• The Journal of the Korea institute of electronic communication sciences
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• v.11 no.4
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• pp.365-372
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• 2016

Recently, UWAC(: UnderWater Acoustic Communication) has been studied by many scholars and researchers. There are several method to estimate the time-difference between the two signals such estimating as the arrival time of the first non-background segment in both signals and calculate the temporal difference, calculating the cross-correlation between the two signal to infer the time-lagged, and estimating the phase delay to infer the time difference. In this paper, we present estimating method by the phase delay to infer the time difference in two signals.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.10
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• pp.895-902
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• 2012

In this paper, we propose a novel equalizer to compensate for the group delay including AM/PM nonlinear distortion characteristics by the nonlinear power amplifier (PA). The group delay characteristic is a nonlinear non-constant time delay that appears differently depending on each frequency component. The phase distortion by AM/PM characteristics arising from the power amplifier is a major factor to increase group delay. By the group delay distortion, the signal in the constellation expands and is rotated. Considering the problem mentioned above, the nonlinear time delay that appears differently depending on each frequency component is classified as a static group delay and AM/PM characteristic of PA, the different phase transitions depending on the size of input signal as a dynamic group delay. Static group delay estimates and compensate for phase distortions in the frequency domain with type-based method and dynamic group delay compensates for phase rotation in the time domain. We confirmed that the group delay compensation techniques were enough to compensate the group delay characteristics including AM/PM characteristics of the power amplifier.

• The Journal of the Acoustical Society of Korea
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• v.39 no.3
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• pp.207-215
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• 2020

There are several methods for the time delay estimation between signals to two receivers. Among these methods, Generalized Cross Correlation (GCC), which estimates the relative delay from the cross-correlation between the different signals at the two receivers, is a traditionally well-known method. However, when using a narrow band Continuous Wave (CW) signal, the GCC method degrades the estimation performance from relatively higher signal-to-noise ratio than when using a wideband signal. To improve this phenomenon, this paper examines four different pre-processors for GCC using narrow band single frequency signals. Simulation shows that the performance gain of the preprocessed GCC is up to 9 dB for a 100 msec CW signal as well as up to 4 dB for a 1 s CW signal.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.5
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• pp.811-816
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• 2019

This paper first proposes a technique to separate clean speech signals and mixed noise signals by using an independent vector analysis algorithm of frequency band for 4 channel speech source signals with a noise. An improved output speech signal from the proposed independent vector analysis algorithm is obtained by using the cross-correlation between the signal outputs from the frequency domain delay-sum beamforming and the output signals separated from the proposed independent vector analysis algorithm. In the experiments, the proposed algorithm improves the maximum SNRs of 10.90dB and the segmental SNRs of 10.02dB compared with the frequency domain delay-sum beamforming algorithm for the input mixed noise speeches with 0dB and -5dB SNRs including white noise, respectively. Therefore, it can be seen from this experiment and consideration that the speech quality of this proposed algorithm is improved compared to the frequency domain delay-sum beamforming algorithm.

• Korean Journal of Optics and Photonics
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• v.27 no.5
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• pp.174-180
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• 2016

A tunable optical delay line is designed, fabricated, and characterized. The tunable delay line consists of four polymer-ring add/drop filters with delay waveguides between adjacent ones. The polymer waveguide is a buried structure, designed to be square with core width and height of $1.8{\mu}m$. The refractive indices of the core and cladding polymer are 1.48 and 1.37 respectively. The large index difference and small cross section of the waveguide enable us to realize a compact device using a small radius of curvature. Four pairs of electrodes are evaporated above the add/drop filters to provide heating currents for thermal tuning. In measurements we can identify variable time delays of 110, 225, and 330 ps in proportion to the number of delay lines.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.909-915
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• 2008

Researches for time delay estimation had been studied broadly. However studies about factors for time delay estimation are insufficient, especially in case of real environment application. In 1997, Brandstein and Siverman announced that performance of time delay estimation deteriorates as reverberant time of room increases. Even though reverberant time of room is same, performance of estimation is different as the specific part of signals. In order to know that reason, we studied and analyzed the factors for time delay estimation using speech signal and room impulse response. In result, we can know that performance of time delay estimation is changed by different R/D ratio and signal characteristics in spite of same reverberant time.

• Journal of the Institute of Convergence Signal Processing
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• v.12 no.2
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• pp.107-112
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• 2011

Several developed countries have been developing their own satellite navigation systems, such as Europe's Galileo, China's BEIDOU, and Japan's QZSS, to cope with clock errors and signal vulnerabilities of GPS. In addition, modernization of Loran, eLoran, for GPS backup has been conducted. In Korea, a dependent navigation system has been required and for GPS backup, the need for utilization of time synchronization infrastructure through the modernization of Loran has been raised. Loran signal uses 100Khz groundwave. A significant factor limiting the ranging accuracy of the Loran signal is the ASF arising from the fact that the groundwave signal is likely to propagate over paths of varying conductivity and topography. Thus, an ASF compensation method is very important for Loran and eLoran navigation. This paper introduces the propagation delay model and then compares and analyzes the estimations from the propagation delay model and measured ASFs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.10A
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• pp.969-979
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• 2002

This paper proposes an novel method of minimizing Interference which causes data decision error in digital wireless communications. In this method, in order to suppress ISI which is caused by the phase difference between the transmitted and received signal phases, the transmitted and received signals are always kept orthogonal by compensating the transmitted signal for detecting the phase noise and the delay of the received signal was implemented by MOS circuits. To delay the phase of the signal, additive white Gaussian noise (AWGN) environment was used. The phase and delay of the signal transmitted through AWGN channel were compensated in the modulator of the transmitter and the compensated signal was demodulated using quasi-direct conversion receiver and QPSK demodulator. ISI suppression was achieved by keeping the orthogonality between the compensated transmitted signal and the receive signal. The error probability of data decision was compared. By simulation the proposed system was proved to be effective in minimizing the ISI.

• Journal of the Korea Society of Computer and Information
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• v.14 no.2
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• pp.111-118
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• 2009

Against Anomaly of GPS, there are several projects of independent satellite navigation systems like Galileo of Europe and QZSS of Japan and modernization of terrestrial navigation system like Loran. In domestic, the need of independent navigation system was proposed and DGPS signal was nominated as the possible substitute. The DGPS signal uses medium frequency, which travels through the surface and cause the additional delay rather than the speed of light according to Conductivities and elevations of the irregular terrain. The similar approach is Locan-C. Loran-C has been widely used as the maritime location system. Loran-C uses the ASF estimation method and provides more precise positioning. However there was rarely research on this area in Korea Therefore, we introduce the legacy guaranteed model of additional delay(ASF) and present the results of implementation. With the comparison of the original Monteath results and BALOR results respectively, we guarantee that the implementation is absolutely perfect. For further works, we're going to apply the ASF estimation model to Korean DGPS system with the Korean terrain data.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.217-220
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• 2002

본 연구는 폐쇄된 임의의 공간상에서 2개의 마이크로폰 어레이를 이용하여 마이크로폰에 수신된 신호들의 도착 시간차를 추정하는 새로운 알고리즘을 제안한다. 제안된 알고리즘은 입력 음성신호를 Discrete wavelet transform을 이용하여 인간의 청각 특성과 가장 유사한 주파수 해상도를 갖도록 대역 분할한 후 각 주파수 대역에서 신호 대 잡음비를 구하여 신호 대 잡음비가 가장 높은 대역만 선택적으로 취하고 해당 대역에서만 최종적인 시간 지연 값을 추정하게 된다. 최종 시간 지연 측정에 사용된 알고리즘은 기존의 CPSP에 해당 대역의 주파수 SNR을 가중치로 주어 구하게된다. 이러한 대역 분할 가중방식은 다양한 형태의 동적인 잡음 환경 하에서 안정적인 성능을 가질 수 있다. 제안된 알고리즘은 저주파와 고주파 각각의 모의 잡음환경 하에서 컴퓨터 실험을 통해 성능을 입증하도록 한다.