• 한국콘텐츠학회논문지
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• 제6권1호
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• pp.137-142
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• 2006

XML 문서가 웹 문서의 표준으로 자리 잡음에 따라 많은 정보들이 XML 문서 형식으로 표현되면서 XML 문서의 보안에 관한 요구도 커지고 있다. 현재까지의 XML 보안에 관한 연구는 암호화와 전자 서명 같은 통신상의 보안에 관한 연구가 중심이 되었으나 XML 문서가 방대해지고 복잡해짐에 따라 XML 문서에 대한 통신상의 보안뿐 아니라 관리적인 보안이 필요하게 되었다. 하지만 XML 문서의 암호화는 단순한 통신상의 보안만을 제공할 뿐 관리적 보안 요소인 다양한 사용자와 다양한 접근 권한 정책을 반영하지 못하고 있다. 본 논문에서는 XML 문서의 보안을 위해 주체별 권한 정책을 반영한 접근 제어를 보장하는 주체 기반 XML문서의 암호화 기법을 제안한다. 접근 제어를 보장하는 암호화를 수행함으로써 다양한 사용자의 다양한 권한 정책을 반영할 수 있다.

• ETRI Journal
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• 제33권2호
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• pp.184-193
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• 2011

Tailored for wireless local area networks, the present paper proposes a cross-layer resource allocation scheme for multiple-input multiple-output orthogonal frequency-division multiplexing systems. Our cross-layer resource allocation scheme consists of three stages. Firstly, the condition of sharing the subchannel by more than one user is studied. Secondly, the subchannel allocation policy which depends on the data packets' lengths and the admissible combination of users per subchannel is proposed. Finally, the bits and corresponding power are allocated to users based on a greedy algorithm and the data packets' lengths. The analysis and simulation results demonstrate that our proposed scheme not only achieves significant improvement in system throughput and average packet delay compared with conventional schemes but also has low computational complexity.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권12호
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• pp.3061-3080
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• 2012

To improve the sensing performance, cooperation among secondary users can be utilized to collect space diversity. In this paper, we focus on the optimization of cooperative spectrum sensing in which multiple cognitive users efficiently cooperate to achieve superior detection accuracy with minimum sensing error probability in multiple cross-over cognitive radio networks. The analysis focuses on two fusion strategies: soft information fusion and hard information fusion. Under soft information fusion, the optimal threshold of the energy detector is derived in both noncooperative single-user and cooperative multiuser sensing scenarios. Under hard information fusion, the optimal randomized rule and the optimal decision threshold are derived according to the rule of minimum sensing error (MSE). MSE rule shows better performance on improving the final false alarm and detection probability simultaneously. By simulations, our proposed strategy optimizes the sensing performance for each cognitive user which is randomly distributed in the multiple cross-over cognitive radio networks.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권2호
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• pp.635-656
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• 2019

In this paper, we investigate the degrees of freedom (DoF) of a multi-cell multi-user multiple-input multiple-output (MIMO) interference broadcast channel (IBC) with non-cooperation distributed base stations (BS), where each BS serves users of its corresponding cell. When all BSs simultaneously transmit their own signals over the same frequency band in the MIMO IBC, the edge users in each cell will suffer the inter-cell interference (ICI) and inter-user interference (IUI) signals. In order to eliminate the ICI and IUI signals, a distributed space time interference alignment (DSTIA) approach is proposed where each BS has only limited access to distributed moderately-delay channel state information at the transmitter (CSIT). It is shown that the DSTIA scheme can obtain the appreciate DoF gains. In addition, the DoF upper bound is asymptotically achievable as the number of antenna at each BS increases. It is shown that the DSTIA method can get DoF gains over other interference alignment schemes with delayed CSIT in literature. Moreover, the DSTIA method can attain higher DoFs than the IA schemes with global CSIT for certain antenna configurations.

• 한국정보통신학회논문지
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• 제21권1호
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• pp.29-34
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• 2017

본 논문은 다수의 사용자가 동시에 전송하는 상향링크 상황에서 밀리미터 파 시스템을 위한 하이브리드 빔포밍을 고려한다. 기존의 디지털 시스템에 비하여, 하이브리드 빔포밍은 저비용 저전력 소비의 특성을 갖는다. 각 사용자는 하나의 송신 안테나만을 사용하며, 하나의 데이터 스트림을 보내고, 기지국은 다수의 수신 안테나와 다수의 라디오 주파수 체인을 사용한다. 따라서, 하이브리드 빔포밍은 기지국 측에서만 수행된다. 각 사용자는 채널 정보를 알기 어렵고, 수신자인 기지국은 채널을 정확히 추정할 수 있다고 가정한다. 이러한 채널 가정 하에서 아웃티지가 발생할 확률이 0이 아니다. 따라서 성능 평가 지표로서, 아웃티지 확률을 컴퓨터 시뮬레이션을 통해 측정한다. 논문에서 고려한 하이브리드 빔포밍의 아웃티지 확률을 디지털 빔포밍의 아웃티지 확률과 비교하며, 하이브리드 빔포밍이 디지털 빔포밍의 성능에 근접할 수 있음을 보인다.

• 전기학회논문지
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• 제59권10호
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• pp.1914-1916
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• 2010

Cognitive radio MAC protocol should allow secondary users to access unused or under-utilized spectrum without interference to primary users. For cognitive MAC protocol, one of the important issues is how to select the channel opportunities for secondary users. In this paper, we propose a novel cognitive MAC protocol to allocate channel opportunities for the secondary users based on the prediction of future availability. The proposed MAC protocol can reduce the interference to primary users and increase throughput using multiple channels.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권11호
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• pp.3860-3875
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• 2014

Cognitive radio networks (CRNs) are composed of mobile users who can use multiple spectrum bands for communication. CRNs allow unlicensed users (called cognitive users) to efficiently utilize unused licensed spectrums without interfering with communications of licensed users (called primary users). The main goals of CRNs are to mitigate spectrum saturation and to improve spectrum utilization. This paper introduces state-of-the-art routing protocols for CRNs and addresses some limitations of these protocols. To resolve the limitations, we suggest a new research direction for routing protocols in CRNs. We implement our protocol to compare with the existing routing protocols for multi-hop CRNs. Our protocol shows good performance compared to the existing routing protocols in terms of network performance and PU protection.

• 한국ITS학회 논문지
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• 제7권3호
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• pp.1-14
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• 2008

국내는 정보통신(IT) 기술의 발달을 기반으로 BIS, BMS, CNS 등을 통해 교통정보가 실시간적으로 제공되고 있어 유비쿼터스 기반의 첨단 통신기술이 정착되게 되면 개인의 취향에 적합한 맞춤형 (대중)교통정보가 가능할 것으로 전망된다. 대중교통 통행정보는 경로탐색알고리즘으로 구현되는데, 대중교통망은 일반 가로망과는 달리 환승과 운행시간 특성을 포함하며 통행자가 경로를 선택하는 과정에서 통행시간, 환승횟수, 환승시간과 같은 복수의 제약 또는 목적의 고려가 요구된다. 본 연구에서는 사용자에게 영향을 미칠 수 있는 요인들을 복수의 목적으로 고려하여 경로를 탐색하며 탐색된 경로에 대하여 자의적으로 선택해 나가는 기법을 제안한다 본 연구는 복합대중교통망을 대상으로 통행시간, 환승횟수, 환승시간등과 같은 통행목적에 대하여 계층별로 별도의 다목적 경로를 탐색하는 방안을 강구하여 계층별로 적용 가능한 사용자 맞춤형 정보제공체계의 기본적인 접근이론을 개발한다. 제안된 다수단, 다계층, 다목적 경로탐색알고리즘은 링크표지에 근거하여 구축되어 복합교통망에 효율적으로 구동할 수 있으며, 수도권 도시철도의 실제 대규모 교통망에 적용한 사례연구를 통하여 다양한 계층을 고려한 경로계획모형(Path Planning)으로 활용될 수 있는 가능성을 예시하였다.

• Journal of Communications and Networks
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• 제17권6호
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• pp.568-581
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• 2015

Predicting locations of users with portable devices such as IP phones, smart-phones, iPads and iPods in public wireless local area networks (WLANs) plays a crucial role in location management and network resource allocation. Many techniques in machine learning and data mining, such as sequential pattern mining and clustering, have been widely used. However, these approaches have two deficiencies. First, because they are based on profiles of individual mobility behaviors, a sequential pattern technique may fail to predict new users or users with movement on novel paths. Second, using similar mobility behaviors in a cluster for predicting the movement of users may cause significant degradation in accuracy owing to indistinguishable regular movement and random movement. In this paper, we propose a novel fusion technique that utilizes mobility rules discovered from multiple similar users by combining clustering and sequential pattern mining. The proposed technique with two algorithms, named the clustering-based-sequential-pattern-mining (CSPM) and sequential-pattern-mining-based-clustering (SPMC), can deal with the lack of information in a personal profile and avoid some noise due to random movements by users. Experimental results show that our approach outperforms existing approaches in terms of efficiency and prediction accuracy.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권4호
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• pp.1351-1372
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• 2022

A self-organizing multiple unmanned aerial vehicles (multi-UAVs) deployment based on virtual forces has a difficulty in ensuring the quality-of-experience (QoE) of users because of the difference between the assumed center for users in a hotspot and an actual center for users in the hotspot. This discrepancy is aggravated in a non-uniform and mobile user distribution. To address this problem, we propose a new density based virtual force (D-VF) multi-UAVs deployment algorithm which employs a mean opinion score (MOS) as a metric of QoE. Because MOS is based on signal-to-noise ratio (SNR), a sum of users' MOS is a good metric not only to secure a wide service area but to enhance the link quality between multi-UAVs and users. The proposed algorithm improves users' QoE by combining virtual forces with a random search force for the exploration of finding multi-UAVs' positions which maximize the sum of users' MOS. In simulation results, the proposed deployment algorithm shows the convergence of the multi-UAVs into the position of maximizing MOS. Therefore, the proposed algorithm outperforms the conventional virtual force-based deployment scheme in terms of QoE for non-uniform user distribution scenarios.