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수중음향통신 시스템의 비트 오류 성능 향상을 위한 등화 모드 선택 방법
김현수,서종필,김재영,김성일,정재학,Kim, Hyeon-Su,Seo, Jong-Pil,Kim, Jae-Young,Kim, Seong-Il,Chung, Jae-Hak 한국음향학회 2012 韓國音響學會誌 Vol.31 No.1
수중음향채널에서 시변 다중경로 전달특성에 의해 발생하는 시변 인접심볼간 간섭을 완화할 수 있는 방법으로 선형 등화와 결정궤환 등화 기법을 사용할 수 있다. 그러나 선형 등화 기법은 간섭성분을 완벽하게 제거하지 못하는 단점이 있고, 결정궤환 등화기는 검출 오류 발생 시 오류 전파가 발생하는 문제를 가지고 있다. 본 논문에서는 이러한 문제점을 개선하기 위해 훈련 시퀀스를 이용하여 등화 모드를 선택하는 기법을 제안한다. 제안된 기법은 훈련시퀀스로부터 산출된 신호 대 잡음비에 따라 등화기법을 선택하여 동작시키는 방법으로 낮은 SNR일 때에는 선형 등화 기법이 적용하여 오류전파를 줄이고, 높은 SNR일 때에는 결정궤환 등화 기법을 적용하여 간섭성분을 제거함으로써 하나의 등화기법을 사용하는 경우보다 오류 성능을 향상시킬 수 있다. 해상실험을 통해 얻은 채널 응답을 이용하여 전산모의실험을 수행한 결과 제안된 기법이 효과적으로 오류 성능이 개선됨을 보였다. The linear and decision-feedback equalization can mitigate time-varying intersymbol interference (ISI) caused by time-varying multipath propagation for underwater acoustic channels. The perfect elimination of interference components, however, is difficult using the linear equalization and the decision feedback equalizer has an error propagation problem. To overcome these shortcomings, this paper proposes an equalizer mode selection method using training sequences. The proposed method selects an equalization mode corresponding to the signal-to-noise ratio (SNR). If the SNR is low, the proposed system operates the linear equalizer for preventing the error propagation and if the SNR is high, the decision feedback equalizer for eliminating the residual ISI. Therefore, the proposed method can improve the error performance compared to the conventional equalizers. The computer simulation shows the proposed method improves the bit error performance using practical underwater channels responses acquired from the sea experiment.
김현수(Kim Hyeon-su) 한국시학회 2011 한국시학연구 Vol.- No.31
Yun, Dong-ju’s 「The First Poem」 is producing a variety of meanings by omitting its meanings and expressing it indirectly. This paper is to understand the meaning of the work, not the intention of the poet, based on the fact that literature is content to exist by itself. The meaning of a work is the real meaning which the work represents through linguistic combination and structure. This poem is divided into two stanzas. The first stanza of 1~8 lines is expressing the poet’s feelings, and the second stanza of 9 lines shows the imaginary scenes of nature. The first stanza is divided into 1~4 lines containing mental distress and 5~8 lines representing love and practice will. The scenes of the second stanza are symbolically representing the heart of the poet who has overcome conflicts and troubles. 「The First Poem」 is a work which has encapsulated the pure heart seeking beautiful and peaceful world with concise and implicative words. In terms of space, this poem is divided into Heaven and Earth, and in terms of conflicts, it shows the process of division and combination of the realistic ego which is tormented in the real world and the essential ego which wishes for the beautiful and peaceful heavenly world. Though the realistic ego is ambivalent and worried about the gap between reality and ideals, it recovers its essential ego through aiming for the heavenly world and pursues the peaceful and pure world which it always longs for inwardly.
GSFM 펄스의 상관도에 기반한 연속 송수신 소나의 신호처리 구간 설정 방법
김현수,김현우,이원오,박송화,이정훈,박규태,Kim, Hyeon-su,Kim, Hyun-woo,Lee, Won-oh,Park, Song-hwa,Lee, Jung-hoon,Park, Gyu-tae 한국음향학회 2021 韓國音響學會誌 Vol.40 No.5
The continuous active sonar technology is effective for detecting and tracking targets because of short target revisiting rate. Generalized Sinusoidal Frequency Modulation (GSFM) pulses suitable for continuous active sonar systems are known to be capable of obtaining high time-bandwidth product while maintaining the orthogonality between pulses. However, it is unknown how to calculate an appropriate length of time to correlate received GSFM pulses in the presence of a target with acceleration. In this paper, we propose a method to calculate the appropriate time length based on the correlation when matching the received signal in the continuous active sonar system using GSFM pulse. The proposed method calculates the correlation according to the acceleration of the target and calculates the signal processing length according to the correlation. It is shown that stable detection performance can be obtained when the signal processing length calculated by the proposed method through the level of the sidelobe is applied.
수중음향채널에서의 시역전 기법을 적용한 양방향 통신 방식의 용량 분석
김현수,권양수,유재호,정재학,김성일,Kim, Hyeon-Su,Kwon, Yang-Soo,Yoo, Jae-Ho,Chung, Jae-Hak,Kim, Seong-Il 한국음향학회 2009 韓國音響學會誌 Vol.28 No.6
본 논문에서는 원거리 수중음향 통신환경에서 중계노드가 사용가능한 센서노드 간의 데이터 교환을 위해 시역전 방법을 적용한 두 단계 양방향 수중 중계노드 통신 방식을 제안한다. 제안된 방법은 기존의 4 단계 중계절차를 2 단계로 줄이기 위해 시역전 기법을 이용한 양방향 통신방법을 적용하였으며 이를 통해 향상된 시스템 통신 용량을 얻는다. 또한 중계노드가 낮은 복잡도로 구현이 가능하기 때문에 효과적으로 전송 거리를 증가시킬 수 있다. 전산모의실험을 통해 제안된 방법이 기존의 방법보다 20 dB의 SNR에서 약 3.2 bps/Hz만큼 향상됨을 보였다. In this paper, we propose a bi-directional communication method applying time reversal technique in underwater acoustic channel in order to exchange data between sensor nodes with an available relay node. The proposed method reduces the conventional 4-step relaying procedure to 2-step and improves the system capacity. Moreover, it increases transmission range efficiently while the relay node can be implemented with low complexity. Simulation results demonstrate that the proposed scheme achieves 3.2 bps/Hz higher capacity than that of the conventional method at SNR 20 dB.
요소 응력을 이용한 겹침 용접부의 피로 강도 평가에 관한 연구
김현수,신상범,김명현,박동환,Kim, Hyeon-Su,Shin, Sang-Beom,Kim, Myung-Hyun,Park, Dong-Hwan 대한용접접합학회 2014 대한용접·접합학회지 Vol.32 No.1
The purpose of this study is to evaluate the applicability of the element stress to establish S-N design curve for the welded lap joint with thin plates below 2mm thickness. In order to do it, the extensive fatigue tests of the welded lap joints with INVAR alloy were performed. With the results, the deign S-N curves for the lap-weld were established by using the reference stresses such as the nominal stress range at the weld throat area, hot spot stress range and element stress range, and compared with regard to the standard deviation. The standard deviation of S-N curves with element stress range was less than that of S-N curves with other reference stresses. In addition, FEA results show the amount of the element stress is less sensitive to mesh size. Based on the results, it can be concluded that the element stress is to be used as the reference stress for the design S-N curves of the welded lap joint.