• Journal of Institute of Control, Robotics and Systems
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• v.8 no.9
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• pp.818-826
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• 2002

Since multipath phenomenon frequently occurs when a Global Positioning System receiver is placed in urban area crowded with large buildings, efficient mitigation of multipath effects is necessary to resolve. In this paper, we propose a new multipath detection technique that is useful in real-time positioning with a general Global Positioning System receiver. The proposed technique is based on a channelwise multipath test statistic that efficiently indicates the degree of fluctuations induced by multipath error. The proposed multipath test statistic is operationally advantageous because it does not require any specialized hardware nor any pre-computation of receiver position, it is directly related to standard $\chi$$^2$-distributions, and it can adjust the detection resolution by increasing the number of successive measurements. Simulation and experiment results verify the performance of the proposed multipath detection technique.

• The Journal of Korea Robotics Society
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• v.2 no.3
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• pp.221-226
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• 2007

A robust position-sensing system is proposed in this paper for ubiquitous mobile robots which move indoor as well as outdoor. The Differential GPS (DGPS) which has position estimation error of less than 5 m is a general solution when the mobile robots are moving outdoor, while an active beacon system (ABS) with embedded ultrasonic sensors is selected as an indoor positioning system. The switching from the outdoor to indoor or vice versa causes unstable measurements on account of the reference and algorithm changes. To minimize the switching time in the position estimation and to stabilize the measurement, a robust position-sensing system is proposed. In the system, to minimize the switching delay, the door positions are stored and updated in a database. The reliability and accuracy of the robust positioning system based on DGPS and ABS are verified through the real experiments using a mobile robot prepared for this research and demonstrated.

• Proceedings of the KSRS Conference
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• 2005.10a
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• pp.349-352
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• 2005

The telematics positioning testbed is an infrastructure to test and verify positioning technology, the sub-component of telernatics system. The positioning testbed provides the environment of performance analysis for acquisition of static and dynamic positioning information using telematics vehicle. This testbed consists of onboard positioning system, positioning reference station and lab positioning server. The onboard positioning system equipped in telematics vehicle, consists of target positioning system, reference positioning system, and analysis tool. A equipment acquiring high precision positioning data obtained from GPS combined with IMU was set as a reference positioning system. Analysis tool compares observed positioning data with high precision positioning information from a reference positioning system, and processes positioning information. Positioning reference station is RTK system used for reducing atmosphere error, and it transmits corrected information to reference positioning system. Positioning server which is located at laboratory manages positioning database and provides monitoring data to integrated testbed operating system. It is expected that the testbed supports commercialization of telernatics technology and services, integrated testing among component technology and verification.

• International Journal of Aeronautical and Space Sciences
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• v.7 no.2
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• pp.56-69
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• 2006

For a relatively small country like Korea, a radionavigation system using airships can be considered, which is to provide the navigation service utilizing the stratospheric airships that are deployed in the stratosphere at the altitude of around 20-23km, and which is an independent or a back-up radionavigation system other than current GPS or GLONASS. In this paper, a feasibility study on the constellation of stratospheric airships for the navigation system has been performed. A measure of a geometrical condition between a receiver and navigation transmitters. called the DOP (Dilution of Precision), determines the resulting positioning error of the navigation system, if the error of range measurement is predictable. Therefore, with assumption that the range measurement error of the stratospheric airship navigation system is quite similar to GPS. the several DOP values have been used to evaluate the performance of the navigation system with comparing with the DOP values of GPS as the reference values. To provide the position information of the navigation transmitters to users, a receiver cluster system fixed on the ground, called an IGPS (inverted GPS), is proposed, and the error is also evaluated using the DOP values. Five areas around five major cities in South Korea have been selected, and then by numerical simulations the DOP values are compared those of GPS to assess the performance of the proposed navigation system using stratospheric airships. The possible frequency bands have been proposed. and then link budget of the navigation transmitter has been analyzed for the proposed navigation system.

• Journal of Astronomy and Space Sciences
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• v.30 no.3
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• pp.207-212
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• 2013

Ionosphere is one of the largest error sources when the navigational signals produced by Global Positioning System (GPS) satellites are transmitted. Therefore it is very important to estimate total electron contents (TEC) in ionosphere precisely for navigation, precise positioning and some other applications. When we provide ionospheric TEC values in real-time, its application can be expanded to other areas. In this study we have used data obtained from nine Global Navigation Satellite System (GNSS) reference stations which have been operated by Korea Astronomy and Space Science Institute (KASI) to detect ionospheric TEC over South Korea in real-time. We performed data processing that covers converting 1Hz raw data delivered from GNSS reference stations to Receiver INdependent Exchange (RINEX) format files at intervals of 5 minutes. We also analyzed the elevation angles of GPS satellites, vertical TEC (VTEC) values and their changes.

• Journal of Positioning, Navigation, and Timing
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• v.4 no.3
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• pp.131-140
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• 2015

Antennas at permanent GPS stations operated by the former Ministry of Government Administration and Home Affairs (MOGAHA) in Korea were replaced in years 2008 and 2009, and these changes caused abrupt discontinuities in precise coordinate time series. In this study, an algorithm that eliminates those breaks was developed based on 15-year-long coordinate time series for the purpose of creating clean and continuous coordinate time series. The newly developed algorithm to correct for sudden jumps and dips in the GPS time series due to the antenna change was designed to consider all the linear and annual signals observed before and after the event. The accuracy of the new algorithm was confirmed to be at the Root Mean Square Error (RMSE) level of 2.3-2.6 mm. The new algorithm was also found to be capable of reflect site-specific characteristics at each station.

• International Journal of Control, Automation, and Systems
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• v.5 no.4
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• pp.388-396
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• 2007

This paper describes a multipath estimation method for Global Positioning System (GPS) dual frequency carrier phase measurements. Multipath is a major error source in high precision GPS applications, i.e., carrier phase measurements for precise positioning and attitude determinations. In order to estimate and remove multipath at carrier phase measurements, an array GPS antenna system has been used. The known geometry between the antennas is used to estimate multipath parameters. Dual frequency carrier phase measurements increase the redundancy of measurements, so it can reduce the number of antennas. The unscented Kalman filter (UKF) is recently applied to many areas to overcome some of the limitations of the extended Kalman filter (EKF) such as weakness to severe nonlinearity. This paper uses the UKF for estimating multipath parameters. A series of simulations were performed with GPS antenna arrays located on a straight line with one reflector. The geometry information of the antenna array reduces the number of estimated multipath parameters from four to three. Both the EKF and the UKF are used as estimation algorithms and the results of the EKF and the UKF are compared. When the initial parameters are far from true parameters, the UKF shows better performance than the EKF.

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

• Journal of the Korean Society for Precision Engineering
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• v.27 no.10
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• pp.52-60
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• 2010

It is generally important to get a precise position information for autonomous unmanned vehicle(AUV) to run safely. For getting the position of AUV, the GPS has been using to navigation in a vehicle. Though it is useful to finding a position, it is difficult to precisely control a trajectory of the AUV due to large measuring error which may reach over 10 meters. Therefore to apply AUV it needs to compensate for the error. This paper proposes a method to more precisely localize AUV using three low-cost differential global positioning systems (DGPS). The distance errors between each DGPS are minimized as using the least square method (LSM) and the Kalman filter to eliminate a Gaussian white noise. The selected DGPS is cheaper and easier to set up than the RTK-GPS. It is also more precise than the general GPS. The proposed method can compensate the relatively position error according to stationary and moving distance of the AUV. For evaluating the algorithm by simulation, the DGPS signal with the Gaussian white noise to any points is generated by the AR model and compared with the measurement signal. It is confirmed that the proposed method can effectively compensate the position error as comparing with the measurement signal. The compensated position signal can be used to localize and control the AUV in the road.

• Journal of Digital Convergence
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• v.11 no.4
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• pp.243-249
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• 2013

In this paper, GPS(Global Positioning System) that can be used outdoors and GPS(Global Positioning System) is not available for indoor Wi-Fi(Wireless Fidelity) using the Android-based location information system has been designed and implemented. Pedestrians in a room in order to estimate the location of the pedestrian's position, regardless of need to obtain the absolute position and relative position, depending on the movement of pedestrians in a row it is necessary to estimate. In order to estimate the initial position of the pedestrian Wi-Fi Fingerprinting was used. Most existing Wi-Fi Fingerprinting position error small WKNN(Weighted K Nearest Neighbor) algorithm shortcoming EWKNN (Enhanced Weighted K Nearest Neighbor) using the algorithm raised the accuracy of the position. And in order to estimate the relative position of the pedestrian, the smart phone is mounted on the IMUInertial Measurement Unit) because the use did not require additional equipment.