• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.6
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• pp.101-108
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• 2013

In this paper, we propose a method in which the negative acknowledge (NACK) message is used as command for cooperation and spectrum sharing. This allows for an automatic request for cooperation and sharing when the direct link of the primary user is in outage, and also allows for saving the number of control messages in cooperation-spectrum sharing based paradigm. In the sharing phase, the selected relay shares a power fraction of $1-{\alpha}$ for secondary transmitted signal while the remaining of ${\alpha}$ is for primary retransmitted signal. In the case of no relay collected, primary transmitter uses NACK as a command to retransmit the signal with fully power fraction (${\alpha}=1$). Both systems are assumed to employ BPSK signals. In this scheme, we propose the joint optimal decoding in the secondary user. The frame error rate (FER) performance at both systems is then analyzed. The theoretical and simulation results validate the analysis and confirm the efficiency of the protocol.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.7
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• pp.766-773
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• 2007

Conventional wireless sensor network(WSN) has limited power and bandwidth. In order to develop multimedia sensor technology, high data rate communication systems are required. Cooperative communication system can help to decrease power consumption through spatial diversity. In cooperative transmission, one partner node assists one sensor node to transmit their data to destination. Instead of using M partners for M sensor nodes, we propose 1 partner for M sensor nodes. Proposed protocol offers similar diversity order as conventional one with much less bandwidth and hardware. It is able to almost reduce scattered nodes interference using orthogonal sub-carriers. In addition, we examined a power allocation between sensor nodes and relay that optimize the system performance.

• Journal of Broadcast Engineering
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• v.21 no.1
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• pp.105-108
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• 2016

In this paper, a cooperative jamming network with multiple relays and multiple eavesdroppers is investigated. Among the relays, one best relay is selected to amplify and forward the signal to destination through two phases. To confuse eavesdroppers, the destination transmits a jamming signal in the first phase and the source transmits jamming signal in the second phase. Secrecy rate of this system is derived, and based on the available channel state information (CSI), relay selection schemes are proposed, respectively. Numerical results show that the performance of the proposed relay selection scheme outperforms than that of random relay selection scheme.

• Journal of Internet Computing and Services
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• v.12 no.2
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• pp.1-8
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• 2011

In this paper, we propose an effective method for cooperative spectrum sensing in cognitive radios where cognitive user(CR) with the highest reliability sensing data is only selected and allowed to report its local decision to FC as only decision making node. The proposed scheme enables CR users to implicitly compare their sensing data reliabilities based on their likelihood ratio, without any collaboration among cognitive radio users. Due to the mechanism, the proposed cooperative scheme can achieves a high spectrum sensing performance while only requiring extremely low cooperation resources such as signaling overhead and cooperative time in comparison with other existing methods such as maximum ratio combination (MRC) based, equal gain combination (EGC) based and conventional hard combination based cooperative sensing methods.

• The Journal of the Korea Contents Association
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• v.9 no.4
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• pp.65-71
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• 2009

In this paper a new space-time diversity relaying strategy using cooperative communication technique is proposed. More than one relaying terminals are included in one cooperative group to share their state information, such as frame error rate and channel state information. The best terminals are selected to send bit information using space-time diversity relay system. An implementation for the proposed scheme is also presented using the TDMA cooperative protocol. The resulting receive signal to transmit signal ratio and computer simulation demonstrate that the proposed strategy outperforms the conventional cooperative system.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.5
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• pp.589-595
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• 2019

Recently, the mobile social networks, which consider both social relationship between users and mobile communication networks, have been received great attention. In this paper, we consider the trust degree of node as the social relationship for the cooperative communication networks. In contrast to the existing works that consider the case of the perfect trust degree information, for the case that transmitter has an imperfect trust degree information, we propose an imperfect trust degree based cooperative communication technique that maximizes a throughput. We first model the imperfect trust degree information as a probability distribution and derive the outage probability using the probability distribution. Then, we propose the transmission scheme that maximizes the throughput, which consider both outage probability and transmission rate. The simulation results show that the proposed cooperative transmission scheme outperforms the conventional scheme in terms of the throughput.

• Proceedings of the Korean Information Science Society Conference
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• 1998.10c
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• pp.685-687
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• 1998

본 연구에서는 협력적 충돌 제어 방식을 도입하여, 공동 저작 도구를 설계한다. 제안된 시스템은 실시간 알림 기능 및 비 실시간 메시지 전송 방식으로 저작자들 간의 의견 교환을 원활히 제공하여, 공동 저작 시에 발생할 수 있는 작업자들간의 충돌 가능성을 최소화한다. 실시간 공동 작업과 비 실시간 공동작업을 위한 방법을 제공하여 저작자들 사이의 공동 작업의 효율성 증대할 수 있으며, 다수 저작자들의 관점에 따라 다중 문서를 생성하는 방법을 도입하여 저작 단계에서 발생할 수 있는 충돌을 배제할 수 있다. 또한, 저작물을 학습하는 학습자가 다수 저작자들의 의견이 수렴된 저작물을 HTML브라우저를 통하여 학습할 수 있으므로 학습자의 다양한 욕구에 부합하는 저작물을 생성할 수 있다.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.8 no.5
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• pp.419-428
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• 2015

Multipath routing technique is recognized as one of the effective approaches to improve the reliability of data forwarding. However, the traditional multipath routing focuses only on how many paths are needed to ensure a desired reliability. For this purpose, the protocols construct additional paths and thus cause significant energy consumption. These problems have motivated the study for the energy-efficient and reliable data forwarding. Thus, this paper proposes an energy-efficient cooperative multipath routing protocol with a small number of paths based on an inter path communication. The inter path communication (namely, cooperative multipath routing) in the proposed protocol helps to reinforce the multipath reliability and reduce the use of network resources. In addition, the proposed protocol provides a reliable end-to-end transmission time by using a transmission recovery method based on the local decision for the path or transmission failures.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.6
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• pp.251-255
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• 2012

In recent years, according to improvement of various vehicle instruments, railway also has been developed in various fields. As a result, to transmit accurate information to each railway system, the efficient communication system is required. In railway communication system, mitigation of wireless fading is very important. So, in this paper we introduced the cooperative relay channel model and cooperative relay scheme. Also we analyzed and simulated the cooperative relay scheme which is suitable for railway communication systems.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.3
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• pp.47-53
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• 2013

In this paper, we propose an incremental cooperative transmission protocol in two-way underlay cognitive radio networks. In the proposed protocol, two secondary sources attempt to transmit their packet to each other with help of a secondary relay under interference constraint. For performance evaluation, we derive exact closed-form expressions of average outage probability over Rayleigh fading channel. Then, we perform Monte Carlo simulations to verify the derivations. Results present that the simulation and theoretical results are in good agreement and the outage performance of the proposed protocol is better than that of two-way direct transmission protocol.