• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권2호
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• pp.545-563
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• 2015

Energy harvesting (EH) and network coding (NC) have emerged as two promising technologies for future wireless networks. In this paper, we combine them together in a single system and then present a time switching-based network coding relaying (TSNCR) protocol for the two-way relay system, where an energy constrained relay harvests energy from the transmitted radio frequency (RF) signals from two sources, and then helps the two-way relay information exchange between the two sources with the consumption of the harvested energy. To evaluate the system performance, we derive an explicit expression of the outage probability for the proposed TSNCR protocol. In order to explore the system performance limit, we formulate an optimization problem to minimize the system outage probability. Since the problem is non-convex and cannot be directly solved, we design a genetic algorithm (GA)-based optimization algorithm for it. Numerical results validate our theoretical analysis and show that in such an EH two-way relay system, if NC is applied, the system outage probability can be greatly decreased. Moreover, it is shown that the relay position greatly affects the system performance of TSNCR, where relatively worse outage performance is achieved when the relay is placed in the middle of the two sources. This is the first time to observe such a phenomena in EH two-way relay systems.

• Journal of Communications and Networks
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• 제16권5호
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• pp.559-567
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• 2014

In this paper, a framework for power allocation of downlink transmissions in orthogonal frequency division multiple access-based decode-and-forward cellular relay networks is investigated. We consider a system with a single base station communicating with multiple users assisted by multiple relays. The relays have limited power which must be divided among the users they support in order to maximize the data rate of the whole network. Advanced power allocation schemes are crucial for such networks. The optimal relay power allocation which maximizes the data rate is proposed as an upper bound, by finding the optimal power requirement for each user based on knapsack problem formulation. Then by considering the fairness, a new relay power allocation scheme, called weighted-based scheme, is proposed. Finally, an efficient power reallocation scheme is proposed to efficiently utilize the power and improve the data rate of the network. Simulation results demonstrate that the proposed power allocation schemes can significantly improve the data rate of the network compared to the traditional scheme.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권4호
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• pp.1911-1930
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• 2017

Overlay routing has emerged as a promising approach to improve reliability and efficiency of the Internet. The key to overlay routing is the placement and maintenance of the overlay infrastructure, especially, the selection and placement of key relay nodes. Spurred by the observation that a few relay nodes with high betweenness centrality can provide more optimal routes for a large number of node pairs, we propose a resilient routing overlay network construction method by introducing Super-Relay nodes. In detail, we present the K-Minimum Spanning Tree with Super-Relay nodes algorithm (SR-KMST), in which we focus on the selection and connection of Super-Relay nodes to optimize the routing quality in a resilient and scalable manner. For the simultaneous path failures between the default physical path and the overlay backup path, we also address the selection of recovery path. The objective is to select a proper one-hop recovery path with minimum cost in path probing and measurement. Simulations based on a real ISP network and a synthetic Internet topology show that our approach can provide high-quality overlay routing service, while achieving good robustness.

• 공학논문집
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• 제3권1호
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• pp.139-146
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• 1998

프레임 릴레이는 다양한 네트워크를 연결하기 위하여 사용되는 고속광역네트워크 기술이다. 패킷교환방식과 회선교환방식의 장점을 결합함으로써, 프레임 릴레이는 오늘날 기업의 다양한 업무환경에 적합한 고성능/고신뢰도의 통신 서비스를 제공한다. 본 논문에서는 프레임 릴레이기술의 기본개념 및 특징을 정리하고, 표준화현황을 고찰하였으며, 국내의 프레임 릴레이 산업 및 서비스 현황을 분석하였다. 또한, 프레임 릴레이를 이용한 기업망 원격접속 다이얼-업 서비스를 위한 시험망을 구성하여, 프레임 릴레이 다이얼-업 서비스의 기능 및 비용효과를 분석하였다.

• Journal of electromagnetic engineering and science
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• 제11권2호
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• pp.133-142
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• 2011

Coded cooperation that integrates channel coding in cooperative transmission has gained a great deal of interest in wireless relay networks. The performance analysis of coded cooperation protocol with multiple relays is investigated in this paper. We show that the diversity order achieved by the coded cooperation in a multi-relay wireless network is not only dependent on the number of cooperating relays but is also dependent on the code-rate of the system. We derive the code-rate bound, which is required to achieve the full diversity gain of the order of cooperating nodes. The code-rate required to achieve full diversity is a linearly decreasing function of the number of available relays in the network. We show that the instantaneous channel state information (CSI)-based relay selection can effectively alleviate this code-rate bound. Analysis shows that the coded cooperation with instantaneous CSI-based relay selection can achieve the full diversity, for an arbitrary number of relays, with a fixed code-rate. Finally, we develop tight upper bounds for the bit error rate (BER) and frame error rate (FER) of the relay selection based on coded cooperation under a Rayleigh fading environment. The analytical upper bounds are verified with simulation results.

• 한국위성정보통신학회논문지
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• 제5권1호
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• pp.94-99
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• 2010

In this paper, we discuss a proposed two hop relay network with PB/MC-CDMA(partial block MC-CDMA) technique. The main advantages of PB/MC-CDMA system are the increased cell capacity and the high quality of performances. In the system, we employ relay scheme to focus on the coverage reduction and hotspot problem, hotspot is a location where a cluster of users are blocked or dropped for the reason of insufficient frequency resources. Frequency resource allocation scheme is put forward in a three cells system according to each problem. The simulation result shows the performance of the two hop transmission is better than the direct transmission and the proposed network can support much more users to relief hotspot effect compared to the conventional one.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2010년도 춘계학술대회
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• pp.894-896
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• 2010

이동형 모바일 무선 센서 네트워크에서는 노드 전체가 이동하게 된다. 클러스터링을 기반으로 하는 모바일 무선 센서 네크워크에서는 노드위치의 빈번한 위치 변화에 따라 잦은 클러스터의 재구성이 이루어진다. 클러스터의 잦은 재구성은 많은 전력소비와 데이터의 손실을 유발할 수 있다. 이러한 문제점을 해결하기위해 중계 노드를 사용하여 클러스터의 재구성 회수를 줄이고 신뢰성있는 데이터 전송을 위한 중계 기법을 제안한다.

• 한국정보통신학회논문지
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• 제20권12호
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• pp.2213-2218
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• 2016

본 논문은 복수 개의 중계기와 도청자가 존재하는 중계기 통신 네트워크에서 보안 오류 확률을 낮출 수 있는 새로운 중계기 선택 기법을 제안한다. 도청자의 복호 확률을 낮추기 위해서 데이터와 함께 재밍 신호를 전송하는 기존의 중계기 선택 방식에서는 수신자의 데이터 복호 확률도 낮아지는 문제점이 있었다. 본 논문에서 제안하는 새로운 중계기 선택 기법은 수신자의 복호 확률을 높이면서 동시에 도청자의 복호 확률을 낮출 수 있는 중계기를 쌍으로 선택하여 보안 오류 확률을 개선하였다. Monte-Carlo 기반 컴퓨터 시뮬레이션을 통한 성능 분석 결과에 따르면, 제안 중계기 선택 방식은 기존 중계기 선택 방식 대비 보안 오류 확률을 약 10~50배 개선시킬 수 있음을 확인하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권9호
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• pp.3008-3028
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• 2022

In this paper, we investigate traffic scheduling for a delay-sensitive multi-hop relay network, and aim to minimize the priority-based end-to-end delay of different data packet via joint relay selection, subcarrier assignment, and power allocation. We first derive the priority-based end-to-end delay based on queueing theory, and then propose a two-step method to decompose the original optimization problem into two sub-problems. For the joint subcarrier assignment and power control problem, we utilize an efficient particle swarm optimization method to solve it. For the relay selection problem, we prove its convexity and use the standard Lagrange method to deal with it. The joint relay selection, subcarriers assignment and transmission power allocation problem for each hop can also be solved by an exhaustive search over a finite set defined by the relay sensor set and available subcarrier set. Simulation results show that both the proposed routing scheme and the resource allocation scheme can reduce the average end-to-end delay.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제5권5호
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• pp.874-887
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• 2011

Compared to nomadic and fixed relay stations, vehicle-mounted mobile relay stations show different characteristics caused by the time-variant topology, due to their mobility. Especially, a relay mounted in a vehicle is differentiated from nomadic or fixed relay by the restricted distance between the relay and associated mobile station and the variable density of relay deployment in a cell. In this paper, we identify the characteristics of vehicle-mounted mobile relay stations and provide some parameters that highly influence the performance of vehicle-mounted relay. Through simulation, we measure the effect of relay density, zone ratio, relay transmission power, and frame transmission mode on the performance of vehicle-mounted relay. The results show that the performance of vehicle-mounted relay is highly susceptible to the above vehicle-mounted relay-specific parameters.