• International Journal of Computer Science & Network Security
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• v.23 no.9
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• pp.8-16
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• 2023

In Japan, high-speed ground transportation service using linear motors at speeds of 500 km/h is scheduled to begin in 2027. To accommodate 5G services in trains, a subcarrier spacing frequency of 30 kHz will be used instead of the typical 15 kHz subcarrier spacing to mitigate Doppler effects in such high-speed transport. Furthermore, to increase the cell size of the 5G mobile system, multiple base station antennas will transmit identical downlink (DL) signals to form an expanded cell size along the train rails. In this situation, the forward and backward antenna signals are Doppler-shifted in opposite directions, respectively, so the receiver in the train may suffer from estimating the exact Channel Transfer Function (CTF) for demodulation. In a previously published paper, we proposed a channel estimator based on Delay and Doppler Profiler (DDP) in a 5G SISO (Single Input Single Output) environment and successfully implemented it in a signal processing simulation system. In this paper, we extend it to 2×2 MIMO (Multiple Input Multiple Output) with spatial multiplexing environment and confirm that the delay and DDP based channel estimator is also effective in 2×2 MIMO environment. Its simulation performance is compared with that of a conventional time-domain linear interpolation estimator. The simulation results show that in a 2×2 MIMO environment, the conventional channel estimator can barely achieve QPSK modulation at speeds below 100 km/h and has poor CNR performance versus SISO. The performance degradation of CNR against DDP SISO is only 6dB to 7dB. And even under severe channel conditions such as 500km/h and 8-path inverse Doppler shift environment, the error rate can be reduced by combining the error with LDPC to reduce the error rate and improve the performance in 2×2 MIMO. QPSK modulation scheme in 2×2 MIMO can be used under severe channel conditions such as 500 km/h and 8-path inverse Doppler shift environment.

• Journal of Communications and Networks
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• v.18 no.6
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• pp.892-901
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• 2016

In the multi-user multiple-input multiple-output (MIMO) system, orthogonal random beamforming (ORBF) scheme is proposed to serve multiple users simultaneously in order to achieve the multi-user diversity gain. The opportunistic space-division multiple access system (OSDMA-S) scheme performs multiple weighting matrices during the training phase and chooses the best weighting matrix to be used to broadcast data during the transmitting phase. The OSDMA-S scheme works better than the original ORBF by decreasing the inter-user interference during the transmitting phase. To save more time in the training phase, a partly random multiple weighting matrices selection scheme is proposed in this paper. In our proposed scheme, the Base Station does not need to use several unitary matrices to broadcast pilot symbol. Actually, only one broadcasting operation is needed. Each subscriber generates several virtual equivalent channels with a set of pre-saved unitary matrices and the channel status information gained from the broadcasting operation. The signal-to-interference and noise ratio (SINR) of each beam in each virtual equivalent channel is calculated and fed back to the base station for the weighting matrix selection and multi-user scheduling. According to the theoretical analysis, the proposed scheme relatively expands the transmitting phase and reduces the interactive complexity between the Base Station and subscribers. The asymptotic analysis and the simulation results show that the proposed scheme improves the throughput performance of the multi-user MIMO system.

• Journal of the Korean Operations Research and Management Science Society
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• v.40 no.3
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• pp.49-61
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• 2015

We study the problem of multiple response optimization (MRO) and focus on the selection of input levels which will produce desirable output quality. We propose an interactive multiple objective optimization approach to the input design. The earlier interactive methods utilized for MRO communicate with the decision maker only using the response variable values, in order to improve the current response values, thereby resulting in the corresponding design solution automatically. In their interaction steps of preference articulation, no account is taken of any active changes in design variable values. On the contrary, our approach permits the decision maker to change the design variable values in its interaction stage, which makes possible the consideration of the preference or economics of the design variable side. Using some typical value functions, we also demonstrate that our method converges reasonably well to the known optimal solutions.

• The Transactions of the Korea Information Processing Society
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• v.5 no.7
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• pp.1791-1800
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• 1998

본 논문에서는 Mamdani 방법과 Koczy 방법의 퍼지 추론 알고리즘에 대햇 병렬머신에 적합한 병렬 퍼지 추론 방법을 제안하고, 효율적인 병렬 퍼지 아키텍처를 설계한다. 제안된 아키텍처는 비교적 높은 성능을 갖고, 확장이 용이한 구조로서, 여러개의 FPE(Fuzzy Processing Element), CP(Control Processor), 메모리 모듈, 상호연결망 및 Min 회로로 구성되어 있다. 이러한 구조의 특징은 iqjsWo의 FPE는 I번째의 전건부 및 I번째의 후건부의 처리만을 수행하기 때문에 전건부, 변수들의 처리는 각각 병렬도 수행되고, 후건부의 처리도 또한 각각 병렬로 수행된다. 따라서 프로세서의 활용도가 높아지며, 전건부와 후건부의 변수, 퍼지규칙의수에 관계없이 쉽게 구성할 수 있다. 이러한 구조는 실시간에 고속추론을 요하는 시스템 또는 전건부와 후건부의 변수가 많은 대규모 전문가 시스템에 사용되어 질 수 있으며, MISO(Multiple-input, Single-output) 시스템보다 MIMO(Multiple-input, Multiple-output) 시스템에 특히 적합하다.

• Journal of Communications and Networks
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• v.7 no.3
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• pp.284-293
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• 2005

A critical issue in applications involving networks of wireless sensors is their ability to synchronize, and mitigate the fading propagation channel effects. Especially when distributed 'slave' sensors (nodes) reach-back to communicate with the 'master' sensor (gateway), low power cooperative schemes are well motivated. Viewing each node as an antenna element in a multi-input multi-output (MIMO) multi-antenna system, we design pilot patterns to estimate the multiple carrier frequency offsets (CFO), and the multiple channels corresponding to each node-gateway link. Our novel pilot scheme consists of non-zero pilot symbols along with zeros, which separate nodes in a time division multiple access (TDMA) fashion, and lead to low complexity schemes because CFO and channel estimators per node are decoupled. The resulting training algorithm is not only suitable for wireless sensor networks, but also for synchronization and channel estimation of single- and multi-carrier MIMO systems. We investigate the performance of our estimators analytically, and with simulations.

• Journal of Communications and Networks
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• v.10 no.2
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• pp.163-174
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• 2008

Performance of downlink transmission strategies exploiting cooperative transmit diversity is investigated for distributed multiple-input single-output (MISO) systems, for which geographically distributed remote antennas (RA) in a cell can either communicate with distinct mobile stations (MS) or cooperate for a common MS. Statistical characteristics in terms of the signal-to-interference-plus-noise ratio (SINR) and the achievable capacity are analyzed for both cooperative and non-cooperative transmission schemes, and the preferred mode of operation for given channel conditions is presented using the analysis result. In particular, we determine an exact amount of the maximum achievable gain in capacity when RAs for signal transmission are selected based on the instantaneous channel condition, by deriving a general expression for the SINR of such antenna selection based transmission. For important special cases of selecting a single RA for non-cooperative transmission and selecting two RAs for cooperative transmission among three RAs surrounding the MS, closed-form formulas are presented for the SINR and capacity distributions.

• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.11-14
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• 2003

본 논문에서는 다중안테나 시스템(Multiple-Input Multiple-Output : MIMO)과 다중코드(Multicode)를 사용하는 코드분할 다중접속(Code Division Multiple Access : CDMA) 시스템의 하향링크(from the base station to the mobile) 환경하에서 채널응답의 중요한 요소인 전송지연시간(Propagation Delay Time)이 기존의 단일안테나(Single-Input Single-Output : SISO) 채널 환경에서 다중안테나 채널 환경으로 바뀌어 적용되었을 때 발생할 수 있는 환경 변화를 찾아보고 그러한 환경이 코드 동기 성능에 미치는 영향과 그러한 문제점을 해결할 수 있는 효율적인 파일롯(Pilot) 전송 기법을 제안 하였다. 또한 모의 실험을 통하여 도착 시간 지연 차이의 분산(variance)값이 검파 성능에 미치는 영향을 확인 하였다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.842-846
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• 2007

Zero Forcing (ZF) 검파 결과는 신호 대 잡음 환경이 양호한 경우 약 80% 이상이 Maximum Likelihood (ML) 검파 결과와 일치한다. 간단한 검증기를 통해 ZF 검파 결과가 ML 검파 결과와 일치하는지 알 수 있다면 검증 결과에 따라 복잡한 ML 검파 과정이나 별도의 검색 과정을 생략할 수 있다. 본 논문에서는 multiple input multiple output (MIMO) 시스템에서 ZF 검파 결과에 대한 검증 방식을 제안하였다. 제안된 검증 방식은 ZF 검파 결과를 이용하여 MIMO 신호를 single input multiple output (SIMO) 신호로 변환한 후 검파를 수행하면 안테나 다이버시티 이득을 얻을 수 있고 잡음 분산이 줄어드는 효과를 이용하였다. 제안된 검증기는 컴퓨터 시뮬레이션 결과 신호 대 잡음이 양호한 경우 80%이상의 정확한 true 판정 확률을 얻었으며 이때 false 판정 확률은 $10^{-4}$이하를 보였다.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.2 no.3
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• pp.215-220
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• 2002

This paper proposes a method to apply the Backpropagation(BP) algorithm of MVL(Multi-Valued Logic) Neural Network to pattern recognition. It extracts the property of an object density about an original pattern necessary for pattern processing and makes the property of the object density mapped to MVL. In addition, because it team the pattern by using multiple valued logic, it can reduce time f3r pattern and space fer memory to a minimum. There is, however, a demerit that existed MVL cannot adapt the change of circumstance. Through changing input into MVL function, not direct input of an existed Multiple pattern, and making it each variable loam by neural network after calculating each variable into liter function. Error has been reduced and convergence speed has become fast.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.14 no.3
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• pp.171-180
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• 2014

In this paper, a multiple sliding surface (MSS) controller for a twin rotor multi-input-multioutput system (TRMS) with mismatched model uncertainties is proposed. The nonlinear terms in the model are regarded as model uncertainties, which do not satisfy the standard matching condition, and an MSS control technique is adopted to overcome them. In order to control the position of the TRMS, the system dynamics are pseudo-decomposed into horizontal and vertical subsystems, and two MSSs are separately designed for each subsystem. The stability of the TRMS with the proposed controller is guaranteed by the Lyapunov stability theory. Some simulation results are given to verify the proposed scheme, and the real time performances of the TRMS with the MSS controller show the effectiveness of the proposed controller.