• Proceedings of the KSME Conference
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.860-865
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• 2000

This Paper Proposes the test pieces of X, Y and Z axes to compensate the shape distortion of Selective Laser Sintering(SLS) parts resulting from the phase change during the sintering process. In no case of the proposed compensation test pieces of X, Y axes the accurate rates of shrinkage can be measured with the reduction of curling which is obtained from adjustment of build orientation and the formula used to get scale factors are proposed with the shrinkage rates of them. The scale factors of X, Y and Z axes are generated by building up proposed compensation test pieces. The generated scale iactors are required to satisfy the dimensional accuracy even if there are changes of the build position and the size of SLS parts in the build chamber. For this reason, it is proposed that the build positions and the size be considered to be noise factors against the compensation test pieces and a method is also proposed that scale factors be selected to robustly maintain the dimensional accuracy of SLS parts under the actual operating conditions with the application of the Taguchi Method.

• Journal of Power Electronics
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• 제17권3호
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• pp.798-810
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• 2017

This paper presents a combined system of a small-capacity inverter and multigroup delta-connected thyristor switched capacitors (TSCs). The system is referred to as a hybrid static compensator (HSC) and has the functions of dynamic reactive power compensation and harmonic suppression. In the proposed topology, the load reactive power is mainly compensated by the TSCs. Meanwhile the inverter is meant to cooperate with TSCs to achieve continuous reactive power compensation, and to filter the harmonics generated by nonlinear loads and the TSCs. First, the structure and mathematical model of the HSC are discussed Then the control method of the HSC is presented. An improved reduced order generalized integrator (ROGI)-based selective current control method is adopted in the inverter to achieve high-performance reactive and harmonic current compensation. Meanwhile, a switch control strategy is proposed to implement precise and fast switching of the TSCs and to avoid changing the time delay needed by the conventional switch strategy. Experiments are implemented on a 20 KVA HSC prototype and the obtained results verify the validity of the proposed HSC system.

• Journal of Power Electronics
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• 제13권5호
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• pp.861-876
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• 2013

Instead of extracting every selected harmonic component, the current reference of selective active power filter (APF) can be also obtained by filtering out the fundamental component from distorted load current for computation efficiency. This type of mixed current reference contains kinds of harmonic components and easily involves noises. In this condition, selective harmonic compensation must be realized by the current controller. With regard that selectivity is the most significant feature of controller, this paper presents specific comparison analysis between two types of resonant controllers: proportional-resonant (PR) controller and vector-resonant (VR) controller. The comparison analysis covers the relations, performances, and stability of both controllers. Analysis results conclude that the poorer selectivity of the PR controller could be relatively improved, but limitations from system stability make the improvement hardly realized. By contrast, the VR controller exhibits excellent selectivity and is more suitable for selective APF with mixed current reference. Experimental results from laboratory prototype validate the reasonability of analysis. And the features of each resonant controller are concluded.

• Proceedings of the IEEK Conference
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• 대한전자공학회 2001년도 하계종합학술대회 논문집(1)
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• pp.13-16
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• 2001

In this paper, We have investigated the SER performance of a OFDM/QPSK system with carrier-frequency offset in a frequency non-selective fading channel. Adaptive linear equalizer is adopted to OFDH/QPSK systems for compensation of performance degradation according to the non-selective fading and carrier frequency offset. As a result of performance analysis, the more frequency offset is, the worse performance of OFDH/QPSK system is. However, when OFDH/QPSK system adopts the adaptive linear equalizer, the SER performance is enhanced to the limit range

• Journal of Families and Better Life
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• 제21권2호
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• pp.145-154
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• 2003

As the life-expectancy is ever-increasing, and the proportion of the elderly population is growing steadily in every society of the world, it is ever more important to establish what factors allow certain elderly people to age successfully and remain relatively independent while others grow old less successfully and require extensive intervention. However, there is no consensus yet as to what successful aging means. Researchers have defined successful aging in a variety of ways. This study attempted to define the concept of successful aging and to clarify some dimensions of it through literature review. Previous approaches of studying successful aging and related themes were examined. Early perspectives including activity, disengagement, and continuity theories, Selective Optimization with Compensation (SOC) model by Baltes and Baltes, three different conceptions of successful aging, that is, psychological well-being, physical health, and wisdom, and MacArthur research on successful aging have been reviewed for this study. The definition derived from the review is: Keeping up continuous developmental processes to achieve wisdom or ego-integrity, without suffering any major disabilities in either physical or mental functioning, while maintaining psychological well-being and employing SOC strategies, and participating in positive relationships with significant others. The dimensions of successful aging are 1) personal resources, including physical health, cognitive competences, self esteem, and social support 2) adaptation process of SOC, and 3) psychological aspects, including psychological well-being and wisdom.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제35권1C호
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• pp.55-64
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• 2010

In this paper, we propose a new compensation scheme for combined channel distortions and RF impairments based on the analysis of the impacts of IQ(In-phase/Quadrature) imbalance and phase noise on the OFDM(Orthogonal Frequency Division Multiplexing) system in the direct conversion transceiver and frequency selective fading channel distortion. The proposed scheme estimates the combined distortion by the use of training symbols and the residual distortion by pilot symbols and compensates the combined distortion, including IQ imbalance, phase noise and multipath fading at the same time. The simulation results show that the proposed scheme compensates the combined distortion of IQ imbalance, phase noise and multipath fading simultaneously.

• Journal of the Korea Institute of Information and Communication Engineering
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• 제12권5호
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• pp.912-920
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• 2008

OFDM (Orthogonal Frequency Division Multiplexing) system is robust to frequency selective fading and narrowband interference in high-speed data communications. However, an OFDM signal consists of a number of independently modulated subcarriers, which can give a large PAPR (Peak-to-Average Power Ratio) when added up coherently. In this paper, we apply clipping and filtering to solve the PAPR problem and compensate the inband compensation using calculated EVM (Error Vector Magnitude). The proposed method can reduce the PAPR and inband distortion. From the results, we analyze the PAPR reducing efficiency and EVM, BER performance of proposed algorithm in the wireless communication system.

• Journal of the Korea Institute of Military Science and Technology
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• 제16권3호
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• pp.365-372
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• 2013

The multibeam surveillance radar is a state-of-art of 3D radar technology. It applies the stacked beams realized by a digital beamformer. In this paper, a hybrid compensation technique on elevation angle errors for low elevation angle targets over the sea in multipath radar environments is proposed. The proposed method can be applied to stacked beam radars. Double null algorithm based on maximum likelihood method in 3-D beamspace domain works well unless the phase difference between the two rays(direct and specular path) is close to $0^{\circ}$ and the magnitude of reflection coefficient is close to 0. To overcome these problems, we propose a hybrid compensation technique which uses the selective double null algorithm and the beam-ratio compensation technique for low-elevation errors on a log scale. Results of computer simulation show that the proposed method outperform conventional monopulse method and double null algorithm only under various multipath environments.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제10권6호
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• pp.855-865
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• 1999

This paper presents the improvement of BER performance using fading compensation method for 16 QAM-TCM to reduce the effects of multi-path fading in mobile radio environments. We propose the multi-pilot symbol aided fading compensation technique using Gausian interpolation method for inter-symbol interference or fading distortion occured in frequency selective fading channel. The proposed system is combined coding and modulation scheme for improving the reliability of a digital transmission system without increasing the transmitted power or the required bandwidth. In the fading compensation, the pilot symbols from a known sequence is multiplexed into the data symbols at regular intervals to from a frames for transmission. And we use a modified bit reversal block interleaver to randomize burst errors. The results show that significant improvements in the bit-error rate performances can be achieved by the proposed techniques.

• The Journal of the Acoustical Society of Korea
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• 제22권7호
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• pp.603-611
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• 2003

This paper proposes an effective feature compensation scheme based on speech model for achieving robust speech recognition. Conventional model-based method requires off-line training with noisy speech database and is not suitable for online adaptation. In the proposed scheme, we can relax the off-line training with noisy speech database by employing the parallel model combination technique for estimation of correction factors. Applying the model combination process over to the mixture model alone as opposed to entire HMM makes the online model combination possible. Exploiting the availability of noise model from off-line sources, we accomplish the online adaptation via MAP (Maximum A Posteriori) estimation. In addition, the online channel estimation procedure is induced within the proposed framework. For more efficient implementation, we propose a selective model combination which leads to reduction or the computational complexities. The representative experimental results indicate that the suggested algorithm is effective in realizing robust speech recognition under the combined adverse conditions of additive background noise and channel distortion.