• 전자통신동향분석
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• 제33권3호
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• pp.1-10
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• 2018

This article presents spectrum sharing policy trends both overseas and domestically. The Federal Communications Commission recently adopted rules for the commercial use of a 150 MHz bandwidth at 3.55 to 3.7 GHz, which has been utilized for defense and satellite services. This frequency band for spectrum sharing is called the citizens broadband radio service (CBRS) band. In Europe, the related regimes for licensed shared access application at 2.3 to 2.4 GHz has been organized, and interface standardization for sharing frequency information has been completed. In Korea, efforts are being made to establish spectrum-sharing policies to improve the efficiency of the frequency utilization. This article also introduces both the IEEE 802 local area network/metropolitan area network and 3GPP standardization activities with regard to frequency sharing technologies. To effectively solve the spectrum-sharing problem in IEEE 802, standardization activities on the CBRS and the mid-band (3.7-24 GHz) are underway. 3GPP is currently developing the standardization of a licensed assisted access technology, which extends mobile communication services provided in the licensed band to unlicensed bands.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권10호
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• pp.3302-3320
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• 2014

An allocation of sensing and reporting times is proposed to improve the sensing performance by scheduling them in an efficient way for cognitive radio networks with cluster-based cooperative spectrum sensing. In the conventional cooperative sensing scheme, all secondary users (SUs) detect the primary user (PU) signal to check the availability of the spectrum during a fixed sensing time slot. The sensing results from the SUs are reported to cluster heads (CHs) during the reporting time slots of the SUs and the CHs forward them to a fusion center (FC) during the reporting time slots of the CHs through the common control channels for the global decision, respectively. However, the delivery of the local decision from SUs and CHs to a CH and FC requires a time which does not contribute to the performance of spectrum sensing and system throughput. In this paper, a super-allocation technique, which merges reporting time slots of SUs and CHs to sensing time slots of SUs by re-scheduling the reporting time slots, has been proposed to sense the spectrum more accurately. In this regard, SUs in each cluster can obtain a longer sensing duration depending on their reporting order and their clusters except for the first SU belonged to the first cluster. The proposed scheme, therefore, can achieve better sensing performance under -28 dB to -10 dB environments and will thus reduce reporting overhead.

• 한국지진공학회논문집
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• 제21권1호
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• pp.31-39
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• 2017

In this study, to estimate the combination of earthquake magnitude ($M_w$) and distance (R) corresponding to the design spectrum defined in Korean Building Code (KBC) 2016, the response spectra predicted from the attenuation relationships with the variation of $M_w$ (5.0~7.0) and R (10~30km) are compared with the design spectrum in KBC 2016. Four attenuation relationships, which were developed based on local site characteristics and seismological parameters in Southern Korea and Eastern North America (ENA), are used. As a result, the scenario ground motions represented by the combinations of $M_w$ and R corresponding to the design spectrum for Seoul defined in KBC 2016 are estimated as (1) when R =10 km, $M_w=6.2{\sim}6.7$; (2) when R = 15 km, $M_w=6.5{\sim}6.9$; and (3) when R = 20 km, $M_w=6.7{\sim}7.1$.

• 한국ITS학회 논문지
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• 제16권5호
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• pp.152-161
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• 2017

CBTC의 통신기술은 IEEE 802.11.x 표준을 사용하고 있으며 ISM밴드 대역중 하나인 2.4GHz를 사용하게 된다. 따라서 CBTC 철도 무선시스템으로서는 통신 지연, 통신 왜곡 및 정보 손실 등이 발생 할 수 있다. 이러한 문제를 극복하기 위해 ISM 대역중 908MHz 일정진폭을 갖는 직접 시퀀스 확산스펙트럼 송신기를 제안하였다. 성능 분석을 위해 주요파라미터인 아이 다이아그램과 scatter diagram을 고려하여 특성 분석을 하였다. 또한 국부발진 신호의 위상잡음 특성은 약 60dBc/Hz로서 기준신호와 비교 시 특성이 상당히 우수함을 알 수 있었다. 또한 2차 국부 발진 신호의 기준 주파수 억압이 50dB이하가 됨을 알 수 있었다. 제안한 변조방법에서 보조신호는 양과 음의 발생확률을 균일하게 함으로써 출력스펙트럼에서의 선스펙트럼성분에 의한 간섭을 제거하였으며 비선형 증폭기를 통과한 후의 스펙트럼의 측대파의 재생율이 현저히 줄어들었음을 볼 수 있었다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권8호
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• pp.1754-1769
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• 2013

For the purpose of enhancing the spectrum efficiency, cognitive radio (CR) technology has been recently proposed as a promising dynamic spectrum allocation paradigm. In CR, spectrum sensing is the key capability of secondary users in a cognitive radio network that aims for reducing the probability of harmful interference with primary users. However, the individual CRs might not be able to carry out reliable detection of the presence of a primary radio due to the impact of channel fading or shadowing. This paper studies the cooperative spectrum sensing scheme as means of optimizing the sensing performance in AWGN and Rayleigh channels. Results generated from simulation provide evidence of the impact of channel condition on the complementary receiver operating characteristic (ROC). Based on the results, it was found that with constant local SNRs at the secondary users, the probability of missed detection ($P_m$) of cooperative spectrum sensing in a cognitive radio network, calculated using a closed form expression, can be significantly minimized. Thus, the paper illustrates that improvement of the detection performance of the CR network can be achieved by establishing a centralized cooperation among neighboring cognitive radio users. Finally, verification of the validity of the fusion schemes utilized for combining the individual CR decisions is provided.

• 대한의용생체공학회:의공학회지
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• 제4권1호
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• pp.29-36
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• 1983

In this paper, center frequency down slift of ultrasonic echo signals which for the measurements of frequency dependent attenuation in the biological tissue are estimated. Center frequency down shift of echo-signals are estimated after signal spectrum analysis of whole echo-signals. In case of signal spectrums are simple, estimation of down shift frequency is very simple and in case of complicate spectrum, estimation of down shift frequency is depend on spectral shape. In case of unable to estimate, frequency dependence of medium is nonlinear(n) 1), in which upper shift of spectrums are presented. In case of unable to estimate, spectrum analysis are performed at local position. At consquence, we know that spectral dispersions are caused complicately by biological tissue layer.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권3호
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• pp.996-1015
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• 2016

A common concern regarding cooperative spectrum sensing (CSS) schemes is the occupied bandwidth and the energy consumption during the transmissions of sensing information to the fusion center over the reporting control channels. This concern is intensified if the number of cooperating secondary users in the network is large. This article presents a new fusion strategy for a CSS scheme, aiming at increasing the energy efficiency of a recently proposed bandwidth-efficient fusion scheme. Analytical results and computational simulations unveil a high increase in energy efficiency when compared with the original approach, yet achieving better performances in some situations, and lower implementation complexity.

• Earthquakes and Structures
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• 제10권6호
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• pp.1347-1367
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• 2016

The purpose of this work is to investigate the seismic behavior of St. Titus Church in Heraklion, Crete, Greece as well as the need of its seismic retrofitting. A numerical model of the Church is constructed using shell finite elements and it is then seismically examined using response spectrum and linear time-history analyses. Effects of soil-structure interaction have been also taken into account. The Church without retrofit is expected to exhibit extensive tensile failures and many compressive ones. Aiming to maintain the architectural character of the structure as well as to increase its seismic resistance, a retrofitting procedure involving injection of cement grout in conjunction with reinforced concrete jacketing to the internal side of the masonry walls is proposed. A numerical implementation of the proposed seismic retrofitting is performed and its effect is evaluated by response spectrum and linear time-history analyses. From the results of these analyses, it is shown that compressive failures are eliminated while only few tensile failures of local character take place.

• ETRI Journal
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• 제38권1호
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• pp.30-40
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• 2016

Co-channel interference between macro-femtocell networks is an unresolved problem, due to the frequency reuse phenomenon. To mitigate such interference, a secondary femtocell must acquire channel-state knowledge about a co-channel macrocell user and accordingly condition the maximum transmit power of femtocell user. This paper proposes a pilot-based spectrum sensing (PSS) algorithm for overlaid femtocell networks to sense the presence of a macrocell user over a channel of interest. The PSS algorithm senses the pilot tones in the received signal through the power level and the correlation metric comparisons between the received signal and the local reference pilots. On ensuring the existence of a co-channel macrocell user, the maximum transmit power of the corresponding femtocell user is optimized so as to avoid interference. Time and frequency offsets are carefully handled in our proposal. Simulation results show that the PSS algorithm outperforms existing sensing techniques, even at poor received signal quality. It requires less sensing time and provides better detection probability over existing techniques.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.394-394
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• 2011

최근 태양전지의 후면에서 통상적으로 사용되는 Al을 이용한 후면의 BSF형성과 그에 관한 연구보다 계면의 recombination을 줄이기 위하여 passivation 특성이 좋은 층을 후면에 형성하고 국부적으로 BSF를 형성하는 back contact을 형성하여 특성을 향상시키는 연구가 많이 이루어지고 있다. 본 연구는 이러한 local back contact을 boron-BSF를 이용하여 형성하고 passivation layer는 oxide를 이용한 구조를 SILVACO 2-dimension simulation을 이용하여 그 특성을 분석하였다. Boron-local back contact 구조에서 boron-BSF의 doping concentration, depth, lateral width, boron-BSF spacing 가변을 통해 태양전지의 특성변화에 대해서 spectrum response를 통한 QE 분석 및 I-V를 분석하여 최적화하였다.