• 대한수학회보
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• 제51권2호
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• pp.595-612
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• 2014

The spectral collocation method for a second order elliptic boundary value problem on a domain ${\Omega}$ with curved boundaries is studied using the Gordon and Hall transformation which enables us to have a transformed elliptic problem and a square domain S = [0, h] ${\times}$ [0, h], h > 0. The preconditioned system of the spectral collocation approximation based on Legendre-Gauss-Lobatto points by the matrix based on piecewise bilinear finite element discretizations is shown to have the high order accuracy of convergence and the efficiency of the finite element preconditioner.

• 한국산업정보학회논문지
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• 제20권6호
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• pp.1-10
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• 2015

본 논문에서는 음영 지역을 위한 다중 중계기 기반의 주파수 효율적인 OFDMA(orthogonal frequency division multiple access) 전송 시스템을 제안한다. 본 논문에서는 다중 중계기를 통해 확보된 다중 경로에 주파수 공간 블록 부호를 적용하여 음영 지역의 시스템 성능을 향상시킨다. 또한, 주기적 프리픽스 부족으로 인해 발생하는 채널 주기성 손실을 복원하는 과정이 포함된 주기적 프리픽스를 사용하지 않는 OFDMA 시스템을 제안한다. 본 논문에서 제안된 주기적 프리픽스를 사용하지 않는 OFDMA 시스템의 성능이 충분한 주기적 프리픽스를 사용하는 기존 OFDMA 시스템의 성능과 거의 동일하여, 기존 시스템 대비 주파수 효율이 향상되는 것을 실험을 통해서 확인할 수 있다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.576-580
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• 2005

New real-time confocal microscopy using spectral encoding technique and slit confocal aperture is proposed and designed. Spectral encoding technique, which encodes one-dimensional spatial information of a specimen in wavelength, and slit aperture make it possible to obtain two-dimensional lateral image of the specimen simultaneously at standard video rates without expensive scanning units such as polygon mirrors and galvano mirrors. The working principle and the configuration of the system are explained. The variation in axial responses for the simplified model of the system with normalized slit width is numerically analyzed based on the wave optics theory. Slit width that directly affects the depth discrimination of the system is determined by a compromise between axial resolution and signal intensity from the simulation result. On the assumption of the lateral sampling resolution of 50 nm, design variables and governing equations of the system are derived. The system is designed to have the mapping error less than the half pixel size, to be diffraction-limited and to have the maximum illumination efficiency. The designed system has the FOV of $12.8um{\times}9.6um$, the theoretical axial FWHM of 1.1 um and the lateral magnification of-367.8.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권1호
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• pp.350-364
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• 2022

Traditionally, in multi-user multi-carrier systems, the neighboring subband will be gapped by one subcarrier, which is set as guard band to reduce multiple access interference (MAI) between neighboring subbands. The empty subcarrier for guard band will degrade the spectral efficiency of the whole system. In order to enhance the spectral efficiency of multi-user filter bank multiple carrier (FBMC) systems, a new subband allocation method is introduced, in which the neighboring subband is gapped by half subcarrier instead of one subcarrier. Meanwhile, in order to implement the proposed resource allocation scheme, an optimized FBMC prototype filter is designed to decrease the inter-subband interference to the neighboring subband. The detailed simulations about the comparison between the proposed spectrum assignment and traditional FBMC are given, as well as the performance in the different interference scenarios. The simulation results show that the combination of the proposed spectrum assignment scheme and the optimized filter has better performance compared to the traditional scheme. The proposed scheme can be used in the system which serves massive users to get higher spectrum efficiency.

• 한국정보통신학회논문지
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• 제15권10호
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• pp.2113-2120
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• 2011

본 논문에서는 셀 경계지역 사용자의 스펙트럼 효율성 향상을 위하여 3GPP LTE-A (Long-Term Evolution-Advanced) 시스템에서 논의되는 셀 간 협력 전송기법 중 하나인 CoMP (Coordinated Multi-Point) 시스템을 소개하고, 성능 검증을 위해 시스템 레벨 시뮬레이터를 개발한다. 셀 간 협력 전송 시 시스템의 성능 개선 정도를 확인하기 위하여 기존 이동통신 시스템 중 가장 높은 성능을 보이는 3GPP LTE-A 시스템을 참조 시스템으로 선정하여 성능 비교를 수행한다. CoMP 시스템 레벨 시뮬레이션은 널리 사용되고 있는 OPNET을 기반으로 하는데, 셀 간 협력 전송 시스템 설계를 바탕으로 CU (Central Unit), CeNB (CoMP eNodeB), UE (User Equipment), MIMO (Multiple-Input Multiple-Output) 채널 모델 등의 모듈을 구현한다. WINNER 무선 채널 모델 및 ITU (International Telecommunication Union) 네트워크 모델 환경을 통하여 하위 5%의 스펙트럼 효율성을 가지는 셀 가장자리 사용자의 성능을 검증할 때, 3GPP LTE-A 참조 시스템 대비 제안한 CoMP 시스템의 용량이 약 2.5배 정도 증가하였음을 보인다.

• 전자공학회논문지
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• 제51권10호
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• pp.41-44
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• 2014

전이중 무선 통신 시스템은 반이중 통신 시스템에 비해 향상된 대역폭 효율을 얻을 수 있다. 전이중 방식의 다중 사용자 다중 안테나 시스템에서는 단말 간 간섭에 의한 성능 열화 문제가 발생한다. 본 논문에서는 단말 간 간섭 채널의 통계적 정보만을 이용하여 시스템의 대역폭 효율을 최대화하는 하향 링크 전력 할당 기법을 제안한다.

• 한국통신학회논문지
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• 제29권3A호
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• pp.248-256
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• 2004

Woerner는 비동기 트레리스 부호화 DS/COMA (asynchronous treilis-coded DS/CDMA systems, A-TC-CDMA) 시스템에 낮은 상관도의 다중 시퀀스 시그날링인 배직교 시퀀스 (biorthogonal sequence)를 이용함으로써 단일 시퀀스 시그날링인 M-ary PSK에 비해 보다 개선된 시스템 성능을 얻을 수 있음을 보여주었다. 본 논문에서는 최근 기 제안된 다중 시퀀스 시그날링 방식인 OPSM (orthogonal plane sequence modulation)과 배직교 시퀀스를 이용한 비동기 트레리스 부호화 CDMA 시스템 성능을 상호 비교 분석한다. 가입자 수신신호의 상호간섭 랜덤변수의 모멘트를 유도하고 그 결과 배직교 시퀀스 시그날링 방식에 비해 적은 수의 심볼당 시퀀스를 갖는 OPSM(orthogonal plane sequence modulation)이 시퀀스간 낮은 상호상관도 특성을 가짐을 보여준다. 또한 컴퓨터 시뮬레이션을 통하여 다중 시퀀스 시그날링 비동기 트레리스 시스템의 전력 효율 및 스펙트럼 효율을 비교 검증한다.

• Journal of Communications and Networks
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• 제12권5호
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• pp.433-441
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• 2010

Multihop transmission is a promising technique that helps in achieving broader coverage (excellent network connectivity) and preventing the impairment of wireless channels. This paper proposes a cluster-based multihop wireless network that makes use of the advantages of multihop relaying, i.e., path loss gain, and partial relay selection in each hop, i.e., spatial diversity. In this partial relay selection, the node with the maximum instantaneous channel gain will serve as the sender for the next hop. With the proposed protocol, the transmit power and spectral efficiency can be improved over those in the case of direct transmission and conventional multihop transmission. Moreover, at a high signal-to-noise ratio (SNR), the performance of the system with at least two nodes in each cluster is dependent only on the last hop and not on any of the intermediate hops. For a practically feasible decode-and-forward relay strategy, a compact expression for the probability density function of the end-to-end SNR at the destination is derived. This expression is then used to derive closed-form expressions for the outage probability, average symbol error rate, and average bit error rate for M-ary square quadrature amplitude modulation as well as to determine the spectral efficiency of the system. In addition, the probability of SNR gain over direct transmission is investigated for different environments. The mathematical analysis is verified by various simulation results for demonstrating the accuracy of the theoretical approach.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권4호
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• pp.1837-1860
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• 2020

We propose a general framework for studying resource allocation problem and the tradeoff between spectral efficiency (SE) and energy efficiency (EE) for downlink traffic in power domain-non-orthogonal multiple access (PD-NOMA) and device to device (D2D) based heterogeneous cloud radio access networks (H-CRANs) under imperfect channel state information (CSI). The aim is jointly optimize radio remote head (RRH) selection, spectrum allocation and power control, which is formulated as a multi-objective optimization (MOO) problem that can be solved with weighted Tchebycheff method. We propose a low-complexity algorithm to solve user association, spectrum allocation and power coordination separately. We first compute the CSI for RRHs. Then we study allocating the cell users (CUs) and D2D groups to different subchannels by constructing a bipartite graph and Hungrarian algorithm. To solve the power control and EE-SE tradeoff problems, we decompose the target function into two subproblems. Then, we utilize successive convex program approach to lower the computational complexity. Moreover, we use Lagrangian method and KKT conditions to find the global optimum with low complexity, and get a fast convergence by subgradient method. Numerical simulation results demonstrate that by using PD-NOMA technique and H-CRAN with D2D communications, the system gets good EE-SE tradeoff performance.

• Journal of Communications and Networks
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• 제14권3호
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• pp.243-251
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• 2012

Under the power-based capture model, a transmission is successfully received at the destination, even in the presence of other transmissions and background noise, if the received signal-to-interference-plus-noise ratio exceeds a capture threshold. We evaluate the spectral efficiency of simple multi-user channels by combining the basic capture model with a communication-theoretic model. The result is a more refined capture model that incorporates key system design parameters (such as achievable bit rate, target bit error rate, channel bandwidth, and modulation signal constellations) that are absent from the basic capture model. The relationships among these parameters can serve as a tool for optimizing the network performance.