• Journal of Communications and Networks
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• 제16권2호
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• pp.209-216
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• 2014

Cognitive radio (CR) has been proposed to solve the spectrum utilization problem by dynamically exploiting the unused spectrum. In CR networks, a spectrum selection scheme is an important process to efficiently exploit the spectrum holes, and an efficient channel allocation scheme must be designed to minimize interference to the primary network as well as to achieve better spectrum utilization. In this paper, we propose a multichannel selection algorithm that uses spectrum hole prediction to limit the interference to the primary network and to exploit channel characteristics in order to enhance channel utilization. The proposed scheme considers both the interference length and the channel capacity to limit the interference to primary users and to enhance system performance. By using the proposed scheme, channel utilization is improved whereas the system limits the collision rate of the CR packets.

• 천문학회보
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• 제39권1호
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• pp.42.2-42.2
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• 2014

We present high-resolution optical spectra of newly selected candidates of intermediate-mass black holes. The sample was selected based on the variability and spectral shape in X-ray. The spectra was taken with Magellan 6.5 m Clay Telescope and cover the rest-frame region 3500-10000A. The high spectral resolution (R~4000) of the spectrum allows us to estimate BH masses of the sources. Interestingly, the majority of the sample appears to have broad emission lines. Using this dataset, we will estimate the BH masses and Eddington ratio in order to understand their physical properties.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권1호
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• pp.287-304
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• 2012

Spectrum sensing is an important functionality for cognitive users to look for spectrum holes before taking transmission in dynamic spectrum access model. Unlike previous works that assume perfect knowledge of the SNR of the signal received from the primary user, in this paper we consider a realistic case where the SNR of the primary user's signal is unknown to both fusion center and cognitive radio terminals. A Kalman filter based adaptive Takagi and Sugeno's fuzzy system is designed to make the global spectrum sensing decision based on the observed energies from cognitive users. With the capacity of adapting system parameters, the fusion center can make a global sensing decision reliably without any requirement of channel state information, prior knowledge and prior probabilities of the primary user's signal. Numerical results prove that the sensing performance of the proposed scheme outperforms the performance of the equal gain combination based scheme, and matches the performance of the optimal soft combination scheme.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권4호
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• pp.613-631
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• 2013

Cognitive radio (CR) is proposed as a key solution to improve spectral efficiency and overcome the spectrum scarcity. Spectrum sensing is an important task in each CR system with the aim of identifying the spectrum holes and using them for secondary user's (SU) communications. Several conventional methods for spectrum sensing have been proposed such as energy detection, matched filter detection, etc. However, the main limitation of these classical methods is that the CR network is not able to communicate with its own base station during the spectrum sensing period and thus a fraction of the available primary frame cannot be exploited for data transmission. The other limitation in conventional methods is that the SU data frames should be synchronized with the primary network data frames. To overcome the above limitations, here, we propose a spectrum sensing technique based on blind source separation (BSS) that does not need time synchronization between the primary network and the CR. Moreover, by using the proposed technique, the SU can maintain its transmission with the base station even during spectrum sensing and thus higher rates are achieved by the CR network. Simulation results indicate that the proposed method outperforms the accuracy of conventional BSS-based spectrum sensing techniques.

• Journal of Photoscience
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• 제6권3호
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• pp.153-156
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• 1999

We have introduced the nonresonant holes in the satellite hole spectrum to examine the interaction of two tautomers of thionin to various polynucleotides, including [d(GC)7]2 , [d(AT)7]2 and calf thymus. The saturated depths of nonresonant holes are much reduced upon interacting with [d(GC)7]2 and calf thymus than with [d(AT)7]2 , implying that the binding affinity of thionin to [d(GC)7]2 and calf thymus is stronger than [d(AT)7]2 . In addition, the less perturbation on the exocyclic amino group of the amino -form of thionin upon interacting with [d(AT)7]2 suggests that a direct hydrogen bond formed between the amino group of thionin and the phosphate of nucleic acids is unlikely.

• 대한수학회보
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• 제43권2호
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• pp.389-393
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• 2006

In this paper it is shown that the spectrum ${\sigma}$ is continuous at every p-hyponormal operator when restricted to the set of essentially p-hyponormal operators and moreover ${\sigma}$ is continuous when restricted to the set of compact perturbations of p-hyponormal operators whose spectral pictures have no holes associated with the index zero.

• 한국항행학회논문지
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• 제24권2호
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• pp.121-127
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• 2020

본 논문에서는 광대역 스펙트럼 인지 무선망에서 인지사용자의 요구자원의 크기에 따라 스펙트럼 홀의 그룹핑 범위를 변화시키는 동적 스펙트럼 홀 그룹핑 방식을 제안하고, 광대역 인지사용자의 서비스를 위한 채널할당에 적용한다. 제안한 동적 스펙트럼 홀 그룹핑 방식은 인지사용자의 요구자원의 크기를 예측하여 필요한 양 만큼 주사용자의 스펙트럼 홀을 그룹핑함으로써 기존의 정적 스펙트럼 홀 그룹핑에 의해 발생 할 수 있는 스펙트럼 자원의 낭비를 개선 할 수 있다. 시뮬레이션을 통하여 동적 스펙트럼 홀 그룹핑 방식과 기존의 정적 스펙트럼 홀 그룹핑 방식에 의한 채널할당의 자원사용률을 비교하여, 허용할 수 있는 인지사용자의 서비스 성능에서 자원이용률을 크게 향상시킬 수 있음을 보인다.

• 한국통신학회논문지
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• 제33권4A호
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• pp.458-466
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• 2008

Spectrum sensing is the key challenge in implementing cognitive radio system, which enables unlicensed users to identify "white holes" in the spectrum allocated to primary users and utilize them efficiently. Recent studies have proposed three major sensing methods for WRAN systems, including matched filter, energy and feature detector. However, there are some drawbacks along with them. In this paper, we propose an enhanced energy detector that extends the ability of conventional one, which can differentiate the primary users from each other as well as the noise with different maximum-to-mean power ratio. Furthermore, a novel structure of cognitive radio detector employing the proposed algorithm is also analyzed to implement spectrum sensing. The simulation result shows that our proposed scheme performs well in the individual sensing environment and can satisfy the requirement with high detection probability.

• 대한수학회지
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• 제54권1호
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• pp.281-302
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• 2017

For a Banach space operator $A{\in}B(\mathcal{X})$, let ${\sigma}(A)$, ${\sigma}_a(A)$, ${\sigma}_w(A)$ and ${\sigma}_{aw}(A)$ denote, respectively, its spectrum, approximate point spectrum, Weyl spectrum and approximate Weyl spectrum. The operator A is polaroid (resp., left polaroid), if the points $iso{\sigma}(A)$ (resp., $iso{\sigma}_a(A)$) are poles (resp., left poles) of the resolvent of A. Perturbation by compact operators preserves neither SVEP, the single-valued extension property, nor the polaroid or left polaroid properties. Given an $A{\in}B(\mathcal{X})$, we prove that a sufficient condition for: (i) A+K to have SVEP on the complement of ${\sigma}_w(A)$ (resp., ${\sigma}_{aw}(A)$) for every compact operator $K{\in}B(\mathcal{X})$ is that ${\sigma}_w(A)$ (resp., ${\sigma}_{aw}(A)$) has no holes; (ii) A + K to be polaroid (resp., left polaroid) for every compact operator $K{\in}B(\mathcal{X})$ is that iso${\sigma}_w(A)$ = ∅ (resp., $iso{\sigma}_{aw}(A)$ = ∅). It is seen that these conditions are also necessary in the case in which the Banach space $\mathcal{X}$ is a Hilbert space.

• 한국항공우주학회지
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• 제41권12호
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• pp.959-966
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• 2013

이 논문에서는 설계정보가 없는 노후 항공기를 사용한 P-3CK 해상초계기 사업을 바탕으로, 끝단거리 부족 결함 수리를 위한 패스너 홀 구조특성 연구를 수행하였다. 이를 위해 끝단거리 결함이 많이 발생했던 낫셀 론저론 부분을 선택하고, 1.5, 1.8, 2.0배 끝단거리에 대한 정적 해석을 수행하여 보수적인 응력을 구하였다. 이 응력을 바탕으로 TWIST의 표준하중 스펙트럼을 적용하여 비행하중을 생성하고, 이 비행하중을 이용하여 균열성장 피로해석을 수행하였다. 이 결과를 통하여 P-3CK 사업 중 수리된 패스너 홀의 유효성을 평가하고 정비주기 및 기준을 설정하였다.