Hybrid Cooperative Spectrum Sensing Scheme

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Abstract. In cognitive radio networks, cognitive users can be coordinated to perform cooperative spectrum sensing so as to detect the primary user more ...
Journal of Computational Information Systems 7:5 (2011) 1500-1507 Available at http://www.Jofcis.com

Hybrid Cooperative Spectrum Sensing Scheme Using Double-Fusion in Cognitive Radio Networks Hong DU†, Zaixue WEI, Yu WANG, Dacheng YANG Wireless Theories and Technologies Lab, Beijing University of Posts and Telecommunications, Beijing 100876, China

Abstract In cognitive radio networks, cognitive users can be coordinated to perform cooperative spectrum sensing so as to detect the primary user more accurately. In this paper, a hybrid cooperative spectrum sensing method is investigated to improve the sensing performance by exploiting double-fusion approach. In special, data fusion and decision fusion are both studied. For the first stage, cognitive users send their energy to the fusion center with data fusion in each cognitive cell. For the second stage, the fusion center in each cognitive cell communicates the decision with each other and makes the final decision by using decision fusion. In addition, we derive the optimal number of cognitive users and cells in the proposed scheme. Numerical results show that the sensing performance is improved significantly as opposed to conventional cooperative spectrum sensing with single fusion. Keywords: Cognitive Radio; Hybrid Cooperative Spectrum Sensing; Double-fusion; Data Fusion; Decision Fusion

1. Introduction In order to tackle the problem with underutilization of spectrum, cognitive radio (CR) arises to be a tempting solution to the spectral congestion problem by introducing opportunistic usage of the frequency bands that are not heavily occupied by licensed users [1]. In cognitive radio networks, primary users have higher priority rights on the usage of a specific part of the spectrum. Cognitive users, which have lower priority, exploit this spectrum in such a way that they do not cause interference to primary users. Therefore, cognitive users need to sense the spectrum reliably to check whether it is being used by a primary user and change the radio parameters to exploit the unused part of the spectrum [2]. Due to the fading and shadowing effects, the performance for local sensing will be degraded. Therefore, cooperative spectrum sensing is proposed as a solution to problem that arises in spectrum sensing. Cooperative sensing decreases the probabilities of miss-detection and false alarm considerably. In addition, cooperation can solve hidden primary user problem and it can decrease sensing time. Recently, the research on cooperative sensing mainly focus on decision fusion scheme in centralized cognitive radio networks [3-4]. In particular, an optimal fusion strategy based cooperative spectrum sensing scheme in a cognitive radio network is investigated and analyzed in [5-6]. Besides, there are multiple fusions approaches in cooperative spectrum sensing, such as in [7] both data fusion and decision fusion for



Corresponding author. Email addresses: [email protected] (Hong DU).

1553-9105/ Copyright © 2011 Binary Information Press May, 2011

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H. Du et al. /Journal of Computational Information Systems 7:5 (2011) 1500-1507

multiple slots and multiple cognitive radio users are illustrated. The optimal sensing time for spectrum sensing is observed on tradeoff between sensing and throughput. In [8], the energy fusion and decision fusion is proposed to decrease the reporting errors introduced by the fading channels. However, the fusion scheme almost adopted in centralized or decentralized network topology. In this paper, we consider a hybrid cooperative spectrum sensing method by using double-fusion to improve the sensing performance. In the proposed approach, base station (BS) in cognitive cell is considered as the fusion center, which collects the sensing results from all the users with data fusion. And then, BS forwards its decision to each other by using decision fusion. Moreover, we derive the sensing performance and the optimal number of cognitive users and cells in the hybrid cooperative spectrum sensing scheme. The rest of this paper is organized as follows. The system model of hybrid cooperative spectrum sensing approach is described in Section 2. Section 3 discusses the problem optimization of the proposed scheme based on double-fusion. Specifically, data fusion and decision fusion are presented, respectively. The numerical results are shown and analyzed in Section 4. Finally, conclusions are drawn in Section 5. 2. System Model In cognitive radio networks, energy detection is explored widely for spectrum sensing owing to its low compute complexity. Therefore, energy detection is also adopted in this paper. For local sensing, CR user has to distinguish between absence (H0) and presence (H1) of primary user. Consider N and M are denoted as the number of CR users and samples, respectively. Then the observed energy value of the jth user is given as follows:

⎧∑ M n 2ji , H0 ⎪ i =1 Yj = ⎨ M 2 ⎪⎩∑ i =1 ( s ji + n ji ) , H1

(1)

where sji and nji, 1