• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.3
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• pp.413-420
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• 2010

An Estimation of VHF data link range for EW(Electronic Warfare) equipment in the sea environment was studied to predict the data link range between transmitting and receiving station. The theoretical estimation predicts within 3% error with actual measurement of VHF data link range at sea. Data link range factors including refraction and reflection are added in the basic wave propagation equation. The effect of refraction and reflection to the range is analysed with quantity level.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.5A
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• pp.279-289
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• 2012

Characteristics, such as the support limit and distortions, of minimum mean-squared error (MSE) N-level uniform and nonuniform scalar quantizers are studied for the family of the generalized gamma density functions as N increases. For the study, MSE-optimal scalar quantizers are designed at integer rates from 1 to 16 bits/sample, and their characteristics are compared with corresponding asymptotic formulas. The results show that the support limit formulas are generally accurate. They also show that the distortion of nonuniform quantizers is observed to converge to the Panter-Dite asymptotic constant, whereas the distortion of uniform quantizers exhibits slow or even stagnant convergence to its corresponding Hui-Neuhoff asymptotic constant at the studied rate range, though it may stay at a close proximity to the asymptotic constant for the Rayleigh and Laplacian pdfs. Additional terms in the asymptote result in quite considerable accuracy improvement, making the formulas useful especially when rate is 8 or greater.

• Journal of Power Electronics
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• v.12 no.6
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• pp.851-858
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• 2012

This paper presents resonant inverter tuning for current source parallel resonant induction heating systems based on a new self oscillating switching technique. The phase error is suppressed in a wide range of operating frequencies in comparison with Phase Locked Loop (PLL) techniques. The proposed switching method has the capability of tuning under fast changes in the resonant frequency. According to this switching method, a multi-frequency induction heating (IH) system is proposed by using a single inverter. In comparison with multi-level inverter based IH systems, the advantages of this technique are its simple structure, better transients and wide range of operating frequencies. A laboratory prototype was built with an operating frequency of 35 kHz to 55 kHz and 300 W of output power. The performance of the IH system shows the validity of the new switching technique.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.6
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• pp.243-251
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• 1998

A method of establishing the tooth modification for gear transmission of vehicles to reduce gear whine noise, caused by tooth impact phenomenon of mating gear, is introduced. The major causes of tooth impact are due to the deflections of gear teeth and shafts of transmission with the loaded condition including various kinds of manufacturing errors. The theoretical shape of tooth surface to avoid tooth impact is derived by the amount of elastic deformation of gear teeth and shaft and overall manufacturing error of machine tool. The surface function is converted with respect to the conventional commercial data usually communicated to the gear inspection system. The proposed method is applied to the gearbox of four wheel drive vehicle and shows the gear whine noise decreased to the 8 dB in the sound level.

• Journal of Power Electronics
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• v.10 no.4
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• pp.357-364
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• 2010

In this paper, a novel analysis of a carrier based PWM method for multilevel inverters is presented. The space vector PWM and carrier based PWM correlations in multilevel inverters are investigated in a nominal two-level switching diagram. The obtained results can be applied to design various carrier PWM techniques. In this paper, a carrier based single-state PWM technique, which reduces the switching number and optimizes the active voltage errors, is presented. This PWM technique can be advantageous if there are a large number of levels. The proposed method is mathematically formulated and demonstrated by simulations and experimental results.

• Proceedings of the KSPS conference
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• 2003.05a
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• pp.219-222
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• 2003

In this paper, we study the usage of phoneme duration information for rejection garbage sentence. First, we build a phoneme duration modeling in a speech recognition system based on dicicion tree state tying, We assume that phone duration has a Gamma distribution. Next, we build a verification module in which word-level confidence measure is used. Finally, we make a comparative study on phoneme duration with speech DB obtained from the live system. This DB consistes of OOT(out-of-task) and ING(in-grammar) utterences. the usage of phone duration information yields that OOT recognition rate is improved by 46％ and that another 8.4％ error rate is reduced when combined with utterence verification module.

• Proceedings of the KSPS conference
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• 2003.05a
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• pp.163-167
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• 2003

Intonation as suprasegmental phonetic features conveys meanings on the postlexical or utterance level in a linguistically structured way. It includes three aspects: tunes, relative prominence, and intonational phrasing. In this article, I will treat how prosodic phrasing is functionally related to the listening comprehension of English by analysing the students' errors of listening comprehension. When utterance meaning is conveyed, it is realized to be divided into intonational phrases. The small intonational phrase is regarded as an intermediate phrase which has a primary accent and a phrase tone or audible break. Most students' errors of listening occurred with linking pronunciation in the intermediate phrases of the fast speech. Thus through the smallest unit with tune we can help students improve their pronunciation and listening ability of English.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.12
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• pp.1379-1387
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• 2011

A PID-feedforward controller and Robust Internal-loop Compensator (RIC) based on reinforcement learning using random variable sequences are provided to auto-tune parameters for each controller in the high-precision position control of PMLSM (Permanent Magnet Linear Synchronous Motor). Experiments prove the well-tuned controller could be reduced up to one-fifth level of tracking errors before learning by reinforcement learning. The RIC compared to the PID-feedforward controller showed approximately twice the performance in reducing tracking error and disturbance rejection.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.8
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• pp.2540-2545
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• 1996

It is well known that in typical displacement-based curved beam elements, the stiffness matrix is overestimated and as a result displacement predictions show gross error for the thin beam case. In this paper, a stain based curved beam element with 2 nodes is formulated based on shallow beam geometry. At the element level, the curvature and membrane strain fields are approximated independently and the displacement fields are obtained by integrating the strain fields. Three test problems are given to demonstrate the numerical performance of the element. Analysis results obtained reveal that the element is free for locking and very effectively applicable to deeply as well as shallowly curved beams.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.2
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• pp.273-279
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• 2007

I evaluate the BER performance of OFDM systems in frequency selective Doppler time variant fading channels, considering the pilot patterns for channel estimation. The performance of the systems is degraded due to channel estimation error. For the reduction of performance degradation in acceptable level, the optimum distance of pilot symbols in pilot pattern is 5 subcarriers in frequency domain and 6 OFDM block in time domain.