• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.05a
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• pp.760-761
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• 2010

As is widely known, SPL measurement using sound level meter (SLM) is limited to higher than 30 dBA, because of the self-noise n(x) of condenser microphone (CM). The authors confirmed n(x) is composed of 3 kinds, each of which is stable enough under the condition -20 ~ +50 deg C to eliminate the influence of n(x) by subtracting its energy from the squared input signal in the integration process, as well as to develop new type of SLM with ultra-low SPL measuring function. This is so-called "0-dB SLM" since it enables to measure SPL down to around 0 dB-SPL. The RMS of n(x) is acquired and stored in ROM in advance, by placing CM in the supersilent space or by using dummy microphone with equivalent capacitance before the actual measurements.

• Journal of Technologic Dentistry
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• v.45 no.1
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• pp.1-7
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• 2023

Purpose: To evaluate the marginal and internal fit of metal coping fabricated by a metal three-dimensional (3D) printer that uses selective laser melting (SLM). Methods: An extraoral scanner was used to scan a die of the prepared maxillary right first molar, and the coping was designed using computer-aided design software and saved as an stereo lithography (STL) file. Ten specimens were printed with an SLM-type metal 3D printer (SLM group), and 10 more specimens were fabricated by casting the castable patterns output generated by a digital light processing-type resin 3D printer (casting the 3D printed resin patterns [CRP] group). The fit was measured using the silicon replica technique, and 8 points (A to H) were set per specimen to measure the marginal (points A, H) and internal (points B~G) gaps. The differences among the groups were compared using the Mann-Whitney U-test (α=0.05). Results: The mean of marginal fit in the SLM group was 69.67±18.04 ㎛, while in the CRP group was 117.10±41.95 ㎛. The internal fit of the SLM group was 95.18±41.20 ㎛, and that of the CRP group was 86.35±32 ㎛. As a result of statistical analysis, there was a significant difference in marginal fit between the SLM and CRP groups (p<0.05); however, there was no significant difference in internal fit between the SLM group and the CRP group (p>0.05). Conclusion: The marginal and internal fit of SLM is within the clinically acceptable range, and it seems to be applicable in terms of fit.

• Journal of Navigation and Port Research
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• v.29 no.8 s.104
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• pp.755-761
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• 2005

In this paper, we propose a high-speed adaptive PTS method which eliminates high PAR (Peak-to-Average Power Ratio) and we compare the proposed method with other conventional methods. In addition, we have designed a combined type SLM-PTS scheme to reduce PAR and evaluate the performance. The system used for evaluating PAR performance can be constructed as COFDM (Coded Orthogonal Frequency Division Multiplexing) applying ETD(Enhabced Time Diversity)-Turbo coding scheme. All the analyses in this paper are focused on the system characteristics according to IFFT's point and modulation method and the performance evaluation are based on the PAR reduction rates. As a result, the SLM-PTS combination method reveals good PAR reduction rate and remarkable reduction in the amount of calculations. Especially, in the case of combine-3 scheme, we can achieve approximately $3.7\~3.9$ dB PAR reduction on a basis of 10-5 BER level. Moreover, we can eliminate the side information in COFDM system because of its adaptive characteristics in evaluating PAR reduction rate, so that the additional errors can be omitted.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.3 s.118
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• pp.248-256
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• 2007

In this paper, we propose a selective DFT spreading method to solve a high PAPR problem in uplink OFDMA system. A selective characteristic is added to the DFT spreading, so the DFT spreading method is mixed with SLM method. However, to minimize increment of computational complexity, differently with common SLM method, our proposed method uses only one DFT spreading block. After DFT, several copy branches are generated by multiplying with each different matrix. This matrix is obtained by linear transforming the each phase rotation in front of DFT block. And it has very lower computational complexity than one DFT process. For simulation, we suppose that the 512 point IFFT is used, the number of effective sub-carrier is 300, the number of allowed sub-carrier to each user's is 1/4 and 1/3 and QPSK modulation is used. From the simulation result, when the number of copy branch is 4, our proposed method has more than about 5.2 dB PAPR reduction effect. It is about 1.8 dB better than common DFT spreading method and 0.95 dB better than common SLM which uses 32 copy branches. And also, when the number of copy branch is 2, it is better than SLM using 32 copy branches. From the comparison, the proposed method has 91.79 % lower complexity than SLM using 32 copy branches in similar PAPR reduction performance. So, we can find a very good performance of our proposed method. Also, we can expect the similar performance when all number of sub-carrier is allocated to one user like the OFDM.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.3 s.94
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• pp.327-334
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• 2005

In this paper, a new PAPR reduction method using correlation of input data sequence is proposed in order to overcome the serious drawbacks, such as necessity of side information transmission or increase of system complexity and calculation which are the basis of previous SLM, PTS and DSI method. A new PAPR reduction method can be classified into Method 1 and Method 2. Method 1 reduces the correlation between the smallest sub-sequence and neighbor smallest sub-sequence. And, to consider the own correlation in detail, the Method 2 reduces two case of correlation between neighbor smallest sub-sequences and neighbor largest sub-sequences. According to simulation result, Method 1 and Method 2 has about 0.5 $\~$ O.8 dB and 1 $\~$ l.2 dB PAPR reduction effect respectively. If more detailed process to reduce the correlation of input data sequence is considered, we can achieve better PAPR reduction performance.

• Transactions of the Society of Information Storage Systems
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• v.3 no.1
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• pp.23-27
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• 2007

Blu-ray disc 이후의 차세대 고밀도 광 기록 기술로 주목받는 홀로그래픽 데이터 스토리지 시스템을 설계, 제작하고 기록 재생 test 를 수행하였다. 시스템은 각도 다중화법을 채택하였고, 파장 405nm, NA 0.55 신호광 Fourier 변환 렌즈로 미디어에 defocus 하여 기록하였다. 1 page 용량은 raw bit 로 0.74Mbit 이고, SLM 과 CCD 의 over-sampling 비율은 1:1.5 가 되도록 구성하였다. 얻어진 raw 이미지는 위치 및 distortion 보상등의 신호처리 후, 70page 다중화 조건에서 bER $1{\times}10-2$ 수준으로 재생해 낼 수 있었다. 온도 변화에 의한 신호 열화를 보상하기 위해 External Cavity Tunable Blue LD 를 개발하여 온도 변화 $10^{\circ}C$까지 보상 가능함을 확인하였다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.12
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• pp.127-134
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• 2005

Lost packet robustness is an most important quality measure for voice over IP networks(VoIP). Recovery of the lost packet from the received information is crucial to realize this robustness. So, this paper proposes the lost packet recovery method from the received information for real-time communication for CELP coder. The proposed BS-PLC (Both Side Packet Loss Concealment) based WSOLA(Waveform Shift OverLab Add) allow the lost packet to be recovered from both the 'previous' and 'next' good packet as the LP parameter and the excitation signal are respectively recovered. The burst of packet loss is modeled by Gilbert model. The proposed scheme is applied to G.729 most used in VoIP and is evaluated through the SNR(signal to noise) and the MOS(Mean Opinion Score) test. As a simulation result, The proposed scheme provide 0.3 higher in Mean Opinion Score and 2 dB higher in terms of SNR than an error concealment procedure in the decoder of G.729 at $20\%$ average packet loss rate.