• Journal of Communications and Networks
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• 제13권4호
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• pp.313-318
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• 2011

When wireless channels undergo fast fading, non-coherent frequency shift keying (FSK) (de)modulation schemes may be considered for amplify-and-forward (AF) cooperative communications. In this paper, we derive the bit-error-rate performance of partial non-coherent receiver as a lower bound of the optimal non-coherent receiver for FSK modulated AF cooperative communications. From the simulation and analytical results, it is found that the derived lower bound is very closed to simulation results. This result shows that knowing partial channel state information may not improve system performance significantly. On the other hand, conventional optimal non-coherent receiver involves complicated integration operation. To address the above complexity issue, we also propose a near optimal non-coherent receiver which does not involve integration operation. Simulation results have shown that the performance gap between the proposed near optimal receiver and the optimal receiver is small.

• 대한전자공학회논문지TC
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• 제49권6호
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• pp.15-26
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• 2012

본 논문에서는 개선된 AF(Amplify-and-Forward)와 DF(Decode-and-Forward) Relay 프로토콜을 결합한 다중 사용자 MIMO (Multiple Input Multiple Output) Relay 네트워크에서 간섭 제거 기술을 논의 한다. 간섭 제거 기술은 Relay 노드가 적용된 전체 전송 시스템의 오류 성능을 향상시키기 위해 eNB(evolved NodeB), Relay 노드(RN: Relay Node)와 UE(User Equipment)에 의해 이루어진다. 간섭 제거를 수행하기 위해 ZF(Zero Forcing), MMSE(Minimum Mean Square Error), SIC(Successive Interference Cancellation)와 OSIC(Ordered Successive Interference Cancellation)가 적용된 DPC(Dirty Paper Coding)와 THP(Thomilson Harashima Precoding)를 사용하였다. 이러한 기본적인 기술이 적용된 Relay 노드 기능들이 연구되고 개선된다. 협력 Relay 노드에서 두 계층 간의 간섭 제거를 강화한 DF는 성능을 향상시킨다. eNB와 RN간의 가중치 벡터를 사용하여 간섭 제거가 수행된다. 연구 최종 결과, 기존의 알고리즘과 비교하여 제안된 알고리즘이 낮은 SNR에서 더 좋은 성능을 나타냈다. 모의실험 결과 LTE-Advanced 시스템에서 제안된 기법이 오류 성능 면에서 상당한 향상을 나타냈다.

• Journal of Communications and Networks
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• 제18권2호
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• pp.261-269
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• 2016

In this paper, the impact of energy constraints on a two-hop network with a source, a relay and a destination under random medium access is studied. A collision channel with erasures is considered, and the source and the relay nodes have energy harvesting capabilities and an unlimited battery to store the harvested energy. Additionally, the source and the relay node have external traffic arrivals and the relay forwards a fraction of the source node's traffic to the destination; the cooperation is performed at the network level. An inner and an outer bound of the stability region for a given transmission probability vector are obtained. Then, the closure of the inner and the outer bound is obtained separately and they turn out to be identical. This work is not only a step in connecting information theory and networking, by studying the maximum stable throughput region metric but also it taps the relatively unexplored and important domain of energy harvesting and assesses the effect of that on this important measure.

• Journal of Communications and Networks
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• 제14권5호
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• pp.524-532
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• 2012

In this paper, we present the performance evaluation of the reliable cooperative media access control (RCO-MAC) protocol, which has been proposed in [1] by us in order to enhance system throughput in bad wireless channel environments. The performance of this protocol is evaluated with computer simulation as well as mathematical analysis in this paper. The system throughput, two types of average delays, average channel access delay, and average system delay, which includes the queuing delay in the buffer, are used as performance metrics. In addition, two different traffic models are used for performance evaluation: The saturated traffic model for computing system throughput and average channel access delay, and the exponential data generation model for calculating average system delay. The numerical results show that the RCO-MAC protocol proposed by us provides over 20% more system throughput than the relay distributed coordination function (rDCF) scheme. The numerical results show that the RCO-MAC protocol provides a slightly higher average channel access delay over a greater number of source nodes than the rDCF. This is because a greater number of source nodes provide more opportunities for cooperative request to send (CRTS) frame collisions and because the value of the related retransmission timer is greater in the RCO-MAC protocol than in the rDCF protocol. The numerical results also confirm that the RCO-MAC protocol provides better average system delay over the whole gamut of the number of source nodes than the rDCF protocol.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권7호
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• pp.2350-2364
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• 2014

This paper addresses the problem of resource allocation in amplify-and-forward (AF) relayed OFDM based cognitive radio networks (CRNs). The purpose of resource allocation is to maximize the overall throughput, while satisfying the constraints on the individual power and the interference induced to the primary users (PUs). Additionally, different from the conventional resource allocation problem, the rate-guarantee constraints of the subcarriers are considered. We formulate the problem as a mixed integer programming task and adopt the dual decomposition technique to obtain an asymptotically optimal power allocation, subcarrier pairing and relay selection. Moreover, we further design a suboptimal algorithm that sacrifices little on performance but could significantly reduce computational complexity. Numerical simulation results confirm the optimality of the proposed algorithms and demonstrate the impact of the different constraints.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권10호
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• pp.3983-4001
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• 2015

Exact average bit error probability (BEP) expressions for mobile-relay-based mobile-to-mobile (M2M) cooperative networks with incremental decode-and-forward (IDF) relaying over N-Nakagami fading channels are derived in this paper. The average BEP performance under different conditions is evaluated numerically to confirm the accuracy of the analysis. Results are presented which show that the fading coefficient, the number of cascaded components, the relative geometrical gain, and the power allocation parameter have a significant influence on the average BEP performance.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2019년도 춘계학술대회
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• pp.288-289
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• 2019

This paper studies the secrecy capacity for a wireless cooperative network with perfect channel state information at the relays, and receiver. A similar assumption is also made for the instance where there exist a direct link between the transmitter and receiver. Physical Layer security techniques are employed in wireless networks to mitigate against the activity of eavesdroppers. It offers a viable alternative to computationally intensive encryption. In this paper the design of a protocol utilizing jamming (via jamming nodes) for better security and relaying (via relay nodes) for the amplify-and-forward (AF) operation, is investigated. A a signal-to-noise variant of secrecy known as secrecy gap is explored because of its use of lesser computational power - preferable for practical systems. Thus we maximize this signal-to-noise approach instead of the conventional secrecy capacity maximization method. With this, an iterative algorithm using geometric programming (GP) and semi-definite programming (SDP) is presented with appreciable benefits. The results show here highlight the benefits of using fractional components of the powers of the relays to offer better secrecy capacity.

• 한국정보통신학회논문지
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• 제20권2호
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• pp.275-280
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• 2016

본 논문은 버퍼가 장착된 복수개의 중계기가 존재하는 연쇄적 데이터 중계 네트워크에서 각 중계기가 이미 복호에 성공한 정보를 활용하여 인접 중계기로부터의 간섭을 원천적으로 제거하는 새로운 중계 기법을 제안한다. 기존의 버퍼기반 중계 선택기술에서는 송신단으로부터 데이터를 수신할 중계기와 수신단으로 데이터를 전송할 중계기를 각각 하나씩 선택한다. 그러나 제안된 중계 기법에서는 수신단으로 데이터를 전송할 중계기가 선택된 후 나머지 모든 중계기들은 송신단으로부터 도착한 신호의 복호를 시도하고 복호에 성공한 모든 중계기들은 자신의 버퍼에 복호된 신호를 저장한다. 제안된 기법에서는 자신이 데이터를 전송했을 때, 자신의 신호가 수신단에 성공적으로 도착하면서 동시에 송신단으로부터 도착한 신호 복호에 성공하는 중계기의 수를 최대화하는 중계기가 선택된다. 컴퓨터 시뮬레이션을 통하여 제안된 중계기 선택 방식이 기존 중계기 선택 기법에 비해 훨씬 더 좋은 성능을 보이는 것을 확인한다.

• 한국인터넷방송통신학회논문지
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• 제16권5호
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• pp.69-76
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• 2016

본 논문에서는 5세대 이동통신 네트워크에서 도입하고자하는 순차 간섭제거(Successive interference cancellation)를 채택한 비직교 다중화(Non-orthogonal multiple access) 시스템에 협동 릴레이를 채택하였을 경우의 시스템 성능을 유도하였다. 그동안의 연구는 단순히 지정된 릴레이를 대상으로 연구가 진행되었지만 본 논문에서는 최대-최소 릴레이 선택법을 적용한 기회전송 증가 릴레이 시스템의 오수신율을 해석적으로 분석하였다. 그리고 현실적인 이동통신 환경을 고려하여 릴레이는 균일 포아송 분포로 모델링하였고, 시스템의 성능을 더욱 개선하기 위하여 목적지에서 최대비 합성(Maximal ration combining)을 적용하였다. 수치적인 해석 결과 원/근 사용자 송신전력비가 클수록 오수신율이 개선되었으며, 직접 경로만 사용하여 정보를 전송하는 경우보다 릴레이를 사용한 협동 시스템의 성능이 항상 우수함을 나타내었다. 또한 포아송 밀도가 높을수록 공간 다이버시티 이득이 커지고 결국 성능이 개선됨을 확인하였다.

• Journal of electromagnetic engineering and science
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• 제12권2호
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• pp.135-141
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• 2012

In this paper, we propose a novel cooperative routing protocol (NCRP) for wireless networks. The proposed protocol uses cooperative transmission to improve end-to-end outage probability. The broadcast nature ensures that the destination can receive a packet from the source or from the relays and if it cannot correctly decode the packet, the successful relays will start a retransmission. The NCRP protocol can skip some transmissions from the intermediate relays, thereby reducing the total power consumption. Theoretical results are derived and verified by simulation results.