• Journal of Positioning, Navigation, and Timing
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• v.5 no.3
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• pp.137-144
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• 2016

In this paper, the performance of ranging measurement, which is generated using two receiver clock offsets in one receiver, was analyzed. A spoofer transmits a counterfeited spoofing signal which is similar to the GPS signal with hostile purposes, so the same tracking technique can be applied to the spoofing signal. The multi-correlator can generate two receiver clock offsets in one receiver. The difference between these two clock offsets consists of the path length from the spoofer to the receiver and the delay of spoofer system. Thus, in this paper, the ranging measurement was evaluated by the spoofer localization performance based on the time-of-arrival (TOA) technique. The results of simulation and real-world experiments show that the position and the system clock offset of the spoofer could be estimated successfully.

• Journal of Positioning, Navigation, and Timing
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• v.7 no.3
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• pp.175-181
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• 2018

The use of dual-frequency measurements from the Global Navigation Satellite System (GNSS) enables us to observe precise ionospheric total electron content (TEC). Currently, many GNSS reference stations in South Korea provide both GPS and GLONASS data. In the present study, we estimated the grid-based TEC values and relative receiver differential code biases (DCB) from a GNSS network operated by the Korea Astronomy and Space Science Institute. In addition, we compared the diurnal variations in a TEC time series from solutions of the GPS only, the GLONASS only, and combined GPS/GLONASS processing. A significant difference between the GPS only TEC and combined GPS/GLONASS TEC at a specific grid point over South Korea appeared near the solar terminator. It is noted that GLONASS measurements can contribute to observing a variation in ionospheric TEC over high latitude regions.

• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.1
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• pp.186-194
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• 1997

The objective of this study is to develope knock control algorithms which can increase engine power without causing frequent knock occurrence. A four cylinder spark-ignition engine is used for the experiments to develop knock control algorithms which use block vibration signals. Knock occurrence is detected accurately by using knock threshold values which consider the difference of transmission path of each cylinder. Spark timing is controlled both simultaneously and individually. With the simultaneous control, torque gain is achieved by retarding the spark timing on knock occurrence in propotion to the knock intensity. The individual knock control algorithm results in higher torque gain than the simultaneous knock control algorithm. The knock occurrence frequency of the individual knock control algorithm is about twice the value of the simultaneous knock control algorithm results. Both control algorithms give similar torque gain of about 3% when they are optimized.

• Proceedings of the IEEK Conference
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• 2002.07c
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• pp.1819-1822
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• 2002

The authors propose a robust symbol timing recovery (STR) for telephone line modems supporting data rates up to 32 Mbps. The STR is initialized by a start signal from carrier sensor, and the novel method is proposed which resolves the difference between the frequency of the transmitter's clock and the receiver's clock, called baud frequency offset. The proposed method is applied on digital receiver in a 16 frequency diverse quadrature amplitude modulation (FDQAM) system.

• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.6
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• pp.76-86
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• 1994

Combustion of diesel engine depends on the mixing of air and evaporating fuel during ignition delay greatly. Variation of air-fuel mixing rate and ignition delay for engine operating condition causes difference of combustion, performance and exhaust emissions. This study is investigated in a turbocharged diesel engine of IDI swirl chamber type. In the results, As injection timing is advanced until $12.6^{\circ}$ BTC, ignition delay decreases. NOx concentration and smoke level in exhaust gas increases for advanced injection timing Ignition delay, combustion period, pressure rise rate and exhaust gas temperature are increased with increasing engine speed. And ignition delay at high load is more decreased than that at low load. Ignition delay and combustion period are decreased with increasing intake pressure. Power increases, temperature and CO, NOx concentration in exhaust gas decreases as intake pressure increases. With increasing load, ignition delay is decreased and combustion period, motoring pressure are increased.

• Journal of Positioning, Navigation, and Timing
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• v.10 no.1
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• pp.29-34
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• 2021

Recently, many studies have considered the effect of atmospheric pressure loading (APL) on precise global navigation satellite system (GNSS) data processing. The APL deforms the Earth's crust. It can often exceed 10 mm in radial displacement. In this study, we analyze the APL effect on Multi-GNSS kinematic precise point positioning (PPP). In addition, observations received at two GNSS reference stations (DAEJ and SUWN) in South Korea were processed. The absolute position changes for the two stations were compared to before and after applying the APL effects from January 1 to February 29, 2020. The crust of South Korea was most affected by the APL in the up direction. With the APL model, the difference in daily position changes was mostly within 4 mm in the radial direction. On the other hand, the horizontal components (east-west and north-south) were relatively less affected than the radial component.

• Journal of Positioning, Navigation, and Timing
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• v.11 no.2
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• pp.127-134
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• 2022

In this paper, a low-cost, flexible GPS simulator based on USRP is designed as a general-purpose software wireless front-end. The simulator consists of a software GPS signal generator and a USRP-based RF transmitter. The simulator supports various scenarios including specified reception time, quantization bit level, I/Q data types, IF frequency, sampling frequency, SNR, ionospheric delay and user dynamics. The generated GPS RF signal is verified using the spectrum analyzer and off-the-shelf GNSS receivers such as U-blox M8T. The experimental results shows that the difference between generated and real live signal is ignorable. It is expected that designed GPS simulator can be used to GNSS signal design, receiver design and signal processing algorithms such as anti-jamming.

• Journal of Positioning, Navigation, and Timing
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• v.12 no.4
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• pp.343-348
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• 2023

The ionosphere acts as the largest error source in the Global Navigation Satellite System (GNSS) signal transmission. Ionospheric total electron content (TEC) is also easily affected by changes in the space environment, such as solar activity and geomagnetic storms. In this study, we analyze changes in the regional ionosphere using the Qusai-Zenith Satellite System (QZSS), a regional satellite navigation system. Observations from 9 GNSS stations in South Korea are used for estimating the QZSS TEC. In addition, the performance of QZSS TEC is analyzed with observations from day of year (DOY) 199 to 206, 2023. To verify the performance of our results, we compare the estimated QZSS TEC and CODE Global Ionosphere Map (GIM) at the same location. Our results are in good agreement with the GIM product provided by the CODE over this period, with an averaged difference of approximately 0.1 TECU and a root mean square (RMS) value of 2.89 TECU.

• Korean journal of applied entomology
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• v.47 no.3
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• pp.209-216
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• 2008

In order to find phenological change of butterflies due to global warming, we analyzed weekly monitoring data of butterfly at Gwangneung forest in 1958 and 2004. It was tested whether the timing of first flight and mean flight of butterflies in 2004 became earlier due to global warming compared with those in 1958 and whether the duration of flight period became longer. No significant difference was found in timing of first flight and in duration of flight period between 1958 and 2004. Furthermore, species showing delayed timing of mean flight was more abundant than species showing earlier timing of mean flight. Hence, the results do not confirm the predicted changes of phonology due to global warming. We discussed reasons on the non-apparent phenological changes despite the increase of temperature, and the problems and solutions in butterfly study on Korean butterfly fauna in utilization of butterflies as indicator for global warming.

• Journal of Korean Neurosurgical Society
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• v.52 no.4
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• pp.396-403
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• 2012

Objective : The predictors of cranioplasty infection after decompressive craniectomy have not yet been fully characterized. The objective of the current study was to compare the long-term incidences of surgical site infection according to the graft material and cranioplasty timing after craniectomy, and to determine the associated factors of cranioplasty infection. Methods : A retrospective cohort study was conducted to assess graft infection in patients who underwent cranioplasty after decompressive craniectomy between 2001 and 2011 at a single-center. From a total of 197 eligible patients, 131 patients undergoing 134 cranioplasties were assessed for event-free survival according to graft material and cranioplasty timing after craniectomy. Kaplan-Meier survival analysis and Cox regression methods were employed, with cranioplasty infection identified as the primary outcome. Secondary outcomes were also evaluated, including autogenous bone resorption, epidural hematoma, subdural hematoma and brain contusion. Results : The median follow-up duration was 454 days (range 10 to 3900 days), during which 14 (10.7%) patients suffered cranioplasty infection. There was no significant difference between the two groups for event-free survival rate for cranioplasty infection with either a cryopreserved or artificial bone graft (p=0.074). Intergroup differences according to cranioplasty time after craniectomy were also not observed (p=0.083). Poor neurologic outcome at cranioplasty significantly affected the development of cranioplasty infection (hazard ratio 5.203, 95% CI 1.075 to 25.193, p=0.04). Conclusion : Neurologic status may influence cranioplasty infection after decompressive craniectomy. A further prospective study about predictors of cranioplasty infection including graft material and cranioplasty timing is necessary.