• IEIE Transactions on Smart Processing and Computing
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• 제3권5호
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• pp.285-297
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• 2014

This paper presents the results of an investigation into bi-directional communication in spectrum sharing-based cognitive radio (Bi-CR) systems. A Bi-CR system can increase the spectral efficiency significantly by sharing the spectrum and through the bi-directional use of spatial resources for two-way communication. On the other hand, the primary user experiences more interference from the secondary users in a Bi-CR system. Satisfying the interference constraint by simply reducing the transmission power results in performance degradation for secondary users. In addition, secondary users also experience self-interference from echo channels due to full duplexing. These imperfections may weaken the potential benefits of the Bi-CR system. Therefore, a new way to overcome these defects in the Bi-CR system is needed. To address this need, this paper proposes some novel power allocation schemes for the Bi-CR system. This contribution is based on two major analytic environments, i.e., noise-limited and interference-limited environments, for providing useful analysis. This paper first proposes an optimal power allocation (OPA) scheme in a noise-limited environment and then analyzes the achievable sum rates. This OPA scheme has an effect in the noise-limited environment. In addition, a power allocation scheme for the Bi-CR system in an interference-limited environment was also investigated. The numerical results showed that the proposed schemes can achieve the full duplexing gain available from the bi-directional use of spatial resources.

• Smart Structures and Systems
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• 제2권1호
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• pp.47-60
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• 2006

Bi-spectrum is a tool in the signal processing for identification of non-linear dynamic behvaiour in systems, and well-known for stationary system where components are non-linearly interacting. Breathing of a crack during shaft rotation is also exhibits a non-linear behaviour. The crack is known to generate 2X (twice the machine RPM) and higher harmonics in addition to 1X component in the shaft response during its rotation. Misaligned shaft also shows similar such feature as a crack in a shaft. The bi-spectrum method has now been applied on a small rotating rig to observe its features. The bi-spectrum results are found to be encouraging to distinguish these faults based on few experiments conducted on a small rig. The results are presented here.

• Nuclear Engineering and Technology
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• 제35권4호
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• pp.336-346
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• 2003

This study is intended to evaluate the dependency of TRU recycling characteristics on the neutron spectrum shift in a Pb-Bi cooled core. Considering two Pb-Bi cooled cores with the soft and the hard spectrum, respectively, various characteristics of the recycled core are carefully examined and compared with each other. Assuming very simplified fuel cycle management with the homogeneous and single region fuel loading, the burnup calculations are performed until the recycled core reached to the (quasi-) equilibrium state. The mechanism of TRU recycling toward the equilibrium is analyzed in terms of burnup reactivity and the isotopic compositions of TRU fuel. In the comparative analyses, the difference in the recycling behavior between the two cores is clarified. In addition, the basic safety characteristics of the recycled core are also discussed in terms of the Doppler coefficient, the coolant loss reactivity coefficient, and the effective delayed neutron fraction.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권10호
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• pp.4808-4824
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• 2016

Signal individual reconnaissance and identification is an extremely important research topic in non-cooperative domains such as electronic countermeasures and intelligence reconnaissance. Facing the characteristics of the complexity and changeability of current communication environment, how to realize radiation source signal individual identification under the low SNR conditions is an emphasis of research. A novel emitter individual identification method combined bi-spectrum analysis with wavelet feature is presented in this paper. It makes a feature fusion of bi-spectrum slice characteristics and energy variance characteristics of the secondary wavelet transform coefficient to identify MFSK signals under the low SNR (signal-to-noise ratios) environment. Theoretical analyses and computer simulation results show that the proposed algorithm has good recognition performance with the ability to suppress noise and interference, and reaches the recognition rate of more than 90% when the SNR is -6dB.

• 한국해안·해양공학회논문집
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• 제31권1호
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• pp.17-27
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• 2019

Bound mode의 외중력파와 이로 인한 보강간섭이 이상파 생성 기작이라는 가설을 확인하기 위해 OpenFoam 기반 Tool box인 ihFoam과 Bi-spectrum에 기초한 수치모의를 수행하였다. 수치모의는 건설 과정에서 이상파가 관측된 삼척 LNG 생산기지 전용부두를 대상으로 수행되었으며, Bound mode의 외중력파는 Bi-spectrum에 기반하여 출현빈도가 높은 주기가 7초인 국지 풍성파와 11.4초인 너울의 difference interaction으로 생성하였다. 또한 비교를 위해 비선형 Cnoidal wave, linear wave를 대상으로 한 수치모의도 병행하여 수행하였다. 모의결과 N 계열 bound mode의 외중력파에 의해 삼척 LNG 생산기지 전용부두를 따라 진행되는 연파가 생성되며, 이상파는 전술한 연파와 남측 도류제로부터의 반사파가 더해져 출현하는 것으로 모의되었다.

• Bulletin of the Korean Chemical Society
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• 제20권3호
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• pp.337-340
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• 1999

Luminescence of bismuth activated CaS, CaS:Bi, prepared in sodium polysulfide is studied. Excitation spectrum of CaS:Bi shows a band at 350 nm due to the recombination process between holes in Na+Ca2+ and electrons in conduction bands, in addition to bands at 260 nm from band gap of CaS, and at 320 nm (1S0→1P1) and at 420 nm (1S0→3P1) from electronic energy transitions of Bi. Emission band at 450 nm is from 3P1→1S0 transition of Bi3+, bands at 500 nm and 580 nm correspond to recombinations of electron donors (Bi3+Ca2+ and VS2-) with acceptors (VCa2+ and Na+Ca2+). Emission band of 3P1→1S0 transition is shifted to longer wavelength from CaS:Bi to BaS:Bi, due to the increase of the Stokes shift by the decrease of the crystal field parameter from CaS:Bi to BaS:Bi.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 F
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• pp.2650-2652
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• 1999

To satisfy the demand for small size, light weight. high density power supply, the switching frequency of DC/DC converters has been increased. The PWM control of the conventional SMPS have a switching frequency that a level of the conducted noise spectra contribute to switching frequency band. So the electronic equipment is not only affected from that but is restricted to internal regulation like CISPR, FCC, and VDE. In this paper, we analyzed Bi-FM. Bi-FM is two fixed switching frequency with a modulation frequency. So emission spectrum of Bi-FM control signal is spreaded and spectral power level is reduced. In this paper, we analyze the spectral analysis of Bi-FM control signal and the spectral comparison between the PWM control and Bi-FM control. And we confirm that reduced the spectrum power level through simulation using Pspice and experiment.

• 비파괴검사학회지
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• 제22권2호
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• pp.170-176
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• 2002

재료 내부를 초음파가 전파하면서 발생되는 비선형 음향효과는 재료의 열화도를 비파괴적으로 평가하는데 우수한 것으로 보고되고 있다. 비선형 음향효과는 재질의 특성에 따라 나타나는 정도가 다르며, 이러한 정도는 비선형 파라미터를 이용하여 정량적으로 평가하는 것이 가능하다. 본 연구에서는 2.25Cr-1Mo 강이 $540^{\circ}C$에서 장시간 노출되었을 때 얼어나는 미세조직의 변화를 얻기 위해 인공 열처리를 수행하고, 2.25Cr-1Mo 강의 열화도와 비선형 음향효과와의 관계를 실험적으로 검증하여 경년 열화도와 비선형 파라미터의 상관관계를 규명하고자 하였다. 비선형 파라미터는 바이스펙트럼법과 파워스펙트럼법을 이용하여 측정되었으며, 실험결과 바이스펙트럼법에 의한 비선형 파라미터는 열화 시간에 매우 민감하게 반응하는 것으로 나타났다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1987년도 한국자동제어학술회의논문집(한일합동학술편); 한국과학기술대학, 충남; 16-17 Oct. 1987
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• pp.842-846
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• 1987

This paper proves that a filter for scramble spectrum is realized by a periodically time-varying digital filter. Further, we propose a design method of this filter by using a bi-frequency map. As an example, we implemented this filter with Digital Signal Processor.

• 산업기술연구
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• 제24권B호
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• pp.59-64
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• 2004

GaAs thin films were grown epitaxially by MOCVD method on (001) GaAs substrate. And as a surfactant, Bi(bismuth) thin films were deposited on GaAs buffer layer by using TMBi(trimethylbismuth) source. In-situ reflectance difference spectroscopy(RDS) was used to monitor the surface reconstruction of GaAs and Bi thin films. As the results, under the exposure of TBAs(tertiarybuthylarsine) and hydrogen atmosphere, the surface reconstruction of GaAs was changed from As-rich c($4{\times}4$) to As-rich ($2{\times}4$), which was due to the adsoption and desorption of As dimers. The first bismuth surface related RDS signal was reported. At the deposition temperature of $450^{\circ}C$, Bi-terminated GaAs surface showed the RDS spectrum similar to that of Sb-terminated GaAs surface, possibly a ($2{\times}4$) surface. And Bi surface layers were rapidly evaporated with increasing the deposition temperature($550^{\circ}C$), finally becoming As-terminated ($2{\times}4$) surface.