• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.4
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• pp.1904-1921
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• 2019

In this paper, we investigate the problem of secure communications in multiple-input-multiple-output interference networks from the perspective of physical layer security. Specifically, the legitimate transmitter-receiver pairs are divided into different categories of active and inactive. To enhance the security performances of active pairs, inactive pairs serve as cooperative jammers and broadcast artificial noises to interfere with the eavesdropper. Besides, active pairs improve their own security by using joint transceivers. The encoding of active pairs and inactive pairs are designed by maximizing the difference of mean-squared errors between active pairs and the eavesdropper. In detail, the transmit precoder matrices of active pairs and inactive pairs are solved according to game theory and linear programming respectively. Experimental results show that the proposed algorithm has fast convergence speed, and the security performances in different scenarios are effectively improved.

• Journal of Communications and Networks
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• v.10 no.2
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• pp.148-155
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• 2008

In wireless data communication systems, retransmission of an erroneous packet is inevitable due to the harsh communication environment. In this paper, an efficient retransmission scheme using cooperation from neighboring nodes is investigated. In the cooperative retransmission scheme, an erroneous packet is transmitted to the destination by cooperative nodes which have favorable channels. This cooperative retransmission scheme requires no a priori information of neighboring nodes and has no limitation on the number of cooperating nodes. Distributed beamforming is used to accommodate multiple cooperating nodes. Phase and frequency offsets of cooperating signals are extracted from the NACK message and used to co-phase retransmitted data packets. The outage probability of the cooperative retransmission scheme is analyzed for the case of perfect synchronization and when the offsets are estimated. To reduce the impact of the residual phase and frequency offsets in cooperating signals, a low-rate feedback scheme is also investigated. It is shown that improved outage probability and reduced packet error rate (PER) performance can be achieved even for long data packets. The proposed cooperative retransmission scheme is found to outperform simple retransmission by the source as well as decode-and-forward cooperation.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.6
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• pp.1668-1688
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• 2012

Cooperative communications and network coding schemes have been proposed to increase system throughput for ad hoc networks. In this paper, we present throughput and delay analysis of the new network coding-enabled cooperative MAC protocol called NC-MAC, which has been proposed by us in order to significantly enhance system performance. This protocol introduces an approach that can accommodate both cooperative communication and network coding for wireless ad hoc networks by slightly increasing overhead and modifying standards. The protocol's performance is evaluated using mathematical analysis and computer simulation and two performance measures, system throughput and average channel access delay, are used for a performance comparison with previous schemes. It is assumed that all the frames exchanged over a wireless channel are susceptible to transmission errors, which is a new but more reasonable assumption differentiating this research from previous research. Numerical results show this protocol provides significantly enhanced system performance compared with conventional cooperative MAC protocols used in previous research. For instance, system performance is 47% higher using the NC-MAC protocol than when using the rDCF protocol.

• Journal of Communications and Networks
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• v.17 no.3
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• pp.256-264
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• 2015

Energy harvesting devices have been proposed for sensor networking applications where batteries cannot be replaced, and cooperative communication schemes have been used to increase energy efficiency for wireless systems. Here, we develop transmission scheduling schemes for multi-terminal cooperative energy harvesting networks that maximize the packet delivery ratio, i.e., the probability that an event is reported successfully. We see that the proposed scheme provides virtually the same performance as the state-of-the-art threshold-based scheme, but does not require auxiliary parameter optimization. The proposed scheme also permits extensions to multiple cooperating nodes and sources, and it can be modified to accommodate fairness constraints.

• Journal of Communications and Networks
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• v.11 no.5
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• pp.445-454
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• 2009

Cooperative transmission protocols are always designed to achieve the largest diversity gain and the network capacity simultaneously. The concept of diversity-multiplexing tradeoff (DMT) in multiple input multiple output (MIMO) systems has been extended to this field. However, DMT constrains a better understanding of the asymptotic interplay between transmission rate, outage probability (OP) and signal-to-noise ratio. Another formulation called the throughput-reliability tradeoff (TRT) was then proposed to avoid such a limitation. By this new rule, Azarian and Gamal well elucidated the asymptotic trends exhibited by the OP curves in block-fading MIMO channels. Meanwhile they doubted whether the new rule can be used in more general channels and protocols. In this paper, we will prove that it does hold true in decode-and-forward cooperative protocols. We deduce the theoretic OP curves predicted by TRT and demonstrate by simulations that the OP curves will asymptotically overlap with the theoretic curves predicted by TRT.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.5
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• pp.589-595
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• 2019

Recently, the mobile social networks, which consider both social relationship between users and mobile communication networks, have been received great attention. In this paper, we consider the trust degree of node as the social relationship for the cooperative communication networks. In contrast to the existing works that consider the case of the perfect trust degree information, for the case that transmitter has an imperfect trust degree information, we propose an imperfect trust degree based cooperative communication technique that maximizes a throughput. We first model the imperfect trust degree information as a probability distribution and derive the outage probability using the probability distribution. Then, we propose the transmission scheme that maximizes the throughput, which consider both outage probability and transmission rate. The simulation results show that the proposed cooperative transmission scheme outperforms the conventional scheme in terms of the throughput.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.3A
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• pp.290-296
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• 2007

We propose new routing scheme, Cooperative Diversity-based Routing (CDR) which utilizes the cooperative space diversity for power saving and performance enhancement of wireless ad-hoc networks. The improved performance is compared with Multi-hop Relay Routing (NRR) by analytical methods. When the required outage probability is $1\times10^{-3}$ at the destination node in ad-hoc networks with 7 nodes, we noticed that each node can save power consumption by 15.5 dB in average, by using our proposed CDR compared to MRR.

• 한국ITS학회:학술대회논문집
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• 2008.11a
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• pp.328-331
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• 2008

• Journal of Communications and Networks
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• v.14 no.4
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• pp.364-373
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• 2012

In this paper, we propose combined relay selection and cooperative beamforming schemes for physical layer security. Generally, high operational complexity is required for cooperative beamforming withmultiple relays because of the required information exchange and synchronization among the relays. On the other hand, while it is desirable to reduce the number of relays participating in cooperative beamforming because of the associated complexity problem, doing so may degrade the coding gain of cooperative beamforming. Hence, we propose combined relay selection and cooperative beamforming schemes, where only two of the available relays are selected for beamforming and data transmission. The proposed schemes introduce a selection gain which partially compensates for the decrease in coding gain due to limiting the number of participating relays to two. Both the cases where full and only partial channel state information are available for relay selection and cooperative beamforming are considered. Analytical and simulation results for the proposed schemes show improved secrecy capacities compared to existing physical layer security schemes employing cooperative relays.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.8
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• pp.1811-1819
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• 2013

In this paper, we carried out a study on how to find an appropriate helper node for cooperative communications, the role of which is very import to enhance system throughput of wireless communication system. The busy tone cooperative MAC (BT-COMAC) protocol proposed in this paper is a new cooperative MAC protocol with a reactive helper node scheme and maximizes the benefits of existing schemes while making up for their shortcomings. We conducted performance evaluation of this new protocol using computer simulation experiment. System throughput in bps and channel access delay are utilized as performance measures. We used a random way point mobility model where every communication node moves independently one another, and slow fading channel where every communication node decided its transmission rate with received power basis. Numerical results show that the new MAC protocol enhances system throughput as much as 15% of the existing scheme.