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

• 대한수학회보
• /
• 제60권1호
• /
• pp.123-135
• /
• 2023

The goal of this article is to introduce the concept of pseudo-weighted Browder spectrum when the underlying Hilbert space is not necessarily separable. To attain this goal, the notion of α-pseudo-Browder operator has been introduced. The properties and the relation of the weighted spectrum, pseudo-weighted spectrum, weighted Browder spectrum, and pseudo-weighted Browder spectrum have been investigated by extending analogous properties of their corresponding essential pseudo-spectrum and essential pseudo-weighted spectrum. The weighted spectrum, pseudo-weighted spectrum, weighted Browder, and pseudo-weighted Browder spectrum of the sum of two bounded linear operators have been characterized in the case when the Hilbert space (not necessarily separable) is a direct sum of its closed invariant subspaces. This exploration ends with a characterization of the pseudo-weighted Browder spectrum of the sum of two bounded linear operators defined over the arbitrary Hilbert spaces under certain conditions.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제11권6호
• /
• pp.3029-3045
• /
• 2017

The main processes of a cognitive radio system include spectrum sensing, spectrum decision, spectrum sharing, and spectrum conversion. Experimental results show that these stages introduce a time delay that affects the spectrum sensing accuracy, reducing its efficiency. To reduce the time delay, the frequency spectrum prediction was proposed to alleviate the burden on the spectrum sensing. In this paper, the deep recurrent neural network (DRNN) was proposed to predict the spectrum of multiple time slots, since the existing methods only predict the spectrum of one time slot. The continuous state of a channel is divided into a many time slots, forming a time series of the channel state. Since there are more hidden layers in the DRNN than in the RNN, the DRNN has fading memory in its bottom layer as well as in the past input. In addition, the extended Kalman filter was used to train the DRNN, which overcomes the problem of slow convergence and the vanishing gradient of the gradient descent method. The spectrum prediction based on the DRNN was verified with a WiFi signal, and the error of the prediction was analyzed. The simulation results proved that the multiple slot spectrum prediction improved the spectrum efficiency and reduced the energy consumption of spectrum sensing.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제8권5호
• /
• pp.1532-1553
• /
• 2014

Radio spectrum is a precious resource and characterized by fixed allocation policy. However, a large portion of the allocated radio spectrum is underutilized. Conversely, the rapid development of ubiquitous wireless technologies increases the demand for radio spectrum. Cognitive Radio (CR) methodologies have been introduced as a promising approach in detecting the white spaces, allowing the unlicensed users to use the licensed spectrum thus realizing Dynamic Spectrum Access (DSA) in an effective manner. This paper proposes a generalized framework for DSA between the licensed (primary) and unlicensed (secondary) users based on Continuous Time Markov Chain (CTMC) model. We present a spectrum access scheme in the presence of sensing errors based on CTMC which aims to attain optimum spectrum access probabilities for the secondary users. The primary user occupancy is identified by spectrum sensing algorithms and the sensing errors are captured in the form of false alarm and mis-detection. Simulation results show the effectiveness of the proposed spectrum access scheme in terms of the throughput attained by the secondary users, throughput optimization using optimum access probabilities, probability of interference with increasing number of secondary users. The efficacy of the algorithm is analyzed for both imperfect spectrum sensing and perfect spectrum sensing.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제6권1호
• /
• pp.361-378
• /
• 2012

Most of the current frequency hopping (FH) based dynamic spectrum access (DSA) methods concern a reactive channel access scheme with synchronous inter-channel spectrum sensing, i.e., FH is reactively triggered by the primary user (PU)'s return reported by spectrum sensing, and the PU channel to be switched to is assumed precisely just sensed or ready to be sensed, as if the inter-channel spectrum sensing moments are synchronous. However, the inter-channel spectrum sensing moments are more likely to be asynchronous, which risks PU suffering more interference. Moreover, the spectrum sensing is usually erroneous, which renders the problem more complex. To address this problem, we propose a proactive FH based DSA method against both erroneous spectrum sensing and asynchronous inter-channel spectrum sensing (moments). We term it as proactive DSA. The optimal FH sequence is obtained by dynamic programming. The complexity is also analyzed. Finally, the simulation results confirm the effectiveness of the proposed method.

• 전자통신동향분석
• /
• 제34권6호
• /
• pp.17-27
• /
• 2019

This paper introduces the 5G spectrum auction in Germany that occurred last summer and ended overheatedly after an extraordinarily long period. We describe the context of the latest German spectrum auction and trace the participants' bidding behavior. This case details the trend of the 5G spectrum auction and the factors that affect the spectrum auction as follows: First, it is determined that investment obligations that force network installations can be a financial burden to mobile network operators (MNOs) and require a careful approach. Second, excess demands can cause auction overheating and the spectrum supply volume needs to be determined by a proper demand forecast and investment incentive. Third, 'Set-Aside' for local usage aids in developing the vertical industry; however it limits the spectrum supply for mobiles and leads to higher bidding prices. Fourth, a modified adoption of a typical spectrum auction can alleviate MNO's financial burdens to secure the broadband spectrum. Finally, competition to secure the necessary bandwidth in the situation of limited spectrum supply may delay the process of the spectrum auction, causing it overheated.

• 산업경영시스템학회지
• /
• 제35권2호
• /
• pp.181-188
• /
• 2012

The fee system on spectrum usage is a usage fee that is charged for using spectrum provided by a wireless tower, and is used for management and promotion of the waves. The current fee system for spectrum usage in South Korea has faced many problems, such as complex calculation for fees, unjustified charges, unfairness in cost sharing among providers, and general inefficiency of operation. This study focuses on comparison of fee systems for spectrum usage of South Korea and other foreign countries, extraction of the root causes and problems by case analyses, and recommendation for better solutions to make a reasonable fee system for spectrum usage. The result of this study can be used as a solution to render spectrum usage more effective.

• 한국전자파학회논문지
• /
• 제30권6호
• /
• pp.452-466
• /
• 2019

최근 전파 자원의 수요 급증에 따라 전파자원의 적기 확보의 중요성이 증대되고 있다. 본 논문에서는 이러한 전파자원 확보를 위한 수단으로서 전파법 제6조에서 규정하고 있는 주파수 효율개선 시책의 시행 우선순위를 평가하는 방안을 제시한다. 전파법에서 규정하는 주파수 효율개선 시행을 위한 고려사항으로부터 평가지표를 도출하고, 지표측정 결과를 수요 시급성과 확보 용이성의 두 범주를 축으로 하는 우선순위 평가 매트릭스를 통해 4단계로 우선순위를 평가하는 방안과 제안된 평가 방안의 실제 적용에 필요한 착안사항 등이 제시되었다. 이러한 평가방식 적용을 통해 선제적인 주파수 확보, 공급뿐만 아니라, 이용자 보호, 전파기반 신사업 창출기회 확대 등을 기대할 수 있다.

• 호남수학학술지
• /
• 제45권4호
• /
• pp.598-609
• /
• 2023

The purpose of this article is to obtain the spectrum, fine spectrum, approximate point spectrum, defect spectrum and compression spectrum of the double band matrix U (a₀, a₁, a₂; b₀, b₁, b₂), b₀, b₁, b₂≠0 on the sequence space ℓ_p (1 < p < ∞).

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 1998년도 가을 학술발표회 논문집
• /
• pp.447-454
• /
• 1998

The paper describes the second half of the research for the development of Neural-Networks-based model for the generation of an Artificial earthquake and a Response Spectrum(NNARS). Based on the redefined traditional processes related to the generation of an earthquake acceleration response spectrum and design spectrum, four neural-networks-based models are proposed to substitute the traditional processes. RS_NN tries to directly generate acceleration response spectrum with basic data that are magnitude, epicentral distance, site conditions and focal depth. The test results of RS_NN are not good because of the characteristics of white noise, which is randomly generated. ARS_NN solve this problem by the introduction of the average concept. IARS_NN has a role to inverse the ARS_NN, so that is applied to generate a ground motion accelerogram compatible with the shape of a response spectrum. Additionally, DS_NN directly produces design spectrum with basic data. As these four neural networks are simulated as a step by step, the paper describes the methods to generate a response spectrum and a design spectrum using the neural networks.