• Journal of Positioning, Navigation, and Timing
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• 제10권2호
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• pp.113-120
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• 2021

The Distance Measuring Equipment (DME) is a ground-based aircraft navigation system and is considered as an infrastructure that ensures resilient aircraft navigation capability during the event of a Global Navigation Satellite System (GNSS) outage. The main problem of DME as a GNSS back up is a poor positioning accuracy that often reaches over 100 m. In this paper, a novel approach of applying deep reinforcement learning to a DME pulse design is introduced to improve the DME distance measuring accuracy. This method is designed to develop multipath-resistant DME pulses that comply with current DME specifications. In the research, a Markov Decision Process (MDP) for DME pulse design is set using pulse shape requirements and a timing error. Based on the designed MDP, we created an Environment called PulseEnv, which allows the agent representing a DME pulse shape to explore continuous space using the Soft Actor Critical (SAC) reinforcement learning algorithm.

• 한국항공운항학회지
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• 제10권1호
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• pp.35-44
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• 2002

Inertial Navigation System(INS) has been used in the field of air navigation for a long time but is not popular in general aviation due to high price. Recently low-price GPS is available but vulnerable to radio interference. As an alternative on these problems, GPS/INS integrated navigation system has been considered. GPS/INS is capable of implementing navigation with low-price inertial sensors but its accuracy is dependent upon how much drift of INS may be calibrated by using GPS. In order to apply GPS/INS to air navigation, it must be investigated how long drift of INS in case of no GPS aiding will be bounded within requirements for safe flight. From the above motivation, the flight test for GPS/INS navigation system was conducted in order to make sense its performance in air navigation and its result was shown.

• 제어로봇시스템학회논문지
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• 제19권2호
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• pp.131-139
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• 2013

In recent years alternative navigation system such as a DBRN (Data-Base Referenced Navigation) system using geophysical information is getting attention in the military navigation systems in advanced countries. Specifically TRN (Terrain Referenced Navigation) algorithm research is important because TRN system is a practical DBRN application in South Korea at present time. This paper presents an integrated navigation algorithm that combines a linear profile-based TRN and INS (Inertial Navigation System). We propose a correlation analysis method between TRN performance and terrain roughness index. Then we propose a conditional position update scheme that utilizes the position output of the conventional linear profile type TRN depending on the terrain roughness index. Performance of the proposed algorithm is verified through Monte Carlo computer simulations using the actual terrain database. The results show that the TRN/INS integrated algorithm, even when the initial INS error is present, overcomes the shortcomings of linear profile-based TRN and improves navigation performance.

• International Journal of Aeronautical and Space Sciences
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• 제17권1호
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• pp.80-88
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• 2016

For next generation global navigation satellite systems, new carrier frequencies in Ku/V band are expected to emerge as a promising alternative to the current frequency windows in L band as they get severely congestive. In the case of higher frequency bands, signal attenuation phenomenon through the atmosphere is significantly different from the L band signal propagation. In this paper, a fundamental investigation is carried out to explore the Ku/V band as a candidate frequency band for a new global satellite navigation carrier signal, wherein specific attention is given to the effects of the dominant attenuation factors through the tropospheric propagation path. For a specific application, a candidate orbit preliminarily designed for the Korean regional satellite navigation system is adapted. Simulation results summarize that the Ku band can provide a promising satellite navigation implementation considering the present satellite's power budget, while the V band still requires technical advances in satellite transceiver system implementations.

• Journal of Positioning, Navigation, and Timing
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• 제6권2호
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• pp.53-57
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• 2017

eLoran refers to a terrestrial navigation system using high-power low-frequency signals. Thus, it can be regarded as a positioning, navigation and timing (PNT) system to back up a global navigation satellite system (GNSS) or an alternative to GNSS. South Korea is vulnerable to interference such as GNSS jamming in particular. Therefore, South Korea has made an effort to develop an independent navigation system through eLoran system. More particularly, an eLoran testbed has been developed to be used in the northwest sea area and research on applicability of eLoran in South Korea has been underway. The present study analyzes expected performance of eLoran according to locations of newly built eLoran transmitting stations as part of the eLoran testbed research. The performance of eLoran is analyzed in terms of horizontal position accuracy, and horizontal dilution of precision (HDOP) information was used since it affects accuracy significantly. The target service areas of the eLoran testbed are Incheon and Pyeongtaek Ports, and the required target performance is positioning accuracy of 20 m position within 30 km coverage of the target service area.

• 로봇학회논문지
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• 제9권3호
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• pp.154-159
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• 2014

The Global Positioning System (GPS) is widely used to aid the navigation of aerial vehicles. However, the GPS cannot be used indoors, so alternative navigation methods are needed to be developed for micro aerial vehicles (MAVs) flying in GPS-denied environments. In this paper, a real-time three-dimensional (3-D) indoor navigation system and closed-loop control of a quad-rotor aerial vehicle equipped with an inertial measurement unit (IMU) and a low-cost light detection and ranging (LIDAR) is presented. In order to estimate the pose of the vehicle equipped with the two-dimensional LIDAR, an octree-based grid map and Monte-Carlo Localization (MCL) are adopted. The navigation results using the MCL are then evaluated by making a comparison with a motion capture system. Finally, the results are used for closed-loop control in order to validate its positioning accuracy during procedures for stable hovering and waypoint-following.

• Journal of Positioning, Navigation, and Timing
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• 제12권4호
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• pp.379-389
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• 2023

According to the Korea Urban Air Mobility (K-UAM) Concept of Operation (ConOps), the Global Navigation Satellite System (GNSS) is recommended as the primary navigation system and the performance specification will be implemented considering the standard of Performance Based Navigation (PBN). However, by taking into account the characteristics of an urban environment and the concurrent operations of multiple UAM aircraft, the current PBN standards for civil aviation seem difficult to be directly applied to an UAM aircraft. Therefore, by referring to technical documents published in the literature, this paper examines the feasibility of applying the proposed performance requirements to K-UAM, which follows the recommendation of navigation performance requirements for K-UAM. In accordance with the UAM ConOps, the UAM aircraft is anticipated to maintain low altitude during approach and landing phases. Subsequently, the navigation performance degradation could occur in the urban environment, and the primary degradation factor is identified as multipath error. For this reason, to ensure the safety and reliability of the K-UAM aircraft, it is necessary to analyze the degree of performance degradation related to the urban environment and then propose an alternative aid to enhance the navigation performance. To this end, the aim of this paper is to model the multipath effects of the GNSS in an urban environment and to carry out the simulation studies using the real GNSS datasets. Finally, the initial navigation performance requirement is proposed based on the results of the numerical simulation for the K-UAM.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.1
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• pp.349-354
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• 2006

For robust INS/GPS navigation system, an efficient multi-filter fusion technique is proposed. In the filtering for nonlinear systems, the representative filter - EKF, and the alternative filters - RHKF filter, SPKF, etc. have individual advantages and weak points. The key concept of the multi-filter fusion is the mergence of the strong points of the filters. This paper fuses the IIR type filter - EKF and the FIR type filter - RHKF filter using the adaptive strategy. The result of the fusion has several advantages over the EKF, and the RHKF filter. The advantages include the robustness to the system uncertainty, temporary unknown bias, and so on. The multi-filter fusion technique is applied to the tightly coupled INS/GPS navigation system and the performance is verified by simulation.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.1
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• pp.333-335
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• 2006

Position of surface objects can be fixed in many ways. The most popular radionavigational systems, including satellite systems, make possible obtaining nearly continuous and very precise ship's position. However, under the water application of radionavigational systems is impossible. Underwater navigation requires other tools and solutions then these encountered in surface and air navigation. In underwater environment vehicles and submarines, operate that have to possess alternative navigational systems. Underwater vehicles, in order to perform their tasks require accurate information about their own, current position. At present, they are equipped with inertial navigational systems (INS). Accuracy of INS is very high but in relatively short periods. Position error is directly proportional to time of working of the system. The basic feature of INS is its autonomy and passivity. This characteristic mainly decides that INS is broadly used on submarines and other underwater vehicles. However, due to previously mentioned shortcoming i.e. gradually increasing position error, periodical calibration of the system is necessary. The simplest calibration method is surface or nearly surface application of GPS system. Another solution, which does not require interruption of performed task and emergence on the surface, is application of comparative navigation technique. Information about surrounding environment of the ship, obtained e.g. by means sonic depth finder or board sonar, and comparing it with accessible pattern can be used in order to fix ship's position. The article presents a structure and a description of working of underwater vehicle navigation system simulator. The simulator works on the basis of comparative navigation methods which exploit in turn digital images of echograms and sonograms. The additional option of the simulator is ability to robust estimation of measurements. One can do it in order to increase accuracy of position fixed with comparative navigation methods application. The simulator can be a basis to build future underwater navigation system.

• 한국항행학회논문지
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• 제27권6호
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• pp.788-797
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• 2023

본 논문은 수직 이착륙 무인 항공시스템의 GPS (global positioning system) 불가 시 대체 항법 시스템으로의 영상보정항법 시스템을 시험하기 위한 검증환경 개발 내용을 소개한다. 개발 중인 영상보정항법 시스템의 시험 및 평가를 위해서는 가상 환경을 활용하는 것이 효율적이지만, 현재 국내에는 적합한 장비가 개발되어 있지 않다. 따라서 제안된 검증환경은 시험 대상 장비의 운용 환경을 모델링 및 시뮬레이션 하여 입력 신호를 생성하고, 출력 신호를 관측함으로써 대상 장비의 성능을 평가할 수 있도록 개발되었다. 연구 과정은 검증환경 요구도 생성, 검증환경 설계에서부터 구성품별 하드웨어 및 소프트웨어 설계, 제작까지 포괄적으로 기술되었다. 이를 바탕으로 제작된 검증환경을 개발 중인 영상기반 보정항법 알고리즘의 성능평가와 시뮬레이션 기반의 사전 비행시험 수행에 활용하였다.