• Journal of Communications and Networks
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• v.8 no.2
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• pp.158-162
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• 2006

Historically, spectrum use has been increased through use of high frequencies, improved modulation, and between antenna techniques. However, these approaches are reaching practical limits. Cognitive radio allows new approaches to improve the intensity of use in spectrum which is licensed but under utilized. This paper addresses two such possible approaches. Real time spectrum markets permit users to exchange spectrum use. Interruptible spectrum would allow public sector spectrum users to recoup economic benefits for allowing others to share their low average, high peak use spectrum subject to preemption.

• Smart Media Journal
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• v.1 no.1
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• pp.17-26
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• 2012

In cognitive radio networks (CRNs), unlicensed users sense the licensed spectrum bands and opportunistically access them without interfering operations of licensed users. Especially, in ad hoc networks, the MAC layer plays an important role in coordinating unlicensed users access to the spectrum and, thus, a number of MAC protocols have been studied recently. In this paper, we comparatively examine MAC protocols in cognitive radio ad hoc networks (CRAHNs). First, we categorize the protocols on the basis of common control channel (CCC) requirements and further review major implementations for each category. Then, we make a qualitative comparison of the protocols in terms of inherent characteristics and performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.11
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• pp.803-809
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• 2014

In this paper, we investigate physical layer security in a cooperative cognitive radio networks (CRN) with a relay selection in the presence of a primary user and an eavesdropper. To protect the CRN from wiretapping by the eavesdropper, we propose employing an opportunistic relay selection scheme and multiple antennas at the destination that work based on the availability of channel state information at the receivers. Under these configurations, we derive an exact closed-form expression for the secrecy outage probability of the CRN, and also derive an asymptotic probability. Numerical results will be presented to verify the analysis.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.5
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• pp.39-44
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• 2010

In this paper, we analyze the performance of the cooperative cognitive radio relay system which is adapted the recently highly focused cognitive radio system. The performance comparison is made between the system with and that without the opportunistic transmission relay. Especially the selection combining is considered at the destination for simple implementation. In this case, the effect of the channel state information (CSI) delay, which is caused essentially by the process during the CSI delivery, to the system performance is considered. It is noticed that the performance of the system with the opportunistic relay degrades up to 0.6 dB at a given condition compared to the system without the opportunistic relay. And it is shown that the system performance is more sensitive to the CSI delay compared to the frequency acquisition probability of the cognitive radio relay.

• Journal of information and communication convergence engineering
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• v.15 no.2
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• pp.79-84
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• 2017

In a cognitive radio network (CRN), cognitive radio users (CUs) should be powered by a small battery for their operations. The operations of the CU often include spectrum sensing and data transmission. The spectrum sensing process may help the CU avoid a collision with the primary user (PU) and may save the energy that is wasted in transmitting data when the PU is present. However, in a time-slotted manner, the sensing process consumes energy and reduces the time for transmitting data, which degrades the achieved throughput of the CRN. Subsequently, the sensing process does not always offer an advantage in regards to throughput to the CRN. In this paper, we propose a scheme to find an optimal policy (i.e., perform spectrum sensing before transmitting data or transmit data without the sensing process) for maximizing the achieved throughput of the CRN. In the proposed scheme, the data collection period is considered as the main factor effecting on the optimal policy. Simulation results show the advantages of the optimal policy.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.8C
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• pp.655-662
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• 2012

In this work, we propose an airborne cognitive radio system that searches a new spectrum band to avoid a communication interruption due to the interference from many radar signals. We develop a method of fast spectrum sensing based on an effective frequency by recognizing the interfering radar as well as geographical information. This effective frequency is calculated by the free-space path loss between a base station and a fighter with the speed parameter. From our analysis, it is verified that the maximum frequency searching time is reduced by half by using our method.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.1
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• pp.34-49
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• 2015

Market means of spectrum trading have been utilized as a vital method of spectrum sharing and access in future cognitive radio system. In this paper, we consider the spectrum trading with multiple primary carrier providers (PCP) leasing the spectrum to multiple secondary carrier providers (SCP) for a short period of time. Several factors including the price of the resource, duration of leasing, and the spectrum quality guides the proposed model. We formulate three trading policies based on the game theory for dynamic spectrum access in a LTE based cognitive radio system (CRS). In the first, we consider utility function based resource sharing (UFRS) without any knowledge of past transaction. In the second policy, each SCP deals with PCP using a non-cooperative resource sharing (NCRS) method which employs optimal strategy based on reinforcement learning. In variation of second policy, third policy adopts a Nash bargaining while incorporating a recommendation entity in resource sharing (RERS). The simulation results suggest overall increase in throughput while maintaining higher spectrum efficiency and fairness.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.8 no.2
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• pp.43-48
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• 2008

In this paper, we discuss the transmit power of user in Cognitive Radio environment. Transmit power of user should be operated in order not to give a bad effect to PU(Primary user) and this power can be considered as SINR(Signal to Interference and Noise Ratio) measured in PU. Exact spectrum sensing is required to see which is the vacant frequency. And this spectrum sensing should be operated repeatedly within certain time because the vacant frequency is time-varying. In this paper, we reduce the existing defect by using orthogonal parameter and show the sensing operation is possible if SINR of PU can be guaranteed.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.9
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• pp.3312-3334
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• 2015

In this paper, a mechanism for spectrum allocation in overlay cognitive radio networks is proposed. In overlay cognitive radio networks, the secondary users (SUs) must first sense the activity of primary users (PUs) to identify unoccupied spectrum bands. Based on their different contributions for the spectrum sensing, the SUs get payoffs that are computed by the fusion center (FC). The unoccupied bands will be auctioned and SUs are asked to bid using payoffs they earned or saved. Coalitions are allowed to form among SUs because each SU may only need a portion of the bands. We formulate the coalition forming process as a coalition forming game and analyze it by game theory. In the coalition formation game, debtor-creditor relationship may occur among the SUs because of their limited payoff storage. A debtor asks a creditor for payoff help, and in return provides the creditor with a portion of transmission time to relay data for the creditor. The negotiations between debtors and creditors can be modeled as a Bayesian game because they lack complete information of each other, and the equilibria of the game is investigated. Theoretical analysis and numerical results show that the proposed auction yields data rate improvement and certain fairness among all SUs.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.11
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• pp.3775-3788
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• 2014

With the increasing number of the wireless and mobile networks, the way that people use the Internet has changed substantively. Wireless multimedia services, such as wireless video streaming, mobile video game, and mobile voice over IP, will become the main applications of the future wireless Internet. To accommodate the growing volume of wireless data traffic and multimedia services, cognitive radio (CR) and Information-Centric Network (ICN) have been proposed to maximize the utilization of wireless spectrum and improve the network performance. Although CR and ICN have high potential significance for the future wireless Internet, few studies have been conducted on collaborative operations of CR and ICN. Due to the lack of infrastructure support in multi-hop ad hoc CR networks, the problem is more challenging for video streaming services. In this paper, we propose a Cross-layer Video Streaming Mechanism (CLISM) for Cognitive Radio Ad Hoc Information Centric Networks (CRAH-ICNs). The CLISM included two distributed schemes which are designed for the forwarding nodes and receiving nodes in CRAH-ICNs. With the cross-layer approach, the CLISM is able to self-adapt the variation of the link conditions without the central network controller. Experimental results demonstrate that the proposed CLISM efficiently adjust video transmission policy under various network conditions.