• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.8
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• pp.696-707
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• 2014

In this paper, firstly, performance degradation due to the Private Distributed Reservation Protocol (DRP) conflict problem caused by devices' mobility is analyzed. And a novel relay transmission protocol combined with Private DRP conflict resolution is proposed to overcome the performance degradation at Private DRP conflicts. In order to give the loser device due to Private DRP conflicts another chance to maintain resources, the proposed relay transmission protocol executed at each device helps the loser device reserve another indirect link maintaining the required resources via a relay node.

• Information and Communications Magazine
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• v.11 no.4
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• pp.62-70
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• 1994

This paper discusses the LAN interface technics physically applicable to the ISDN exchange system through frame relay without changing of the basic exchange architecture. To ensure the success of frame relaying, it's interworking with the existing X.25 services is very imported, and for this purpose both X.75 and 1.122-based interworking alternative must be considered. Definition required to frame relay, interconnection of remote bridge and ways to design the Frame Handler carrying a frame realying in the ISDN node was introduced here. Subsequently, alternatives using the X.25 and X.75 or 1.122 as well as interconnection mechanism LAN and ISDN for the LAN interface and LAN and/or LAN interface and ISDN through frame relay was individually introduced. Through frame relay applications in the major countries, the achievement of high speed frame relaying service to the LAN was introduced.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.11
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• pp.4483-4501
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• 2015

In this paper, we investigate a security transmission scheme at the physical layer for cooperative wireless relay networks in the presence of a passive eavesdropper. While the security scheme has been previously investigated with perfect channel state information(CSI) in the presence of a passive eavesdropper, this paper focuses on researching the robust cooperative relay beamforming mechanism for wireless relay networks which makes use of artificial noise (AN) to confuse the eavesdropper and increase its uncertainty about the source message. The transmit power used for AN is maximized to degrade the signal-to-interference-plus-noise-ratio (SINR) level at the eavesdropper, while satisfying the individual power constraint of each relay node and worst-case SINR constraint at the desired receiver under a bounded spherical region for the norm of the CSI error vector from the relays to the destination. Cooperative beamforming weight vector in the security scheme can be obtained by using S-Procedure and rank relaxation techniques. The benefit of the proposed scheme is showed in simulation results.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.4
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• pp.1390-1405
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• 2014

This paper investigates optimal relay selection and power allocation under an aggregate power constraint for cooperative wireless sensor networks assisted by amplify-and-forward relay nodes. By considering both transmission power and circuit power consumptions, the received signal-to-noise ratio (SNR) at the destination node is calculated, based on which, a relay selection and power allocation scheme is developed. The core idea is to adaptively adjust the selected relays and their transmission power to maximize the received SNR according to the channel state information. The proposed scheme is derived by recasting the optimization problem into a three-layered problem-determining the number of relays to be activated, selecting the active relays, and performing power allocation among the selected relays. Monte Carlo simulation results demonstrate that the proposed scheme provides a higher received SNR and a lower bit error rate as compared to the average power allocation scheme.

• ETRI Journal
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• v.36 no.4
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• pp.599-608
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• 2014

This paper studies a parallel relay network where the relays employ an amplify-and-forward (AF) relaying scheme and are subjected to individual power constraints. We consider correlated effective relay noise arising from practical scenarios when the relays are exposed to common interferers. Assuming that the noise covariance and the full channel state information are available, we investigate the problem of finding the optimal AF scheme in terms of maximum end-to-end transmission rate. It is shown that the maximization problem can be equivalently transformed to a convex semi-definite program, which can be efficiently solved. Then an upper bound on the maximum achievable AF rate of this network is provided to further evaluate the performance of the optimal AF scheme. It is proved that the upper bound can be asymptotically achieved in two special regimes when the transmit power of the source node or the relays is sufficiently large. Finally, both theoretical and numerical results are given to show that, on average, noise correlation is beneficial to the transmission rate - whether the relays know the noise covariance matrix or not.

• Journal of the Korea Institute of Military Science and Technology
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• v.12 no.3
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• pp.333-343
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• 2009

Tactical Information Communication Network(TICN) is a concept-type integrated Military Communication system that enables precise command control and decision making by unifying the diversified military communication network and conveying diverse range of battle field information on real-time, at right place at right time. TICN is designed to advance into high speed, large capacity, long distance wireless relay transmission. To support mobility in battlefield environments, the application of Ad-hoc networking technology to its wireless communication has been examined. Ad-hoc network is consist of mobile nodes and nodes in the network depends on the cooperation of other nodes for forwarding of packets. In this context, some non-cooperating nodes may delay forwarding of packets or drop the packets. This may hamper the network as a whole and disrupt communication between the cooperating nodes. To solve this problem, we present a solution with a Node Weight Management Server(NWMS), which manages each node's weight according to its behavior in local area. When the NWMS detects misbehaving node, it increases the node's weight. If the node's weight exceeds a predefined threshold then the NWMS broadcasts the node's information into network to isolate the misbehaving node from the network. These mechanisms show that they are highly effective and can reliably detect a multitude of misbehaving node.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2012.05a
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• pp.278-280
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• 2012

We are propose the position of the node context-awareness information and the validity of the head node in the path according to the clustering how to elect one of the energy efficiency ECOPS (Energy Conserving Optimal path Schedule) algorithm. Existing LEACH algorithm to elect the head node when the node's energy probability distribution function based on the management of the head node is optional cycle. However, in this case, the distance of the relay node status information including context-awareness parameters does not reflect. These factors are not suitable for the relay node or nodes are included in the probability distribution, if the head node selects occurs. In particular, to solve the problems from the LEACH-based hierarchical clustering algorithms, this study defines location with the status context information and the residual energy factor in choosing topology of the structure adjacent nodes. ECOPS algorithm that contextual information is contributed for head node selection in topology protocols. The proposed ECOPS algorithm has the head node replacement situations from the candidate head node in the optimal path and efficient energy conservation that is the path of the member nodes. The new head node election show as the entire node lifetime and network management technique improving the network lifetime and efficient management the simulation results.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.1
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• pp.95-101
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• 2009

Wireless Sensor Network (WSN) has limited power and bandwidth. In order to high data rate and high speed communication systems are required. Cooperative communication system can help to decrease power consumption through spatial diversity. In cooperative transmission, one partner node assists one sensor node to transmit their data to destination. Instead of using M partners for M sensor nodes, we propose 1 partner for M sensor nodes. And we proposed relay selection scheme base on ARQ. Proposed protocol offers higher diversity order as conventional one with much less bandwidth and power. The destination will consider the one packets received from the best relay to reduce the complexity of the system. We verified BER performance for the proposed protocol through Monte-Carlo simulation over Rayleigh fading plus AWGN.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.8C
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• pp.645-654
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• 2012

In this paper, we consider a two-way relay (TWR) system, where two user nodes exchange their information within two transmission phases, by the help of a relay node adopting physical layer network coding. In the system, two users transmit their binary phase shift keying symbols simultaneously in the first phase, and the relay node decodes the XORed version of two user data and broadcasts it back to two users in the second phase. The performance of the system is analyzed in terms of the average end-to-end symbol error probability in Nakagami-m fading channels, for which a tight upper bound is derived in a closed form to provide an accurate and handy estimate on the performance. The results show that our upper bounds are almost indistinguishable from simulation results for various channel and system configurations. In addition, the optimal relay location and power allocation for various conditions can be obtained quickly with our analysis.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.7A
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• pp.646-653
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• 2010

This paper provides a unified framework for the joint optimal subchannel and power allocation in multi-hop relay network, where each node in the network has multiple parallel subchannels such as in OFDM or MIMO system. When there are multiple parallel subchannels between nodes, the relay node decides how to match the subchannel at the first hop with the one at the second hop aside from determining the power allocation. Joint optimal design of subchannel matching and power allocation is, in general, known to be very difficult to solve due to the combinatorial nature involved in subchannel matching. Despite this difficulty, we use a simple rearrangement inequality and show that seemingly difficult problems can be efficiently solved. This includes several existing solution methods as special cases. We also provide various design examples to show the effectiveness of the proposed framework.