 2.7 cm and 3.7 cm, respectively. At AT01, correlations were 0.96 and 0.87, with larger mean differences due to the spatial offset from the reference gauge. The results demonstrate that GNSS-R can effectively monitor tidal changes even during extreme weather conditions and can serve as a practical complement to traditional tide gauges. For implementation in Korea, further in-situ validation to account for local tidal characteristics, infrastructure compatibility, and vertical datum alignment should be performed.

This paper presents the design and implementation of a multi-constellation Global Navigation Satellite System (GNSS) spoofer utilizing a multicore Asymmetric Multi-Processing (AMP) architecture based on the Zynq UltraScale+ RFSoC platform. The proposed system can simultaneously generate L1 band signals for GPS, GLONASS, and BeiDou and manipulate the target receiver's position solution in real time. For system implementation, three cores of the Cortex-A53 quad-core processor were operated in independent real-time OS environments, with each core performing signal generation parameter calculations for different constellations. The calculated parameters are shared through on-chip memory (OCM) and transferred to the signal generator in the programmable logic (PL) region for real-time GNSS signal synthesis. To achieve precise time synchronization between authentic GNSS signals and spoofing signals, the system delay time was measured and calibrated. The calibration results confirmed a time synchronization accuracy of 0.03 chips (approximately 30 ns) based on C/A code. Spoofing tests were conducted on a commercial GNSS receiver, the Septentrio SB3 Pro+. The results confirmed that the target receiver could be successfully spoofed to manipulate its position solution along an intended trajectory even in an environment where authentic GNSS signals and spoofing signals coexist.

Through the Space Pioneer Program, researchers are striving to develop navigation code and message generators at a level comparable to leading nations, with the aim of replacing foreign technology currently relied upon for satellite payload systems. The ultimate goal is to achieve Technology Readiness Level (TRL) 7 and develop a qualification model (QM) for navigation code and message generators tailored to the Korean satellite navigation system. To this end, various activities are undertaken, including the development of an engineering model (EM) and electrical ground support equipment (EGSE), functionality and performance testing, space environment testing, payload assembly support, and payload testing and analysis of the obtained results. This paper presents the design concept, configuration, and verification test results of the code and message generator EM. The results verify that the EM, produced using components compatible with space-grade parts for satellite integration, meets all reviewed requirements to date.

The ring laser gyro, a representative optical gyro, has an area where small angular velocity inputs are not measured due to backscattering of the reflector. This area, referred to as a lock-in, is typically removed by applying a very large sinusoidal vibration to the gyro body. A mechanical device that applies sinusoidal vibration to the gyro body is called a dither. Dithers have various shapes depending on the gyro size, and when the gyro optical path is relatively large, a single-axis dither is applied. In the case of a single-axis dither, it is located at the center of the gyro body, but if the optical path of the gyro is small, a cluster dither that simultaneously applies sinusoidal vibration to the 3-axis gyro should be used. In the cluster dither, unlike the single-axis dither, a gyro body tilted at a certain angle is mounted on the spoke of the dither, and the gyro mounting part for mounting the gyro is attached at the end of the spoke. In addition, the dither fixing hole is located in the center of the gyro body in the case of single-axis dither, whereas is located on the outside of the dither in the case of the cluster dither. Therefore, unlike the single-axis dither, the rotation center of the cluster dither does not coincide with the center of the gyro body, but rather is located at the center of the cluster dither. Depending on the shape of the cluster dither, the dither natural frequency varies and a different dither frequency analysis method must be applied. In this paper, we analyze natural frequency characteristics according to the shape of a cluster dither and present the results. We also verify the results through modeling and simulation.

Monitoring the integrity of global navigation satellite systems is important to continuously and stably operate their navigation systems. KF-RAIM has been developed to guarantee the integrity of high-precision navigation solutions such as PPP. This paper presents a KF-RAIM algorithm with an OpenMP-based parallel structure. Compare with the serial structure, the proposed structure provides the same protection levels and thresholds while reducing the KF-RAIM execution time. The use of a look-up table can further decrease the execution time with only centimeter-level differences in the protection level. The simulation results validate the effectiveness of the proposed structure in the view of the computation time.

Guided weapon systems operating in maritime environments, such as the Vertical Launch System (VLS), form a core element of modern naval capabilities. Although vertical launch provides an advantage in confined spaces, the dynamic motion of the platform (ship) is directly transferred to the launch vehicle until just before launch, making navigation initialization challenging. Weapon systems deployed on offshore platforms are continuously affected by environmental disturbances such as waves, wind, and currents, as well as the ship's propulsion and steering. Consequently, assuming a stationary initial state when estimating the weapon's attitude using an Inertial Measurement Unit (IMU) introduces significant limitations. The process of determining this initial attitude, known as alignment, is critical in IMU-based navigation systems. Errors in initial attitude estimation directly propagate through the entire guidance phase. This leads to accumulated navigation errors and ultimately degrades missile accuracy. Although Global Navigation Satellite System (GNSS) updates can correct navigation solutions during the midcourse phase, IMU-based inertial navigation is indispensable during the early post-launch phase-before GNSS data become available. Moreover, GNSS corrections may be unavailable in jamming or spoofing environments. It is therefore important to accurately determine the initial attitude and rapid transition to inertial navigation mode to ensure the required guidance performance of ship-launched missiles. This study compares and analyzes three representative alignment methods applicable to maritime environments: one-shot alignment, one-shot mixed alignment, and shipboard transfer alignment, under identical sea conditions. To quantitatively reflect the dynamic nature of the marine environment, simulation data based on wave conditions were generated using the Marine System Simulator (MSS). The initial alignment accuracy of each method was evaluated using these data, and the subsequent inertial navigation performance was analyzed. From the obtained results, one-shot mixed alignment, which utilizes missile-mounted IMU acceleration data, exhibited large alignment errors due to hull motion effects, while transfer alignment using attitude and velocity data from the Master Inertial Navigation System (MINS) achieved higher accuracy. It was confirmed that in high sea state conditions, the transfer alignment method utilizing continuous velocity and attitude information from the MINS provided the highest performance in estimating the missile's attitude.

The autonomous landing of multirotor UAVs on ship decks is challenging due to wave-induced deck motion, degraded visibility, Global Positioning System (GPS) interference, and communication uncertainties. To address this, a reward design framework based on reinforcement learning for vertical drone landing on a heaving shipborne platform using the Deep Deterministic Policy Gradient (DDPG) algorithm is developed in this study. The training environment combines a simplified vertical UAV dynamics model with wave profiles generated from the JONSWAP spectrum to enable randomized and realistic heave motion in each episode. To enhance training stability and policy robustness, we introduce a distance-based reward, a strict terminal penalty for failed landings, and hyperparameter scaling consistent with vehicle dynamics. MATLAB simulation results show that the proposed reward design achieves stable policy convergence and landing performance across diverse wave conditions. These results demonstrate the proposed reward model effectively improves the learning efficiency and robustness of autonomous shipboard landing systems.

Development of the Korean Positioning System (KPS) was started in order to provide satellite navigation service over the East Asian area and full operational capability (FOC) is anticipated in 2035. Synergy of satellite navigation service quality can be expected when the KPS and China’s BDS are combined. In this paper, the status of the BDS is presented and the BDS research trend at Chinese universities is surveyed. BDS development history, Chinese government organization of BDS related to development, BDS services, BDS performance and future development trends are described. In order to survey the research trend of Chinese universities, journal papers related to the BDS from Jan. 2021 to Feb. 2025 written by research groups at Chinese universities were searched. In addition, papers presented at CSNC 2024 were evaluated. The searched papers are classified by the university and by the field.

Global Navigation Satellite Systems (GNSS) are vulnerable to radio interference, which creates challenges in determining vessel positions at sea. In response, by extending the functionality of the VHF Data Exchange System (VDES) for maritime navigation support, the VDES Ranging Mode (VDES R-Mode) has been proposed. A testbed was established around Daesan Port, and both static and dynamic trials were conducted to assess its feasibility. Initial correction was applied to mitigate bias errors. The results show that positioning errors varied with line-of-sight conditions, transmitter-receiver distance, signalto-noise ratio (SNR), and horizontal dilution of precision (HDOP). The positioning performance remained stable without persistent bias errors. Excluding geographical constraints specific to the west coast of Korea, the results demonstrate the potential of VDES R-Mode as a maritime auxiliary navigation technology.

This study evaluates the dynamic real-time navigation performance of the Satellite-Based Augmentation System (SBAS) and Real-Time Kinematic (RTK) positioning through helicopter flight tests conducted along the K-UAM Grand Challenge 2nd phase (GC 2-1) demonstration route. In previous studies, flight tests were conducted. However, it was not possible to transmit or receive real-time RTK correction data. Consequently, the RTK performance was analyzed using post-processed raw measurements. In contrast, this study conducted thirteen helicopter flight missions along the Ara Waterway section (GC 2-1 demonstration route) connecting the Geyang Vertiport and the KIAST Drone Certification Center. During these missions real-time correction data were received and applied. The flight tests covered all operational phases, including take-off, cruise, and landing. Due to aircraft safety regulations and electromagnetic interference management standards, the GNSS antenna was installed inside the aircraft cabin (beneath the canopy). Although this configuration could cause signal attenuation and multipath effects, both navigation modes (SBAS and RTK) were operated under identical conditions to ensure a reliable comparison of relative performance. The results show that the mean horizontal and vertical position errors of SBAS were approximately 1.94 m and 1.62 m, respectively, while those of RTK were about 0.07 m and 0.09 m. This study experimentally demonstrates the dynamic performance characteristics of real-time SBAS and RTK navigation in K-UAM flight environments and is expected to contribute to the establishment of Navigation System Error (NSE) and Total System Error (TSE) standards for navigation systems within UAM corridors and vertiports.