• Proceedings of the KIEE Conference
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• 2007.11a
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• pp.204-205
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• 2007

We have developed a new measurement system by using GPS to complement those errors. In general, GPS receivers are composed of an antenna, tuned to the frequencies transmitted by the satellites, receiver-processors, and a highly-stable clock. The GPS mounted on the roof of TT4 in KHST receives a signal from the RS232 communication port, and it is connected to the network system in TT3 after converting with TCPIP communication. It is able to track the position of vehicle and synchronize the signal from different measurement system simultaneously. Therefore it is able to chase the fault occurrence, track inspection and electrical interruptionat real-time situation more accurately. There is not an error coursed by vehicle conditions such as slip and the slide.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.7
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• pp.737-745
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• 2010

This paper describes the operation results of the GPS receiver system for KSLV (Korea Space Launch Vehicle)-I on the launch site at Naro Space Center that is the first spaceport of South Korea located at Goheung. All equipments of KSLV-I including the GPS receiver system should be monitored and controlled through hard-wired interface during KSLV-I is on standby at the launch pad. The GPS receiver for KSLV-I is connected to triple almost omni-directional patch antennas mounted on the cylindrical surface of KSLV-I that should be erected vertically on the launch pad until lift-off. Signal interference and multipath effects observed in the GPS receiver on the launch site are analyzed in this paper based on the GPS signals received from each GPS antenna.

• Journal of Institute of Control, Robotics and Systems
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• v.3 no.6
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• pp.602-612
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• 1997

With GPS carrier phase measurements from more than two antenna which attached to the vehicle, precise attitude can be easily obtained if the integer ambiguity included in carrier phase measurement is resolved. Recently some special products which use dual frequencies or has one receiver engine with multiple antenna are announced. But there are still strong requirements for the conventional single frequency off-the-shelf receiver. To meet these requirements, an efficient integer ambiguity resolution technique is indispensable. In this paper, a new technique to resolve integer imbiguity with single frequency receivers is proposed. The proposed method utilize the known baseline length as a constraint of independent elements of integer ambiguities. With this constraints, the size of search volume can be greatly reduced. Thus the true integer ambiguity can be easily determined with less computational burden and number of measurements. The proposed method is applied to real data to show its effectiveness.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.69.1-69
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• 2001

In this paper, observability properties of a multiantenna GPS measurement system for the estimation of errors in INS are presented. It is shown that time-invariant INS error models are observable with measurements from at least three GPS antennas on the vehicle. There is at least one unobservable mode with two antennas. There are three unobservable modes with one antenna. It is also shown that time-varying INS error models are instantaneously observable with measurements from three GPS antennas. A numerical simulation results are given to verify the effectiveness of the multiantenna measurement system on the INS error estimation. In the simulation, a GPS measurement system is considered in which a trade-off between computational load and accuracy of estimation is achieved.

• Journal of Institute of Control, Robotics and Systems
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• v.11 no.7
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• pp.621-626
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• 2005

With precise GPS carrier positioning result, we can get attitude information if GPS antenna has adequate attaching position on the vehicle. In this case, baseline length information can be bandied as an additional measurement or constraint. In this paper, we have proposed a method to improve the attitude accuracy. To overcome nonlinearity of baseline observation model, we analyze attitude estimation result using existing estimation method like a least square method and Kalman filter, and apply a new nonlinear estimation method an unscented Kalman filter Finally we confirm the improvement of attitude estimation result in the case of appling the unscented Kalman filter.

• Journal of Positioning, Navigation, and Timing
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• v.5 no.3
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• pp.109-118
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• 2016

The present paper proposes a method that can estimate a roll rate of spinning vehicles utilizing GPS receivers. The proposed method analyzes a relation between received signal and correlation value and utilizes a phenomenon that received signal power that changes according to a signal incident direction affects a correlation value. That is, a roll-rate estimation method using zero crossing detection method for correlation value, which has sinusoidal periodicity according to rotations of vehicles, is proposed. A correlation value in real environments experiences a jitter so that the proposed method includes a pre-processing filter and detection threshold setting way is also considered to reduce the effect of received signal power. In order to verify the operation of the proposed method and analyze the performance, a signal generator and software-defined receiver (SDR) are designed. The signal generator generates intermediate frequency (IF) signal by taking the rotation of vehicles, antenna gain, and signal power into consideration, and a correlation value is acquired by taking the generated IF signals into consideration. Using the generated correlation value, the operation of the proposed roll rate estimation method is verified and the performance is analyzed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.11A
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• pp.1078-1084
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• 2010

The tracking performance of a big parabola tracking antenna system for tracking and receiving of the signal from the vehicle is impacted by many factors of the internal and the external of the system. In this paper, we analyze the tracking error due to the radio refraction in the application of the tracking and positioning of the vehicle by using radio frequency. The real measurement data are used for the analysis which had been acquired by using GPS and the tracking systems of C- and S-band frequencies in NARO Space centre. To verify the correlation between the tracking errors measured and the radio refraction, we review the error factors and the accuracies of the tracking systems, and the characteristics of the refractivity. The analysis shows that there are angular errors which are due to the radio refraction and not to be neglected, compared to the accuracies of the tracking systems, in case of low elevation angle less than 10 degrees. Also, the tracking errors depend on the target altitude as well as the elevation angle for the case of the target in the troposphere. It is recommended to correct the tracking angle considering the target altitude and elevation angle for the precise target positioning.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.10
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• pp.987-994
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• 2011

This paper presents An efficient method of antenna placement considering EMI(Electromagnetic Interference) between equipments which are mounted on the UAV(Unmanned Air Vehicle). The analysis is accomplished for voice communication radio, control datalink, TCAS(Traffic Alert Collision & Avoidance System) and GPS(Global Positioning System) which are vulnerable to EMI because the frequencies are close to each other. There are two steps for analysis procedure : The first one is selecting antenna position on the UAV by monitoring return loss and pattern variation of each antenna. The second one is analyzing EMI via antennas between equipments. In the EMI analysis, spurious level of each transmitter, coupling level between antennas and system noise property are considered. This procedure can be used to predict EMI between equipments in development stage.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.10 no.1
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• pp.111-116
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• 2017

We propose the compact circular polarized antenna. The radiation elements of the proposed antenna is designed using FR4 substrate with the size of $25mm{\times}3.2mm{\times}5mm$ and stand on four corners of the feed network substrate. The feeder network is designed on FR4 substrate with the size of $40mm{\times}40mm{\times}0.8mm$ and has four oupt signals with same magnitude and $90^{\circ}$ phase difference. The input impedances of the designed radiation elements and the output impedances of the feeder network are $100{\Omega}$. The designed antenna has the dimension of $40mm{\times}40mm{\times}5.8mm$ and the operated frequency band of 1.559 - 1.609 GHz. The fabricated antenna has RHCP radiation pattern and the measured results of axial ratio less than 3.5 dB and radiated gain more than 1.5 dBic. The fabricated antenna can apply to GLONASS and Beiodu systems as well as GPS system.

• Journal of Positioning, Navigation, and Timing
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• v.4 no.2
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• pp.57-65
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• 2015

Global Navigation Satellite System (GNSS) including Global Positioning System (GPS) is an important element for navigation of both the military and civil Unmanned Aerial Vehicle (UAV). Contrary to the military UAVs, the civil UAVs use the civil signals which are unencrypted, unauthenticated and predictable. Therefore if the civil signals are counterfeited, the civil UAV’s position can be manipulated and the appropriate movement of the civil UAV to the target point is not achieved. In this paper, spoofing on the autonomous navigation UAV is implemented through field experiments. Although the demanded conditions for appropriate spoofing attack exists, satisfying the conditions is restricted in real environments. So, the Way-point of the UAV is assumed to be known for experiments and assessments. Under the circumstances, GPS spoofing signal is generated based on the Software-based GNSS signal generator. The signal is emitted to the target UAV using the antenna of the spoofer and the effect of the signal is analyzed and evaluated. In conclusion, taking the UAV to the target point is hardly feasible. To implement the spoofing as expectation, the position and guidance system of the UAV has to be known. Additionally, the GPS receiver on the UAV could be checked whether it appropriately tracks the spoofing signal or not. However, the effect of the spoofing signal on the autonomous UAV has been verified and assessed through the experimental results. Spoofing signal affects the navigation system of the UAV so that the UAV goes off course or shows an abnormal operation.