• Journal of Communications and Networks
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• 제14권5호
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• pp.471-480
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• 2012

Reliable detection of primary user activity increases the opportunity to access temporarily unused bands and prevents harmful interference to the primary system. By extracting a global decision from local sensing results, cooperative sensing achieves high reliability against multipath fading. For the effective combining of sensing results, which is generalized by a likelihood ratio test, the fusion center should learn some parameters, such as the probabilities of primary transmission, false alarm, and detection at the local sensors. During the training period in supervised learning, the on/off log of primary transmission serves as the output label of decision statistics from the local sensor. In this paper, we extend unsupervised learning techniques with an expectation maximization algorithm for cooperative spectrum sensing, which does not require an external primary transmission log. Local sensors report binary hard decisions to the fusion center and adjust their operating points to enhance learning performance. Increasing the number of sensors, the joint-expectation step makes a confident classification on the primary transmission as in the supervised learning. Thereby, the proposed scheme provides accurate parameter estimates and a fast convergence rate even in low signal-to-noise ratio regimes, where the primary signal is dominated by the noise at the local sensors.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 1998년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Spring 1998
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• pp.52-57
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• 1998

Becaruse of the continual occurrence of minor and moderate earthquake in Korean peninsula, it is generally considered that Korean is nor located in safe region against probable earthquake and more, even though being recognized as a safe contry in earthquake. It is in particular noted that nowadays there has been much concern about undesirable disaster due to unexpected earthquake since the disaster of 1995 Kobe earthquake. Thus, the objective of this research is to develop appropriate design spectrum which could be practicably used in seismic design of important structures taking into consideration of local physical characteristics. Particularly, we have to keep in mind the lessons from 1985 Mexico earthquake which had disregarded deep research on local ground conditions, being a possible magnification phenomena of ground motions in weak soil layer. Various spectra has been described based on the analysis of historical earthquakes, and appropriate design spectrum has been proposed herein.

• 충청수학회지
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• 제28권3호
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• pp.419-429
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• 2015

In this paper, we study properties SVEP, Bishop's property (${\beta}$), property (${\delta}$), decomposability, property $({\beta})_{\epsilon}$, subscalarity, Kato spectrum, generalized Kato decomposition, finite ascent for bounded linear operators in Banach spaces.

• 한국인터넷방송통신학회논문지
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• 제13권4호
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• pp.39-46
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• 2013

단일 노드 스펙트럼 센싱과 비교했을 때, 협력스펙트럼 센싱은 스펙트럼 센싱의 신뢰도를 크게 향상 시킬 수 있다. 또한 고유값(Eigenvalue)기반의 스펙트럼 센싱 기법은 에너지 검출 기반의 센싱 기법에 비해 센싱 성능을 제공할 수 있기 때문에 최근 많은 관심을 끌고 있다. 고유값(Eigenvalue)기반의 스펙트럼 센싱 기법의 성능은 smoothing factor (SF)가 증가함에 따라 더 좋은 센싱 결과를 얻을 수 있으나, SF값이 증가함에 따라 더 긴 센싱 시간이 요구된다. 더나가 협력 스펙트럼의 경우, 노드수가 증가함에 따라 더 많은 전송시간이 요구됨으로, 고유값(Eigenvalue)기반의 협력 스펙트럼 센싱의 경우 SF값이 센싱 시간을 결정하는 중요한 요소가 된다. 이에 본 논문에서는 센싱 시간을 증가하지 않고 SF값을 증가시킬 수 있는 고유값 및 중첩기반의 협력 스펙트럼 센싱 기법을 제안한다. 제안된 방식에서는 SF값을 증가시키기 위하여 전송(reporting) 시간을 활용한다. 시뮬레이션을 통해 제안된 방식이 기존 고유값 (Eigenvalue)기반의 센싱기법에 비교하여 더 작은 센싱 시간을 유지하면서 국부(local) 센싱값 및 전체(global) 센싱값을 향상 시킬 수 있음을 보였다.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2015년도 추계학술대회
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• pp.808-811
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• 2015

Cognitive radio 기술은 유망한 동적 주파수 스펙트럼 할당 기법으로 연구되어왔다. Cognitive radio의 주파수 스펙트럼 감지 기술은 주파수 면허대역에서 주사용자(면허대역 사용자)에게 간섭을 유발하지 않으면서 부사용자(비면허 사용자)가 면허대역을 사용할 수 있는 방법을 제공한다. 그러나 스펙트럼을 감지함에 있어서 면허대역을 주사용자가 사용하고 있는지 여부를 한 개의 부 사용자가 판단하여 결정하면 무선채널에서의 페이딩, 잡음 불확실성에 의한 새도우잉, 그리고 히든 노드 문제 등 의해 오류가 발생할 수 있다. 이를 해결하기 위해 협력 스펙트럼 감지 기술이 등장하였다. 본 논문에서는 면허대역 사용여부를 퓨전센터에서 결정하는 협력 스펙트럼 감지기술을 제안하였다. 부사용자는 세 개의 threshold를 사용하여 주사용자 존재여부를 판단하며, 판단 결과를 퓨전센터로 전송한다. 퓨전센터의 협력 스펙트럼 감지기술로 OR 기법을 사용하였고, 컴퓨터 모의실험을 통해 성능평가를 수행하였으며, 성능평가 결과에 따르면 OR 기법의 성능이 가장 우수함을 알 수 있었다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권3호
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• pp.1633-1649
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• 2017

In remote sensing image processing, the traditional fusion algorithm is based on the Intensity-Hue-Saturation (IHS) transformation. This method does not take into account the texture or spectrum information, spatial resolution and statistical information of the photos adequately, which leads to spectrum distortion of the image. Although traditional solutions in such application combine manifold methods, the fusion procedure is rather complicated and not suitable for practical operation. In this paper, an improved IHS transformation fusion algorithm based on the local variance weighting scheme is proposed for remote sensing images. In our proposal, firstly, the local variance of the SPOT (which comes from French "Systeme Probatoire d'Observation dela Tarre" and means "earth observing system") image is calculated by using different sliding windows. The optimal window size is then selected with the images being normalized with the optimal window local variance. Secondly, the power exponent is chosen as the mapping function, and the local variance is used to obtain the weight of the I component and match SPOT images. Then we obtain the I' component with the weight, the I component and the matched SPOT images. Finally, the final fusion image is obtained by the inverse Intensity-Hue-Saturation transformation of the I', H and S components. The proposed algorithm has been tested and compared with some other image fusion methods well known in the literature. Simulation result indicates that the proposed algorithm could obtain a superior fused image based on quantitative fusion evaluation indices.

• 한국전자파학회논문지
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• 제22권8호
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• pp.761-767
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• 2011

본 논문에서는 에너지 검출 기법의 성능을 향상시키기 위해 각각의 SU(Secondary User)에서 수신한 PU(Primaty User) 신호의 크기를 바탕으로 대수적 연산을 통해 에러 확률이 가장 낮은 최적의 임계값을 찾아 PU의 신호를 검출하는 기법을 제안하며 최적의 임계값을 고려해 생성된 local decision을 바탕으로 가장 낮은 에러 확률을 보이는 K-out-of-n 법칙에 적용하는 방법을 연구한다. 각각의 SU에서 최적의 임계값을 찾고 본 논문에서 제안하는 기법의 성능 평가를 위해 Matlab을 이용하여 이를 시뮬레이션하고, 기존의 협력 스펙트럼 검출 기법 중 하나인 OR 법칙과 비교 분석한다. Matlab을 이용한 시뮬레이션 결과, 최적의 임계값을 이용한 K-out-of-n 법칙이 기존의 OR 법칙에 비해 오 경보 확률 및 미 검출 확률이 감소한 것을 알 수 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제5권4호
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• pp.649-664
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• 2011

Cooperative spectrum sensing (CSS) with decision fusion is considered as a key technology for tackling the challenges caused by fading/shadowing effects and noise uncertainty in spectrum sensing in cognitive radio. However, most existing solutions assume an error-free decision transmission, which is obviously not the case in realistic scenarios. This paper extends the general decision-fusion-based CSS scheme by considering the fading/shadowing effects and noise corruption in the common control channels. With this more practical model, the fusion centre first estimates the local decisions using a binary minimum error probability detector, and then combines them to get the final result. Theoretical analysis and simulation of this CSS scheme are performed over typical channels, which suggest some performance deterioration compared with the pure case that assumes an error-free decision transmission. Furthermore, the fusion strategy optimization in the proposed cooperation model is also investigated using the Bayesian criteria. The numerical results show that the total error rate of noisy CSS is higher than that of the pure case, and the optimal values of fusion parameter in the counting rule under both cases decrease as the local detection threshold increases.

• Journal of Information Processing Systems
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• 제15권3호
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• pp.604-615
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• 2019

Single-user spectrum sensing is susceptible to multipath effects, shadow effects, hidden terminals and other unfavorable factors, leading to misjudgment of perceived results. In order to increase the detection accuracy and reduce spectrum sensing cost, we propose an adaptive cooperative sensing strategy based on an estimated signal-to-noise ratio (SNR). Which can adaptive select different sensing strategy during the local sensing phase. When the estimated SNR is higher than the selection threshold, adaptive double threshold energy detector (ED) is implemented, otherwise cyclostationary feature detector is performed. Due to the fact that only a better sensing strategy is implemented in a period, the detection accuracy is improved under the condition of low SNR with low complexity. The local sensing node transmits the perceived results through the control channel to the fusion center (FC), and uses voting rule to make the hard decision. Thus the transmission bandwidth is effectively saved. Simulation results show that the proposed scheme can effectively improve the system detection probability, shorten the average sensing time, and has better robustness without largely increasing the costs of sensing system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제3권5호
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• pp.461-474
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• 2009

The cognitive radio (CR) technique is a useful tool for improving spectrum utilization by detecting and using the vacant spectrum bands in which cooperative spectrum sensing is a key element, while avoiding interfering with the primary user. In this paper, we propose a novel cluster-based cooperative spectrum sensing scheme in cognitive radio with two solutions for the purpose of improving in sensing performance. First, for the cluster header, we use the double adaptive energy thresholds and a multi-bit quantization with different quantization interval for improving the cluster performance. Second, in the common receiver, the weighed HALF-voting rule will be applied to achieve a better combination of all cluster decisions into a global decision.