• Journal of Ocean Engineering and Technology
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• v.33 no.5
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• pp.470-478
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• 2019

Because the global positioning system (GPS) is not available in underwater environments, an inertial navigation system (INS)/doppler velocity log (DVL) integrated navigation system is generally implemented. In general, an INS/DVL integrated system adopts a loosely coupled method. However, in this loosely coupled method, although the measurement equation for the filter design is simple, the velocity of the body frame cannot be accurately measured if even one of the DVL transducer signals is not received. In contrast, even if only one or two velocities are measured by the DVL transducers, the tightly coupled method can utilize them as measurements and suppress the error increase of the INS. In this paper, a filter was designed to regenerate the measurements of failed transducers by taking advantage of the tightly coupled method. The regenerated measurements were the normal DVL transducer measurements and the estimated velocity in RPM. In order to effectively estimate the velocity in RPM, a filter was designed considering the effects of the tide. The proposed filter does not switch all of the measurements to RPM if the DVL transducer fails, but only switches information from the failed transducer. In this case, the filter has the advantage of being able to be used as a measurement while continuously estimating the RPM error state. A Monte Carlo simulation was used to determine the performance of the proposed filters, and the scope of the analysis was shown by the standard deviation ($1{\sigma}$, 68%). Finally, the performance of the proposed filter was verified by comparison with the conventional tightly coupled method.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.3
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• pp.352-361
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• 2021

An underwater positioning method that can be applied to structures for underwater construction is being developed at the Korea Institute of Ocean Science and Technology. The method uses an extended Kalman filter (EKF) based on an inertial navigation system for precise and continuous position estimation. The observation matrix was configured to be variable in order to apply asynchronous measured sensor data in the correction step of the EKF. A Doppler velocity logger (DVL) can acquire signals only when attached to the bottom of an underwater structure, and it is difficult to install and recover. Therefore, a complex sensor device for underwater structure attachment was developed without a DVL in consideration of an underwater construction environment, installation location, system operation convenience, etc.. Its performance was verified through a water tank test. The results are the measured underwater position using an ultra-short baseline, the estimated position using only a position vector, and the estimated position using position/velocity vectors. The results were compared and evaluated using the circular error probability (CEP). As a result, the CEP of the USBL alone was 0.02 m, the CEP of the position estimation with only the position vector corrected was 3.76 m, and the CEP of the position estimation with the position and velocity vectors corrected was 0.06 m. Through this research, it was confirmed that stable underwater positioning can be carried out using asynchronous sensors without a DVL.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.05a
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• pp.685-688
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• 2016

SBAS(Satellite Based Augmentation System) broadcasts the correction message based on satellite communication to improve the positioning accuracy of GNSS user. For this reason, SBAS is actively being utilized on navigation part. To apply SBAS to navigation part, it should satisfy not only accuracy but also integrity, continuity, availability, coverage requirements and so on. Since SBAS reference station is the base infrastructure of SBAS, it is the main factor to determine the environment, position, and geometry of reference stations to achieve SBAS service performance. Therefore, a site environmental analysis should be performed prior to the selection of SBAS reference station. In this paper, it performs the environmental analysis of NDGPS(Nationwide Differential GPS) reference station sites on the premise that SBAS reference station will be co-operated in the same site of NDGPS operated by MOF(Ministry of Oceans and Fisheries). The environmental analysis is conducted as carrying out the visibility analysis of GPS satellite and interference analysis. This paper also presents the brief procedures and requirements for site survey of SBAS reference station.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.4
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• pp.491-499
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• 2011

Starting with maritime DGPS base stations of Palmido, Ochongdo which have been operated since 1999, truly our nation has become the most powerful country possessed with total of 17 DGNSS base stations in the field of DGNSS operation infrastructure. This paper examines into the country's DGNSS services as measuring the service range of the maritime DGPS base stations in the domestic ferry lines which sections are from Jeju to Incheon, from Busan to Jeju, from Jeju to Nokdong, the propagation characteristics of the radio waves of 300 kHz bands on sea and land path. As a result of identifying the service range of the DGPS in the sea routes of the southern sea and the western sea, the measured results of the DGPS signals are confirmed more than 100 NM(recommended service range). It can be possible to practical use the position information, which is safe navigation and various marine traffic management systems. It will be useful an expansion of maritime DGPS reference station in the near future.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.7
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• pp.1344-1349
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• 2012

The Korean DGPS station transmits the 200 bps GPS enhancement signal using the MSK modulation in frequency range of 283.5 kHz to 325 kHz. The land-based stations of 6 sites provide the service area of 80 km with the output power of 500 W. The ocean-based stations of 11 sites provide the output power of 300 W, which provide the DGPS service to 185 kM. Some places are serviced from two or three DGPS stations. The interferences among the DGPS stations using the high power can be occurred. Also, the performances of the user terminasl in dual service area can be degraded. In this paper, the protection ratios for the DGPS service are defined. Using the MF wave propagation model, the interferences among the DGPS stations and the adjacent wireless ground stations are analyzed. Also, the performances of DGPS user terminals are analyzed in the viewpoint of interference.

• Journal of Advanced Navigation Technology
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• v.27 no.5
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• pp.643-648
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• 2023

The Korea Augmentation Satellite System is an SBAS system being developed with the goal of providing SoL (Safety of Life) in accordance with ICAO (International Civil Aviation Organization) standards by December 2023. Monitoring the status of the system is essential for the continuous provision of KASS services, and a status monitoring tool should be developed for this purpose. The development of a status monitoring tool was divided into SYSRT (SYStem Real Time monitoring tool), SMSPP (Subsystem Monitoring Statistics tool for Post Processing) depending on the purpose. Tool development was completed through a series of procedures: requirements definition, design, development, and verification. To verify the status monitoring tool, the KASS system's real data (August 2023) were used to verify it, and the results were statistically analyzed to derive operating time and operating rate. It plans to use these tools to support continuous service provision for SoL service starting after this year.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.5
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• pp.1022-1027
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• 2014

Based on the modeling of DGPS antenna and antenna site environment, the DGPS short-monopole antenna performance according to the antenna surrounding environment are analyzed in this paper. The DGPS antenna site modeling that considers the ground conductivity and radio wave obstacles is performed and the general requirements for DGPS antenna site are proposed. In case of antenna site with proper radials on the ground plane of the fixed scale, the effect for antenna matching network due to the ground conductivity and radio wave obstacles is small but the impact on the radiation efficiency is large. To provide the stable DGPS service, it is important to install the DGPS antenna on the flat ground plain with good conductivity and without radio wave obstacles.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.565-567
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• 2018

The rover acquires its own position information using satellites signals provided by several satellites(at least four or more). For the present, GNSS systems are widely used in various fields. However, there are many factors that cause accuracy errors in positioning between rovers and GNSS satellites. Due to satellite time error, orbit error, ionospheric & convective refraction, multipath, etc., rover can't acquire precise position. Differential GPS(DGPS) and Real-Time Kinematic(RTK) have been developed as compensation techniques to reduce such errors. In this paper, we intend to develop a terminal with RTK technique to acquire precise position information of mobile station.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.11 no.4
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• pp.401-407
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• 2018

The transmission bandwidth of shorted-monopole antenna in the frequency range of LF and MF was analyzed and the transmission mode considering the permissible data rate dependant on the transmission bandwidth was analyzed in this paper. Based on the required ERP, the output power of transmitter was deduced by considering the antenna efficiency. The analyses are for DGPS and time information transmission system in the frequency range of 283.5kHz and 65kHz respectively. The transmission antenna was modeled as TLM antenna that designed in the limited antenna site. The antenna equivalent circuit and antenna bandwidth were deduced based on the simulation analysis of antenna characteristics. The analyzed antenna bandwidth was compared with the simulated antenna bandwidth. Also the transmission mode for transmitter of LF and MF was proposed by considering the antenna bandwidth.

• Journal of Cadastre & Land InformatiX
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• v.50 no.1
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• pp.107-123
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• 2020

With stabilization of the recent multi-GNSS infrastructure, and as multi-GNSS has been proven to be effective in improving the accuracy of the positioning performance in various industrial sectors. In this study, in view that SF(Single frequency) GNSS receivers are widely used due to the low costs, evaluate effectiveness of SF Real Time Point Positioning(SF-RT-PP) based on four multi-GNSS surveying methods with RTCM-SSR correction streams in static and kinematic modes, and also derive response challenges. Results of applying SSR correction streams, CNES presented good results compared to other SSR streams in 2D coordinate. Looking at the results of the SF-RT-PP surveying using SF signals from multi-GNSS, were able to identify the common cause of large deviations in the altitude components, as well as confirm the importance of signal bias correction according to combinations of different types of satellite signals and ionospheric delay compensation algorithm using undifferenced and uncombined observations. In addition, confirmed that the improvement of the infrastructure of Multi-GNSS allows SF-RT-SPP surveying with only one of the four GNSS satellites. In particular, in the case of code-based SF-RT-SPP measurements using SF signals from GPS satellites only, the difference in the application effect between broadcast ephemeris and SSR correction for satellite orbits/clocks was small, but in the case of ionospheric delay compensation, the use of SBAS correction information provided more than twice the accuracy compared to result of the Klobuchar model. With GPS and GLONASS, both the BDS and GALILEO constellations will be fully deployed in the end of 2020, and the greater benefits from the multi-GNSS integration can be expected. Specially, If RT-ionospheric correction services reflecting regional characteristics and SSR correction information reflecting atmospheric characteristics are carried out in real-time, expected that the utilization of SF-RT-PPP survey technology by multi-GNSS and various demands will be created in various industrial sectors.