• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권1호
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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.

• 한국전자파학회논문지
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• 제18권4호
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• pp.448-454
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• 2007

본 논문에서는 CR(Cognitive Radio)의 가장 적합한 인공지능 기술로 주목받고 있는 게임 이론을 전력 제어 방식에 적용해 CDMA 시스템 기반의 사용효율과 효용에 대한 성능 평가 결과를 제시하였다. 사용자와 네트워크 동시 최적화를 위한 효용함수식을 정의하였으며 모의실험을 통해 FOM(Figure of Merit)과 형평성(Fairness)에서 기존의 폐루프 전력 제어 방식보다 월등한 성능을 입증하였다. 또한 게임 이론을 적용한 전력 제어 방식은 통신 환경을 인지하고 연산하여 적합한 최적의 서비스를 제공하는 CR의 여러 분야에 확장 적용 가능함을 제시하였다.

• Journal of Information Processing Systems
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• 제12권2호
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• pp.295-309
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• 2016

Spectrum sensing is an essential function that enables cognitive radio technology to explore spectral holes and resourcefully access them without any harmful interference to the licenses user. Spectrum sensing done by a single node is highly affected by fading and shadowing. Thus, to overcome this, cooperative spectrum sensing was introduced. Currently, the advancements in multiple antennas have given a new dimension to cognitive radio research. In this paper, we propose a multiple energy detector for cooperative spectrum sensing schemes based on the evidence theory. Also, we propose a reporting mechanism for multiple energy detectors. With our proposed system, we show that a multiple energy detector using a cooperative spectrum sensing scheme based on evidence theory increases the reliability of the system, which ultimately increases the spectrum sensing and reduces the reporting time. Also in simulation results, we show the probability of error for the proposed system. Our simulation results show that our proposed system outperforms the conventional energy detector system.

• 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.

• 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.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권9호
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• pp.3004-3015
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• 2014

This letter proposes an efficient joint resource allocation scheme for OFDM-based cooperative cognitive radio networks (CRNs) under various practical limitations. Compared with those traditional approaches, which guarantee the transmission rates of cognitive users, the proposed scheme ensures that cognitive users are maintained in proportion to the predefined target rates. Numerical simulation shows that the proposed scheme can achieve a reasonable tradeoff between performance and computational complexity.

• 한국정보통신학회논문지
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• 제16권8호
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• pp.1606-1612
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• 2012

인지라디오 네트워크는 현재 주파수 사용 현황을 인지하여 허가받은 주 사용자가 사용하지 않는 채널을 통해 데이터 통신을 하는 기술로써, 이러한 유휴 채널을 효율적으로 이용하기 위해서는 스펙트럼 할당 기술이 중요하다. 하지만 인지라디오 네트워크는 기존의 네트워크와는 달리 사용가능한 스펙트럼이 유동적이므로 자원 할당 시 이러한 자원 변화를 효율적으로 활용할 필요가 있다. 본 논문에서는 인지라디오 사용자들 간의 공평성과 시스템 수율을 동시에 만족시키기 위해 비례공정 채널할당기법을 적용하였다. 이때 유동적인 인지라디오 채널 변화를 고려하여 인지라디오 네트워크의 사용자 간섭 확률을 줄일 수 있도록 기존의 스케줄러를 수정한 스펙트럼 할당기법을 제안하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권9호
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• pp.2323-2340
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• 2012

Recent advances in cognitive radio technology have drawn immense attention to higher layer protocols above medium access control, such as transmission control protocol (TCP). Most proposals to improve the TCP performance in cognitive radio (CR) networks have assumed that either all nodes are in CR networks or the TCP sender side is in CR links. In those proposals, lower layer information such as the CR link status could be easily exploited to adjust the congestion window and improve throughput. In this paper, we consider a TCP network in which the TCP sender is located remotely over the Internet while the TCP receiver is connected by a CR link. This topology is more realistic than the earlier proposals, but the lower layer information cannot be exploited. Under this assumption, we propose an enhanced TCP protocol for CR networks called TCP for cognitive radio (TCP-CR) to improve the existing TCP by (1) detection of primary user (PU) interference by a remote sender without support from lower layers, (2) delayed congestion control (DCC) based on PU detection when the retransmission timeout (RTO) expires, and (3) exploitation of two separate scales of the congestion window adapted for PU activity. Performance evaluation demonstrated that the proposed TCP-CR achieves up to 255% improvement of the end-to-end throughput. Furthermore, we verified that the proposed TCP does not deteriorate the fairness of existing TCP flows and does not cause congestions.

• ETRI Journal
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• 제34권2호
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• pp.175-183
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• 2012

Conventional synchronization algorithms for impulse radio require high-speed sampling and a precise local clock. Here, a phase-locked loop (PLL) scheme is introduced to acquire and track periodical impulses. The proposed impulse PLL (iPLL) is analyzed under an ideal Gaussian noise channel and multipath environment. The timing synchronization can be recovered directly from the locked frequency and phase. To make full use of the high harmonics of the received impulses efficiently in synchronization, the switching phase detector is applied in iPLL. It is capable of obtaining higher loop gain without a rise in timing errors. In different environments, simulations verify our analysis and show about one-tenth of the root mean square errors of conventional impulse synchronizations. The developed iPLL prototype applied in a high-speed ultra-wideband transceiver shows its feasibility, low complexity, and high precision.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권8호
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• pp.2675-2690
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• 2014

We study the problem of optimal opportunistic spectrum access with unknown and heterogeneous channel dynamics in cognitive radio networks. There is neither statistic information about the licensed channels nor information exchange among secondary users in the respective systems. We formulate the problem of maximizing network throughput. To achieve the desired optimization, we propose a win-shift lose-stay algorithm based only on rewards. The key point of the algorithm is to make secondary users tend to shift to another channel after receiving rewards from the current channel. The optimality and the convergence of the proposed algorithm are proved. The simulation results show that for both heterogeneous and homogenous systems the proposed win-shift lose-stay algorithm has better performance in terms of throughput and fairness than an existing algorithm.