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수중 음향통신에서 위상고정루프와 결합된 등화기의 성능분석
김승환,김인수,도대원,고석준,Kim, Seunghwan,Kim, In Soo,Do, Dae-Won,Ko, Seokjun 한국음향학회 2022 韓國音響學會誌 Vol.41 No.2
In this paper, the performance of joint equalizer and phase-locked loop in underwater communications is analyzed. In the channel where the Doppler frequency exists, it is difficult to recover the transmitted data only by the equalizer. To compensate for the Doppler frequency, the phase-locked loop is used. For removing the time-varying multipath and the Doppler frequency simultaneously, the equalizer and the phase-locked loop operate jointly. Also, if the initial Doppler frequency error obtained by Fast Fourier Transform (FFT) is compensated, the convergence speed of the joint equalizer and phase-locked loop can be improved. To verify the performance, lake and sea experiments were conducted. As a result, it was showed that the joint equalizer and phase-locked loop converges sufficiently in the preamble (known data) period regardless of whether the Doppler frequency is compensated or not. And, the bit error in random data period is not occurred. However, we can increase the convergence speed of the equalizer more than twice through the compensation of Doppler frequency.
송승언,신한섭,김대오,고석준,Song, Seungeon,Shin, Han-Seop,Kim, Dae-Oh,Ko, Seokjun 대한임베디드공학회 2017 대한임베디드공학회논문지 Vol.12 No.4
An angle error is a factor obstructing to track accurate position in tracking radars. And the noise incurring the angle error can be divided as follows; thermal noise and glint. In general, Extended Kalman filter used in tracking radars is designed with considering thermal noise only. The Extended Klaman filter uses a fixed measurement error covariance when updating an estimate state by using ahead state and measurement. But, a noise power varies according to the range. Therefore we purposes the adaptive Kalman filter which changes the measurement noise covariance according to the range. In this paper, we compare the performance of the Extended Kalman filter and the proposed adaptive Kalman filter by considering KSLV-I (Korean Satellite Launch Vehicles).
수중 음향통신에서 binary phase shift keying신호의 프레임동기 방법
양경필,김완진,도대원,고석준,YANG, Gyeong-pil,KIM, Wan-Jin,DO, Dae-Won,KO, Seokjun 한국음향학회 2022 韓國音響學會誌 Vol.41 No.2
In this paper, a frame synchronization structure for the Binary Phase Shift Keying (BPSK) modulation method in underwater acoustic communication was proposed. The proposed frame synchronization structure is largely divided into two. First, the approximate position and frequency offset of the frame are obtained by non-coherent correlation and sliding Fast Fourier Transform (FFT) method. Second, after compensating for the frequency error to the received signal, the exact position of the frame is obtained by coherent correlation method. Maritime experiments were conducted to confirm the performance of the 2-STEP frame synchronization structure. It was showed that the limitations of the non-coherent correlation and sliding FFT method can be verified when the power of the received signal was greatly reduced due to the channel characteristics. As a result, stable frame synchronization could be obtained by compensating for the frequency error and then using the coherent correlation method.
복잡한 목표물의 Glint와 RCS 모델링 및 시뮬레이션
송승언,신한섭,김대오,강철웅,고석준,Song, Seungeon,Shin, Han-Seop,Kim, Dae-Oh,Kang, Chul-Ung,Ko, Seokjun 대한임베디드공학회 2017 대한임베디드공학회논문지 Vol.12 No.1
The signal transmitted from radar is not reflected from a single point when the signal reflected by complex target. Resultantly, the amplitude and phase of the received signal can be changed because the target has lots of scatterers. The changes of the amplitude and the phase mean Glint and RCS, respectively. Although the Glint and RCS that caused by the same scatters are uncorrelated, however, they are not independent completely. Therefore, this paper proposes a method for generating the Glint and RCS by using same random number generator. And the time correlations of the Glint and RCS are respectively implemented in frequency domain by using each power spectral density of them.
송승언(Seung-Eon Song),신한섭(Han-Seop Shin),고석준(Seokjun Ko) 한국정보기술학회 2015 한국정보기술학회논문지 Vol.13 No.12
Angle error is a factor obstructing to track accurate position in tracking radars. Noise can be divided as follows; thermal noise, servo noise, and glint. Kalman filter used in tracking radars is generally designed with assuming thermal noise (e.g. Additive White Gaussian Noise). But we need to assess the performance of Kalman filter in condition of glint as considered in this paper because the characteristics of glint is different from thermal noise. In this paper, glint is modeled by using a power spectral density in frequency domain and a mixed Gaussian and Laplacian distribution statistically. We can also verify an effect of glint in monopulse radar and an ability of Kalman filter to track KSLV-Ⅰ(Korean Satellite Launch Vehicles). It is shown that Extended Kalman filter can estimate and reduce about 20% of glint’s RMS.