• 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.

• Journal of Communications and Networks
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• v.12 no.3
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• pp.231-239
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• 2010

In cluster-based wireless sensor networks, the energy could be saved when the nodes that have data to transmit participate in cooperative multiple-input multiple-output (MIMO). In this paper, by making the idle nodes that have no data to transmit participate in the cooperative MIMO, it is found that much more energy could be saved. The number of the idle nodes that participate in the cooperative MIMO is optimized to minimize the total energy consumption. It is also found that the optimal number of all the nodes participating in cooperative communication does not vary with the number of nodes that have data to transmit. The proposition is proved mathematically. The influence of long-haul distance and modulation constellation size on the total energy consumption is investigated. A cooperative MIMO scheme with help-node participation is proposed and the simulation results show that the proposed scheme achieves significant energy saving.

• Journal of electromagnetic engineering and science
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• v.12 no.1
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• pp.13-19
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• 2012

In this paper, we investigate cooperative transmission in one-dimensional random wireless networks. In this scheme, a stationary source communicates with a stationary destination with the help of N relays, which are randomly placed in a one-dimensional network. We derive exact and approximate expressions of the average outage probability over Rayleigh fading channels. Various Monte-Carlo simulations are presented to verify the accuracy of our analyses.

• Journal of electromagnetic engineering and science
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• v.9 no.2
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• pp.66-70
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• 2009

The decode-and-forward cooperative communication protocol allows single-antenna users in wireless environments to obtain the powerful benefits of multi-antenna systems without the need for physical arrays. Evaluating the performance of this protocol through simulations is time-consuming and therefore, a need exists for an analytical BER expression to serve as a reference. This paper proposed such an expression for coherently BPSK-modulated data.

• Proceedings of the Korean Information Science Society Conference
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• 2011.06d
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• pp.267-268
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• 2011

Recent research activities in cooperative communication focus on achieving energy efficiency and reliability. Relay selection strategy for cooperative communication improves the performance significantly. However, due to imbalance consumption of power, network might die earlier and more than 90% energy remains unused. In this paper, we provide a framework of an energy-efficient medium access control protocol that minimizes these problems and improves energy efficiency.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.3
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• pp.121-129
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• 2010

In this paper, we analyze effects of positions of relays on the performance of cooperative communication networks. From this, the best relays are chosen to assist transmitting the signal to the destination or to replace the source to retransmit the signal to the destination whenever the destination incorrectly receives the signal from the source. As the results, we show the significant improvement on performance of schemes choosing best relays, which is compared to the performance of other cooperative schemes. Moreover, the simulation results that match exactly with the theoretical results prove the correctness of the analysis.

• 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.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.10
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• pp.1931-1933
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• 2015

This paper proposes inter-cell cooperative transmission scheme in order to improve the reliability of the wireless communication system at the heterogeneous network environments. The heterogeneous network can increase data rate by using existing network technologies. However, degradation of communication performance in the cell edge has been a serious problem. Therefore, this letter proposes an adaptive transmission scheme according to the diverse situations in order to solve this problem.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.3
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• pp.1357-1372
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• 2017

Energy harvesting techniques, particularly radio frequency energy harvesting (RF-EH) techniques, which are known to provide feasible solutions to enhance the performance of energy constrained wireless communication systems, have gained increasing attention. In this paper, we consider a wireless-powered cooperative communication network (WPCCN) for transferring energy in the downlink and forwarding signals in the uplink. The objective is to maximize the average transmission rate of the system, subject to the total network power constraint. We formulate such a problem as a form of wireless energy transmission based on resource allocation that searches for the joint subcarrier pairing and the time and power allocation, and this can be solved by using a dual approach. Simulation results show that the proposed joint optimal scheme can efficiently improve system performance with an increase in the number of subcarriers and relays.

• Journal of Internet Computing and Services
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• v.12 no.6
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• pp.35-42
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• 2011

Cooperative relay communication for wireless networks has been extensively studied due to its ability to mitigate fading effectively via spatial diversity. In this paper, we propose a balanced transmit scheme in cooperative relay communication with decode-and-forward DF) scheme. The proposed scheme selects the feedback bits to obtain the maximum cooperative diversity gain. The simulation results show that the proposed scheme improves the bit error rate BER) performance as compare with a conventional scheme.