PNT System Research Articles

Resilient satellite-based PNT system design and key technologies

Resilient satellite-based PNT system design and key technologies

Demand and key technology for a LEO constellation as augmentation of satellite navigation systems

A Low Earth Orbit (LEO) constellation augmenting satellite navigation is important in the future development of Global Navigation Satellite System (GNSS). GNSS augmented by LEO constellations can improve not only the accuracy of Positioning, Navigation, and Timing (PNT), but also the consistency and reliability of secure PNT system. This paper mainly analyzes the diverse demands of different PNT users for LEO augmented GNSS, including the precision demand in real-time, the availability demand in special areas, the navigation signal enhancement demand in complex electromagnetic environments, and the integrity demand with high security. Correspondingly, the possible contributions of LEO constellations to PNT performance are analyzed from multiple aspects. A particular attention is paid to the special PNT user requirements that cannot be fulfilled with existing GNSS, such as the PNT service demand in the polar regions and the onboard GNSS orbit determination demand of some LEO satellites. The key technologies to be considered in the constellation design, function realization, and payload development of the LEO-augmented navigation system are summarized.

Development trends of the national secure PNT system based on BDS

Development trends of the national secure PNT system based on BDS

Lunar PNT system concept and simulation results

Abstract The revived interest of many countries and the growing number of ongoing and scheduled missions to the Moon increases the significance of supporting navigation system development. A number of publications are based on multi-Global Navigation Satellite System (GNSS) signal reception from the opposite side of the Earth using high-gain antennas and lunar augmentation constellations. While the accuracy of such systems could be sufficient, the positioning, navigation, and timing (PNT) service dependency on circumterestrial navigation sources prevents the use of advanced navigation technologies honed in circumlunar space for further Mars and other celestial body missions, which is one of the major goals of lunar exploration. Moreover, orbit determination and time synchronization (ODTS) method descriptions and estimations are usually skipped in the studies of lunar augmentations. An alternative concept of the Lunar Navigation Satellite System (LNSS) is proposed based on Earth-dependency reduction principal and on-board ODTS. The advantage of the proposed approach is that LNSS-like systems could be adapted for other celestial bodies taking into account aspects such as their shape, dynamics, perturbations, as well as exploration priority regions. The baseline LNSS constellation of three circular orbits with three satellites each has been chosen as the result of multicriterion analysis of orbital stability and geometry. Station keeping requires less than 15 m/s for 10 years without significant changes in navigation performance in the prioritized Polar Regions. The full cycle of LNSS operation from ODTS and signal generation to its reception, processing, and obtaining navigation solutions has been simulated to obtain positioning accuracy for different types of users. Positioning accuracy of space users in approach/departure phases, in near-lunar orbits, as well as static users on a lunar surface is confirmed on a level of a few tens of meters. The same accuracy is achievable by dynamic users on a lunar surface during route stops or also in motion in case of LNSS constellation expansion or deployment of ground-based augmentation beacons in on-site exploration zones.

Collaborative Navigation: Supporting PNT System Operational Anomaly Detection

Modern Positioning, Navigation, and Timing (PNT) systems heavily rely on Global Navigation Satellite Systems (GNSS). Meanwhile, GNSS-based PNT systems are increasingly becoming susceptible to unintentional and deliberate Radio Frequency (RF) interference. In particular, as technology keeps advancing and hardware is becoming so inexpensive, it takes a modest effort to disrupt the normal operation of almost any PNT systems, thus posing an extreme threat to autonomous transportation systems that rely on precise PNT. As communication capabilities are expanding, a group of vehicles can easily share data when they operate in close vicinity. This gives opportunity to position and navigate the vehicles based on a jointly computed navigation solution, which is usually called collaborative navigation, resulting in a potentially more accurate and reliable operation. In this study, the feasibility and performance potential of collaborative navigation on the detection and mitigation of GNSS-based PNT system operational anomalies are evaluated on some real data and simulated anomaly scenarios. By incorporating an outlier detection method based on least squares adjustment, the collaborative navigation has shown to be able to maintain the differences to the reference solution to within 0.2 m, 0.5 m, and 3.0 m for the biased case, noisy case, and anchor case, respectively, for all test vehicles.

Concise Definition of Aviation PNT User Requirements Based on OFD

Definition of aviation is the core of PNT system requirements analysis and research, The quality of PNT user requirements definition will directly affect the scientificity and effectiveness of other research work of the system, QFD(Quality Function Deployment) is a systematic technical method and management method. In the process of product development, all activities are driven by users’ needs. QFD has been widely used in manufacturing, industrial and commercial military fields, and achieved great results. House of quality(HOQ) is the basic tool for establishing QFD system and essence of OFD method. The typical house of quality framework and analytical solution method can be used not only in the development process of new products, but also in the whole process of analysis in other fields. In this paper, aiming at the concise definition of PNT user requirements, QFD technology is used to build QFD model of PNT user requirements and PNT system technology based on the analysis of existing PNT information requirements and future aviation navigation development trend. In order to facilitate the analysis and simplify the approach of aviation navigation as the user requirements, and GNSS, SBAS, DEM, VOR, NDB, ILS and GBAS as the main system technologies. Finally, the technical quality house model of PNT system of aviation navigation task is given, so as to complete the concise definition of PNT user requirements of aviation users.

GNSS interference reduction method for CORS site planning

Precision, Navigation, and Timing (PNT) system based on Global Navigation Satellite System (GNSS) becomes significant in the air, land, and sea traffic management. Integrity of GNSS is significant to provide a reliable real time PNT system such as CORS (Continuously Operating Reference Stations). GNSS Interference due to intentional or unintentional surrounding signal source may decrease the integrity of GNSS signal. Monitoring and identification of potential GNSS interference sources in the surrounding environment of CORS is significant. This paper proposed a methodology to reduce potential GNSS interference in a planned CORS site by first simulating the radiation pattern of potential source of interference to GNSS signal in the planned CORS sites. Thereafter ambient noise levels in the location of CORS may be measured to provide a reference point for analyzing the other potential sources of interferences. Based on these results, optimal location of CORS is chosen with the lowest possible unintentional interference signal from their surrounding. Measurement has been conducted in the location of CORS owned by BIG (Indonesian Agency for Geospatial Information), which is located in the rooftop of a building neara telecommunication tower.This method is necessary for CORS site planning to reduce potential GNSS interference sources in the environment of alternative sites.

ELoran Signal Strength and Atmospheric Noise Simulation over Korea

GPS is the most widely-used Positioning, Navigation, and Timing (PNT) system. Since GPS is an important PNT infrastructure, the vulnerability of GPS to signal jamming has received significant attention. Especially, South Korea has experienced intentional high-power jamming from North Korea for the past three years, and thus realized the necessity of a complementary PNT system. South Korea recently decided to deploy a high-power terrestrial navigation system, eLoran, as a complementary PNT system. According to the plan, the initial operational capability of the Korean eLoran system is expected by 2016, and the full operational capability is expected by 2018. As a necessary research tool to support the Korean eLoran program, an eLoran performance simulation tool for Korea is under development. In this paper, the received signal strength, which is necessary to simulate eLoran performance, from the suggested Korean eLoran transmitters is simulated with the consideration of effective ground conductivities over Korea. Then, eLoran signal-to-noise ratios are also simulated based on atmospheric noise data over Korea. This basic simulation tool will be expanded to estimate the navigation performance (e.g., accuracy, integrity, continuity, and availability) of the Korean eLoran system.