The Global Positioning System (GPS) broadcasts almanac data to assist users in rapidly acquiring satellite signals by providing approximate satellite ephemeris and clock correction information. GPS Civil Navigation (CNAV) messages introduce two types of almanacs: the Midi almanac, identical to the almanac used in the Legacy Navigation (LNAV) message, and the reduced almanac, which is newly defined with a simplified set of parameters. This paper analyzes and compares the Midi and reduced almanacs, focusing on their impact on satellite position estimation accuracy and data transmission efficiency. The results show that the reduced almanac can transmit data for the entire satellite constellation up to seven times faster than the Midi almanac, offering a significant advantage in terms of acquisition time. However, due to its simplified parameter set, the reduced almanac yields lower accuracy in estimating satellite position. When the resulting errors are expressed in angular terms, however, the reduced almanac maintains sufficient precision for identifying satellites above the horizon. These findings suggest that the reduced almanac is suitable for applications where fast signal acquisition is prioritized, such as initial receiver startup, whereas the Midi almanac is more appropriate for scenarios requiring more accurate satellite orbit information.

Global Navigation Satellite Systems (GNSS) provide worldwide positioning services whereas Regional Navigation Satellite Systems (RNSS) offer services for specific areas. Korea has been developing a RNSS called the Korean Positioning System (KPS), which includes a Wide Area Differential-RNSS (WAD-RNSS) concept that transmits both navigation and correction signals simultaneously. In satellite navigation, Signal-In-Space (SIS) User Range Error (URE) represents errors in navigation signals, while User Range Accuracy (URA) provides a conservative estimate of the standard deviation of the SIS URE. The navigation signals are transmitted in either Legacy Navigation (LNAV) or Civil Navigation (CNAV) formats, with the latter offering advantages including improved flexibility, shorter update intervals, and separate error component representation. CNAV therefore achieves smaller UREs and provides a more sophisticated URA in a format different from that of LNAV. This paper proposes a CNAV URA calculation model for the Korean WAD-RNSS including mathematical expressions for both Elevation-Dependent (ED) and Non-Elevation-Dependent (NED) URA parameters specifically designed for WAD-RNSS satellite orbital characteristics. Simulation results show that the proposed CNAV URA conservatively bounds the Worst User Location (WUL) URE within the service area. Furthermore, our analysis shows that the proposed CNAV URA allows for a more precise representation compared to the LNAV URA without compromising conservatism. The proposed method can contribute to the development of modernized navigation messages for WAD-RNSS.

The Dual-Frequency Multi-Constellation (DFMC) Satellite-Based Augmentation System (SBAS) is a next-generation augmentation system that supports L1/L5 dual-frequency signals and multiple constellations, including GPS, GLONASS, Galileo, and BeiDou, whereas the legacy L1 SBAS operates on the L1 C/A single frequency and supports only GPS. DFMC SBAS employs ionosphere-free linear combination (IFLC) to eliminate first-order ionospheric delay errors and does not require an ionospheric correction message. Furthermore, Fast Correction (FC) messages have been removed from DFMC SBAS due to improved satellite clock stability and the discontinuation of Selective Availability (SA), which allows for more efficient use of bandwidth. With these structural improvements DFMC SBAS can support up to 92 satellites across multiple constellations, whereas the L1 legacy SBAS supported only up to 51 satellites. In this study, we provide a detailed comparison between L1 SBAS and DFMC SBAS, focusing on the differences in correction parameters and message structure. Key enhancements of DFMC SBAS include the integration of correction and integrity data into a single message (MT 32) and a flexible integrity broadcasting structure (MT 34-36). These refinements simplify the message structure, expand service coverage, and significantly improve integrity and positioning performance, particularly in regions with high ionospheric variability.

The Lunar Navigation Satellite System (LNSS) is designed to provide precise positioning information to users on the lunar surface, similar to the Global Navigation Satellite System (GNSS) on Earth. However, various perturbative forces can cause the orbits of lunar navigation satellites to change over time, degrading navigation performance. Given the high cost of lunar orbit insertion, maintaining stable orbits is critically important. This paper presents the design of satellite orbits that offer long-term, reliable navigation services at the lunar south pole. To maintain orbital stability, we analytically derived the conditions for lunar frozen orbits, considering the dominant perturbative influence of Earth's three-body gravity using the Lagrange planetary equations. Additionally, we analyzed the stability changes of Frozen orbits when additional perturbative forces due to the Moon's oblateness are considered, specifically incorporating the J2 term. Among the candidate stable frozen orbits that account for both Earth's three-body gravity and lunar perturbations, we selected the optimal orbits based on their superior navigation performance, which was evaluated using the Dilution of Precision (DOP) metric. The long-term navigation performance at the lunar south pole was then verified through orbital propagation simulations.

An analysis was performed on eight parameters constituting the Klobuchar ionosphere model of GPS navigation messages. By analyzing the value of the Klobuchar parameters over a long period of 23 years, the change trend was identified and a correlation with the solar activity index F10.7 was established. Among the Klobuchar parameters, α₀ and β₀, which represent the average of the intensity and period of the Klobuchar ionosphere delay function, showed a high correlation with F10.7, while other parameters representing the change in the ionosphere delay value along the geomagnetic latitude showed a very low correlation. Some parameters are characterized by repeated use with very few types of values. A limited number of combinations of α_n and β_n values were used over 23 years. The combination of Klobuchar parameters thus can be selected by grouping input variable values such as F10.7 or the day number of year and entering them in a simplified form.

Multi- Global Navigation Satellite System (GNSS) integration is widely recognized as an effective approach to improve positioning accuracy and reduce convergence time. However, issues of performance degradation regarding certain satellite constellations have been raised, particularly some BeiDou satellites in Geostationary Earth Orbit (GEO), due to orbit-related errors. To address this, the present study proposes a novel weighting model that maintains the advantages of multi-GNSS integration while minimizing the adverse effects by applying differential weights based on satellite constellation characteristics. The proposed model calculates satellite weights by comprehensively considering satellite-to-receiver range, elevation angle, and signal-to-noise ratio (SNR), and quantitatively reflects the physical characteristics of each constellation-Medium Earth Orbit (MEO), Inclined Geosynchronous Orbit (IGSO), and GEO. Using GNSS data collected over a 12-hour period, this study applies a least-squares-based Precise Point Positioning method using pseudorange measurements with State Space Representation (SSR) corrections. The positioning performance of two weighting strategies is compared: one using elevation and SNR, and the other incorporating range, elevation, and SNR. The results show that the model considering all three factors-range, elevation, and SNR-improved the average positioning accuracy by 3.1%, with a maximum improvement of 9.7%. Additionally, a low standard deviation of 4.1% indicates consistent performance enhancement, and demonstrates the effectiveness of the proposed differential weighting approach.

Inha University and PP-Solution Inc. have been developing the Kinematic Position and Precision Orbit Provider (KPOP) as domestic software for Precise Orbit Determination (POD) for the Global Navigation Satellite System (GNSS) since 2023. As of May 2025, the development of the first version of KPOP is in the POD performance verification stage and this version is equipped with GPS-only POD technology. In general, a GNSS data pre-processing technique is required to improve POD performance. KPOP is applied with detection and repair technology for clock jump and cycle slip. In this paper, we introduce the clock jump and cycle slip detection and repair techniques applied to KPOP and analyze the results of the developed preprocessing algorithms. For the results analysis, GNSS data generated by Inha University and IGS permanent observatories were used, and the results of quality checking programs developed by overseas organizations such as the G-Nut/Anubis and the RINGO were compared. From the results, the detection and repair success ratio of clock jump and cycle slip was in a range of 86-92%, and the data processing time was two seconds for 24-hour observations with a 30-second epoch. These results show that the performance of the KPOP pre-processing algorithm is similar to that of RINGO and G-Nut/Anubis.

This paper presents the selection and analysis of PRN code groups with superior autocorrelation and cross-correlation properties based on truncated Gold codes for application in satellite navigation systems. Gold codes were generated by varying the order of the Linear Feedback Shift Register (LFSR) while maintaining a constant code length. The code groups were then selected by applying balance properties and correlation criteria. The number of codes satisfying the maximum even autocorrelation power of -28 dB, maximum odd autocorrelation power of -27.5 dB, and cross-correlation maximum powers of -26.4 dB and -25 dB were compared. The results indicate that, under a fixed code length, increasing the LFSR order tends to yield a greater number of codes that meet the cross-correlation criteria. Increasing the LFSR order is therefore expected to effectively enhance cross-correlation performance.

This paper presents a reconfigurable Global Navigation Satellite System (GNSS) signal generation simulator that supports multi-constellation and multi-frequency signal generation, including Korean Positioning System (KPS) civil candidate signals in the L6 and S bands. The generator allows flexible configuration of Pseudo Random Noise (PRN) code, modulation, and navigation message. To validate the performance of the simulator, digital Intermediate Frequency (IF) signal tests and Over the Air (OTA) experiments using a Software Designed Receiver (SDR) were conducted. The results confirm successful signal generation, acquisition, tracking, and positioning. Despite interference in the S band, the generator can be effectively applied for candidate signal evaluation and future KPS signal development.

To enhance the resilience of the national Positioning, Navigation, and Timing (PNT) infrastructure and address the vulnerabilities of satellite navigation systems, the Republic of Korea has initiated the deployment of the Enhanced Loran (eLoran) system, a terrestrial navigation technology led by the Ministry of Oceans and Fisheries (MOF). Currently, three eLoran transmitting stations are operational in Pohang, Gwangju, and Socheongdo, providing service coverage across the West Sea region. In parallel, differential reference stations (dLoran) have been installed at the ports of Incheon, Pyeongtaek, and Daesan, providing positioning accuracy within 20 meters for vessels. This paper presents a comparative analysis of eLoran service coverage based on both simulation-based predictions and field measurements collected from 26 locations nationwide. The analysis evaluates the signal strength (SS) and signal-to-noise ratio (SNR) of the eLoran transmissions. Furthermore, a regression model is developed using empirical data to improve the accuracy of coverage prediction. The results are expected to contribute to a clearer understanding of the current eLoran service area and provide a policy basis for future expansion of the system.