• ETRI Journal
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• 제37권3호
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• pp.471-479
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• 2015

Traditional designs of cognitive radio (CR) focus on maximizing system throughput. In this paper, we study the joint overlay and underlay power allocation problem for orthogonal frequency-division multiple access-based CR. Instead of maximizing system throughput, we aim to maximize system energy efficiency (EE), measured by a "bit per Joule" metric, while maintaining the minimal rate requirement of a given CR system, under the total power constraint of a secondary user and interference constraints of primary users. The formulated energy-efficient power allocation (EEPA) problem is nonconvex; to make it solvable, we first transform the original problem into a convex optimization problem via fractional programming, and then the Lagrange dual decomposition method is used to solve the equivalent convex optimization problem. Finally, an optimal EEPA allocation scheme is proposed. Numerical results show that the proposed method can achieve better EE performance.

• ETRI Journal
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• 제43권3호
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• pp.436-446
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• 2021

In this paper, we propose an energy-efficient unmanned aerial vehicle (UAV) relaying network. In this network, the channels between UAVs and ground transceivers are model-free. A UAV acting as a flying relay explores better channels to assist in efficient data delivery between two ground nodes. The full-duplex relaying mode is applied for potential energy efficiency (EE) improvements. With the genetic algorithm, we manage to optimize the UAV trajectory for any arbitrary radio map scenario. Numerical results demonstrate that compared to other schemes (eg, fixed trajectory/speed policies), the proposed algorithm performs better in terms of EE. Additionally, the impact of self-interference on average EE is also investigated.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권6호
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• pp.1479-1495
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• 2012

Spectrum scarcity seems to be the most challenging issue to be solved in new wireless telecommunication services. It is shown that spectrum unavailability is mainly due to spectrum inefficient utilization and inappropriate physical layer execution rather than spectrum shortage. Daily increasing demand for new wireless services with higher data rate and QoS level makes the upgrade of the physical layer modulation techniques inevitable. Orthogonal Frequency Division Multiple Access (OFDMA) which utilizes multicarrier modulation to provide higher data rates with the capability of flexible resource allocation, although has widely been used in current wireless systems and standards, seems not to be the best candidate for cognitive radio systems. Filter Bank based Multi-Carrier (FBMC) is an evolutionary scheme with some advantages over the widely-used OFDM multicarrier technique. In this paper, we focus on the total throughput improvement of a cognitive radio network using FBMC modulation. Along with this modulation scheme, we propose a novel uplink radio resource allocation algorithm in which fairness issue is also considered. Moreover, the average throughput of the proposed FBMC based cognitive radio is compared to a conventional OFDM system in order to illustrate the efficiency of using FBMC in future cognitive radio systems. Simulation results show that in comparison with the state of the art two algorithms (namely, Shaat and Wang) our proposed algorithm achieves higher throughputs and a better fairness for cognitive radio applications.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2012년도 한국컴퓨터종합학술대회논문집 Vol.39 No.1(D)
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• pp.265-267
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• 2012

This paper analyzes network selection issues of secondary users (SUs) in Cooperative Cognitive Radio Networks (CRNs) by utilizing Queuing Model. Coordinating with Handover Cost-Based Network selection, this paper also addresses an opportunity for the secondary users (SUs) to enhance QoS as well as economics efficiency. In this paper, network selection of SUs is the optimal association between Overall System Time Minimization Problem evaluation of Secondary Connection (SC) and Handover Cost-Based Network selection. This will be illustrated by simulation results.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2008년도 춘계종합학술대회 A
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• pp.921-924
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• 2008

최근 극초단파의 펄스를 사용하는 UWB(Ultra-WideBand) 기술이 다양한 무선 통신기기에 응용되고 있다. UWB 기기들은 기존의 동일한 무선주파수대역을 공동으로 사용하기 때문에 상호 간섭에 의한 장애가 발생하게 되는데, 이와 같이 다양한 무선 응용 기술들이 혼재된 상황은 주파수 자원의 효율적 이용에 대한 요구를 강화할 것으로 예상된다. 최근 한정된 UWB 대역의 주파수 자원을 효율적으로 이용하는 기술이 소개되고 있다. 특히 인지적(Cognitive) UWB 기술은 스펙트럼 사용 효율을 높이기 위해 스펙트럼 활용을 위한 기술로서 UWB 시스템에서 사용되지 않는 주파수를 감지하여 이를 효율적으로 공유하여 사용할 수 있는 무선통신 개념이 적용되는 방식이다. 본 논문에서는 UWB와 인지적 기술이 합해진 기술을 소개하고, 시뮬레이션을 통하여 원하는 마스크를 충족시키고 타 시스템으로부터의 간섭을 회피하여 성능이 개선됨을 보였다.

• 대한전자공학회논문지TC
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• 제48권2호
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• pp.43-48
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• 2011

무선인지(cognitive radio) 시스템은 특정 대역에 면허권을 갖는 주사용자(primary user)의 유휴 스펙트럼을 부사용자(secondary user)가 기회적으로 사용하는 것을 허용하는 것으로 주파수 부족 문제의 해결책으로 부각되고 있다. 특히, 스펙트럼 센싱(spectrum sensing) 기술은 특정 스펙트럼을 사용하고자 하는 부사용자가 주변에서 해당 스펙트럼을 사용 중인 주사용자를 검출하는 것으로 무선인지 시스템의 핵심을 이룬다. 기존의 스펙트럼 센싱 기술은 부사용자가 주사용자 송신기를 센싱하지만 부사용자가 주사용자 수신기를 센싱할 수 있다면 주사용자에 미치는 간섭을 최소화하고 스펙트럼 사용 효율을 최대화할 수 있다. 본 논문에서는 수신기 중심(receiver-centric) 스펙트럼 센싱 기술을 제안하고 성능 분석을 통해 기존의 송신기 중심스펙트럼 센싱 기술에 비해 주파수 효율 측면에서 성능 개선이 있음을 검증한다.

• 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 information and communication convergence engineering
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• 제13권4호
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• pp.241-247
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• 2015

Cognitive radio has been attracting increased attention as an effective approach to improving spectrum efficiency. One component of cognitive radio, spectrum sensing, has an important relationship with the performance of cognitive radio. In this paper, after a summary and analysis of the existing spectrum-sensing algorithms, we report that the existing eigenvalue-based semi-blind detection algorithm and blind detection algorithm have not made full use of the eigenvalues of the received signals. Applying multi-antenna systems to cognitive users, we design a variety of spectrum-sensing algorithms based on the joint distribution of the eigenvalues of the received signal. Simulation results validate that the proposed algorithms in this paper are able to detect whether the signal of the primary user exists or not with high probability of detection in an environment with a low signal-to-noise ratio. Compared with traditional algorithms, the new algorithms have the advantages of high detection performance and strong robustness

• 동의신경정신과학회지
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• 제22권3호
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• pp.1-11
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• 2011

Objectives : As the number of patient with dementia increases, interest in mild cognitive impairment (MCI), which is a pre-dementia stage, has been expanding. In this study, we investigated the effects from selected clinical research articles to evaluate the effectiveness of non-pharmacological interventions. Methods : We searched MCI related articles on MEDLINE and the Web of Science using keywords related to MCI. We selected 26 articles, and 13 evaluated efficiency using the Jadad score. Results : Physical exercise and cognitive remediation techniques were effective for improving MCI. Transcutaneous electrical nerve stimulation, taichi, and music belonged to "perhaps" effectiveness group. Many of the 13 articles that evaluated MCI using the Jadad score evaluated them as "good" or "poor", and only three articles evaluated MCI as "excellent". Conclusions : The present evidence suggests that cognitive remediation techniques to improve memory and physical exercise were effective for people with MCI. However, further studies are needed to identify the physical exercise effects.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권7호
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• pp.1533-1546
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• 2013

Wireless multicast is considered as an effective transmission mode for the future mobile social contact services supported by Long Time Evolution (LTE). Though wireless multicast has an excellent resource efficiency, its performance suffers deterioration from the channel condition and wireless resource availability. Cognitive Radio (CR) and Device to Device (D2D) are two solutions to provide potential resource. However, resource allocation for cognitive wireless multicast based on D2D is still a great challenge for LTE social networks. In this paper, a joint sub-carriers and power allocation model based on D2D for general cognitive radio multicast (CR-D2D-MC) is proposed for Orthogonal Frequency-Division Multiplexing (OFDM) LTE systems. By opportunistically accessing the licensed spectrum, the maximized capacity for multiple cognitive multicast groups is achieved with the condition of the general scenario of imperfect spectrum sensing, the constrains of interference to primary users (PUs) and an upper-bound power of secondary users (SUs) acting as multicast source nodes. Furthermore, the fairness for multicast groups or unicast terminals is guaranteed by setting a lower-bound number of the subcarriers allocated to cognitive multicast groups. Lagrange duality algorithm is adopted to obtain the optimal solution to the proposed CR-D2D-MC model. The simulation results show that the proposed algorithm improves the performance of cognitive multicast groups and achieves a good balance between capacity and fairness.