• Journal of Communications and Networks
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• v.16 no.4
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• pp.430-435
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• 2014

The performance of a distributed database system depends particularly on the site-allocation of the fragments. Queries access different fragments among the sites, and an originating site exists for each query. A data allocation algorithm should distribute the fragments to minimize the transfer and settlement costs of executing the query plans. The primary cost for a data allocation algorithm is the cost of the data transmission across the network. The data allocation problem in a distributed database is NP-complete, and scalable evolutionary algorithms were developed to minimize the execution costs of the query plans. In this paper, quadratic assignment problem heuristics were designed and implemented for the data allocation problem. The proposed algorithms find near-optimal solutions for the data allocation problem. In addition to the fast ant colony, robust tabu search, and genetic algorithm solutions to this problem, we propose a fast and scalable hybrid genetic multi-start tabu search algorithm that outperforms the other well-known heuristics in terms of execution time and solution quality.

• ETRI Journal
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• v.26 no.5
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• pp.405-412
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• 2004

MC-CDMA, a multicarrier (MC) modulation scheme based on code division multiple access (CDMA), is the most likely candidate for the next generation of mobile radio communications. The rate compatible punctured turbo (RCPT) coded hybrid automatic repeat request (HARQ) has been found to give improved throughput performance in a direct sequence (DS) CDMA system. However, the extent to which the RCPT HARQ improves the throughput performance of an MC-CDMA system has not been fully understood. In this paper, we apply the RCPT HARQ to MC-CDMA and evaluate by computer simulations its performance in a frequency selective Rayleigh fading channel. We found that the performance of RCPT HARQ MC-CDMA is almost insensitive to channel characteristics. The performance can be drastically improved with receive diversity combined with space-time transmit diversity. In addition, the comparison of RCPT HARQ MC-CDMA, orthogonal frequency division multiplexing, and DS-CDMA shows that under similar conditions the throughput of MC-CDMA is the best in a frequency selective fading channel.

• Electronics and Telecommunications Trends
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• v.11 no.4 s.42
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• pp.63-75
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• 1996

본 고에서는 일반 가정 및 소규모 업무용 가입자들에 대한 광대역화의 가장 경제적인 대안으로 관심을 끌고 있는 Hybrid fiber-coax 구조의 CATV 전송망에 대한 표준화 동향에 대해 조사 분석한 내용을 기술한다. HFC 액세스망에 대한 표준화는 IEEE 802.14 그룹, DAVIC, ATM Forum, IETF(Internet Engineering Task Force)와 Cable TV업계 등 여러기구에서 추진하고 있다. 지금까지 물리계층, MAC계층 등에 대한 주요 표준규격에 대해 DAVIC과 IEEE 802.14에서 주도하고 있으나, 앞으로는 데이터 서비스에 상대적 우선 순위를 두고 표준화를 추진하는 IEEE 802.14그룹에서 주도하게 될 것으로 보인다. 또한 인터넷 접속과 고속 데이터 서비스를 위한 인터페이스와 IP 접속 프로토콜에 대한 표준화를 발 빠르게 추진하고 있는 IETF와 MCNS(Multimedia Cable Network System) 등의 역할이 커질 것으로 전망된다.

• International journal of advanced smart convergence
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• v.12 no.1
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• pp.1-8
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• 2023

Smart IoT over high speed network and high performance smart devices explodes the ubiquitous services and applications. Nearest Neighbor(NN) query is one of the important type of queries that have to be supported for ubiquitous information services. In order to process efficiently NN queries in the wireless broadcast environment, it is important that the clients determine quickly the search space and filter out NN from the candidates containing the search space. In this paper, we propose a hybrid index of Voronoi and grid partition to provide quick search space decision and rapid filtering out NN from the candidates. Grid partition plays the role of helping quick search space decision and Voronoi partition providing the rapid filtering. We show the effectiveness of the proposed index by comparing the existing indexing schemes in the access time and tuning time. The evaluation shows the proposed index scheme makes the two performance parameters improved than the existing schemes.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 2002.11a
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• pp.495-498
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• 2002

The need for network protection, accounting and resource management in foreign administrative domain requires appropriate security services. In this paper, we propose an access control protocol to support the authentication between mobile node and visiting subnet. Our hybrid way of approach aims to reduce computational overhead and minimize the use of network bandwidth. We also propose non-certificate based public-key cryptography to provide non-repudiation, which does not require CRL retrieval and certificate validation.

• Proceedings of the KIEE Conference
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• 2000.07a
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• pp.564-566
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• 2000

To provide more noiseless upstream service on the HFC(Hybrid-Fiber Coaxial) Access Network, we should conduct upstream band analysis and have related operation skill. In this paper, we studied the upstream signal measurement to get goof transmission quality, effective operation and maintenance, also showed the method of noise analysis and that of upstream band frequency selection. Finally we tested the signal in the field and showed the analyzed result.

• Annual Conference of KIPS
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• 2003.05b
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• pp.1253-1256
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• 2003

HFC(Hybrid Fiber Coax)망은 광케이블 구간과 동축케이블 구간으로 나뉘어져 있으며 광케이블 구간은 성형(Star)구조를 가지며 동축케이블 전송구간은 수지분기형(Tree and Branch)구조로 되어있다. HFC망의 상향채널은 가입자에서 헤드앤드로 데이터 전송 시 500가입자 이상이 공유하기 때문에 이를 제어하기 위한 매체접근제어(Medium Access Control)프로토콜이 필요하다. 특히, 음성, 비디오 그리고 데이터와 같은 트래픽의 QoS(Quality of Service)를 만족시키기 위해서는 서비스별로 우선 순위를 고려한 충돌해결알고리즘이 요구되어진다. 그러므로, 본 논문에서는 기존 알고리즘의 문제점을 분석하여 트래픽 특성에 따라 우선순위를 제공하는 충돌해결알고리즘을 제안하였다.

• Journal of Communications and Networks
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• v.8 no.4
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• pp.401-409
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• 2006

Orthogonal frequency division multiplexing (OFDM) and multiple input multiple output (MIMO) technologies provide additional dimensions of freedom with spectral and spatial resources for radio resource management. Multi-dimensional radio resource management has recently been identified to exploit the full dimensions of freedom for more flexible and efficient utilization of scarce radio spectrum while provide diverse quality of service (QoS) guarantees. In this work, a multi-dimensional radio resource scheduling scheme is proposed to achieve above goals in hybrid orthogonal frequency division multiple access (OFDMA) and space division multiple access (SDMA) systems. Cochannel interference (CCI) introduced by frequency reuse under SDMA is eliminated by frequency division and time division between highly interfered users. This scheme maximizes system throughput subjected to the minimum data rate guarantee. for heterogeneous users and transmit power constraint. By numerical examples, system throughput and fairness superiority of the our scheduling scheme are verified.

• The Journal of Information Technology
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• v.4 no.3
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• pp.65-75
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• 2001

Code-division multiple access has been widely accepted as the major multiple access scheme in mobile communication systems. Wide-band CDMA and its hybrid associate time-division CDMA are key elements in the mobile communication. Since 10 years ago, there has been enormous research activity in analysis of the capacity of these CDMA-based systems. Recently, upgrading service, high quality and the different service classes in radio resource allocation has recently increased. This paper presents an overview of Radio Resource Allocation on the CDMA-based systems that are flexible, support traffic services, minimize call blocking rate and have acceptable radio resource utilization.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.13-16
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• 1999

The terrestrial/satellite hybrid network may replace or supply the terrestrial network in some areas or certain application. Futhermore, it can play an important role in the development of B-ISDN due to their features of flexible wide coverage, independent of ground distances and geographical constraints, multiple access and multipoint broadcast. Also, satellite have the capability to supply terrestrial ATM and B-ISDN with flexible links for access networks as well as trunk networks. This paper describes the design and verification of the interworking protocol between terrestrial B-ISDN and satellite network. For the verification, the designed interworking protocol is modeled by Petri-net and analyzed by reachability tree.