• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.1
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• pp.108-122
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• 2014

Massive antenna array is an attractive candidate technique for future broadband wireless communications to acquire high spectrum and energy efficiency. However, such benefits can be realized only when proper channel information is available at the transmitter. Since the amount of the channel information required by the transmitter is large for massive antennas, the feedback is burdensome in practice, especially for frequency division duplex (FDD) systems, and needs normally to be reduced. In this paper a novel channel feedback reduction scheme based on the theory of distributed compressive sensing (DCS) is proposed to apply to massive antenna arrays with spatial correlation, which brings substantially reduced feedback load. Simulation results prove that the novel scheme is better than the channel feedback technique based on traditional compressive sensing (CS) in the aspects of mean square error (MSE), cumulative distributed function (CDF) performance and feedback resources saving.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.1
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• pp.177-190
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• 2011

The purpose of this study is to explore the determinants of actual demand for wireless broadband (WiBro) services in Korea. To this end, this study identifies conceptual definitions of diverse latent variables and determines the significance of the causal relationship between independent and dependent variables. It then presents the nomadic user concept by testing the moderator effect. This study also proposes a revised Unified Theory of Acceptance and Use of Technology (UTAUT) model, which is an appropriate model for wireless communication services and users' attributes. Prior research has concentrated exclusively on the Technology Acceptance Model (TAM) based on future potential users. Compared to previous studies, the current research model and analysis results are useful in not only academic but also industry contexts.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.9
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• pp.1596-1612
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• 2011

Coordinated Multi-Point (CoMP) transmission / reception is being studied in Long Term Evolution-Advanced (LTE-A) for future evolution of the $3^{rd}$ Generation Partnership Project (3GPP) LTE. Support of soft handover is essential for improving the performance of cell edge users. CoMP provides a natural framework for enabling soft handover in the LTE system. This paper evaluates the soft handover gain in LTE-A downlink. Mathematical analysis of signal to interference plus noise ratio (SINR) gain and the handover margins for soft handover and hard handover are derived. CoMP system model is developed and an inter-cell and intra-cell interference model is derived, taking into account the pathloss, shadowing, cell loading, and traffic activity. Reference signal received power (RSRP) is used to define the triggers and the measurements for soft handover. Our results indicate that parameter choices such as handover margin and the CoMP set size impact CoMP performance gain.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.9
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• pp.1653-1667
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• 2011

Privacy is one of the most important and difficult research issues in ubiquitous computing. It is qualitative rather than quantitative. Privacy preserving mainly relies on policy based rules of the system, and users cannot adjust their privacy disclosure rules dynamically based on their wishes. To make users understand and control their privacy measurement, we present a scheme to quantize the personal privacy. We aim to configure the person's privacy based on the numerical privacy level which can be dynamically adjusted. Instead of using the traditional simple rule engine, we implement this scheme in a complex way. In addition, we design the scenario to explain the implementation of our scheme. To the best of our knowledge, we are the first to assess personal privacy numerically to achieve precision privacy computing. The privacy measurement and disclosure model will be refined in the future work.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.1
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• pp.24-45
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• 2012

In this paper, we present a survey of security and privacy preserving issues in M2M communications in Cyber-Physical Systems. First, we discuss the security challenges in M2M communications in wireless networks of Cyber-Physical Systems and outline the constraints, attack issues, and a set of challenges that need to be addressed for building secure Cyber-Physical Systems. Then, a secure architecture suitable for Cyber-Physical Systems is proposed to cope with these security issues. Eventually, the corresponding countermeasures to the security issues are discussed from four aspects: access control, intrusion detection, authentication and privacy preserving, respectively. Along the way we highlight the advantages and disadvantages of various existing security schemes and further compare and evaluate these schemes from each of these four aspects. We also point out the open research issues in each subarea and conclude with possible future research directions on security in Cyber-Physical Systems. It is believed that once these challenges are surmounted, applications with intrinsic security considerations will become immediately realizable.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.1
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• pp.46-63
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• 2012

The concept of an "intelligent building" received significant attention from academic, industry and standard development organizations when technically termed a building management system (BMS). Wireless sensor networks (WSNs) and their recent development enhanced monitoring and control applications for the building's areas. This paper surveys and analyzes advantages of the main current and emerging approaches that may be fit for BMS. Specifically, we discuss challenges including interoperability, integration, overhead, and bandwidth limitation of WSNs in BMS. Based on analyses, we highlight the advantages of an IP-based and RESTful architecture approach as the most suitable solution for BMS using WSNs (BMS-WSN). The paper also describes our future direction and design for BMS-WSN based on these advantages. The purpose is to enable interaction of users with BMS-WSN in the same way as with any website while ensuring energy efficiency. A test-bed implementation and evaluation of a BMS application is also introduced in this paper to demonstrate the feasibility and benefits of IP-based and RESTful architecture for BMS.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.9
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• pp.3250-3265
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• 2014

Integrated WiMAX and WiFi networks is of great potential for the future due to the wider coverage of WiMAX and the high data transport capacity of WiFi. However, seamless and secure handover (HO) is one of the most challenging issues in this field. In this paper, we present a novel vertical HO authentication scheme with privacy preserving for WiMAX-WiFi heterogeneous networks. Our scheme uses ticket-based and pseudonym-based cryptographic methods to secure HO process and to achieve high efficiency. The formal verification by the AVISPA tool shows that the proposed scheme is secure against various malicious attacks and the simulation result indicates that it outperforms the existing schemes in terms of communication and computation cost.

• Proceedings of the Korean Information Science Society Conference
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• 2007.10b
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• pp.212-216
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• 2007

3D 스캐너의 보급으로 3차원 모델 생성이 가능하게 되었으나 결과로 얻은 형상이 아직 사진에서와 같은 사실적 묘사에 미치지 못하고 있다. 본 논문에서는 얼굴의 3D 스캔 데이터에 효율적인 텍스처 매핑을 통해 사실적 렌더링 결과를 얻을 수 있는 방법을 기술한다. 3D 얼굴 스캔 데이터와 얼굴의 사진 이미지의 좌표를 정확하게 맞추어 3D 스캔 데이터와 얼굴 이미지의 버덱스를 매치시켜주고, 얼굴 이미지의 해당 버텍스에 들어 있는 칼라 값을 3D 스캔 데이터의 버텍스에 넘겨주는 텍스처 매핑을 구현한다. 본 논문에서는 정면, 좌측, 우측 3장의 이미지를 이용하여 간단히 멀티텍스처 매핑을 수행하는 방법과 이 때 발생하는 사진 간의 경계선에서 발생하는 문제 해결에 대해 기술한다.

• Journal of Korea Multimedia Society
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• v.24 no.9
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• pp.1211-1223
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• 2021

Internet of Things(IoT) services have increased the demand for connectivity among electronics devices. As a result, various types of novel wireless communication technologies have been standardized and developed. In this paper, we evaluate the performance of low power wireless communication technologies such as Bluetooth, IEEE 802.15.4, DASH 7, IEEE 802.15.4g, LoRa, and SigFox in various environments. This is the first experiment evaluating various low power wireless communication technologies in real testbed. We expect that the evaluation results will be useful data to other researchers in applying the IoT technology in the future.

• International Journal of Internet, Broadcasting and Communication
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• v.13 no.2
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• pp.36-42
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• 2021

This study aims to examine whether there are some differences in the cost stickiness of R&D expenses of IT companies before and after the COVID-19 crisis. Before COVID-19, IT companies did not reduce R&D expenses even if sales decreased, resulting in cost stickiness. As a result, it appears that during the COVID-19, IT companies adjust R&D expenses in proportion to changes in sales. This is interpreted as a reduction in R&D investment, which takes a long time to create results, in case of a decrease in sales due to uncertainty in future management performance due to the COVID-19 pandemic. In other words, during the COVID-19 risk period, IT companies, like other companies, reduced R&D expenses as sales decreased, resulting in reduced cost stickiness. This study differs from existing literature in that it examines the impact of the COVID-19 pandemic on the R&D expenditure behavior of companies in the IT industry.