• 한국인터넷방송통신학회논문지
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• 제9권3호
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• pp.179-185
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• 2009

인지 라디오(CR : Cognitive Radio)는 주파수 자원을 효율적으로 사용하기 위해 제안된 기술로 최근 주파수 자원의 부족 현상을 완화하기 위한 방법으로 연구 되고 있다. 인지 라디오는 주파수 정책에 따라 주파수를 할당받은 우선순위 사용자(Primary user)가 해당 주파수를 사용하고 있지 않을 때 부 사용자(Secondary user)가 빈 주파수를 검출하여 해당 주파수를 사용하는 기술이다. 부 사용자가 우선순위 사용자를 검출하는 기술인 스펙트럼 센싱은 수행하는 과정에서 다중경로 페이딩문제로 인해 성능이 낮아지는데 이를 보완하기 위해 본 논문에서는 다이버시티기법을 사용한다. 다이버시티 기술에는 시간 다이버시티, 주파수 다이버시티, 공간 다이버시티 등이 있는데 본 논문에서는 공간 다이버시티의 한 종류인 안테나 다이버시티를 적용하여 다중경로 페이딩 문제를 해소하며 스펙트럼 센싱의 성능 및 신회성이 높아짐을 모의실험의 결과를 통하여 제시한다.

• 한국콘텐츠학회논문지
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• 제9권3호
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• pp.39-48
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• 2009

스펙트럼 센싱 기술은 차세대 무선통신 기술들 중 하나인 Cognitive Radio (CR) 시스템에서의 핵심 기술이다. CR 시스템은주변의 허가된 무선국을 보호하기 위해 주변 무선 환경을 탐색하여 빈 주파수 대역을 찾아 임시적으로 주파수 대역을 사용할 수 있도록 하는 기술이다. 본 논문은 임베디드 보드에서 CR 기술 기반의 효율적인 스펙트럼 센싱 기법들을 구현하였다. 6MHz 대역폭을 가진 DVB-H 신호를 입력 신호로 실험하였으며, Modified Periodogram Method, Welch's Method, SCF Method을 통하여 스펙트럼 센싱 결과를 확인하였다. 또한, 각각의 스펙트럼 센싱 모듈의 성능과 세부 기능들의 실행 속도를 TI320C6416 DSP 보드를 통하여 비교하였다.

• 천문학회보
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• 제39권2호
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• pp.68.2-68.2
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• 2014

High Frequency Peakers (HFPs) are radio-loud Active Galactic Nuclei (AGN), which are regarded as being in the earliest evolutionary phase (102-103 years) of radio galaxies. They are expected to be small in size (< ~1 kpc) compared to their host galaxies (~a few 10s kpc), and have convex spectra, which are peaking at high radio frequency (> 5 GHz). Their size and spectral shape are the most obvious supporting evidence of extremely young ages. HFPs are therefore ideal targets to probe the earliest stage of radio sources. To date however, the young radio source classification has been relying mainly on the spectral shape which usually does not cover high enough frequencies where the true peak flux is located. Hence HFPs are often confused with blazars which may show a similar spectral shape and apparent compactness but are a somewhat evolved form of AGNs. Therefore, we have been challenging to identify HFPs among the sample of 19 candidates using the Korean VLBI Network (KVN) which enables us to extend the radio spectrum baseline up to 22 and 43 GHz. These are higher than the frequencies used in most previous studies of HFPs, allowing us to select genuine HFPs. By long-term monitoring of 18 epochs, we have also inspected the variability of the sample to select out blazars which are highly variable yet with a similar radio spectrum. In this work, we present the light curves and spectral properties of the HFP candidates. We discuss the results of our re-identification of HFPs.

• Journal of Communications and Networks
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• 제11권2호
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• pp.148-156
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• 2009

The fixed spectrum assignment policy in today's wireless networks leads to inefficient spectrum usage. Cognitive radio network is a new communication paradigm that enables the unlicensed users to opportunistically use the spatio-temporally unoccupied portions of the spectrum, and hence realizing a dynamic spectrum access (DSA) methodology. Interference temperature model proposed by Federal Communications Commission (FCC) permits the unlicensed users to utilize the licensed frequencies simultaneously with the primary users provided that they adhere to the interference temperature constraints. In this paper, we formulate two NP-hard optimal scheduling methods that meet the interference temperature constraints for cognitive radio networks. The first one maximizes the network throughput, whereas the second one minimizes the scheduling delay. Furthermore, we also propose suboptimal schedulers with linear complexity, referred to as maximum frequency selection (MFS) and probabilistic frequency selection (PFS). We simulate the throughput and delay performance of the optimal as well as the suboptimal schedulers for varying number of cognitive nodes, number of primary neighbors for each cognitive node, and interference temperature limits for the frequencies. We also evaluate the performance of our proposed schedulers under both additive white gaussian noise (AWGN) channels and Gilbert-Elliot fading channels.

• 한국통신학회논문지
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• 제32권10A호
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• pp.984-991
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• 2007

Cognitive Radio is an advanced enabling techlology for efficient utilization of under-utilized spectrum since it is able to sense the temporally available spectrum and adapt its parameters to fully utilize the frequency band. Recent investigation suggests that spectrum sensing is compromised when a cognitive radio user suffers from the environment with fading or shadowing. In order to combat the effect, collaborative sensing is considered to be a promising way, which combines the sensing result of each user to achieve good performance. However, the conventional collaborative sensing is not efficient when users suffer different fading environments. In this paper, we propose a weighted-collaborative scheme that considers using the weights of each collaborative CR user, which can achieve better sensing performance under both fast and slow fading environments. The analysis of the simulation resultsproves that the weighted-collaborative scheme improves sensing performance obviously and outperforms the conventional method.

• 전자통신동향분석
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• 제34권6호
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• pp.1-16
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• 2019

The paper presents five strategic opinions for promoting the fourth industry revolution through the supply of 5G additional frequency. The assessments are on the basis of 5G frequency utilization technologies and services, with reference to 3GPP 5G New Radio standards, after investigating the domestic 1G, 2G, 3G, 4G, and 5G mobile communication services as well as the use of mobile radio frequency and spectrum. The presented opinions contain the frequency supply of contiguous-wide bandwidth channels, harmonized frequency supply between licensed and unlicensed spectrum, the existing 4G frequency recycle for increasing 5G coverage and capacity, balance frequency supply in the multi-band for 5G services, and the development of 5G vertical frequency for industry. The aim is that the presented five strategic opinions can offer guidance for the upcoming plan of domestic 5G additional frequency supply.

• International Journal of Computer Science & Network Security
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• 제23권12호
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• pp.13-26
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• 2023

Recently, the development of wireless network technologies has been advancing in several directions: increasing data transmission speed, enhancing user mobility, expanding the range of services offered, improving the utilization of the radio frequency spectrum, and enhancing the intelligence of network and subscriber equipment. In this research, a series of contradictions has emerged in the field of wireless network technologies, with the most acute being the contradiction between the growing demand for wireless communication services (on operational frequencies) and natural limitations of frequency resources, in addition to the contradiction between the expansions of the spectrum of services offered by wireless networks, increased quality requirements, and the use of traditional (outdated) management technologies. One effective method for resolving these contradictions is the application of artificial intelligence elements in wireless telecommunication systems. Thus, the development of technologies for building intelligent (cognitive) radio and cognitive wireless networks is a technological imperative of our time. The functions of artificial intelligence in prospective wireless systems and networks can be implemented in various ways. One of the modern approaches to implementing artificial intelligence functions in cognitive wireless network systems is the application of fuzzy logic and fuzzy processors. In this regard, the work focused on exploring the application of fuzzy logic in prospective cognitive wireless systems is considered relevant.

• Journal of Communications and Networks
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• 제8권4호
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• pp.401-409
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• 2006

Orthogonal frequency division multiplexing (OFDM) and multiple input multiple output (MIMO) technologies provide additional dimensions of freedom with spectral and spatial resources for radio resource management. Multi-dimensional radio resource management has recently been identified to exploit the full dimensions of freedom for more flexible and efficient utilization of scarce radio spectrum while provide diverse quality of service (QoS) guarantees. In this work, a multi-dimensional radio resource scheduling scheme is proposed to achieve above goals in hybrid orthogonal frequency division multiple access (OFDMA) and space division multiple access (SDMA) systems. Cochannel interference (CCI) introduced by frequency reuse under SDMA is eliminated by frequency division and time division between highly interfered users. This scheme maximizes system throughput subjected to the minimum data rate guarantee. for heterogeneous users and transmit power constraint. By numerical examples, system throughput and fairness superiority of the our scheduling scheme are verified.

• ETRI Journal
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• 제30권1호
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• pp.21-32
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• 2008

Cognitive radio (CR) has been proposed as an effective technology for flexible use of the radio spectrum. The interference between primary users and CR users, however, becomes a critical problem when they are using adjacent frequency channels with different transmission power levels. In this paper, a robust CR orthogonal frequency division multiplexing (OFDM) architecture, which can effectively suppress interference to nearby primary users and overcome adjacent channel interference (ACI) to the CR user, is proposed. This new approach is characterized by adaptive data repetition for subcarriers under heavy ACI, and adaptive time spreading for subcarriers near the borders of the CR user's spectrum. The data repetition scheme provides extra power gain against the ACI coming from primary users. Time spreading guarantees an acceptable interference level to nearby primary users. By computer simulation, we demonstrate that, under a CR environment, the proposed CR OFDM architecture outperforms conventional OFDM systems in terms of throughput and BER performance.

• Journal of Communications and Networks
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• 제14권3호
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• pp.252-256
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• 2012

We consider resource allocation in femto-cell networks to maximize the throughput while minimizing interference to macro-users nearby. This can be achieved by allocating spectrum resource in a cognitive radio way. The proposed resource allocation is performed in two steps; spectrum sensing and resource scheduling. The femto base station detects idle frequency assignments (FAs) free from the occupation by macro-users and then allocates sub-channels in an idle FA to femto-users, effectively managing the interference problem. Finally, the effectiveness of the proposed scheme is verified by computer simulations.