• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.3A
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• pp.250-258
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• 2011

In this paper we propose a load balancing scheme for heterogeneous multiple AS's (Application Server) in IMS (IP Multimedia Subsystem) based network. In IMS network, to perform load balancing among multiple ASs with different registration pattern, different weight value should be set for each AS. In previous systems, there exists an inconvenience that the weight value should be set manually by the operator after monitoring the result. In this paper we propose a method to calculate optimal weight in automatic manner and to perform load balancing simultaneously. We also propose a simplified algorithm to reduce calculation in specific situation and present a way to apply our proposed scheme in adaptive manner according to the situation. Through simulation result, we verify that our proposing scheme outperforms previous schemes in load balancing and adjusts well to the change of the system in automatic manner with fast convergence.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.5B
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• pp.498-508
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• 2009

In wireless mobile environments, large bandwidth and high QoS (Quality of Service) are recently required to support the increased demands for multimedia services. LTE (Long Term Evolution) is one of the promising solutions for the next generation broadband wireless access systems. To efficiently use downlink resource and effectively support QoS, packet scheduling algorithm is one of the important features in LTE system. In this paper, we proposed DAPS (Delay-Aware Packet Scheduling) algorithm to consider QoS requirements of delays for various traffic classes as well as channel condition and fairness. To reflect delay experiences at scheduling instance, DAPS observes how queue waiting time of packet is closed to maximum allowable delay. The simulation results show that the DAPS algorithm yields better performance for delay experience by increasing the number of transmitted packets with satisfying the required delay time compared with existing scheduling algorithms.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.6A
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• pp.648-656
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• 2007

This paper is about band pass filter, using Ceramics in the condition of center frequency 370Hz at milli-wave. The band pass filter is applied to Broadband Convergence Network, representing WLL(Wireless Local Loop) and LMDS(Local Multi-point Distribution Service). Sticking ceramic between strip line on a dielectric material substrate with which conductor's covers upper and basal surface, One will house the exterior by using structural resonance. In this Non Radiative Microstrip Line Filter structure, based upon simulations, generalized the two formulas finding resonant frequency of 1step ceramic resonator and bandwidth of 4step ceramic resonator. Also, As a result of experiment, using Network Analyzer, about created a experiment of structure based on the simulation result of 4-step ceramic resonator, It showed good characteristic of targeted bandwidth, comparing simulated result of 36.58GHz$\sim$37.650GHz with experimented result of 36.6GHz$\sim$37.65GHz.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.12C
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• pp.997-1005
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• 2008

In this paper, we proposed advanced T-DMB system which is based on Eureka-147 using UEP coding methods and hiererchical modulation for providing additional services while maintaining BER performance. We simulated the proposed advanced T-DMB system using unequal l6QAM modulation scheme combined with various bit split methods and coding methods such as double binary turbo code of DVB-RCS standard and LDPC code of DVB-S2 standard. In the simulation results, double binary turbo code and LDPC code of proposed advanced T-DMB system have coding gain of 2dB and 3.5dB compared to conventional T-DMB system respectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.11
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• pp.1159-1166
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• 2014

In this paper, a resource management scheme for enhancing the network connectivity and reliability in wireless USB system is proposed. Wireless USB protocol is suitable for the application that supports the real-time multimedia service in Ship Area Network since it supports high speed data transfer. However, the device's mobility is caused the dramatic change of link state and network topology, and is occurred the degradation of network performance. Therefore, a resource management scheme for wireless USB system is proposed in this paper. The proposed technique can intelligently treat the change of link state, and solve the degradation of network performance. The simulation results show that proposed protocol can enhance the throughput and delay performance by selecting relay device with better link state.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.10
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• pp.858-864
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• 2013

In the 4G wireless environment, one of the important issues is to discover and select an access network suited for users. In this thesis, we propose a new network selection mechanism using group decision making and evaluate the effect of network selection schemes for vertical handover in heterogeneous wireless networks. We consider the group of users with similar QoS requirements search for the available access network simultaneously and a service area consist of multiple access networks with various characteristics. We divide the access networks with similar characteristics split into a group. Between each group, the one group is selected and within that group, the best access networks will be assigned according to priority order by network selection algorithm. We evaluate and compare the performance of three representative MADM schemes: GRA, SAW and TOPSIS. The MATLAB simulation results indicate the proposed algorithm can make a more effective choice according to the networks' characteristics and user's preference.

• Journal of Communications and Networks
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• v.18 no.4
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• pp.559-566
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• 2016

Software defined network (SDN) can effectively improve the performance of traffic engineering and will be widely used in backbone networks. Therefore, new energy-saving schemes must take SDN into consideration; this action is extremely important owing to the rapidly increasing energy consumption in telecom and Internet service provider (ISP) networks. Meanwhile, the introduction of SDN in current networks must be incremental in most cases, for technical and economic reasons. During this period, operators must manage hybrid networks in which SDN and traditional protocols coexist. In this study, we investigate the energy-efficient traffic engineering problem in hybrid SDN/Internet protocol (IP) networks. First, we formulate the mathematical optimization model considering the SDN/IP hybrid routing mode. The problem is NP-hard; therefore, we propose a fast heuristic algorithm named hybrid energy-aware traffic engineering (HEATE) as a solution. In our proposed HEATE algorithm, the IP routers perform shortest-path routing by using distributed open shortest path first (OSPF) link weight optimization. The SDNs perform multipath routing with traffic-flow splitting managed by the global SDN controller. The HEATE algorithm determines the optimal setting for the OSPF link weight and the splitting ratio of SDNs. Thus, the traffic flow is aggregated onto partial links, and the underutilized links can be turned off to save energy. Based on computer simulation results, we demonstrate that our algorithm achieves a significant improvement in energy efficiency in hybrid SDN/IP networks.

• Journal of Electrical Engineering and Technology
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• v.5 no.2
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• pp.228-238
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• 2010

There is an increasing interest in research to help overcome the energy crisis that has been focused on energy storage applications in various parts of power systems. Energy storage systems are good at enhancing the reliability or improving the efficiency of a power system by creating a time gap between the generation and the consumption of power. As a contribution to the various applications of storage devices, this paper describes a novel algorithm that determines the power and storage capacity of selected energy storage devices in order to improve upon railroad system efficiency. The algorithm is also demonstrated by means of simulation studies for the Korean railroad lines now in service. A part of this novel algorithm includes the DC railroad powerflow algorithm that considers the mobility of railroad vehicles, which is necessary because the electric railroad system has a distinct distribution system where the location and power of vehicles are not fixed values. In order to derive a more accurate powerflow result, this algorithm has been designed to consider the rail voltage as well as the feeder voltage for calculating the vehicle voltage. By applying the resultant control scheme, the charging or discharging within a specific voltage boundary, energy savings and a substation voltage stabilization using storage devices are achieved at the same time.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.8
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• pp.1854-1863
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• 2003

In the recent digital communication systems, the performance of Turbo Code using the mr correction coding depends on the interleaver influencing the free distance determination and the recursive decoding algorithms that is executed in the huh decoder. However, performance depends on the interleaver depth that needs many delays over the reception process. Moreover, turbo code has been blown as the robust coding methods with the confidence over the fading channel. International Telecommunication Union(ITU) has recently adopted it as the standardization of the channel coding over the third generation mobile communications(IMT­2000). Therefore, in this paper, we preposed the interleaver that has the better performance than existing block interleaver, and modified turbo decoder that has the parallel concatenated structure using MAP algorithm. In the real­time voice and video service over third generation mobile communications, the performance of the proposed two methods was analyzed and compared with the existing methods by computer simulation in terms of reduced decoding delay using the variable decoding method over AWGN and fading channels for CDMA environments.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.9
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• pp.2169-2175
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• 2014

In this paper we have proposed a new distributed architecture of session-based instant message system, in which multiple servers can distribute loads effectively to improve system extendability. The server of session-based instant message system should manage SIP sessions to transfer instant message with multimedia data to each users, and it should process large amount of presence informations from each users. Therefore load of the server should be distributed as the number of users increases. In our system, when server load increases according to large user numbers, the load are distributed by selecting a server with the lowest load value, or new server is created to allocate the message processing. Therefore the overall load of instant message system can be dynamically distributed. A new presence information data format with added elements for controlling server load has been designed for this purpose, and SIP messages exchanging procedure between servers and users has been also suggested. The performance of our proposed system has been analysed by simulation, and showed improvement of performance.