• Proceedings of the KIEE Conference
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• 2006.07d
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• pp.1759-1760
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• 2006

GPS 수신기에서 항법을 수행하기 위해서 신호탐색, 신호추적, 데이터 동기, 데이터 복조, 측정치 생성 및 위치 계산의 과정을 거쳐야 한다. TTFF(Time To First Fix)는 이러한 시간의 합으로 수신기의 성능을 나타내는 중요 평가지수 중의 하나이다. 일반적인 수신기의 TTFF는 80~90초인 것으로 알려져 있으며, 고속으로 운동하는 항체의 경우, 빠른 TTFF를 필요로 하므로 가장 긴 시간이 소비하는 신호탐색 과정의 시간을 줄여야 한다. 본 논문에서는 고속으로 운동하는 항체에서 GPS 신호의 코드 탐색 시간을 줄이기 위하여 다중 상관기 구조를 가지는 수신기를 설계 하고자한다. 설계한 수신기는 수신된 신호의 코드위상을 여러 개의 상관기에서 동시에 탐색하도록 다중 상관기를 구성하여 코드위상 검색에 소요되는 시간을 단축시킨다. 이를 검증하기 위하여 GPS 모의 신호 발생기를 이용하여 실험을 수행하였다. GPS 신호는 IF 데이터 수집 장치로부터 수집된 신호를 이용하며, 실험 수행 결과 다중 상관기를 이용하였을 때 TTFF가 단축되는 것을 확인하였다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2016.05a
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• pp.22-25
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• 2016

해상에서의 선박 항해에 있어서 GPS와 같은 위성항법시스템에 대한 의존도가 매우 높다. 하지만 전파 교란 등과 같은 열악한 환경이 선박 주위에 가해질 경우 선박에 탑재된 GPS 수신기에서 위치를 추정할 수 없기 때문에 정상적인 항해가 어렵게 된다. 본 논문에서는 위와 같은 약한 전파 교란 환경을 가정하여 열악한 환경 내에서 GPS 수신기가 위치 추정 정확도는 열화되더라도 자신의 위치를 처음 파악하는 데 걸리는 시간인 TTFF(Time To First Fix)를 감소시켜 선박의 신속한 위치 계산을 위한 개략 위치 추정 기법을 설계하였다. 또한 열악한 신호 환경을 가정하여 진행된 실험에서 기존 GPS TTFF와의 비교를 통해 설계된 기법을 검증하였다.

• Proceedings of the KIEE Conference
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• 2007.04a
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• pp.404-406
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• 2007

본 논문에서는 유도 무기와 같이 고속으로 운동하는 항체에서 GPS 신호 탐색 시간을 줄이기 위하여 INS와 다중 상관기를 이용한 신호 획득 기법을 제안한다. 신호의 코드위상을 여러 개의 상관기에서 동시에 탐색하도륵 다중 상관기를 구성하여 코드위상 검색에 소요되는 시간을 단축시키며 INS로부터의 속도와 위치를 이용하여 도플러 주파수를 추정하고 이것을 도플러 검색 초기 값으로 사용하여 검색시간을 줄인다. 제안한 기법을 검증하기 위하여 GPS와 IMU 시뮬레이터를 이용하여 실험을 수행하였다. 실험 결과 INS와 다중 상관기를 이용하였을 때 TTFF가 매우 크게 단축되는 것을 알 수 있다.

• Journal of Positioning, Navigation, and Timing
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• v.7 no.4
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• pp.205-215
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• 2018

The recent emergence of new Global Navigation Satellite Systems (GNSS) has resulted in a gradual improvement in the performance of positioning services. This paper verifies the degree of improvement in positioning performance of Assisted-GNSS (A-GNSS) receivers using assistance information compared to standalone-GNSS receivers that do not use assistance information in various urban environments in Korea. For this purpose, field tests are performed in various urban and indoor environments in Korea. The assistance information is provided by u-blox's AssistNow Online and low-cost commercial receivers are used for mobile station receivers. Through experiments, the Time to First Fix (TTFF), acquisition sensitivity, and position accuracy performance improvement are analyzed. The results of the experiments show that using assistance data improved the performance in all experiment locations, and, in particular, a significant performance improvement in terms of TTFF.

• Journal of Advanced Navigation Technology
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• v.24 no.2
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• pp.92-100
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• 2020

Satellite-based argumentation systems (SBAS) is a system that enhances the accuracy, integrity, availability and continuity of GNSS navigation users by using geostationary orbit (GEO) satellites to send correction information and the failures of global navigation satellite system (GNSS) satellites in the form of messages. The correction information provided by SBAS is pseudorange error, satellite orbit error, clock error, and ionospheric delay error at 250 bps. Therefore, A lot of message processing are required for the SBAS navigation. There is a need to reduce SBAS time to first fix (TTFF) for using SBAS navigation in systems with short operating time. In this paper, A-SGNSS operation method was proposed for reducing SBAS TTFF. Also, A-SGNSS TTFF and availability were analyzed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.11B
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• pp.1618-1623
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• 2010

In this paper, we propose a new assisted global positioning system (A-GPS) using terrestrial digital multimedia broadcasting (T-DMB) data services. Because of the weak signal strength from GPS satellite and the signal blockage, it is difficult for the telematics terminal to determine the position in urban area. Proposed A-GPS system calculates pseudo range (PR) from timing information of GPS satellites and obtains the satellite information such as ephemeris from T-DMB station to determine the current position. Compared to conventional GPS system, the proposed system has better performance in terms of the fast time to first fix (TTFF), low horizontal dilution of precision (HDOP). Experimental results show that the proposed system is a feasible and robust solution.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2006.04a
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• pp.39-45
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• 2006

This paper describes an effective and fast algorithm for GPS carrier-phase ambiguity resolution (AR) which can apply for structure monitoring, and a series of simulation analyses have been carried out to demonstrate the performance of the algorithm. The results show that single-frequency AR performance is significantly improved In term of Time-To-Fix-First (TTFF) ambiguity.

• Journal of Institute of Control, Robotics and Systems
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• v.17 no.1
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• pp.61-67
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• 2011

The GPS new civil signal is modulated on the L2 carrier at a frequency of 1227.6MHz. The L2C signal is composed of two multiplexed code signals, which include CM code with a 10,230 chip sequency repeating every 20ms, and CL code which has a 767,250 chip sequency repeating every 1.5 seconds. Thus, the new civil signal have much improved cross correlation properties so that the position fixing can be possible even with very weak signals. However, it requires very long acquisition time because of its long code length. This paper presents an efficient signal acquisition method for L2C AGPS receiver. Snapshot mode and coarse time assistance are assumed and total integration time is given by 1.5 sec. By SNR worksheet and computer simulation, it is proven that L2C signal can be acquired with very weak power less than -150dBm. Considering the acquisition time and the sensitivity, it is recommended that the highest power signal is acquired with CM code first to reduce TTFF. By the timing synchronization, at this time, search space of the code phase for other signals can be greatly reduced so that CL code can be used in signal acquisition to maximize sensitivity with small computation.

• Proceedings of the KIEE Conference
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• 2004.07d
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• pp.2350-2352
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• 2004

This paper presents the implementation-tation of the real-time software GPS Receiver based on FFT and FLL assisted PLL tracking algorithm. The FFT(fast fourier transform) based GPS si-gnal acquisition scheme provides a fast TTFF(time to first fix) performance. The tracking based on FLL assisted PLL enables tracking of GPS signal in a high dynamic environment. The designed software GPS receiver uses the indexing method for generating replica carrier to reduce computation load. The performance of the implemented GPS receiver is evaluated using high-dynamic simulated data from a simulator and real static data.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.114.4-114
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• 2001

Recently, variety services are more and more developed due to supply of PDA, cellular phone, and etc. Also, a services based on location information are very helpful in traffic, shopping, and emergency. Thus the user position is positively necessary for these services. One of the latest applications in GPS is the E911 call service for wireless phones. In this case, current GPS Navigation accuracy meets the FCC requirements but the hardware size and power consumption of GPS is issued for implementation. And, some case of applications need to snapshot location solution with fast TTFF(Time-To-Fist-Fix) than continuous location solution. The software GPS receiver could be the solution ...