• 한국통신학회논문지
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• 제33권4A호
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• pp.361-370
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• 2008

Cooperative relaying permits one or more relay to transmit a signal from the source to the destination, thereby increasing network coverage and spectral efficiency. The performance of cooperative relaying is often measured as outage probability. However, appropriate measure for the channel quality is outage capacity. Although the outage probability for cooperative relaying protocol has been analyzed before, very little research has been addressed for the outage capacity. This paper is the first of its kind to derive a closed-form analytical solution of outage capacity using fixed decode and forward relaying and amplify and forward relaying in dissimilar Rayleigh fading channels, considering channel coefficients known to the receiver side. The analytical results show a tradeoff between the SNR and the number of relays for specific outage capacity. A comparison between decode and forward relaying and amplify and forward relaying shows that decode and forward relaying outperforms amplify and forward relaying for a large number of relays.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권10호
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• pp.2455-2472
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• 2012

Although underlay spectrum sharing has been shown as a promising technique to promote the spectrum utilization in cognitive radio networks (CRNs), it may suffer bad secondary performance due to the strict power constraints imposed at secondary systems and the interference from primary systems. In this paper, we propose a two-phase based cooperative transmission protocol with the interference cancellation (IC) and best-relay selection to improve the secondary performance in underlay models under stringent power constraints while ensuring the primary quality-of-service (QoS). In the proposed protocol, IC is employed at both the secondary relays and the secondary destination, where the IC-based best-relay selection and cooperative relaying schemes are well developed to reduce the interference from primary systems. The closed-form expression of secondary outage probability is derived for the proposed protocol over Rayleigh fading channels. Simulation results show that, with a guaranteed primary outage probability, the proposed protocol can achieve not only lower secondary outage probability but also higher secondary diversity order than the traditional underlay case.

• Journal of Communications and Networks
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• 제16권1호
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• pp.10-17
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• 2014

This work investigates two important performance metrics of underlay cooperative cognitive radio (CR) networks: Interference cumulative distribution function of licensed users and outage probability of unlicensed users. These metrics are thoroughly analyzed in realistic operating conditions such as imperfect fading channel information and strict transmit power constraint, which satisfies interference power constraint and maximum transmit power constraint, over Nakagami-m fading channels. Novel closed-form expressions are derived and subsequently validated extensively through comparisons with respective results from computer simulations. The proposed expressions are rather long but straightforward to handle both analytically and numerically since they are expressed in terms of well known built-in functions. In addition, the offered results provide the following technical insights: i) Channel information imperfection degrades considerably the performance of both unlicensed network in terms of OP and licensed network in terms of interference levels; ii) underlay cooperative CR networks experience the outage saturation phenomenon; iii) the probability that the interference power constraint is satisfied is relatively low and depends significantly on the corresponding fading severity conditions as well as the channel estimation quality; iv) there exists a critical performance trade-off between unlicensed and licensed networks.

• 한국전자파학회논문지
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• 제20권9호
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• pp.890-899
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• 2009

차세대 이동 위성 시스템의 주요 서비스중 하나는 멀티미디어 방송 및 멀티캐스팅 서비스가 될 것이다. 이러한 서비스를 효과적으로 제공하기 위해 통합 위성 지장 네트워크가 고려될 수 있다. 본 논문에서는 차세대 이동위성 시스템에 적합한 통합 위성 지상 시스템의 구조를 소개하고, 효율적인 이동 위성 멀티미디어 방송 및 멀티캐스팅 서비스를 제공하기 위한 위성과 지상 보조 장치 간의 협력적 전송 기법들을 제안하였다. 성능 분석 시뮬레이션 결과, 제안한 구조가 시스템 성능을 보다 향상시킬 수 있으며 효과적인 전송을 할 수 있음을 보여준다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권6호
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• pp.2095-2110
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• 2015

This paper presents a design for a throughput-efficient online relay selection scheme for dual-hop multi-relay cooperative networks. Problems arise with these networks due to unpredictability of the relaying link quality and high time-consumption to probe the dual-hop link. In this paper, we firstly propose a novel probing and relaying protocol, which greatly reduces the overhead of the dual-hop link estimation by leveraging the wireless broadcasting nature of the network. We then formulate an opportunistic relay selection process for the online decision-making, which uses a tradeoff between obtaining more link information to establish better cooperative relaying and minimizing the time cost for dual-hop link estimation to achieve higher throughput. Dynamic programming is used to construct the throughput-optimal control policy for a typically heterogeneous Rayleigh fading environment, and determines which relay to probe and when to transmit the data. Additionally, we extend the main results to mixed Rayleigh/Rician link scenarios, i.e., where one side of the relaying link experiences Rayleigh fading while the other has Rician distribution. Numerical results validate the effectiveness and superiority of our proposed relaying scheme, e.g., it achieves at least 107% throughput gain compared with the state of the art solution.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권1호
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• pp.102-122
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• 2017

Nanotechnology has provided a set of tools that the engineers can use to design and manufacture integrated nano devices, which are capable of performing sensing, computing, data storing and actuation. One of the main hurdles for nano devices has been the amount of power that it can generate for transmission of data. In this paper, we proposed cooperative nano communication in the Terahertz (THz) Gap frequency band to increase the range of transmission. Outage probability (OP) performances for the proposed cooperative nano communication networks in the THz band (0.1 - 10THz) have been evaluated for the following scenarios; A) A single decode-and-forward (DF) relay over independent identically distributed (i.i.d.) Rayleigh fading channels, B) DF multi-relay network with best relay selection (BRS) over i.i.d. Rayleigh fading channels, and C) DF multi-relay network with multiple hops with BRS over i.i.d. Rayleigh fading channels. The results show that the transmission distance can be improved significantly by employing DF relays. Also, it is shown that by increasing the number of hops in a relay the OP performance is marginally degraded. The analytical results have been verified by Monte-Carlo simulation.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권10호
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• pp.5035-5057
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• 2019

Advancements in nanotechnology and novel nano materials in the past decade have provided a set of tools that can be used to design and manufacture integrated nano devices, which are capable of performing sensing, computing, data storing and actuation. In this paper, we have proposed cooperative nano communication using Power Switching Relay (PSR) Wireless Power Transfer (WPT) protocol and Time Switching Relay (TSR) WPT protocol over independent identically distributed (i.i.d.) Rayleigh fading channels in the Terahertz (THz) Gap frequency band to increase the range of transmission. Outage Probability (OP) performances for the proposed cooperative nano communication networks have been evaluated for the following scenarios: A) A single decode-and-forward (DF) relay for PSR protocol and TSR protocol, B) DF multi-relay network with best relay selection (BRS) for PSR protocol and TSR protocol, and C) DF multi-relay network with multiple DF hops with BRS for PSR protocol and TSR protocol. The results have shown that the transmission distance can be improved significantly by employing DF relays with WPT. They have also shown that by increasing the number of hops in a relay the OP performance is only marginally degraded. The analytical results have been verified by Monte-Carlo simulations.

• 한국전자파학회논문지
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• 제21권7호
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• pp.815-822
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• 2010

중계기 선택 기반 양방향 중계 기법은 중계기 수에 따른 선택 다이버시티 이득을 얻을 수 있으며, 기존의 단방향 중계 기법보다 높은 데이터 율을 가진다. 그러나 기존의 중계기 선택 기반 양방향 중계 기법에서는 사용자 간의 직접 통신 링크를 고려하지 않아 협력 통신의 장점인 결합 이득을 얻을 수 없었다. 본 논문에서는 다수의 중계기가 존재하는 네트워크에서 선택 다이버시티 이득과 결합 이득 모두를 얻을 수 있는 기회주의적 협력양방향 중계 기법과 증분형 협력 양방향 중계 기법을 제안한다. 제안하는 두 기법이 중계기 수에 따른 선택 다이버시티 이득과 결합 이득을 모두 얻음으로써 기존의 양방향 중계 기법보다 우수한 성능을 가짐을 시뮬레이션 결과를 통해 증명한다.

• 정보처리학회논문지C
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• 제13C권7호
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• pp.865-872
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• 2006

최근 협력통신은 안테나의 물리적인 배치 없이 공간 다중화를 얻을 수 있는 효과적인 방법으로 많은 주목을 받고 있다. 따라서 협력적인 위치를 가진 다중 안테나 시스템에서 잘 알려진 시공간 블록 코드(STBC, Space Time Block Code)는 분산환경 하의 단일 안테나 사용자들에게도 이용될 수 있다. 본 논문에서는 3/4 시공간블록 코드를 사용한 협력적인 신호 구조를 제안하고, 수학적으로 증명한 전송 전력 제한과 네트워크 기하학을 이용하여 이론상의 BER (Bit Error Ratio) 표현을 유도한다. 다양한 환경에서의 시뮬레이션과 잘 증명된 수학적인 결과는 파트너가 적절한 위치에 있을 때, 직접 전송보다 매우 성능이 우수한 협력 통신을 증명하였다.

• 한국정보통신학회논문지
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• 제13권9호
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• pp.1819-1828
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• 2009

최근에는 Ad Hoc 네트워크에서 시스템 성능을 더욱 향상시키기 위해 협력통신에 대한 연구가 많이 진행되었다. 본 논문에서는 시스템 성능을 더욱 개선하기 위하여 협력통신을 지원하는 망구조에서 네트워크 코딩을 지원하는 NC-MAC 프로토콜을 제안하고 확률을 이용한 수학적인 접근방법을 사용하여 성능평가를 수행하였다. 도출된 성능평가 결과를 통해 IEEE 802.11 표준인 DCF 기법에 비해 시스템 처리량이 월등히 개선되며, 기존 연구에서 제안된 rDCF 기법 및 CO-MAC 기법보다도 최대 48%까지 시스템 처리량 성능이 증가함을 확인할 수 있었다.