• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.7
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• pp.51-58
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• 2005

In 1990, GPS which had been developed for the military purposes became available to the civilian community. Since then these satellite navigation systems have been used extensively in the industrial areas such as car navigation, airplanes, communications, science and surveying. If we are dependent on GPS, however, there are some foreseeable problems in the areas of national security and sovereignty. Current GPS satellite constellation provides limited performance for the country like Korea and Japan where mountain area and urban canyon do not allow the wide skyline. To solve these problems, many countries plan to make other alternative navigation systems.In this paper, RNSS(Regional Navigation Satellite System) is designed to provide communication service with high elevation angle. It is shown, that system does not only have good navigation performance, but also improve GPS performance in Korea and its neighboring areas.

• Journal of Positioning, Navigation, and Timing
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• v.13 no.1
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• pp.53-61
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• 2024

Global Navigation Satellite Systems are expected to meet system-defined integrity requirements when users utilize the system for safety critical applications. While the guaranteed integrity performance of GPS and Galileo is publicly available, their integrity assurance procedure and related methodology have not been released to the public in an official document format. This paper summarizes the integrity assurance procedures of Global Positioning System (GPS) and Galileo, which were utilized during their system development, through a literature survey of their integrity assurance methodology. GPS Block II assures system integrity using the following methods: continuous performance monitoring and maintenance on Space Segment (SS) and Control Segment (CS), through a cause and effect analysis of anomalies and a failure analysis. In GPS Block III, to achieve more stringent integrity performance, safety requirements are integrated into the system design and development from its starting phase to the final phase. Galileo's integrity performance is provided in the Integrity Support Message (ISM) format, as Galileo utilizes a Dual Frequency Multi Constellation (DFMC) Satellite Based Augmentation System (SBAS) and Advanced Receiver Autonomous Integrity Monitoring (ARAIM) to serve safety critical applications. The integrity performance of Galileo is ensured by using a methodology similar to GPS Block II (i.e. continuous performance monitoring and maintenance on the system). The integrity assurance procedures reviewed in this paper can be utilized for a new satellite navigation system that will be developed in the near future.

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

• Journal of Positioning, Navigation, and Timing
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• v.12 no.1
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• pp.75-81
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• 2023

In this study, we design an optimized Graphics Processing Unit (GPU)-based GNSS signal processing technique with the goal of designing and implementing a GNSS Software Defined Receiver (SDR) that can operate in real time all-in-view mode under multi-constellation and multi-frequency signal environment. In the proposed structure the correlators of the existing GNSS SDR are processed by the GPU. We designed a memory structure and processing method that can minimize memory access bottlenecks and optimize the GPU memory resource distribution. The designed GNSS SDR can select and operate only the desired GNSS or desired satellite signals by user input. Also, parameters such as the number of quantization bits, sampling rate, and number of signal tracking arms can be selected. The computing capability of the designed GPU-based GNSS SDR was evaluated and it was confirmed that up to 2400 channels can be processed in real time. As a result, the GPU-based GNSS SDR has sufficient performance to operate in real-time all-in-view mode. In future studies, it will be used for more diverse GNSS signal processing and will be applied to multipath effect analysis using more tracking arms.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.10
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• pp.728-737
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• 2019

In this study, the minimized on-board computer (OBC) module for integrated navigation is developed, which provides satellites' relative position information in formation flying and cluster operation situations. The scalability is considered to apply the user-selected wireless communication module and Global Positioning System (GPS) receiver for navigation, while considering to meet the structural design standard of nano-satellites. As a result of the product development and production, the processing speed of integrated navigation and real-time data synchronization is satisfied for cluster operation nano-satellites by using micro controller unit (MCU). From a heat/vacuum, vibration and radiation test, the OBC was confirmed to be operated in space environments. From these results, a mass production system of OBC was made which is a key part of development on satellite formation flying and cluster/constellation missions that the community demands are increasing.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.4
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• pp.299-307
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• 2018

Considering a nonlinear high power amplifier(HPA) and a predistorter, we have designed a four-dimensional 8-ary phase shift keying trellis-coded modulation(4D-8PSK-TCM) system, which is recommended for X-band satellite communications. Subsequently, we have evaluated and analyzed the spectrum, constellation characteristics, and BER performance of the system. In satellite communications, owing to the limited power, nonlinear characteristics that determine the operating point of the HPA must be analyzed because the HPA consumes high power. We herein report the design of the 4D-8PSK-TCM system, with efficiencies of 2 and 2.25 bits/channel-symbol. The simulation results confirmed that a 0.35 roll-off value is effective, considering the low peak-to-average power ratio(PAPR) characteristic and the narrow occupation bandwidth of the spectrum. It also confirmed that approximately 15~20 dB of output backoff(OBO) value is required at the HPA when the predistorter is not used, and approximately 1 dB of the OBO value is required when the predistorter is used.