• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.7
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• pp.1422-1428
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• 2009

In this paper, we consider an independent type cognitive radio system where secondary users can utilize empty channels that are not currently used by primary users having the license to these channels. In the previous works, secondary users search channels sequently or randomly to detect activities of primary user on channels. These channel searching methods however are not suitable to the characteristics of the wireless environment. Therefore, we propose a channel searching method based on the channel list for the purpose of reducing the channel searching time and improving the throughput of secondary users. In the proposed method, we firstly determine weighting value of each channel based on the history of channel activities of primary users and add the weighing value to current channel state buffer. And then, we search an empty channel from channel with smallest value to one with the biggest value. Finally, we compare the performances of the proposed method with those of the sequential channel searching and the random channel searching methods in terms of average channel searching time and average number of transmissions of secondary user.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.5A
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• pp.429-435
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• 2009

Cooperative spectrum sensing allows secondary users of a cognitive radio(CR) network to collaborate to determine whether a primary user occupies the spectrum of interest or not. It usually performs spectrum sensing by combining the individual decisions of each second user into a final one and the k-out-of-n fusion rule is a general approach for decision fusion. This rule declares that the spectrum is occupied only when the decisions from more than k-1 secondary users indicate the presence of a primary user. In this paper, we analyze a cooperative spectrum sensing scheme with the fusion rule under the constraint that its detection probability is maintained to be no less than a given level and its numerical results for the case of a CR network with 10 secondary users.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.2
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• pp.253-263
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• 2015

Lately, spectrum sensing performance has been improved by using cooperate spectrum sensing which each results of sensing of several secondary users are reported to the fusion center. Using Cognitive Radio, secondary user is able to share a bandwidth allocated to primary user. In this paper, we propose a new decentralized cooperative spectrum sensing scheme which compensates the performance degradation of existing decentralized cooperative spectrum sensing considering the error probability of the channel which sensed result of the secondary user is delivered to the fusion center in decentralized cooperative spectrum sensing. In addition, a sensing threshold optimization of minimizing the error probability of decentralized cooperative spectrum sensing is introduced by deriving the equation and the optimal sensing threshold has been confirmed to maximize the decentralized cooperative spectrum sensing performance.

• Journal of Communications and Networks
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• v.11 no.2
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• pp.175-186
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• 2009

A new medium access control (MAC) scheme embedding physical channels into multiband carrier sense multiple access/collision avoidance (CSMA/CA) networks is proposed to provide strict quality of service (QoS) guarantee to high priority users. In the proposed scheme, two priority classes of users, primary and secondary users, are supported. For primary users physical channels are provided to ensure strict QoS, whereas secondary users are provided with best-effort service using CSMA/CA modified for multiband operation. The performance of the proposed MAC scheme is investigated using a new multiband CSMA/CA Markov chain model capturing the primary user activity and the operation of secondary users in multiple bands. The throughput of secondary users is obtained as a function of the primary user activity and other CSMA/CA parameters. It is shown that the new MAC scheme yields larger throughput than the conventional single-band CSMA/CA when both schemes use the same bandwidth.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.10
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• pp.3887-3907
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• 2015

This paper introduces a full duplex single secondary user multiple-input multiple-output (FD-SSU-MIMO) cognitive radio network, where secondary user (SU) opportunistically accesses the authorized spectrum unoccupied by primary user (PU) and transmits data based on FD-MIMO mode. Then we study the network achievable average sum-rate maximization problem under sum transmit power budget constraint at SU communication nodes. In order to solve the trade-off problem between SU's sensing time and data transmission time based on opportunistic spectrum access (OSA) and the power allocation problem based on FD-MIMO transmit mode, we propose a simple trisection algorithm to obtain the optimal sensing time and apply an alternating optimization (AO) algorithm to tackle the FD-MIMO based network achievable sum-rate maximization problem. Simulation results show that our proposed sensing time optimization and AO-based optimal power allocation strategies obtain a higher achievable average sum-rate than sequential convex approximations for matrix-variable programming (SCAMP)-based power allocation for the FD transmission mode, as well as equal power allocation for the half duplex (HD) transmission mode.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.11
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• pp.944-954
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• 2013

Cognitive radio technology gives secondary users chances that they can use specific spectrum of the primary user when the primary user doesn't use it. This paper proposes the algorithm that maximizes the benefit of the primary user considering spectrum price and auction period by using the auction game theory. According to the ratio of spectrum that secondary users bid, primary user allocates spectrum to secondary users. In the process of repeated auction, the primary user gets to find the optimal price of spectrum. Using the price and the proposed utility function of primary user, we derive the optimal auction period. At the same time, the primary user finally determines the price of spectrum appropriate for the optimal period.

• Journal of Satellite, Information and Communications
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• v.10 no.1
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• pp.49-55
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• 2015

In cognitive radio network (CRN), spectrum sensing is an elementary level of technology for non-interfering to licensed user. Required sample number for spectrum sensing is directly related to the throughput of secondary user and makes the tradeoff between the throughput of secondary user and interference to primary user. Required spectrum sensing sample is derived from required false alarm, detection probability and minimum required SNR of primary user (PU). If we make clustering and minimize the required transmission boundary of secondary user (SU), we can relax the required PU SNR for spectrum sensing because the required SNR for PU signal sensing is related to transmission range of SU. Therefore we can achieve efficient throughput of CRN by minimizing spectrum sensing sample. For this, we design the tradeoff between gain and loss could be obtained from clustering, according to the size of cluster members through game theory and simulation results confirm the effectiveness of the proposed method.

• Journal of Communications and Networks
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• v.11 no.2
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• pp.104-114
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• 2009

In this paper, a technique is proposed that enables secondary users to evaluate channel availability in cognitive radio networks. Here, secondary users estimate the utilization of channels via predicting the traffic pattern of primary user, and select a proper channel for radio transmission. The proposed technique reduces the channel switching rate of secondary users (the rate of switching from one channel to another) and the interference on primary users, while maintaining a reasonable call blocking rate of secondary users.

• ETRI Journal
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• v.38 no.5
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• pp.941-951
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• 2016

In this paper, cognitive radio and simultaneous wireless information and power transfer (SWIPT) are effectively combined to design a spectrum-efficient and energy-efficient transmission paradigm. Specifically, a novel SWIPT-based primary-secondary cooperation model is proposed to increase the transmission rate of energy/spectrum constrained users. In the proposed model, a multi-antenna secondary user conducts simultaneous energy harvesting and information forwarding by means of power splitting (PS), and tries to maximize its own transmission rate under the premise of successfully assisting the data delivery of the primary user. After the problem formulation, joint power splitting and beamforming optimization algorithms for decode-and-forward and amplify-and-forward modes are presented, in which we obtain the optimal PS factor and beamforming vectors using a golden search method and dual methods. Simulation results show that the proposed SWIPTbased primary-secondary cooperation schemes can obtain a much higher level of performance than that of non-SWIPT cooperation and non-cooperation schemes.

• Journal of Satellite, Information and Communications
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• v.12 no.3
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• pp.98-102
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• 2017

In this paper, we study RF-powered backscatter cognitive radio networks to improve the performance for the secondary user which is backscatter radio based wireless sensors. In our proposed model, we consider an avoiding the doubly round-trip attenuation to add a carrier emitter and utilization of spectrum sensing information. When the primary channel is busy, the secondary user is able to harvest RF energy from the channel through a hybrid-access point (H-AP) and a carrier emitter. When the channel becomes idle, the secondary user will be use the harvested energy to operate wireless sensors, to use the sensing and to backscatter through the carrier emitter. We model mathematically the deterministic and multisource elements of a number of tagged channels. In the proposed communication environment, we show the BER performance of the backscatter communication using WiFi signal.