• Information and Communications Magazine
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• v.26 no.5
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• pp.30-35
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• 2009

본고에서는 무선 가시광 통신을 위한 Medium Access Control (MAC) 프로토콜의 설계에 관해 기술한다. 조명등을 이용한 가시광 무선랜 네트워크는 고정된 상태의 Access Point (AP)에 의한 인프라를 Mobile Node (MN)를 상대로 구성하고 인터넷과 같은 기존의 인프라와 연결되는 구조적 특징을 가진다. 이러한 네트워크에 사용되는 무선 가시광 통신 채널의 특성을 이해하고 MAC프로토콜의 기능에 대한 요구조건을 도출하였다. 주어진 가시광 통신 채널을 효율적으로 사용할 수 있도록 시 분할다중 접속 방식과Full duplex를 도입하는 Frame 구조를 구성하였고 가시성을 이용한 접속 절차를 제안하였다.

• JSTS:Journal of Semiconductor Technology and Science
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• v.16 no.6
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• pp.719-727
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• 2016

This paper proposes a unified medium access control (MAC) design methodology and presents the implementation of the IEEE 802.11ac down-link multi-user multi-input and multi-output wireless local area network MAC using the proposed design methodology. The proposed methodology employs unified code for both network simulation and system implementation. Because the unified code closely relates these two processes, the performance of the implemented MAC system can be estimated before implementation. The MAC architecture for an access point implemented using the proposed design methodology is verified on an ARM-based platform, and it is applied to a 65 nm CMOS library.

• Journal of Korea Multimedia Society
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• v.20 no.2
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• pp.396-403
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• 2017

In recent years, the use of touch screens has expanded, and devices such as remote controllers have been developed in various ways to control and access contents at long range. The wireless-based touch screen is used in classroom, seminar room, and remote video conversation in addition to the TV remote control. The purpose of the study is to design a smart phone-based intuitive interface that can perform the role of a wireless mouse and a wireless keyboard at range using Bluetooth and to develop an application that integrates functions of a mouse and a keyboard. Firstly, touch interaction model for controlling software such as PowerPoint by connecting to a general PC on a smart phone has been studied. The most simple touch operation interface is used to reproduce the function of existing devices and design more simply. The studies of the extension of interfaces with various functions are important, but development of optimized interfaces for users will become more important in the future. In this sense, this study is valuable.

• Journal of Communications and Networks
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• v.11 no.5
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• pp.518-528
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• 2009

IEEE 802.11 wireless local area network (WLAN) has become the prevailing solution for wireless Internet access while transport control protocol (TCP) is the dominant transport-layer protocol in the Internet. It is known that, in an infrastructure-based WLAN with multiple stations carrying long-lived TCP flows, the number of TCP stations that are actively contending to access the wireless channel remains very small. Hence, the aggregate TCP throughput is basically independent of the total number of TCP stations. This phenomenon is due to the closed-loop nature of TCP flow control and the bottleneck downlink (i.e., access point-to-station) transmissions in infrastructure-based WLANs. In this paper, we develop a comprehensive analytical model to study TCP dynamics in infrastructure-based 802.11 WLANs. We calculate the average number of active TCP stations and the aggregate TCP throughput using our model for given total number of TCP stations and the maximum TCP receive window size. We find out that the default minimum contention window sizes specified in the standards (i.e., 31 and 15 for 802.11b and 802.11a, respectively) are not optimal in terms of TCP throughput maximization. Via ns-2 simulation, we verify the correctness of our analytical model and study the effects of some of the simplifying assumptions employed in the model. Simulation results show that our model is reasonably accurate, particularly when the wireline delay is small and/or the packet loss rate is low.

• Journal of electromagnetic engineering and science
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• v.19 no.1
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• pp.20-30
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• 2019

A wide-band multiple-input multiple-output (MIMO) antenna with dual-band (2.4 and 5 GHz) operation is proposed for premium indoor access points (IAPs). Typically, an omni-directional pattern is used for dipole antennas and a directional radiation pattern is used for patch antennas. In this paper, both antenna types were used to compare their performance with that of the proposed $2{\times}2$ MIMO antenna. We simulated and measured the performance of the MIMO antenna, including the isolation, envelope correlation coefficient (ECC), mean effective gain (MEG) for the IAPs, and the throughput, in order to determine its communication quality. The performance of the antennas was analyzed according to the ECC and MEG. The proposed antenna has sufficient performance and excellent characteristics, making it suitable for IAPs. We analyzed the communication performance of wireless networks using the throughput data of a typical office environment. The network throughput of an 802.11n device was used for the comparison and was conducted according to the antenna type. The results showed that the values of the ECC, MEG, and the throughput have unique characteristics in terms of their directivity, antenna gains, isolation, etc. This paper also discusses the communication performance of various aspects of MIMO in multipath situations.

• Journal of the Korea Society of Computer and Information
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• v.20 no.3
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• pp.75-80
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• 2015

Vulnerability management is in compliance with security policies, and then, this is to ensure the continuity and availability of the business. In this paper, the application vulnerability management and IT infrastructure of the system is that it must be identified. And a viable vulnerability management plan should be drawn from the development phase. There are many that are not defined vulnerability in the area of identification and authentication, encryption, access control in identification and classification of vulnerabilities. They define the area without missing much in technical, managerial, and operational point of view. Determining whether the response of the identified vulnerability, and to select a countermeasure for eliminating the vulnerability.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1384-1385
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• 2006

Platinum is a candidate of top and bottom electrode in ferroelectric random access memory and dynamic random access memory. High dielectric materials and ferroelectric materials were generally patterned by plasma etching, however, the low etch rate and low etching profile were repoted. We proposed the damascene process of high dielectric materials and ferroelectric materials for patterning process through the chemical mechanical polishing process. At this time, platinum as a top electrode was used for the stopper for the end-point detection as Igarashi model. Therefore, the control of removal rate in platinum chemical mechanical polishing process was required. In this study, an addition of $H_{2}O_{2}$ oxidizer to alumina slurry could control the removal rate of platinum. The removal rate of platinum rapidly increased with an addition of 10wt% $H_{2}O_{2}$ oxidizer from 24.81nm/min to 113.59nm/min. Within-wafer non-uniformity of platinum after chemical mechanical polishing process was 9.93% with an addition of 5wt% $H_{2}O_{2}$ oxidizer.

• Journal of Internet Computing and Services
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• v.10 no.2
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• pp.29-40
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• 2009

The development of information technology such as the internet has brought about rapidly changes the old medical technology, e-Healthcare has been to raise social issue. The e-Healthcare which new turning point of paradigm in the medical information develops the medical policy in Korea and the technology, the prospective of reverse engineering in internet environment is incurring problems such as distribution of critical information and invasion and infringement of privacy, etc. In this research, we suggest the Role Based Access Control System, HPIP-e-Healthcare Privacy Information Protection, for solving above problem. The HPIP is composed 4 mechanisms such as Consolidate User Identity, Hospital Authorization, Medical Record Access Control, Patient Diagnosis and we are also prototyping the HPIP for feasible approach in the real computing environment.

• Journal of Power Electronics
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• v.11 no.2
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• pp.194-201
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• 2011

The air flow supplied to a fuel cell system is one of the most significant factors in determining fuel efficiency. The conventional method of controlling the air flow is to fix the oxygen supply at an estimated constant rate for optimal efficiency. However, the actual optimal point can deviated from the pre-set value due to temperature, load conditions and so on. In this paper, the maximum efficiency point tracking (MEPT) algorithm is proposed for finding the optimal air supply rate in real time to maximize the net-power generation of fuel cell systems. The fixed step MEPT algorithm has slow dynamics, thus it affects the overall efficiency. As a result, the variable step MEPT algorithm is proposed to compensate for this problem instead of a fixed one. The complete small signal model of a PEM Fuel cell system is developed to perform a stability analysis and to present a design guideline. For a design example, a 1kW PEM fuel cell system with a DSP 56F807 (Motorola Inc) was built and tested using the proposed MEPT algorithm. This control algorithm is very effective for a soft current change load like a grid connected system or a hybrid electric vehicle system with a secondary energy source.

• Journal of KIISE:Information Networking
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• v.28 no.4
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• pp.527-539
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• 2001

The wireless asynchronous transfer mode (ATM) system has the advantage of providing the broadband services with various quality-of-service requirements to the mobile terminal efficiently by utilizing the ATM technology developed for the wired ATM system. The available bit rate (ABR) service among various ATM services utilizes the available bandwidth remaining in the ATM link, which allows the efficient bandwidth usage. During the handoff of the mobile terminal, however, the queue length in the access point (AP) which resides in the boundary of the wired ATM network and the wireless ATM network may increase abruptly. In this paper, we propose a scheme which prevents the buffer-overflow and buffer-underflow in the AP during the handoff of the wireless ABR connection in the wireless ATM system using binary feedback rate-based ABR traffic control. This scheme controls the source's cell generation rate during both handoff period and some time interval after the completion of the handoff procedure. The simulation results show that the proposed scheme prevents the buffer-overflow and buffer-underflow. The proposed scheme can contribute to increasing the throughput of the wireless ABR service during handoff by preventing the buffer overflow and underflow during handoff period.