• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권3호
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• pp.749-761
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• 2014

Improving spectrum utilization efficiency is a fundamental goal of dynamic spectrum access technology. The definition of spectrum holes determines how to detect and exploit them. Current definitions of spectrum holes are ineffective in exploiting spatial-temporal spectrum holes. In this paper, a novel definition of spectrum holes is proposed, in which throughput loss indicates the impact of secondary users on primary users. The definition specifies spectrum holes, unifies the impact of secondary users on primary users and is effective exploiting spatial-temporal spectrum holes. Theoretical analysis and numerical simulations show that the new definition proposed in this paper significantly improves the spectrum utilization efficiency.

• Journal of Communications and Networks
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• 제8권2호
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• pp.169-174
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• 2006

In this paper, the algorithm of a methodology for the calculation of spectrum requirements was implemented. As well, the influence of traffic distribution ratio among radio access technology groups, spectral efficiency, and flexible spectrum usage (FSU) margin was analyzed in terms of the spectrum requirements, with a view toward for future development of international mobile telecommunication (IMT)-2000 and systems beyond IMT-2000. The calculated spectrum requirement in the maximum spectral efficiency case is reduced by approximately 40% compared to a minimum spectral efficiency case. The effect of the distribution ratio on the required spectrum is smaller than the effect of the spectral efficiency. As the flexible spectrum usage margin increases by 1.0 dB, the total spectrum requirement decreases by 0.9 dB. The required spectrum for the market input parameter, ${\rho}$ = 0.5 is 801.63 MHz, while the required spectrum for ${\rho}$ = 1.0 is 6295.4 MHz. This is equivalent to an increase of 785.32 %.

• Bulletin of the Korean Chemical Society
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• 제22권8호
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• pp.807-815
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• 2001

Two-dimensional (2D) correlation method, which generates the synchronous and the asynchronous 2D spectrum by complex cross correlation of the Fourier transformed spectra, is an analysis method for the changes of the sample spectrum induced by vari ous perturbations. In the present work, the 2D electronic correlation spectra have been simulated for the cases where the sample spectrum composed of two gaussian bands changes linearly. When only the band amplitudes of the sample spectrum change, the synchronous spectrum shows strong peaks at the band centers of the sample spectrum, but the asynchronous spectrum does not make peaks. When the sample spectrum shifts without changing intensity and width, the synchronous spectrum shows peaks around the initial and final positions of the band maximum and the asynchronous spectrum shows long peaks spanning the shifting range. The band width change produces the complex 2D correlation spectra. When the sample spectrum shifts with band broadening, the width change by 50% of full width at half maximum (FWHM) does not give so large an effect on the correlation spectrum as the spectral shift by one half of FWHM of the sample spectrum.

• Journal of Communications and Networks
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• 제12권1호
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• pp.19-29
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• 2010

Recently, spectrum sensing has been intensively studied as a key technology in realizing the cognitive radio. There have been advances in the performance of spectrum sensing through both multi-antenna and cooperative sensing schemes. In this paper, the performances and complicated scenarios of the latest spectrum sensing schemes are analytically compared and arranged into a technical tree while considering practical concerns. This paper will give a macroscopic view of spectrum sensing and will also provide insight into future spectrum sensing works.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권3호
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• pp.1199-1212
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• 2019

This paper proposes two wideband spectrum sensing approaches: (i) method A, the cumulative sum (CUSUM) algorithm with short-time Fourier transform, taking advantage of the time-frequency analysis for wideband spectrum. (ii)method B, the quickest spectrum sensing with short-time Fourier transform and compressed sensing, shortening the time of perception and improving the speed of spectrum access or exit. Moreover, method B can take advantage of the sparsity of wideband signals, sampling in the sub-Nyquist rate, and it is more suitable for wideband spectrum sensing. Simulation results show that method A significantly outperforms the single serial CUSUM detection for small SNRs, while method B is substantially better than the block detection based spectrum sensing in small probability of the false alarm.

• 한국전자파학회논문지
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• 제17권1호
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• pp.81-88
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• 2006

본 논문에서는 임의 위치에서 기존의 무선 통신 시스템에서 사용되는 주파수 대역이 전체 스펙트럼 자원에 존재하는 비율로서 정의되는 스펙트럼 사용 계수를 이용하여 스펙트럼 사용량을 정량적으로 나타내는 방법을 제안하였다. 기존 무선 시스템과 동일 공간에서 스펙트럼을 사용하기 위해 기존 시스템의 안테나 패턴과 송신 전력 등의 함수로 스펙트럼 사용 계수를 나타내었고, 계산된 결과를 서울 지역의 실제 고정 서비스 무선국에 적용하여 스펙트럼 사용량을 계산하였다. 본 논문에서 나타낸 스펙트럼 사용 계수를 이용하면 새로운 무선 시스템을 동일 공간에서 사용하고자 하는 경우 사용되는 스펙트럼을 정량적으로 나타낼 수 있기 때문에, 스펙트럼이 사용되지 않는 공간을 단순한 빈 공간이 아닌 정량적으로 나타낼 수 있게 되어 스펙트럼 공간을 효율적으로 사용할 수 있다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 C
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• pp.1850-1851
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• 2001

광전자실험에 사용되고있는 수동 광학소자로는 lense, mirror, grating, prism, polarizer 등 이 있다. 본 연구에서는 각 소자들에 대한 수학적 모델과 실질적 구조에 의한 수치 해석적 모델인 Split-step을 angular spectrum 방법을 구현하고 이를 이용한 실험적 결과를 이론치와 비교 분석하여 모델의 정확성을 분석하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1998년도 추계학술대회 논문집
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• pp.57-60
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• 1998

Poly(3-hexylthiophene)(P3HT) was synthesized by use of FeCl$_3$ as a oxidizing agent at $25^{\circ}C$. The infrared spectrum of our polymer gave good evidence for the conjugation of 3-hexylthiophene monomer unit. P3HT contains the HT(head-to-tail) linkage larger than 64% based on NMR analysis. Electronic absorption and photoluminescence studies show that cast films of P3HT have three exciting state. Absorption spectrum was separated with three maximum peaks by Giese-French method and shifted to the shorter wavelength with increasing temperature. Separated absorption spectrum of P3HT is well adapted to PL peak appeared at longer wavelength. Low temperature PL spectrum is well separated at 669nm, 733nm and 812nm.

• Current Optics and Photonics
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• 제7권1호
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• pp.47-53
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• 2023

We propose a centralized passive-optical-network monitoring scheme using the resonance-spectrum properties of a Fabry-Perot cavity based on fiber Bragg gratings. Each cavity consists of two identical uniform fiber Bragg gratings and a varying cavity length or grating length, which can produce a unique single-mode resonance spectrum for the drop-fiber link. The output spectral properties of each cavity can be easily adjusted by the cavity length or the grating length. The resonance spectrum for each cavity is calculated by the transfer-matrix method. To obtain the peak wavelength of the resonance spectrum more accurately, the effective cavity length is introduced. Each drop fiber with a specific resonance spectrum distinguishes between the peak wavelength or linewidth. We also investigate parameters such as reflectivity and bandwidth, which determine the basic performance of the fiber Bragg grating used, and thus the output-spectrum properties of the Fabry-Perot cavity. The feasibility of the proposed scheme is verified using the Optisystem software for a simplified 1 × 8 passive optical network. The proposed scheme provides a simple, effective solution for passive-optical-network monitoring, especially for a high-density network with small end-user distance difference.

• 한국전자파학회논문지
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• 제17권2호
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• pp.110-116
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• 2006

본 논문에서는 4세대 이동통신 주파수 소요량 산출 방법론을 구현하고, 주파수 소요량의 변화에 큰 영향을 미치는 RATG간 트래픽 배분을, 주파수 효율성, FSU 이득과 시장 데이터 입력 파라미터 ${\rho}$에 따른 주파수 소요량의 변화를 시뮬레이션 하였다. 트래픽 배분율에 따른 주파수 소요량 변화는 $1\;GHz/20\;\%$정도였으며, 주파수 효율성에 따른 변화는 $5{\sim}9\;GHz$였다. 그리고 FSU 이득이 1 dB 증가하면 주파수 소요량은 약 0.9 dB 정도 감소하였다. 시장 데이터 입력 파라미터 ${\rho}=0.5$ 일 때 주파수 소요량은 801.63 MHz, ${\rho}=1.0$ 일 때는 6295.4 MHz로, 시장 데이터 입력 파라미터가 주파수 소요량에 미치는 영향이 가장 크다.