• Journal of Positioning, Navigation, and Timing
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• 제9권4호
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• pp.293-304
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• 2020

In this paper, various modulation techniques, including the legacy Global Navigation Satellite System (GNSS) signal modulation techniques, are introduced and the spectral characteristics and correlation characteristics of signals with various modulation techniques are analyzed based on numerical simulation. With the development of various GNSS services, the limited frequency band has become increasingly saturated, and issues of interoperability and compatibility have emerged in the new GNSS design. Since the efficient allocation of frequency resources is closely related to spectrum design, modulation techniques are one of the important signal design parameters of new signal design. Signal modulation techniques are closely related to various figure of merits (FoMs) as well as spectrum characteristic, and in some cases there is a complicated trade-off between FoMs. Thus, the FoMs associated with modulation technology should be analyzed and the best signal candidates should be chosen carefully via the trade-off analysis for FoMs. In this paper, we define the modulation technique based on Phase Shift Keying (PSK), Binary Offset Carrier (BOC) and Continuous Phase Modulation (CPM) for the design of KPS signals, and the FoMs of signals in terms of spectrum and correlation function are evaluated. Signals with various modulation techniques are implemented through a numerical simulation, and the relevant FoMs are analyzed.

• Journal of Positioning, Navigation, and Timing
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• 제9권4호
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• pp.305-317
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• 2020

The navigation message is composed of the information contained in the message and the structure for transmitting this information. In order to design a navigation message, considerations in terms of message content and message structure must be elicited. For designing a Korea Positioning System (KPS) navigation message, this paper explains performance indicators in terms of message structure and message content. Most of the performance analysis of GNSS navigation messages already in operation was performed only for Time-to-first-fix-Data (TTFFD). However, in the navigation message, the message content is composed of Clock-Ephemeris Data (CED) and additional information. So, this paper proposes a new performance indicator R_(Non-CED) that can be analyzed from the viewpoint of receiving additional information along with an explanation of TTFFD focusing on the CED reception time. This paper analyze the performance in terms of message structure using these two performance indicators. The message structures used for analysis are the packetized message protocol like GPS CNAV and the packetized and fixed pattern message protocol like GPS CNAV-2. From the results, it is possible to proffer how KPS navigation messages can have better performance than GPS navigation messages. And, these two performance indicators, TTFFD and R_Non-CED, can help to design the minimum TTFF required performance of KPS navigation messages.

• 분석과 대안
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• 제6권1호
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• pp.223-258
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• 2022

The 2018 local elections completely upended the composition of Busan's city council, with the council membership changing from being solidly and consistently conservative to being over 80% liberal. What explains this anomalous outcome? While existing literature suggests the outcome of the 2018 city council elections was the consequence of a combination of structural and strategic factors, such as the decline of regional voting, we argue that the individual-level evaluation of President Moon Jae-in is one of the primary factors driving this result. Although coattails effects are commonly considered in concurrent national legislative elections, the Presidentialized and nationalized politics of Korea makes it possible for Presidential elections to affect local elections as well. We assess our explanation through an analysis of repeated cross-sectional survey data collected just before the 2018 local elections. The results of the analysis show that support for the Democratic Party is very strongly predicted by individual-level evaluation of President Moon. When considered in the context of the timing of presidential and local elections, the results suggest that Presidential coattail effects are capable of destabilizing established political patterns, such as regional voting, if perhaps only in a sporadic and idiosyncratic fashion, depending on whether or not local elections are held early on in a President's term.

• Journal of Positioning, Navigation, and Timing
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• 제11권3호
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• pp.181-189
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• 2022

The public open signals from Global Navigation Satellite System (GNSS) including Global positioning system (GPS) are used widely by many peoples in the world except for the public regulated restriction signals which are encrypted. Nowadays there are growing concerns about GNSS signal spoofing which can deceive the GNSS receivers by abusing these open services. To counter these spoofing threats, many researches have been studied including array antenna techniques which can detect the direction of arrival by means of Multiple Signal Classification (MUSIC) algorithm. Originally the array antenna techniques were developed to countermeasure the jamming signal in electronic warfare by using the nulling or beamforming algorithm toward a certain direction. In this paper, we study the anti-spoofing techniques using array antenna to overcome the jamming and spoofing issues simultaneously. First, we will present the theoretical analysis results of spoofing signal response of Minimum Variance Distortionless Response (MVDR) algorithm in array antenna. Then the eigenvector algorithm of covariance matrix is suggested and verified to work with the existing anti-jamming method. The modeling and simulation are used to verify the effectiveness of the anti-spoofing algorithm. Also, the field test results show that the array antenna system with the proposed algorithms can perform the anti-spoofing function. This anti-spoofing method using array antenna is very effective in the view point of solving both the jamming and spoofing problems using the same array antenna hardware.

• Journal of Positioning, Navigation, and Timing
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• 제12권2호
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• pp.167-176
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• 2023

This study presents the performance analysis of real-time orbit determination and prediction for navigation message generation of Regional Navigation Satellite System (RNSS). Since the accuracy of ephemeris and clock correction in navigation message affects the positioning accuracy of the user, it is essential to construct a ground segment that can generate this information precisely when designing a new navigation satellite system. Based on a real-time architecture by an extended Kalman filter, we simulated orbit determination and prediction of RNSS satellites in order to assess the accuracy of orbit and clock prediction and signal-in-space ranging errors (SISRE). As a result of the simulation, the orbit and clock accuracy was at 0.5 m and 2 m levels for 24 hour determination and six hour prediction after the determination, respectively. From the prediction result, we verified that the SISRE of RNSS for six hour prediction was at a 1 m level.

• Journal of Positioning, Navigation, and Timing
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• 제12권4호
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• pp.423-430
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• 2023

One recent notable method for real-time elimination of ionospheric errors in geodetic applications is the Predicted Global Ionosphere Map (PGIM). This study analyzes the level of accuracy achievable when applying the PGIM provided by the Center for Orbit Determination of Europe (CODE) to the Korean Peninsula region. First, an examination of the types and lead times of PGIMs provided by the International GNSS Service (IGS) Analysis Center revealed that CODE's two-day prediction model, C2PG, is available approximately eight hours before midnight. This suggests higher real-time usability compared to the one-day prediction model, C1PG. When evaluating the accuracy of PGIM by assuming the final output of the Global Ionosphere Map (GIM) as a reference, it was found that on days with low solar activity, the error is within ~2 TECU, and on days with high solar activity, the error reaches ~3 TECU. A comparison of the errors introduced when using PGIM and three solar activity indices-Kp index, F10.7, and sunspot number-revealed that F10.7 exhibits a relatively high correlation coefficient compared to Kp-index and sunspot number, confirming the effectiveness of the prediction model.

• Journal of Positioning, Navigation, and Timing
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• 제13권1호
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• pp.103-110
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• 2024

In this paper, a test bed for real-time network Real-Time Kinematic (RTK) research was constructed using reference stations of the NGII. A group of candidate station networks was derived, including three stations in Seoul. The group consisted of four stations with a distance of less than 100 km between them. Among several candidates, a network composed of stations with short distances between them and demonstrating good data quality for all reference stations was selected as the test bed. After collecting real-time data in Radio Technical Committee for Maritime services (RTCM) format from the selected stations and conducting a noise analysis on measurements, mm-level carrier phase measurement noise was confirmed. Afterwards, the user set the reference station inside the test bed and analyzed the network RTK positioning performance of the MAC method using the GPS L1 frequency as post-processing. From the result of the analysis it was confirmed that the residual error for all users was within 10 cm after applying the correction. Additionally, after determining integer ambiguities through Least-squares AMBiguity Decorrelation Adjustment (LAMBDA), it was confirmed that the fix rate was 100%, and all ambiguities were resolved as true values.

• 재무관리연구
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• 제25권2호
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• pp.33-68
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• 2008

본 연구에서는 전통적 자본구조 이론인 정태적 상충이론과 자본조달순위이론 뿐만 아니라 최근 새로 등장하고 있는 시장적시성이론의 타당성과 거시 경제변수가 자본구조에 미치는 영향을 종합적인 틀에서 분석하였다. 목표자본구조 결정과 자본조달 선택의 2단계 분석 결과, 자본구조의 특정이론이 일관성 있게 지지되기보다는 각 이론이 부분적으로 지지되는 결과가 나타났다. 1단계 목표자본구조 식의 추정에 있어서 기업 특성변수의 계수는 전반적으로 정태적 상충이론보다는 자본조달순위이론을 지지하였으나 2단계의 자본조달 선택요인의 분석에서는 정태적 상충이론에서 주장하듯 기업이 목표자본구조를 설정하고 이를 추구하는 경향이 있는 것으로 분석되었다. 또한, 자금이 부족한 기업일수록 회사채보다는 오히려 주식을 발행하는 경향이 강한 것으로 나타나 단순한 형태의 자본조달순위이론의 예측과는 부합하지 않았다. 그러나 주가가 상대적으로 고평가된 기업일수록 회사채보다 주식을 발행할 가능성이 높게 나타나 시장적시성이론이 지지되는 결과를 보였다. 한편 본 연구에서는 Korajczyk and Levy(2003)와 달리 기간 스프레드와 신용 스프레드 등 거시경제 변수가 자본구조 결정에 미치는 영향은 미미하였고, 재무적 제약이 있는 기업보다 재무적 제약이 없는 기업이 자본조달 시기를 조절할 수 있기 때문에 거시경제 변수나 시장 적시성 변수의 영향이 더 클 것이라는 그들의 주장을 지지하는 직접적 증거도 발견되지 않았다.

• 대한토목학회논문집
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• 제35권4호
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• pp.897-905
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• 2015

본 연구에서는 충격파 모형을 이용하여 능동식 우선신호의 최적 신호시간을 산정하기 위한 모형을 제시하였다. 본 신호 최적화 모형을 이용하여 능동형 우선신호 기법 중 Early green 및 Green extension이 적용되는 조건에서 충격파 면적을 산정할 수 있다. 본 연구에서는 평균통행시간 및 교차로 진출시각을 이용해 충격파의 발생 속도를 산정하기 위한 방법을 제시하였으며, 이를 이용해 우선신호로 인한 현시 변화량에 따라 충격파 면적 변화량을 산정할 수 있다. 또한 교차로 전체의 충격파 면적이 최소화되는 신호시간을 산정하여 우선신호로 인해 증가하는 일반차량의 지체를 최소화할 수 있도록 하였다. 우선신호 신호시간 산정 모형의 효과평가를 위해 VISSIM과 ComInterface를 이용한 미시적 시뮬레이션 분석을 시행하였으며, 이동류의 포화상태를 고려하여 지체 최소화를 위한 신호시간이 산정됨을 확인하였다. 독립교차로를 대상으로 하는 사례분석에서 우선신호를 위해 비우선현시를 균일하게 단축하는 전략 대비 본 모형에서 일반차량 지체가 10% 이상 개선됨을 확인하였다. 본 연구는 트램, BRT, 중앙버스 전용차로 등 대중교통 우선시설이 확산되고 있는 최근 국내 상황에서 신호교차로의 운영효율을 높이기 위한 새로운 우선신호 제어 방법을 제시하였다는데 의의가 있겠다.

• Journal of Advanced Marine Engineering and Technology
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• 제38권6호
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• pp.681-687
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• 2014

본 논문에서는 해군함정의 추진용 디젤엔진의 연료로 사용되는 선박용 디젤연료와 바이오디젤을 단기통 엔진에 적용시켜 연료분사시기에 따른 실린더 내 연소특성, 엔진성능 및 질소산화물 배출 특성을 분석하고, 초고속 카메라를 이용하여 선박용 디젤연료와 바이오디젤연료의 연소과정을 분석하는데 초점을 두었다. 연료분사시기가 $BTDC25^{\circ}CA$에서 $BTDC5^{\circ}CA$까지 지각될수록 실린대 내 연소최고압력은 점점 떨어졌으나, 토크는 증가하는 경향을 보였다. 질소산화물은 $BTDC15^{\circ}CA$에서 가장 높게 측정되었으며, $BTDC15^{\circ}CA$를 기준으로 지각 및 진각조건에서는 저감되는 것으로 분석되었다. 연료분사시기가 $BTDC5^{\circ}CA$일 때 선박용 디젤연료와 바이오디젤연료의 연소과정을 비교한 결과 산소가 포함된 바이오디젤연료의 착화시기가 선박용 디젤연료보다 빠르나, 화염이 확산되어 발달할수록 화염강도는 선박용 디젤연료가 큰 것으로 분석되었다.