• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.05a
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• pp.63-66
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• 2015

As smart-phones become popular, mobile data traffic has been dramatically increasing and intensive researches on the next-generation mobile communication network is in progress to meet the increasing demand for mobile data traffic. In particular, heterogeneous network (HetNet) is attracting much interest because it can significantly enhance the network capacity by increasing the spatial resue with macro and small cells. In the HetNet, we have several problems such as load imbalance and interference because of the difference in transmit power between macro and small cells and cell range expansion (CRE) can mitigate the problems. In this paper, we propose a new cell selection scheme with adaptive cell range expansion bias (CREB) for ultra dense HetNet and we analyze the performance of the proposed scheme in terms of average cell transmission rate through system-level simulations and compare it with those of other schemes.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.20 no.2
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• pp.103-108
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• 2020

This paper related with the performance evaluation of mDSE-MMA adaptive equalization algorithm which is possible to reduce the distortion that occurs in nonlinear communication channel like as additive noise, intersymbol interference and fading when transmitting the QAM signal. The DSE-MMA algorithm is possible to reduce the computational load compared to the presently MMA algorithm, it has the degraded equalization performance by this. In order to improve the performance degradation of DSE-MMA, the mDSE-MMA controls the step size according to the existence of arbitrary radius circle of equalizer output is centered at transmitted symbol point. The performance of proposed mDSE-MMA algorithm were compared to present DSE-MMA using the same channel and noise environment by computer simulation. For this, the recoverd signal constellation which is the output of equalizer, residual isi and MD, MSE learning curve which is represents the convergence performance and SER were applied as performance index. As a result of simulation, the mDSE-MMA has more superior to the DSE-MMA in every performance index.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.4B
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• pp.584-591
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• 2010

In this paper, we propose an adaptive Relay Station (RS) coverage extension scheme for the Mobile Multi-hop Relay (MMR) systems. The MMR system with a non-transparent mode RS can be used to extend BS coverage using the remaining capacity of the Base Station(BS). Thus, the call blocking may occur in RSs when calls arrive very often in Multi-hop Relay Base Station (MR-BS). In the proposed scheme, RSs can be connected to the neighbor MMR system as the 2ndtier RSs if the neighbor MMR system services low traffic load when calls are frequently arrived in MR-BS or RSs. By doing so, the MMR system can accept a new call without call blocking. Through numerical results, we demonstrate that the proposed scheme outperforms the conventional MMR system in terms of the throughput and call blocking probability of MMR systems.

• Journal of Broadcast Engineering
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• v.13 no.5
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• pp.586-595
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• 2008

In this paper, we propose an adaptive multi-view video service framework suitable for mobile environments. The proposed framework generates intermediate views in near-realtime and overcomes the limitations of mobile services by adapting the multi-view video according to the processing capability of a mobile device as well as the user characteristics of a client. By implementing the most of adaptation processes at the server side, the load on a client can be reduced. H.264/AVC is adopted as a compression scheme. The framework could provide an interactive service with efficient video service to a mobile client. For this, we present a multi-view video DIA (Digital Item Adaptation) that adapts the multi-view video according to the MPEG-21 DIA multimedia framework. Experimental results show that our proposed system can support a frame rate of 13 fps for 320{\times}240 video and reduce the time of generating an intermediate view by 20 % compared with a conventional 3D projection method.

• Journal of KIISE:Computer Systems and Theory
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• v.29 no.6
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• pp.346-353
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• 2002

The explosive increase of World Wide Web usage has incurred significant amount of network traffic and server load. To overcome these problems, web proxy caching replicates frequently requested documents in the web proxy closer to the users. Cache utilization depends on the replacement policy which tries to store frequently requested documents in near future. Temporal locality and Zipf frequency distribution, which are commonly observed in web proxy workloads, are considered as the important properties to predict the popularity of documents. In this paper, we propose a novel cache replacement policy, called Adaptive LFU (ALFU), which incorporates 1) Zipf frequency distribution by utilizing LFU and 2) temporal locality adaptively by measuring the amount of the popularity reduction of documents as time passed efficiently. We evaluate the performance of ALFU by comparing it to other policies via trace-driven simulation. Experimental results show that ALFU outperforms other policies.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.59 no.3
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• pp.279-287
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• 2010

Interior permanent magnet synchronous motor(IPMSM) adjustable speed drives offer significant advantages over induction motor drives in a wide variety of industrial applications such as high power density, high efficiency, improved dynamic performance and reliability. This paper proposes efficiency optimization control of IPMSM drive using adaptive fuzzy learning controller(AFLC). In order to optimize the efficiency the loss minimization algorithm is developed based on motor model and operating condition. The d-axis armature current is utilized to minimize the losses of the IPMSM in a closed loop vector control environment. The design of the current based on adaptive fuzzy control using model reference and the estimation of the speed based on neural network using ANN controller. The controllable electrical loss which consists of the copper loss and the iron loss can be minimized by the optimal control of the armature current. The minimization of loss is possible to realize efficiency optimization control for the proposed IPMSM. The optimal current can be decided according to the operating speed and the load conditions. This paper considers the design and implementation of novel technique of high performance speed control for IPMSM using AFLC. Also, this paper proposes speed control of IPMSM using AFLC1, current control of AFLC2 and AFLC3, and estimation of speed using ANN controller. The proposed control algorithm is applied to IPMSM drive system controlled AFLC, the operating characteristics controlled by efficiency optimization control are examined in detail.

• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.6
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• pp.594-601
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• 2011

In this paper, a new current controller with the compensation of an unbalance and distorted grid voltages has been proposed. Generally, in the three-phase power system, single phase or nonlinear loads can be connected with the 3 phase linear load simultaneously on the same point of common coupling. Therefore, The source voltage unbalance and distortion problem can be occurred. Under these unbalance and distorted grid voltage conditions, the input current of 3 phase PWM rectifiers also have unbalance and distortion. In this paper, a current controller with the simple Model Reference Adaptive System based unbalance and distorted voltages observer is proposed to get a sinusoidal input current. The performance of the proposed algorithm is verified through the simulation and the experiment.

• The KIPS Transactions:PartB
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• v.15B no.6
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• pp.585-594
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• 2008

The issues that we should consider in the process of providing mobile web service using a mobile device are seamless service and QoS-guaranteed service. HMIPv6 has MAP because of improving packet loss and transmission delay due to disconnection. However, a load is concentrated on HMIPv6 because of receiving and delivering packet for MN. Owing to this, real time data fails to be processed quickly, and also adaptive mobile service is required for QoS guaranteed service. However, this method demands the response time cost of contents service owing to the hardware differences of various devices. Therefore, we improve the process performance of real time data by applying a queue in MAP for seamless service in this paper. For decreasing response time cost, we propose mobile web service method which has reusable cache of contents using the elements of contents. The result of a numerical formula and simulation shows that our proposed method is superior under various system conditions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.3
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• pp.369-374
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• 2010

Linear motors are easily affected by load disturbances, force ripples, friction, and parameter variations because there are no mechanical transmissions that can reduce the effects of model uncertainties and external disturbance. In this study, a nonlinear adaptive controller to achieve high-speed/high-accuracy position control of a two-axis linear motor is designed. The operation of this controller is based on a cross-coupling algorithm. Nonlinear effects such as friction and force ripples are estimated and compensated for. An enhanced cross-coupling algorithm is proposed for effectively improving the biaxial contour accuracy while achieving closed-loop stability. The proposed controller is evaluated by performing computer simulations.

• Journal of Electrical Engineering and Technology
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• v.5 no.2
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• pp.179-190
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• 2010

This paper describes a new stochastic heuristic algorithm in engineering problem optimization especially in power system applications. An improved particle swarm optimization (PSO) called adaptive particle swarm optimization (APSO), mixed with simulated annealing (SA), is introduced and referred to as APSO-SA. This algorithm uses a novel PSO algorithm (APSO) to increase the convergence rate and incorporate the ability of SA to avoid being trapped in a local optimum. The APSO-SA algorithm efficiency is verified using some benchmark functions. This paper presents the application of APSO-SA to find the optimal location, type and size of flexible AC transmission system devices. Two types of FACTS devices, the thyristor controlled series capacitor (TCSC) and the static VAR compensator (SVC), are considered. The main objectives of the presented method are increasing the voltage stability index and over load factor, decreasing the cost of investment and total real power losses in the power system. In this regard, two cases are considered: single-type devices (same type of FACTS devices) and multi-type devices (combination of TCSC, SVC). Using the proposed method, the locations, type and sizes of FACTS devices are obtained to reach the optimal objective function. The APSO-SA is used to solve the above non.linear programming optimization problem for better accuracy and fast convergence and its results are compared with results of conventional PSO. The presented method expands the search space, improves performance and accelerates to the speed convergence, in comparison with the conventional PSO algorithm. The optimization results are compared with the standard PSO method. This comparison confirms the efficiency and validity of the proposed method. The proposed approach is examined and tested on IEEE 14 bus systems by MATLAB software. Numerical results demonstrate that the APSO-SA is fast and has a much lower computational cost.