• 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.

• 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.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.8
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• pp.39-44
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• 2013

Long Term Evolution (LTE) - Advanced has developed Heterogeneous Network (HetNet) that consists of a mix of macrocells and low-power nodes such as picocells to improve the system performance. Also, to encourage data offloading in HetNet, Cell Range Expansion (CRE) have been introduced. In this paper, we propose a cell selection scheme based on Signal to Interference plus Noise Ratio (SINR) for optimal offloading effect. And we manage the interference for user located in cell range expanded region using Almost Blank Subframe (ABS) with flexible ABS ratio to improve the spectrum efficiency in time domain. Simulation results show that proposed scheme can improve spectrum efficiency of macrocell and picocell user. Eventually, proposed scheme can imporve overall user performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.6
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• pp.520-527
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• 2013

In this paper, a joint cell grouping and user association technique proposed for a semi-dynamic grouped network MIMO in a clustered heterogeneous cellular network (HCN). With the conventional macro BSs, small cells are being overlaid to increase a spectral efficiency per area and these small cells are expected to be concentrated to support exponentially increasing data traffic in hot spot areas. The main culprits of performance degradation in the clustered HCN are interference and load imbalance. The proposed scheme jointly handles them to maximize a proportional-fair metric. It is shown that the proposed technique can largely improve user average rate and proportional fairness among users than any other conventional schemes in the clustered HCN.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.6B
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• pp.483-488
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• 2012

With the fast growing data traffic, the performance of the convergent overlay network environment under the cognitive networking environment is crucial for the implementation of the efficient network structure. In order to achieve high capacity and reliable link quality in wireless communication of the overlay convergent networks with the cognitive networking based on the advanced capability of the mobile terminal, a Distributed Wireless Communication System (DWCS) can provide the capability of ambient-aware dual cell system's operation. This paper has considered virtual cell: the Dual Virtual Cell (DVC), and also proposes DVC employment strategy based on DWCS network. One is the Active Virtual Cell which exists for user's actual data traffic and the other is the Candidate Virtual Cell which contains a set of candidate antennas to protect user's link quality from performance degradation or interruption. The considered system constructs DVC by using cognitive ability of finding useful virtual signals. Also, for multi-user high-rate data transmission, the DWCS system exploits Space-Time Trellis Codes. The effects of changing environments on the system performance has been investigated thereafter.

• Journal of Internet Computing and Services
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• v.4 no.6
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• pp.69-73
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• 2003

ATM and Ethernet are desirable transport mechanisms for the realization MAN(Metropolitan Area Networks). A relatively small sized switching system for MAN based on ATM is proposed and its performance is evaluated in this paper. For the performance evaluation, traffics should be firstly modeled because they are highly bursty. By varing the ratio of VBR traffics, detrimental effect of VBR traffics may be observed. Traffic load at each input port is also varied, From the results of simulation, operation conditions of the system to meet required QoS are obtained.

• Information and Communications Magazine
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• v.31 no.10
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• pp.80-86
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• 2014

스마트 폰을 비롯한 모바일 기기들은 멀티미디어 정보를 포함하는 대용량 무선 데이터 서비스를 위해 진화하고 있다. 이에 따라 통신 서비스 제공업체의 네트워크들은 점점 더 복잡해지고 다양한 서비스를 위한 장비들로 구성되고 있다. 스몰셀 기지국(access point, Henb)들은 기존의 매크로셀과 같이 이동통신 사업자에 의해 지정된 최적의 위치에 설치되는 것이 아니고 사용자가 개별적으로 구매하여 설치하기 때문에, 셀의 배치를 위한 지역적인 설계가 없다. 따라서 스몰셀 기지국 스스로가 주변 환경을 탐지하여, 각종 파라미터를 최적으로 설정하는 것을 기본 성능으로 요구한다. 이에 따라, 과거 일정한 커버리지를 갖는 소형의 기지국 장비들을 지칭하던 펨토셀, 피코셀 등의 명칭도 현재에는 적응적인 커버리지 조절의 기능을 고려하여 스몰셀(small cell)로 통칭되고 있다. 스몰셀 기술은, 3GPP에서 스몰셀 기술이 제안되기 시작하면서 급증하고 있으며 국내외 학계와 업계가 표준을 기반으로 하는 R&D와 특허 출원을 현재에도 진행하고 있다. 각 국가들의 스몰셀 기술은 현재까지 발전기에 속하여 앞으로도 지속적인 연구개발과 표준화, 그리고 특허 출원으로 이어지는 국가간의 경쟁이 치열할 것으로 전망된다. 본 고에서는 스몰셀 표준을 통해 세부 기술을 도출하고, 이로부터 관련 특허를 검색하고 분석하여 향후 표준 특허로 확보하는 방법론을 제시한다.

• Information and Communications Magazine
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• v.28 no.2
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• pp.17-24
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• 2011

휴대 가능한 이동 단말의 광범위한 보급과 무선 인터넷 기술을 근간으로 하는 모바일 컴퓨팅의 급속한 확대는 무선 네트워크 용량의 획기적인 증대를 요구하게 됐다. 본 논문에서는 공간 재사용(Spatial Reuse)을 통한 전송 용량 증대를 달성하기 위해 소형화된 셀 기반의 무선 네트워크 구조를 제안한다. 특히, 이 네트워크를 구성하기 위한 핵심기술을 분산화된 계층 교차 최적화, 초소형셀을 위한 이동성 지원, 무선 네트워크 가상화로 구분, 현재 진행중인 연구 내용을 자세하게 기술하고 이와 관련된 주요 이슈들을 함께 다루도록 한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.10
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• pp.664-673
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• 2014

This paper analyzes the power allocation scheme to maximize the sum-rate for heterogeneous networks based on asynchronous time division duplex. We consider heterogeneous networks where a small cell exists in the macro cell coverage and the small cell and the macro cell share the same time-frequency resources. We formulate the optimization problem which maximizes the sum-rate of the heterogeneous network subject to the target signal-to-interference-plus-noise ratio. We analyze the feasible region in order for the optimal solution to exists and the optimal power allocation scheme for maximizing the sum-rate. Simulation results show that the proposed power allocation schemes outperform the maximum power transmission scheme.

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.12
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• pp.20-26
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• 2012

The newly introduced model of a STTC-based Distributed Wireless Communication System (DWCS) can provide the capability of joint control of the signals at multiple cells. This paper has considered the virtual cell systems: the Dual Virtual Cell (DVC), and also proposes DVC employment strategy based on DWCS network. The considered system constructs DVC by using antenna selection method. Also, for multi-user high-rate data transmission, the proposed system introduces multiple antenna technology to get a spatial and temporal diversity gain and exploits space-time trellis codes known as STTC to increase a spectral efficiency.