• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권2호
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• pp.389-405
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• 2014

Outdated Channel State Information (CSI) was proved to have negative effect on performance in two-way relay networks. The diversity order of widely used opportunistic relay selection (ORS) was degraded to unity in networks with outdated CSI. This paper proposed a multiple relay selection scheme for amplify-and-forward (AF) based two-way relay networks (TWRN) with outdated CSI. In this scheme, two sources exchange information through more than one relays. We firstly select N best relays out of all candidate relays with respect to signal-noise ratio (SNR). Then, the ratios of the SNRs on the rest of the candidate relays to that of the Nth highest SNR are tested against a normalized threshold ${\mu}{\in}[0,1]$, and only those relays passing this test are selected in addition to the N best relays. Expressions of outage probability, average bit error rate (BER) and ergodic channel capacity were obtained in closed-form for the proposed scheme. Numerical results and Simulations verified our theoretical analyses, and showed that the proposed scheme had significant gains comparing with conventional ORS.

• 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.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제15권1호
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• pp.365-382
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• 2021

This paper proposes a novel two-way relaying (TWR) approach for a two-relay wireless network based on non-orthogonal multiple access (NOMA), where two terminals exchange messages with a cellular base station (BS) via two intermediate relay stations (RSs). We propose a NOMA-based TWR approach with two relaying schemes, i.e., amplify-and-forward (AF) and decode-and-forward (DF), referred to as NOMA-AF and NOMA-DF. The sum-rate performance of our proposed NOMA-AF and NOMA-DF is analyzed. A closed-form sum-rate upper bound for the NOMA-AF is obtained, and the exact ergodic sum-rate of NOMA-DF is also derived. The asymptotic sum-rate of NOMA-AF and NOMA-DF is also analyzed. Simulation results show that the proposed scheme outperforms conventional orthogonal multiple access based transmission schemes. It is also shown that increasing the transmit power budget of the relays only cannot always improve the sum-rates.

• 방송공학회논문지
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• 제14권2호
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• pp.134-143
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• 2009

본 논문에서는 양방향 다중 중계기 채널(two-way multiple relay channel)에서의 중계기 선택 기법을 제안한다. 양방향 다중 중계기 채널에서는 2명의 사용자가 다수의 중계기의 도움을 받아 서로 정보를 주고받는다. 단방향 중계 채널에서와 같이 중계기는 복호화 재전송 프로토콜 또는 증폭 재전송 프로토콜을 기반으로 정보를 중계하며, 정보 전송에 필요한 채널 자원을 줄이기 위해 정보의 결합 과정을 추가로 적용한다. 특히, 중계기가 다수인 환경에서는 정보 전송 경로의 수가 증가함으로 인해 다이버시티 이득이 증가한다는 것이 알려져 있다. 따라서 본 논문에서는 다수의 중계기 중 채널 조건을 바탕으로 가장 좋은 중계기를 선택하는 기법을 제안하고 이를 통해 다이버시티 이득의 향상을 확인한다. 우선, 중계기들은 핸드셰이킹(handshaking) 과정을 이용하여 채널 정보의 크기를 얻고, 이를 바탕으로 데이터의 전송이 이루어지기 전에 분산된 방식으로 최적의 중계기 선택이 이루어진다. 중계기 선택 기준은 각각의 사용자와 중계기 간 일시적 채널 이득을 바탕으로 사용자-사용자 간(end-to-end) 경로 조건의 최대값을 계산하는 메트릭(metric)을 사용한다. 또한, 전송량을 계산하기 위해 자동반복요구(automatic repeat request, ARQ)를 사용한 알고리즘을 제안하고, 이를 통해 전송량을 분석한다. 모의실험을 통해, 제안된 중계기 선택 기법은 사용 가능한 중계기의 수가 증가함에 따라 전송량이 증가함을 보이고, 사용 가능한 중계기의 개수에 해당하는 다이버시티 이득을 얻을 수 있음을 보여준다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권2호
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• pp.593-607
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• 2016

This paper analyzes interference alignment in the two-way relay network with compute-and-forward in both single relay and multiple relays networks. The advantages of compute-and-forward over other relaying strategies are that it can relay only linear combinations of the useful signals and remove the noise. The algorithm proposed in this paper adopts the criterion of maximum SINR to derive the pre-coding matrix. The experimental results show that the performance of interference alignment in two-way relay channel via compute-and-forward is better than that of amplify-and-forward, and the total sum rate in the two-way multiple relay networks is larger than that in the two-way single relay networks.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권3호
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• pp.890-910
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• 2014

This paper investigates the spectrum hole utilization of cooperative schemes for the two-way relaying model in order to improve the utilization efficiency of limited spectrum holes in cognitive radio networks with imperfect spectrum sensing. We propose two specific bidirectional secondary data transmission (BSDT) schemes with two-step and three-step two-way relaying models, i.e., two-BSDT and three-BSDT schemes, where the spectrum sensing and the secondary data transmission are jointly designed. In the proposed cooperative schemes, the best two-way relay channel between two secondary users is selected from a group of secondary users serving as cognitive relays and assists the bi-directional communication between the two secondary users without a direct link. The closed-form asymptotic expressions for outage probabilities of the two schemes are derived with a primary user protection constraint over Rayleigh fading channels. Based on the derived outage probabilities, the spectrum hole utilization is calculated to evaluate the percentage of spectrum holes used by the two secondary users for their successful information exchange without channel outage. Numerical results show that the spectrum hole utilization depends on the spectrum sensing overhead and the channel gain from a primary user to secondary users. Additionally, we compare the spectrum hole utilization of the two schemes as the varying of secondary signal to noise ratio, the number of cognitive relays, and symmetric and asymmetric channels.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권12호
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• pp.5862-5887
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• 2019

In this paper, we propose a two-way relaying scheme using non-orthogonal multiple access (NOMA) technology. In this scheme, two sources transmit packets with each other under the assistance of the decode-and-forward (DF) relays, called as a TWDFNOMA protocol. The cooperative relays exploit successive interference cancellation (SIC) technique to decode sequentially the data packets from received summation signals, and then use the digital network coding (DNC) technique to encrypt received data from two sources. A max-min criterion of end-to-end signal-to-interference-plus-noise ratios (SINRs) is used to select a best relay in the proposed TWDFNOMA protocol. Outage probabilities are analyzed to achieve exact closed-form expressions and then, the system performance of the proposed TWDFNOMA protocol is evaluated by these probabilities. Simulation and analysis results discover that the system performance of the proposed TWDFNOMA protocol is improved when compared with a conventional three-timeslot two-way relaying scheme using DNC (denoted as a TWDNC protocol), a four-timeslot two-way relaying scheme without using DNC (denoted as a TWNDNC protocol) and a two-timeslot two-way relaying scheme with amplify-and-forward operations (denoted as a TWANC protocol). Particularly, the proposed TWDFNOMA protocol achieves best performances at two optimal locations of the best relay whereas the midpoint one is the optimal location of the TWDNC and TWNDNC protocols. Finally, the probability analyses are justified by executing Monte Carlo simulations.

• 한국인터넷방송통신학회논문지
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• 제13권4호
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• pp.193-200
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• 2013

최근 이동통신 뿐 만 아니라 TV방송 등에서도 릴레이를 이용한 양방향 무선채널의 전송효율을 높이기 위한 네트워크 코딩에 관한 연구가 활발히 진행되고 있다. 본 논문에서는 동시에 여러 개의 릴레이가 전송하는 대신 최선의 릴레이를 이용하여 양방향 데이터를 전송하는 네트워크 코딩 시스템의 평균 전송용량 및 오수신율을 유도하였다. 일반적으로 양방향 통신 시스템의 경우 순방향 및 역방향 링크의 데이터 비대칭성이 존재하므로, 데이터 대칭 링크와 비대칭 링크도 포함하여 성능을 유도하였다. 유도한 결과 병렬 릴레이의 수가 증가할수록 공간 다이버시티에 의한 신호 대 잡음비(SNR) 이득이 증가함을 알 수 있었고, 대칭 링크의 경우 주어진 조건하에서 단일 릴레이를 사용하였을 때보다 9개의 릴레이가 존재하는 경우 11.4 dB의 SNR 이득을 얻을 수 있었다. 또한 비대칭 링크의 경우, 오수신율은 데이터 비대칭성보다는 릴레이의 수에 민감하다는 결과를 얻었다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권6호
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• pp.1418-1432
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• 2013

This paper studies the problem of secure information exchange between two sources via multiple relays in the presence of an eavesdropper. To this end, we propose a relay beamforming scheme, i.e., relay beamforming with artificial noise (RBwA), where the relay beamforming vector and the artificial noise vector are jointly designed to maintain the received signal-to-interference-ratio (SINR) at the two sources over a predefined Quality of Service (QoS) threshold while limiting the received SINR at the eavesdropper under a predefined secure threshold. For comparison, the relay beamforming without artificial noise (RBoA) is also considered. We formulate two optimization problems for the two schemes, where our goal is to seek the optimal beamforming vector to minimize the total power consumed by relay nodes such that the secrecy of the information exchange between the two sources can be protected. Since both optimization problems are nonconvex, we solve them by semidefinite program (SDP) relaxation theory. Simulation results show that, via beamforming design, physical layer secrecy of two-way relay networks can be greatly improved and our proposed RBwA outperforms the RBoA in terms of both low power consumption and low infeasibility rate.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권12호
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• pp.3275-3295
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• 2012

In this paper, we analyze the performance of an amplify-and-forward (AF) two-way relaying system, where two sources exchange information via the aid of an intermediate relay that is selected among multiple relays according to max-min criterion. We consider a practical scenario, where one source-relay link undergoes Rician fading, and the other source-relay link is subject to Rayleigh fading. To be specific, we derive a tight lower bound for the outage probability. From this lower bound, the asymptotic outage probability and average symbol error rate (SER) expressions are derived to gain insight into the system performance at high signal-to-noise ratio (SNR) region. Furthermore, we investigate the optimal power allocation (PA) with fixed relay location (RL), optimal RL with fixed PA and joint optimization of PA and RL to minimize the outage probability and average SER. The analytical expressions are verified through Monte Carlo simulations, where the positive impact of Rician factor on the system performance is also illustrated. Simulation results also validate the effectiveness of the proposed PA and relay positioning schemes.