• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권3호
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• pp.997-1010
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• 2014

Today, as the hierarchical cellular system is getting more attention than before, some recent studies introduce delay based admission control (AC) scheme which delays the admission to the macro-embedded small cell for a relatively short time to prevent unnecessary handover caused by the short-term visitors of the small cell area. In such delay based ACs, when we use improper delay parameter, the system frequently makes incorrect handover decisions such as where unnecessary handover is allowed due to too short delaying, or where necessary handover is denied due to too long delaying. In order to avoid these undesirable situations as much as possible, we develop a new delay parameter decision method based on probabilistic cell residence time approximations. By the extensive numerical and analytical evaluations, we determine the proper delay parameter which prevents the incorrect handover decision as much as possible. We expect our delay parameter decision method can be useful system administration tips in hierarchical cellular system where delay based AC is adopted.

• Journal of Information Processing Systems
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• 제6권3호
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• pp.403-412
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• 2010

Multi-Relay Networks should accommodate mobile users of various speeds. The cellular system should meet the minimum residency time requirements for handover calls while considering an efficient use of available channels. In this paper, we design speed-sensitive handover under dynamic hierarchical cellular systems, in which mobile users are classified according to the mean speed of mobile users and each class has its cellular layer. In order to meet the minimum residency time, the cell size of each cellular layer is dynamically determined depending on the distributions of mean speeds of mobile users. Since the speed-dependent non-preferred cell can provide a secondary resource, overflow and take-back schemes are adopted in the system. We develop analytical models to study the performance of the proposed system, and show that the optimal cell size improves the blocking probability.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권5호
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• pp.2243-2257
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• 2019

A heterogeneous cellular network (HCN) is useful to increase the spectral and energy efficiency of wireless networks and to reduce the traffic load from the macro cell. The performance of the secondary user equipment (SUE) is affected by interference from the eNodeB (eNB) in a macro cell. To decrease the interference between the macro cell and the small cell, allocating resources properly is essential to an HCN. This study considers the scenario of a software-defined heterogeneous cellular network and performs the resource allocation process. First, we show the system model of HCN and formulate the optimization problem. The optimization problem is a complex process including power and frequency resource allocation, which imposes an extremely high complexity to the HCN. Therefore, a hierarchical resource allocation scheme is proposed, which including subchannel selection and a particle swarm optimization (PSO)-based power allocation algorithm. Simulation results show that the proposed hierarchical scheme is effective in improving the system capacity and energy efficiency.

• Journal of Communications and Networks
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• 제7권2호
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• pp.178-191
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• 2005

Fourth-generation (4G) wireless networks will be the IP-based cellular networks integrating Internet with the existing cellular networks. Two important issues should be concerned in the IP-based cellular networks, IP mobility, and quality-of-service (QoS) guarantees. In this paper, we proposed two mechanisms to solve the problems with IP mobility and RSVP-based QoS provisioning. First, virtual-IP (VIP) allocation scheme in areas with a large rate of handoff can minimize the wireless signaling overhead due to IP mobility. The access routers (ARs) create dynamically the VIP zone by using the measured handoff rate derived from the history of the handoff into neighboring ARs. We show that VIP allocation scheme reduces the binding update messages in the wireless link than hierarchical mobile IPv6. Second, the new advance resource reservation protocol called proportional aggregate RSVP (PA-RSVP) can minimize waste of bandwidth and soft state refresh overhead due to IP mobility. It allocates the bandwidth in advance between the mobility anchor point and neighboring ARs using proportional aggregate reservation. We also show that PA-RSVP provides an improved performance over existing protocols.

• 한국통신학회논문지
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• 제31권1B호
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• pp.1-8
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• 2006

현재 유${\cdot}$무선 통합망에서 인터넷 서비스를 제공하기 위한 많은 작업이 진행 중이며 IP 이동성 문제를 해결하기 위한 방식으로 Mobile IP를 사용하고 있다. 그러나 Mobile IP는 셀룰러 기반의 무선 접속망에서 잦은 핸드오프를 처리하는데 있어서 여러 가지 제한점을 갖는다. 이러한 문제점을 해결하기 위해서 마이크로 이동성 프로토콜이 제안되고 있으며, 마이크로 이동성 프로토콜 방식으로 Cellular IP, HAWAII, Hierarchical Mobile IP 등이 있다. Cellular IP는 일정 지역 내에서 seamless 한 이동성을 제공하기 때문에 특별한 관심을 받고 있다. 그러나 Cellular IP 인다이렉트 핸드오프 방식은 핸드오프가 발생할 경우 새로운 영역의 BS이 핸드오프를 인식하는 과정이 필요하기 때문에 핸드오프 인식과정에서 패킷 유실 및 중복이 발생하여 UDP 및 TCP 성능저하가 발생한다. 본 논문에서는 Cellular IP 인다이렉트 핸드오프 방식을 개선한 핸드오프 방식을 제안하였으며, 문제점을 해결하기 위하여 크로스오버 노드를 통한 시그널링 과정과 버퍼링 과정을 사용하였다. 새로운 영역의 BS에게 핸드오프 사실을 알리기 위해서 게이트웨이까지 전송되는 핸드오프 요청 패킷을 크로스오버 노드에서 처리함으로서 불필요한 시그널링 트래픽을 감소 시켰다.

• 한국통신학회논문지
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• 제34권6A호
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• pp.476-483
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• 2009

최근 들어 실내에서의 고속 무선 통신과 음영지역 해소를 위한 해결책의 하나로 옥내용 기지국인 펨토셀(femtocell)을 활용하는 계층구조 방안이 제시되고 있으며, 이동통신 표준화 단체에서 관련 이슈에 대한 표준화 작업이 활발히 진행되고 있다. 그러나 펨토셀 환경에서 발생할 수 있는 여러 가지 기술적 문제들이 존재하며 그 중 가장 중요한 문제가 간섭으로 인한 시스템의 열화이다. 따라서 전체 시스템의 안정적이고 효율적인 운용을 위해 펨토셀 환경에서의 상호 간섭과 이에 따른 시스템 성능 분석이 요구된다. 본 고에서는 펨토셀 설치 주변의 다양한 전파 환경을 고려하여 매크로셀(macrocell)이나 펨토셀간 상호 간섭에 따른 시스템 용량 및 서비스 영역을 살펴본다. 특히 펨토셀의 주 설치 지역이 되는 실내 환경에서 매크로셀과 펨토셀간의 거리, 펨토셀 내에서 사용자의 위치, 옥내 구조물의 특징 등을 반영한 의전파전파 모델을 적용하고 그에 따른 주파수 효율성과 서비스 반경 등의 시스템 성능을 분석한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 학술회의 논문집 정보 및 제어부문 A
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• pp.163-166
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• 2003

In recent years, there has been increased to access multimedia service through the Internet due to rise of the access speed. We suppose the co-existence of the various access networks in adjacent area in the future, such as wireless LAN, Bluetooth, and 3G Cellular So, the size of the cell will be smaller and the number of access point will be increased. In other words, the potable devices need the efficient mobility scheme due to move between cells frequently Currently, the several of the scheme, which is Cellular IP, HAWAII, Mobile IPv4 regional registration, and hierarchical Mobile IPv6, is suggested to support micro-mobility but Mobile IPv4 is standard scheme to support the mobility of the mobile node. MPLS, which forwards the packet through switching instead of routing using IP address, has begun to deploy in the internet backbone to increase the performance of mobility protocol. The integration of both MPLS and Mobile IP improves the scalability of the Mobile IP data forwarding process by leveraging on the features MPLS which are fast switching and high scalability. Moreover it abbreviates IP-in-IP tunneling between HA and FA. In this paper, we suggest efficient mobility scheme through integration of both MPLS and hierarchical Mobile IPv6.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권1호
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• pp.1-19
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• 2015

With the recent popularity of smart terminals, the demand for high-data-rate transmission is growing rapidly, which brings a new challenge for the traditional cellular networks. Both device-to-device (D2D) communication and small cells are effective to improve the transmission efficiency of local communication. In this paper, we apply D2D communication into a small cell network system (SNets) and study about the optimization problem of resource allocation for D2D communication. The optimization problem includes system scheduling and resource allocation, which is exponentially complex and the optimal solution is infeasible to achieve. Therefore, in this paper, the optimization problem is decomposed into several smaller problems and a hierarchical scheme is proposed to obtain the solution. The proposed hierarchical scheme consists of three steps: D2D communication groups formation, the estimation of sub-channels needed by each D2D communication group and specific resource allocation. From numerical simulation results, we find that the proposed resource allocation scheme is effective in improving the spectral efficiency and reducing the outage probability of D2D communication.

• Bioinformatics and Biosystems
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• 제2권2호
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• pp.71-74
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• 2007

Cell phenotypes are determined by groups of functionally related genes. Microarray profiling of gene expression provides us response of cellular state to its perturbation. Several methods for uncovering a cellular network show reliable network reconstruction. In this study, we present reconstruction of genetic regulatory network of inflammation bowel disease in human peripheral blood mononuclear cell. The microarray based on Affymetrix Gene Chip Human Genome U133 Array Set HG-U133A is processed and applied network reconstruction algorithm, ARACNe. As a result, we will show that inferred network composed of 450 nodes and 2017 edges is roughly scale-free network and hierarchical organization. The major hub, CCNL2 (cyclin A2), in inferred network is shown to be associated with inflammatory function as well as apoptotic function.

• 한국정보과학회논문지:정보통신
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• 제32권5호
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• pp.551-560
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• 2005

이동시 발생하는 시그널링 메시지의 양을 줄이기 위한 방법으로 지역성을 고려한 계층적 이동성 제공 방식인 HMIPv6(Hierarchical Mobile IPv6)가 제안되었다. 이동 노드가 방문 링크로 이동하면 링크 사용을 위한 인증 절차를 먼저 수행해야한다. 이를 위해 무선 랜 및 Cellular 망을 중심으로 AAA(Authentication, Authorization and Account) 인증 서비스 도입이 진행되고 있다. 그러나 AAA 인증 서비스는 지역화 된 이동성 제공을 위한 최적화된 시그널링 교환을 제공하지 않는다 이는 실시간 응용을 필요로 하는 세션을 가진 경우 이동 노드에 대한 서비스 지연을 초래할 수도 있다. 본 논문에서는 지역 이동시 인증 과정을 최적화 할 수 있는 인증 위덤 방식을 기존의 HMIPv6 구조에 통합함으로써 인증 발생 시 시그널링의 양을 최소화 하고 서비스 지연 시간을 줄일 수 있는 방법을 제안한다. 계층적 인증 통합 모델을 제안하며 제안된 모델에 대해 이동 특성, 트래픽 특성, 도메인 크기 등에 따르는 인증 비용을 분석하고 기존의 방식과 비교하였는데 평균 $33.6\%$의 비용 절감 효과를 얻을 수 있었다.