• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권3호
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• pp.1333-1343
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• 2016

Spectrum sharing in centrally controlled cognitive radio (CR) networks has been widely studied, however, research on channel access for distributively controlled individual cognitive users has not been fully characterized. This paper conducts an analysis of random channel access of cognitive users controlled in a distributed manner in a CR network. Based on the proposed estimation method, each cognitive user can estimate the current channel condition by using its own Markov-chain model and can compute its own blocking probability, collision probability, and forced termination probability. Using the proposed scheme, CR with distributed control (CR-DC), CR devices can make self-controlled decisions based on the status estimations to adaptively control its system parameters to communicate better.

• 한국ITS학회:학술대회논문집
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• 한국ITS학회 2010년도 춘계학술대회
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• pp.37-42
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• 2010

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제4권3호
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• pp.289-304
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• 2010

This paper proposes a novel scheme for cooperative spectrum sensing on distributed cognitive radio networks. A fuzzy logic rule - based inference system is proposed to estimate the presence possibility of the licensed user's signal based on the observed energy at each cognitive radio terminal. The estimated results are aggregated to make the final sensing decision at the fusion center. Simulation results show that significant improvement of the spectrum sensing accuracy is achieved by our schemes.

• Journal of Communications and Networks
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• 제14권1호
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• pp.51-62
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• 2012

The exponential growth in wireless services has resulted in an overly crowded spectrum. The current state of spectrum allocation indicates that most usable frequencies have already been occupied. This makes one pessimistic about the feasibility of integrating emerging wireless services such as large-scale sensor networks into the existing communication infrastructure. Cognitive radio is an emerging dynamic spectrum access technology that can be used for flexibly and efficiently achieving open spectrum sharing. Cognitive radio is an intelligent wireless communication system that is aware of its radio environment and that is capable of adapting its operation to statistical variations of the radio frequency. In ad hoc cognitive radio networks, a common control channel (CCC) is usually used for supporting transmission coordination and spectrum-related information exchange. Determining a CCC in distributed networks is a challenging research issue because the spectrum availability at each ad hoc node is quite different and dynamic due to the interference between and coexistence of primary users. In this paper, we propose a novel CCC selection protocol that is implemented in a distributed way according to the appearance patterns of primary systems and connectivity among nodes. The proposed protocol minimizes the possibility of CCC disruption by primary user activities and maximizes node connectivity when the control channel is set up. It also facilitates adaptive recovery of the control channel when the primary user is detected on that channel.

• 인지과학
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• 제11권1호
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• pp.67-80
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• 2000

분산 협동 정보시스템은 분산. 이질적인 정보환경에서 다양한 지식원과 문제 해결 능력 등을 가지면서 이들이 서로 통합되어 사용되는 시스템을 말한다. 이러한 시스템에서는 구성 정보를 서로 활용하고 제어할 수 있는 조정기능이 필요하고 이러한 조정기능의 역할에 따라 전체 시스템의 양태가 다양하게 결정된다. 본 논문에서는 다중에이전트 패러다임을 적용하여 분산 협동 정보시스템의 한 가지 모델을 제시하고 테스트 시스템을 구현해보았다. 제안 시스템은 분산된 구성원을 에이전트화하고 이들 간의 협동을 원활하게 할 수 있도록 조정 에이전트를 사용하고 조정 에이전트를 사용하고 있다. 본 시스템에서 제안된 조정 에이전트는 지식의 세밀도(granularity) 레벨을 이용하여 에이전트 활성화 순서를 조정한다. 즉, 처음에는 단수하면서도 빠른 속도의 지식 형태를 활용하고 그 결과에 따라 좀 더 복잡한 지식 베이스를 활용하도록 하는 것이다. 제안구조는 동일한 주제에 대하여 여러 레벨의 지식원이 존재할 때 이들을 적절히 순서화함으로써 마치 인지과정에서 의식의 초점(focusing)이 자연스럽게 바뀌는 것과 같은 효과를 얻을 수 있을 것이다.

• 지능정보연구
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• 제5권2호
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• pp.79-97
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• 1999

Knowledge management (KM) is emerging as a robust management mechanism with which an organization can remain highly intelligent and competitive in a turbulent market. Organization knowledge is at the heart of KM success. As a vehicle of acquiring organizational knowledge in a distributed decision-making environment, we applied a fuzzy cognitive map (FMM) technique and proved its effectiveness in a distributed knowledge management environment. Our approach was applied to the financial statement analysis problem, yielding a robust result.

• Journal of Communications and Networks
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• 제14권2호
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• pp.188-194
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• 2012

Cognitive networks (CNs) are capable of enabling dynamic spectrum allocation, and thus constitute a promising technology for future wireless communication. Whereas, the implementation of CN will lead to the requirement of an increased energy-arrival rate, which is a significant parameter in energy harvesting design of a cognitive user (CU) device. A well-designed spectrum-sensing scheme will lower the energy-arrival rate that is required and enable CNs to self-sustain, which will also help alleviate global warming. In this paper, spectrum sensing in a multi-user cognitive ad hoc network with a wide-band spectrum is considered. Based on the prospective spectrum sensing, we classify CN operation into two modes: Distributed and centralized. In a distributed network, each CU conducts spectrum sensing for its own data transmission, while in a centralized network, there is only one cognitive cluster header which performs spectrum sensing and broadcasts its sensing results to other CUs. Thus, a wide-band spectrum that is divided into multiple sub-channels can be sensed simultaneously in a distributed manner or sequentially in a centralized manner. We consider the energy consumption for spectrum sensing only of an analog-to-digital convertor (ADC). By formulating energy consumption for spectrum sensing in terms of the sub-channel sampling rate and whole-band sensing time, the sampling rate and whole-band sensing time that are optimal for minimizing the total energy consumption within sensing reliability constraints are obtained. A power dissipation model of an ADC, which plays an important role in formulating the energy efficiency problem, is presented. Using AD9051 as an ADC example, our numerical results show that the optimal sensing parameters will achieve a reduction in the energy-arrival rate of up to 97.7% and 50% in a distributed and a centralized network, respectively, when comparing the optimal and worst-case energy consumption for given system settings.

• 한국통신학회논문지
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• 제34권11A호
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• pp.822-830
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• 2009

The spectrum efficiency of mobile communication networks can be improved dramatically adopting multiple antennas technologies. In order to guarantee the licensed rights of primary user (PU), the cognitive radio system should perform in a relatively low interference manner when it gets access to the spectrum of licensed networks. In this paper, we explore a uniformly distributed circular antenna array to implement beamforming algorithm that is accomplished by optimization method at the base station of cognitive radio networks, and therefore we can suppress the interference to PU by steering quite low transmission power toward PU and constructing a narrow beam toward cognitive user (CU). By reducing the constraint number of the optimization problem, we also propose a null steering algorithm that steers rather low radiation power toward PU, while the other areas in the same cell are covered by radiation power except the local area around PU. It is pursued to reduce the computation load and enlarge the capacity of cognitive radio networks extremely. The simulation results demonstrate that the proposed algorithms process superior performance.

• 인지과학
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• 제12권1_2호
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• pp.1-9
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• 2001

본 논문에서는 각기다른 장소에 다양한 형태로 분산되어 있는 여러 가지 언어자원들을 웹 기반에서 객체화시키는 모델을 제안한다. 웹 기반에서 객체화된 언어자원들은 다양한 응용 시스템 개발에 간단한 방법으로 이용되어 강력한 자연언어처리 응용 시스템을 구성할 수 있다. 또한, 초기 개발 이후에 이루어진 각 언어자원들의 개량은 별도의 처리과정 없이 자동으로 각 응용 시스템에 반영되므로 효과적인 유지보수가 가능하다는 장점이 있다. 제안한 모델의 적합성을 검증하기 위해 사전 개발 시스템 YDK2000를 설계하고 구현하였다. 개발한 YDK 2000은 기존의 각종 사전의 여러 가지 사전정보를 통합할 수 있을 뿐 아니라 여러 자연언어처리 시스템들과의 인터넷 접속을 통해 언어처리를 위한 사전정보를 손쉽게 통합할 수 있어 고품질의 사전을 개발할 수 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권12호
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• pp.3003-3017
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• 2013

In this paper, we investigate the outage performance of a cognitive relay network. We consider mutual interference in an independent, non-identically distributed Nakagmai-m fading environment. We first derive the close-form outage probability expression, which provides an efficient means to evaluate the effects of several parameters. This allows us to study the impact of several parameters on the network's performance. We then derive the asymptotic expression and reveal that the diversity order is strictly determined by the fading severity of the cognitive system. It is not affected by the primary network. Moreover, the primary network only affects the coding gain of the cognitive system. Finally, Monte Carlo simulations are provided, which corroborate the analytical results.