• International Journal of Computer Science & Network Security
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• 제22권4호
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• pp.329-339
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• 2022

Small cells, particularly femtocells, are regarded a promising solution for limited resources required to handle the increasing data demand. They usually boost wireless network capacity. While widespread usage of femtocells increases network gain, it also raises several challenges. Interference is one of such concerns. Interference management is also seen as a main obstacle in the adoption of two-tier networks. For example, placing femtocells in a traditional macrocell's geographic area. Interference comes in two forms: cross-tier and co-tier. There have been previous studies conducted on the topic of interference management. This study investigates the principle of categorization of interference management systems. Many methods exist in the literature to reduce or eliminate the impacts of co-tier, cross-tier, or a combination of the two forms of interference. Following are some of the ways provided to manage interference: FFR, Cognitive Femtocell and Cooperative Resource Scheduling, Beamforming Strategy, Transmission Power Control, and Clustering/Graph-Based. Approaches, which were proposed to solve the interference problem, had been presented for each category in this work.

• 한국시뮬레이션학회논문지
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• 제20권1호
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• pp.107-116
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• 2011

최근 가정 또는 사무실과 같은 실내 환경에서 음영지역을 해소하고 고품질의 서비스 제공을 위한 방안으로 초소형 기지국인 펨토셀(Femtocell)이 많은 관심을 받고 있다. 펨토셀은 사업자 및 사용자에게 다양한 이점을 제공하지만 펨토셀의 도입을 위해 서는 채널 선택에 따른 간섭제어, 네트워크 동기화, 자기 최적화 등 다양한 기술적 문제점이 해결되어야 한다. 이를 위해 본 연구에서는 펨토셀의 도입으로 인하여 발생 가능한 다양한 신호간섭 문제들에 대한 분석을 용이하게 하기 위한 LTE(Long Term Evolution) 시스템 기반 펨토셀 시뮬레이터를 개발하였다. 개발된 시뮬레이터는 단말 이동성, 스케줄러, 호 수락 제어, 트래픽 생성, MCS(Modulation and Coding Scheme) 결정의 5개의 블록과 이를 연결하고 관리하는 메인 모듈로 구성되어 있다. 또한 사용자의 편의성을 도모하기 위하여 시뮬레이션 결과를 실시간으로 관측할 수 있는 GUI(Graphical User Interface)를 적용하였다. 본 시뮬레이터는 실제와 유사한 환경에서 매크로셀과 펨토셀 사이의 간섭영향을 면밀히 분석하고 이동통신 시스템의 성능을 효과적으로 평가할 수 있도록 지원하며, 다양한 펨토셀 시스템을 개발하는데 크게 기여할 수 있을 것으로 예상된다.

• 한국컴퓨터정보학회논문지
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• 제20권10호
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• pp.53-59
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• 2015

In this paper we propose a resource management scheme which allocates hierarchical resources stepwise based on the users' QoS requirement of each service in the macro-femtocell overlaid LTE-Advanced network. Our proposed scheme adjusts the transmission rate to the minimum which guarantees the allowable minimum requirement of delay for each user service. In this way it minimizes the interference on the adjacent channels and it is able to increase the resource utilization efficiency. Simulation results show that our scheme provides better performances than the conventional one in respect of the outage probability and data transmission throughput.

• 인터넷정보학회논문지
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• 제19권1호
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• pp.11-17
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• 2018

본 논문에서는 회사 또는 백화점 등과 같은 고층 건물에 다수의 펨토셀 기지국들(Femtocell base stations, fBSs)이 밀집되어 배치되는 기업형 펨토셀 네트워크(Enterprise femtocell network, EFN) 환경에서 부분 주파수 재사용 (Fractional frequency reuse, FFR) 자원할당 방법을 이용하여 하향링크에 대한 시스템 성능을 분석한다. 이를 위해, 먼저 매크로셀과 펨토셀 사이의 주파수 간섭을 완화시키는 Split reuse 주파수 할당 방법에 대해 소개하고, 이후 EFN의 fBS들에게 주파수 간섭 완화 및 주파수 효율을 극대화할 수 있는 FFR을 이용한 자원할당 방법을 제안한다. 마지막으로 시뮬레이션을 통해 제안하는 FFR 자원할당 방법의 시스템 성능을 분석하고, EFN 환경에서 주파수 재사용 계수(Frequency reuse factor: FRF)를 4로 사용하는 전형적인 FRF 4 방법보다 제안하는 FFR 자원할당 방법이 평균 fUE 용량, 전체 EFN 용량, 그리고 Outage probability 측면에서 우수한 성능임을 보인다.

• ETRI Journal
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• 제34권3호
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• pp.297-307
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• 2012

A femtocell is a small cellular base station, typically designed for use in a home or small business. The random deployment of a femtocell has a critical effect on the performance of a macrocell network due to co-channel interference. Utilizing the advantage of a multiple-input multiple-output system, each femto base station (FBS) is able to form a cluster and generates a precoding matrix, which is a modified version of conventional single-cell block diagonalization, in a cooperative manner. Since interference from clustered-FBSs located at the nearby macro user equipment (MUE) is the dominant interference contributor to the coexisting networks, each cluster generates a precoding matrix considering the effects of interference on nearby MUEs. Through simulation, we verify that the proposed algorithm shows better performance respective to both MUE and femto user equipment, in terms of capacity.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2008년도 정보통신설비 학술대회
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• pp.454-458
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• 2008

This article describes an interference reduction scheme for Mobile WiMAX in an indoor environment. The feasibility of user deployed femtocells in the same frequency channel as an existing macro cell network is investigated. One of the important requirements for co-channel operation of femtocells such as auto-configuration and self optimization are discussed. In femtocell deployments, leakage of the pilot signal to the outside of a house can result of the higher number of mobility events caused by passing user of macrocell. This interference effect can be minimized by reducing the pilot power using proper scheme. This paper introduces existing auto-configuration method of power control and proposed interference reduction scheme using power control for Mobile WiMAX in an indoor environment.

• 한국통신학회논문지
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• 제39B권2호
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• pp.61-74
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• 2014

In recent years, development of femtocells are receiving considerable attention towards increasing the network coverage, capacity, and improvement in the quality of service for users. In 3GPP LTE-Advanced (LTE-A) system, to efficiently utilize the bandwidth, femtocell and macro cell uses the same frequency band, but this deployment poses a technical challenge of cross-tier interference to macro users. In this paper, the novel quality of service based fractional power control (QoS-FPC) scheme under the heterogeneous networks environment is proposed, which considers the users priority and QoS-requirements during the power allocation. The proposed QoS-FPC scheme has two focal points: firs, it protects the macrocell users uplink communication by limiting the cross-tier interference at eNB below a given threshold, and second, it ensures the optimization of femtocell users power allocation at each power adjustment phase. Performance gain is demonstrated with extensive system-level simulations to show that the proposed QoS-FPC scheme significantly decreases the cross-tier intereference and improves the overall users throughput.

• 한국통신학회논문지
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• 제38A권3호
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• pp.268-276
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• 2013

본 연구에서는 Heterogeneous Network에서의 간섭제어에 관한 기술 동향을 살펴보고, 간섭 제어 기술 중 3GPP release 10에서의 주요 기술 enhanced Inter-Cell Interference Coordination (enhanced ICIC, eICIC)을 택하여 성능을 분석해 보았다. eICIC기술 중 시간영역에서의 간섭 제어인 Almost Blank Subframe (ABS)와 Cell Range Expansion (CRE) 기술에 의한 성능을 분석하였다. Heterogeneous Network에서 macrocell과 femtocell 간의 간섭 제어를 적절히 하기 위해서는 ABS기술과 CRE 기술 간의 조합이 중요할 것으로 보인다. Heterogeneous Network의 전체 성능 평가는 정량적으로는 분석되기 어려워 system level simulation에 의해서 평가하였다. 본 연구에서는 SLS 방식으로 다양한 환경에 대한 성능을 분석함으로써 Heterogeneous Network 운영에 있어 각각의 요소가 미치는 영향을 파악할 수 있도록 하였으며, Heterogeneous Network에서의 ABS와 CRE의 결합에 의한 효과를 분석하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권6호
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• pp.2595-2618
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• 2018

In this paper, we investigate secure communication with the presence of multiple eavesdroppers (Eves) in a two-tier downlink dense heterogeneous network, wherein there is a macrocell base station (MBS) and multiple femtocell base stations (FBSs). Each base station (BS) has multiple users. And Eves attempt to wiretap a macrocell user (MU). To keep Eves ignorant of the confidential message, we propose a physical-layer security scheme based on cross-layer cooperation to exploit interference in the considered network. Under the constraints on the quality of service (QoS) of other legitimate users and transmit power, the secrecy rate of system can be maximized through jointly optimizing the beamforming vectors of MBS and cooperative FBSs. We explore the problem of maximizing secrecy rate in both non-colluding and colluding Eves scenarios, respectively. Firstly, in non-colluding Eves scenario, we approximate the original non-convex problem into a few semi-definite programs (SDPs) by employing the semi-definite relaxation (SDR) technique and conservative convex approximation under perfect channel state information (CSI) case. Furthermore, we extend the frame to imperfect CSI case and use the Lagrangian dual theory to cope with uncertain constraints on CSI. Secondly, in colluding Eves scenario, we transform the original problem into a two-tier optimization problem equivalently. Among them, the outer layer problem is a single variable optimization problem and can be solved by one-dimensional linear search. While the inner-layer optimization problem is transformed into a convex SDP problem with SDR technique and Charnes-Cooper transformation. In the perfect CSI case of both non-colluding and colluding Eves scenarios, we prove that the relaxation of SDR is tight and analyze the complexity of proposed algorithms. Finally, simulation results validate the effectiveness and robustness of proposed scheme.

• ETRI Journal
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• 제40권3호
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• pp.318-329
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• 2018

Femtocell (FC) technology envisaged as a cost-effective approach to attain better indoor coverage of mobile voice and data service. Deployment of FCs over macrocell forms a heterogeneous network. In urban areas, the key factor limits the successful deployment of FCs is inter-cell interference (ICI), which severely affects the performance of victim users. Autonomous FC transmission power setting is one straightforward way for coordinating ICI in the downlink. Application of intelligent control using soft computing techniques has not yet explored well for wireless networks. In this work, autonomous FC transmission power setting strategy using Adaptive Neuro Fuzzy Inference System is proposed. The main advantage of the proposed method is zero signaling overhead, reduced computational complexity and bare minimum delay in performing power setting of FC base station because only the periodic channel measurement reports fed back by the user equipment are needed. System level simulation results validate the effectiveness of the proposed method by providing much better throughput, even under high interference activation scenario and cell edge users can be prevented from going outage.