• Journal of Advanced Navigation Technology
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• v.6 no.2
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• pp.104-112
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• 2002

Nowadays, many countries are interested in using CPS far navigation system of aircrafts, because it has technical and economic benefits. For the CPS based navigation system, the most important thing is reliability of the system. GPS navigation solution is very accurate. But when some faults are raised in the CPS navigation system of an aircraft, if they cannot be detected and alerts are not generated for pilots, the aircraft cannot be safe. So, I implemented an DGPS integrity monitoring system that detects faults of measurements and exclude the fault measurement from the satellite constellation used for calculating a navigation solution. This paper introduces 'the Least Square Residual Method' used to detect faults of measurements and the implemented real time integrity monitoring system using DGPS. To test the system, I operated the system under many different conditions. And from analysis of the data recorded, I could conclude that when the number of visible satellites was enough to detect faults, the system could detect the faults of measurements perfectly, isolate and exclude the fault measurement well. But for more reliable system, the measurement errors must be estimated more accurately and integrations of CPS and other instruments must be developed.

• Journal of Advanced Navigation Technology
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• v.3 no.2
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• pp.132-138
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• 1999

This paper describes the development of an automatic dependent surveillance system(ADS) with Java on Web environment. The ADS consists of a server module and a client one. The server module performs a database server for gathering GPS data from airplanes. It also dose an Web server function for sending Java applet to clients. The applet enables each client to obtain the current flight information from the server via the Internet without a special client software. This client-server based ADS with Java environment has several advantages over other systems. One is not to need for installing special client software on each client system. The other is its simplicity on system maintenance. The reason why it has simplicity is to require only server program modification including the applet without updating client software. After testing the ADS system with the flight information of a Mooney, we can show that the prototype system can be a candidate for developing commercial products.

• Journal of Advanced Navigation Technology
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• v.19 no.3
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• pp.199-206
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• 2015

For real-time precise positioning, IGS provides ephemeris predictions (IGS ultra-rapid, IGU) and real-time ephemeris estimates (real-time service, RTS). Due to the RTS data latency, which ranges from 5 s to 30 s, a short-term prediction process is necessary before applying the RTS corrections. In this paper, the real-time performance of the RTS correction and IGU prediction are compared. The RTS correction availability for the GPS satellites observed in Korea is computed as 99.3%. The RTS correction is applied to broadcast ephemeris to verify the accuracy of the RTS correction. The 3D orbit RMS error of the RTS correction is 0.043 m. Prediction of the RTS correction is modeled as a polynomial, and then the predicted value is compared with the IGU prediction value. The RTS orbit prediction accuracy is nearly equivalent to the IGU prediction, but RTS clock prediction performance is 0.13 m better than the IGU prediction.

• Journal of Advanced Navigation Technology
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• v.21 no.1
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• pp.12-20
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• 2017

A maritime DGPS in Korea offers pseudo-range correction information and monitors integrity of correction data by using multiple GNSS receivers. The maritime DGPS reference station and integrity monitor service sets alarm threshold value about integrity monitoring parameters for preventing service interruption status. However there is no way to avoid system interruption according to malfunction of backup systems and outside factors. Therefore, in this paper, warning threshold values were proposed for maritime DGPS operator can be counteract in advance. And Markov analysis method was carried out for selection of these warning threshold values.

• KIPS Transactions on Software and Data Engineering
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• v.5 no.4
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• pp.181-186
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• 2016

Recently, the surveillance system research has focused because Unmanned Aerial Vehicle(UAV) has the ability to monitor wide area. When the wide area are monitored, controlling UAVs repeatedly by pilots invokes the cost problem to operate UAVs. If monitoring path can be defined in advance, the cost problem can be solved by controlling UAVs autonomously based on the monitoring path. The traditional approach generates multiple motor primitives based on flied GPS locations. However, the monitoring points by UAVs are not considered by the generated motor primitives, the surveillance by UAVs is not performed properly. This paper proposes a motor primitive structure for surveillance UAVs to be flied autonomously. Motor primitives are generated automatically by setting surveillance points to denote surveillance targets accurately.

• Journal of Information Processing Systems
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• v.7 no.2
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• pp.221-240
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• 2011

Vehicular networks are a promising application of mobile ad hoc networks. In this paper, we introduce an efficient broadcast technique, called CB-S (Cell Broadcast for Streets), for vehicular networks with occlusions such as skyscrapers. In this environment, the road network is fragmented into cells such that nodes in a cell can communicate with any node within a two cell distance. Each mobile node is equipped with a GPS (Global Positioning System) unit and a map of the cells. The cell map has information about the cells including their identifier and the coordinates of the upper-right and lower-left corner of each cell. CB-S has the following desirable property. Broadcast of a message is performed by rebroadcasting the message from every other cell in the terrain. This characteristic allows CB-S to achieve an efficient performance. Our simulation results indicate that messages always reach all nodes in the wireless network. This perfect coverage is achieved with minimal overhead. That is, CB-S uses a low number of nodes to disseminate the data packets as quickly as probabilistically possible. This efficiency gives it the advantage of low delay. To show these benefits, we give simulations results to compare CB-S with four other broadcast techniques. In practice, CB-S can be used for information dissemination, or to reduce the high cost of destination discovery in routing protocols. By also specify the radius of affected zone, CB-S is also more efficient when broadcast to a subset of the nodes is desirable.

• Korean Journal of Remote Sensing
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• v.33 no.1
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• pp.69-77
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• 2017

S The need for an automated geo-positioning approach for near real-time results and to boost cost-effectiveness has become increasingly urgent. Following this trend, a new approach to automatically compensate for the bias of the rational function model (RFM) was proposed. The core idea of this approach is to remove the bias of RFM only using tie points, which are corrected by matching with the digital elevation model (DEM) without any additional ground control points (GCPs). However, there has to be a additional evaluation according to the quality of DEM because DEM is used as a core element in this approach. To address this issue, this paper compared the quality effects of DEM in the conduct of the this approach using the Shuttle Radar Topographic Mission (SRTM) DEM with the spatial resolution of 90m. and the National Geographic Information Institute (NGII) DEM with the spatial resolution of 5m. One KOMPSAT-2 stereo-pair image acquired at Busan, Korea was used as experimental data. The accuracy was compared to 29 check points acquired by GPS surveying. After bias-compensation using the two DEMs, the Root Mean Square (RMS) errors were less than 6 m in all coordinate components. When SRTM DEM was used, the RMSE vector was about 11.2m. On the other hand, when NGII DEM was used, the RMSE vector was about 7.8 m. The experimental results showed that automated geo-positioning approach can be accomplished more effectively by using NGII DEM with higher resolution than SRTM DEM.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• v.22 no.1
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• pp.1.2-5
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• 1994

Ionospheric sounding experiments have been conducted at RRL (Radio Research Laboratory), Ministry of Communications, using Digisonde 256 since its installation in 1990. Routine observations of the vertical sounding are carried out 48 times (or 39 times) a day, at every 24 hour. In addition, we also made oblique sounding experiments to obtain the real time data of Maximum Usable Frequency (MUF) and detect the anomalous HF propagation, as a part of the joint study between RRL and CRL (Communications Research Laboratory) of Japan. The two stations involved in the study were Anyang (RRL, Korea) and Kokubunji (CRL, Japan). The ionosondes used in both stations were Digisonde 256, developed by ULCAR (University of Lowell, Center for Atmospheric Research), U. S. A. , and the synchronization of time was accomplished with the help of GPS receiver. During most part of the experiments RRL transmitted non-modulated pulses, and CRL received them. The experiment was scheduled from October 25 through October 29, 1993. However, the ionosphere was not developed well enough to conduct the experiment with pre-set operation parameters. The experiment became successful (from 0500 UT to 0800 UT, October 29) only after the operation parameters had been changed, and the continuous ionograms were obtained by CRL at 0718 UT and 0733 UT in October 29, 1993. We believe this type of experiment will ensure the qualitative enhancement of solar-terrestrial physics research and a routine observation of the oblique ionospheric sounding. In this report, we present the results of the fore-mentioned oblique sounding as well as the vertical sounding results obtained by Digisonde 256 at Anyang station of RRL.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.11B
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• pp.772-783
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• 2005

In this paper, we propose an effective multicasting protocol in wireless ad-hoc networks. Conventional wired and wireless network multicast protocols do not perform well in wireless ad hoc networks because they were designed without consideration of ad hoc environments such as node mobility, limited bandwidth, high error probability. To solve this problem, some multicasting protocols for ad hoc network have been proposed in the literature. However, these protocols can not provide high packet delivery ratio, low control packet overhead and low expended bandwidth at the same time. Therefore, in this paper, we propose RTMA that improves multicasting performance in wireless ad hoc networks. RTMA calculates its current region from its position information by using GPS in order to make tree among the multicast group nodes in the same region. The proposed region-based tree method is for high packet delivery ratio, low control packet overhead when many senders send data packets. RTMA makes a reliable tree by using speed information to fill a gap of the weak points of the tree structure. When searching the routing path, RTMA selects the reliable path excluding high speed nodes.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.5
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• pp.775-784
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• 2008

It is not easy to access very high speed Internet services at sea due to some technical and economical problems. In order to realize the very high speed Internet services at sea like on land, new communication network models based on MANET should be adopted. In this paper, a new MANET model at sea is provided, which considered the ocean environments, and the characteristics and movement of vessels. On the basis of the fact that most vessels navigate on the predetermined courses, which are the shortest paths between source and destination ports in most cases, a type of location oriented routing protocol is proposed in this paper. The Hybrid Course-Based Routing Protocol(HCBR) makes use of the static information such as courses and positions of ports to proactively find the shortest paths not only among ports but also the cross points of courses. HCBR also makes use of the locational information of vessels obtained via GPS and AIS systems to reactively discover the shortest route by which data packets are delivered between them. We have simulated the comparison of the performance of HCBR with those of LAR scheme 1 and scheme2, the most typical protocols using geographical information. The simulation results show that HCBR guarantees the route discovery even without using any control packet. They also show that HCBR is more reliable(40%) and is able to obtain more optimal routes(10%) than LAR scheme1 and scheme2 protocols.