• Journal of Positioning, Navigation, and Timing
• /
• v.1 no.1
• /
• pp.7-14
• /
• 2012

Due to inaccurate safe navigation estimates, maritime accidents have been occurring consistently. In order to solve this, the precise positioning technology using carrier phase information is used, but due to high buildings near inland waterways or inclination, satellite signals might become weak or blocked for some time. Under this weak signal environment for some time, the GPS raw measurements become less accurate so that it is difficult to search and maintain the integer ambiguity of carrier phase. In this paper, a method to generate code and carrier phase measurements under this environment and maintain resilient navigation is proposed. In the weak signal environment, the position of the receiver is estimated using an inertial sensor, and with this information, the distance between the satellite and the receiver is calculated to generate code measurements using IGS product and model. And, the carrier phase measurements are generated based on the statistics for generating fractional phase. In order to verify the performance of the proposed method, the proposed method was compared for a fixed blocked time. It was confirmed that in case of a weak or blocked satellite signals for 1 to 5 minutes, the proposed method showed more improved results than the inertial navigation only, maintaining stable positioning accuracy within 1 m.

• Journal of Institute of Control, Robotics and Systems
• /
• v.10 no.1
• /
• pp.96-102
• /
• 2004

For sensitivity enhancement, the general assisted-GPS acquisition method adopts not only the coherent accumulation technique but also the non-coherent accumulation technique since the long coherent accumulation period increases the number of frequency search cells. But the non-coherent accumulation technique causes tile squaring loss, which is a dominant factor among the acquisition losses of assisted GPS dealing with weak GPS signals. This paper derives the squaring loss of the previous assisted-GPS acquisition method and proposes an assisted-GPS acquisition method for solving the problem of squaring loss in weak signal environment. In this paper, it is explained that the proposed assisted-GPS acquisition method prevents the squaring loss using a coupled coherent accumulation technique and the number of search cells of the proposed assisted-GPS acquisition method is much smaller than that of the previous assisted-GPS acquisition method. Finally, through the simulation by the GPS simulator, the acquisition success rate of the proposed assisted-GPS acquisition method is compared with that of the previous assisted-GPS acquisition method and the acquisition improvements are shown in weak signal environment.

• Journal of Institute of Control, Robotics and Systems
• /
• v.19 no.7
• /
• pp.646-652
• /
• 2013

EU's Galileo project is a market-based GNSS (Global Navigation Satellite System) that is under development. It is expected that Galileo will provide the positioning services based on new technologies in 2020s. Because Galileo E1 signal for OS (Open Service) shares the same center frequency with GPS L1 C/A signal, CBOC (Composite Binary Offset Carrier) modulation scheme is used in the E1 signal to guarantee interoperability between two systems. With E1 signal consisting of a data channel and a pilot channel at the same frequency band, there exist several options in designing signal acquisition for Assisted-Galileo receivers. Furthermore, compared to SNR worksheet of Assisted-GPS, some factors should be examined in Assisted-Galileo due to different correlation profile and code length of E1 signal. This paper presents SNR worksheets of Galileo E1 signals in E1-B and E1-C channel. Three implementation losses that are quite different from GPS are mainly analyzed in establishing SNR worksheets. In the worksheet, hybrid long integration of 1.5s is considered to acquire weak signal less than -150dBm. Simulation results show that the final SNR of E1-B signal with -150dBm is 19.4dB and that of E1-C signal is 25.2dB. Comparison of relative computation shows that E1-B channel is more profitable to acquire the strongest signal in weak signal environment. With information from the first satellite signal acquisition, fast acquisition of the weak signal around -155dBm can be performed with E1-C signal in the subsequent satellites.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2011.06a
• /
• pp.329-330
• /
• 2011

This paper concerns to the acquisition of Global Positioning System L1 C/A coded signals. It specifically addresses the issues of acquiring very low power signals which are attenuated due to special circumstances such as indoor environment or forest canopy etc. The proposed post-processing algorithm applies modified signal folding coherent integration scheme on weak signal record. It dynamically compensates the doppler effect on the length of C/A code before integrating the signal power. Experimental results show effectiveness of the algorithm on weak GPS signals recorded in a real environment.

• Journal of Korea Technology Innovation Society
• /
• v.12 no.1
• /
• pp.189-211
• /
• 2009

The importance of searching the weak signal has been increasingly recognized to cope with rapidly changing circumstances as an environmental analysis technique. This study proposed the NEST process for the searching for the weak signal. The NEST (New & Emerging Signals of Trends) is a micro environmental analysis process based on both quantitative and qualitative method. For this, the weak signal Searching Board is developed and traditional methods as global monitoring, trend analysis, brainstorming and delphi method are implemented to NEST. The NEST process is consists of three stage modules; the global monitoring stage in search of seeds information related to the environmental change, the weak signal analysis stage using the weak signal Tracking Board, and the delphi valuation stage for objectifying the final result. The NEST provides the weak signal of the promising technology which can bring new paradigm and the Up-Coming Trends which can lead new trend in the future. These outputs can be used to select promising technology from firm level to national level. The NEST system can be effectively operated as well as in small group so that small and medium innovative firms can develop and execute their own NEST process individually.

• Journal of Positioning, Navigation, and Timing
• /
• v.6 no.4
• /
• pp.135-140
• /
• 2017

This paper proposes a signal merging algorithm to increase the signal-to-noise ratio (SNR) of a GPS correlator output to estimate the roll angle of a rotating vehicle in a weak GPS signal environment. Rotation Locked Loop (RLL) algorithm is used to estimate a roll angle using the characteristics that the power of the GPS signal measured at the receiver of a rotating vehicle varies periodically. First, delay times are calculated to synchronize GPS signals using satellites' and receiver's positions and the rotation frequency of a vehicle, and then correlator outputs are delayed in time and merged with each other, resulting in the increase of an SNR in a correlator output. Finally, simulations are conducted and the performance of the proposed algorithm is validated.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.1C
• /
• pp.1-7
• /
• 2006

Based on the new detection criterion proposed in Part 1 for the detecton of weak M-ary signals, a detection scheme for ultra wideband multiple access systems is investigated in the presence of impulsive interference. Simulation results show that the proposed detector, requiring less complexity, possesses almost the same performance as the maximum likelihood detector. In impulsive interference, the proposed detector also offers performance improvement over the detector optimized for Gaussian environment.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2009.10a
• /
• pp.112-115
• /
• 2009

PI code searching method of RDS(Radio Data System) are unique method of maintain desired channel on moving machine like vehicle. Efficient and fast PI code search method are researching on the all of RDS related systems for both find more better channel before Original channel signal go to bad and find desired good signal quickly when get out of Weak signal Area. But Embedded system has limited environment like memory size, so It is very difficult to apply many well known PI code searching method. This thesis suggests simple and effective method of searching PI code, considering a Embedded System Environment.

• Progress in Superconductivity
• /
• v.4 no.2
• /
• pp.121-126
• /
• 2003

The single layer direct-coupled YBCO SQUID magnetometers have been fabricated and characterized for the purpose of the measurement of weak magnetic signals in unshielded environment. Two types of magnetometers have been designed and fabricated using 10 mm$\times$ 10 mm substrates. We could operate the conventional 3-mm-wide solid pickup loop magnetometers more stably than the 12-parallel-line pickup loop magnetometers in laboratory environment. We developed a first-order electronic gradiometer system using the SQUID sensors with axial displacement of 80 mm without any mechanical alignment of magnetometers. The system with a software filter using calculation of discrete Fourier transform could record clearly weak pulse signal of 100 pT in a magnetically disturbed environment.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.18 no.11
• /
• pp.2745-2752
• /
• 2014

In recent years, Transport Demand Management has been conducted for the efficient management of transport. In ITS applications in particular, the prerequisite is accurate and reliable positioning. However, the major problems are satellite signal outage, and multipath. This paper proposes that outage and multipath measurement can be detected and estimated using elevation angle and signal to noise ratio data association relation in stand-alone GPS. In order to verify the performance of the proposed method, it is then evaluated by the car test. the evaluation test environment has low accuracy and unreliable positioning because of signal outage or multipath such as steep hill and high buildings. In the evaluation test result, 918times abnormal signal occurred and it was confirmed that the proposed method showed more improved 9.48m(RMS) horizontal positioning error than without proposed method.