• 정보통신설비학회논문지
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• 제8권3호
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• pp.111-115
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• 2009

Cognitive Radio (CR) technology is proposed for using the unused spectrum band efficiently because of the spectrum scarcity problems. Spectrum sensing is one of the most challenging issues in cognitive radio system. In this paper, we focus on the signal detection of WiBro system band. As most of the modulated signals can be treated as cyclostationary random process, we can detect the signal of the OFDM signals in WiBro system. OFDM symbols using WiBro system have several pilot subcarriers and periodic pilots have cyclostationary characteristic. To improve the detection performance, we get diversity gain using multiple antennas.

• 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.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2008년도 정보통신설비 학술대회
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• pp.379-383
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• 2008

Cognitive Radio (CR) technology is proposed for using the unused spectrum band efficiently because of the spectrum scarcity problems. Spectrum sensing is one of the most challenging issues in cognitive radio system. In this paper, we focus on the signal detection of WiBro system band. As most of the modulated signals can be treated as cyclostationary random process, we can detect the signal of the OFDM signals in WiBro system. OFDM symbols using WiBro system have several pilot subcarriers and periodic pilots have cyclostationary characteristic. To improve of the detection performance, we get diversity gain using multiple antennas.

• 한국전자파학회논문지
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• 제22권4호
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• pp.416-422
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• 2011

본 논문에서는 개별 센싱 결과를 결합하기 위해 센싱의 성능은 연판정 방식보다 낮지만, 시스템의 부담이 적고 비교적 단순한 방식인 경판정 방식을 적용하였으며, 센싱의 성능을 높이기 위해 각 CR 기기의 검출 확률을 반영하여 가중치를 설정하고, 계산된 가중치가 개별 센싱 결과에 재반영되어 결합하는 최적화된 경판정 방식을 제안한다. 기존의 경판정 방식과 달리 가중치를 적용하여 센싱 성능을 높이도록 하였고, 모의 실험 및 분석을 통하여 성능을 나타내었다. 1차 사용자의 신호는 OFDM 기반의 시스템을 가정하였고, 1차 사용자와 CR 기기 사이의 무선 채널은 가우시안(Gaussian) 채널로 모델링하였다.

• ETRI Journal
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• 제37권3호
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• pp.460-470
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• 2015

Orthogonal frequency-division multiplexing (OFDM) is one of the most widely used technologies in current wireless communication systems and standards. Cognitive radio (CR) provides a robust solution to the problem of spectrum congestion as it offers opportunistic usage of frequency bands that are not occupied by primary users. Due to the underlying sensing, spectrum shaping, scaling, and interoperable capabilities of OFDM, it has been adapted as a best transmission technology for CR wireless systems. However, the performance of an OFDM-based CR wireless system is affected by the existence of narrowband interference (NBI) from other users. Further, due to carrier frequency offset in NBI sources, NBI energy may spread over all subcarriers of an OFDM signal. In this paper, a fixed Amplify-and-Forward (AF) relay that operates at a frequency band that is different from that of direct mode is introduced to suppress the effect of NBI. Analytical expressions are derived for outage probability in direct, AF-relay, and incremental relaying modes. The outage performance of the proposed AF relay-based CR network is proven to be better than that of direct mode.

• 한국정보통신학회논문지
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• 제13권3호
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• pp.564-571
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• 2009

본 논문에서는 다중 주파수 채널이 운용중인 CR 기지국에서 외부대역 협력 스펙트럼 센싱 방식을 제안하였다. 그리고 ATSC 디지털 TV 신호인 경우에 대한 신호검출결과를 제시하였고 주파수 선택적 Rayleigh 페이딩 채널에서 외부대역 협력 센싱 방법에 대한 신호검출확률과 오경보 확률을 유도하였다. 수치해석 결과로는 CR 기지국에서 통신 중인 다중 주파수 채널의 CR단말기들이 측정한 incumbent 신호의 채널 전력이 유사한 경우에는 외부대역 협력 스펙트럼 센싱을 시행함으로써 incumbent 신호의 센싱 성능이 향상됨을 보여주고 있다.

• 한국전자통신학회논문지
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• 제13권5호
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• pp.1043-1050
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• 2018

본 논문은 인지 무선(CR, Cognitive Radio) 네트워크에서 우선 사용자(Primary User)의 존재 유무를 2차 사용자(Secondary User)가 결정하기 위하여 협력 센싱을 사용하는 환경에서 스펙트럼 센싱의 감지 성능을 높이기 위해 강화 학습(Reinforce learning) 기반으로 최적의 인지 무선 사용자 선택하는 협력 센싱 방안을 제안한다. 협력 센싱을 통해 파악한 전역 센싱 결과와 인지 무선 사용자의 센싱 결과 간의 유사도에 따라 정확도가 높은 사용자를 파악한다. 이 정확도를 강화학습의 보상으로 사용하여 협력 센싱을 수행할수록 전역 결정과 일치하는 센싱 정보를 전송하는 사용자를 선택할 수 있다. 실험 결과 제안한 기법이 기존 협력 센싱 대비 향상된 스펙트럼 감지 성능을 보임을 확인할 수 있다.

• IEIE Transactions on Smart Processing and Computing
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• 제2권6호
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• pp.357-366
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• 2013

Spectrum sensing, as a fundamental functionality of Cognitive Radio (CR), enables Secondary Users (SUs) to monitor the spectrum and detect spectrum holes that could be used. Recently, the security issues of Cognitive Radio Networks (CRNs) have attracted increasing research attention. As one of the attacks against CRNs, a Primary User Emulation (PUE) attack compromises the spectrum sensing of CR, where an attacker monopolizes the spectrum holes by impersonating the Primary User (PU) to prevent SUs from accessing the idle frequency bands. Energy detection is often used to sense the spectrum in CRNs, but the presence of PUE attack has not been considered. This study examined the effect of PUE attack on the performance of energy detection-based spectrum sensing technique. In the proposed protocol, the stationary helper nodes (HNs) are deployed in multiple stages and distributed over the coverage area of the PUs to deliver spectrum status information to the next stage of HNs and to SUs. On the other hand, the first stage of HNs is also responsible for inferring the existence of the PU based on the energy detection technique. In addition, this system provides the detection threshold under the constraints imposed on the probabilities of a miss detection and false alarm.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권9호
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• pp.2120-2133
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• 2013

In this paper, we address the problem of linear minimum mean-squared error (MMSE) transmitter design for the cognitive radio (CR) multi-user multiple-input single-output (MU-MISO) broadcasting channel (BC), where the cognitive users are subject to not only a sum power constraint, but also a interference power constraint. Evidently, this multi-constraint problem renders it difficult to solve. To overcome this difficulty, we firstly transform it into its equivalent formulation with a single constraint. Then by utilizing BC-MAC duality, the problem of BC transmitter design can be solved by focusing on a dual MAC problem, which is easier to deal with due to its convexity property. Finally we propose an efficient two-level iterative algorithm to search the optimal solution. Our simulation results are provided to corroborate the effectiveness of the proposed algorithm and show that this proposed CR MMSE-based scheme achieves a suboptimal sum-rate performance compared to the optimal DPC-based algorithm with less computational complexity.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권9호
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• pp.2101-2119
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• 2013

The spectrum allocation is an attractive issue for mobile cognitive radio (CR) network. However, the time-varying characteristic of the spectrum allocation is not fully investigated. Thus, this paper originally deduces the probabilities of spectrum availability and interference constrain in theory under the mobile environment. Then, we propose a prediction mechanism of the time-varying available spectrum lists and the dynamic interference topologies. By considering the node mobility and primary users' (PUs') activity, the mechanism is capable of overcoming the static shortcomings of traditional model. Based on the mechanism, two prediction-based spectrum allocation algorithms, prediction greedy algorithm (PGA) and prediction fairness algorithm (PFA), are presented to enhance the spectrum utilization and improve the fairness. Moreover, new utility functions are redefined to measure the effectiveness of different schemes in the mobile CR network. Simulation results show that PGA gets more average effective spectrums than the traditional schemes, when the mean idle time of PUs is high. And PFA could achieve good system fairness performance, especially when the speeds of cognitive nodes are high.