• Proceedings of the Korea Information Processing Society Conference
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• 2021.11a
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• pp.856-859
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• 2021

Image transmission by means of telecommunications is an essential task for information sharing. For considerable distances, wireless channels can be utilized and tuned for proper uses of image data exchange. However, the disturbances that a radio wave encounter during transmission causes partial or total loss of information. Result of such communications is a distorted image at the receiver's end. This paper proposes an auto-encoder architecture as an image enhancement method for narrow-bandwidth radio images. With this method, a distorted image can be improved for better receiver satisfaction. The proposed auto-encoder is trained with many narrow-bandwidth radio image data; hence it enhances a given distorted image. Also, the results were verified with the original image data being the reference images.

• Electronics and Telecommunications Trends
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• v.33 no.3
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• pp.1-10
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• 2018

This article presents spectrum sharing policy trends both overseas and domestically. The Federal Communications Commission recently adopted rules for the commercial use of a 150 MHz bandwidth at 3.55 to 3.7 GHz, which has been utilized for defense and satellite services. This frequency band for spectrum sharing is called the citizens broadband radio service (CBRS) band. In Europe, the related regimes for licensed shared access application at 2.3 to 2.4 GHz has been organized, and interface standardization for sharing frequency information has been completed. In Korea, efforts are being made to establish spectrum-sharing policies to improve the efficiency of the frequency utilization. This article also introduces both the IEEE 802 local area network/metropolitan area network and 3GPP standardization activities with regard to frequency sharing technologies. To effectively solve the spectrum-sharing problem in IEEE 802, standardization activities on the CBRS and the mid-band (3.7-24 GHz) are underway. 3GPP is currently developing the standardization of a licensed assisted access technology, which extends mobile communication services provided in the licensed band to unlicensed bands.

• Journal of Korea Multimedia Society
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• v.14 no.12
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• pp.1549-1558
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• 2011

In this paper, we address the problem of bandwidth sharing among multiple primary users and multiple secondary users in a cognitive radio network. In cognitive radio networks, effective spectrum assignment for primary and secondary users is a challenge due to the available broad range of radio frequency spectrum as well as the requisition of harmonious coexistence of both users. To handle this problem, firstly, Bertrand game model is used to analyze a spectrum pricing in which multiple primary users emulate with each other to acquire maximal profit. After that, we employ Cournot game to model the spectrum sharing of secondary users to obtain optimal profit for each user also. Simulation results show that our scheme obtains optimal solution at Nash equilibrium.

• Journal of Communications and Networks
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• v.4 no.3
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• pp.209-220
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• 2002

In this paper, we propose a hierarchical packet scheduling technique to closely approximate a hierarchical extension of the generalized processor sharing model, Hierarchical Generalized Processor Sharing (H-GPS). Our approach is to undertake the tasks of service guarantee and hierarchical link sharing in an independent manner so that each task best serves its own objective. The H-GPS model is decomposed into two separate service components: the guaranteed service component to consistently provide performance guarantees over the entire system, and the excess service component to fairly distribute spare bandwidth according to the hierarchical scheduling rule. For tight and harmonized integration of the two service components into a single packet scheduling algorithm, we introduce two novel concepts of distributed virtual time and service credit, and develop a packet version of H-GPS called Hierarchical Fair Queueing (HFQ). We demonstrate the layerindependent performance of the HFQ algorithm through simulation results.

• Journal of the Korea Society of Computer and Information
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• v.20 no.10
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• pp.91-97
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• 2015

In this paper, we propose a MCFQ I/O scheduler that is implemented by modifying the existing Linux CFQ I/O scheduler. MCFQ observes whether the user requested I/O bandwidth weight is well distributed. Based on the I/O bandwidth observation, we improved I/O performance of the existing bandwidth distribution ability by dynamically controlling the I/O time-slice of the virtual machine. The use of SSDs as storage has been increasing dramatically in recent computer systems due to their fast performance and low power usage. As the usage of SSD increases and prices fall, virtualized system administrators can take advantage of SSDs. However, studies on guaranteeing SLA(Service Level Agreement) services when multiple virtual machines share the SSD is still incomplete. In this paper was conducted to improve performance of the bandwidth distribution when multiple virtual machine are sharing a single SSD storage in a virtualized environment. In particular, it was observed that the performance of the bandwidth distribution varied widely when garbage collection occurs in the SSD. In order to reduce performance variance, we add a MoTS(Manager of Time Slice) on existing CFQ I/O scheduler.

• Journal of Korea Society of Digital Industry and Information Management
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• v.11 no.1
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• pp.89-96
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• 2015

The various services applied internet have been provided by the rapid development of wireless networks and providing multimedia contents are also increasing. It is caused a number of problems such as increasing of network traffic rapidly. P2P technique is gaining popularity for solving these problems. In particular, P2P technique in a wireless network environment has gained much popularity. Among them, MANET-based P2P techniques has been studied actively. It is not easy to be applied the existing technique as it is due to the dynamic topology and low bandwidth by moving nodes in MANET that is consisted of only mobile nodes. In this paper, we proposed sharing group construction technique for providing a stable connection between mobile nodes and reducing the load of network traffic and overhead of sharing group reconfiguration in order to improve data transmission performance between mobile nodes. The sharing group member nodes applied virtual sharing group generation technique with neighboring nodes of 1-hop distance in order to reduce traffic for file sharing. We performed comparative experiments with DHT technique to evaluate the performance of the proposed technique in this paper and the excellent performance is confirmed through experiments.

• Journal of Power Electronics
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• v.16 no.6
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• pp.2315-2326
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• 2016

This paper discusses the elimination of DC voltage deviation and the enhancement of load current sharing accuracy in multi-terminal high voltage direct current (MT-HVDC) systems. In order to minimize the power line losses in different parallel network topologies and to insure the stable operation of systems, a decentralized control method based on a modified droop control is presented in this paper. Averaging the DC output voltage and averaging the output current of two neighboring converters are employed to reduce the congestion of the communication network in a control system, and the decentralized control method is implemented. By minimizing the power loss of the cable, the optimal load current sharing proportion is derived in order to achieve rational current sharing among different converters. The validity of the proposed method using a low bandwidth communication (LBC) network for different topologies is verified. The influence of the parameters of the power cable on the control system stability is analyzed in detail. Finally, transient response simulations and experiments are performed to demonstrate the feasibility of the proposed control strategy for a MT-HVDC system.

• Proceedings of the IEEK Conference
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• 2000.07a
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• pp.117-120
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• 2000

As the use of real-time multimedia applications increases, a considerable amount of “greedy” UDP traffic would easily dominate network bandwidth and packet loss. As a result, bandwidth available to TCP connections is oppressed and their performance extremely deteriorates. In or-der that both TCP and UDP sessions fairly co-exist in the Internet, it is vital that we consider the fairness among both protocols. In this work, we implement a “TCP-friendly” rate control mechanism suitable to video applications and con-sider its applicability to a real system through observation of the video quality at the receiver and the connection state. It is shown that we can achieve high-quality and stable video transfer fairly sharing the network bandwidth with TCP by applying our rate control at a control interval of 32 times as long as RTT.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1668-1669
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• 2007

In this paper, we propose nonlinear congestion controller for active queue management of differentiated-services networks. Two important issues in differentiated-services architecture are bandwidth guarantee and fair sharing of unsubscribed bandwidth among TCP flows with and without bandwidth reservation. The nonlinear congestion controller was composed fuzzy logic controller and state feedback controller. The nonlinear congestion controller methodology has been applied to a TCP network. We use NS-2 simulation to demonstrate that the proposed control methodology achieves the desired behavior of the network, and possesses important attributes.

• Proceedings of the Korea Information Processing Society Conference
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• 2010.11a
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• pp.1482-1484
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• 2010

A new TCP protocol can succeed for large bandwidth delay product when it meets network bandwidth utilization efficiency and fair sharing. We introduce a novel congestion control algorithm which employs queueing delay information in order to calculate the amount of congestion window increment in increase phase, and reduces congestion window to optimal estimated bound as packet loss occurs. Combination of such methods guarantees that the proposal utilizes fully network bandwidth, recovers quickly from packet loss in wireless link, and preserves fairness for competing flows mixed short RTT and long RTT. Our simulations show that features of the proposed TCP meet the desired requirements.