• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.1
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• pp.52-60
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• 2001

In this paper proposes a multi-carrier MFSK-DPSK/DS-CDMA combined modulation techniques in Nakagami fading environment. Also, multi-carrier DS-CDMA combined system is a promising technique for mobile communications systems, since it has a strong immunity to multipath fading and increasing bandwidth efficiency. The modulations under consideration are noncoherent M-ary frequency shift keying (MFSK)and an MFSK based joint frequency phase modulation utilizing differential phase shift keying (DPSK). With the result, performance improvement of power efficiency and bandwidth efficiency combined system in multi-carrier MFSK-DPSK/DS-CDMA are better then conventional communication system.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.6
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• pp.547-550
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• 2017

This paper presents a loss analysis and compares three pulse width modulation (PWM) methods applied in a three-phase grid-connected bidirectional inverter for an energy storage system. The losses in switching devices and output low pass filters are theoretically analyzed by using PWM control techniques. Grid-connected bidirectional inverters are designed by using PWM techniques, and the designed inverters are simulated to verify the analysis results.

• Journal of Communications and Networks
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• v.5 no.4
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• pp.354-364
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• 2003

A general method for the evaluation of the symbol error probability (SER) of ultra wideband (UWB) systems with various kind of modulation schemes (N-PAM, M-PPM, Bi-Orthogonal), in presence of multipath channel, multiuser and strong narrowband interference, is presented. This method is shown to be able to include all the principal multiaccess techniques proposed so far for UWB, time hopping (TH), direct sequence (DS) and optical orthogonal codes (OOC). A comparison between the performance of these multiple access and modulation techniques is given, for both ideal Rake receiver and minimum mean square error (MMSE) equalizer. It is shown that for all the analyzed multiple access schemes, a Rake receiver exhibits a high error floor in presence of narrowband interference (NBI) and that the value of the error floor is in-fluenced by the spectral characteristics of the spreading code. As expected, an MMSE receiver offers better performance, representing a promising candidate for UWB systems. When the multiuser interference is dominant, all multiple access techniques exhibit similar performance under high-load conditions. If the number of users is significantly lower than the spreading factor, then DS outperforms both TH and OOC. Finally 2PPM is shown to offer better performance than the other modulation schemes in presence of multiuser interference; increasing the spreading factor is proposed as a more effective strategy for SER reduction than the use of time diversity.

• Proceedings of the IEEK Conference
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• 2000.06e
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• pp.17-20
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• 2000

Usually, in many applications, high frequency resonant inverters are used, and the PAM(Pulse Amplitude Modulation), PFM(Pulse Frequency Modulation) or PWM(Pulse Width Modulation) techniques are used to control the output power of resonant inverters. In this paper, a new switching scheme is proposed as a PWM control method. With the proposed method, it can be obtained that unity output displacement factor under the variable resonant frequency. The detail algorithm of the proposed PWM switching scheme and its charicteristics are discussed. And the validity of the proposed method is confirmed with the experimental results.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.2 no.2
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• pp.59-63
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• 1988

In a fixed AC power source the PWM techniques were used to vary the voltage and the fundamental frequency. The conventional PWM techniques due to the problem of commutation number and filter size have been studied the PWM output waveforms which applied the motor drive. However in this paper, the carrier frequency with sinusoidal PWM waveform is modulated from 10(KHz) to 45(KHz) using termination devices with high - speed switching capacity and applying LPF(Low Pass Filter) with small capacity to output of inverter and the PAM(Pulse Amplitude Modulation)is obtained. Considering the property of the speed and the control, the sinusoidal PWM control circuit was composed of the microprocessor and analog circuit. In experment result, the system properties are study on the sinusoidal voltage waveform with modulation index changing from 0.6 to 1.0.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.11 no.2
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• pp.122-136
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• 1986

In this paper, the new modulation system, the digital phase-frequency hybrid modulation system is proposed for mobile radio communications. The error rate and the outage equation of PFSK(Phase-Frequency Shift Keying) signal transmitted through the fading channel has been derived considiering deversity techniques. The error rate and the outgae rate performances of PFSK system have been evaluated and shown in figures in terms of carrier-to-noise power ratio(CNR), fading figure, numbers of diversity branches, correlation coefficient among the diversity branches. And the performance of PFSK system is superior to that of QDPSK system. And by using diversity techniques, system performances can be improved 13dB above in CNR.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.6
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• pp.419-427
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• 2014

Nonlinear features of ultrasonic waves are more sensitive to the presence of a fatigue crack than their linear counterparts are. For this reason, the use of nonlinear ultrasonic techniques to detect a fatigue crack at its early stage has been widely investigated. Of the different proposed techniques, laser nonlinear wave modulation spectroscopy (LNWMS) is unique because a pulse laser is used to exert a single broadband input and a noncontact measurement can be performed. Broadband excitation causes a nonlinear source to exhibit modulation at multiple spectral peaks owing to interactions among various input frequency components. A feature called maximum sideband peak count difference (MSPCD), which is extracted from the spectral plot, measures the degree of crack-induced material nonlinearity. First, the ratios of spectral peaks whose amplitudes are above a moving threshold to the total number of peaks are computed for spectral signals obtained from the pristine and the current state of a target structure. Then, the difference of these ratios are computed as a function of the moving threshold. Finally, the MSPCD is defined as the maximum difference between these ratios. The basic premise is that the MSPCD will increase as the nonlinearity of the material increases. This technique has been used successfully for localizing fatigue cracks in metallic plates.

• Proceedings of the KIPE Conference
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• 2002.07a
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• pp.498-501
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• 2002

In the conventional PWM converter, high-frequency switching techniques was used for high-density of energy, but occurred a lot of problems such as switching losses, switching voltage/current stresses, EMI(Electromgnetic Interference) and so on. To overcome these problems, various soft switching techniques have been presented. However these techniques are focused on reducing switching losses and voltage/current stresses . The simulation and experimental results are shown that the active clamp ZVS flyback converter with the proposed RPWM(Random Pulse Width Modulation) technique reduces the conducted noise.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.52 no.7
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• pp.352-360
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• 2003

This paper deals with a simple method in order to analyze and compare the harmonic characteristics in the multi-level inverter. Generally, the magnitude of harmonic components becomes different according to the multi-carrier Pulse Width Modulation(PWM) techniques, the modulation index($M_i$) and the switching frequency The previous papers analyzed the harmonic characteristics from the viewpoint of the space voltage vector. Hence, the calculation of the harmonic vector becomes more difficult and complex in 4-level or over 5-level. However, the proposed method has reduced an amount of calculation and simplified the process of it, using the relationship between the reference voltage and the output phase voltage to the load neutral point. It is applied to the 5-level cascade inverter and the harmonic characteristics for each multi-carrier PWM technique are compared through the simulation.

• Journal of Positioning, Navigation, and Timing
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• v.11 no.3
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• pp.147-156
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• 2022

In this paper, we propose Time-Division-Multiplexing Tertiary Offset Carrier (TDMTOC), a novel GNSS modulation based on Tertiary Offset Carrier (TOC) modulation. The TDMTOC modulation multiplexes two three-level signals (i.e., -1, 0, and 1) while crossing over time, and is a type of TOC modulation designed specifically for signal multiplexing. The proposed modulation generates TDMTOC subcarriers of two different phases by simply combining two Binary Offset Carrier (BOC) subcarriers by addition or subtraction. TDMTOC has better correlation and spectral properties than conventional BPSK, BOC, and MBOC modulation techniques, and has good power and spectral efficiency since it can multiplex signals without power loss similar to time division multiplexing. To prove this, we introduce the multiplexing process of TDMTOC, and compare TDMTOC with Binary Phase Shift Keying (BPSK), BOC, Composite BOC (CBOC), and Time Multiplexed BOC (TMBOC) that are currently serviced in GNSS by simulations of various aspects. Through the simulation results, we prove that TDMTOC has better correlation property than modulations currently used in GNSS, less intersystem interference due to its wide spectrum property, and robustness in multipath and noise channel environments.