• 대한전자공학회논문지
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• 제26권12호
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• pp.1903-1909
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• 1989

In this paper, the mobile communication CH simulator is implemented in the baseband, using the Digital Signal Processor(TMS320C25), A/D and D/A converters. The Rayleigh CH is modeled by shaping the random noise source power spectrum. The statistical characteristics(Level Crossing Rate, Cumulative distribution Function, Probability Density Function) and the received fading signal's power's spectrum is observed when the doppler frequency is varied according to the variation of the vehicular velocity at the 222MHz band. And also the BER is measured when the baseband mobile CH simulator is applied to the GMSK(Gaussian Minimum Shift Keying` transmission rate: 16kbps, Bb T=0.25) modulator. The results shows the similar characteristics to be compared with the theoritically derived BER values of the discriminator type GMSK detection.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 ITC-CSCC -2
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• pp.973-976
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• 2000

This paper proposes a new polarization diversity scheme for OPFDM (Orthogonal Polarization and Frequency Division Multiplexing). OPFDM is an extension of OFDM (Orthogonal Frequency Division Multiplexing) in conjunction with polarization multiplexing in order to ensure the orthogonality amongst subcarriers. Since OPFDM uses two orthogonally polarized channels, it can easily employ the polarization diversity. In order to get the diversity gain effectively in a frequency selective fading channel, the proposed scheme combines the signals in subcarrier-by-subcarrier basis. The computer simulation results confirm that the proposed scheme is superior to conventional one in the two orthogonally polarized two-ray Rayleigh fading channels with cross-talk between the two channels.

• 전자공학회논문지A
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• 제29A권7호
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• pp.1-9
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• 1992

In this thesis, the trellis detection scheme is proposed to improve the error performance of the noncoherent detection in the TFM system. Trellis detection takes advantage of the trellis property of TFM-encoded signals. The trellis property is created by giving correlations among adjacent TFM-encoded signals at the transmitter. The performance of the trellis detection scheme is analyzed by means of the Bernoulli trials with the average symbol error probability, and is compared to that of the bit-by-bit detection scheme. As a result,when the SNR is below 20 dB in the Rayleigh fading and AWGN channel, the trellis detection is inferior to the bit-by-bit detections. But when SNR is above 20 dB, the trellis detection is superior to the bit-by-bit detection, and its performance enhancement is better as the SNR increases.

• 한국통신학회논문지
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• 제16권10호
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• pp.951-963
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• 1991

본 논문에서는 주파수 대역을 효과적으로 이용하기 위한 이동통신용 M진 PSK 시스템을 실현 하였으며 주파수 대역을 제한하기 위하여 구형대역특성을 갖는 저역통과필터 대신에 raesed-cosine 필터를 사용하여 ISI 및 지터의 영향을 고찰하였다. 한편 fast Rayleigh 페이팅 환경하에서 Canonic 수신기를 시용한 QPSK와 8·PSK 시스템의 오율 및 스펙트럼 오율을 해석한 결과 나이버시티 수신을 하지않은 경우보다 k=2인 다이버시티 수신을 한 경우가 약 3~5배 개선됨을 알 수 있었다.

• Journal of Communications and Networks
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• 제9권2호
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• pp.177-184
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• 2007

Alamouti space-time code (STC) is a part of the UMTS-WCDMA standard. However, up to the best of our knowledge no exact closed-form outage and bit error probability (BEP) formulas for this famous code exists. Evaluating its performance through simulations is time-consuming and therefore, there should be analytical performance graphs to serve as a reference which are derived in this paper for coherently MPSK-modulated data. Additionally, analytical results take into account different channel fading levels from transmit antennas to receive ones.

• International Journal of Air-Conditioning and Refrigeration
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• 제9권4호
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• pp.10-16
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• 2001

An experimental study for free convective heat transfer in a thermal diode type enclosure is presented. The thermal diode is a device which allows heat to be transferred in one direction by convection due to density difference of the fluid, and consists of a rectangular-paralle-logrammic enclosure with a guide vane. It is used as heat collection system of solar energy due to its simple construction and low cost. Experimental parameters were guide vane thickness, the inclination angles of the parallelogrammic enclosure, and the lengths of the rectangular enclosure part. The parameter range of the flux Rayleigh numbers was $2.4\times{10}^8$~$9.8\times{10}^8$. The heat transfer rate of this system was shown 10~47% higher than that of other earlier research results without the guide vane. The correlation for fixed $\phi=60^\circ$ was obtained, Nu=0.0037(Ra^*)^{0.429}(d^*)^ {0.050}(Lr/H)^{0.0415}$.

• International Journal of Computer Science & Network Security
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• 제24권9호
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• pp.21-29
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• 2024

Precoding of the orthogonal frequency division multiplexing (OFDM) with Walsh Hadamard transform (WHT) is known in the literature. Instead of performing WHT precoding and inverse discrete Fourier transform separately, a product of two matrix can yield a new matrix that can be applied with lower complexity. This resultant transform, T-transform, results in T-OFDM. This paper extends the limited existing work on T-OFDM significantly by presenting detailed account of its computational complexity, a lower complexity receiver design, an expression for PAPR and its cumulative distribution function (cdf), sensitivity of T-OFDM to timing synchronization errors, and novel analytical expressions signal to noise ratio (SNR) for multiple equalization techniques. Simulation results are presented to show significant improvements in PAPR performance, as well improvement in bit error rate (BER) in Rayleigh fading channel. This paper is Part II of a three-paper series on alternative transforms and many of the concepts and result refer to and stem from results in generalized multicarrier communication (GMC) system presented in Part I of this series.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권3호
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• pp.890-910
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• 2014

This paper investigates the spectrum hole utilization of cooperative schemes for the two-way relaying model in order to improve the utilization efficiency of limited spectrum holes in cognitive radio networks with imperfect spectrum sensing. We propose two specific bidirectional secondary data transmission (BSDT) schemes with two-step and three-step two-way relaying models, i.e., two-BSDT and three-BSDT schemes, where the spectrum sensing and the secondary data transmission are jointly designed. In the proposed cooperative schemes, the best two-way relay channel between two secondary users is selected from a group of secondary users serving as cognitive relays and assists the bi-directional communication between the two secondary users without a direct link. The closed-form asymptotic expressions for outage probabilities of the two schemes are derived with a primary user protection constraint over Rayleigh fading channels. Based on the derived outage probabilities, the spectrum hole utilization is calculated to evaluate the percentage of spectrum holes used by the two secondary users for their successful information exchange without channel outage. Numerical results show that the spectrum hole utilization depends on the spectrum sensing overhead and the channel gain from a primary user to secondary users. Additionally, we compare the spectrum hole utilization of the two schemes as the varying of secondary signal to noise ratio, the number of cognitive relays, and symmetric and asymmetric channels.

• 대한전자공학회논문지TC
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• 제44권11호
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• pp.19-24
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• 2007

본 논문은 직교 분할 다중 반송파 다중 접속 방식(OFDMA, Orthogonal Frequency Division Multiple Access)에서 그리디 방법(GA, Greedy Approach)을 사용한 동적 채널 할당 알고리즘의 성능분석에 관한 것이다. GA를 기반으로 한 동적 채널 할당의 경우 사용자간의 다이버시티 효과를 통하여 성능 이득을 얻을 수 있다. 본 논문에서는 동적 채널 할당 알고리즘에서 다중 사용자 다이버시티 계수인 할당 가능한 사용자 수(NAU, Number of Allocable Users)를 모델링하고, 이를 통하여 GA를 기반으로 한 동적 채널 할당 알고리즘의 성능(실패 확률 및 데이터 전송량)을 분석한다. 분석된 결과를 기반으로 GA를 기반으로 한 동적 채널 할당 알고리즘의 성능을 최대화 할 수 있는 조건을 제시할 수 있다.

• 전기전자학회논문지
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• 제3권1호
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• pp.141-149
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• 1999

차세대 고속 데이터 전송을 위해 연구되고 있는 MC-CDMA 방식은 이동통신환경에서 송신 신호의 주기가 채널의 지연확산보다 충분히 크지 않으면 심볼간의 간섭이 발생하여 성능이 열화된다. 본 논문에서는 이러한 문제점을 해결하기 위해 직 병렬 변환기를 통과시킴으로써 채널의 지연확산보다 충분히 큰 주기 신호를 만들고, 직 병렬 변환기의 서브채널 수에 따라 스펙트럼 효율을 가변적으로 높일 수 있다. 또한 이동통신환경에서 성능향상을 위해 MC-CDMA에 병렬 주파수 다이버시티 블럭을 첨가한다. 제안된 모델의 스펙트럼 효율을 계산하여 MC-CDMA의 스펙트럼 효율과 비교하고, 다중 경로 레일리 페이팅 채널 모델에서 성능 향상을 시뮬레이션을 통해 검증한다.