• 한국컴퓨터정보학회논문지
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• 제18권10호
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• pp.63-70
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• 2013

본 논문에서는 다중 경로 페이딩 채널을 고려한 환경에서 디지털 M/W전송 시스템의 동기에 관한 모의 시뮬레이터를 구성하여 주파수 동기를 수행하였고, 송신단과 수신단의 주파수 허용 편차(오실레이터 간 오차 범위)로 발생되는 주파수 옵셋에 보상 알고리즘을 적용하여 신호 성좌도(constellation)의 성능 개선 정도를 평가하였다. 성능 분석 결과, 송 수신단의 주파수 허용 편차가 큰 상태에서는 주파수 옵셋을 보상해도 주파수 허용 편차가 이미 크기 때문에 잔류 주파수의 영향을 상대적으로 많이 받게 됨을 알 수 있었다. 결과적으로 송수신단의 주파수 허용 편차에 따라 잔류 주파수 옵셋이 시스템 성능에 큰 영향을 미치게 됨을 알 수 있었다. 본 결과물은 향후 방송중계용 시스템의 대역 이전 시 필요한 주파수 동기 기준으로 활용 가능할 것이다.

• Journal of Communications and Networks
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• 제9권2호
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• pp.192-197
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• 2007

We analyze the performance of code division multiple access (CDMA) system with multicarrier (MC) that employs precoding in synchronous downlink channels. Even though considerable efforts are undergoing for frequency offset estimation and correction, it is inevitable for the system to bear the remaining frequency offset. Therefore it is important to predict accurately the system performance in the presence of the residual frequency offset. We obtain the bit error rate (BER) performance in terms of the number of users, the spreading factor, the number of sub-carriers, and frequency offset. We assume that the spreading factor is equal to the number of sub-carriers, although we can generalize the case. The simulation results show that the BER of MC-CDMA with precoding shows a performance that varies with frequency offset as well as system loading.

• 정보과학회 컴퓨팅의 실제 논문지
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• 제20권9호
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• pp.483-491
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• 2014

현대의 컴퓨터 시스템에서는 동적 전압/주파수 조정(DVFS: Dynamic Voltage/Frequency Scaling) 기법을 이용하여 성능과 전력 소모의 균형을 이루도록 한다. DVFS 정책의 유용성은 높아진 주파수에 따른 소모 전력에 대한 성능 향상 정도에 달려있다. 특히 메모리 I/O가 많은 응용의 경우 CPU 주파수 상승에 비례하여 성능이 향상되지 않는 경우가 많다. 본 논문에서는 메모리 접근 빈도에 기반하여 CPU 주파수 조정의 상한을 결정하도록 하였다. 명령어 당 메모리 접근(최종 수준 캐시 미스) 빈도에 따라 CPU 주파수 상향으로 인한 성능 향상이 제한되는 것을 실험으로 확인하고, 성능 향상의 이득이 작아지는 CPU 주파수를 제시하도록 한다. 본 논문의 기법을 적용한 실험 결과는 메모리 접근 빈도가 높은 응용에 대하여 30% 이상의 에너지 효율 상승이 있음을 보인다.

• 대한물리치료과학회지
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• 제28권1호
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• pp.54-61
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• 2021

Background: The present study was performed to examine the factors required for active engagement of participants in exercise therapy by surveying the frequency of participation, fidelity of performance, and supporting materials and rewards provided to encourage participation in the study. Design: Cross-sectional study. Methods: The survey was conducted in a population of 103 participants in at least one exercise treatment study. A 12-item questionnaire was designed to determine the frequency of exercise participation and fidelity of participant performance. Results: The results were subjected to frequency analysis and Pearson's correlation analysis. The subjects were less likely to exercise with the therapist and less likely to exercise at home. In addition, the provision of supplementary materials, to be considered when exercising at home, was insufficient. A strong positive correlation was found between the frequency of exercise in the presence of a therapist and the fidelity of participant performance (r=0.812, p=0.001), whereas a weak negative correlation was found between the frequency of unperformed exercises and the fidelity of participant performance (r=-0.523, p=0.023). Conclusion: The results of the present study suggested that it is necessary to increase the number of times that exercises are performed with the therapist to motivate increased frequency of exercise participation and fidelity of participant performance. In addition, appropriate rewards and periodic management are required.

• Journal of Communications and Networks
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• 제9권1호
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• pp.34-42
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• 2007

Orthogonal frequency division multiplexing (OFDM) combined with time division multiplexing (TDM), in this paper called OFDM/TDM, can overcome the high peak-to-average-power ratio (PAPR) problem of the conventional OFDM and improve the robustness against long time delays. In this paper, the bit error rate (BER) performance of OFDM/FDM in a frequency-selective Rayleigh fading. channel is evaluated by computer simulation. It is shown that the use of frequency-domain equalization based on minimum mean square error criterion (MMSE-FDE) can significantly improve the BER performance, compared to the conventional OFDM, by exploiting the channel frequency-selectivity while reducing the PAPR or improving the robustness against long time delays. It is also shown that the performance of OFDM/FDM designed to reduce the PAPR can bridge the conventional OFDM and single-carrier (SC) transmission by changing the design parameter.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 ITC-CSCC -1
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• pp.521-524
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• 2000

It is well known that the OFDM system is weak against the frequency offset. The frequency offset attenuates the received signal power and makes the performance bound in the OFDM transmission. We show the performance bound of the OFDM transmission with the frequency offset under the additive white Gaussian noise channel by the numerical method. According to the results, increasing the transmitting power is not useful to improve the performance, when the frequency offset exits. The performance degradation is very severe as the frequency offset increases.

• Journal of electromagnetic engineering and science
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• 제4권2호
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• pp.72-78
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• 2004

In this paper, we evaluate the performance of the digital modulation schemes described in the APCO Project 25 FDMA specifications which can be used for applying the ultra-narrowband technology to the current domestic simple two-way radio systems, and discuss difficulties in the DSP implementation of the systems. We analyze the effect on the systems' BER performance of receiver non-matched filter and frequency-offset between the transmitter and receiver oscillators. And we present a frequency offset compensation method for improving the system performance. The results of performance analysis showed that the CQPSK of APCO Project 25 using non-matched filter degraded the BER by 0.5～1.0 ㏈ comparing with PI/4 DQPSK using matched filter. In the event of 2 % frequency offset, about 1 ㏈ performance loss was produced at the BER of $$10^{-3}TEX>. With the frequency-offset compensation method implemented in the systems using phase recovery scheme of PSK synchronization detection, the performance degradation of about 1.0 ㏈ was occurred at the BER of $$10^{-3}TEX> for 10 % of frequency offset. The proposed method can be used for the improvement of system performance.

• 수산해양기술연구
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• 제54권3호
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• pp.255-261
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• 2018

High power trends in the diesel engines due to engine downsizing do not provide noise attenuation that can be satisfied with the performance of the existing silencer on account of high frequency increases in the exhaust noise. This study improves the attenuation performance of the exhaust silencer of the diesel engine and suggests silencer structure that performs best attenuation performance, especially at the high frequency range in the exhaust noise. It proposes dual silencer structure with an average attenuation performance of 6.4 dB and a maximum of 10.7 dB in the high frequency range (over 500 Hz), and analyzes its characteristics compared with the existing silencer. The performance analysis is performed according to 'Measurements on silencers in situation-ISO 11820:1996 Acoustics' and describes the results of comparative analysis with the existing silencer.

• 대한전자공학회:학술대회논문집
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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

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 하계종합학술대회 논문집 I
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• pp.461-464
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• 2003

This paper explains the impact of frequency error on the performance of WCDMA mobile communication systems and what brings about the frequency error between the base station and the mobile station, and then presents automatic frequency error correction method in mobile receiver. On the basis of system requirement related to frequency stability, the integration test between the base station and the mobile station was accomplished. After applying automatic frequency error correction to mobile receiver, 4 Hz of frequency error at transmitting frequency was obtained. The result met frequency error requirement of 0.1ppm(about 200 Hz). Performance degradation due to frequency error was measured by means of Error Vector Magnitude (EVM)