• International Journal of Computer Science & Network Security
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• v.23 no.1
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• pp.96-102
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• 2023

In this paper, we proposed Channel Transfer Function estimation based on Delay and Doppler Profile for underwater acoustic OFDM communication system. It improved the estimation accuracy of the channel transfer function by linear time interpolation the change of Scattered Pilot (SP) insertion frequency in the time direction and the time by Delay and Doppler profile that analyzes the multipath situation of the channel investigated the performance of interpolation by simulation and report it. Previous works is inserted SP every 4 OFDM. It was effective under the environment without multipath, but it has observed that the effect of CTF compensation has been lowered in multipath channel condition. In addition to be better when inserted SP every 2 OFDM. But the amount of sending data will be decrease. Therefore, we conducted research to improve 4 OFDM with new interpolator. A computer simulation was performed as a comparison of SP inserted every 4 OFDM, SP inserted every 2 OFDM, and 4 OFDM with new interpolator. the performance of the proposed system is overwhelmingly improved, and the performance is slightly improved even 64 QAM.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.4
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• pp.88-94
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• 2007

This paper deals with the performance analysis of 3-dimensional array antenna by DOA estimation and beamforming in GPS receiver for performance improvement by interference elimination. The array antenna in GPS receiver can improve the system performance by estimating DOA of arriving signal direction, making the main beam for desired direction and elimate the jammer signal by nulling while keeping the GPS signal direction by spatial filtering. In this paper, we propose five types of 3-dimensional array antenna and analyze the estimation error via MUSIC algorithm which is used for the estimation of DOA of arrived signal and beamforming performance. In analyzing DOA performance, we measure DOA estimation error, while in analyzing beamformig performance, we measure BER. In beamforming performance analyzing, we use various jammer power and the existence of GPS signal and angle spread. By performing through the computer simulation, Curved (B) 7-element antenna in proposed 3-dimensional array antenna exhibits the superior performance in the DOA estimation, estimation error, BER characteristic and angle spread compared to the rest four array antenna types.

• Journal of Digital Convergence
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• v.12 no.12
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• pp.329-335
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• 2014

In this paper, to improve the performance of PB/MC-CDMA system, we have researched about the decision feedback channel estimation method using the pilot symbol with data symbol. The PB/MC-CDMA system is able to obtain the improved BER by frequency diversity gain and frequency domain equalizer in the frequency selective fading channel. However, when it is not the estimating of channel exactly, it is degrading the performance of BER in the system for occurred the interference among users. To improve the performane system in the multi-user environment the proposed system is using the decision feedback to estimate channel using the channel estimated value of the first stage and second stage. The proposed system is evaluated by computer simulation. The proposed system is not only able to improve the performance of BER by decreasing the interference to each user, but also the proposed system is possible to reduce number of pilot symbol to estimate the channel. Therefore, it confirmed the proposed system improves the performance than the conventional system.

• Journal of Positioning, Navigation, and Timing
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• v.9 no.1
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• pp.7-13
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• 2020

As a countermeasure against the threat of jamming which can disrupt operation of the Global Positioning System (GPS) receivers, various kinds of technique to estimate the Direction-Of-Arrivals (DOAs) of incoming jamming signals have been widely studied, and among them, the MUltiple SIgnal Classification (MUSIC) algorithm is known to provide very high resolution. However, since the previous studies regarding the MUSIC algorithm does not consider the orientation of each antenna element of antenna arrays, there is a possibility that DOA estimation performance degrades in the case of a misaligned antenna array whose antenna elements are not oriented along the same direction. As an effort to solve this problem, there exists a previous work which presents an MUSIC-based method for DOA estimation. However, the error between the real and measured values of each antenna orientation is not taken into consideration. Therefore, in this paper, the effect of the aforementioned error on the DOA estimation performance in the case of a misaligned antenna array is analyzed by simulations.

• Journal of Power System Engineering
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• v.18 no.5
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• pp.129-136
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• 2014

This paper proposes improvement on sensorless vector control performance of a permanent magnet synchronous motor (PMSM) with sliding mode observer. An adaptive observer gain and second order cascade low-pass filter (LPF) were used to improve the estimation accuracy of the rotor position and speed. The adaptive observer gain was applied to suppress the chattering intensity and obtained by using the Lyapunov's stability criterion. The second order cascade LPF was designed for the system to escalate the filtering performance of the back-emf estimation. Furthermore, genetic algorithm was used to optimize the system PI controller's performance. Simulation results showed the effectiveness of the suggested improvement strategy. Moreover, the strategy was useful for the sensorless vector control of PMSM to operate on the low-speed area.

• Journal of Astronomy and Space Sciences
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• v.18 no.2
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• pp.137-144
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• 2001

This paper presents the REA thrusters performance estimation results for the KOREASAT F1&F2 launched in 1995 The satellite tracking data obtained from the ground system from end of 1999 to beginning of the 2000 are used to estimate the thruster performance. The estimation algorithm is derived from the least square estimation theory and designed to estimate the velocity change induced by the on-boarded thruster firing as well as the orbit parameter. The estimation results show that the Koreasat F1 thruster are in bad thruster condition of 64% performance for REA when it fires in on-pulse mode. Here, the performance is defined by the ratio of the resulted velocity change to that of planned. But, in the case o( the Koreasat F2, it is found that the performance approximately reaches up to 100%, even after the 5 years of the mission.

• Proceedings of the KIEE Conference
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• 2006.07d
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• pp.1787-1788
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• 2006

In this paper, a noisy passive telemetry sensor system using Unscented Kalman Filter (UKF) is proposed. To overcome these trouble problems such as a power limitation and a estimation complexity that the general passive telemetry sensor system including IC chip has, the principle of inductive coupling was applied to the modelling of a passive telemetry sensor system (PTSS) and its noisy capacitive parameter was estimated by the UKF algorithm. Specialty, to show the effective tracking performance of the UKF, we compared with the tracking performance of Recursive Least Square Estimation (RLSE) using linearization

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.7A
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• pp.623-631
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• 2010

In this paper, various of pilot-assisted channel estimation techniques for 3GPP LTE downlink are tested under multipath Rayleigh fading channel. At first, the conventional channel estimation techniques are applied with linear zero-forcing (ZF) equalizer, such as one dimensional least square (1-D LS) linear interpolation, two dimensional (2-D) wiener filter, the time and frequency dimension separate wiener filter and maximum likelihood estimator (MLE). Considering the practical implementation, we proposed two channel estimation techniques by combining time-dimension wiener filter and MLE in two manners, which showed a good tradeoff between system performance and complexity when comparing with conventional techniques. The nonlinear decision feedback equalizer (DFE) which can show a better performance than linear ZF equalizer is also implemented for mitigating inter-carrier interference (ICI) in our system. The complexity of these algorithms are calculated in terms of the number of complex multiplications (CMs) and the performances are evaluated by showing the bit error rate (BER).

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.2
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• pp.84-91
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• 2014

This paper introduces the application of supervisory monitoring system for substation automation based on IEC 61850. The objective of proposed system is detection of such a malfunction or degradation of devices. The supervisory monitoring procedure consists of a two step - topology processor and state estimation. The topology processor using artificial intelligence is a preprocessing step of state estimation. Topology processor identifies the topology structure of switches in substation and detects an error of ON/OFF state data. The state estimation is an algorithm that minimizes an error between optimal estimation values and real values. The proposed system is applied to standard digital substation based on IEC 61850 for performance verification.

• Journal of the Korea Management Engineers Society
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• v.23 no.4
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• pp.159-164
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• 2018

Human-machine serial systems must be normal in both systems. Though the failure of machine is irreducible by itself, the human errors are of recurring type. When the human performance is described quantitatively, non-homogeneous Poisson Process model of human errors can be developed. And the model parameters can be estimated by maximum likelihood estimation and numerical analysis method. System reliability is obtained by multiplying machine reliability by human reliability.