• Journal of Korea Multimedia Society
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• v.20 no.12
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• pp.1849-1855
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• 2017

The main purpose of cooperative communications is improvement of communication quality and efficient use of transmission power. In this paper, a cooperative retransmission method is proposed, where neighbor nodes that receive messages correctly between transmit and receive nodes will participate in retransmission of the erroneous packet of the direct link. When the proposed retransmission method is used, the performance of the PER can be greatly improved. In case that the limited information is included in the NACK message, the transmit power of the retransmission packet can be reduced using the proper power control method.

• Proceedings of the IEEK Conference
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• 2007.07a
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• pp.195-196
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• 2007

The purpose of this paper is to analyze the resource allocation problem in a self organizing network from the viewpoint of game theory. The main focus is to suggest the model and analyze a power control algorithm in wireless ad-hoc networks using non cooperative games. Our approach is based on a model for the level of satisfaction and utility a wireless user in a self organizing network derives from using the system. Using this model, we show a distributed power control scheme that maximizes utility of each user in the network. Formulating this as a non-cooperative game we will show the feasibility of such power control as well as existence of the Nash Equilibrium achieved by the non-cooperative game.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.9
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• pp.1221-1225
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• 2012

This paper describes CSC(Current Sourced Converters)-based HVDC operational strategy for voltage stability enhancement in the power system. In case of CSC-based HVDC system, rectifier and inverter consume reactive power up to about 60% of converter rating. Therefore, CSC-based HVDC is basically not useful system for voltage stability even if AC filters and shunt capacitors are attached. But, If the particular power system condition is fulfilled, CSC-based HVDC also can be the rapid reactive power source for voltage stability enhancement using a cooperative control with converter and AC filters/Shunt Capacitors. In this paper, the cooperative control algorithm is presented and simulated to ${\pm}80kV$ 60MW HVDC system in Jeju island.

• Journal of Institute of Control, Robotics and Systems
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• v.14 no.10
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• pp.1029-1037
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• 2008

When a humanoid robot pushes an object with its force, it is essential to adequately control its posture so as to maximize the surplus torque far all joints. For such purpose, this study proposes a method to find an optimal posture of a humanoid robot using a genetic algorithm in such a way that the surplus torque for all joints is maximized. In this study, pushing motion of an 18-DOF humanoid robot is considered. When the robot takes a cooperative motion to push an object, the palms and soles are assumed to be fixed at the object and ground respectively, and are subjected to sense the reaction force from the object and the ground. Then, the torques for all joints are calculated and reflected to fitness function of the genetic algorithm. To verify the effectiveness of the proposed method, a number of simulations with different fitness functions are carried out. The simulation result shows that the proposed method can be adopted to find optimized posture in cooperative motion of a humanoid robot.

• Journal of Fisheries and Marine Sciences Education
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• v.20 no.2
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• pp.297-308
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• 2008

This study developed career education program applying cooperative learning structures (Kagan, 1993, 1995, 1997), and tested its effect on elementary school children's career development. Sixth grade students of 2 classes were divided into experimental and control group, and 14 sessions of the program were applied to the experimental group for 8 weeks. Career development test(Lee, 2005) were performed before and after the program. Students in both groups were retested 3 months after the post-test to test continuing effects of the program. Score tendencies and their differences between experimental group and control group of children in 3 career development areas - self-awareness, educational and occupational exploration, and career planing - were tested and the results are as follows: development of 3 areas of self-awareness, educational and occupational exploration, and career planing were consistently increasing along the experimental sequence in experimental group, while the development of 3 areas showed no changes or declining tendencies in control group. Self-awareness and educational and occupational exploration did not show the statistically significant differences between the groups. Meanwhile, the career plaining showed statistically significant difference between the groups in post-test, meaning that the career education program with cooperative structure has positive effects on the career planing in 6th grade students.

• The Journal of Korean Association of Computer Education
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• v.21 no.1
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• pp.23-30
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• 2018

In this paper, the elementary students from the Information class of the Science Education Institute for the Gifted were divided into the experimental and control groups. The two groups took Scratch programming classes and the changes in their sociality were analyzed. The experimental group used the Scratch remix function, an educational programming language, to perform the LT cooperative learning. The control group took general instructor-led classes. The experimental group carried out a team project in which learners should cooperate with each other to produce certain results using the remix function. Twelve 3-hour lessons were taken by the experimental and control groups consisting of 30 and 30 students respectively to verify changes depending on remix-based cooperative learning. According to t-test using the survey results, the experimental group that performed cooperative learning using the Scratch remix function showed more improved sociality than the control group did. There was a statistically significant difference as well.

• Journal of Institute of Control, Robotics and Systems
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• v.16 no.9
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• pp.891-897
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• 2010

This paper proposes a cooperative control algorithm for a dual-arms robot which is carrying an object to the desired location. When the dual-arms robot is carrying an object from the start to the goal point, the optimal path in terms of safety, energy, and time needs to be selected among the numerous possible paths. In order to quantify the carrying efficiency of dual-arms, DAMM (Dual Arm Manipulability Measure) has been defined and applied for the decision of the optimal path. The DAMM is defined as the intersection of the manipulability ellipsoids of the dual-arms, while the manipulability measure indicates a relationship between the joint velocity and the Cartesian velocity for each arm. The cost function for achieving the optimal path is defined as the summation of the distance to the goal and inverse of this DAMM, which aims to generate the efficient motion to the goal. It is confirmed that the optimal path planning keeps higher manipulability through the short distance path by using computer simulation. To show the effectiveness of this cooperative control algorithm experimentally, a 5-DOF dual-arm robot with distributed controllers for synchronization control has been developed and used for the experiments.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.10
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• pp.3810-3830
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• 2015

In this paper, we investigate the differential game theoretic approach for distributed dynamic cooperative power control in cognitive radio ad hoc networks (CRANETs). First, a payoff function is defined by taking into consideration the tradeoff between the stock of accumulated power interference to the primary networks and the dynamic regulation of the transmit power of secondary users (SUs). Specifically, the payoff function not only reflects the tradeoff between the requirement for quickly finding the stable available spectrum opportunities and the need for better channel conditions, but also reveals the impact of the differentiated types of data traffic on the demand of transmission quality. Then the dynamic power control problem is modeled as a differential game model. Moreover, we convert the differential game model into a dynamic programming problem to obtain a set of optimal strategies of SUs under the condition of the grand coalition. A distributed dynamic cooperative power control algorithm is developed to dynamically adjust the transmit power of SUs under grand coalition. Finally, numerical results are presented to demonstrate the effectiveness of the proposed algorithm for efficient power control in CRANETs.

• Journal of Korean Home Economics Education Association
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• v.13 no.1
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• pp.55-72
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• 2001

This study is to develop teaching aids in the area of Clothing and Textiles based on cooperative learning as an alternative to increase the quality of Home Economics class. It is very difficult to control students because of noise coming from activities. when teachers teach students with cooperative learning strategy a classroom with restricted space. Sometimes the activities will disturb other classes in the school. which will harm the real purpose of cooperative learning. However. we have more positive results from cooperative learning method. because students have more chance to improve their personal skills. easily solve a problem together and openly express their opinions. Moreover. we found that they understand the subjects and increase their attention much better because they are tested right after learning. We anticipate that the developed teaching aids will be a great help to improve middle school Home Economics class.

• 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.