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이상국 ( Lee Sangkug ) 부산연구원 2019 연구보고서 정책연구 Vol.2019 No.0
Despite their contribution to the regional development, railways of Busan, severing its center, are pointed out as the causes of traffic inconvenience, property loss, and urban underdevelopment. Currently, intra-city movement using national rail networks is not competitive due to inconveniences of transit and excessive waiting time. This study is to provide the base line data for the usage of railway facilities to introduce a new type of hybrid railway system (tram-train) that connects national railways, continuously severing center of Busan and persisting the urban underdevelopment, with the urban railways and utilize them. In Western Europe, tram-train contributes to the improvement of transportation service through operation that is familiar to the citizens. Karlsruhe, Mulhouse, and Cádiz are some of the representative cases. A case where additional law is enacted for the operation of the tram-train has not yet been observed in European countries; rather, they are easily adopted into the railroad laws, the tram laws, and the traffic laws. This study proposes three tram-train routes connected to Uam line. The tram-train is also in line with the principle of Busan city to construct a railway-based public transportation system through expansion of railway infrastructure that reduces its finance and cooperates with the nearby cities. Tram-train is an important project in which its inclusion must be considered in the national railroad network plan of the Korean government or the urban rail network plan of Busan city. The suggested routes are as follows. ① Uam Line : 8.50km (Train 3.40km + Tram 5.10km) ② Connecting Uam Line ~ Gyeongbu Line : 42.77km (Train 31.77km + Tram 11.0km) ③ Connecting Uam Line ~ Gaya Line ~ Bujeon-Masan Line ~ Busan-New Port Line : 43.06km (Train 36.49km + Tram 6.57km) ④ Connecting Donghae Line ~ Jeonggwan Line : 17.07km (Train 5.10km + Tram 12.60km) It is meaningful that railway infrastructure policy is a new approach to the utilization of public railway in the urban railway system of Busan metropolitan planning area. Tram-train can be utilized as an alternative for the expansion of railway infrastructure, utilizing the existing railways to improve the transportation service, considering that a tremendous amount of investment into the railway infrastructure must be accompanied in order to improve the level of service.
최강훈,황인성,이상국,최지웅,Choi, Kang-Hoon,Hwang, In-Seong,Lee, Sangkug,Choi, Jee Woong 한국음향학회 2022 韓國音響學會誌 Vol.41 No.2
Underwater acoustic wave in shallow water is propagated through multipath that has a large delay spread causing Inter-Symbol Interference (ISI) and these characteristics deteriorate the performance in the communication system. In order to analyze the communication performance and investigate the correlation with multipath delay spread in a reverberant environment, an underwater acoustic communication experiment using Binary Phase-Shift Keying (BPSK) signals with symbol rates from 100 sym/s to 8000 sym/s was conducted in a 5 × 5 × 5 m<sup>3</sup> water tank. The acoustic channels in a well-controlled tank environment had the characteristics of dense multipath delay spread due to multiple reflections from the interfaces and walls within the tank and showed the maximum excess delay of 40 ms or less, and the Root Mean Squared (RMS) delay spread of 8 ms or less. In this paper, the performances of Bit Error Rate (BER) and output Signal-to-Noise Ratio (SNR) were analyzed using four types of communication demodulation techniques. And the parameter, Symbol interval to Delay spread Ratio in reverberant environment (SDR<sub>rev</sub>), which is the ratio of symbol interval to RMS delay spread in the reverberant environment is defined. Finally, the SDR<sub>rev</sub> was compared to the BER and the output SNR. The results present the reference symbol rate in which high communication performance can be guaranteed.
돌고래 휘슬을 이용한 지연시간 기반 생체 모방 통신 기법
이호준,안종민,김용철,이상국,정재학,Lee, Hojun,Ahn, Jongmin,Kim, Yongcheol,Lee, Sangkug,Chung, Jaehak 한국음향학회 2019 韓國音響學會誌 Vol.38 No.5
In this paper, we propose a biomimetic communication method using a dolphin whistle to covertly transmit the communication signal. A conventional CSS (Chirp Spread Spectrum) modulation technique divides dolphin whistle into several slots and modulates with up and down chirp signals. That causes the time-frequency characteristic difference between the original dolphin whistle and the camouflage performance is degraded. In this paper, we propose a delay based modulation scheme to eliminate distortions. The simulation results show that the bit error rate of the proposed method is better performance than that of the conventional CSS modulation method by about 3.5 dB to 8 dB. And the camouflage performance that evaluated through the cross correlation in the time-frequency domain is also better than that of the CSS modulation method. 본 논문에서는 은밀하게 통신 신호를 전송하기 위해 돌고래 휘슬음을 모방한 통신 기법을 제안하였다. 기존의 CSS(Chirp Spread Spectrum) 변조 기법은 돌고래 휘슬음을 정해진 시간 단위에 따라 여러 슬롯으로 나누고 각 슬롯에 상향 및 하향 처프 신호를 통해 변조하는 기법이다. 이에 따라 본래의 돌고래 휘슬음과의 시간-주파수 특성 차이가 발생하게 되어 모방 성능이 저하된다. 본 논문에서는 이러한 왜곡을 제거하기 위해 지연 시간을 기반으로 하는 변조 기법을 제안하였다. 전산 모의실험 결과 기존의 CSS 변조 기법에 비해 제안 방법의 비트오류율 성능이 약 3.5 dB ~ 8 dB 우수하였으며 시간-주파수 영역에서의 상호 상관도를 통한 모방 성능 평가에서도 CSS 변조 기법에 비해 우수한 것을 보였다.
수중 센서 네트워크에서 계층적 주소를 기반으로 한 TCP ACK 병합 기법
신동승(Dongseung Shin),이성원(Sungwon Lee),이상국(Sangkug Lee),김동균(Dongkyun Kim) 한국정보과학회 2013 정보과학회논문지 : 정보통신 Vol.40 No.2
무선 센서 네트워크에서 통신 프로토콜을 이용하여 데이터를 전송할 때 종단간 전송신뢰성(end-to-end reliability) 보장이 필요한 경우가 있다. 종단간 신뢰성을 향상시키는 방법 중의 하나인 TCP는 ACK 메시지를 이용하여 수신측에서 데이터를 확실히 수신했음을 알림으로써 신뢰성을 보장한다. 하지만 ACK 메시지는 일반적으로 송신측에서 보내려고 하는 데이터보다 아주 작은 크기를 가지기 때문에 멀티홉 방식으로 통신하는 무선 센서 네트워크에서는 MAC과 같은 하위 계층의 프로토콜에서 많은 전송 오버헤드가 발생한다. 특히 수중 센서 네트워크에서는 지상과 달리 음파를 사용하여 통신하기 때문에 낮은 대역폭과 높은 전파지연, 높은 에러율 등의 통신 제약을 가지고 있어 ACK 전송에 따른 대역폭 낭비와 전송 성능 감소가 심각한 편이다. 본 논문에서는 노드에 계층적으로 할당된 주소를 이용하여 TCP ACK 메시지를 병합하여 전송하는 기법을 제안한다. 네트워크 시뮬레이션 기반의 실험을 통해 제안된 기법이 TCP와 비교하여 5~20%의 전송성능 향상과 18~27%의 ACK 전송 횟수를 감소시킴을 확인하였다. In data communication protocols for wireless sensor networks, an end-to-end reliability from a source node to destination node should be guaranteed. TCP, as one of the most reliable communication protocol, guarantees the reliability by notifying to the source node with ACK messages after the proper data reception at the designation node. In multi-hop wireless sensor networks, however, because the ACK message size from the designation node is usually much smaller than the data packet size from the source node, transmissions of the ACK message causes an overhead at underlying communication layers and hampers the transmission of data packets. Especially in underwater sensor network using an acoustic wave, the ACK message transmission will increase latency on the network which is already suffering by its inherent performance bottlenecks, such as low bandwidth, long propagation time and high bit error rate. Thus, to solve this problem, we propose a TCP ACK aggregation method, which aggregates several ACK messages into one aggregated-ACK message and transmits it to source nodes. Through experiments based on network simulator, we confirms that the proposed method shows 5~20% percent improvement in the transmission performance and 18~27% reduction in the number of ACK transmission compared to TCP.