• Proceedings of the IEEK Conference
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• 2002.06a
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• pp.29-32
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• 2002

본 논문은 수평적 시공간 부호화 기법(Horizontal Space-Time Coding)과 송수신단에 별도의 빔형성 기법을 결합한 JBSTC(Joint Beamforming Space-Time Coding) 구조에 대한 제안 및 동작원리를 기술하고 성능을 분석하였다. JBSTC는 MIMO(Multi-Input Multi-Output) 송수신 시스템 채널 모델링을 기반으로 송신측 안테나간 상호 상관 행렬과 수신측 안테나간 상호 상관 행렬을 이용하여 송수신 빔형성기의 안테나 가중치들을 계산한다. 본 논문에서 제안하는 JBSTC 방식은 송수신단에서 발생하는 안테나 간격과 각퍼짐에 따른 상호 상관 값을 효과적으로 보정함으로써 기존의 수평적 시공간 부호화 기법보다 우수함을 알 수 있다.

• Journal of Power Electronics
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• v.11 no.5
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• pp.662-668
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• 2011

This paper presents an analysis of a 4th order LCLC resonant converter with a capacitive output filter using the state-space approach. The analysis of the converter shows that there are four intervals in a half period. In each interval, the state-space equations are obtained. Due to the soft switching of the converter, an exact equation for the Zero Voltage Switching (ZVS) time and the maximum dead time of the inverter switches are presented. The simulation and experimental results obtained from a 10kv, 370w prototype confirm the validity of the theoretical analysis.

• Educational Technology International
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• v.8 no.2
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• pp.113-140
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• 2007

This study purports to contribute in deepening our understanding of ISD (instructional systems design/development) from Edward Hall's concept of intercultural communication. Renowned anthropologist Edward Hall introduced three concepts of cultural differences: time, space, and context. This paper explores how theses cultural dimensions - time, space and context- are reflected in ISD and compares the cultural differences between the east and the west that emerge in the process of applying ISD.

• Journal of Astronomy and Space Sciences
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• v.36 no.1
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• pp.35-43
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• 2019

The Optical Wide-field patroL-Network (OWL-Net) is a global optical network for Space Situational Awareness in Korea. The primary operational goal of the OWL-Net is to track Low Earth Orbit (LEO) satellites operated by Korea and to monitor the Geostationary Earth Orbit (GEO) region near the Korean peninsula. To obtain dense measurements on LEO tracking, the chopper system was adopted in the OWL-Net's back-end system. Dozens of angle-only measurements can be obtained for a single shot with the observation mode for LEO tracking. In previous work, the reduction process of the LEO tracking data was presented, along with the mechanical specification of the back-end system of the OWL-Net. In this research, we describe an integrity assessment method of time-position matching and verification of results from real observations of LEO satellites. The change rate of the angle of each streak in the shot was checked to assess the results of the matching process. The time error due to the chopper rotation motion was corrected after re-matching of time and position. The corrected measurements were compared with the simulated observation data, which were taken from the Consolidated Prediction File from the International Laser Ranging Service. The comparison results are presented in the In-track and Cross-track frame.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.29B no.11
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• pp.36-45
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• 1992

A numerical trajectory planning method for path-constrained trajectory planning is proposed which ensures collision-free and time-optimal motions for two robotic manipulators with limited actuator torques and velocities. For each robot, physical constraints of the robots such as limited torques or limited rotational velocities of the actuators are converted to the constraints on velocity and acceleration along the path, which is described by a scalar variable denoting the traveled distance from starting point. Collision region is determined on the coordination space according to the kinematic structures and the geometry of the paths of the robots. An Extended Coordination Space is then constructed` an element of the space determines the postures and the velocities of the robots, and all the constraints described before are transformed to some constraints on the behaviour of the coordination-velocity curves in the space. A dynamic programming technique is them provided with on the discretized Extended Coordination Space to derive a collision-free and time-optimal trajectory pair. Numerical example is included.

• Journal of Communications and Networks
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• v.5 no.2
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• pp.124-134
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• 2003

In this paper, we investigate the error probability performance of noncoherently detected orthogonal modulation combined with Alamouti space-time block coding. We find that there are two types of pair-wise error probabilities that characterize the performance. We employ methods that allow a direct evaluation of exact, closed-form expressions for these error probabilities. Theoretical as well as numerical results show that noncoherent orthogonal modulation combined with space-time block coding (STBC) achieves full spatial diversity. We derive an expression for approximate average bit error probability for-ary orthogonal signaling that allows one to show the tradeoff between increased rate and performance degradation.

• Journal of Communications and Networks
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• v.5 no.2
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• pp.135-140
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• 2003

In this paper, we investigate the error performance of a serially concatenated system using a nonrecursive convolutional code as the outer code and a recursive QPSK space-time trellis code as the inner code on quasi-static and rapid Rayleigh fading channels. At the receiver, we consider iterative decoding based on the maximum a posteriori (MAP) algorithm. The performance is evaluated by means of computer simulations and it is shown that better error performance can be obtained by using low complexity outer and/or inner codes and the Euclidean distance criterion based recursive space-time inner codes. We also obtain new systems with large number of trasmit and/or receive antennas providing good error performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.11A
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• pp.1043-1052
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• 2008

This paper compares the performances with space time coding and cyclic delay diversity techniques for OFDM systems in interference-limited environments. While a communication system usually use a diversity technique to improve its own performance, it is also necessary to consider the interference effects to other users as well if the system is operated in interference-limited environments. When there is no interference from or to other users, space time coding technique results in better performance than cyclic delay diversity. However, cyclic delay diversity can be better than space time coding if interferences to other users are considered.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.3
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• pp.15-18
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• 2009

In this paper, we propose ST-MWSK (space-time M-ary orthogonal Walsh sequence keying) employing MWSK which does not require channel estimation at the receiver. The computational complexity for the noncoherent ML (maximum-likelihood) detector of ST-MWSK is significantly reduced compared to that of ST-FSK (ST frequency-shift keying). Also, the performance of ST-MWSK is virtually identical to that of ST-FSK.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.4C
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• pp.303-309
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• 2006

By combining the space-time diversity technique and iterative turbo codes, space-time turbo codes(STTCS) are able to provide powerful error correction capability. However, the multi-path transmission and iterative decoding structure of STTCS make the decoder very complex. In this paper, we propose a low complexity decoder, which can be used to decode STTCS as well as general iterative codes such as turbo codes. The efficient implementation of the backward recursion and the log-likelihood ratio(LLR) update in the proposed algorithm improves the computational efficiency. In addition, if we approximate the calculation of the joint LLR by using the approximate ratio(AR) algorithm, the computational complexity can be reduced even further. A complexity analysis and computer simulations over the Rayleigh fading channel show that the proposed algorithm necessitates less than 40% of the additions required by the conventional Max-Log-MAP algorithm, while providing the same overall performance.