• Journal of Power Electronics
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• v.14 no.6
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• pp.1334-1344
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• 2014

A novel single phase Phase-Locked Loop (PLL) is proposed in this paper to accurately and rapidly estimate the instantaneous phase angle of a grid. A conjugate rotating vector pair is proposed and defined to synthesize the single phase signal in the stationary reference frame. With this concept, the proposed PLL innovatively sets one phase input of the PARK transformation to a constant zero. By means of a proper cancellation, a zero steady state phase angle estimation error can be achieved, even under magnitude and frequency variations. The proposed PLL structure is presented together with guidelines for parameters adjustment. The performance of the proposed PLL is verified by comprehensive experiments. Satisfactory phase angle estimation can be achieved within one input signal cycle, and the estimation error can be totally eliminated in four input cycles for the most severe conditions.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.89-90
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• 2008

We present an implementation and it's real-sea test of an underwater acoustic communication system, which allows the system to reduce complexity and increase robustness in time variant underwater environments. For easy adaptation to complicated and time-varying environments of the ocean, all-digital transmitter and receiver systems were implemented. For frame synchronization the CAZAC sequence was used, and QPSK modulation/demodulation method with carrier frequency of 25kHz and a bandwidth of 5kHz were applied to generate 10kbps transmission rate including overhead. To improve transmission quality, we used several techniques and algorithms such as adaptive beamforming, adaptive equalizer, and convolution coding/Viterbi decoding. For the verification of the system performance, measurement of BER has been done in a very shallow water with depth of 20m at JangMok, Geoje. During the experiment, image data were successfully transmitted up to about 9.6km.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.276.2-278
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• 2000

In a recent years, a number of approaches have been studied, including passive, active, and hybrid mode-locking of semi-conductor lasers for short pulse generation and research has been devoted to achieve low timing-jitter operation since the timing jitter is unfavorable for system applications. Among the methods of mode locking, passive mode locking does not need external rf drives, and therefore the operation and fabrication procedures are simplified. In spite of these attractive advantages of passive mode-locked laser, it has critical drawbacks such as large timing jitter and the difficulty in synchronization with external circuits. Their inherent large timing jitter value was shown to be suppressed to certain levels by means of hybrid mode-locking technique$^{(1)}$ , where the saturable absorber section was modulated by an external signal with the cavity round trip frequency. Furthermore, the subharmonic mode-locking (SHML) technique alleviates the restrictions of high speed driving electronics. It has been demonstrated experimentally$^{(1)}$ that the hybrid subharmonic mode-locking technique has lead to significant reduction of the timing jitter. (omitted)

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.11
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• pp.211-216
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• 2012

Such as disaster rescue in deep water, undersea exploration and monitering for environmental pollution, many applications require the acoustic communication for high data rate over underwater acoustic channel. As underwater channel is very complex and is time-varying, In this paper, The proposed OFDM system with synchronization errors and multipath delay spread is analyzed for high data rate and reliability and rubust service over UWA channels.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.283-286
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• 2003

In this paper, we represent an implementation of burst QPSK receiver for underwater acoustic communication. Transmitter sends 5,000 symbols at 25kHz frequency with 200 kHz D/A sampling rate. The received signal is sampled at 100 kHz. Implemented receiver acquires the frame synchronization, coarse symbol timing estimate, and coarse phase offset estimate using 32 symbol length preamble. The estimated phase offset is used to initiate of 2nd order PLL. The transmission experiment results show that PLL is a mandatory to compensate Doppler shift due to the variation of tidal current.

• Journal of Electrical Engineering and Technology
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• v.9 no.1
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• pp.334-343
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• 2014

In this paper, we suggest a method to improve the fusion of an accelerometer and gyro sensor by using a Kalman filter to produce a more high-quality respiration signal to supplement the weakness of using a single accelerometer. To evaluate our proposed algorithm's performance, we developed a chest belt-type module. We performed experiments consisting of aerobic exercise and muscular exercises with 10 subjects. We compared the derived respiration signal from the accelerometer with that from our algorithm using the standard respiration signal from the piezoelectric sensor in the time and frequency domains during the aerobic and muscular exercises. We also analyzed the time delay to verify the synchronization between the output and standard signals. We confirmed that our algorithm improved the respiratory rate's detection accuracy by 4.6% and 9.54% for the treadmill and leg press, respectively, which are dynamic. We also confirmed a small time delay of about 0.638 s on average. We determined that real-time monitoring of the respiration signal is possible. In conclusion, our suggested algorithm can acquire a more high-quality respiration signal in a dynamic exercise environment away from a limited static environment to provide safer and more effective exercises and improve exercise sustainability.

• Proceedings of the Korean Society for Emotion and Sensibility Conference
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• 2002.05a
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• pp.44-50
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• 2002

The fast Fourier transform (FFT) is a good method to estimate spectral density, but the frequency resolution is limited to the sampling window, and thus the precise characteristics of the spectral density for short signals are not clear. To solve the limitation, a multiple band-pass filter was introduced to estimate the precise time course of the spectral density for flash visual evoked potentials (VEPs). Signals were recorded during -200 and 600 ms using balanced noncephalic electrodes, and sampled at 1 K Hz in 12 bits. With 1 Hz and 10 ms resolutions, spectral density was estimated between 10 and 100 Hz. Background powers at the alpha-and beta-bands were high over the posterior scalp, and powers around 200ms were evoked at the same bands over the same region, corresponding to P110 and N165 of VEPs. normalized's spectral density showed evoked powers around 200 ms and suppressed powers following the evoked powers over the posterior scalp. The evoked powers above the 20Hz band were not statistically significant. However, the gamma band was significantly evoked intra-individually; details in the gamma bands were varied among the subjects. Details of spectral density were complicated even for a simple task such as watching flashes; both synchronization and desynchronization occurred with different distributions and different time courses.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2005.11a
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• pp.81-84
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• 2005

지상파 디지털 방송신호의 방송구역 확장이나 난시청지역 해소를 위해 사용되는 동일채널중계기(On-Channel Repeater : OCR)는 수신신호와 송신신호의 주파수를 완벽히 일치시켜야한다. 송수신신호의 주파수가 일치하지 않을 경우 주 송신신호와 중계신호가 동시에 수신되는 중첩지역에서 수신기의 수신성능이 현저히 저하되기 때문이다. 본 논문에서는 ATSC 지상파 디지털 방송신호를 중계하는 등화형 동일채널중계기(Equalization Digital On-Channel Repeater : EDOCR)에서 송수신신호의 주파수를 일치시키는 알고리즘에 대해 기술한다. 등화형 동일채널중계기는 주 송신신호를 수신하여 복조한 후 재 변조 하므로 송수신신호의 주파수를 일치시키기 위한 별도의 장치나 알고리즘이 반드시 사용되어야 한다. 제안하는 알고리즘은 주 송신신호의 동기복원 과정에서 획득한 주파수 오차 정보를 재 변조 과정에 사용함으로써 GPS와 같은 별도의 장치 없이 송수신신호의 주파수를 일치시킨다. 반송파 복원과정에서 획득한 반송파 오차와 심볼타이밍 복원과정에서 획득한 심볼타이밍 오차를 재 변조 신호에 추가하면 수신신호와 송신신호가 같은 주파수 오차를 갖게 되어 두 신호의 중심주파수가 일치된다.

• Aerospace Engineering and Technology
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• v.10 no.1
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• pp.45-53
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• 2011

This paper is technical review about Direct Sequence Spread Spectrum(DSSS) to apply in launch vehicle system. First, we introduce communication protocol(carrier frequency, code length, process gain, data rate, chip rate etc) about several application system using DSSS. And then, we survey and summarize the effect of doppler shift to the DSSS. The doppler shift is important error factor for PN code tracking in the fast moving system like launch vehicle. So, spread spectrum code acquisition technique for a direct sequence system in the presence of doppler effect must be investigated.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.12
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• pp.44-53
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• 2007

In this paper, we focus on the developments of complex location awareness algorithms for real-time location based service and precise/stable localization in the outdoor. In the case of using galileo satellite system along with GPS, several error factor such as the ionosphere can be reduced for an increment of used frequency and visible satellites. Therefore, localization estimation error is no longer having problems with location awareness. But, chips synchronization error induces the error of acquisition and tracking, and the performance of receiver can be decreased. In order to solve this problem, this paper proposes a correlator for performance improvement of receiver in the precise localization.