• Journal of Positioning, Navigation, and Timing
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• 제13권3호
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• pp.221-235
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• 2024

Errors included in Global Navigation Satellite System (GNSS) measurements degrade the performance of user position estimation but can be mitigated by spatial correlation properties. Augmentation systems providing correction data can be broadly categorized into State Space Representation (SSR) and Observation Space Representation (OSR) methods. The satellite-based cm-level augmentation service based on the SSR broadcasts correction data via satellite signals, unlike the traditional Real-Time Kinematic (RTK) and Network RTK methods, which use OSR. To provide a large amount of correction data via the limited bandwidth of the satellite communication, efficient message structure design considering service area, correction generation, and broadcast intervals is necessary. For systematic message design, it is necessary to analyze the influence of error components included in GNSS measurements. In this study, errors in satellite orbits, satellite clocks for GPS, Galileo, BeiDou, and QZSS satellite constellations ionospheric and tropospheric delays over one year were analyzed, and their spatial decorrelations and linear modeling characteristics were examined.

• 제어로봇시스템학회논문지
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• 제21권7호
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• pp.669-676
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• 2015

In this paper, we described the simulation results of the phase offset performance of a clock in holdover mode which was normally operated in GPS Disciplined Oscillator (GPSDO). In the TIE model, we included the time error term caused by environmental temperature variation because one of the most important parameters of clock phase error is the frequency offset and drift caused by the variation of temperature. For the simulation, we employed Maximum Time Interval Error (MTIE) for the performance evaluation when the frequency offset and drift are estimated by using an Unbiased Finite Impulse Response (UFIR) filter with ladder algorithm. We assumed that the noise in the GPS measurement is white Gaussian with zero mean and 1 ns standard deviation, and temperature linearly varies with a slope of $1{^{\circ}C}$ per hour. From the simulation results, the followings were observed. First, with the estimation error of temperature of less than 3 % and the temperature compensation period of less than 900 seconds, the requirement of CDMA2000 phase synchronization under 10 us could be achieved for more than 40,000 seconds holdover time if we employ an OCXO (Oven Controlled Crystal Oscillator) clock. Second, in order to achieve the requirement of LTE-TDD under 1.5 us for more than 10,000 seconds holdover time, below 3 % estimation error and 500 seconds should be retained if a Rubidium clock is adopted.

• 한국항행학회논문지
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• 제24권2호
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• pp.92-100
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• 2020

SBAS는 정지 궤도 위성을 이용하여 보정 정보와 GNSS 위성의 고장 유무 등을 메시지 형태로 전송하여 GNSS 항법 사용자의 정확성과 무결성, 가용성, 연속성을 보강하는 시스템이다. SBAS가 제공하는 보정 정보는 250 bps의 통신 속도로 제공되며, 의사거리 오차, 위성 궤도 오차, 위성 시계 오차, 이온층 지연 오차 등의 다수의 메시지 수신이 필요하다. 따라서 SBAS가 적용된 초기 위치 결정에는 기존 GNSS에 비해 많은 시간이 소요되며, 수신기 동작 초기부터 SBAS 보강 항법의 활용에는 어려움이 있다. 본 논문에서는 SBAS 초기 위치 결정 시간의 단축을 위한 A-SGNSS 운용 개념을 제안한다. 그리고 제안한 A-SGNSS의 효용성 검토 및 운용 시 필요한 최소 메시지 정보를 정리하였으며, 제안한 방안을 적용한 SBAS 초기 위치 결정 소요 시간을 분석 하였다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2002년도 ICCAS
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• pp.33.3-33
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• 2002

Pseudolite (PL) is a kind of signal generator, which transmits GPS-like signal at the ground. However our own made PL is different from a GPS satellite in clock accuracy. GPS satellites are synchronized by use of high precision atomic clocks. But because our PLs use low cost temperature controlled oscillators (TCXO), so it is very difficult to synchronize them. Hence, we should install reference station and use Differential GPS (DGPS) algorithm to calculate user position. By use of this method, we already developed indoor navigation system a few years ago. We named it as 'Asynchronous Pseudolite Indoor Navigation System'. However, this system requires that sampling times of all the receivers...

• Journal of Positioning, Navigation, and Timing
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• 제3권1호
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• pp.31-36
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• 2014

Precise Point Positioning (PPP) is a stand-alone precise positioning approach. As the quality of satellite orbit and clock products from analysis centers has been improved, PPP can provide more precise positioning accuracy and reliability. A combined use of Global Positioning System (GPS) and Global Orbiting Navigation Satellite System (GLONASS) in PPP is now available. In this paper, we explained about an approach for combined GPS and GLONASS PPP measurement processing, and validated the performance through the comparison with GPS-only PPP results. We also used the measurement obtained from the GRAS reference station for the performance validation. As a result, we found that the combined GPS/GLONASS PPP can yield a more precise positioning than the GPS-only PPP.

• 제어로봇시스템학회논문지
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• 제6권2호
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• pp.228-233
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• 2000

It is common to apply the technology of FPGA (Fie이 Programmable Gate Array) which is one of the design methods for ASIC(Application Specific IC)to the active components used in the data processing at the digital system of satellite aircraft missile etc for compact lightness and integration of Printed Circuit Board (PCB) In carrying out the digital data processing the FPGAs are designed for the various functions of the Process Control Interrupt Control Clock Generation Error Detection and Correction (EDAC) as the individual module. In this paper an FPGA chip for Single Error Correction and Double Error Detection (SEC-DED) for EDAC is designed and simulated by using a VLSI design software LODECAP.

• 한국항공운항학회지
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• 제21권1호
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• pp.8-14
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• 2013

As GNSS(Global Navigation Satellite System) is used in various filed, many countries establish GNSS system independently. But GNSS system has the limitation of accuracy and stability in stand-alone mode, because this system has error elements which are ionospheric delay, tropospheric delay, orbit ephemeris error, satellite clock error, and etc. For overcome of accuracy limitation, the DGPS(Differential GPS) and RTK(Real-Time Kinematic) systems are proposed. These systems perform relative positioning using the reference and user receivers. ETRI(Electronics and Telecommunications Research Institute) is developing precision navigation system in point of extension of GNSS usage. The precision navigation system is for providing the precision navigation solution to common users. If this technology is developed, GNSS system can be used in the fields which require precision positioning and control. In this paper, we introduce the precision navigation system and perform design and algorithm verification.

• Korean Journal of Geomatics
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• 제4권2호
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• pp.47-52
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• 2004

We can process and compute the position, velocity and time by satellite signals of GPS. The signals are used to compute positioning of three dimensions and timing offset of the receiver clock when we can track the tour satellite signals at least. One of the specified aims is to use less expensive single frequency code/carrier phase GPS receivers, which are typically around half the price of dual frequency receivers. In the study, the author analyzed the accuracy and applicability of frequence linear combination using triangulation points evaluated distance limitation.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2003년도 Proceedings of ACRS 2003 ISRS
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• pp.1121-1123
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• 2003

The CCD (Charge coupled device) detector that is used to convert the light into electronic data is very important component in satellite camera. A Linear CCD Spectral detector shall be used in the MSC (Multi-Spectral Camera, to obtain data for high-resolution images) Payload. In this paper, the design concept of the CCD detector control module in the MSC CEU (Camera electronic unit) system which will be a payload on KOMPSAT is described in terms of H/W (clock speed and accuracy).

• Journal of Positioning, Navigation, and Timing
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• 제10권3호
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• pp.159-168
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• 2021

Precise Point Positioning-Real Time Kinematic (PPP-RTK) is an improved PPP method that provides the user receiver with satellite code and phase bias correction information in addition to the satellite orbit and clock, thus enabling single-receiver ambiguity resolution. Single station PPP-RTK concept is special case of PPP-RTK in that corrections are computed, instead of a network, by only one single GNSS receiver. This study is performed to experimentally verify the positioning accuracy performance of single baseline RTK level by a user who utilizes correction for a single station PPP-RTK using dual frequencies. As an experimental result, the horizontal and vertical 95% accuracy was 2.2 cm, 4.4 cm, respectively, which verify the same performance as the single baseline RTK.