• Journal of Positioning, Navigation, and Timing
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• v.9 no.3
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• pp.229-236
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• 2020

The trend of water vapor contents in atmosphere is one of key elements for studying climate change. The tropospheric products, i.e., ZTD values achieved through GPS data processing can retrieve the amount of water vapor with higher temporal and spatial resolution than any other instruments. In this study, the tropospheric products of KASINET for a time period from 2001 to 2014 are reprocessed using PPP strategy and the products from the CODE's 2nd reprocessing campaign. For consistency with reprocessing activities of other networks like EPN, the VMF1 mapping function and non-tidal loading effect due to atmospheric pressure are applied in the process. The reprocessing results are investigated through comparing with the CODE's 2nd reprocessing products by including some IGS stations in the process and also calculating weekly coordinate repeatability to see the quality of the processing. After removing outliers based on the variation of averaged formal error, all processed stations have similar variations of formal error about 2 mm which is lower than that of the IGS final product. Comparison results with the CODE's 2nd reprocessing products show that the overall mean difference is found to be -0.28±5.54 mm which is similar level of the previous studies. Finally, the ZTD trends of all KASINET stations are calculated and the averaged trend is achieved as 0.19 mm/yr. However, the trend of each month shows different amounts and directions from -1.26 mm/yr in May to 1.18 mm/yr in August. In conclusion, the reprocessed tropospheric product and applied strategy of this study has enough quality as one of reliable solution for a reference product for Korean Peninsula which is needed to use GPSbased tropospheric product for climate change research.

• Journal of Positioning, Navigation, and Timing
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• v.7 no.3
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• pp.127-138
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• 2018

Spoofing attacks including meaconing can provide a bogus position to a victim GPS receiver, and those attacks are notably difficult to detect at the point of view on the receiver. Several countermeasure techniques have been studied to detect, classify, and cancel the spoofing signals. Based on the countermeasure techniques, we have developed an anti-spoofing equipment that detects and mitigates or eliminates the spoofing signal based on raw measurements. Although many anti-spoofing techniques have been studied in the literatures, the evaluation test system is not deeply studied to evaluate the anti-spoofing equipment, which includes detection, mitigation, and elimination of spoofing signals. Each study only has a specific test method to verify its anti-spoofing technique. In this paper, we propose the performance evaluation test system that includes both spoofing signal injection system and its injection scenario with the constraints of stand-alone anti-spoofing techniques. The spoofing signal injection scenario is designed to drive a victim GPS receiver that moves to a designed position, where the mitigation and elimination based anti-spoofing algorithms can be successively evaluated. We evaluate the developed anti-spoofing equipment and a commercial GPS receiver using our proposed performance evaluation test system. Although the commercial one is affected by the test system and moves to the designed position, the anti-spoofing equipment mitigates and eliminates the injected spoofing signals as planned. We evaluate the performance of anti-spoofing equipment on the position error of the circular error probability, while injecting spoofing signals.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.4A
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• pp.429-438
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• 2004

In this paper, a decision-feedback coherent code tracking loop is designed for WCDMA systems and its performance is analyzed in terms of jitter variance considering the effect of phase and symbol estimation errors for both AWGN and fading environments. An analytical closed-form formula for jitter variance is Int derived for AWGN environments as a function of a pulse-shaping filter, timing offset, signal-to-interference ratio, and loop bandwidth while involving the phase estimation error and bit error rate, and the upper bound of jitter variance is derived for fading environments. Finally a second-order coherent code tracking loop is designed with the DPCH frame format #13 of the WCDHA forward link selected as a target system, and its performance is evaluated by the closed-form formula and compared with the simulation results for both AWGN and Rayleigh fading environments.

• Journal of Positioning, Navigation, and Timing
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• v.6 no.3
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• pp.105-116
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• 2017

Several wireless localization algorithms are evaluated for the IR-UWB-based indoor location with the assumption that the ranging measurements contain the channelwise Non-Calibration Error (NCE). The localization algorithms can be divided into the Model-free Localization (MfL) methods and Model-based Kalman Filtering (MbKF). The algorithms covered in this paper include Iterative Least Squares (ILS), Direct Solution (DS), Difference of Squared Ranging Measurements (DSRM), and ILS-Common (ILS-C) methods for the MfL methods, and Extended Kalman Filter (EKF), EKF-Each Channel (EKF-EC), EKF-C, Cubature Kalman Filter (CKF), and CKF-C for the MbKF. Experimental results show that the DSRM method has better accuracy than the other MfL methods. Also, it demands smallest computation time. On the other hand, the EKF-C and CKF-C require some more computation time than the DSRM method. The accuracy of the EKF-C and CKF-C is, however, best among the 9 methods. When comparing the EKF-C and CKF-C, the CKF-C can be easily used. Finally, it is concluded that the CKF-C can be widely used because of its ease of use as well as it accuracy.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.6 s.360
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• pp.24-30
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• 2007

In this paper, an energy detection-based low power, low complexity IR-UWB receiver in multipath impulse radio channel is presented. The proposed receiver has a simple 1-bit sampler for energy detection. Also, multipath signal received from multipath impulse radio channel is amplified and envelope of the signal is detected. Then, energy detection technique using integrator by summing multipath signals in certain period is adopted to minimize the BER loss by simple energy detection. In particular, in acquisition of a sample signal, SNR is additionally improved using a digital sampler. Symbol decision using several sampled signals is performed and thus the process of symbol synchronization is significantly simplified. Also, it is effectively designed to be compatible with influences of multipath and timing error. In addition, the proposed receiver complexity is reduced using pulse decision window. The performance of the proposed receiver is simulated based on IEEE 802.15.4a channel model and the algorithms are implemented on FPGA.

• Journal of Positioning, Navigation, and Timing
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• v.8 no.3
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• pp.95-105
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• 2019

A method that applies space-time adaptive signal processing (STAP) algorithm based on an array antenna consisting of multiple antenna elements has been known to be effective to remove wide-band jamming signals in GPS receivers. However, the occurrence of phase distortion in navigation signals has been a problem when navigation signals, from which jamming signals are removed using STAP, are supplied to global positioning system (GPS) receivers. This paper verified the navigation performance degradation as a result of phase distortion. To mitigate this phenomenon, this paper proposes a mode switching scheme, in which a bypass mode is adopted to make the best use of the tracking performance of receivers without performing signal processing when jamming signals are not present or weak, and a STAP mode is employed when jamming signals exceed the threshold value. In this paper, the mode switching scheme is proposed for two environments: when receivers are stationary, and when receivers are moving. This paper confirmed that the performance of position error improved because phase distortion could be excluded due to STAP if the bypass mode was adopted under a condition where the jamming signal power level was below the threshold value in an environment where receivers were stationary. However, this paper also observed that the navigation failed due to the instability of tracking performance of receivers due to phase distortion that occurred at the switching time, although the number of switching could be reduced dramatically by proposing a dual threshold scheme of on- and off-thresholds that switched a mode due to the array antenna characteristics of varying gains according to the jamming signal incident direction in an environment where receivers were moving. The analysis results verified that running the STAP algorithm at all times is more efficient than the mode switching, in terms of maintaining stable navigation and ensuring position error performance, to remove jamming signals in an environment where receivers were moving.

• Journal of Positioning, Navigation, and Timing
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• v.12 no.2
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• pp.113-119
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• 2023

Satellite navigation systems, with the exception of the GLObal NAvigation Satellite System (GLONASS), adopt ionosphere models and provide ionospheric coefficients to single-frequency users via navigation messages to correct ionospheric delay, the main source of positioning errors. A Global Navigation Satellite System (GNSS) mostly has its own ionospheric models: the Klobuchar model for Global Positioning System (GPS), the NeQuick-G model for Galileo, and the BeiDou Global Ionospheric delay correction Model (BDGIM) for BeiDou satellite navigation System (BDS)-3. On the other hand, a Regional Navigation Satellite System (RNSS) such as the Quasi-Zenith Satellite System (QZSS) and BDS-2 uses the Klobuchar Model rather than developing a new model. QZSS provides its own coefficients that are customized for its service area while BDS-2 slightly modifies the Klobuchar model to improve accuracy in the Asia-Pacific region. In addition, BDS broadcasts multiple ionospheric parameters depending on the satellites, unlike other systems. In this paper, we analyzed the different ionospheric models of GPS, QZSS, and BDS in Korea. The ionospheric models of QZSS and BDS-2, which are based in Asia, reduced error by at least 25.6% compared to GPS. However, QZSS was less accurate than GPS during geomagnetic storms or at low latitude. The accuracy of the models according to the BDS satellite orbit was also analyzed. The BDS-2 ionospheric model showed an error reduction of more than 5.9% when using GEO coefficients, while in BDS-3, the difference between satellites was within 0.01 m.

• Journal of applied mathematics & informatics
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• v.14 no.1_2
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• pp.461-471
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• 2004

In recent years, large volumes of data are transferred between a computer system and various subsystems through digital logic circuits and interconnected wires. And there always exist potential errors when data are transferred due to electrical noise, device malfunction, or even timing errors. In general, parity checking circuits are usually employed for detection of single-bit errors. However, it is not sufficient to enhance system reliability and availability for efficient error detection. It is necessary to detect and further correct errors up to a certain level within the affordable cost. In this paper, we report a generation of 3-distance code using the characteristic matrix of a PBCA.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.2A
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• pp.96-101
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• 2003

This paper is on the user equipment (UE) side time tracker design and implementation of the wideband code division multiple access (WCDMA) system. The time tracker is constructed as a second order closed loop including time error detector (TED), loop filter (LP), numerically controlled oscillator (NCO), and sample selector (SS). Through the simulation, we found the gain of the TED as a function of the CPICH power contribution to the total transmission power of the base station. Also we derived the transfer function of the loop and the BER versus DPCH power relationships where timing offsets and loop noise bandwidths are used as parameters. In the curve, we can conclude that there are appropriate loop noise bandwidths according to the given environments for the better performance.

• Journal of Advanced Navigation Technology
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• v.18 no.5
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• pp.429-436
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• 2014

This paper proposes three methods of the time synchronization for Pseudolite and GPS and analyzes pseudolite time synchronization error factors for software based performance evaluation on proposed time synchronization methods. Proposed three time synchronization methods are pseudolite time synchronization station construction method, method by using UTC(KRIS) clock source and GPS timing receiver based time synchronization method. Also, we analyze pseudolite time synchronization error factors such as errors of pseudolite clock and reference clock, time delay as clock transmission line, measurement error of time interval counter and error as clock synchronization algorithm to design simulation platform for performance evaluation of pseudolite time synchronization.