• Journal of Communications and Networks
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• v.13 no.3
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• pp.266-276
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• 2011

In wireless networks, it is well-known that intermediate nodes can be used as cooperative relays to reduce the transmission energy required to reliably deliver a message to an intended destination. When the network is under a central authority, energy allocations and cooperative pairings can be assigned to optimize the overall energy efficiency of the network. In networks with autonomous selfish nodes, however, nodes may not be willing to expend energy to relay messages for others. This problem has been previously addressed through the development of extrinsic incentive mechanisms, e.g., virtual currency, or the insertion of altruistic nodes in the network to enforce cooperative behavior. This paper considers the problem of how selfish nodes can decide on an efficient energy allocation and endogenously form cooperative partnerships in wireless networks without extrinsic incentive mechanisms or altruistic nodes. Using tools from both cooperative and non-cooperative game theory, the three main contributions of this paper are (i) the development of Pareto-efficient cooperative energy allocations that can be agreed upon by selfish nodes, based on axiomatic bargaining techniques, (ii) the development of necessary and sufficient conditions under which "natural" cooperation is possible in systems with fading and non-fading channels without extrinsic incentive mechanisms or altruistic nodes, and (iii) the development of techniques to endogenously form cooperative partnerships without central control. Numerical results with orthogonal amplify-and-forward cooperation are also provided to quantify the energy efficiency of a wireless network with sources selfishly allocating transmission/relaying energy and endogenously forming cooperative partnerships with respect to a network with centrally optimized energy allocations and pairing assignments.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.8
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• pp.1770-1785
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• 2013

In this paper, a multi-hop transmission protocol based on parallel communication of secondary users (SUs) is proposed. The primary multi-hop network coexists with a set of SUs by cooperative spectrum sharing. The main optimization target of our protocol is the overall performance of the secondary system with the guarantee of the primary outage performance. The energy consumption of the primary system is reduced by the cooperation of SUs. The aim of the primary source is to communicate with the primary destination via a number of primary relays. SUs may serve as extra decode-and-forward relays for the primary network. When an SU acts as a relay for a primary user (PU), some other SUs that satisfy the condition for parallel communication are selected to simultaneously access the primary spectrum for secondary transmissions. For the proposed protocol, two opportunistic routing strategies are proposed, and a search algorithm to select the SUs for parallel communication is described. The throughput of the SUs and the PU is illustrated. Numerical results demonstrate that the average throughput of the SUs is greatly improved, and the end-to-end throughput of the PU is slightly increased in the proposed protocol when there are more than seven SUs.

• Journal of Digital Convergence
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• v.13 no.2
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• pp.127-133
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• 2015

In order for location information to deliver the collected information, it needs Sensor Nodes in an environment of Sensor Network. Each sensor sends data to a base station through the process of routing in a wireless sensor network environment. Therefore, Offering accurate location information is very important in a wireless sensor network environment. Most of existed routing methods save all the informations of nodes at the area of 1-hop. In order to save these informations, unnecessary wasted energy and traffics are generated. Routing Protocol proposed in this paper doesn't save node's location information, and doesn't exchange any periodic location information to reduce wasted energy. It includes transmission range of source nodes and nodes with the location information, however it doesn't include any nodes' routing near 1-hope distance.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.2
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• pp.46-53
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• 2007

Extension of the mobile communication and the rapidly developing services connected with wireless multimedia(W-CDMA, DMB, Wibro, and so on) need great many base station transceiver systems, antennas, and many signal transmission line to embody these services. The min communication appliances system is exposed always in danger of transient overvoltage by direct stroke or induced lightning surge flowing in through antenna because the antenna of base station transceiver system or relay equipment is combined with expensive communication network equipments through signal transmission line. Now, gas discharge tube(GDT) or narrow band stub arrestor which is used by the surge protector for communication use is exposing limitations as for lightning surge protective means of the communication facility with high speed and wide frequency band. Therefore, for improving performance of surge arrestor, we applied ceramic filter which can reduce lightning surge invading from antenna effectively, and proved that ceramic filter is effective in residual voltage reduction through the experimental research.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.11
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• pp.2113-2119
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• 2006

In this paper, we design the r-Sensor protocol for reliable data transmission in the Intelligent Home Service based on the wireless sensor network environment. The r-Sensor protocol improve the reliability of data transmission and node fairness using simple routing algorithm, congestion control, and loss recovery method that minimize the load of relay node. Reposed routing algorithm find out upstream and downstream nodes using the Network Management packet. Meanwhile, loss recovery algorithm uses the Aggregated-Nack. To apply supposed algorithm, the IHS-AMR(Intelligent Home Service - Automatic Meter Reader) and sensor node are designed and implemented in hardware. The IHS-AMR provides remote metering service and also offers home safety service by internetworking with sensor network, mobile phone network and internet.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.10
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• pp.997-1005
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• 2008

Linear motor stage is a useful device in precision engineering field because of its simple power transmission mechanism and accurate positioning. Even though linear motor stage shows fine positioning accuracy along travel axis, geometric dependent errors which relay on machining and assembling accuracy should be addressed to increase total positioning performances. In this paper, we suggests a cost effective yaw error compensation servo-system which is mounted on platform of the stage and nullify travel position dependent yaw error. This paper also provides a method of designing a sliding mode control which is robust to existing friction disturbance and model uncertainties. The reachability condition of slinding mode control for the yaw error compensating servo-system has been established. From some experimental results by using an experimental set-up, the sliding mode control showed its effective in disturbance rejection and its performance was superior to conventional linear controls.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.2
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• pp.714-727
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• 2015

The hierarchical structure in networks is widely applied in many practical scenarios especially in some emergency cases. In this paper, we focus on a tree network with and without packet loss where one source sends data to n destinations, through m relay nodes employing random linear network coding (RLNC) over a Galois field in parallel transmission systems. We derive closed-form probability expressions of successful decoding at a destination node and at all destination nodes in this multicast scenario. For the convenience of computing, we also propose an upper bound for the failure probability. We then investigate the impact of the major parameters, i.e., the size of finite fields, the number of internal nodes, the number of sink nodes and the channel failure probability, on the decoding performance with simulation results. In addition, numerical results show that, under a fixed exact decoding probability, the required field size can be minimized. When failure decoding probabilities are given, the operation is simple and its complexity is low in a small finite field.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.7
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• pp.566-572
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• 2014

We propose a two-way multi-hop relaying scheme improving the throughput as well as enlarging the coverage for ship-to-ship communications in multi-ship marine networks. The proposed scheme reduces the time slots required for the data exchange by designing data transmission and network coding procedures in a sophisticated way based on two-phase digital network coding. Simulation results show that the proposed two-way multi-hop relaying scheme improves the throughput of the conventional one about 5/3 times.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.8
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• pp.1360-1365
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• 2010

In this paper, we propose a distance relaying algorithm using a Discrete Fourier Transform (DFT)-based modified phasor estimation method to eliminate the adverse influence of exponentially decaying DC offsets. Most distance relays are based on estimating phasors of the voltage and current signals. A DFT is generally used to calculate the phasor of the fundamental frequency component in digital protective relays. However, the output of the DFT contains an error due to exponentially decaying DC offsets. For this reason, distance relays have a tendency to over-reach or under-reach in the presence of DC offset components in a fault current. Therefore, the decaying DC components should be taken into consideration when calculating the phasor of the fundamental frequency component of a relaying signal. The error due to DC offsets in a DFT is calculated and eliminated using the outputs of an even-sample-set DFT and an odd-sample-set DFT, so that the phasor of the fundamental component can be accurately estimated. The performance of the proposed algorithm is evaluated for a-phase to ground faults on a 345 kV, 50 km, simple overhead transmission line. The Electromagnetic Transient Program (EMTP) is used to generate fault signals. The evaluation results indicate that adopting the proposed algorithm in distance relays can effectively suppress the adverse influence of DC offsets.

• KIISE Transactions on Computing Practices
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• v.24 no.3
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• pp.145-150
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• 2018

Forwarding in opportunistic networks shows low performance because there may be no connecting paths between the source and the destination nodes due to the intermittent connectivity. Currently, social network analysis has been researched. Specifically, similarity is one of methods of social networks analysis. In this paper, we propose forwarding schemes based on representative similarities, and evaluate how much the forwarding performance increases. As a result, since the forwarding schemes are based on similarities, these schemes only forward messages to nodes with higher similarity as relay nodes, toward the destination node. These schemes have low network traffic and hop count while having stable transmission delay.