• Journal of Electrical Engineering and Technology
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• v.10 no.1
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• pp.138-145
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• 2015

In this paper, a novel static overmodulation scheme (OVM) for space-vector PWM (SVPWM) is proposed. The proposed static OVM scheme uses the concept of adding offset voltages in linear region as well as overmodulation region to fully utilize DC-link voltage. By employing zero sequence voltage injection, the proposed scheme reduces procedures for achieving SVPWM such as complicated gating time calculation. In addition, this paper proposes a stepwise discontinuous angle movement in high modulation region in order to reduce Total Harmonic Distortion (THD). The validity of the proposed scheme is verified through theoretical analysis and experimental results.

• Proceedings of the IEEK Conference
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• 2004.06a
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• pp.51-54
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• 2004

In this paper, we analyze the performance of LDPC decoder for DVB-S2 system. The performance analysis is performed by computer simulations based on AWGN channel and high order modulation technique including 16APSK and 32APSK. For normal frame codeword length N = 64800, the performance of LDPC decoder is only away 0.7dB to 1dB from Shannon limit with respect to each modulation. The constructions and encoding process of LDPC codes which are used for DVB-S2 system are also presented and described.

• Proceedings of the KIEE Conference
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• 1991.07a
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• pp.600-604
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• 1991

In this paper, an advanced PWM modulation strategy for driving a variable-speed induction motor is introduced. According to this method, the technique of efficiently eliminating harmonics component is achived. A switching pattern was computed making use of the near-proportionality of voltage and frequency in AC machines operating with constant flux. At low magnitudes and low frequencies of the foundamental, many more harmonics are eliminated than at high magnitudes and frequencies. In order to keep the inverter switching frequency constant over the output frequency range, chopping times diminishes as the frequency of the fundamental increases.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.5
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• pp.69-79
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• 1998

In this paper, we have proposed a new row signal modulation method in order to display multi-gray image using super-twisted nematic liquid crystal display (STN-LCD), which has no complex computation, high selection ratio, and low driving voltage. By the proposed method, we have implemented a 320*240, 8-gray video-rate STN-LCD. For achieving a video-rate STN-LCD, 6 lines are selected at a time. Each row line is selected 8 times by equally distributed pulses throughout one frame. As a result, we can get 8 gray, video-rate image. The repetive horizontal pattern and the filckering was analyzed and the improvements have been presented.

• Proceedings of the IEEK Conference
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• 1999.11a
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• pp.775-779
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• 1999

This paper presents design of AGC(Automatic Gain Control) and DC offset remover suitable for cable modem which makes use of QAM(Quadrature Amplitude Modulation) scheme. Since QAM has multi-level signal characteristic, for high-order QAM, the constellation is dense and the distance of decision boundary between adjacent symbols is short. So AGC and DC offset remover must be designed optionally for preventing performance degradation. AGC is designed into feedback type and is related to the STR(Symbol Timing Recovery)and Paff interpolation algorithm. Whereas AGC need to perform average power detection during many symbols by comparison with the reference power, DC offset remover uses only the instant polarity decision such that simple implementation can be achieved with good performance. Though the AGC and DC offset remover are simulated here only for 256 QAM scheme for convenience'sake, it can be applied to other multi-level QAM or PSK modulation scheme.

• Proceedings of the KIPE Conference
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• 2002.07a
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• pp.489-493
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• 2002

This paper discover another boost vectors in high modulation index In steady states, modulation index of converter operation is normally $0.7\~0.8[p.u]$. Even though zero vectors are not imposed, DC-Link voltage is constant because 3-level boost convert has another boost vectors. and this paper proposes the analysis and the comparison for NPC and H-Bridge converter. It proposed the calculation method for the voltage ripple and charging current of each capacitor and deals with voltage balance problems of each link capacitor they are associated with the switching state, the position of reference voltage vector. Simulation and analysis are used in order to prove validity of the proposed methods.

• 정보저장시스템학회:학술대회논문집
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• 2005.10a
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• pp.103-110
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• 2005

We present a powerful error control decoder which can be used in all of the commercial DVD systems. The decoder exploits the error information from the modulation decoder in order to increase the error correcting capability. We can identify that the modulation decoder in DVD system can detect errors more than $60\%$ of total errors when burst errors are occurred. In results, fur a decoded block, error correcting capability of the proposed scheme is improved up to $25\%$ more than that of the original error control decoder. In addition, the more the burst error length is increased, the better the decoder performance. Also, a pipeline-balanced RSPC decoder with a low hardware complexity is designed to maximize the throughput. The maximum throughput of the RSPC decoder is 740Mbps@100MHz and the number of gate counts is 20.3K for RS (182, 172, 11) decoder and 30.7K for RS (208, 192, 17) decoder, respectively

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.12
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• pp.2177-2182
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• 2016

Using the existing exact but quite complicated symbol error rate (SER) expressions for M-ary phase shift keying (M-PSK) and M-ary differential phase shift keying (M-DPSK), we derive effective and concise closed-form asymptotic SER formulas especially in Rician-Nakagami fading channels. The derived formulas can be utilized to efficiently verify the achievable error rate performances of M-PSK and M-DPSK systems for the Rician-Nakagami fading environments. In addition, by exploiting the modulation gains directly obtained from the asymptotic SER formulas, we also theoretically demonstrate that M-DPSK suffers an asymptotic SER performance loss of 3.01dB with respect to M-PSK for a given M in Rician-Nakagami fading channels at high signal-to-noise ratio (SNR).

• Journal of Communications and Networks
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• v.14 no.2
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• pp.206-212
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• 2012

In this paper, in order to effectively apply unitary space-time modulation to the direct-sequence spread-spectrum multiple-access (DSSS-MA) networks, we propose a low-rate, noncoherent, unitary, and space-time modulated DSSS system supporting any number of transmit antennas based on Walsh matrices. The proposed scheme simultaneously performs bandwidth spreading and space-time coding and outperforms those using high-rate, conventional unitary space-time constellations. Furthermore, the proposed scheme allows for a simple detector structure based on fast Walsh transforms.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.2 s.257
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• pp.202-207
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• 2007

In order to understand the phenomena of combustion instability, an experimental study was conducted at the moderate pressure and ambient temperature conditions. The flame behavior and the pressure fluctuations were measured in a dump combustor. Various types of combustion modes occurred in accordance with the equivalence ratio and the fuel supplying conditions. The fluctuation of pressure, heat release and equivalence ratio were measured by piezoelectric pressure sensor, high speed Intensified Charge Coupled Device (HICCD) camera and gas chromatography respectively. Two representative modes were self-excited pressure oscillations at the resonance of combustion chamber (200Hz) and instabilities related to the modulated fuel flow rate through the fuel holes (10Hz). It is found that, especially in an unchoked fuel flow condition, the modulation of the fuel flow rate affects the characteristics of flame behavior and pressure fluctuations in a lean premixed flame.