• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.5
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• pp.69-76
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• 2016

In this paper, we investigate the system performance of a cooperative relaying system of Non-orthogonal multiple access (NOMA) with successive interference cancellation (SIC), which is considered promising application in fifth generation (5G) cellular networks. Previous studies have focused on the selected relays, however we include the maxmin relay selection and derive analytical outage probability of opportunistic incremental relaying systems. For the realistic mobile environment, the distributions of relays are modeled as a homogeneous Poisson point process (PPP). And maximal ratio combining (MRC) is adapted to improve the system performance at the destination node. Analytical results demonstrate the outage probability improves with the near/far user power ratio, and the cooperative relaying scheme can achieve low outage probability in comparison to the no relaying scheme. It is also conformed that the increase of the intensity of PPP cause higher gains of the spacial diversity and hence the performance improves.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.6
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• pp.1496-1501
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• 2013

IEEE 802.11 has become the main technology in wireless network. However, performance anomalies, especially in terms of fairness, arise in its use in ad hoc networks. Two independent emitters nodes can easily monopolize the medium, preventing other nodes to send packets. This paper proposes the modified (m,k)-firm scheme which is based on T-MAC to improve fairness. The basic idea is to assign higher priorities to nodes that are closer to a dynamic failure so as to improve their chances of meeting their deadlines. The simulation result shows that the proposed scheduling scheme helps improve the fairness of the DCF.

• Journal of KIISE:Information Networking
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• v.36 no.6
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• pp.528-535
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• 2009

This paper proposes a mechanism to increase performance using cooperative communications in IEEE 802.11 environment. Existing algorithms use one relay between a source and a destination, which is a 2 hop relay. The proposed algorithm utilizes more than one relay to complement inefficiency of using one relay. In the proposed mechanism, an AP manages network information (rate), which is used to select relays of a source by the AP. The AP notifies the selected relays to the source and neighbor nodes, and the source transmits data to the relays for cooperative communications. Moreover, relays are given to have an opportunity to send its own data right after relaying the source's data. So relays are compensated for the power to send the source's data and overall throughput is improved.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.6
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• pp.15-21
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• 2011

Cooperative diversity system can be applied to an ad-hoc network for reduction of the power consumption, for expansion of the communication range, and for improving the system performance. In a selection relay cooperative diversity system which selects the maximal SNR(Signal-to-noise ratio) relay for transmitting the source information, the selected strong relay transmits continuously under slow fading channel, consequently it reduces the network lifetime. To overcome this defect, recently the uniform power relay selection has been studied to expand the network life time. We apply the uniform power relay selection to a DOT(Double opportunistic transmit) cooperative system that select the transmit relays, of which the SNR of the transmit relays exceed both of the source-relay and the relay-destination threshold. And the performance of the system is analytically derived. The performance comparisons are made among SC(Selection combining), MRC(Maximal ratio combining), and uniform power relay selection of the cooperative diversity system. We noticed that the performance of the uniform power relay selection is inferior to that of others. It is interpreted that the uniform transmit opportunity to the selected relays for extension of the network lifetime degrades the performance.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.8
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• pp.1804-1810
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• 2013

In this paper, we study the opportunistic cooperation scheme that improves the outage performance through the efficient selection between a cooperative mode and a non-cooperative mode. Especially, in decode-and-forward relaying systems, we analyze the outage performance for the opportunistic cooperation using partial relay selection, where closed-form expressions of exact and asymptotic outage probabilities are derived assuming independent and identically distributed Rayleigh fading channels. In the numerical results, we verify the derived expressions, and investigate the outage performances for various target data rates and different numbers of relays. Also, we compare the outage performances of the conventional cooperation scheme and the opportunistic cooperation scheme.

• Proceedings of the Korean Information Science Society Conference
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• 2003.10c
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• pp.304-306
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• 2003

최근 이질적인 네트워크 환경에 적합한 다양한 멀티미디어 데이터를 서비스할 수 있는 연구가 광범위하게 이루어 지고 있다. 따라서 유동적인 네트웍 상황에 맞추어 전송되는 스트리밍 데이터는 사용자에게 보다 우수한 품질의 서비스를 제공받을 수 있는 기회를 준다. 본 논문에서는 대용량의 멀티미디어 데이터를 서비스하는 과정에서 발생하는 스트리밍 데이터의 에러 발생을 최소화할 수 있는 기법인 적응형 FEC 기법을 제안한다. 이 기법은 멀티미디어 데이터의 전송량을 최소화하면서 고화질 영상의 전송을 가능하게 한다.

• TTA Journal
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• s.138
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• pp.24-29
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• 2011

인류가 전기를 발견한 것은 기원전 600년으로 알려져 있지만 널리 이용할 수 있게 된 것은 불과 200년 안팎이다. 이 짧은 기간에 인류는 과학적 차원을 넘어서 전기공학 뿐만 아니라 전기를 이용하는 전자공학, 통신공학, 제어공학, 컴퓨터공학 분야에서 비약적인 발전을 이끌었으며 지금은 우주선부터 나노 로봇까지 모든 과학, 공학, 생활 분야에서 전기 없는 발전을 기대할 수 없게 되었다. 작은 반도체 소자 내에서의 수 ${\mu}V$회로 구성부터 765kV의 고압 송전망까지 그 형태는 다양하지만, 전기는 전선을 통해 전달되며, 전기의 이용은 곧 전선 인프라의 구축을 의미하고 있다. 전기의 이용에 있어서 필연적인 전선의 남용은 그 도를 넘어서 가정, 직장뿐만 아니라 도로에서도 공해 수준으로 펼쳐져 있고, 이들은 천연 자원의 고갈을 촉진할 뿐만 아니라 잘못 관리되었을 때에는 전기적 쇼크, 화재 등 커다란 재난으로 다가서 기도한다. 무선전력공급 기술은 이러한 전선으로부터의 자유를 추구하는 것으로 소비자가 가장 원하는 기술의 하나이다. 이는 예약된 시장을 말하고 있는 것이며 산업체는 또 다른 산업 기회를 창출할 수 있는 기회를 맞고 있는 것이다. 호언컨대 5년 이내에 대부분의 휴대폰과 노트북 충전기는 무선방식으로 전환될 것으로 보인다. 이번 특집에서는 무선전력공급 기술, 시장, 표준화 동향을 살펴보고 그 응용 개발 및 정책 방향까지 다양한 제언들을 묶어 보았다.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.3
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• pp.109-115
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• 2009

Recently, the relay communication is focused for the power saving and coverage extension of ad-hoc networks. For the high date rate transmission, it is proposed to adapt OFDMA relays. In this paper, we assume the 2 hop cooperative OFDMA relays between the source and the destination. The performance of 3 different relaying methods are derived and compared. We noticed that the selective OFDMA relaying method has the best performance followed by opportunistic OFDMA relaying and repetition-based OFDMA relaying method under the same threshold mutual information rate.

• Journal of IKEEE
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• v.20 no.3
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• pp.322-325
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• 2016

This paper proposed Enhanced Segmentized Clear Channel Assesment(ESCCA) for the IEEE 802.15.4 networks. This method divides original CCA into two groups to check precise channel status and perform additional CCA to increase throughput performance. Through the proposed method, the device can access the channel more often, so the transmission efficiency of the IEEE 802.15.4 network improves. To confirm the feasibility and usability of the proposed method, computer simulation has been performed. In the simulation, a star topology with one coordinator and a lot of devices is considered and the traffic flows are all one way, with the communication directed to the coordinator. Simulation results_ show the proposed method is improving maximum 10 kbps of throughput and decreasing maximum 15 of the average number of total CCA than IEEE 802.15.4 CCA method.

• Journal of KIISE:Information Networking
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• v.41 no.4
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• pp.186-191
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• 2014

Previous work only focuses on a maximization of network coding opportunity since it can reduce the number of packets in network system. However, it can make congestion in a relay node as each source node may transmit each packet with the maximum transmission rate based on the channel qualities. Therefore, in this paper, we propose CmNC (Congestion minimized Network Coding over unreliable wireless links) performing opportunistic network coding to guarantee the network coding gain with the consideration of the congestion and channel qualities. The relay node selects the best network code set based on the objective function for reducing the packet loss and congestion via a dynamic programming. With Qualnet simulations, we show CmNC is better up to 20% than the previous work.