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- 저자 : 김동현(Donghyeon Kim) (검색결과 131 건)
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거리 종속 환경에서의 배열 불변성 기반 거리추정과 상응 거리와의 관계
김동현,변기훈,김대환,김재수,Donghyeon Kim,Gihoon Byun,Daehwan Kim,Jeasoo Kim 한국음향학회 2024 韓國音響學會誌 Vol.43 No.4
천해역에서 효과적인 거리추정 방법으로 알려진 배열 불변성은 도파관 불변성으로 요약될 수 있는 이상적인 도파관 내에서의 광대역 확산 특징을 기반으로 개발되었으며, 배열 기울기가 존재하는 상황에서도 배열 기울기와 거리를 동시에 추정할 정도로 강인하다. 최근에는 도파관 불변성의 각도 종속성을 완전히 고려할 수 있도록 확장되었다. 하지만, 거리-종속 환경에 대해 거리-독립 환경의 배열 불변성 기법을 적용한다면, 해저 지형 오정합에 의해 거리추정오차가 발생하게 된다. 본 논문에서는 이러한 거리추정 오차를 상응 거리 개념을 도입하여 해석하고자 한다. 거리-종속 환경에서의 수치 시뮬레이션 수행과 해상 실험 데이터를 통해 거리추정의 오차와 상응 거리 사이의 관계를 입증하였다. In shallow water, the array invariant, known as the effective range estimation method, is developed based on the broadband dispersion characteristics in an ideal waveguide, which can be summarized by the waveguide invariant. It is robust enough to estimate both the array tilt and range simultaneously, even in situations where array tilt exists. Recently, it has been extended to fully consider the angle dependence of the waveguide invariant. However, applying the array invariant in range-dependent environments instead of range-independent environments can lead to range estimation errors due to bathymetry mismatch. In this paper, we interpret such range estimation errors by introducing the concept of effective range. Through numerical simulations and experimental data in a weakly range-dependent environment, we demonstrate the relationship between range estimation errors and effective range.
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Long-range multiple-input-multiple-output underwater communication in deep water
김동현,김대환,김재수,한주영,Kim, Donghyeon,Kim, Daehwan,Kim, J.S.,Hahn, Joo Young The Acoustical Society of Korea 2021 한국음향학회지 Vol.40 No.5
Long-range communication in deep waters must overcome the low data rate due to limited bandwidth. This paper presents the performance of Multiple-Input-Multiple-Output (MIMO) system to increase the data rate. In MIMO system, communication performance is degraded by crosstalk between users and an adaptive passive Time Reversal Processing (TRP) is widely used to eliminate this. In October 2018, long-range underwater acoustic communication experiment was conducted in deep water (1,000 m ~) off the east of Pohang, South Korea. During the experiment, a vertical line array was utilized and communication signals modulated by binary phase shift keying and quadrature phase shift keying with a symbol rate of 512 sps were transmitted. To generate MIMO communication signals, received signals from ranges of 26 km and 30 km is synthesized. Compared to the conventional passive TRP, the adaptive passive TRP eliminates the crosstalk between users and achieves error-free performance with an increase of output signal-to-noise ratio. Therefore, two users separated by 4 km in range achieves an aggregate data rate of 1,024 symbols/s.
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김동현,김재수,한주영,Kim, Donghyeon,Kim, J.S.,Hahn, Joo Young The Acoustical Society of Korea 2021 한국음향학회지 Vol.40 No.5
For long-range communication in deep water, low carrier frequency is efficient due to a decrease in transmission loss. However, there is a limitation in that the data rate decreases due to a narrow bandwith. In order to increase the data rate in an environment with a limited bandwidth, it is necessary to design a higher-order modulation scheme. This paper analyzes the long-range communication data modulated by higher-order modulation schemes. The long-range communication experiment (23 km ~) was conducted in East Sea in October 2020. During the experiment, a vertical line array was utilized and communication sequences were modulated by Phase Shift Keying (PSK) and Quadrature Amplitude Modulation (QAM) schemes and transmitted by a towed source. In more detail, PSK modulation consists of quadrature PSK and 8PSK, QAM modulation consists of 8QAM and 16QAM. Time reversal processing is applied to mitigate inter-symbol interference by utilizing the correlation between received signals and channel impulse responses. All modulation schemes show successful results at 23 km range, demonstrating the feasibility of higher-order modulation in long-range communication.
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나카가미 페이딩 채널에서 딥러닝 기반 송신 전력 제어 기법을 이용하는 무선통신 시스템에 대한 성능 분석
김동현,김동연,이인호,Kim, Donghyeon,Kim, Dongyon,Lee, In-Ho 한국정보통신학회 2020 한국정보통신학회논문지 Vol.24 No.6
In this paper, we propose a deep learning based transmit power control (TPC) scheme to improve the spectral and energy efficiency of wireless communication systems. In the wireless communication system, the positions of multiple transceivers follow a uniform distribution, and the performances of spectral and energy efficiency for the proposed TPC scheme are analyzed assuming the Nakagami fading channels. The proposed TPC scheme uses batch normalization to improve spectral and energy efficiency in deep learning based training. Through simulation, we compare the results of the spectral and energy efficiency of the proposed TPC scheme and the conventional one for various area sizes that limit the position range of the transceivers and Nakagami fading factors. Comparing the performance results, we verify that the proposed scheme provides better performance than the conventional one.
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심해에서의 빔 다이버시티를 이용한 수중음향통신 성능 분석
김동현,박희진,김재수,박정수,한주영,Kim, Donghyeon,Park, Heejin,Kim, J. S.,Park, Joung-Soo,Hahn, Joo Young 한국음향학회 2019 한국음향학회지 Vol.38 No.6
Underwater communication performance is degraded by the influence of Inter-Symbol Interference (ISI) due to multipath. Passive time reversal processing is the most effective technique for mitigating multipath, and the diversity combining method can be used to improve its performance. This paper analyzed communication performance using the beam diversity combining method, which combines signals obtained through the beam steering to various angles. Directions of arrival were estimated through the beam-time migration, which, in turn, was estimated from probe signals received by a vertical line array. The performance was analyzed based on the number and type of combinations among the estimated angles. In this paper, the data obtained from the Biomimetic Long range Acoustic Communications 2018 (BLAC18) experiment, which was conducted in the East sea, ~50 km east of Pohang, in October 2018, were used for the analysis. The output Signal to Noise Ratio (SNR) was used as communication indicators.
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음선 기반 블라인드 디컨볼루션의 장거리 심해 환경으로의 적용
김동현,박희진,김재수,한주영,Kim, Donghyeon,Park, Heejin,Kim, J.S.,Hahn, Joo Young 한국음향학회 2022 한국음향학회지 Vol.41 No.2
When the source waveform is unknown, the Green's function can be estimated by Ray-based Blind Deconvolution (RBD) based on the simple array signal processing. In previous papers, RBD was successfully demonstrated using simulation and experiments in shallow water environment. In this paper, we investigate the applicability of RBD for a long-range communication (e.g., 30 km, 60 km, and 90 km) in a deep water environment (1,000 m ~), using experimental data conducted in the east of Pohang, South Korea, in October 2018. Data results are presented to demonstrate Green's function estimation of a communication signal (2.2 kHz ~ 2.9 kHz) using a 16-element, 42-m long vertical array. The results show that the Green's function estimated from RBD is comparable to that of matched filter result. Additional communication performance at a maximum range of 90 km will be also presented.
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CFRP로 보강된 낙엽송 각재적층목 기둥-보 접합부의 모멘트 저항 내력 성능 평가
김동현 ( Donghyeon Kim ),백승엽 ( Seongyeop Baek ),유석훈 ( Seokhoon Yu ),송요진 ( Yojin Song ),이인환 ( Inhwan Lee ),홍순일 ( Soonil Hong ) 한국목재공학회 2021 한국목재공학회 학술발표논문집 Vol.2021 No.1
본 연구에서는 Carbon Fiber Reinforced Plastic(CFRP)로 보강된 낙엽송 각재 적층목 강판삽입형 드리프트핀 접합부의 모멘트 저항 내력 성능을 평가하였다. 각재 적층목은 4개의 소경 각재를 접착하여 1000 mm (L) x 170 (W) x 220 (T)의 크기의 적층목을 제작하었다. TYPE A 시험편은 중앙부위 강판 슬릿의 내부 양면 및 슬릿을 기점으로 좌우 2.5D(D: 드리프트 핀의 직경, 16 mm) 거리에 슬릿 가공 후 220 mm (L) x 110 mm (W) x 1.4 mm (T)의 CFRP sheet를 삽입, 접착 시켜 제작하였다(체적비: 3.6%). TYPE B 시험편은 강판 슬릿의 내부 양면 및 슬릿으로부터 좌우 1.5D 그리고 3D 거리에 CFRP sheet를 보강 시켜 제작하였다.(체적비:5.4%). 모멘트 저항 접합부의 내력 시험은 번형각이 ± 1/600, ± 1/450, ± 1/300, ± 1/200, ± 1/150, ± 1/100, ± 1/75, ± 1/50 rad.에 도달할 때 까지 정·부가력을 각각 3회씩 가하여 실험을 실시하였다. CFRP 보강안한 대조군 시험편의 평균 최대모멘트는 17.40 kN·m, TYPE A는 23.95 kN·m, TYPE B는 26.75 kN·m로 CFRP보강 시험편의 평균 최대모멘트는 CFRP를 보강하지 않은 대조군 대비 각각 37 %, 53% 모멘트 저항 내력이 증가하였다. 대조군, TYPE A, TYPE B 시험편의 평균 항복 모멘트 내력은 각각 7.2, 14.0, 14.6 kN·m였다. 대조군의 파괴형상은 기둥, 보 부재 모두 끝면거리 방향으로 할렬 파단이 발생하였으나, 보강된 시험편은 CFRP보강으로 끝면거리 할렬 파단이 억제 되는 것을 확인하였다.
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