• Journal of the Korea Society of Computer and Information
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• v.18 no.10
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• pp.63-70
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• 2013

In this paper, we investigated frequency synchronization through computer simulation of digital M/W transmission system in multipath fading channel. we suggested frequency offset correction algorithm against frequency offset between transmitter and receiver, then evaluated the degree of constellation performance enhancement. From the performance evaluation, in case of large frequency offset, although adopting frequency offset correction scheme, residual frequency offset degraded system performance. As a result, according to frequency offset value between transmitter and receiver residual frequency offset affects system performance significantly. The results of this paper should be utilized for frequency synchronization criterion when frequency band of broadcasting system is rearranged.

• Journal of Communications and Networks
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• v.9 no.2
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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.

• KIISE Transactions on Computing Practices
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• v.20 no.9
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• pp.483-491
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• 2014

Contemporary computer systems exploits DVFS (Dynamic Voltage/Frequency Scaling) technology for balancing performance and power consumption. The efficiency of DVFS depends on how much performance we get for larger power consumption due to elevated CPU frequency. Especially for memory-bounded applications, higher CPU frequency often does not result in higher performance. In this paper, we present an upper bound of CPU frequency scaling based on memory accesses. It is observed that the performance gain due to higher CPU frequency is limited by memory accesses (last level cache misses) per instructions by experiments. Using the results, we present the CPU frequency upper bound with little performance gain. Experimental results show that for a memory-bounded application, applying the frequency upper bound enhances the energy efficiency of the application by above 30%.

• Journal of Korean Physical Therapy Science
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• v.28 no.1
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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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• v.9 no.1
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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.

• Proceedings of the IEEK Conference
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• 2000.07a
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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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• v.4 no.2
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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.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.54 no.3
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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.

• Proceedings of the IEEK Conference
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• 2001.06a
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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

• Proceedings of the IEEK Conference
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• 2003.07a
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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)