• 제목/요약/키워드: Cross-Spectrum

검색결과 370건 처리시간 0.03초

Cross Entropy 기반의 주파수 영역에서 스펙트럼 센싱 성능 개선 (An Improved Cross Entropy-Based Frequency-Domain Spectrum Sensing)

  • 타사미아;구준롱;장성진;김재명
    • 대한전자공학회논문지TC
    • /
    • 제48권3호
    • /
    • pp.50-59
    • /
    • 2011
  • 본 논문은 주파수 영역에서 과거와 현재에 센싱된 결과들의 관계를 이용한 스펙트럼 센싱기법을 제안하였다. 기존에 제안된 대부분의 스펙트럼 센싱기법은 해당 시간에 센싱된 우선사용자의 신호만을 다루고 있다. 해당 시간 이전의 우선사용자의 상태는 조건부확률을 사용하여 검출기의 신뢰성을 증가시킬 수 있다. 따라서, 본 논문은 이전 시간과 해당 시간의 스펙트럼 센싱 결과를 사용하는 cross entropy 기반의 스펙트럼 센싱기법을 제안하며 이를 통해 우선사용자 신호 검출 성능을 향상시키고 잡음에 강인한 성능을 가질 수 있다. 이전 시간에 검출된 신호가 잡음인 경우 cross entropy 기반의 스펙트럼 센싱 성능 감소는 기존의 entropy 기반의 센싱기법과 동일하게 된다. 이러한 문제를 해결하기 위해 본 논문에서는 보다 향상된 cross entropy 센싱기법을 제안하였다. 본 논문은 시뮬레이션을 통해 가장 최근에 제안된 주파수 영역에서의 entropy 기반 스펙트럼 센싱기법 보다 제안된 방법이 더 나은 성능을 보이는 것을 보였다.

Improved Correlation Identification of Subsurface Using All Phase FFT Algorithm

  • Zhang, Qiaodan;Hao, Kaixue;Li, Mei
    • KSII Transactions on Internet and Information Systems (TIIS)
    • /
    • 제14권2호
    • /
    • pp.495-513
    • /
    • 2020
  • The correlation identification of the subsurface is a novel electrical prospecting method which could suppress stochastic noise. This method is increasingly being utilized by geophysicists. It achieves the frequency response of the underground media through division of the cross spectrum of the input & output signal and the auto spectrum of the input signal. This is subject to the spectral leakage when the cross spectrum and the auto spectrum are computed from cross correlation and autocorrelation function by Discrete Fourier Transformation (DFT, "To obtain an accurate frequency response of the earth system, we propose an improved correlation identification method which uses all phase Fast Fourier Transform (APFFT) to acquire the cross spectrum and the auto spectrum. Simulation and engineering application results show that compared to existing correlation identification algorithm the new approach demonstrates more precise frequency response, especially the phase response of the system under identification.

Spectrum Reuse with Power Control for Two-Tier Femtocell Networks

  • Kim, Youngju;Wang, Hano;Hong, Daesik
    • IEIE Transactions on Smart Processing and Computing
    • /
    • 제3권5호
    • /
    • pp.275-284
    • /
    • 2014
  • This paper considers two-tier networks consisting of macrocells and femtocells operating in the same spectrum. This paper proposes a femtocell spectrum reuse scheme that determines the shared spectrum and transmit power for the femtocells to mitigate the effects of cross-tier interference between the macrocells and femtocells. The proposed scheme provides macrocell throughput that is unaffected by the increasing number of femtocells per cell site and improves the femtocell signal quality at the same time by limiting the cross-tier interference. This study analyzed the per-tier signal-to-interference ratio (SIR) and outage probability of the proposed scheme to investigate the macrocell and femtocell performance. The total throughput of the proposed scheme was analyzed based on the outage probabilities. The analysis and numerical results proved that high femtocell throughput can be achieved using only a small fraction of the spectrum while protecting the macrocell throughput. As a result, an improved total throughput was achieved enforcing higher spatial reuse.

IEEE 802.15.4a CSS를 위한다중 선형 Chirp 전송 기법 (Multiple Linear Chirp Based Transmission Scheme for IEEE 802.15.4a Chirp Spread Spectrum)

  • 김광열;이승우;김용신;이재생;김진영;신요안
    • 한국통신학회논문지
    • /
    • 제40권10호
    • /
    • pp.1937-1939
    • /
    • 2015
  • Chirp 기반의 전송 기법에서 Cross-coherence는 전송 성능에 영향을 미치며, 전송 성능의 향상을 위해서는 Cross-coherence가 적은 Chirp 조합을 사용해야 한다. 이에 본 논문은 IEEE 802.15.4a CSS (Chirp Spread Spectrum)의 전송 성능을 향상시키기 위한 Chirp 조합으로 다중 선형 Chirp 기법을 제안한다. 모의실험 결과, 제안된 기법인 다중 선형 Chirp 기법이 단일 선형 Chirp 기법 보다 Cross-coherence가 적은 부분이 있음을 확인하였고, 이 조합을 이용하여 전송하였을 때 전송 성능이 향상됨을 확인하였다.

Adaptive energy group division in the few-group cross-section generation for full spectrum reactor modeling with deterministic method

  • Yichen Yang;Youqi Zheng;Xianan Du;Hongchun Wu
    • Nuclear Engineering and Technology
    • /
    • 제56권6호
    • /
    • pp.2019-2028
    • /
    • 2024
  • Advanced nuclear reactors, especially the newly developed small and micro-reactors have complex neutron spectrum, which makes the deterministic reactor core calculations sensitive to the energy group structure of few-group cross-sections. To avoid significantly increasing the cost of energy discretization in the core calculation, two energy group structures with 31 groups and 33 groups were adopted for typical thermal and fast reactor cores, respectively. Then, an adaptive scheme of group division for reactor cores with a medium neutron spectrum was proposed. The works were based on the full spectrum nuclear reactor analysis code SARAX/TULIP. An equivalent one-dimensional model of the core was proposed to capture the key neutron spectrum features of the reactor core. Such features were used to adaptively determine a few-group structure for the following reactor core calculations. Then, the neutron spectrum in different zones with more details was calculated. With this spectrum, the cross-sections were condensed into the determined energy groups. Three tests based on different neutron spectrum were calculated to verify the schemes. The results show that using the adaptive energy group division scheme, the following core calculation can meet the accuracy requirement of different reactors with different neutron spectra.

회전 표적의 고주파수 후방산란단면적 해석 (High-frequency Back-scattering Cross Section Analysis of Rotating Targets)

  • 김국현;조대승;김진형
    • 한국군사과학기술학회지
    • /
    • 제10권3호
    • /
    • pp.16-24
    • /
    • 2007
  • The high-frequency analysis method of back-scattering cross section spectrum of rotating targets is established. The time history of the back-scattering cross section is calculated using a quasi-stationary approach, based on a physical optics and a physical theory of diffraction, combining an adaptive triangular beam method to consider the shadow effect. And the spectra of back-scattering cross section by the Doppler effect are analyzed applying a simple fast Fourier transform method to its time history. The numerical calculation for rotating targets, such as rotating metal plates and underwater propeller, are carried out. The time history appears to be periodic with respect to the number of wings. The backscattering cross section spectrum level and its frequency shift are dependent on the rotating speed, direction, and the shape of the targets.

크로스 엔트로피 기반 스펙트럼 센싱에서 채널 점유 시간 변화에 따른 히스토그램 Bin 개수 선택 기법 (Histogram Bin Number Selection Method Robust to the Variations of Channel Occupancy for Cross Entropy)

  • 용슬바로;장성진;김재명
    • 한국ITS학회 논문지
    • /
    • 제12권1호
    • /
    • pp.88-97
    • /
    • 2013
  • 기존에 제안된 대부분의 스펙트럼 센싱 기법은 해당 시간에 센싱 된 우선사용자의 신호만을 다루고 있다. 하지만 해당 시간 이전의 우선사용자의 상태를 이용하게 되면 조건부 확률을 사용하여 검출기의 신뢰성을 증가시킬 수 있다. 따라서 크로스 엔트로피(Cross Entropy) 기반의 스펙트럼 센싱 기법에서는 해당 시간 이전의 우선사용자의 상태도 함께 이용하는 기법을 제안하였으며 이를 통해 우선사용자 신호 검출 성능을 향상시키고 잡음에 강인한 성능을 갖도록 하였다. 그러나 이러한 크로스 엔트로피 기반의 스펙트럼 센싱 기법은 모두 실제 이상적인 센싱 환경만을 고려하였다. 다시 말해, 우선사용자의 채널 점유 시간이 항상 일정하다고 가정한 상태에서 센싱을 수행하였다. 하지만 실제 상황에서는 우선사용자가 채널을 점유하는 시간이 이상적인 상황보다 길어질 수도, 반대로 짧아질 수도 있으며 이로 인해 스펙트럼 센싱 성능이 변화 할 수 있다. 따라서 본 논문에서는 이러한 실제 상황에서도 센싱 성능을 일정하게 유지할 수 있는 기법을 제안하였으며 이를 시뮬레이션을 통해 확인하였다.

축대칭 3차원 물체의 유동 소음 스펙트럼 측정 (A measurement of flow noise spectrum of an axisymmetric body)

  • 박연규;김양한
    • 대한기계학회논문집B
    • /
    • 제22권6호
    • /
    • pp.725-733
    • /
    • 1998
  • The pressure fluctuation on the surface of a submerged body has been recognized as a dominant noise source. There have been many studies concerning the flow induced noise on a flat plate. However, the noise over an axisymmetric body has not been well reported. This paper addresses the way in which we have investigated the mechanism of noise generation due to an axisymmetric body. The associated experiments and signal processing methods are introduced. A 3-dimensional axisymmetric body whose length and diameter were 2 m and 10.4 cm, was prepared as a test specimen. The wall pressure on the surface of the body was measured in a large scale low noise wind tunnel at KIMM(Korea Institute of Machinery and Metals). To measure the wall pressure, we used two microphone arrays which were tangential and normal to the flow. Based on the measured signal, frequency-wavenumber spectrum which explains the structure of turbulence noise, was estimated. Tangential to the flow, there exists convective ridge at a relatively higher wavenumber region; this can cause spatial aliasing. To circumvent this problem, the cross spectrum was interpolated. The interpolation has been performed by unwrapping the phase and smoothing the cross spectrum. The phase unwrapping was done based on the Corcos model; the phase of cross spectrum decreases linearly with the distance between microphones. Aforementioned signal processings are possible by employing the experimental results that the estimated wavenumber spectrum quite resembles the Corcos model. We try to modify the Corcos model which is applicable to the flat plate, by altering the magnitude of cross spectrum to fit the experimental data more accurately. We proposed that this wavenumber spectrum model is suitable for the 3-dimensional axisymmetric body. Normal to the flow, there exists a little correlation between signals of different microphones. The circumferential wavenumber spectrum contains uniform power along the wavenumbers.

Effects of Neutron Spectrum and Cross-section Library on Displacements per Atom (dpa)

  • Park, Duck-Gun;Shimakawa, S.;Nagao, Y.;Kang, Young-Hwan
    • 한국원자력학회:학술대회논문집
    • /
    • 한국원자력학회 1997년도 춘계학술발표회논문집(1)
    • /
    • pp.125-130
    • /
    • 1997
  • Effect of cross-section libraries on displacements per atom (dpa) was investigated under the spectrum which is calculated in the outer and inner of capsule in the JMTR fuel region. The variation of dpa value of iron was calculated by TENJIN2 code using several cross section libraries (ENDFB-lV, JENDL 3.1 and JENDL 3.2). The dependency of input spectrum on total damage (dpa) is more clearly appeared in case or ENDFB-IV in JENDL 3.2 and JENDL 3.1 libraries. The gas production rate calculated by ENDFB-IV library showed slightly larger value than that by JENDL library, and it responded more sensitively in neutron spectrum.

  • PDF

Neutron yield and energy spectrum of 13C(alpha,n)16O reaction in liquid scintillator of KamLAND: A Nedis-2m simulation

  • Vlaskin, Gennady N.;Bedenko, Sergey V.;Ghal-Eh, Nima;Vega-Carrillo, Hector R.
    • Nuclear Engineering and Technology
    • /
    • 제53권12호
    • /
    • pp.4067-4071
    • /
    • 2021
  • The 13C (α,n)16O reaction cross-section is important data for nuclear physics, astrophysical, and neutrino physics experiments, however, they exhibit uncertainties due to the discrepancies in the experimental data. In this study, using the Nedis-2m program code, the energy spectrum of α-induced neutrons in a thin carbon target was calculated and the corresponding reaction cross-section was refined in the alpha particle energy range of 5-8 MeV. The results were used to calculate the intensity and energy spectrum of background neutrons produced in the liquid scintillator of KamLAND. The results will be useful in a variety of astrophysical and neutrino experiments especially those based on LS or Gd-LS detectors.