• 한국통신학회논문지
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• 제38A권12호
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• pp.1135-1144
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• 2013

급증하는 데이터 트래픽을 셀룰러 망에서 처리하기 위한 대안으로 스몰셀이 관심을 받고 있다. 나아가, 스몰셀의 배치밀도는 점차 높아지고 있어 Ultra Dense Network (UDN) 환경이 도래할 것으로 예상된다. 따라서 본 논문에서는 UDN환경에서 소형기지국의 온/오프를 제어하기 위한 방법을 연구한다. 본 논문에서는 소형 Access Point(AP), user equipment (UE), Small Cell Controller (SCC)로 구성된 프레임워크를 제안하고 이를 기반으로 켜져 있는 기지국 수는 최소화 하며, 네트워크 쓰루풋을 유지시키기 위한 소형기지국 온/오프 방법으로 UE와 같은 사용자 디바이스가 SCC로 피드백하는 채널정보를 활용하는 DANCE 알고리즘을 제안한다. DANCE 알고리즘은 피드백이 1-bit인 경우와 N-bit인 경우, 그리고 활성화시키는 소형AP를 선택하는 기준에 따른 AP-first, UE-first, Proximity ON 등으로 세분화할 수 있다. 본 연구에서는 시뮬레이션을 통해 UE의 수와 네트워크의 쓰루풋, 에너지 효율의 관계를 분석한 후, DANCE 알고리즘을 통해 에너지 효율을 높일 수 있음을 보인다.

• ETRI Journal
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• 제40권2호
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• pp.227-236
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• 2018

Ultra-dense small cell networks (UD-SCNs) have been identified as a promising scheme for next-generation wireless networks capable of meeting the ever-increasing demand for higher transmission rates and better quality of service. However, UD-SCNs will inevitably suffer from severe interference among the small cell base stations, which will lower their spectral efficiency. In this paper, we propose a software-defined networking (SDN)-based hierarchical agglomerative clustering (SDN-HAC) framework, which leverages SDN to centrally control all sub-channels in the network, and decides on cluster merging using a similarity criterion based on a suitability function. We evaluate the proposed algorithm through simulation. The obtained results show that the proposed algorithm performs well and improves system payoff by 18.19% and 436.34% when compared with the traditional network architecture algorithms and non-cooperative scenarios, respectively.

• International journal of advanced smart convergence
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• 제9권2호
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• pp.58-67
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• 2020

In this paper, we propose a data-driven-based beam selection scheme for massive multiple-input and multiple-output (MIMO) systems in ultra-dense networks (UDN), which is capable of addressing the problem of high computational cost of conventional coordinated beamforming approaches. We consider highly dense small-cell scenarios with more small cells than mobile stations, in the millimetre-wave band. The analog beam selection for hybrid beamforming is a key issue in realizing millimetre-wave UDN MIMO systems. To reduce the computation complexity for the analog beam selection, in this paper, two deep neural network models are used. The channel samples, channel gains, and radio frequency beamforming vectors between the access points and mobile stations are collected at the central/cloud unit that is connected to all the small-cell access points, and are used to train the networks. The proposed machine-learning-based scheme provides an approach for the effective implementation of massive MIMO system in UDN environment.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권10호
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• pp.4703-4723
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• 2018

In recent years, dense small cell network has been deployed to address the challenge that has resulted from the unprecendented growth of mobile data traffic and users. It has proven to be a cost efficeient solution to offload traffic from macro-cells. Software defined heterogeneous wireless network can decouple the control plane from the data plane. The control signal goes through the macro-cell while the data traffic can be offloaded by small cells. In this paper, we propose a framework for cell virtualization and user association in order to satisfy versatile requirements of multiple tenants. In the proposed framework, we propose an interference graph partioning based virtual-cell association and customized physical-cell association for multi-homed users in a software defined small cell network. The proposed user association scheme includes 3 steps: initialization, virtual-cell association and physical-cell association. Simulation results show that the proposed virtual-cell association outperforms the other schemes. For physical-cell association, the results on resource utilization and user fairness are examined for mobile users and infrastructure providers.

• 전자공학회논문지
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• 제53권5호
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• pp.13-18
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• 2016

LTE-A(Long Term Evolution-Advanced)에서는 비용 효율적 방법으로 급증하는 무선 데이터 서비스를 대처하고 사용자의 QoS(Quality of Service)를 만족시키기 위해 SCE(Small Cell Enhancement)에 대한 연구가 활발히 진행되고 있다. 하지만 수많은 소형셀이 밀집하여 불규칙하게 배치되기 때문에 전송품질 저하 등 많은 문제가 발생하게 된다. 본 논문에서는 밀집한 소형셀 네트워크에서 클러스터링 기반 간섭 관리 기법을 제안한다. 제안 기법은 UE(User Equipment)로부터 받은 RSRP(Reference Signal Received Power)를 비교하여 소형셀의 클러스터를 구성한다. 클러스터 내에서 ABS를 적용하여 소형셀 간 간섭을 완화시킨다. 또한, 전력제어를 적용하여 클러스터 간 간섭을 줄인다. 모의실험 결과, 제안한 기법에서 소형셀 사용자의 SINR(Signal to Interference plus Noise Ratio), 전송률 및 스펙트럼 효율이 향상되어 전체적인 셀 성능이 향상 되는 것을 볼 수 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권2호
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• pp.494-513
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• 2019

A multi-channel access problem based on hypergraph model in ultra-dense small cell networks is studied in this paper. Due to the hyper-dense deployment of samll cells and the low-powered equipment, cumulative interference becomes an important problem besides the direct interference. The traditional binary interference model cannot capture the complicated interference relationship. In order to overcome this shortcoming, we use the hypergraph model to describe the cumulative interference relation among small cells. We formulate the multi-channel access problem based on hypergraph as two local altruistic games. The first game aims at minimizing the protocol MAC layer interference, which requires less information exchange and can converge faster. The second game aims at minimizing the physical layer interference. It needs more information interaction and converges slower, obtaining better performance. The two modeled games are both proved to be exact potential games, which admit at least one pure Nash Equilibrium (NE). To provide information exchange and reduce convergecne time, a cloud-based centralized-distributed algorithm is designed. Simulation results show that the proposed hypergraph models are both superior to the existing binary models and show the pros and cons of the two methods in different aspects.

• 전자통신동향분석
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• 제37권2호
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• pp.83-95
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• 2022

5G goes beyond people to serve indoor and outdoor companies and industries, as well as campuses such as halls, industrial complexes, educational institutions, stadiums, dense urban areas, rural areas, and government institutions. Therefore, a new approach to small cells is needed. Accordingly, 3GPP and Small Cell Forum are researching 5G small cell architecture; 3GPP, Small Cell Forum, and 5G Alliance for Connected Industries and Automation are also researching private networks tailored to meet the specific requirements of various companies and local governments. In particular, in the UK, a small cell-based technology is required for realizing the Joint Operator Technical Specifications-Neutral Host In-Building specification to cost-effectively secure indoor coverage. Further, the research on the SON(Self-Organizing Network) technology for small cells in 5G, where commercialization has begun, is required. The 5G-based small cell structure, private network, and Neutral Host In-Building and SON reviewed in this study are at the initial research stages; therefore, additional research is needed to secure the competitiveness of the small cell technology in 5G and Beyond 5G.

• 전자통신동향분석
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• 제33권5호
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• pp.33-41
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• 2018

The paradigm of mobile communication technology has changed from an increase in transmission capacity to service-based technologies satisfying various types of service requirements. One of the new paradigms is a service that provides users with a QoE (Quality Of Experience (QoE), at anytime and anywhere. 5G defines various technologies such as dense network structures and beam selection for increasing the transmission capacity and ensuring the quality of experience so as to satisfy this requirement, and related research is underway. In this paper, we describe the definition of a 5G small cell and 5G network structure as well as research trends of standardization and related technologies for constructing optimal solutions for mobile users in dense networks based on small cells.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권9호
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• pp.4108-4122
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• 2016

To address challenges of an unprecedented growth in mobile data traffic, the ultra-dense network deployment is a cost efficient solution to off-load the traffic over other small cells. However, the real traffic is often much lower than the peak-hour traffic and certain small cells are superfluous, which will not only introduce extra energy consumption, but also impose extra interference onto the radio environment. In this paper, an elastic energy efficient cell management scheme is proposed based on flow scheduling among multi-layer ultra-dense cells by a SDN controller. A significant power saving was achieved by a cell-level energy manager. The scheme is elastic for energy saving, adaptive to the dynamic traffic distribution in the office or campus environment. In the end, the performance is evaluated and demonstrated. The results show substantial improvements over the conventional method in terms of the number of active BSs, the handover times, and the switches of BSs.

• 인터넷정보학회논문지
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• 제23권5호
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• pp.25-31
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• 2022

초고밀도 네트워크(Ultra dense network, UDN)는 5G 이동통신 시스템에서 많은 수의 스몰셀 기지국(Small-cell access point, SAP)이 매크로셀의 서비스 영역에 배치되기 때문에 매크로 단말(Macro user equipment, MUE)이 수신하는 간섭량이 증가하여 시스템 용량이 크게 감소한다. 따라서, 본 논문은 UDN에서 SAP의 수가 증가하여도 MUE의 성능을 보장하기 위한 상향링크 유동적 채널할당 방법을 제안한다. 제안하는 유동적 채널할당 방법은 간섭량이 높은 MUE와 동일한 부채널을 사용하지 않도록 SAP들이 사용하는 부채널을 제어하여 MUE의 신호 대 간섭 잡음비(Signal to interference and noise ratio)를 주어진 임계값 이상으로 보장하는 것을 목표한다. 시뮬레이션을 통해 제안하는 유동적 채널할당 방법이 다른 방법들과 비교해 스몰셀 사용자 단말의 성능은 크게 감소되지 않으면서 MUE의 평균 전송 용량이 향상됨을 보인다.