• 한국항행학회논문지
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• 제23권4호
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• pp.322-327
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• 2019

본 논문에서는 셀룰러 인지 라디오 망에서 주 사용자들 (PU; primary user)의 다중 채널상에서 발생하는 스펙트럼 홀 (spectrum hole)을 그룹핑(grouping)하여, 광대역 인지 사용자 (WCRU; wideband cognitive radio user)의 서비스 품질 (QoS; quality of service)을 향상시킬 수 있는 방법을 제안한다. 제안하는 스펙트럼 홀 그룹핑 방법은 같은 시간에 발생하는 스펙트럼 홀들을 위너예측과정으로 예측하고, 예측된 스펙트럼 홀을 그룹핑하여 광대역 인지 사용자를 지원함으로써 인지 사용자의 서비스 품질을 향상시킨다. 시뮬레이션을 통하여 단일 스펙트럼 홀 채널을 이용한 경우와 비교하여 핸드오프 호의 손실률과 초기 발생 호의 차단률을 줄일 수 있음을 보인다.

• 융합신호처리학회논문지
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• 제13권3호
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• pp.156-161
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• 2012

임의 접속(random access) 프로토콜은 기본적으로 센싱 기능을 가지고 있으며, 이것을 이용하여 분산형 무선 네트워크 시스템 구축에 적합한 특징을 가지고 있다. 이러한 기술적 특징은 중앙식 제어(centralized control)가 어려운 이기종 시스템들이 동작하는 인지 무선 통신 환경에 대하여 장점을 가지며, 인지 무선 통신 환경에서 임의 접속의 성능을 검증해 보아야 한다는 동기를 제공한다. 이 논문에서 우리는 인지 무선 통신 환경에서 CSMA/CA(carrier-sensing multiple access with collision avoidance)기법을 도입하고, 성능을 분석하는 기본 틀을 제공한다.

• 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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• 제7권4호
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• pp.613-631
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• 2013

Cognitive radio (CR) is proposed as a key solution to improve spectral efficiency and overcome the spectrum scarcity. Spectrum sensing is an important task in each CR system with the aim of identifying the spectrum holes and using them for secondary user's (SU) communications. Several conventional methods for spectrum sensing have been proposed such as energy detection, matched filter detection, etc. However, the main limitation of these classical methods is that the CR network is not able to communicate with its own base station during the spectrum sensing period and thus a fraction of the available primary frame cannot be exploited for data transmission. The other limitation in conventional methods is that the SU data frames should be synchronized with the primary network data frames. To overcome the above limitations, here, we propose a spectrum sensing technique based on blind source separation (BSS) that does not need time synchronization between the primary network and the CR. Moreover, by using the proposed technique, the SU can maintain its transmission with the base station even during spectrum sensing and thus higher rates are achieved by the CR network. Simulation results indicate that the proposed method outperforms the accuracy of conventional BSS-based spectrum sensing techniques.

• Journal of Communications and Networks
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• 제16권2호
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• pp.155-161
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• 2014

Mobility can lead to continual loss of data and service interruptions during communications in multi-hop cognitive radio networks. Mobility of primary users (PUs) or cognitive users (CUs) requires adjustment of multi-hop communications among CUs to avoid any interference to PUs. To provide durable and reliable data routing that ensures continuous network service, we propose mobility-aware cognitive routing (MCR) for multi-hop cognitive radio networks. MCR examines the risk level of each node against interference regions and selects the most reliable path for data delivery using a Markov predictor. Through simulation, we verify that the proposed scheme can avoid route destruction preemptively and achieve reliable data delivery.

• Journal of Communications and Networks
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• 제17권4호
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• pp.394-405
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• 2015

This paper considers a wideband cognitive radio network which can simultaneously sense multiple narrowband channels and thus aggregate the detected available channels for transmission and proposes a novel cognitive radio system that exhibits improved sensing throughput and can save power consumption of secondary user (SU) compared to the conventional cognitive radio system studied so far. More specifically, under the proposed cognitive radio system, we study the problem of designing the optimal sensing time and power allocation strategy, in order to maximize the ergodic throughput of the proposed cognitive radio system under two different schemes, namely the wideband sensing-based spectrum sharing scheme and the wideband opportunistic spectrum access scheme. In our analysis, besides the average interference power constraint at primary user, the average transmit power constraint of SU is also considered for the two schemes and then a subgradient algorithm is developed to obtain the optimal sensing time and the corresponding power allocation strategy. Finally, numerical simulations are presented to verify the performance of the two proposed schemes.

• Journal of Communications and Networks
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• 제11권2호
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• pp.148-156
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• 2009

The fixed spectrum assignment policy in today's wireless networks leads to inefficient spectrum usage. Cognitive radio network is a new communication paradigm that enables the unlicensed users to opportunistically use the spatio-temporally unoccupied portions of the spectrum, and hence realizing a dynamic spectrum access (DSA) methodology. Interference temperature model proposed by Federal Communications Commission (FCC) permits the unlicensed users to utilize the licensed frequencies simultaneously with the primary users provided that they adhere to the interference temperature constraints. In this paper, we formulate two NP-hard optimal scheduling methods that meet the interference temperature constraints for cognitive radio networks. The first one maximizes the network throughput, whereas the second one minimizes the scheduling delay. Furthermore, we also propose suboptimal schedulers with linear complexity, referred to as maximum frequency selection (MFS) and probabilistic frequency selection (PFS). We simulate the throughput and delay performance of the optimal as well as the suboptimal schedulers for varying number of cognitive nodes, number of primary neighbors for each cognitive node, and interference temperature limits for the frequencies. We also evaluate the performance of our proposed schedulers under both additive white gaussian noise (AWGN) channels and Gilbert-Elliot fading channels.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권2호
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• pp.371-388
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• 2014

Cognitive Radio (CR) has been recently proposed as a promising technology to remedy the problems of spectrum scarcity and spectrum underutilization by enabling unlicensed users to opportunistically utilize temporally unused licensed spectrums in a cautious manner. In Cognitive Radio Ad Hoc Networks (CRAHNs), data routing is one of the most challenging tasks since the channel availability and node mobility are unpredictable. Moreover, the network performance is severely degraded due to large numbers of path failures. In this paper, we propose the Fault-Tolerant Cognitive Ad-hoc Routing Protocol (FTCARP) to provide fast and efficient route recovery in presence of path failures during data delivery in CRAHNs. The protocol exploits the joint path and spectrum diversity to offer reliable communication and efficient spectrum usage over the networks. In the proposed protocol, a backup path is utilized in case a failure occurs over a primary transmission route. Different cause of a path failure will be handled by different route recovery mechanism. The protocol performance is compared with that of the Dual Diversity Cognitive Ad-hoc Routing Protocol (D2CARP). The simulation results obviously prove that FTCARP outperforms D2CARP in terms of throughput, packet loss, end-to-end delay and jitter in the high path-failure rate CRAHNs.

• Journal of Communications and Networks
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• 제17권4호
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• pp.406-418
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• 2015

Cognitive radio networks (CRNs) have emerged as a promising solution to the problem of spectrum under utilization and artificial radio spectrum scarcity. The paradigm of dynamic spectrum access allows a secondary network comprising of secondary users (SUs) to coexist with a primary network comprising of licensed primary users (PUs) subject to the condition that SUs do not cause any interference to the primary network. Since it is necessary for SUs to avoid any interference to the primary network, PU activity precludes attempts of SUs to access the licensed spectrum and forces frequent channel switching for SUs. This dynamic nature of CRNs, coupled with the possibility that an SU may not share a common channel with all its neighbors, makes the task of multicast routing especially challenging. In this work, we have proposed a novel multipath on-demand multicast routing protocol for CRNs. The approach of multipath routing, although commonly used in unicast routing, has not been explored for multicasting earlier. Motivated by the fact that CRNs have highly dynamic conditions, whose parameters are often unknown, the multicast routing problem is modeled in the reinforcement learning based framework of learning automata. Simulation results demonstrate that the approach of multipath multicasting is feasible, with our proposed protocol showing a superior performance to a baseline state-of-the-art CRN multicasting protocol.

• Journal of Communications and Networks
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• 제16권2호
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• pp.146-154
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• 2014

This paper proposes a bandwidth-aware localized-routing algorithm that is capable of sensing the available spectrum bands within a two-hop neighboring for choosing the highly opportunistic routes. A mixed-integer linear programming (MILP) is utilized to formulate the optimization problem. Then, the proposed algorithm is used to determine the maximum bandwidth possible of link pairs via a bandwidth approximation process of relaxed variables. Thereby, the proposed algorithm can allow selected routes corresponding to maximum bandwidth possible between cognitive radio (CR) users through link pairs in cognitive radio networks. By comparing the solution values to previous works, simulation results demonstrate that the proposed algorithm can offer a closed-optimal solution for routing performance in cognitive radio networks. The contribution of this paper is achieved through approximately 50% throughput utilized in the network.