• 한국전자파학회논문지
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• 제28권6호
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• pp.444-451
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• 2017

본 논문에서는 고속 데이터 송수신을 위해 2차원 iDFT(inverse Discrete Fourier Transform) 및 DFT(Discrete Fourier Transform) 연산을 이용하여 Delay-Doppler 스프레딩 영향을 고속 수신 처리하는 OTFS(Orthogonal Time Frequency Space) 변조 시스템과 OTFS-MIMO(Multiple Input Multiple Output) 시스템을 평가하고 분석한다. 특히 OTFS 변조를 사용하는 MIMO 시스템은 높은 Doppler 효과가 존재하는 채널에서도 시스템의 용량 저하가 거의 없이 모든 데이터 스트림을 전송할 수 있다. 시뮬레이션 결과, $1{\times}1$ OTFS 변조 시스템의 전송률은 $2{\times}2$ OTFS-MIMO 시스템에서 한 스트림의 전송률과 유사함을 확인할 수 있다. 즉, $2{\times}2$ OTFS-MIMO 시스템은 높은 Delay-Doppler 영향이 존재하는 환경에서도 $1{\times}1$ OTFS 변조 시스템과 비교하여 거의 2배의 전송률을 확보할 수 있음을 확인할 수 있다.

• 한국통신학회논문지
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• 제29권2C호
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• pp.206-212
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• 2004

본 논문에서는 다중 경로 페이딩 환경에서 고속 데이터 전송에 적합한 STF(Space-Time-Frequency) coded OFDM(Orthogonal Frequency Division Multiplexing) 전송 기법을 제안한다. 2개의 안테나를 통해 신호를 전송함으로써 전송 다이버시티 특성을 이용하는 기법으로 STBC(Space Time Block Coding) 기법이 개발되었으며 이를 OFDM에 적용한 기법으로 ST-OFDM(Space-Time Block Coded OFDM)과 SF-OFDM(Space-Frequency Block Coded OFDM) 전송 기법 등이 제안되었다. 본 논문에서는 시간과 공간, 그리고 주파수 영역에서 부호화를 수행하는 STF-OFDM 전송 기법을 제안한다. 본 논문에서 제시하는 STF-OFDM 전송 기법은 기존의 ST-OFDM 전송 기법에서 주파수 다이버시티 효과를 이용함으로써 ST-OFDM의 성능을 향상시키는 방식이다.

• Structural Engineering and Mechanics
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• 제35권2호
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• pp.175-190
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• 2010

One of the intractable problems in multiresolution structural analysis is the decoupling computation between scales, which can be realized by the operator-orthogonal wavelets based on the lifting scheme. The multiresolution finite element space is described and the formulation of multiresolution finite element models for structural problems is discussed. Various operator-orthogonal wavelets are constructed by the lifting scheme according to the operators of multiresolution finite element models. A dynamic multiresolution algorithm using operator-orthogonal wavelets is proposed to solve structural problems. Numerical examples demonstrate that the lifting scheme is a flexible and efficient tool to construct operator-orthogonal wavelets for multiresolution structural analysis with high convergence rate.

• 한국통신학회논문지
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• 제32권9A호
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• pp.871-877
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• 2007

본 논문은 다중 송신 안테나를 사용하는 직교 주파수 분할 다중 반송파(OFDM: orthogonal frequency division multiplexing) 시스템에서 윈도윙 기법을 이용하여 송신 다이버시티 효과를 얻는 새로운 기법을 제안한다. 제안된 기법은 윈도우 함수의 형태에 따라 송신 다이버시티 효과가 달라지며 송신 다이버시티를 최대화하기 위한 윈도우 함수의 조건을 제시한다. 제안된 기법은 윈도우 함수의 형태에 따라 순환 지연 다이버시티 (CDD: cyclic delay diversity) 기법, 직교 송신 다이버시티(OTD: orthogonal transmit diversity) 기법, 주파수 스위치 송신 다이버시티(FSTD: frequency switched transmit diversity) 기법을 일반화한 기법으로 해석될 수 있다.

• 전기학회논문지P
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• 제65권2호
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• pp.136-141
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• 2016

This paper proposes an alternate time-switched multiplexed space-time block coding technique for orthogonal frequency division modulation systems. The traditional multiplexed space-time block coding technique can provide more data rate owing to multiple transmit and receive technique, which causes a lot of hardware burden. Alternate time-switched scheme of transmitting time-domain zeros can reduce this hardware burden by half with time-domain switches only. Simulation results show that alternate time-switched scheme has almost same performance with half of baseband and RF modules in comparison with a multiplexed space-time block coding for orthogonal frequency division modulation systems with twice repetitive transmission.

• 한국통신학회논문지
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• 제33권12C호
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• pp.1062-1067
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• 2008

ABBA codes, a class of quasi-orthognal space-time block codes (QoSTBC) proposed by Tirkkonen and others, allow full rate and a fast maximum likelihood (ML) decoding, but do not have full diversity. In this paper, a linear complex precoder is proposed for ABBA codes to achieve full rate and full diversity. Moreover, the same diversity produce as that of orthogonal space-time block code with linear complex precoder (OSTBC-LCP) is achieved. Meanwhile, the size of the linear complex precoder can be reduced by half without affecting performance, which means the same complexity of decoding as that of the conventional ABBA code is guaranteed.

• 대한수학회지
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• 제58권6호
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• pp.1485-1500
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• 2021

A curve is rectifying if it lies on a moving hyperplane orthogonal to its curvature vector. In this work, we extend the main result of [Chen 2017, Tamkang J. Math. 48, 209] to any space dimension: we prove that rectifying curves are geodesics on hypercones. We later use this association to characterize rectifying curves that are also slant helices in three-dimensional space as geodesics of circular cones. In addition, we consider curves that lie on a moving hyperplane normal to (i) one of the normal vector fields of the Frenet frame and to (ii) a rotation minimizing vector field along the curve. The former class is characterized in terms of the constancy of a certain vector field normal to the curve, while the latter contains spherical and plane curves. Finally, we establish a formal mapping between rectifying curves in an (m + 2)-dimensional space and spherical curves in an (m + 1)-dimensional space.

• Journal of information and communication convergence engineering
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• 제20권1호
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• pp.1-7
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• 2022

Herein, a new space-time block coding technique is proposed for a MIMO 2 × 2 multiple-input multiple output (MIMO) system to minimize the bit error rate (BER) in Rayleigh fading channels with reduced decoding complexity using ZF and MMSE linear detection techniques. The main objective is to improve the service quality of wireless communication systems and optimize the number of antennas used in base stations and terminals. The idea is to exploit the correlation product technique between both information symbols to transmit per space-time block code and their own orthogonal Walsh-Hadamard sequences to ensure orthogonality between both symbol vectors and create a full-rate orthogonal STBC code. Using 16 quadrature amplitude modulation and the quasi-static Rayleigh channel model in the MATLAB environment, the simulation results show that the proposed space-time block code performs better than the Alamouti code in terms of BER performance in the 2 × 2 MIMO system for both cases of linear decoding ZF and MMSE.

• 한국자동차공학회논문집
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• 제14권4호
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• pp.123-131
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• 2006

The majority of pedestrian fatalities and injuries are caused by vehicle-pedestrian accidents. Recently, it has been recognized as a serious problem. Injuries of occupants in a vehicle have been decreased considerably. However, efforts for protection of pedestrians are still insufficient. These days, many advanced industries are striving for a better protection of pedestrians by using an active hood lift system, rather than reforming the existing structure. In this research, the active hood lift system is designed to enhance the performance for protection. The active hood lift system is analyzed by using the nonlinear finite element method. An optimization problem is formulated by incorporation of the analysis results. Orthogonal arrays are utilized to solve the formulated problem. An iterative optimization algothrithm using orthogonal arrays is utilized for design in the discrete space. It is found that the method can remarkably decrease the number of function evaluations.

• 한국통신학회논문지
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• 제35권5C호
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• pp.415-422
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• 2010

본 논문에서는 주파수 비선택성이고 준정적인 동일 분포 독립 Nakagami-m 페이딩 채널에서 GLCODs(Generalized Linear Complex Orthogonal Designs)와 GCIODs(Generalized Coordinate Interleaved Orthogonal Designs)로 얻은 STBCs(Space-Time Block Codes)의 에르고딕 용량을 Meijer의 G함수로 표현되는 닫힌꼴로 유도한다. 유도된 해석적 결과는 Monte-Carlo 모의실험 결과와 매우 잘 일치함을 보였다. 그러므로 대규모 Monte-Carlo 모의실험 없이 다양한 안테나 구성과 상이한 채널환경에서 GLCODs와 GCIODs로 얻은 STBCs의 에르고딕 용량 성능을 분석하고 예측하는 유용한 기법이 제안되었다고 할 수 있다. 마지막에는 유도된 식의 정확도를 입증하는 수치적인 결과들을 제시한다.