• 문화기술의 융합
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• 제3권4호
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• pp.191-198
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• 2017

본 논문은 수중의 시간적으로 긴 다중 경로 채널 환경에서 Code Division Multiple Access(CDMA)와 Orthogonal Frequency Division Multiplexing(OFDM)의 전송성능을 비교 분석한다. 이를 위해 서해 정점의 수중 환경 자료를 기반으로 Bellhop을 /통해 수중 다중 경로 채널을 생성한다. 이를 기반으로 한 다양한 수중 채널을 통해 수중 음향 통신방식으로 사용되는 CDMA와 OFDM의 BER 성능을 비교 분석하였다. 실험 결과 CDMA의 경우 수중 채널의 다중 경로 시간이 Spreading Factor(SF)에 의한 시간보다 짧은 경우 OFDM보다 성능이 우수하였지만 채널의 시간 지연이 길어짐에 따라 OFDM이 CDMA 보다 BER 성능이 우수함을 보였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권2호
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• pp.564-582
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• 2015

This paper proposes a novel swarm intelligence optimization method which integrates bacterial foraging optimization (BFO) with quantum computing, called quantum bacterial foraging optimization (QBFO) algorithm. In QBFO, a multi-qubit which can represent a linear superposition of states in search space probabilistically is used to represent a bacterium, so that the quantum bacteria representation has a better characteristic of population diversity. A quantum rotation gate is designed to simulate the chemotactic step for the sake of driving the bacteria toward better solutions. Several tests are conducted based on benchmark functions including multi-peak function to evaluate optimization performance of the proposed algorithm. Numerical results show that the proposed QBFO has more powerful properties in terms of convergence rate, stability and the ability of searching for the global optimal solution than the original BFO and quantum genetic algorithm. Furthermore, we examine the employment of our proposed QBFO for cognitive radio spectrum allocation. The results indicate that the proposed QBFO based spectrum allocation scheme achieves high efficiency of spectrum usage and improves the transmission performance of secondary users, as compared to color sensitive graph coloring algorithm and quantum genetic algorithm.

• 정보통신설비학회논문지
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• 제2권4호
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• pp.17-27
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• 2003

본 논문에서는 IEEE802.11a에서 STBC를 이용하는 시스템에 적합한 채널 추정 기법을 제안하였다. 일반적으로 STTC를 이용하는 OFDM 시스템에 대해 강인한 채널 추정기법이 제안된 바 있으나, 이 방법은 상당한 계산량을 요구한다. 따라서 이 논문에서는 Curve Fitting을 이용하는 채널 추정 기법으로 계산량을 줄이고 채널 추적 성능을 향상시키기 위한 방법이다. 제안된 방법으로 지연확산 도플러 주파수등 여러 그룹의 크기와 수에 따른 성능을 컴퓨터 시뮬레이션에 의해 비교분석하였다. 실험결과 도플러 주파수 편이는 주파수 옵셋과 동일한 영향을 미친다는 사실을 확인하였고, 채널추정 성능이 기존방법보다 0.9dB의 SNR 개선을 가짐을 확인하였다.

• 전기학회논문지
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• 제60권6호
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• pp.1255-1260
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• 2011

In this paper, we study on the reliability of Very High-rate Power Line Communication (VH-PLC) for Smart Grid, so that the resultant data rate is over 400Mbps at a physical layer. Firstly, reviewing the research trend of the PLC, we discuss the required techniques for supporting the Smart Grid. Considering a pre-specification with the value of several parameters, we investigate a multi-carrier modulation technique to overcome limitations of higher rate transmission under power line channel environments. Then, we propose a system specification of the VH-PLC in the sense of enhancing two features. One is resolving the problem of the co-existence of the deployed high-speed PLC according to the published standardization of KS X 4600-1 in Korea. The other is getting better performance on the grid adopting the diverse element techniques, such as multi-carrier modulation, a subcarrier utilization mode, a variable rate LDPC (Low Density Parity Check) code, and a time and frequency diversity technique. Further, a simulation tool, composed of an Event-Driven simulator and a Time-Driven simulator, is developed for the purpose of verifying the system performance and continuously cross-checking the test bench signal of the proposed VH-PLC system.

• 한국멀티미디어학회논문지
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• 제10권12호
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• pp.1632-1644
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• 2007

Wireless Mesh Networks aim to attain large connectivity with minimum performance degradation, as network size is increase. As such, scalability is one of the main characteristics of Wireless Mesh Networks that differentiates it from other wireless networks. This characteristic creates the need for bandwidth efficiency strategies to ensure that network performance does not degrade as the size of the network increase. Several researches have been done to realize mesh networks. However, the researches conducted were mostly focused on a per TCP/IP layer basis. Also, the studies on bandwidth efficiency and bandwidth improvement are usually dealt with as separate issues. This paper aims to simultaneously study bandwidth efficiency and improvement. Aside from optimizing the bandwidth given a fixed capacity, the capacity is also increased using results of physical layer studies. In this paper, the capacity is improved by using the concept of non-overlapping channels for wireless communication. A channel allocation scheme is conceptualized to choose the transmission channel that would optimize the network performance parameters with consideration of chosen Quality of Service (QoS) parameters. Network utility maximization is used to optimize the bandwidth after channel selection. Furthermore, a routing scheme is proposed using the results of the network utilization method and the channel allocation scheme to find the optimal path that would maximize the network gain.

• 수산해양기술연구
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• 제53권1호
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• pp.19-40
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• 2017

A scientific and objective sound exposure criterion for underwater sound damage on fish has been required since there has been many disputes between an underwater sound maker and a fish damage receiver. The existing criteria are still incomplete scientifically owing to a degree of variability of underwater sounds, diversity of fish hearing sensitivity and damage types, etc. This study reviews existing studies on a hearing mechanism of fish species, manmade underwater sound characteristics and sound exposure assessment parameters, and recent sound exposure criteria. A governing equation for damage coverage estimation and damage coverage dependency on sound source level, ambient noise and transmission loss are also reviewed and interpreted based on sound exposure environments. The foreign and Korean (National Environmental Dispute Medication Commission) criteria are reviewed and compared based on scientific aspects. In addition, the deficit and limit of Korean criteria are presented. The objective of this study is to give a direction for related researches and legislation of sound exposure criteria on fish.

• 한국ITS학회 논문지
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• 제8권6호
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• pp.73-81
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• 2009

무선 매체로의 전송은 유선 매체로의 전송에 비해 낮은 신뢰성과 전송의 안정성이라는 단점을 갖는다. 이를 위한 하나의 대안으로 협업 통신의 다이버시티 효과와 채널 코딩 방법을 통한 오류 정정 효과를 사용하고자 한다. 본 문에서는 전송의 신뢰성 향상을 위해 RCPC codes와 Hybrid-ARQ type-2 전송 방식을 사용한 협업 통신 시스템을 제안하고 그에 대한 시뮬레이션을 실시하였다. 그 결과로 기존의 전송에 비해 제안한 시스템이 낮은 BER값을 가져옴을 보였다. 또한 릴레이 노드와 목적지 노드 사이의 채널 상태보다 소스 노드와 릴레이 노드 사이의 채널 상태가 시스템 성능에 더 중요하다는 사실을 확인하였다.

• Journal of information and communication convergence engineering
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• 제6권1호
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• pp.1-5
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• 2008

In this paper, we propose and analyze the AMC (Adaptive Modulation and Coding) system with efficient turbo coded V-BLAST (Vertical-Bell-lab Layered Space-Time) technique. The proposed algorithm adopts extrinsic information from a MAP (Maximum A Posteriori) decoder with iterative decoding as a priori probability in two decoding procedures of V-BLAST scheme; the ordering and the slicing. Also, we consider the AMC system using the conventional turbo coded V-BLAST technique that simply combines the V-BLAST scheme with the turbo coding scheme. And we compare the proposed decoding algorithm to a conventional V-BLAST decoding algorithm and a ML (Maximum Likelihood) decoding algorithm. In addition, we apply a STD (Selection Transmit Diversity) scheme to the systems for better performance improvement. Results indicate that the proposed systems achieve better throughput performance than the conventional systems over the entire SNR range. In terms of transmission rate performance, the suggested system is close in proximity to the conventional system using the ML decoding algorithm.

• Journal of Communications and Networks
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• 제12권2호
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• pp.130-139
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• 2010

Environmental issues and the need to reduce energy consumption for lowering operating costs have pushed power efficiency to become one of the major issues of current research in the field of wireless networks. This paper addresses a number of multiple input multiple output (MIMO) precoding and scheduling techniques across the PHY and MAC layers that can operate under a reduced link budget and collectively improve the transmit power efficiency of a base station, while maintaining the same levels of service. Different MIMO transmission and precoding schemes proposed for LTE, achieving varying degrees of multiuser diversity in both the time, frequency as well as the space domain, are examined. Several fairness-aware resource allocation algorithms are applied to the considered MIMO schemes and a detailed analysis of the tradeoffs between power efficiency and quality of service is presented. This paper explicitly examines the performance of a system serving real-time, VoIP traffic under different traffic loading conditions and transmit power levels. It is demonstrated that by use of efficient scheduling and resource allocation techniques significant savings in terms of consumed energy can be achieved, without compromising QoS.

• 전자공학회논문지
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• 제49권12호
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• pp.20-26
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• 2012

인지 기반 융합 중첩 네트워크 환경 하에서의 시스템의 성능이 중요한 이슈로 떠오르는 가운데 단말기의 기능성이 좋아짐에 따라 스마트한 지능을 기반으로 접속 자원의 효과적 활용에 적합한 개별 이종 네트워크의 특성분석과 특성을 반영하는 시스템 측면의 접속 최적화가 매우 중요하다고 할 수 있다. 본 논문에서는 기지국의 소형화와 다집적화, 가상화, 지능화가 진행되는 가운데 기지국 hotelling과 같은 기지국 집중화를 통한 통합적 최적화가 가능하므로 이에 대응한 이중 가상 셀 시스템의 특성에 대해 살펴보고 활용도 측면의 성능을 분석하고 향후 다뤄져야 할 사항들을 확인하였다.