• 한국ITS학회 논문지
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• 제9권1호
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• pp.19-26
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• 2010

In this paper, we propose an efficient decision rule in order to get better chance to detect the unused spectrum assigned to a licensed user and improve reliability of spectrum sensing performance. Each secondary user receives the signals from the licensed user. And the resulting signals input to an energy detector. Then, each sensing result is combined and used to make a decision whether the primary user is present at the licensed spectrum band or not. In order to make the reliable decision, we apply an efficient decision rule that is called as a majority rule in this paper. The simulation results show that spectrum sensing performance with the proposed decision rule is more reasonable and efficient than that with conventional decision rules.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권10호
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• pp.4661-4680
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• 2016

Cognitive radio (CR) technology is an effective solution to the spectrum scarcity issue. Collaborative spectrum sensing is known as a promising technique to improve the performance of spectrum sensing in cognitive radio networks (CRNs). However, collaborative spectrum sensing is vulnerable to spectrum data falsification (SSDF) attack, where malicious users (MUs) may send false sensing data to mislead other secondary users (SUs) to make an incorrect decision about primary user (PUs) activity, which is one of the key adversaries to the performance of CRNs. In this paper, we propose a coalition based malicious users detection (CMD) algorithm to detect the malicious user in CRNs. The proposed CMD algorithm can efficiently detect MUs base on the Geary'C theory and be modeled as a coalition formation game. Specifically, SSDF attack is one of the key issues to affect the resource allocation process. Focusing on the security issues, in this paper, we analyze the power allocation problem with MUs, and propose MUs detection based power allocation (MPA) algorithm. The MPA algorithm is divided into two steps: the MUs detection step and the optimal power allocation step. Firstly, in the MUs detection step, by the CMD algorithm we can obtain the MUs detection probability and the energy consumption of MUs detection. Secondly, in the optimal power allocation step, we use the Lagrange dual decomposition method to obtain the optimal transmission power of each SU and achieve the maximum utility of the whole CRN. Numerical simulation results show that the proposed CMD and MPA scheme can achieve a considerable performance improvement in MUs detection and power allocation.

• 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.

• Journal of information and communication convergence engineering
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• 제12권2호
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• pp.97-103
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• 2014

In spectrum sensing, there is a tradeoff between the probability of missed detection and the probability of a false alarm according to the value of the sensing threshold. Therefore, it is important to determine the sensing threshold suitable to the environment of cognitive radio networks. In this study, we consider a cognitive radio-based ad hoc network where secondary users directly communicate by using the same frequency band as the primary system and control their transmit power on the basis of the distance between them. First, we investigate a condition in which the primary and the secondary users can share the same frequency band without harmful interference from each other, and then, propose an algorithm that controls the sensing threshold dynamically on the basis of the transmit power of the secondary user. The analysis and simulation results show that the proposed sensing threshold control algorithm has low probabilities of both missed detection and a false alarm and thus, enables optimized spectrum sharing between the primary and the secondary systems.

• Journal of information and communication convergence engineering
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• 제11권4호
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• pp.223-228
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• 2013

Cognitive radio has been recently considered a promising technology to improve spectrum utilization by enabling secondary access to licensed bands that are not used by primary users temporarily or spatially. A prerequisite to this secondary access is the lack of interference to the primary system. This requirement makes spectrum sensing a key process for cognitive radio. In this study, we consider amplify and forward (AF)-based cooperative spectrum sensing for cognitive radio networks where multiple relay nodes are utilized to amplify and forward the primary user signal for better spectrum sensing, and maximum ratio combining is used for fusion detection by a cognitive coordinator. Further, the detection probability and the bit error rate of AF-based cooperative spectrum sensing are analyzed in fading multiple cognitive relay channels. The simulation results show that the AF-based cooperative spectrum sensing scheme outperforms the conventional scheme.

• 한국위성정보통신학회논문지
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• 제10권1호
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• pp.49-55
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• 2015

인지무선 네트워크에서 스펙트럼 센싱은 우선사용자에게 간섭을 주지 않기 위해 기본적으로 수행해야 하는 단계이다. 스펙트럼 센싱에 요구되는 샘플 수는 2차 사용자의 성능에 직접적으로 영향을 주기 때문에, 2차 사용자의 성능과 우선사용자에 대한 간섭은 트레이드오프 관계에 있다. 스펙트럼 센싱에 필요한 샘플 수는 요구되는 오검출 확률, 검출확률 및 우선 사용자의 최소 요구 SNR로 부터 얻어진다. 우선 사용자 센싱에 요구되는 SNR은 2차 사용자의 전송반경과 관련 있기 때문에, 2차사용자들을 모아 센싱집합으로 구성하고 요구되는 전송영역을 최소화시킴으로써 스펙트럼 센싱에 요구되는 우선사용자의 SNR을 완화시킬 수 있다. 따라서 스펙트럼 센싱에 필요한 최소 샘플 수를 줄임으로써 인지무선 네트워크의 전송량을 향상시킬 수 있다. 본 논문에서는 이를 위해 센싱집합인 클러스터링을 통해 게임이론으로 클러스터의 크기에 따라 얻는 이득과 손실을 트레이드오프로 디자인하고, 시뮬레이션을 통해 제안된 방법의 성능을 확인한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권10호
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• pp.2338-2356
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• 2013

In cognitive radio networks, acquiring the position information of the primary user is critical to the communication of the secondary user. Localization of primary users can help improve the efficiency with which the spectrum is reused, because the information can be used to avoid harmful interference to the network while simultaneity is exploited to improve the spectrum utilization. Despite its inherent inaccuracy, received signal strength based on range has been used as the standard tool for distance measurements in the location detection process. Most previous works have employed the path-loss propagation model with a fixed value of the path loss exponent. However, in actual environments, the path loss exponent for each channel is different. Moreover, due to the complexity of the radio channel, when the number of channel increases, a larger number of RSS measurements are needed, and this results in additional energy consumption. In this paper, to overcome this problem, we propose using the Bayesian compressive sensing method with a calibrated path loss exponent to improve the performance of the PU localization method.

• Journal of Communications and Networks
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• 제15권5호
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• pp.514-526
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• 2013

With a long sensing period, the inter-frame spectrum sensing in IEEE 802.22 standard is vulnerable to the effect of the traffic of the primary user (PU). In this article, we address the two degrading factors that affect the inter-frame sensing performance with respect to the random arrival/leaving of the PU traffic. They are the noise-only samples under the random arrival traffic, and the PU-signal-contained samples under the random leaving traffic. We propose the model in which the intra-frame sensing cooperates with the inter-frame one, and the inter-frame sensing uses the time-of-arrival (ToA), and time-of-leave (ToL) detectors to reduce the two degrading factors in the inter-frame sensing time. These ToA and ToL detectors are used to search for the sample which contains either the ToA or ToL of the PU traffic, respectively, which allows the partial cancelation of the unnecessary samples. At the final stage, the remaining samples are input into a primary user detector, which is based on the energy detection scheme, to determine the status of PU traffic in the inter-frame sensing time. The analysis and the simulation results show that the proposed scheme enhances the spectrum-sensing performance compared to the conventional counter-part.

• 한국통신학회논문지
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• 제35권3A호
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• pp.296-305
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• 2010

CR 네트워크에서 기존의 단일 노드를 기반으로 하는 센싱 방법은 PU 보호를 위한 센싱 요구조건을 만족시키기 위해 주기적이고 빈번한 센싱을 요구한다. 그러나 각각의 노드는 동작 채널을 결정하기 위해 넓은 대역의 스펙트럼을 관찰해야 하기 때문에, 이 같은 단일 노드에 의한 지속적인 센싱 동작은 센싱 오버헤드를 크게 증가시키게 되어, 확보한 동작 채널에서의 정상적인 송수신 (normal operation) 기회를 감소시키는 것은 물론, 센싱 오버헤드로 인해 노드의 수명이 짧아지는 등의 많은 문제점을 야기할 수 있다. 이러한 문제점을 해결하기 위해, 본 논문에서는 동일한 센싱 결과가 예측되는 센싱 zone 기반의 분산적 공정 센싱 방법을 제안하고, 제안된 센싱 동작이 PU 시스템을 보호하기 위한 센싱 요구조건을 만족하도록 하는 프레임 구조를 설계하였다. 또한 이렇게 설계된 프레임 구조를 바탕으로 시뮬레이션 실험을 수행하였으며, 그 결과 제안된 방법이 PU 시스템 보호를 위한 요구조건을 만족시키면서 동시에 기존의 개별적 센싱 방법에 비해 센싱 오버헤드를 크게 감소시킬 수 있음을 보였다.

• ETRI Journal
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• 제35권4호
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• pp.644-654
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• 2013

In this paper, a signal detection scheme for cognitive radio (CR) based on the Bussgang theorem is proposed. The proposed scheme calculates the statistical difference between Gaussian noise and the primary user signal by applying the Bussgang theorem to the received signal. Therefore, the proposed scheme overcomes the noise uncertainty and gives scalable complexity according to the zero-memory nonlinear function for a mobile device. We also present the theoretical analysis on the detection threshold and the detection performance in the additive white Gaussian noise channel. The proposed detection scheme is evaluated by computer simulations based on the IEEE 802.22 standard for the wireless regional area network. Our results show that the proposed scheme is robust to the noise uncertainty and works well in a very low signal-to-noise ratio.