Sang-Jeong Lee

Development of advanced I&C in nuclear power plants: ADIOS and ASICS

In this paper Automatic Startup Intelligent Control System (ASICS) that automatically controls the PWR plant from cold shutdown to 5% of reactor power and Alarm and Diagnosis-Integrated Operator Support System (ADIOS) that is integrated with alarms, process values, and diagnostic information to an expert system focused on alarm processing are described. Nuclear Power Plant is manually controlled from cold shutdown to 5% according to the general operation procedures for startup operation of nuclear power plant. Alarm information is the primary sources to detect abnormalities in nuclear power plants or other process plants. The conventional hardwired alarm systems, characterized by one sensor-one indicator may lead the control room operators to be confused with avalanching alarms during plant transients. ASICS and ADIOS are designed to reduce the operator burden. The advances in computer software and hardware technology and also in information processing provide a good opportunity to improve the control systems and the annunciator systems of nuclear power plants or other similar process plants. It is very important to test and evaluate the performance and the function of the computer- or software-based systems like ASICS and ADIOS. The performance and the function of ASICS and ADIOS are evaluated with the real-time functional test facility and the results have shown that the developed systems are efficient and useful for operation and operator support.

L1/L2CS GPS Receiver Implementation with Fast Acquisition Scheme

The L2 Civil Signal (L2CS) will be transmitted by modernized IIR(IIR-M), IIF and all subsequent GPS satellites. It contains two codes of different length; CM code contains 10,230chips, repeats every 20milliseconds and is modulated with message data, and CL code contains 767,250chps, repeats every 1.5second Z-count and has no data modulation. And the message data is encoded for Forward Error Correction (FEC). Although it has a good cross-correlation performance by the long code length, but the acquisition time should be long. Because the acquisition time is directly proportional to the code length and/or code period. Therefore it takes about 100 hours for L2C signal acquisition in case of 20ms integration. So, there should be a fast signal acquisition scheme. There are many methods to reduce the acquisition time, but most of them require the modification of the correlator. The L1 aiding method does not require any modifications and it can acquire the L2C signal as fast as the L1 signal. Finally, the L1 aiding method would be confirmed by experimental results in this paper and the acquisition and tracking of L1 and L2C signal also would be shown.

A Novel GPS Initial Synchronization Scheme with Decomposed Differential Matched Filter

A novel GPS initial synchronization scheme with low hardware complexity is proposed. The proposed method has the decomposed differential matched filter, which consists of 25% multiplier and adder of the conventional matched filter. This paper presents the generalized mean acquisition time of initial synchronization scheme with multiple correlator. It is shown that the proposed method, in spite of its low hardware complexity, has the equal performance to the conventional method. The performance of the proposed method is verified through the simulation test by the GPS simulator. It is shown that the proposed method prevents the squaring loss of non-coherent integration.

Atomic clock error modeling for GNSS software platform

This paper presents satellite atomic clock error model for generating the satellite clock error in GNSS software platform for the GPS Ll C/A code signal, L2 civil signal, L5 signal, and Galileo El, E5a signals. Scheme to simulate the clock error through phase error characteristics of the atomic clock are given. Rubidium, cesium and hydrogen maser clock are considered for GPS or Galileo satellites and Quartz oscillator is considered for user receiver. The clock error consists of five typical noises such as white noise on phase, flicker noise on phase, white noise on frequency, flicker noise on frequency, random walk on frequency. The analysis software for the Allan variance, the Hadamard variance and the PSD (power spectral density) of the clock error is also included. The clock error model is implemented and its validity is analyzed by comparing with theoretical ones.

Characteristics of the Float Solutions in Epoch-by-epoch GNSS Precise Positioning

This paper describes characteristics of the float solutions of epoch-by-epoch GNSS precise positioning. It is shown that the accuracy of the floating solutions which are obtained using both code and carrier phase measurements are same as that of the code measurements only solution. It implies that to get more accurate floating position, the quality of code measurements are more important than that of carrier phase measurements. The results are expanded to multiple frequencies applications to get the same conclusions.

Implementation of a Performance Evaluation Platform for Relative Navigation and Its Application to Performance Improvements

The positions of vessels in JTIDS where each vessel broadcasts its position, can be found using the relative navigation method. Besides positioning, the relative navigation could be adopted for identification friend or foe, tracking targets, monitoring battle field and etc. In this paper, we have explained the fundamental operation and technical structure for the relative navigation and implemented the simulation platform to evaluate the basic function and performance of the system in arbitrary environment. Using platform, the availability of relative navigation within the group network and the characteristic of the algorithm for position prediction was verified. Based on the simulation result, it was verified that EKF based navigation algorithm could produce great initial error and need quite convergence time. To improve the performance, we proposed a new navigation algorithm which uses the minimum norm estimation algorithm until the EKF converges. The simulation results reveal the relative navigation can be effectively used in the formation flight and collision avoidance system.

Design of a Adaptive Code Tracking Loop for GPS L1/L2C/L5 Receivers

In this paper, an adaptive signal tracking loop for a GPS L1/L2C/L5 receiver is designed. The design parameters is adjusted according to the receiver`s operating conditions such as the signal strength and the receiver dynamics by using the different characteristics of GPS L1, L2C and L5 signal. Simulation results show that the tracking accuracy of the proposed signal tracking loop is better than those of L1, L2C and L5 only signal tracking loop.

An analysis on ASF variations and temperature

This paper is aimed to analyze a relationship between the temporal ASF and the temperature in Loran-C signal. Through explanations of the ground-wave propagation model and its application, the relationship between the conductivity and the temperature are explained for understanding the ASF in LORAN signal. To verifying the relationship, the experimental environment is proposed with several assumptions. The relative ASF and the temperature measurements are shown with its analysis results. Also, the temperature compensation results reflecting the analysis results are represented to verify an availability of relationship between the temporal ASF and the temperature in Loran-C signal.

The Improved Spatial Nuller with Frequency Swept Jammer

Recent years, the GNSS has a diverse and wide application field. It provides the services that using the personal location information. But, for the some people, it is undesirable service. Therefore, these people start using the Personal Privacy Devices. A study about the impact of PPDs and effective countermeasure to PPDs are required. In this paper, we analyze the effect on the anti-jamming technique by the PPD jammer. And we show the effect of frequency swept jammer is removed by applying reduced-rank approach. We also analyzed the performance of reduced-rank approach.

A study on the optimal geometrical placement of eLoran stations in Korea

In the eLoran navigation system, the dominant deterioration factors of navigation accuracy are the TOA measurement errors on user receiver and the GDOP between the receiver and the transmitters. But if the ASF data measured at dLoran reference station are provided for users through the Loran data channel, it will be possible to correct the TOA measurement errors. The position accuracy can be determined by the DOP depending on the geometry of receiver-transmitters, and their optimal placement improves the navigation accuracy. In this study we determined the geometric placement in case of up to six stations, and evaluated the performance of position accuracy for the receiver-transmitter geometry set of eLoran stations. The proposed geometry of eLoran stations can be referred for the construction of eLoran infrastructure meeting the capability of HEA for maritime, and time/frequency users in Korea.