• Journal of Positioning, Navigation, and Timing
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• 제10권4호
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• pp.315-333
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• 2021

Due to the Global Navigation Satellite System (GNSS) modernization, recently launched GNSS satellites transmit signals at various frequency bands such as L1, L2 and L5. Considering the Korean Positioning System (KPS) signal and other GNSS augmentation signals in the future, there is a high probability of applying more complex communication techniques to the new GNSS signals. For the reason, GNSS receivers based on flexible Software Defined Radio (SDR) concept needs to be developed to evaluate various experimental communication techniques by accessing each signal processing module in detail. This paper proposes a novel SDR-based A-GNSS receiver capable of processing multi-GNSS/RNSS signals at multi-frequency bands. Due to the modular structure, the proposed receiver has high flexibility and expandability. For real-time implementation, A-GNSS server software is designed to provide immediate delivery of satellite ephemeris data on demand. Due to the sampling bandwidth limitation of RF front-ends, multiple SDRs are considered to process the multi-GNSS/RNSS multi-frequency signals simultaneously. To avoid the overflow problem of sampled RF data, an efficient memory buffer management strategy was considered. To collect and process the multi-GNSS/RNSS multi-frequency signals in real-time, the proposed SDR A-GNSS receiver utilizes multiple threads implemented on a CPU and multiple NVIDIA CUDA GPGPUs for parallel processing. To evaluate the performance of the proposed SDR A-GNSS receiver, several experiments were performed with field collected data. By the experiments, it was shown that A-GNSS requirements can be satisfied sufficiently utilizing only milliseconds samples. The continuous signal tracking performance was also confirmed with the hundreds of milliseconds data for multi-GNSS/RNSS multi-frequency signals and with the ten-seconds data for multi-GNSS/RNSS single-frequency signals.

• Journal of Positioning, Navigation, and Timing
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• 제6권1호
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• pp.35-41
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• 2017

Precise Point Positioning (PPP) method is based on dual-frequency data of Global Navigation Satellite Systems (GNSS). The recent multi-constellations GNSS (multi-GNSS) enable us to bring great opportunities for enhanced precise positioning, navigation, and timing. In the paper, the multi-GNSS PPP with a combination of four systems (GPS, GLONASS, Galileo, and BeiDou) is analyzed to evaluate the improvement on positioning accuracy and convergence time. GNSS observations obtained from DAEJ reference station in South Korea are processed with both the multi-GNSS PPP and the GPS-only PPP. The performance of multi-GNSS PPP is not dramatically improved when compared to that of GPS only PPP. Its performance could be affected by the orbit errors of BeiDou geostationary satellites. However, multi-GNSS PPP can significantly improve the convergence speed of GPS-only PPP in terms of position accuracy.

• Journal of Positioning, Navigation, and Timing
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• 제6권4호
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• pp.205-210
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• 2017

Multi-Global Navigation Satellite System (GNSS) can significantly improve the positioning accuracy and convergence speed. The reliability and availability of multi-GNSS precise point positioning (PPP) is steadily increasing with the rapid development of GNSS satellites. In this study, multi-GNSS PPP analysis is performed to compare the positioning precision by processing the observations from different GNSS systems (GPS, GLONASS, Galileo and BeiDou). To improve the positioning performance of the multi-GNSS PPP, we employed the weighed measurement noise (WMN) method. After applying WMN method to multi-GNSS PPP, positioning precision is improved by approximately 26.3% compared to the GPS only solutions, and by approximately 9.1% compared to combined GPS, GLONASS, and Galileo PPP.

• Journal of Positioning, Navigation, and Timing
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• 제8권1호
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• pp.1-12
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• 2019

In this paper, we implement a navigation software of a Global Navigation Satellite System (GNSS) receiver based on a commercial purpose GNSS software receiver platform and verify its performance by performing experimental tests for various GNSS signals available in Korea region. The SX3, employed in this paper, is composed of an application program and a Radio Frequency (RF) frontend, and can capture and process multi-constellation and multi-frequency GNSS signals. All the signal processing procedure of SX3 is accessible by the receiver software designer. In particular for an easy research and development, the Application Programing Interface (API) of the SX3 has a flexible architecture to upgrade or change the existing software program, equipped with a real-time monitoring function to monitor all the API executions. Users can easily apply and experiment with the developed algorithms using a form of Dynamic Link Library (DLL) files. Thus, by utilizing this flexible architecture, the cost and effort to develop a GNSS receiver can be greatly reduced.

• Journal of Positioning, Navigation, and Timing
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• 제12권3호
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• pp.295-306
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• 2023

This paper presents a multi-frequency and multi-constellation Global Navigation Satellite System (GNSS) signal generator that simulates intermediate frequency level digital signal samples for testing GNSS receivers. GNSS signal generators are ideally suited for testing the performance of GNSS receivers and algorithms under development in the laboratory for specific user locations and environments. The proposed GNSS signal generator features a fully-reconfigurable structure with the ability to adjust signal parameters, which is beneficial to generate desired signal characteristics for multiple scenarios including multi-constellation and frequencies. Successful signal acquisition, tracking, and navigation are demonstrated on a verified Software Defined Radio (SDR) in this study. This work has implications for future studies and advances the research and development of new GNSS signals.

• Journal of Positioning, Navigation, and Timing
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• 제4권4호
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• pp.205-211
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• 2015

The Global Navigation Satellite System (GNSS) is undergoing dramatic changes. Nowadays, much more satellites are transmitting navigation data at more frequencies. A multi-GNSS analysis is performed to improve the positioning accuracy by processing combined observations from different GNSS. The multi-GNSS technique can improve significantly the positioning accuracy. In this paper, we present a combined Global Positioning System (GPS), the GLObal NAvigation Satellite System (GLONASS), the China Satellite Navigation System (BeiDou), and the Quasi-Zenith Satellite System (QZSS) standard point positioning (SPP) method to exploit all currently available GNSS observations at Mokpo (MKPO) station in South Korea. We also investigate the multi-GNSS data recorded at MKPO reference station. The positioning accuracy is compared with several combinations of the satellite systems. Because of the different frequencies and signal structure of the different GNSS, intersystem biases (ISB) parameters for code observations have to be estimated together with receiver clocks in multi-GNSS SPP. We also present GPS/GLONASS and GPS/BeiDou ISB values estimated by the daily average.

• 지적과 국토정보
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• 제50권1호
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• pp.107-123
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• 2020

최근, Multi-GNSS 위성시스템 인프라 환경의 안정화와 이종 위성 조합 활용에 대한 효용성이 입증되면서 측위, 항법 및 시간 정보 관련 응용 등 다양한 산업 분야에서 실시간 Multi-GNSS 조합 활용의 분위기가 높아지고 있다. 본 연구의 목적은 가장 수요층이 많은 저가형 1주파 GNSS 위성 수신기 사용자를 대상으로 정적 및 동적 환경에서 4가지 Multi-GNSS 측량기법에 RTCM-SSR 보정류(streams)를 적용, Multi- GNSS 위성의 1주파 실시간 단독측위(SF-RT-PP)의 효용성을 평가하고 대응 과제를 도출하는 것이다. SSR 보정류를 4가지 Multi-GNSS 측위 기법에 연계하여 정적 및 동적 시험장에 적용한 결과, CNES의 SSRa00CNE0 서비스가 2차원 좌표성분에서 다른 SSR 보정류에 비해 양호한 결과를 제시하였다. Multi-GNSS 위성의 Carrier를 활용한 SF-RT-PP 측위 결과, 공통적으로 고도성분에서 큰 편차가 발생되었는데 이에 대한 원인 규명 및 SF-RT-PPP 측위에서 비차감 비조합 전리층 지연보정과 이종 위성조합에 따른 신호 Bias 보정의 중요성을 확인할 수 있었다. 또한, Multi-GNSS 위성의 인프라 환경 향상으로 4종의 GNSS 위성 중, 1종 위성만으로도 SF-SPP 측위가 가능함을 확인하였다. 특히, GPS 위성의 1주파 신호만을 활용한 RT-SPP 측위에서 Code 기반 SF-RT-SPP 측위의 경우, 위성궤도/시계 보정관련 보통력과 SSR 보정 간 효과는 미소한 반면, 전리층 보정의 경우는 Klobuchar 모델에 비해 SBAS 보정 정보를 활용한 경우가 높이에서 약 2배 이상의 정확도 향상 효과를 공통적으로 확인할 수 있었다. 향후, 2020년말 Galileo 및 BDS 위성 인프라가 완성되면서 Multi-GNSS 위성의 지역 특성이 반영된 실시간 전리층지연 및 기상특성을 반영한 SSR 조정 서비스가 진행될 경우, SF-RT-PPP 활용성 및 여러 산업부문의 다양한 수요 창출이 기대된다.

• 지적과 국토정보
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• 제52권2호
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• pp.53-65
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• 2022

GNSS 위성측위시스템의 고도화에 따라 다채널 GNSS 수신기, 다 주파 외장안테나 및 모바일 앱(App)기반 공개형 측위해석 소프트웨어 등 사용자 부문에서도 정확성과 경제성을 반영한 하드웨어 및 운용 소프웨어의 모듈(Module)화가 구현되어 사용자의 목적에 따라 능동적 구성방식(DIY, Do it yourself)의 다채널 GNSS RTK 측위가 가능하다. 특히, Multi-GNSS 위성의 활용 인프라가 확대되고 다양한 모듈의 조합에 따른 활용·확대의 잠재성이 부각되면서 다채널 저가 GNSS 수신기 모듈의 활용에 대한 관심이 점차 높아지고 있다. 본 연구의 목적은 다양한 형태로 대중시장에 등장하고 있는 다채널 저가 GNSS 수신기를 검토하고 다채널 저가 GNSS 측위 모듈 기반 RTK 측량 시스템(이하, "다채널 GNSS RTK 모듈 측위 시스템")을 구성하여 행정안전부의 "주소정보시설 조사사업"의 활용 방안을 분석하고 활용 가능성을 평가하였다. 이를 위해 U-blox사의 F9P 칩셋, 안테나, GNSS 관측자료의 Ntrip 전송 및 RTK 측위용 해석 앱(App) 등 관련 모듈을 스마트폰을 매개로 조합, 저가형 "다채널 GNSS RTK 모듈 측위 시스템"을 구성하고 원형 궤적에 대한 동적측위 실시 및 주소정보시설을 대상으로 정적측위를 수행하였다. 실험대상지 내 고정점 5점을 대상으로 측지용 수신기 정적측량성과와 비교분석한 결과 평균 ± 1.2cm의 표준편차로 양호한 정적측량성과를 획득할 수 있었다. 또한, 드론영상 해석으로 구성한 정사영상 내 원형구조물의 외곽선에 대한 검사점과 저비용 RTK GNSS 수신기의 동적측량 궤적과 비교한 결과, 평균 ± 2.5cm의 표준편차로 매우 근접한 궤적 성과를 확인할 수 있었다. 특히, 주소정보시설에 적용한 결과, 고가의 상업용 측지형 수신기 대비 저렴한 비용으로 공간정보구축의 효용성을 검증할 수 있었으므로 지적분야에서 본 연구에서 구성한 "다채널 GNSS RTK 모듈 측위 시스템"의 다양한 활용성이 기대된다.

• Journal of Positioning, Navigation, and Timing
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• 제10권4호
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• pp.279-289
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• 2021

GNSS receivers capable of tracking multiple Global Navigation Systems (GNSSs) simultaneously are widely used. In order to estimate accurate user position and velocity, it is necessary to consider the key elements that contribute to the interoperability of the different GNSSs. Typical examples are the time system and the coordinate system. Each GNSS is operated based on its own reference time system depending on when the system was developed and whether the leap seconds are applied. In addition, each GNSS is designed based on its own coordinate system based on earth model constant values. This paper addresses the interoperability issues from the viewpoint of Single Point Positioning (SPP) users utilizing multiple GNSS signals from GPS, GLONASS, BeiDou, and Galileo. Since the broadcast ephemerides of each GNSS are based on their own time and coordinate systems, the time and the coordinate systems should be unified for any user algorithm. For this purpose, this paper proposes a method of converting each GNSS coordinate system into the reference coordinate system through Helmert transformation. The error of the broadcast ephemerides was calculated with the precise ephemerides provided by the International GNSS Service (IGS). The effectiveness of the proposed multi-GNSS correction and transformation method is verified using the Multi-GNSS Experiment (MGEX) station data.