• Journal of Communications and Networks
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• 제14권3호
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• pp.257-266
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• 2012

A decode-and-forward two-way relay system benefits from orthogonal frequency division multiplexing (OFDM) and relay transmission. In this paper, we consider a decode-and-forward two-way relay system over OFDMwith two strategies: A joint subcarrier matching algorithm and a power allocation algorithm operating with a total power constraint for all subcarriers. The two strategies are studied based on average capacity using numerical analysis by uniformly allocating power constraints for each subcarrier matching group. An optimal subcarrier matching algorithm is proposed to match subcarriers in order of channel power gain for both transmission sides. Power allocation is defined based on equally distributing the capacity of each hop in each matching group. Afterward, a modified water-filling algorithm is also considered to allocate the power among all matching groups in order to increase the overall capacity of the network. Finally, Monte Carlo simulations are completed to confirm the numerical results and show the advantages of the joint subcarrier matching, power allocation and water filling algorithms, respectively.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제5권9호
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• pp.1513-1527
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• 2011

This paper investigates the capacity rate problems for a joint decode-and-forward (JDF) based two-way relaying with network coding. We first characterize the achievable rate region for a conventional three-node network scenario along with the calculation of the corresponding maximal sum-rate. Then, for the goal of maximizing the system sum-rate, opportunistic relay selection is examined for multi-relay networks. As a result, a novel strategy for the implementation of relay selection is proposed, which depends on the instantaneous channel state and allows a single best relay to help the two-way information exchange. The JDF scheme and the scheme using relay selection are analyzed in terms of outage probability, after which the corresponding exact expressions are developed over Rayleigh fading channels. For the purpose of comparison, outage probabilities of the amplify-and-forward (AF) scheme and those of the scheme using relay selection are also derived. Finally, simulation experiments are done and performance comparisons are conducted. The results verify that the proposed strategy is an appropriate method for the implementation of relay selection and can achieve significant performance gains in terms of outage probability regardless of the symmetry or asymmetry of the channels. Compared with the AF scheme and the scheme using relay selection, the conventional JDF scheme and that using relay selection perform well at low signal-to-noise ratios (SNRs).

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권11호
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• pp.3008-3025
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• 2012

In this paper, the downlink resource allocation of OFDMA system with decode-and-forward (DF) relaying is investigated. A non-convex optimization problem maximizing system throughput with users' satisfaction constraints is formulated with joint relay selection, subcarrier assignment and power allocation. We first transform it to a standard convex problem and then solve it by dual decomposition. In particular, an Optimal resource allocation scheme With Time-sharing (OWT) is proposed with combination of relay selection, subcarrier allocation and power control. Due to its poor adaption to the fast-varying environment, an improved version with subcarrier Monopolization (OWM) is put forward, whose performance promotes about 20% compared with that of OWT in the fast-varying vehicular environment. In fact, OWM is the special case of OWT with binary time-sharing factor and OWT can be seen as the tight upper bound of the OWM. To the best of our knowledge, such algorithms and their relation have not been accurately investigated in cooperative OFDMA networks in the literature. Simulation results show that both the system throughput and the users' satisfaction of the proposed algorithms outperform the traditional ones.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권5호
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• pp.1957-1975
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• 2016

The outage probability (OP) performance of multiple-relay-based incremental hybrid decode-amplify-forward (IHDAF) relaying mobile-to-mobile (M2M) networks with transmit antenna selection (TAS) over N-Nakagami fading channels is investigated in this paper. The closed-form expressions for approximate OP of the optimal and suboptimal TAS schemes are derived. The power allocation problem is formulated for performance optimization. Then the OP performance under different conditions is evaluated through numerical simulations to verify the analysis. The simulation results showed that optimal TAS scheme has a better OP performance than suboptimal TAS scheme; the power-allocation parameter has an important influence on the OP performance.

• 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.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권5호
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• pp.2047-2066
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• 2016

In this paper, we investigate joint power allocation and relay selection (PARS) schemes in non-orthogonal cooperative protocol (NOCP) based cognitive relay networks. Generally, NOCP outperforms the orthogonal cooperative protocol (OCP), since it can provide more transmit diversity. However, most existing PARS schemes in cognitive relay networks focus on OCP, which are not suitable for NOCP. In the context of NOCP, we first derive the joint constraints of transmit power limit for secondary user (SU) and interference constraint for primary user (PU). Then we formulate optimization problems under the aforementioned constraints to maximize the capacity of SU in amplify-and-forward (AF) and decode-and-forward (DF) modes, respectively. Correspondingly, we derive the closed form solutions with respect to different parameters. Numerical results are provided to verify the performance improvement of the proposed PARS schemes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권1호
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• pp.1-19
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• 2020

In an underlay cognitive simultaneous wireless information and power transfer (SWIPT) network, communication from secondary user (SU) to secondary destination (SD) is accomplished with decode-and-forward (DF) relays. Multiple energy-constrained relays are assumed to harvest energy from SU via power splitting (PS) protocol and complete SU secure information transmission with beamforming. Hence, physical layer security (PLS) is investigated in cognitive SWIPT network. In order to interfere with eavesdropper and improve relay's energy efficiency, a destination-assisted jamming scheme is proposed. Namely, SD transmits artificial noise (AN) to interfere with eavesdropping, while jamming signal can also provide harvested energy to relays. Beamforming vector and power splitting ratio are jointly optimized with the objective of SU secrecy capacity maximization. We solve this non-convex optimization problem via a general two-stage procedure. Firstly, we obtain the optimal beamforming vector through semi-definite relaxation (SDR) method with a fixed power splitting ratio. Secondly, the best power splitting ratio can be obtained by one-dimensional search. We provide simulation results to verify the proposed solution. Simulation results show that the scheme achieves the maximum SD secrecy rate with appropriate selection of power splitting ratio, and the proposed scheme guarantees security in cognitive SWIPT networks.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권12호
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• pp.5803-5819
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• 2017

In this paper, we proposed a contract theory based cooperative spectrum sharing scheme with joint power and bandwidth optimization under asymmetric information, where the primary user (PU) does not know the secondary users' (SUs) private information. To improve performance, PU needs to provide incentives to stimulate nearby SUs to help forward its signal. By using contract theory, PU and SUs' negotiations are modeled as a labor market. PU and SUs act as the employer and employees, respectively. Specifically, SUs provide labor (i.e. the relay power, which can be used for forwarding PU's signal) in exchange for the reward (i.e. the spectrum access bandwidth which can be used for transmitting their own signals). PU needs to overcome a challenge how to balance the relationship between contributions and incentives for the SUs. We study the optimal contract design which consists of relay power and spectrum access bandwidth allocation. We show that the most efficient SUs will be hired by the PU to attend the cooperative communication. PU can achieve the same maximum utility as in the symmetric information scenario. Simulation results confirm that the utility of PU is significantly enhanced with our proposed cooperative spectrum sharing scheme.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권2호
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• pp.288-307
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• 2013

This paper formulates resource allocation for decode-and-forward (DF) relay assisted multi-cell orthogonal frequency division multiple (OFDM) networks as an optimization problem taking into account of inter-cell interference and users fairness. To maximize the transmit rate of system we propose a joint interference coordination, subcarrier and power allocation algorithm. To reduce the complexity, this semi-distributed algorithm divides the primal optimization into three sub-optimization problems, which transforms the mixed binary nonlinear programming problem (BNLP) into standard convex optimization problems. The first layer optimization problem is used to get the optimal subcarrier distribution index. The second is to solve the problem that how to allocate power optimally in a certain subcarrier distribution order. Based on the concept of equivalent channel gain (ECG) we transform the max-min function into standard closed expression. Subsequently, with the aid of dual decomposition, water-filling theorem and iterative power allocation algorithm the optimal solution of the original problem can be got with acceptable complexity. The third sub-problem considers dynamic co-channel interference caused by adjacent cells and redistributes resources to achieve the goal of maximizing system throughput. Finally, simulation results are provided to corroborate the proposed algorithm.

• 대한전자공학회논문지TC
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• 제46권6호
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• pp.94-102
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• 2009

참고문헌 [1]에서 full diversity를 달성할 수 있을 뿐만 아니라 각 relay node에서의 시간 지연을 제거하기 위해서 새로운 기법을 제안했다. 그러나 복호 후 전달 (DF) 모델 연산 모드는 relay에 더욱 많은 처리 부담을 준다. 본 논문에서는 [2],[3]에서 제안한 증폭 후 전달 (AF) model로 확장할 뿐만 아니라 source-relay link와 relay-destination link로 이루어진 모든 채널의 결합 채널 계수의 순서를 정하고 다음 복호 절차에서 이전의 복호된 심벌을 지우는 효율적인 복호 알고리즘을 제안한다. 컴퓨터 모의실험 결과를 통하여 제안한 알고리즘을 이용하면 높은 SNR 영역에서 참고문헌 [1]과 비교하여 상대적으로 2-3dB의 이득을 가져오기에 효율적으로 성능을 향상시킬 수 있다는 것을 알 수 있었다. 또한 제안한 알고리즘이 원래의 알고리즘과 비교하여 상대적으로 3dB 이상의 이득을 얻을 수 있는 복호 후 전달 (DF)에 유용하다는 것을 알 수 있었다.