• 제어로봇시스템학회논문지
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• 제21권11호
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• pp.1076-1080
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• 2015

An inventory control system was developed for a distribution system consisting of a single multiproduct warehouse serving a set of customers and purchasing products from multiple vendors. Purchase orders requesting multiple products are delivered to the warehouse in a process. The receipt of customer orders by the warehouse proceeded in order intervals and in order quantities that are subject to random fluctuations. The objective of warehouse operation is to minimize the total cost while maintaining inventory levels within the warehouse capacity by adjusting the purchase order intervals and quantities. An adaptive model predictive control algorithm was developed using a periodic square wave model to represent the material flows. The adaptive concept incorporated a stabilized minimum variance control-type input calculation coupled with input/output stream parameter predictions. The effectiveness of the scheme was demonstrated using simulations.

• 한국경영과학회:학술대회논문집
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• 대한산업공학회/한국경영과학회 2006년도 춘계공동학술대회 논문집
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• pp.1707-1714
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• 2006

In order to enhance sustainable war fighting capabilities, it is important to maintain a good ammunition support system. In this paper, we evaluate the performance of Ammunition companies using Imprecise Data Envelopment Analysis (IDEA)-BCC and IDEA-Additive model, which can deal with imprecise data in DEA. In order to select a list of input and output variables, we used a multiple regression analysis. We could choose input variables that have significant effects on the output performance with stepwise regression model. From the regression analysis, the number of soldiers, officers, and ammunition warehouses were selected as the input variables. Seven out of sixteen Ammunition companies were found to be inefficient by the IDEA-BCC model. And using IDEA-Additive model, we could identify the input excess and the output shortfall in reaching at a point on the efficiency frontier.

• 한국정보통신학회논문지
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• 제13권10호
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• pp.2197-2204
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• 2009

본 논문에서는 다중입력 다중출력 (Multiple Input Multiple Output: MIMO) 시스템에서 Maximum Likelihood (ML) 수신기와 같은 성능을 가지지만 복잡도가 낮은 Sphere Decoding (SD) 알고리즘에 대해 분석하고 그 성능을 평가한다. 각각의 송신 안테나에서 채널로 전송되는 독립적인 신호는 QPSK 와 16QAM 방식을 사용하여 변조되며, 채널은 산란이 활발하게 일어나는 레일리 (Rayleigh) 평탄 페이딩 채널로 가정한다. 수신기에서 수신된 신호는 Fincke & Pohst SD 알고리즘에 의해 각 송신 안테나로부터의 독립적인 신호로 검파되며, 그 성능이 ZF (Zero Forcing), MMSE (Minimum Mean Square Error), SIC (Successive Interference Cancelation), 그리고 ML 수신기의 성능과 비교되었다. 추가적으로 복잡도를 줄이기 위해 개선된 형태인 Viterbo & Boutros SD 알고리즘을 이용하여 검파된 신호의 BER 성능과 부동 소수점 연산량(Floating Point Operations: FLOPS)이 각각 비교 분석되었다.

• ETRI Journal
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• 제45권2호
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• pp.213-225
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• 2023

Physical layer security (PLS) can improve the security of both terrestrial and nonterrestrial wireless communication networks. This study proposes a simplified framework for nonterrestrial cyclic prefixed orthogonal variable spreading factor (OVSF)-encoded multiple-input and multiple-output nonorthogonal multiple access (NOMA) systems to ensure complete network security. Various useful methods are implemented, where both improved sine map and multiple parameter-weighted-type fractional Fourier transform encryption schemes are combined to investigate the effects of hybrid PLS. In addition, OVSF coding with power domain NOMA for multi-user interference reduction and peak-toaverage power ratio (PAPR) reduction is introduced. The performance of $\frac{1}{2}$-rated convolutional, turbo, and repeat and accumulate channel coding with regularized zero-forcing signal detection for forward error correction and improved bit error rate (BER) are also investigated. Simulation results ratify the pertinence of the proposed system in terms of PLS and BER performance improvement with reasonable PAPR.

• 한국통신학회논문지
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• 제33권2A호
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• pp.121-129
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• 2008

본 논문은 ECMA(European Computer Manufacturers Association)의 표준인 MB-OFDM (MultiBand-Orthogonal Frequency Division Multiplexing) UWB(Ultra Wide-Band) 시스템에서 SISO(Single Input Single Output) 성능을 유지하면서 데이터 전송률을 2배로 올리기 위한 공간 다중화 MIMO(Multiple Input Multiple Output) 수신기 구조의 성능을 비교, 분석하였다. 이를 위해 송신단은2개의 안테나를 가지는 수평 부호화 방식과 대각 부호화 방식을 사용하였으며 수신단은 2, 3개 안테나에 대한 다양한 공간다중화 수신기 방식을 고려하였다. 다양한 공간 다중화 수신단 구조의 연산 복잡도 비교와 전산 모의 실험을 통해 $2{\times}2$ 구조의 MML 방법 또는 $\2{times}3$ 구조의 ZF 방법이 SISO 성능을 열화시키지 않고 전송률을 높이는 MIMO MB-OFDM의 간단한 수신단 구조임을 확인하였다.

• 디지털산업정보학회논문지
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• 제7권3호
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• pp.55-61
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• 2011

This paper presents an implementation of Lattice Reduction (LR)-aided detector for Multiple-Input Multiple-Output (MIMO) system using Graphics Processing Unit (GPU). GPU is a parallel processor which has a number of Arithmetic Logic Units (ALUs), thus, it can minimize the operation time of LR algorithm through the parallelization using multiple threads in the GPU. Through the implemented LR-aided detector, we verify that the LR-aided detector operates a lot faster than Maximum Likelihood (ML) detector. The implemented LR-aided detector has been applied to WiMAX system to show the feasibility of its real-time processing. In addition, we demonstrate that the processing time can be reduced at the cost of 3dB SNR loss by limiting the repeating loop in Lenstra-Lenstra-Lovasz (LLL) algorithm which is frequently used in LR-aided detector.

• Journal of Communications and Networks
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• 제17권3호
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• pp.241-246
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• 2015

In this paper, we consider a relaying system which employs a single relay in a wireless network with distributed sources and destinations. Here, all source, destination, and relay nodes are equipped with multiple antennas. For amplify-and-forward relay systems, we confirm the achievable sum rate through a joint multiple source precoders and a single relay filter design. To this end, we propose a new linear processing scheme in terms of maximizing the sum rate performance by applying a blockwise relaying method combined with geometric programming techniques. By allowing the global channel knowledge at the source nodes, we show that this joint design problem is formulated as a standard geometric program, which can guarantees a global optimal value under the modified sum rate criterion. Simulation results show that the proposed blockwise relaying scheme with the joint power allocation method provides substantial sum rate gain compared to the conventional schemes.

• Journal of Communications and Networks
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• 제13권5호
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• pp.463-471
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• 2011

Cooperative communications using relays in wireless networks have similar effects of multiple-input and multiple-output without the need of multiple antennas at each node. To implement cooperation into a system, efficient protocols are desired. In IEEE 802.11 families such as a/b/g, mobile stations can automatically adjust transmission rates according to channel conditions. However throughput performance degradation is observed by low-rate stations in multi-rate circumstances resulting in so-called performance anomaly. In this paper, we propose active relay-based cooperative medium access control (AR-CMAC) protocol, in which active relays desiring to transmit their own data for cooperation participate in relaying, and it is designed to increase throughput as a solution to performance anomaly. We have analyzed the performance of the simplified AR-CMAC using an embedded Markov chain model to demonstrate the gain of AR-CMAC and to verify it with our simulations. Simulations in an infrastructure network with an IEEE 802.11b/g access point show noticeable improvement than the legacy schemes.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2007년도 학술대회
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• pp.46-49
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• 2007

Multiple Antenna Technologies such as Multiple-Input Multiple-Output (MIMO) and Beamforming provide the increase of channel capacity and the reliability of wireless link. To obtain these advantages, WiBro, Mobile WiMAX and $4^{th}$ Generation System are employing multiple antenna technologies. There exist, however, many technical issues in considering the application of the technologies or the providing of services using them. In this paper, various technical topics are discussed and simple solutions are proposed. Beamforming has several technical issues which include coverage imbalance, difficulties in providing Multicast-Broadcast Service (MBS). In Addition, network planning is a critical point from a cell extension and initial network entry point of view. In case of MIMO, network deployment is discussed in that cellular data network such as WiBro has many repeaters. MIMO mode selection for maximizing the cell capacity is also covered.

• 한국통신학회논문지
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• 제33권12A호
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• pp.1209-1216
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• 2008

무선통신 시스템에 있어서 스펙트럼 효율성과 전송속도의 극대화를 위해 MIMO(Multiple Input Multiple Output) 기술을 시스템에 적용하는 노련이 계속되고 있다. 최근 대두되고 있는 WiMAX와 LTE는 OFDM 기반 기술로서 CDMA보다 MIMO기술을 적용하기 쉽다는 장점에 의해 MIMO 기술을 기본으로 채택하고 있다. 하향 링크에서는 STC(Space Time Coding) 방식과 SM(Spatial Multiplexing) 방식을 사용하여 MIMO 방식을 기본 기술로 적용하였으며 상향링크에서는 C-MIMO(Collaborative MIMO) 기술이 사용된다. 특히, 상향링크는 양방향 데이터 통신을 활용한 다양한 신규 서비스가 제안되고 있어 전송 성능을 개선시킬 수 있는 C-MIMO의 성능향상이 기술 쟁점이 되고 있다. 본 논문에서는 C-MIMO 성능 향상을 위하여 기존에 사용되고 있는 신호간 직교성(OF: Orthogonal Factor)의 성질을 이용하여 단말 조합을 선택하는 방식(DPS: Determinant Pairing Scheduling)과 신호간 직교성을 사용하지 않고 단말 조합을 선택하는 방식(RPS: Random Pairing Scheduling)을 분석하였다. 또한 DPS와 RPS 방식을 보완한 새로운 알고리즘을 제안 하여 스펙트럼 효율을 높이는 방법을 고안하였다. 결과에 의하면 새로운 알고리즘을 통하여 RPS 대비 $2{\sim}3dB$ 이득을 보았으며 DPS에 비하여 현격하게 복잡도를 감소 시켰다.