• ETRI Journal
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• 제38권3호
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• pp.455-462
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• 2016

Frequency hopping (FH) is a common characteristic of a wide variety of communication systems. On the other hand, software-defined radio (SDR) is an increasingly utilized technology for implementing modern communication systems. The main challenge when trying to realize an SDR FH system is the frequency tuning time, that is, the higher the hopping rate, the lower the required frequency tuning time. In this paper, significant universal hardware driver tuning options (within GNU Radio software) are investigated to discover the tuning option that gives the minimum frequency tuning time. This paper proposes an improved SDR frequency tuning algorithm for the generation of a target signal (with a given target frequency). The proposed algorithm aims to improve the frequency tuning time without any frequency deviation, thus allowing the realization of modern communication systems with higher FH rates. Moreover, it presents the design and implementation of an original GNU Radio Companion block that utilizes the proposed algorithm. The target SDR platform is that of the Universal Software Radio Peripheral USRP-N210 paired with the RFX2400 daughter board. Our results show that the proposed algorithm achieves higher hopping rates of up to 5,000 hops/second.

• Journal of Electrical Engineering and Technology
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• 제6권4호
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• pp.439-446
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• 2011

Frequency is an important operating parameter for the protection, control, and stability of a power system. Thus, it must be maintained very close to its nominal frequency. Due to the sudden change in generation and loads or faults in a power system, however, frequency deviates from its nominal value. An accurate monitoring of the power frequency is essential for optimum operation and prevention of wide area blackout. Most conventional frequency estimation schemes are based on the DFT filter. In these schemes, the gain error could cause defects when the frequency deviates from the nominal value. We present an advanced frequency estimation technique using gain compensation to enhance the DFT filter-based technique. The proposed technique can reduce the gain error caused when the frequency deviates from the nominal value. Simulation studies are performed using both the data from EMTP-RV software and the user-defined arbitrary signals to demonstrate the effectiveness of the proposed algorithm. Results show that the proposed algorithm achieves good performance under both steady state tests and dynamic conditions.

• Journal of Electrical Engineering and Technology
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• 제6권6호
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• pp.776-785
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• 2011

Since the Internet-based real-time Global Positioning System(GPS) synchronized widearea power system frequency monitoring network (FNET) was proposed in 2001, it has been monitoring the power system frequency in interconnected United States power systems and numerous interesting behaviors have been observed, including frequency excursion propagation. We address the consistency of a frequency excursion detection order of frequency disturbance recorders in FNET in relation to the same generation trip, as well as the ability to recreate by power systems dynamic simulation. We also propose a new method, as an application of FNET measurement, to locate a tripped generator using power systems dynamic simulation and wide-area frequency measurement. The simulation database of all the possible trips of generators in the interconnected power systems is created using the off-line power systems dynamic simulation. When FNET detects a sudden drop in the monitoring frequency, which is most likely due to a generation trip in power systems, the proposed algorithm locates a tripped generator by finding the best matching case of the measured frequency excursion in the simulation database in terms of the frequency drop detection order and the time of monitoring points.

• Transactions on Electrical and Electronic Materials
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• 제18권4호
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• pp.185-189
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• 2017

This paper proposes a low power frequency divider for an integrated CMOS phase-locked loop (PLL). An injection-locked frequency divider (ILFD) was designed, along with a current-mode logic (CML) frequency divider in order to obtain a broadband and high-frequency operation. A ring oscillator was designed to operate at 1.2 GHz, and the ILFD was used to divide the frequency of its input signal by two. The structure of the ILFD is similar to that of the ring oscillator in order to ensure the frequency alignment between the oscillator and the ILFD. The CML frequency divider was used as the second stage of the divider. The proposed frequency divider was applied in a conventional PLL design, using a 0.18 ${\mu}m$ CMOS process. Simulation shows that the proposed divide-by-two ILFD and the divide-by-eight CML frequency dividers operated as expected for an input frequency of 1.2 GHz, with a power consumption of 30 mW.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2008년도 정보통신설비 학술대회
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• pp.437-440
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• 2008

In this paper, we present and analyze a robust frequency offset estimation scheme for orthogonal frequency division multiplexing (OFDM) systems over radio communication channels. When there exists frequency offset, the loss of orthogonality occurs and the interference problem among several subcarriers in OFDM signals is introduced. The guard interval of OFDM signals is employed for estimating the frequency offset. Furthermore, in order to enhance the frequency offset estimation performance, a ternary sequence is utilized. A frequency offset is estimated based on the synchronized correlator output. The proposed frequency offset estimation scheme can be applied to track the carrier frequency offset of OFDM systems.

• 소음진동
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• 제3권4호
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• pp.341-352
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• 1993

Although a frequency analysis by FFT algorithm has been widely used in the vibration community, this approach has somewhat limited features when an analysist want to see the details of frequency trends because FFT shows only energy contents along frequencies. So the concept of instantaneous frequency that represents the dominant frequency component at each time needs to be introduced. In this paper, to get the instantaneous frequency, two methods are used. Methods using Hilbert transform and evolutionary spectrum are those. One of the problems of estimating instantaneous frequency using Hilbert transform is that it is normally very sensitive to signal to noise ratio(SNR) because of the differentiation. Moving window is applied on the estimation of instantaneous frequency, and instantaneous frequency histogram are used to handle this problem and proved to be very effective. Computer simulations for various signals have been done to understand the characteristics of instantaneous frequency. The usefulness of signal analysis using instantaneous frequency was tested by three simple experiments, which were engine experiment, beam experiment, and car door experiment. The instantaneous frequency analysis is found to be a useful technique to analyze the signals that have time varying frequencies.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제50권12호
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• pp.622-626
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• 2001

HID(high intensity discharge)lamps are high pressure mercury lamp, high pressure sodium lamp and metalhalide lamp. metalhalide lamp among these lamps has considered to be one of the most effective artificial light sources and this lamp has good efficiency, good color rendition and good focusing capability, But the shortcorning of metalhalide lamp is known as acoustic resonance phenomena in the discharge tube when lighted by electronic ballast and then acoustic resonance cause various problems such as the arc instability, light output fluctuations. In this paper, to reduce the acoustic resonence phenomena, the electronic ballast was designed by three methods for high frequency operation wish frequency-modulated sinusodial waves in acoustic resonance frequency band. These frequency-modulated methods are resonance frequency and resonance frequency, resonance frequency and non-resonance frequency non-resonance frequency and non-resonance frequency Experiment results could't show the Presence of acoustic resonance visually and it proved that the resonance-generating conditions can be avoided by continuously changing the two operating frequencies in acoustic resonance band (20.59kHz∼94.2kHz).

• 대한간호학회지
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• 제14권1호
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• pp.1-20
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• 1984

This study was attempted to evaluate and explain the correlation between stress and utilization of Dispensary, Frequency of absence, Frequency of accident as the health condition of bluecollared workers. The subjects for this study were 260 workers selected conveniently from 360 workers working at one chemical manufacturer located in Seoul. The dataas measure the Stress was collected through SRRS (The Social Readjustment Rating Scale) which is developed by Holmes ＆ Rahe (1976) from 27th July to 10th August, 1983. The data of Utilization of Dispensary and Frequency of Accident were brought out from the record of Dispensary during past 8 months. The Frequency of Abscence from January to August were collected through diligence and indolence cards of each department. All collected data were analysed based on the SPSS (Statistical Package for the Social Science) program. The results of the study are as follows: 1. The average of Utilization of Dispensary was 7.4, Frequency of abscence 14.6, frequency of Accident 0.4. 2. The average score of Stress was 134 (minimum : 0, maximum : 593, Standard deviation : 109. 3) It can be considered as a slight stressed group by the requlations of Holmes and Rahe. 3. According to the analysed results of correlation between Stress and the Utilization of Dispensary, Frequency of Absence, frequency of Accident, the Utilization of dispensary and stress were significantly related (r= .1955, p<.001), the Frequency of Absence (r=.0284, p >, 05), and the Frequency of Absence (r=.0284, p>.05), and the Frequency of Accident (r= .0831, p>.05) were not significantly related with Stress. 4. In the relation between general characters of subjects and the Utilization of Dispensary, 20 to 25 aged group, women, single, christian, lent-house dwelling, 1 to 5 years employed group used at a high ratio. 5. In the relation between general character of subjects and the Frequency of Absence, men, 51 to 55 aged group, 21 to 25 years employed group indicated high Frequency, and other char-noters were not significantly related. 6. In the relation between general characters of subjects and the Frequency of Accident, women. single, 20 to 25 aged group, catholic, lent-house dwelling, below 1 year employed group showed high frequency. 7. Stress showed a significant difference only with a religion. Catholic group represented mode-rate stressed scored 209.67, and not significantly related with other general characters.

• 조명전기설비학회논문지
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• 제25권11호
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• pp.98-102
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• 2011

This paper describes inverse E class frequency multiplier which is lower inductance and peak switching voltage than E class frequency multiplier. The frequency multiplier is designed to generate 5.8[GHz] frequency by doubling the input frequency 2.9[GHz]. The peak switching voltage of designed inverse E class frequency multiplier with 11[V] is lower 4[V] than that of E class frequency multiplier with 15[V]. The inverse E class frequency multiplier has a conversion gain 6[dB] at output power 21[dBm] and maximum 35[%] power efficiency.

• 대한물리의학회지
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• 제13권4호
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• pp.67-74
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• 2018

PURPOSE: This study was conducted to investigate the effects of vibration frequency and amplitude on scapular winging during the knee push-up plus exercise. METHODS: A total of 26 female subjects with scapular winging were evaluated while performing the knee push-up plus exercise with no vibration, low-frequency/low-amplitude (5 Hz/3 mm) vibration, low-frequency/high-amplitude (5 Hz/9 mm) vibration, high-frequency/low-amplitude (15 Hz/3 mm) vibration, and high-frequency/high-amplitude (15 Hz/9 mm) vibration. The surface EMG of the serratus anterior (SA) muscle was compared between the vibration frequency and amplitude. The EMG amplitude was normalized using the maximal voluntary isometric contraction (MVIC). The statistical significance of the results was evaluated using one-way ANOVA. RESULTS: The SA muscle EMG values increased at low-frequency/low-amplitude vibration and at low-frequency/high-amplitude vibration compared to no vibration. Furthermore, the same values increased at high-frequency/low-amplitude vibration and high-frequency/high-amplitude vibration compared to no vibration. In general, a higher vibration frequency and amplitude was associated with higher EMG values of the SA muscle, with particularly greater increases observed during high-frequency/high-amplitude vibration. There was also a significant difference between each condition with a high-frequency/high-amplitude vibration (p<.05). CONCLUSION: This study suggests that there were remarkable clinical effect of the knee push-up plus exercise with vibration, which enhanced the SA muscle activation in persons with scapular winging. Furthermore, applying a higher vibration frequency and amplitude more effectively increased for increasing SA muscle activation.