• Journal of Korea Multimedia Society
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• v.21 no.4
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• pp.493-498
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• 2018

In this paper, we provide the performance analyses of a dual-hop amplify-and-forward(AF) relay transmission composed of asymmetric radio-frequence(RF) and free-space optical(FSO) links. In the mixed RF/FSO system, a relay is equipped with two receive antennas for RF signals and one additional transmit antenna for FSO signals. In order to improve a performance of RF link, a switch-and-stay (SSC) diversity technique is applied at the relay which can provide a proper link performance with a low complexity. Specifically, we offer the performance analyses of the proposed system in terms of outage probability and secrecy outage probability. In numerical examples, we compare the system performances with no diversity and selection combining systems and verify our analytical results via computer-based Monte-Carlo simulations.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.11 no.3
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• pp.40-47
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• 2012

In dual-hop relaying systems, the conventional partial relay selection is based on the channel information only for the first hop. On the other hand, the efficient partial relay selection is based on the channel information for the hop with the minimum of the average channel powers for the first and second hops at each end-to-end link since the correlation coefficient between the end-to-end link quality and the link quality of the hop with the minimum of the average channel powers for the first and second hops is larger than that between the end-to-end link quality and the link quality of the other hop. In this paper, the outage probability of the conventional partial relay selection and the efficient partial relay selection in dual-hop decode-and-forward relaying systems is analyzed for non-identically distributed Rayleigh fading channels. Through numerical investigation, the outage performance of the efficient partial relay selection is compared with the outage performances of the conventional partial relay selection and the best relay selection based on all the channel information for the first and second hops.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.9C
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• pp.887-895
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• 2009

This paper proposes a cooperative power allocation with the use of partial channel information (e.g., the average signal-to-noise ratio (SNR) and transmit correlation) in multi-cell dual-hop multi-input single-output (MISO) relay systems. In a dual-hop MISO relay channel, it is desirable to allocate the transmit power between dual-hop links to maximize the end-to-end capacity. We consider the maximization of the end-to-end capacity of a dual-hop MISO relay channel under sum-power constraint. The proposed scheme adaptively allocates the transmit power considering the average channel gain of the target relay and the transmit correlation of the desired and inter-relay interference channel from adjacent relays. It is shown by means of upper-bound analysis that the end-to-end capacity can be maximized by making the angle difference of the principal eigenvectors of the desired and inter-relay interference channel orthogonal in highly-correlated channel environments. Finally, the performance of the proposed scheme is verified by computer simulation.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.8
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• pp.1-6
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• 2011

In this paper, another analytical approach for dual-hop amplify-and-forward(AF) relay systems is proposed over Rayleigh fading channels. Previous approaches derived the moment generating function(MGF) by using the cumulative distribution function(CDF) or probability density function(PDF) of the received signal-to-noise ratio(SNR) for source-relay-destination(S-R-D) link. Then, the average symbol error rate is expressed based on derived MGFs. In this paper, another new approach is proposed. It means that the MGF is directly derived by utilizing PDFs of both source-relay(S-R) and relay-destination(R-D) links. Additionary, the newly derived MGF is compared and analyzed with previous ones. Furthermore, simulation results are presented to validate the accuracy of proposed analytical expression. Based on this, it is confirmed that the proposed analytical approach can be a another solution for dual-hop AF relay systems.

• The Journal of the Korea institute of electronic communication sciences
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• v.12 no.1
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• pp.69-74
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• 2017

Due to the advantage of communication coverage extension and removement of shadowing area, relay can be applied in various wireless communication systems. In this paper, we analyze performance of downlink with dual-hop communication systems which use a relay in railway environments. We adopted asymmetric communication system which use coherent modulation scheme in base station-relay link and differential modulation scheme in relay-destination link. The performance of communication system is analyzed using symbol error rate, and performance comparison with the systems which adopts fully coherent scheme is studied. We also investigate the performance of system depending on relay distance and energy allocation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.1
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• pp.42-49
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• 2014

The conventional best relay selection based on all the channel information for the first and second hops in dual-hop systems has a large consumption of resources for channel feedback. In this paper, we analyze the average bit error rate for partial relay selection based on the channel information only for the first hop in dual-hop decode-and-forward relaying systems, where we assume independent Rayleigh fading channels. In particular, we provide an exact and closed-form expression for the average bit error rate of M-ary QAM. Also, through numerical investigation, the performance of the partial relay selection is compared with the performance of the best relay selection, and the performance is evaluated for different numbers of relays and various average channel power ratios for the first and second hops.

• Journal of KIISE:Computer Systems and Theory
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• v.29 no.9
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• pp.503-513
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• 2002

Since CC-NUMA architecture has to access remote memory, the interconnection network determines the performance of the CC-NUMA system. Bus which has been used as a popular interconnection network has many limits in a large-scale system because of the limited physical scalability and bandwidth. The dual ring interconnection network, composed of high-speed point-to-point links, is made to resolve the defects of the bus for the large-scale system. However, it also has a problem, in that the response latency is rapidly increased when many nodes are attached to the snooping based CC-NUMA system with the dual ring. In this paper, we propose a ring architecture with repeater nodes in order to overcome the problem of the dual ring on a snooping based CC-NUMA system, and design a repeater node adapted to this architecture. We will also analyze the effects of proposed architecture on the system performance and the response latency by using a probability-driven simulator.

• International Journal of Contents
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• v.14 no.1
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• pp.18-27
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• 2018

The objective of this study was to derive approximate closed-form error rates for M-ary burst symbol transmission (MBST) of dual-hop adaptive decode-and-forward (ADF) cooperative relay systems over quasi-static Rayleigh fading channels. Within a burst, there are pilot symbols and data symbols. Pilot symbols are used for channel estimation schemes and each relay node's transmission mode selection schemes. At first, our focus was on ADF relay systems' error-events at relay nodes. Each event's occurrence probability and probability density function (PDF) were then derived. With error-event based approach, we derived a tractable form of PDF for combined signal-to-noise ratio (SNR). Averaged error rates were then derived as approximate expressions for arbitrary link SNR with different modulation orders and numbers of relays. Its accuracy was verified by comparison with simulation results.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.07a
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• pp.96-97
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• 2010

다중 홉 중계기술은 차세대 무선통신을 위한 핵심 기술로 최근 전 세계적으로 활발히 연구되고 있으며, 셀 용량 증대, 셀영역 확장, 음영지역 축소 등의 장점으로 인하여, IEEE 802.11s, 802.15.4, 802.16j 등의 표준화에의 반영을 위한 논의가 활발히 진행되고 있다. 본 논문에서는 간섭신호가 존재하지 않는 이상적 네트워크 환경을 고려한 기존 연구의 한계를 극복하기 위해, 다중 간섭신호가 존재하는 레일레이(Rayleigh) 페이딩 채널에서 이중 홉(dual-hop) 복호후재전송(DF : decode-and-forward) 중계시스템의 시스템 모델을 제안하고, 모의실험을 통하여 불능확률 및 4진 직교 진폭 변조(4-QAM)를 위한 평균비트오율 (average bit error rate) 성능을 살펴본다.

• ETRI Journal
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• v.36 no.4
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• pp.625-634
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• 2014

This paper studies a dual-hop multiple-access relay network where two independent source nodes transmit information to a common destination node with the aid of multiple single-antenna amplify-and-forward relays. Each relay node is subject to an individual power constraint. We focus on the design of distributed beamforming schemes for the relays to support the transmission rate requirements of the two sources. To this end, we first characterize the achievable rate region for this network via solving a sequence of corner point optimization problems proposed in this paper. We also develop several low-complexity suboptimal schemes in closed form. Two inner bounds of the achievable rate region are theoretically shown to be approximately optimal in two special scenarios. Finally, numerical results demonstrate the effectiveness of our proposed approaches.