• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.2A
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• pp.86-96
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• 2006

In recent year, EPON(Ethernet PON) system is expected to be more attractive solutions for high speed, broadband access networks in next generation access networks due to the conversionce of low-cost ethernet equipment and low-cost fiber infrastructure. Upstream channel control algorithm is essential to hare upstream bandwidth in EPON. In this paper, we suggest HUHG(High Utilization and Hybrid Granting) algorithm for supporting high bandwidth utilization and QoS for different service class. This algorithm improves bandwidth utilization as removing or diminishing idle time of upstream channel using characteristics of fixed EF(Expedited Forwarding) sub-cycle. The proposed algorithm also minimizes the packet delay and delay variation of EF class. We conduct detailed simulation experiments using OPNET to study the performance and validate the effectiveness of the proposed algorithm.

• Korean Security Journal
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• no.9
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• pp.237-260
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• 2005

Development of IT technology as well as arrival of information-oriented society raise the curtain of 'the era of Ubiquitous Computing', implying accessing computers beyond boundary of time and space. In this era, it is expected that IT paradigms and life-styles would be transformed immensely above the experiences of 20th century. However, improvement of technology summons a new risk of cyber terrorism which have not been in the past. Thus, it is urgent to prepare for the threats in the national level. This paper point out five major threats relating to 'the security in the era of Ubiquitous Computing'. : First, spread of threats in connection with BcN establishment, second, vulnerable information-security for wireless communication, third, leakage of private information, fourth, cyber terror and deterioration of security, fifth, security problems of Korea including the drain of military information and solutions in the views of organization, personnel, technology and budget, comparing with other countries.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.2
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• pp.83-90
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• 2000

In this paper, a stacked circular-disk microstrip 1${\times}$4 array antenna was designed and manufactured and tested to apply in next generation mobile communication, on IMT-2000 system(up-link: 1.885 GHz∼2.025 GHz, down-link: 2.11 GHz∼2.2 GHz) base station which has dual frequency, broadband and high-gain characteristics. The experimental results are as follows : resonant frequency of 1.885 GHz and 2.178 GHz VSWR (1.064 , 1.432), return loss (-30.19 dB , -24.99 dB), band width (VSWR<2) are 402 MHz, -3dB beam width at radiation pattern are ${\alpha}$E-16.8$^{\circ}$, ${\alpha}$H-69$^{\circ}$(1.885 GHz) and ${\alpha}$E-l5.2$^{\circ}$, ${\alpha}$H-51.5$^{\circ}$(2.178 GHz), gain(13.7 dBi∼15.21 dBi).

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.12
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• pp.55-67
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• 2010

The electrical properties of a back drilled via-hole (BDH) without the open-stub and the plated through via-hole (PTH) with the open-stub, which is called the conventional structure, in a high-count multi~layered (HCML) printed circuit board (PCB) were investigated for a high-speed digital system, and a selected inner layer to transmit a high-speed signal was farthest away from the side to mount the component. Within 10 GHz of the broadband frequency, a design of experiment (DOE) methodology was carried out with three cause factors of each via-hole structure, which were the distance between the via-holes, the dimensions of drilling pad and the anti-pad in the ground plane, and then the relation between cause and result factors which were the maximum return loss, the half-power frequency, and the minimum insertion loss was analyzed. Subsequently, the empirical formulae resulting in a macro model were extracted and compared with the experiment results. Even, out of the cause range, the calculated results obtained from the macro model can be also matched with the measured results within 5 % of the error.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.17 no.5
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• pp.128-134
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• 2018

In this paper, two ports feeding a microstrip patch antenna using a quadrature hybrid circuit was proposed to enhance the bandwidth for the global positioning system(GPS). The square patch was designed, and the probe feeding was applied. The quadrature hybrid chip circuit for two-port feeding was designed, and output ports that have a 90-degree phase difference feed to the patch antenna. The designed patch and quadrature hybrid circuit were implemented on an FR4 board, and were combined. The measurement of the bandwidth within a voltage standing wave ratio(VSWR) of 2:1 and axial ratio(AR) in 3dB were wide band as 29% BW (1,230~1,700 MHz) and 15.87% BW (1,400~1,650 MHz), respectively. Antenna gain were measured 2.75dBi at the center frequency.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.6
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• pp.169-173
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• 2014

In order to satisfy user's requirements of needs for various services and to efficiently use of frequency, a communication system using one platform can support many communication services. Tunable filters must be used in the front end of broadband communication systems which provide and support various communication methods. In this paper we design and implement a filter bank to verify the feasibility of cavity tunable filter with the operation frequency of 800 MHz ~ 1600 MHz. The filter bank is composed of five bandpass filters and each bandpass filter has the same operation frequency band of the tunable filter. The implemented filter bank has the maximum insertion loss of 0.326 dB, the bandwidth of 37 MHz ~ 84 MHz, and the attenuation of minimum 19.974dB and mximum 37.812dB at the band edge ${\pm}60MHz$ over the operating frequency band.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.8C
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• pp.803-811
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• 2002

Asynchronous Transfer Mode-Passive Optical Network(ATM-PON) Technology is one of the best solutions for implementation of broadband access network. In this paper, we propose a new Dynamic Bandwidth Allocation (DBA) algorithm for ATM-PON systems. The DBA is a key technique for data traffic management. DBA has been studied widely to allow ATM-PON to transport data traffic cost-effectively and efficiently, and currently a hot standardization issue in Full Service Access Network(FSAN) and ITU-T. The proposed DBA algorithm efficiently manages the user traffics according to their service categories. Performance of the proposed algorithm, in aspect of Cell Transfer Delay(CTD) and Cell Delay Variation(CDV), is evaluated using computer simulation.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.1
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• pp.78-84
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• 2008

In this paper, the reconfigurable annular ring slot antenna with circular polarization diversity is proposed for SDMB(Satellite Digital Multimedia Broadcasting) system. The proposed antenna consists of a ring slot with four tuning stubs. Four PIN diodes are attached to switch circular polarization diversity. By switching the diodes ON or OFF, the proposed antenna can be operated either RHCP mode or LHCP mode. The experimental result shows that the proposed antenna has an impedance bandwidth(VSWR${\leq}$2) of 570MHz(2.47-3.04GHz) at LHCP mode, an impedance bandwidth (VSWR${\leq}$2) of 560MHz(2.45-3.01GHz) at RHCP mode, a maximum gai of 3.1dBi at RHCP mode, 4.76dBi at LHCP mode. The 3dB CP bandwidth of about 100MHz at both RHCP and LHCP mode is achieved at the center frequency 2.63GHz. The proposed antenna is suitable for application such as mobile satellite communications, WLAN(Wireless Local Area Networks), and broadband wireless communication systems.

• Journal of IKEEE
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• v.24 no.2
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• pp.453-460
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• 2020

This paper, UHF band integrated communication antenna for ship communication is designed as a flat type that can be mounted on the integrated mast among integrated communication antennas such as integrated communication, ship communication, broadcasting, and telephone of the ship. The unified mast mounted antenna is an integrated communication antenna applied to the Navy's KDDX, which is an optimized type of integrated communication antenna including a 'composite slope' structure including operational capability, survivability, and improved operability and maintainability. The existing rotary radar and a plurality of monopole-type communication antennas were changed from an irregularly attached shape to the mast exterior to an integrated mast shape including a flat-type integrated communication antenna. the radar reflection area index (RCS) is significantly lowered and compared to overseas products. The goal is to develop a gain broadband antenna.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.3
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• pp.158-164
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• 2002

2-6 GHz digital phase shifter module has been designed and fabricated. For the broadband operation and performance, MMIC phase shifter chip for phase shifter module was designed and fabricated by using the reflection-type circuits with Lange coupler. The fabricated phase shifter module shows 6.1$^{\circ}$RMS phase error, 13.5 dB maximum insertion loss, and 8 dB and 10 dB input and output return losses, respectively. Computer controlled measurement systems are realized in order to get the measured data of 32 phase states. The RMS insertion phase error and the average insertion loss deviation among 8${\times}$8 modules for the phased-array system are less than ${\pm}$0.5$^{\circ}$and ${\pm}$0.5 dB, respectively. The size of fabricated phase shifter module is 45 ${\times}$ 22.5 ${\times}$60㎣.