• Journal of Institute of Control, Robotics and Systems
• /
• v.15 no.6
• /
• pp.649-654
• /
• 2009

In this paper, an frequency tracking algorithm for weak signal tracking is proposed. The proposed frequency tracking algorithm uses a FMS (Fast Minus Slow) discriminator for frequency error estimation. This frequency tracking algorithm shows good frequency estimation performance under weak signal condition and is a computationally efficient for embedded software GNSS receiver. The software GNSS receiver implementing the proposed weak signal tracking algorithms could track GPS signal down to - 159dBm signal strength in the signal generator test and real GPS signal under dense urban condition.

• Journal of Institute of Control, Robotics and Systems
• /
• v.9 no.3
• /
• pp.242-250
• /
• 2003

We propose the monitoring system scheme for the CPS/INS integrated navigation system. The design requirements of the monitoring system are suggested and the software scheme based on GUI is proposed. The proposed monitoring system consists of an I/O interface part, a navigation data display part, and a post-processing part. The I/O interface part is responsible for data communication between the monitoring system and a navigation computer unit. The navigation data display part provides various display methods to show the navigation data to user in real-time. The post-processing part collects the navigation data to analyze the performance of navigation system. The proposed monitoring system software was developed using the Visual C++ programming language and a van test was carried out to demonstrate the real-time operation of the monitoring system. The test result shows that the proposed monitoring system can be effectively applied to the CPS/INS integrated navigation system.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2020.05a
• /
• pp.587-590
• /
• 2020

스마트폰, GPS 장비, 위치 기반 소셜네트워크의 발달로 방대한 이동 경로 데이터 수집이 가능하게 됐다. 이를 통해 다양한 분야에서 GPS 데이터를 가지고 사람의 이동성을 분석하고 POI를 예측하는 기회가 많아졌다. 실생활에서 사람의 이동성은 다양한 상황에 영향을 받지만, 실제 GPS 데이터는 위치, 시간 정보의 수준이다. 따라서 다양한 상황을 내재하는 정보가 사람의 이동성 분석과 POI 예측에 필요하다. 본 논문에서는 POI의 순위, 사용자의 POI 활동, 카테고리 선호도 같은 맥락적 특징을 이용하여 이에 관련된 상황에 맞는 POI 시퀀스를 예측하는 Contextual LSTM 기반 딥러닝 기법을 제안한다. Contextual LSTM은 사람의 이동성에 영향을 주는 시퀀스의 맥락적 특징을 모델에 통합하기 위해 LSTM을 확장한다. 제안된 기법은 HITS 알고리즘과 여러 제약조건 기반으로 추출한 맥락적 특징별로 딥 러닝 모델에 통합하여 각각 POI 시퀀스를 검출했으며, 다양한 맥락적 특징에 대해서 공공 데이터와 수집한 데이터로 평가하였다.

• Journal of Advanced Navigation Technology
• /
• v.14 no.6
• /
• pp.783-790
• /
• 2010

For safety navigation of ships at sea, ships monitor their location obtained from Global Positioning Satellite System (GNSS). In this study, we computed near-real-time positions of a ship at sea using GPS Precise Point Positioning (PPP) technique and analyzed precision of the near-real-time positions. We conducted ship borne GPS observations in the south sea of Korea. To process the GPS data using PPP technique, GIPSY-OASIS (GPS Inferred Positioning System-Orbit Analysis and Simulation Software) developed by the Jet Propulsion Laboratory was used. Antenna phase center variations, ocean tidal loading displacements, and azimuthal gradients of the atmosphere were corrected or estimated as standard procedures of high-precision GIPSY-OASIS data processing. As a result, the precisions of near-real-time positions was ~1cm.

• KIPS Transactions on Software and Data Engineering
• /
• v.4 no.10
• /
• pp.439-446
• /
• 2015

Recently, semantic trajectories which combine GPS positions and POIs(Point of Interests) become more popular in order to expand location based services. To construct semantic trajectories, the existing algorithms exploit the extent information of POIs described as polygons and find overlapping regions between GPS positions and the extents. However, the algorithms are not applicable in the condition where the extent information is not provided such as in Google Map, Naver Map, OpenStreetMap and most of the open geographic information systems. In this paper, we provide a novel algorithm to construct semantic trajectories only with GPS positions and POI points but without POI extents.

• Bulletin of the Korean Space Science Society
• /
• 2008.10a
• /
• pp.26.3-26.3
• /
• 2008

This research develops a GPS-based formation-flying testbed (FFTB) for formation navigation and control. The FFTB is a simulator in which spacecraft simulation and modeling software and loop test capabilities are integrated for test and evaluation of spacecraft navigation and formation control technologies. The FFTB is composed of a GPS measurement simulation computer, flight computer, environmental computer for providing true environment data and 3D visualization computer. The testbed can be simulated with one to two spacecraft, thus enabling a variety of navigation and control algorithms to be evaluated. In a formation flying simulation, GPS measurement are generated by a GPS measurement simulator to produce pseudorange, carrier phase measurements, which are collected and exchanged by the flight processors and subsequently processed in a navigation filter to generate relative and/or absolute state estimates. These state estimates are the fed into control algorithm, which are used to generate maneuvers required to maintain the formation. In this manner, the flight processor also serves as a test platform for candidate formation control algorithm. Such maneuvers are fed back through the controller and applied to the modeled truth trajectories to close simulation loop. Currently, The FFTB has a closed-loop capability of simulating a satellite navigation solution using software based GPS measurement, we move forward to improve using SPIRENT GPS RF signal simulator and space-based GPS receiver

• Journal of Satellite, Information and Communications
• /
• v.7 no.1
• /
• pp.128-133
• /
• 2012

In this paper, we analysis the effect of error of code tracking and frequency tracking according to the chip delay of spoofing signal through the simulation. Firstly, we investigate the type of spoofing signal and defense technical of spoofing attack. For simulation, we generated the intermediate spoofing signal using the software GNSS signal generator simulator(SGGS), the intermediate spoofers synchronize its counterfeit GPS signals with the current broadcast GPS signals. The software GPS receiver simulator(SGRS) received the spoofing signal and normal signal from SGGS, and process the signals. In paper, we can check that the DLL and PLL tracking loop error are generated and pseudo-range is changed non-linear according to chip delay of spoofing signal when the spoofing signal is entered. As a result, we can check that navigation solution is incorrectly effected by spoofing signal.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.26 no.3
• /
• pp.456-462
• /
• 2022

In this paper, we introduce a method of predicting time offset by applying LSTM, a deep learning model, to a precision time comparison technique based on measurement data extracted from code signals transmitted from GPS satellites to determine Universal Coordinated Time (UTC). First, we introduce a process of extracting time information from code signals received from a GPS satellite on a daily basis and constructing a daily time offset into one time series data. To apply the deep learning model to the constructed time offset time series data, LSTM, one of the recurrent neural networks, was applied to predict the time offset of a GPS satellite. Through this study, the possibility of time offset prediction by applying deep learning in the field of GNSS precise time transfer was confirmed.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.66 no.9
• /
• pp.1409-1415
• /
• 2017

The navigation and EDR(Event Data Recorder) have a different roles but also a lot of similar or common functions and elements. A representative element is a GPS. The GPS of navigation is a more higher than the that of EDR in performance. The high performance GPS has a very short initialization time and more accurate than the GPS of EDR. And the informations of OBD(On Board Diagnostics) is able to be shared in navigation and EDR. But these inter-working product between the navigation and EDR has been not yet shown. So, this paper is aimed to show how to interwork in two devices. We utilize USB bulk communication in two devices for inter-working. It is very simple ways and it could interwork in GPS, event video and ODB II data. It could be effective in cost competence and convenience. These was implemented by hardware and software and proved by the standard test.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• v.2
• /
• pp.211-215
• /
• 2006

In this paper, design and applications of a generalized, versatile and customizable IF signal generator that can model the modernized GPS and Galileo signal is given. It generates IF sampled data that can be directly used by a software receiver. Entire constellation of satellites which is independent of satellite-user geometry is easily determined using a real or simulated ephemeris data. Since the IF center frequency, sampling frequency and quantization bit number are user location dependent parameters, their effects are also considered in IF signal generator. The generalized IF signal generator will be very well suited for the development phase of a software receiver due to its versatility. The full access to the sampling frequency, front-end filter definition and ADC parameters also offers a great opportunity for cost-effective analysis of tracking loops and error mitigation techniques at the receiver level. Interference sources can be easily added to the generator to simulate specific environments. This software IF signal generator can also be used to feed a multi-frequency multi-system software receiver for the prototyping of a combined GPS/Galileo receiver. The test result using the generated signals and a real software receiver shows the effectiveness of the implemented IF signal generator.