• Proceedings of the IEEK Conference
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• 2003.07b
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• pp.863-866
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• 2003

Recently, there has been growing interests in the magneto-resistive random access memory (MRAM) because of its great potential as a future nonvolatile memory. In this paper, a CMOS macro-model for MRAM cell based on a twin cell structure is proposed. The READ and WRITE operations of the MTJ cell can be emulated by adopting data latch and switch blocks. The behavior of the circuit is confirmed by HSPICE simulations in a 0.35-${\mu}{\textrm}{m}$ CMOS process. We expect the macro model can be utilized to develope the core architecture and the peripheral circuitry. It can also be used for the characterization and the direction of the real MTJ cells.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.3
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• pp.277-288
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• 2013

3GPP LTE-Advanced (Third Generation Partnership Project Long Term Evolution-Advanced) as a next generation mobile communication standard introduced small base stations such as femto cells or pico cells, and D2D (Device-to-Device) communications between mobiles in the proximity in order to satisfy the needs of rapidly growing wireless data traffic. A diverse range of topics has been studied to solve various interference situations which may occur within a single cell. In particular, an introduction of a small base station along with D2D communication raises important issues of how to increase the channel capacity and frequency efficiency in HetNets (Heterogeneous Networks). To this end, we propose in this paper methods to manage the interference between the macro cell and other small cells in the HetNet to improve the frequency efficiency. The proposed CCN (Cluster Coordinator Node)-assisted ICI (Inter-Cell Interference) avoidance methods exploit the CCN to control the interference in HetNet comprising of an MeNB (Macro enhanced Node-B) and a large number of small cells. A CCN which is located at the center of a number of small cells serves to avoid the interference between macro cell and small cells. We propose methods of resource allocation to avoid ICI for user equipments within the CCN coverage, and evaluate their performance through system-level computer simulations.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.3
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• pp.556-560
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• 2013

Recently, solutions to accommodate explosively growing mobile data traffic have attracted intensive attentions since the emergence of high-performance smartphones. Spectrum which can be exploited for mobile communications is very limited. Thus, femto cell is considered as an alternative because it can efficiently offload mobile data traffic from macro cells without using additional spectrum. In this paper, we mathematically analyzed the coverage of femto cell when it is deployed in an area where there exists signals from existing macro base stations. Our numerical results indicate that the coverage of femto cell increases as the total power of femto cell increases or the ratio of power allocated to pilot channel increases. However, it is also shown that the coverage of femto cell is very limited despite its high power when interference signals from macro base stations are strong.

• Journal of Communications and Networks
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• v.14 no.3
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• pp.252-256
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• 2012

We consider resource allocation in femto-cell networks to maximize the throughput while minimizing interference to macro-users nearby. This can be achieved by allocating spectrum resource in a cognitive radio way. The proposed resource allocation is performed in two steps; spectrum sensing and resource scheduling. The femto base station detects idle frequency assignments (FAs) free from the occupation by macro-users and then allocates sub-channels in an idle FA to femto-users, effectively managing the interference problem. Finally, the effectiveness of the proposed scheme is verified by computer simulations.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.4
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• pp.2058-2074
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• 2017

Dense Heterogeneous Cellular Networks(HCNs) offer a promising approach to meet the target of 1000x increase in aggregate data rates in 5G wireless communication systems. However how to best utilize the available radio resources at densely deployed small cells remains an open problem as those small cells are typically unplanned. In this paper we focus on balancing loads across macro cells and small cells by offloading users to small cells, as well as dynamically switching off underutilized small cells. We propose a joint user association and base station(BS) sleep mangement(UA-BSM) scheme that proactively offloads users to a fraction of the densely deployed small cells. We propose a heuristic algorithm that iteratively solves the user association problem and puts BSs with low loads into sleep. An interference relation matrix(IRM) is constructed to help us identify the candidate BSs that can be put into sleep. User associations are then aggregated to selected small cells that remain active. Simulation results show that our proposed approach achieves load balancing across macro and small cells and reduces the number of active BSs. Numerical results show user signal to interference ratio(SINR) can be improved by small cell sleep control.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.584-589
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• 2008

It is known that slab thermal storage which uses concrete slab as thermal material is effective in the load leveling and using the nighttime electric power. The temperature distribution is not constant in plenum in thermal storage time by beams, ducts such as several factor. It is considered that this fact will effect on efficiency of thermal storage and indoor thermal environment. The purpose of this paper is to examine the thermal environment inside plenum. A macro model was made for the analysis of indoor thermal environment as the first step. The flow rate distribution and temperature distribution of object room model was examined by use of basic equations such as airflow by the pressure difference between unit cells, heat flow by air and heat transfer.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.12A
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• pp.962-970
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• 2009

This paper proposes a self-organizing scheme which collects the information of neighboring cells, and then assigns a Physical Cell Identifier (PCI) for a newly deployed cell in LTE systems. The number of PCIs are limited, so the reuse of PCIs in different cells is unavoidable. In a dense urban environment where many small cells such as Pico/Femto cells are deployed under macro cells, it is expected that the number of PCIs becomes more limited. Therefore, the limited number of PCIs needs to be allocated very efficiently. We propose a PCI allocation scheme for a newly deployed cell that can autonomously select a PCI to increase PCI reuse efficiency by utilizing the levels of received signal strength from neighboring cells. To evaluate the performance of the proposed scheme, simulations have been developed and performed with two scenarios on the coverage types of newly deployed cells. When the proposed scheme is applied, the simulation results show that the number of PCIs required for the operation of the system can be saved so that PCIs can be efficiently reused.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.11A
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• pp.844-851
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• 2009

Handover is needed in multi-hop relay systems to support mobility. The main purpose of handover is to provide the continuous connection when a MS migrates from the air-interface of one BS to another air-interface provided by another BS. Especially the handover between different systems is essential to next generation network. Vertical Handover technology in Mobile WiMAX MMR system is very useful for operators to introduce to Mobile WiMAX system in an overlaid cell environment. This technology will be applied to technology which hands MRS(Mobile Relay Station) over to different systems for system performance enhancement in Ubiquitous environment overlaid between Micro ce11(Frequency 1,FA1) and Macro cell(Frequency 2,FA2). In this paper, FA1 and FA2 are used in order to perform Vertical Handover of MRS(Mobile Relay Station) according to suggested conditions. interferences from neighboring BS or other sectors of 6 macro cells surrounding center Macro cell are analyzed and throughputs are measured according to suggested conditions.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.628-631
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• 2014

Recently, the proliferation of new applications, e.g., mobile TV, Internet gaming, large file transfer, and the various of user terminals, e.g., smart phones and notebooks, has dramatically increased user traffic and network load. In order to meet this traffic growth, vendors and cellular operators are working on the development of new technologies and cellular standards. Within them, small cell deployment has been heralded as one of most promising way to increase both coverage and capacity of future cellular network. Small cell technology enables to improve capacity of cellular radio network by tight cooperation between small cell and macro cell in multi-tier network where small cells are densely deployed within macro cell coverage. In this paper, we describe the deployment scenarios for cooperation between macro cell and small cells and state-of-the-art technologies related to dense small cell deployment. Then, we also provide design principles and standardization trends for small cell enhancement in 3GPP.

• The Journal of Korean Institute of Next Generation Computing
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• v.13 no.5
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• pp.104-112
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• 2017

The CRE (Cell Range Expansion) that selects the small cell with more efficient uplink resources has been developed by 3GPP to relieve the problem of the traffic imbalance due to the power differences between macro and small cells in HetNet. In addition, ABS (Almost Blank Subframes) has been proposed to resolve the signal interference problem due to the operation CREs. This paper proposes an effective method to calculate the ABS ratio by considering the proportion of the number of UEs in CRE and macro cell ranges, as well as the number of small cells in a macro cell. The proposed method has been implemented on the LTESim simulator, and compared with previously proposed methods. The experimental results show that the proposed method can improve the throughput and packet loss ratio performances. In particular, it is also shown that CRE bias values affect those performances, and there exist effective CRE bias values to derive the best performances.