• 한국항공운항학회지
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• 제20권3호
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• pp.28-34
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• 2012

The recent transition to Performance Based Navigation in aviation enhances the accuracy of aircraft position, safety and efficiency in air traffic operations by using satellite-based navigation system such as GNSS. However, intentional interferences with GNSS signal as well as ones coming from natural phenomena such as solar storm increase. GNSS have very low power and therefore their signals are more susceptible to interferences than ground-based navigation signals. This paper introduces requirements of alternative positioning, navigation and timing(APNT) system and relevant technologies when the GNSS signals are not valid.

• 한국항행학회논문지
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• 제19권6호
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• pp.499-506
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• 2015

GNSS (global navigation satellite systems)은 민 군 차원에서 매우 다양한 분야에 활용되고 있다. 그러나 GNSS 신호는 재밍에 상당히 취약해 쉽게 방해 받을 가능성이 상존하기에 GNSS을 사용 불가능할 시에도 일정 수준의 항법성능을 보장하여 주는 일련의 백업 또는 대체항법 시스템이 필요하다. 본 논문에서는 의사위성 또는 트랜시버를 장착한 고고도 장기체공 무인기(HALE UAV; high altitude long endurance unmanned aerial vehicle)의 개념을 도입하여 국지적인 지역에서 백업 또는 대체항법 시스템을 제안하고자 하였다. 제안된 대체항법 시스템을 기반으로 고고도 장기체공 무인기의 위치 오차를 추정하고, 이를 바탕으로 최종적인 사용자 위치정확도를 산출하여 본 연구에서의 국지적 대체항법의 성능을 나타내었다.

• 한국항행학회논문지
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• 제20권1호
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• pp.37-44
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• 2016

한국은 성능기반항행 (PBN; performance-based navigation)으로 전환하기 위한 단계적 PBN 이행계획을 2010년에 수립하고 로드맵에 따른 새로운 비행절차를 개발 중에 있다. PBN 비행절차에는 GNSS (global navigation satellite systems), DME (distance measuring equipment), VOR (VHF omnidirectional range), INS (inertial navigation system) 등의 항행시설 (NAVAID; navigation aid)이 활용되는 것으로 되어있다. 그 중에서 GNSS를 이용한 PBN 업무제공이 중심을 이루고 있는 실정이다. 그러나 위성항법신호의 인위적, 자연적 간섭에 의한 취약성이 발견됨에 따라 세계 각국은 다양한 대안항법(APNT; alternative positioning, navigation and timing) 기술을 연구하고 있다. 본 논문에서는 GNSS 신호가 가용하지 않을 경우 기존의 항행시스템으로 지속적인 PBN 운항이 가능한지를 분석하였으며, 결과적으로 국내 일부 공항은 접근 단계 구역에서 대안항법의 구축이 필요한 것으로 나타났다.

• 제어로봇시스템학회논문지
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• 제21권9호
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• pp.898-902
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• 2015

Alternative radio-navigation technologies aim at providing continuous navigation solution even if one cannot use GNSS (Global Navigation Satellite System). In shadowing region such as indoor environment, GNSS signal is no longer available and the alternative navigation system should be used together with GNSS to provide seamless positioning. For soldiers in battlefield where GNSS signal is jammed or in street battle, the alternative navigation system should work without positioning infrastructure. Moreover, the radio-navigation system should have scalability as well as high accuracy performance. This paper presents a TWR (Two-Way-Ranging)-based cooperative positioning system (CPS) that does not require location infrastructure. It is assumed that some members of CPS can obtain GNSS-based position and they are called mobile anchors. Other members unable to receive GNSS signal compute their position using TWR measurements with mobile anchors and neighboring members. Error propagation in CPS is analytically studied in this paper. Error budget for TWR measurements is modeled first. Next, location error propagation in CPS is derived in terms of range errors. To represent the location error propagation in the CPS, Location Error Propagation Indicator (LEPI) is proposed in this paper. Simulation results show that location error of tags in CPS is mainly influenced by the number of hops from anchors to the tag to be positioned as well as the network geometry of CPS.

• Journal of information and communication convergence engineering
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• 제6권3호
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• pp.239-244
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• 2008

Cargo tracking issue on train transportation is challenging area because of long distance haulage, theft, terror attack and customer service. This paper aims at evaluating various cargo tracking systems in terms of cost and technology. The contents of this paper consist of the research trend of cargo tracking system in the railroad transportation and reviewing of technical alternatives in cost and service side. GNSS and RFID are reviewed as location tracking technology, Internet and Satellite technology like INMASAT and Low Earth Orbit are also reviewed as communication infrastructure. This paper selects cost and service factors in two alternatives of GNSS-Satellite and RFID-Internet, among GNSS-Internet, GNSS, Satellite, RFID-Internet, RFID-Satellite and evaluate each alternative in terms of cost and service. In a result, in terms of cost, RFID-Internet type is superior to GNSS-Satellite type, but in service GNSS-Satellite type is preferred to RFID-Internet in point of area coverage and service coverage.

• Journal of information and communication convergence engineering
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• 제8권5호
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• pp.524-527
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• 2010

As the GPS(Global Positioning System) vulnerabilities were introduced, alternative systems to GPS backup have been studied for several years. Enhanced Loran(eLoran) as the worldwide ground-based supplementary radio navigation system was recommended as the cost effective alternative to GPS backup. Many efforts on adoption of eLoran as GPS backup have been presented. The US has been the leading role and announced that 70% enhancement for eLoran was established last year. However, the Obama administration cut off the eLoran budget on the fiscal year 2010 budget proposal while GAO's reports submitted that GPS service gap would be possible just some years later. Besides the US's condition, there are still many positive opinions on eLoran to GPS backup. This paper introduces the historical and technical aspects of eLoran and Korea's research topics.

• Smart Structures and Systems
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• 제30권4호
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• pp.411-420
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• 2022

Monitoring large structures is a significant issue involving public health on which new studies are constantly carried out. Although the Global Navigation Satellite System (GNSS) is the most preferable method for measuring structural displacements, total stations, one of the classical geodetic instruments, are the first devices that come to mind in cases that require complementary usage and auxiliary measurement methods. In this study, the relative displacements of the structural movements of a tower were determined using robotic total stations (RTS) and GNSS. Two GNSS receivers and two RTS observations were carried out simultaneously for 10 hours under normal weather conditions. The spectral analysis of the GNSS data was performed using fast Fourier transform (FFT), and while the dominant modal frequencies were determined, the total station data were balanced with the least-squares technique, and the position and position errors were calculated for each measurement epoch. It has been observed that low-frequency structural movements can be determined by both methods. This result shows that total station measurements are a helpful alternative method for monitoring large structures in situations where measurements are not possible due to the basic handicaps of GNSS or where it is necessary to determine displacements with short observations.

• 한국군사과학기술학회지
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• 제16권6호
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• pp.762-770
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• 2013

Korean military is currently using and operating a precision approach and landing system, called RAPCON (ASR/PAR), which is imported from overseas. However, drawbacks of this system are operational and cost problems that come along, e.g. straightness of the radio waves, limited ability of narrow searching, lack of interoperability, and high cost of installation and maintenance. Moreover, as the civilian air traffic control uses a similar system compared to the military, the so called DME/VOR/ILS, disturbance between these two systems triggered the consideration of GNSS as alternative system. In this paper, we conduct a research on trends in the field of precise approach and landing systems based on GNSS, analyze weaknesses of GNSS(jamming, fault) and consider possible solutions. Furthermore, we propose the precise approach and landing system based on GNSS to be used by the Korean military as we found it to be also suitable for military purposes. Finally, we examine the benefits of a domestic development with different focuses(development/cost of mass production/operational advantages and potential for increased performance).

• Journal of Positioning, Navigation, and Timing
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• 제10권4호
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• pp.253-262
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• 2021

Global Navigation Satellite Systems (GNSS) based precise positioning using Real Time Kinematic (RTK) technique has been proposed as an enabler of the formation operation of moving vehicles. In RTK methods, the integer ambiguity of GNSS carrier phase measurements must be resolved. Although there have been many proposed algorithms for the integer ambiguity resolution, the widelane combination of carrier phase measurements and LAMBDA methods have gained the most popularity in literatures when dual frequency GNSS measurements were used. In this paper, we evaluated five alternative methods to determine relative positions of moving base and rover receivers; the round-off scheme of widelane carrier phase, instant least-squares and Kalman filter-based LAMBDA with widelane carrier phase, instant least-squares and Kalman filter-based LAMBDA with dual frequency measurements. The paper presented the performance of each method using flight test data, which showed their strength and weakness in the aspects of time-to-first-fix, ambiguity resolution success ratio, and relative position errors. Based on that, we provided practical recommendations of RTK operations for moving vehicles.

• 한국측량학회지
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• 제36권5호
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• pp.403-412
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• 2018

Recently, GNSS (Global Navigation Satellite System)-derived orthometric height determination has been studied to improve the time and cost-effectiveness of traditional leveling surveying. However, the accuracy of this new survey method was evaluated when unknown points are located lower than control points. In this study, the accuracy of GNSS-derived orthometric height was examined using TPs (Triangulation Points) to verify the stability of surveying in mountainous areas. The GNSS survey data were obtained from Mungyeong, Unbong/Hadong, Uljin, and Jangseong. Three unknown points were surrounded by more than three UCPs (Unified Control Points) or BMs (Benchmarks) following the guideline for applying GNSS-derived orthometric height determination. A newly developed national geoid model, KNGeoid17 (Korean National Geoid 2017), has been applied for determining the orthometric height. In comparison with the official orthometric heights of the TPs, the heights of the unknown points in Mungyeong and Unbong/Hadong differ by more than 20 cm. On the other hand, TPs in Uljin and Jangseong show 15-16 cm of local bias with respect to the official products. Since the precision of official orthometric heights of TPs is known to be about 10 cm, these errors exceed the limit of the precision. Therefore, the official products should be checked to offer more reliable results to surveyors. As an alternative method of verifying accuracy, three different GNSS post-processing software were applied, and the results from each software were compared. The results showed that the differences in the whole test areas did not exceed 5 cm. Therefore, it was concluded that the precision of the GNSS-derived orthometric height was less than 5 cm, even though the unknown points were higher than the control points.