• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2C
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• pp.206-212
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• 2004

In this paper, we propose a STF(Space-Time-Frequency) coded OFDM(Orthogonal Frequency Division Multiplexing) transmission scheme as an attractive solution for high bit rate data transmission in a multipath fading environment. STBC(Space-Time Block Coding) has been proposed as a simple diversity scheme using two transmit antennas. Also ST-OFDM(Space-Time Block Coded OFDM) and SF-OFDM(Space-Frequency Block Coded OFDM) transmission scheme, that the STBC is applied to the OFDM, has been proposed. In this paper, we propose STF-OFDM transmission scheme that to coded in time, space and frequency domain. The STF-OFDM transmission scheme that we propose in this paper is the way to improve a performance of conventional ST-OFDM, by using frequency diversity.

• Proceedings of the Korean Information Science Society Conference
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• 2002.10e
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• pp.64-66
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• 2002

공간-시간 부호(Space-Time Code)는 다중 안테나 시스템에서 기존의 기술에 비해서 부가적인 대역폭이 필요 없이 부호화 이득을 얻을 수 있다. 지금까지 공간-시간 부호(Space-Time Code)는 다이버시티 이득의 관점에서는 신호행렬들의 차가 완전-계수(Full-Rank)를 가져야 하고, 코딩 이득의 관점에서는 신호행렬들의 차의 determinant 값이 최소값을 가져야 한다. 본 논문에서는 공간-시간 블록 부호 디자인(Space-Time Block Code) 관점에서 직교-디자인(Orthogonal-design) 즉, 최소거리가 5이면서 완전-계수(Full-Rank)인 디자인을 비교대상으로 완전-계수(Full-Rank)가 아니면서 최소거리가 5와7인두 부호에 관하여 연구되어졌다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.6A
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• pp.640-650
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• 2004

Channel estimation schemes are proposed for Multiple Input-Multiple output Orthogonal Frequency Division Multiplexing(MIMO-OFDM) systems based on the physical layer specification of the IEEE 802.1 la. By combining the space-time block coding(STBC)/ space-frequency block coding(SFBC) techniques with the transform domain interpolation, the proposed algorithms achieve more accurate channel coefficients for the MIMO channels such that improve the BER performance. The performance improvements of the proposed algorithms are evaluated by simulations under the various multipath fading channel environments and various transmission rates.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.66 no.1
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• pp.48-52
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• 2017

This paper proposes a hybrid algorithm of space-time block coding and space-frequency block coding using alternate time switch. The traditional alternate time-switched space-time or space-frequency block coding technique for orthogonal frequency division multiplexing system does not provide a good performance with a variety of communication environments. This hybrid algorithm has searched good performance ranges in various environments in view points of mobile speed and doppler frequency. In this paper, we investigate better performance ranges for two algorithms, suggest a hybrid algorithm for dynamically changing communication environments, propose a structure for transmitter and receiver, and show that its performance is better than the traditional algorithm by simulations.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.23 no.3
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• pp.91-104
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• 2020

This study was conducted to analyze the characteristics of defects according to the type of block and spatial type by quantitatively examining defects occurring in block pavement in apartment complex. According to the research results, depending on the type of block, defects have occurred 1,394.3ea/100㎡ in interlocking paver blocks, 464.8ea/100㎡ in clay brick paver blocks, and 235.1ea/100㎡ in shot blasted paver blocks. By space type, the defects were occurred 1,576.0ea/100㎡ on the access road paved by interlocking paver blocks and the defects were found 1,139.6ea/100㎡ in interlocking paver blocks, 235.1ea/100㎡ in shot blasted paver blocks, and 797.1ea/100㎡ in clay brick paver blocks, on the sidewalk. Also the defects are occurred 455.6ea/100㎡ on the resting space and 403.2ea/100㎡ on the gym space paved by clay brick paver blocks. Through the size analysis of the defects in the block paver, in the case 'peeling', the largest volume of 2,539.0㎣ on the sidewalk paved with shot blasted paver blocks, and 'Subsidence' occurred at the widest area of 2,096.0㎠ on the sidewalk where interlocking paver block was constructed. The difference in defect occurrence according to the type of block is considered to be influenced by the block production process, and the space type is considered to be caused the difference in the occurrence of defects according to the cause of construction and the usage pattern of residents. This study conducted a survey on defects in block and analyzed the defect characteristic according to paver material and space type. Base on this, it is judged that it can be used as an efficient basic data for material replacement, improvement, paver planning and construction in the future.

• Proceedings of the KIEE Conference
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• 2001.10a
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• pp.168-174
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• 2001

In this paper, a new space vector RPPWM (Random Position PWM) is proposed. In the proposed RPPWM, each of three phase pulses is located randomly in each switching interval. Based on the space vector modulation technique, the duty ratio of the pulses is calculated. Along with the randomization of the PWM pulses, we can obtain the effects of spread spectra of voltage, current as in the case of randomly changed switching frequency. To verify the validity of the proposed RPPWM, simulation study was tried using Matlab/simulink. The main model described in Simulink block diagrams includes the space vector modulation block, pulse position randomization block, inverter block, 3 phase induction motor block, and so on. By the simulation study, the harmonics of the output voltage, and the current of inverter are predicted in different PWM methods- SVPWM, LLPWM, proposed RPPWM.

• Journal of Advanced Navigation Technology
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• v.8 no.1
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• pp.10-18
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• 2004

As a technique for high-quality multimedia service in down-link, the transmit diversity schemes using a orthogonal space-time block codes were proposed. But if the number of transmit antenna is three or more, it was impossible to obtain full diversity gain because of the decline of spectral efficiency. Accordingly, the quasi-orthogonal space-time block code that not required a additional bandwidth was proposed. But using a space-time block codes, the transmit diversity schemes were verified over quasi-static and frequency non-selective channels. Therefore, in this paper, we analyze the performance of OFDM systems, which a frequency selective channel equalized a frequency non-selective channel, adapting the quasi-orthogonal space-time block code, and compare they to the conventional orthogonal space-time block coded OFDM systems.

• Journal of Communications and Networks
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• v.10 no.3
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• pp.253-257
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• 2008

In this paper, the performance of generic orthogonal space-time block codes (OSTBCs) introduced by Alamouti [2], Tarokh [3], and Su and Xia [11] is analyzed. We first define one-dimensional component symbol error function (ODSEF) from the exact expression of the pairwise error probability of an OSTBC. Utilizing the ODSEF and the bit error probability (BEP) expression for quadrature amplitude modulation (QAM) introduced by Cho and Yoon [9], the exact closed-form expressions for the BEP of linear OSTBCs with QAM in quasi-static Rayleigh fading channel are derived. We also derive the exact closed-form of the BEP for some OSTBCs which have at least one message symbol transmitted with unequal power via all transmit antennas.

• Korean Journal of Mathematics
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• v.6 no.2
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• pp.341-348
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• 1998

In this paper, we show that Schlumprecht space is reflexive and the Dual of Schlumprecht space has the Banach-Saks property and study behavior of block basic sequence in Schlumprecht space.

• Journal of Communications and Networks
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• v.8 no.3
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• pp.275-285
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• 2006

Suitable for multi-input multi-output (MIMO) communications, the joint beamforming space-time block coding (JBSTBC) scheme is proposed for high-speed downlink transmission. The major functionality of the scheme entails space-time block encoder and joint transmit and receive eigen-beamformer (EBF) incorporating with block-ordered layered decoder (BOLD), and its operating principle is described in this paper. Within these functionalities, the joint EBFs will be utilized for decorrelating fading channels to cause an enhancement in the spatial diversity gain. Furthermore, to fortify the capability of layered successive interference cancellation (LSIC) in block-ordered layered decoding process, this paper will develop a simple ad-hoc transmit power discrimination scheme (TPDS) based on a particular power discrimination function (PDF). To confirm the superior behavior of the proposed JBSTBC scheme employing ad-hoc TPDS, computer simulations will be conducted under various channel conditions with the provision of detailed mathematical derivations for clarifying its functionality.