This study explores the applicability of Low Earth Orbit Positioning, Navigation, and Timing (LEO PNT) technology to enhance the performance of Korean satellite navigation systems. While LEO PNT technology is actively being developed worldwide, Korea has made significant advances in satellite navigation with the successful development and launch of the Korea Augmentation Satellite System (KASS) and the commencement of the Korean Positioning System (KPS) development. This paper proposes a configuration of a LEO PNT system to augment the performance of KASS and KPS, thereby improving the independence and accuracy of Korean satellite navigation systems. Utilizing simulation techniques, the study evaluates the performance of a PNT system using a small number of LEO satellites and analyzes the potential impacts and benefits of the LEO PNT on satellite navigation systems. It is anticipated that the results of this research can be used to suggest a direction for the development of Korean satellite navigation systems and will contribute to enhancing the international competitiveness of future satellite navigation technology.

Real-time localization is essential for autonomous driving of robots. This paper presents the implementation and a performance analysis of a localization algorithm. To estimate the position and attitude of a robot, a visual inertial odometry (VIO) algorithm based on a multi-state constraint Kalman filter is used. The sensors employed in this study are a stereo camera and an inertial measurement unit (IMU). The performance is analyzed through experiments using three different camera view directions: floor-view, front-view, and ceiling-view. The number of detected features also affects navigation performance. Even if the number of recognized feature points is large, performance degrades if the correspondence between feature points is not accurately identified. The results show that VIO improves navigation performance even with low-cost sensors, thus facilitating map building as well as autonomous navigation.

In this study, we designed a USRP-based multi-antenna GPS L1 C/A RF signal generator and verified its performance using commercial receivers. The designed RF signal generator consists of a software-based signal generation module that generates multiple GPS L1 C/A IF signals, and an RF signal transmission module that up-converts the generated IF signals to RF signals for transmission. The multi-GPS signals are generated by reflecting time delays, according to the arrangement and structure of the antennas, in the code and carrier, and each signal is transmitted through its respective RF front-end. The RF signals were verified using a commercial U-blox receiver, and the operation and performance of the multi-antenna signals were confirmed using an attitude determination system configured with two U-blox receivers. The designed signal generator can be used not only for precise navigation and attitude determination but also for the development of various array signal processing systems such as A/DOA, beamforming, and nulling.

The purpose of the Global Navigation Satellite System/Inertial Navigation System (GNSS/INS) simulator is to provide GNSS signals and iInertial mMeasurement uUnit (IMU) data in a real environment. If the GNSS/INS simulator provides unsynchronized GNSS signals and IMU data, the performance of the GNSS/INS integrated navigation system cannot be accurately evaluated. In this paper, a design method of a time synchronization system for the GNSS/INS simulator is proposed using a PC, timer card, and Universal Software Radio Peripheral (USRP) board. The USRP board up-converts the GNSS IF data into an RF signal and provides the Pulse Per Second (PPS) signal. The timer card generates an interrupt request signal to the PC at the same rate as the IMU data from the PPS signal of the USRP board. The PC provides the GNSS IF signal and IMU data and synchronizes the time of the IMU data to the GNSS IF data based on the interrupt request signal. In order to show demonstrate the usefulness of the proposed method, the time synchronization results of IMU data are checked along the GNSS signal in the GNSS/INS simulator, and the effect of the time synchronization of the GNSS/INS simulator on the navigation system is checkedevaluated. The experimental results show that the proposed time synchronization method generates the GNSS IF signals and IMU data very similar to that closely correspond with the real environment.

Satellite navigation systems provide services such as positioning, navigation, and timing (PNT), by transmitting navigation messages through signals. However, there is possibility that the signals can be spoofed and fake PNT information can be transmitted to the receiver. To prevent spoofing attacks, navigation messages should be authenticated. Although the Japanese Quasi-Zenith Satellite System (QZSS) recently adopted authentication services for L1C/A, L1C, and L5, it does not yet provide authentication services for its Centimeter Level Augmentation Service (CLAS). To adopt authentication functionality for the existing CLAS that already has its own message structure, only reserved fields can be used for authentication. In this study, we propose two compact navigation message authentication protocols using reserved fields of QZSS CLAS message. They are based on the Elliptic Curve Digital Signature Algorithm (ECDSA) and Timed Efficient Stream Loss-tolerant Authentication (TESLA), which have been widely considered for other signal authentication services such as GPS Chimera and Galileo Open Service Navigation Message Authentication (OSNMA). According to our experiments, the proposed ECDSA-only method needs 6 to 12 min for authentication and the proposed ECDSA-TESLA method requires 4 to 6 min.

The public regulated restriction signals are encrypted generally with the very long period code in Global Navigation Satellite System (GNSS) including Global positioning system (GPS). Unlike civilian navigation signals, the long period code is used for the security enhancement purpose. The navigation signals with the long period code are very difficult to acquire due to their own non-periodic characteristics. The application of Acquisition Code (AC) is required for the proper working of the long period navigation signals. In this paper, we present the design and analysis results of the navigation signal with acquisition code. Specifically, the acquisition performance and Time To First Acquisition (TTFA) are presented analytically. In the process of the navigation signal design, we include AC length, insertion pattern, code rate, and filter effects. Also, the navigation signal receiving process include the effects of Side Band Filter (SBF), doppler frequency and code phase errors. The indicators that used to evaluate navigation signal acquisition performance are the detectability and TTFA.

The International GNSS Service (IGS) provides real-time satellite orbit, clock, and bias corrections through its Real-Time Service (RTS). In addition, Galileo has offered the Galileo High Accuracy Service (HAS) since January 24, 2023, further improving positioning accuracy for GPS and Galileo satellites. HAS data are available through Galileo's E6 signal and Ntrip, enhancing positioning accuracy for GPS and Galileo satellites. This study compared Galileo HAS corrections data and IGS RTS corrections data obtained from the BKG Ntrip client (BNC) on February 1 and June 23, 2024. The orbit, clock, and bias corrections of each satellite were analyzed, revealing that HAS and IGS RTS correction values followed similar trends for most satellites. Additionally, satellite position and clock values computed from these corrections were compared with SP3 and CLK data for accuracy. To perform positioning using HAS, a Code-PPP algorithm was developed, and positioning accuracy was evaluated for GPS-only, Galileo-only, and multi-constellation modes using both GPS and Galileo. Tropospheric errors were mitigated using the Global Model of Pressure and Temperature (GPT) with the Global Mapping Function (GMF), and ionospheric corrections were applied using the Global Ionospheric Map (GIM). As a result, sub-meter level positioning accuracy was achieved. Among the correction types, IGS RTS corrections provided better accuracy for GPS-only measurements, while Galileo HAS corrections yielded superior accuracy for Galileo-only positioning.

In this study, we propose a collision avoidance algorithm for Urban Air Mobility (UAM). The proposed algorithm uses Dynamic Programming (DP) techniques to optimize trajectory planning and collision avoidance strategies. The algorithm includes a dynamic and adaptive framework that can effectively manage a variety of unpredictable urban airspace scenarios. Through a comprehensive analysis of the surrounding environment, the algorithm formulates collision avoidance decisions by considering the state of the aerial vehicle. By utilizing DP, the algorithm optimally balances the trade-off between minimizing collision risk and ensuring efficient path planning. The effectiveness of the proposed algorithm is tested in various urban environments through simulations. These tests demonstrate its ability to manage complex airspace scenarios. The results show a significant reduction in collision risk while maintaining acceptable path efficiency, compared to other collision avoidance algorithms.

Autonomous driving requires safe and efficient navigation in complex environments. This has led to an increased demand for reliable test methods, where driving simulators are widely used to simulate sensors in autonomous vehicles. In addition, the concept of digital twins, which combines real and simulated environments, is being applied to autonomous vehicles for efficient and realistic testing. However, inaccuracies in vehicle modeling in simulators can lead to cumulative position errors, especially during sharp maneuvers, undermining the reliability of test results. This paper presents a method to correct cumulative errors in a driving simulator environment by synchronizing the vehicle position and orientation using navigation data. The system periodically adjusts the vehicle dynamics in the simulator to reflect real-world dynamics, eliminating cumulative position errors and narrowing the gap between the simulation and the real-world environments. This approach is particularly effective for interaction-based tests such as Autonomous Emergency Braking (AEB), where position accuracy is crucial. To demonstrate the feasibility of this mixed-reality system architecture, experiments were conducted in accordance with the Euro-NCAP AEB protocol. The results illustrate the benefits of the proposed method in mitigating simulator errors and enhancing the overall reliability of autonomous driving testing.

The quasi-zenith satellite system (QZSS) provides sub-meter level augmentation service (SLAS) to improve the positioning accuracy of single-frequency GPS L1 receiver users. The SLAS correction consists of differential GPS information (DGPS) and the corrections are transmitted via quasi-zenith satellites (QZS). The DGPS correction reduces the effect of pseudo-range errors due to satellite orbit, clock and atmospheric delay errors. Thirteen SLAS reference stations in Japan generate the correction data. The performance of the DGPS correction depends on several factors, including location of reference stations, distance between the user and reference station, etc. The long-term performance of the SLAS corrections was evaluated by processing data over a five-year period (2019-2023). The SLAS corrections were applied to GPS observations at the IGS stations in Japan and the positioning accuracy was evaluated. The correlation with the ionospheric activity and the latitude of the SLAS reference stations was also evaluated.

As autonomous navigation technology advances and the importance of positional information in maritime environments increases, it is necessary to develop alternatives to the Global Navigation Satellite System (GNSS) in consideration of its vulnerabilities. Ranging Mode (R-Mode) technology is emerging as a GNSS backup system, utilizing existing maritime communication infrastructure to provide position, navigation, and timing (PNT) information through a terrestrial navigation system. This paper introduces a test-bed system developed to validate the feasibility and performance of medium frequency (MF) R-Mode technology in the context of South Korea. The MF R-Mode test-bed's transmitters are upgraded from four existing DGNSS systems, and positioning performance was evaluated based on data received in a static environment from actual signal broadcasts.

This paper presents a method for utilizing State Space Representation (SSR) corrections generated by the Korean national maritime Precision Positioning and Integrity Monitoring (POINT) system, a Precise Point Positioning - Real-Time Kinematic (PPP-RTK) service, with commercial RTK receivers. Specifically, a real-time SSR to Observation Space Representation (OSR) conversion algorithm is designed and implemented. We describe the structure of SSR corrections provided by the POINT system, including satellite orbit, satellite clock, signal bias, ionospheric delay, tropospheric delay, and coordinate transformation parameters. Additionally, we analyze the positioning accuracy of commercial receivers, such as Trimble, NovAtel, and U-blox, using OSR corrections converted from SSR data. The results demonstrate that the converted OSR corrections can achieve the required centimeter-level accuracy, satisfying the performance criteria for maritime applications. Through this study, we demonstrate that the SSR to OSR conversion software, when integrated with commercial receivers, can effectively enhance positioning accuracy, meeting the stringent requirements for maritime navigation.

This study compares and analyzes CLAS correction messages received by an actual GNSS receiver with CLAS L6 data from the QZSS public archive. The Quasi-Zenith Satellite System (QZSS) broadcasts Centimeter Level Augmentation Service (CLAS) correction messages via the L6 band, providing correction information for satellite orbit, clock, code and phase biases, as well as ionospheric and tropospheric errors for GPS, Galileo, and the QZSS constellations. In this study, data collected from the Septentrio AsteRx4 GNSS receiver and the QZSS public archive from October to December 2023 were used for a comparative analysis, with a focus on the variations in the Message Generation Facility (MGF) ID, which indicates the institution generating the CLAS message, and their impact on correction values and positioning accuracy. The results showed that changes in the MGF ID led to variations in correction information, causing differences of about 1-2 cm in the PPP-RTK positioning results.

In preparation for cases where Unmanned Aerial Vehicles (UAVs) are abused for surveillance or terrorism, this study proposes a technique to guide a UAV to a target point using a spoofing signal that interferes with the Global Navigation Satellite System (GNSS). However, the waypoint estimation-based approach used in spoofing requires repetitive computations, making real-time processing challenging and reducing its responsiveness to target point changes. This paper proposes a technique that uses reinforcement learning to guide UAV spoofing paths in real time by dynamically learning and adapting to changes in flight states without the need for waypoint estimation. To effectively learn real-time flight state change data, the Advantage Actor-Critic (A2C) reinforcement learning model is utilized. In the simulation, a spoofing path guided simulation that controls flight in real time through reinforcement learning was developed. The proposed reinforcement learning model was applied, and the reinforcement learning model was verified through a simulation experiment where the target point of guided spoofing was changed.

The aim of this study is to evaluate the performance of navigation during take-off and landing by conducting Satellite-Based Augmentation System (SBAS) flight tests equipped with various SBAS enabled GNSS receivers on the Korea Urban Air Mobility (K-UAM) demonstration routes to measure the positional accuracy and to assess the Real-Time Kinematic (RTK) positional accuracy near Vertiports. The flight tests were conducted by repeatedly traveling along the Ara Waterway route between Gaeyang vertiport and the Drone Certification Center of KIAST, designated as the GC 2-1 demonstration route. During the flight tests, SBAS navigation positions and raw observational data were recorded, while RTK positions and raw observational data were recorded near vertiports. Using the stored data, dynamic reference position data were generated through post-processed RTK, and the positional accuracy of SBAS on the demonstration route and RTK near vertiports were evaluated. The results indicated that the SBAS performance on the route ranged between 1.5 to 2.6 meters, while RTK demonstrated highly precise accuracy of under 10 cm. This study provides essential foundational data for evaluating the performance of navigation systems related to K-UAM initial commercialization. By statistically calculating and analyzing the Navigation System Errors (NSE) within corridors and at vertiports, this study is expected to contribute to establishing Total System Error (TSE) evaluation criteria. Additionally, it is anticipated to play a significant role in future GC Phase 2 demonstration trials and technical development.