• 한국인터넷방송통신학회논문지
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• 제10권6호
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• pp.263-268
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• 2010

본 논문에서는 802.11n WLAN 시스템에서 우수한 오류성능을 유지하고 시스템 용량을 개선하기 위해 순환 지연 다이버시티와 블록 대각화 프리코딩 기법을 적용한 다중 사용자 MIMO OFDM 시스템을 제안하였다. 순환 지연 다이버시티(CDD : Cyclic Delay Diversity) 기법은 주파수 다이버시티를 이용하여 OFDM 시스템의 성능을 향상시키는 기법이다. 또한 블록 대각화 프리코딩 기법은 다중 사용자 MIMO 채널 환경에서 만들어진 여러 거지 프리코딩 기법 중 하나로 특이값 분해를 이용하여 zero-forcing을 하는 간단한 방법으로 구성되어 있다. 모의실험 결과를 통해 본 논문에서 제안하는 방법이 기존의 프리코딩을 사용하지 않는 CDD MIMO-OFDM 시스템에 비하여 높은 시스템 용량 성능을 보임을 확인할 수 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권10호
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• pp.4738-4758
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• 2017

Resource allocation plays a crucial role in multiuser multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) systems to improve overall system performance. While previously proposed resource allocation algorithms are mainly designed from the point of view of the information-theoretic, we formulate the resource allocation problem as an average bit error rate (BER) minimization problem subject to a total power constraint when considering employing realistic MIMO detection techniques. Subsequently, we derive the optimal subcarrier and power allocation algorithms for three types of well-known MIMO detectors, including the maximum likelihood (ML) detector, linear detectors, and successive interference cancellation (SIC) detectors. To reduce the complexity, we also propose a two-step suboptimal algorithm that separates subcarrier and power allocation for each detector. We also analyze the diversity gain of the proposed suboptimal algorithms for various MIMO detectors. Simulation results confirm that the proposed suboptimal algorithm for each detector can achieve a comparable performance with the optimal allocation with a much lower complexity. Moreover, it is shown that the suboptimal algorithms perform better than the conventional algorithms that are known in the literature.

• 한국통신학회논문지
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• 제35권11A호
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• pp.1027-1037
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• 2010

본 논문에서는 블록 대각화 프리코딩 기법을 사용하는 다중 사용자 MIMO-OFDM 하향링크 시스템에서 전체시스템의 복잡도와 계산양을 감소시키기 위한 선형 보간법 기반 블록 대각화 프리코딩 근사화 기법을 제안한다. 일반적인 블록 대각화 프리코팅 기법을 다중 사용자 MIMO-OFDM 시스템에 그대로 적용할 경우 계산양이 부반송파의 수에 비례하여 증가하는 단점이 존재한다. 제안하는 선형 보간법 기반 블록 대각화 프리코딩 근사화 기법은 시스템의 복잡도와 계산양을 감소시키기 위하여 선형 보간법을 프리코딩 행렬의 근사화에 사용하여 성능을 최대한 유지하면서 계산양을 매우 크게 감소시킬 수 있다. 본 논문에서 제안된 선형 보간법 기반 블록 다각화 프리코딩 근사화 기법을 이용하여 시스템의 계산양을 매우 감소시킬 수 있음을 모의실험을 통해 증명했다.

• ETRI Journal
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• 제26권6호
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• pp.565-574
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• 2004

Differential unitary space-time modulation (DUSTM) has emerged as a promising technique to obtain spatial diversity without intractable channel estimation. This paper presents a study of the application of DUSTM on multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems with frequency-selective fading channels. From the view of a correlation analysis between subcarriers of OFDM, we obtain the maximum achievable diversity of DUSTM on MIMO-OFDM systems. Moreover, an efficient implementation strategy based on subcarrier reconstruction is proposed, which transmits all the signals of one signal matrix in one OFDM transmission and performs differential processing between two adjacent OFDM blocks. The proposed method is capable of obtaining both spatial and multipath diversity while reducing the effect of time variation of channels to a minimum. The performance improvement is confirmed by simulation results.

• 한국전자파학회논문지
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• 제16권9호
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• pp.855-861
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• 2005

DS-CDMA 다중 안테나 시스템에서 순방향 링크의 다중화를 위한 2차원 직교 가변 확산 부호를 제시하였다. 다중 사용자 환경 하에서의 AWGN 및 레일라이 페이딩 MIMO 채널을 위한 비트 오류율 성능을 평가하였다. 분석 결과로부터 제안 기법에 의한 유연한 부호율과 낮은 최대 상관값을 실현할 수 있음을 확인하였다.

• JSTS:Journal of Semiconductor Technology and Science
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• 제10권3호
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• pp.185-192
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• 2010

This paper presents a hardware-efficient auto-correlation scheme for the synchronization of MIMO-OFDM based wireless local area network (WLAN) systems, such as IEEE 802.11n. Carrier frequency offset (CFO) estimation for the frequency synchronization requires high complexity auto-correlation operations of many training symbols. In order to reduce the hardware complexity of the MIMO-OFDM synchronization, we propose an efficient correlation scheme based on time-multiplexing technique and the use of reduced samples while preserving the performance. Compared to a conventional architecture, the proposed architecture requires only 27% logic gates and 22% power consumption with acceptable BER performance loss.

• Journal of the Optical Society of Korea
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• 제19권1호
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• pp.74-79
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• 2015

A novel color clustered optical RGB multiple-input multiple-output (MIMO) system is presented. As visible light can be divided into three primary regions of red, green and blue, data can be modulated and transmitted separately using these three color clusters. Each color cluster comprised of 30 RGB LEDs is modulated using on-off-keying (OOK), and selection combining is performed at the receiver, producing a diversity effect within that color cluster. The simulations demonstrate that the proposed RGB MIMO VLC system provides high performance via a relatively simple design of MIMO. Moreover, the proposed system ensures sufficient illumination from LEDs and offers extended distance if more LEDs are applied.

• 한국통신학회논문지
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• 제30권7A호
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• pp.628-638
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• 2005

The analysis of maximum diversity order and coding gain for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems over time-and frequency-selective (or doubly-selective) channels is addressed in this paper. A novel channel time-space correlation function is developed given the spatially correlated doubly-selective Rayleigh fading channel model. Based on this channel-model assumption, the upper-bound of pairwise error probability (PEP) for MIMO-OFDM systems is derived under the maximum likelihood (ML) detection. For a certain space-frequency code, we quantify the maximum diversity order and deduce the expression of coding gain. In this wort the impact of channel time selectivity is especially studied and a new definition of time diversity is illustrated correspondingly

• ETRI Journal
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• 제40권5호
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• pp.592-603
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• 2018

In order to obtain better target identification performance, an efficient waveform design method with high range resolution and low sidelobe level for orthogonal frequency division multiplexing (OFDM) multiple-input multiple-output (MIMO) radar is proposed in this paper. First, the wideband CP-based OFDM signal is transmitted on each antenna to guarantee large bandwidth and high range resolution. Next, a complex orthogonal design (COD) is utilized to achieve code domain orthogonality among antennas, so that the spatial diversity can be obtained in MIMO radar, and only the range sidelobe on the first antenna needs suppressing. Furthermore, sidelobe suppression is expressed as an optimization problem. The integrated sidelobe level (ISL) is adopted to construct the objective function, which is solved using the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm. The numerical results demonstrate the superiority in performance (high resolution, strict orthogonality, and low sidelobe level) of the proposed method compared to existing algorithms.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2006년도 하계종합학술대회
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• pp.19-20
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• 2006

In this paper, to reduce uplink feedback information for the beam weight and simultaneously maintaining the performance, we propose a MIMO-OFDM (Multi Input Multi Output-Orthogonal Frequency Division Multiplexing) system based on beamforming with antenna selection. In the proposed system, to perform the beamforming with more useful transmit antennas, the optimal combination of transmit antennas with maximum MRT (Maximum Ratio Transmission) beamforming gain is selected. Simulation results reveal that the proposed MIMO-OFDM system adopting the beamforming with antenna selection can reduce the feedback information for the beam weights as compared to the system using all the transmit antennas without serious degradation of system performance.