• Journal of Communications and Networks
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• 제17권1호
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• pp.84-92
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• 2015

Multi-hop relay networks have been widely considered as a promising solution to extend the coverage area and to reduce the deployment cost by deploying the relay stations (RSs) in mobile communication systems. Suitable deployment for the RSs is one of the most important features of the demand nodes (DNs) to obtain a high data transmission rate in such systems. Considering a tradeoff among the network throughput, the deployment budget, and the overall coverage of the systems, efficient RS deployment schemes and corresponding algorithms must be developed and designed. A novel cluster-based RS deployment scheme is proposed in this paper to select the appropriate deployment locations for the relay stations from the candidate positions. To make an ideal cluster distribution, the distances between the DNs are calculated when deploying the RSs. We take into account the traffic demands and adopt a uniform cluster concept to reduce the data transmission distances of the DNs. On the basis of the different candidate positions, the proposed scheme makes an adaptive decision for selecting the deployment sites of the RSs. A better network throughput and coverage ratio can be obtained by balancing the network load among the clusters. Simulation results show that the proposed scheme outperforms the previously known schemes in terms of the network throughput and the coverage ratio. Additionally, a suitable deployment budget can be implemented in multi-hop relay networks.

• Journal of Communications and Networks
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• 제17권1호
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• pp.47-57
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• 2015

With the ever growing demand of data applications, the joint macro-relay networks are emerging as a promising heterogeneous deployment to provide coverage extension and throughput enhancement. However, the current cellular networks are usually designed to be performance-oriented without enough considerations on the traffic variation, causing substantial energy waste. In this paper, we consider a joint macro-relay network with densely deployed relay stations (RSs), where the traffic load varies in both time and spatial domains. An energy-efficient scheme is proposed to dynamically adjust the RS working modes (active or sleeping) according to the traffic variations, which is called traffic-aware relay sleep control (TRSC). To evaluate the performance of TRSC,we establish an analytical model using stochastic geometry theory and derive explicit expressions of coverage probability, mean achievable rate and network energy efficiency (NEE). Simulation results demonstrate that the derived analytic results are reasonable and the proposed TRSC can significantly improve the NEE when the network traffic varies dynamically.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권10호
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• pp.3409-3422
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• 2014

The frequency spectrum available for the wireless communication is extremely crowded. In order to improve the spectral efficiency, the two-way relay networks have aroused great attention. A simple $N^{th}$ best-relay selection criterion for the opportunistic two-way relay networks is proposed, which can be implemented easily by extending the distributed timer technique in practice, since the proposed criterion is mainly based on the channel gains. The outage performance of the proposed relay selection scheme is analyzed under the outdated channel state information (CSI), and a tight closed-form lower bound and asymptotic value of the outage probability over Rayleigh fading channels are obtained. Simulation results demonstrate that the tight closed-form lower bound of the outage probability very closely matches with simulated ones in the whole SNR region, and the asymptotic results provide good tight approximations to the simulation ones, especially in the high SNR region.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권3호
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• pp.1111-1130
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• 2016

Cooperative communications can significantly improve the wireless transmission performance with the help of relay nodes. In cooperative communication networks, relay selection and power allocation are two key issues. In this paper, we propose a relay selection and power allocation scheme RS-PA-PSACO (Relay Selection-Power Allocation-Particle Swarm Ant Colony Optimization) based on PSACO (Particle Swarm Ant Colony Optimization) algorithm. This scheme can effectively reduce the computational complexity and select the optimal relay nodes. As one of the swarm intelligence algorithms, PSACO which combined both PSO (Particle Swarm Optimization) and ACO (Ant Colony Optimization) algorithms is effective to solve non-linear optimization problems through a fast global search at a low cost. The proposed RS-PA-PSACO algorithm can simultaneously obtain the optimal solutions of relay selection and power allocation to minimize the SER (Symbol Error Rate) with a fixed total power constraint both in AF (Amplify and Forward) and DF (Decode and Forward) modes. Simulation results show that the proposed scheme improves the system performance significantly both in reliability and power efficiency at a low complexity.

• 한국통신학회논문지
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• 제33권10A호
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• pp.972-979
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• 2008

양방향 중계 채널 (two-way relay channel)은 2개의 단말이 중계기 (relay)의 도움을 받아 양방향의 정보를 주고 받는 협력 통신 (cooperative communication) 채널이다. 기존의 협력 통신에서는 중계기가 시간 또는 주파수 자원을 나누어 양방향으로 신호를 송신하지만, 네트워크 부호화 (network coding)를 사용한 양방향 중계 채널에서는 중계기가 동일 자원을 사용하여 두 단말로 신호를 동시에 송신하므로 기존 기법보다 높은 통신용량을 얻을 수 있다. 본 논문에서는 ARQ환경에서 네트워크 부호화를 사용한 헙력통신 프로토콜을 보이고, 이를 스테이트 다이어그램 (state diagram) 을 이용하여 성능을 분석하였다.

• Journal of Communications and Networks
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• 제18권3호
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• pp.299-310
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• 2016

In practical wireless relay communication systems, non-destination nodes are assumed to be idle not receiving signals while the relay sends messages to a particular destination node, which results in reduced bandwidth efficiency. To improve the bandwidth efficiency, we relax the idle assumption of non-destination nodes and assume that non-destination nodes may receive signals from sources. We note that the message relayed to a particular node in such a system gives rise to interference to other nodes. To study such a more general relay system, we consider, in this paper, a relay system in which the relay first listens to the source, then routes the source message to the destination, and finally produces interference to the destination in sending messages for other systems. We obtain capacity upper and lower bounds and study the optimal method to deal with the interference as well as the optimal routing schemes. From analytic results obtained, we find the conditions on which the direct transmission provides higher transmission rate. Next, we find the conditions, by numerical evaluation of the theoretical results, on which it is better for the destination to cancel and decode the interference. Also we find the optimal source power allocation scheme that achieves the lower bound depending on various channel conditions. We believe that the results provided in this paper will provide useful insights to system designers in strategically choosing the optimal routing algorithms depending on the channel conditions.

• Journal of Communications and Networks
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• 제9권2호
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• pp.118-127
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• 2007

We propose a link adaptation and selection method for the links constituting an orthogonal frequency division multiplexing (OFDM) based wireless relay network. The proposed link adaptation and selection method selects the forwarding, modulation, and channel coding schemes providing the highest end-to-end throughput and decides whether to use the relay or not. The link adaptation and selection is done for each sub-channel based on instantaneous signal to interference plus noise ratio (SINR) conditions in the source-to-destination, source-to-relay and relay-to-destination links. The considered forwarding schemes are amplify and forward (AF) and simple adaptive decode and forward (DF). Efficient adaptive modulation and coding decision rules are provided for various relaying schemes. The proposed end-to-end link adaptation and selection method ensures that the end-to-end throughput is always larger than or equal to that of transmissions without relay and non-adaptive relayed transmissions. Our evaluations show that over the region where relaying improves the end-to-end throughput, the DF scheme provides significant throughput gain over the AF scheme provided that the error propagation is avoided via error detection techniques. We provide a frame structure to enable the proposed link adaptation and selection method for orthogonal frequency division multiple access (OFDMA)-time division duplex relay networks based on the IEEE 802.16e standard.

• 한국통신학회논문지
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• 제35권6A호
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• pp.594-599
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• 2010

본 논문은 멀티홉 셀룰러 네트워크에서 릴레이 노드의 배치 위치가 하향링크 SINR에 미치는 영향을 분석한다. 분석 모델에서는 릴레이 노드가 셀 안쪽으로 배치되는 것과 인접한 두 셀의 경계지역에 배치되는 두 가지 시나리오를 가정한다. 본 논문에서는 위 두 가지 시나리오의 하향링크 SINR을 비교 분석하기 위한 수학적 모델을 도출한다. 제안하는 수학적 모델에서는 멀티-셀 구조 및 셀 간 간섭 등을 고려한다. 수학적 분석 결과는 릴레이 노드들을 셀 안쪽에 배치하는 경우에 셀 간 간섭의 증가에도 불구하고 수신 신호 세기의 증가로 인해 릴레이 노드들을 셀 경계에 배치하는 경우에 비해 SINR이 증가함을 보인다.

• 한국통신학회논문지
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• 제35권6A호
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• pp.568-576
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• 2010

본 논문은 복호 후 전달 (decode-and-forward, DF) 프로토콜 하에서 전이중 통신방식 릴레이 (full duplex relay, FDR) 의 오수신 확률 (outage probability) 성능을 페이딩 채널하에서 유도하였다. 준기지국 형태의 고정된 릴레이를 가정하여 송신단과 릴레이 사이의 채널은 LOS (line of sight) 전파가 존재하는 Rician 채널을, 다른 링크 채널은 Rayleigh 채널을 고려하였다. 또한, 이 분석을 통해 전이중 통신 (full duplex, FD)으로 인한 간섭 문제와 자원의 효율성 향상 측면을 고려하여 실제적으로 FDR이 반이중 통신방식 릴레이 (half duplex relay, HDR) 보다 낮은 오수신 확률 성능을 가지기 위한 조건을 제시하였다. 분석된 오수신 확률 성능의 정확성은 모의 실험을 통하여 검증되었다.

• 한국산업정보학회논문지
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• 제14권5호
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• pp.1-9
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• 2009

중계기를 활용한 다중 입력 기술이 차세대 광대역 무선 이동 통신의 유력한 후보로 연구되고 있다. 본 논문에서는 채널 선택적 중계기 기반의 다중 입력 전송 시스템을 제안한다. 본 전송 시스템은 상하향 전송을 위해 SC-FDMA (Single Carrier Frequency Division Multiple Access)와 OFDMA (Orthogonal Frequency Division Multiple Access) 방식을 각각 채택한다. 단말기와 기지국 간 사용되는 부채널을 고정하고, 중계기와 단말기 또는 중계기와 기지국 사이의 채널 상태에 따라 선택적으로 부채널을 사용함으로써 수신 성능을 크게 향상시킬 수 있다. 실험 결과를 통해, 제안된 중계기 기반 시스템의 성능이 기존의 중계기 기반 시스템의 성능보다 우수함을 확인한다.