• Proceedings of the KIEE Conference
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• 2002.07c
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• pp.1871-1873
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• 2002

Partial Discharge is radiated in the form of electromagnetic wave from variable sources. It can be taken by UHF antenna and the signal pulse from that has a nonstationary time-series which can be evaluated with several methods. One of them is STFT(short time fourier transform) processed in frequency region. Statistical results using STFT show the possibility being able to discriminate between several PD sources.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.41-45
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• 2006

To get accurate positions of GPS antennas, one should apply phase center variations (PCV) corrections in the data processing. Until recently, relative calibrations, originally proposed by National Geodetic Survey of United States, were the international standard. However, in late 2006, International GNSS Service will switch to absolute calibration methods. In this study, we compared the position differences caused by different PCV models, and their effects on the calculations of Precipitable Water Vapor (PWV) in the atmosphere. Data from ${\sim}40$ permanent GPS stations in Korea were processed and we found that the vertical position differences reach up to 5 cm, depending on the model selected. Also the PWV values varied quite significantly: the maximum bias in the computed PWV values was ${\sim}4$ mm.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.17 no.5
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• pp.1471-1483
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• 2023

One of the fastest-growing mobile services accessible today is mobile payments. For the safety of this service, the Near Field Communication (NFC) technology is used. However, NFC standard protocol has prioritized transmission rate over authentication feature due to the proximity of communicated devices. Unfortunately, an adversary can exploit this vulnerability with an antenna that can eavesdrop or alter the exchanged messages between NFC-enabled devices. Many researchers have proposed authentication methods for NFC connections to mitigate this challenge. However, the security and privacy of payment transactions remain insufficient. We offer a privacy-preserving, anonymity-based, safe, and efficient authentication protocol to protect users from tracking and replay attacks to guarantee secure transactions. To improve transaction security and, more importantly, to make our protocol lightweight while ensuring privacy, the proposed protocol employs a secure offline session key generation mechanism. Formal security verification is performed to assess the proposed protocol's security strength. When comparing the performance of current protocols, the suggested protocol outperforms the others.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.40.1-40.1
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• 2021

Gwacheon National Science Museum(GNSM) has a 7.2m radio telescope, which is only one possessed by a science museum in Korea. In 2020, performance of the telescope had been improved in the way of a new antenna control system, receiver system, control and analysis software. New AC motors, limiters and encoders was installed and the new receive system can observe L-band(1.4GHz) and S-band(2.8GHz), L-band and Ka-band(33GHz) equipped previously. Using theses upgraded system we have developed educational programs, which are 'The Sun seen in radio' and 'The Universe seen in radio'. In the former, the sun is observed with several methods and show analysed data to participants. In the latter, various radio sources, the moon, supernova remnants and HI gas, and even signal from artificial satellites are observed. In addition, SETI demo data can be shown and demonstrates how to find artificial signal extraterrestrial intelligence could send.

• Journal of Korea Society of Digital Industry and Information Management
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• v.8 no.4
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• pp.99-105
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• 2012

Recently, there are many user selection algorithms in multi user multiple-input multiple-output (MU-MIMO) systems. One of well-known user selection methods is Semi orthogonal user selection (SUS). It is an algorithm maximizing channel capacity. However, it is applicable only when user's antenna is one. We propose a generalized user selection algorithm regardless of the number of user's antennas. In the proposed scheme, Base station (Bs) selects the first user who has the highest determinant of channel and generates a user group that correlation with first user's channel is less than allowance of correlation. Then, each determinant of channels made up of first user's channel and a user's channel in the generated group is calculated and BS selects the next user who has the highest determinant of that. BS selects following users by repeating above procedure. In this paper, we get better performance because of selecting users who have the highest determinant of channel as well as allowance of correlation optimally calculated through matrix operations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.8
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• pp.896-902
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• 2016

In this paper, we investigate a minimum mean-squared error based nonlinear successive precoding method as a practical solution of dirty paper coding for multiuser downlink channels where each user has more than one antenna in the presence of other cell interference (OCI). Unlike conventional zero-forcing (ZF) based methods, the proposed scheme takes the OCI plus noise into account when suppressing the inter-cell multiuser interference, which results in improvement of the received signal-to-interference-plus-noise ratio. Simulation results show that the proposed scheme outperforms conventional methods in terms of sum rate for various OCI configurations.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.5
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• pp.84-90
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• 2012

Since the major cellular data service providers in U.S, Japan as well as in Korea started the LTE (Long Term Evolution) service, there has been more strong need for the methods that can accurately measure the MIMO (Multi Input-Multi Outout) OTA (Over The Air) performance of LTE handsets because the performance of the MIMO antenna determines the packet data rates in the downlink and therefore the higher system throughput of the network. In this regard, there has been a lot discussions in 3GPP on the candidate MIMO OTA test solutions. In this paper, a faire comparison has been done for the conventional method, the Envelop Correlation Coefficient (ECC) measurements, and the anechoic chamber based MIMO OTA test solution, one of the candidate system being discussed in 3GPP. The evaluations and the comparisons are conducted by numerically and experimentally.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.05a
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• pp.111-114
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• 2003

It has well known that MUSIC and ESPRIT algorithms estimate angle of arrival(AOA) with high resolution by eigenvalue decomposition of the covariance matrix which were obtained from the array antennas. In the case that 2-D large-sized array antenna is required, however, one of the disadvantages of MUSIC and ESPRIT is that they are computationally ineffective, and then they are difficult to implement in real time. To alleviate the computational complexity, several method using neural model have been study. For multiple signals, those methods require huge training data prior to AOA estimation. This paper proposes the algorithm for AOA estimation by interconnected hopfield neural model. Computer simulations show the validity of the proposed algorithm.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.5
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• pp.61-65
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• 2014

In this paper, we propose a method using cooperative spectrum sensing to avoid multipath and frequency selective fading. One of methods in conventional scheme was multi input multi output (MIMO) solution. However, in the wireless environment, mobile device hardly supports multi antenna because of limitation of hardware. Motivated from above problems, the proposed method provides the information of excellent channel to transmitter. As a result, quality of service (QoS) required by users can be satisfied. Finally, performance of the proposed protocol is analyzed in term of bit error rate (BER).

• Journal of Korea Society of Digital Industry and Information Management
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• v.5 no.3
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• pp.175-184
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• 2009

We are entering into a era of enterprise computing that is characterized by an emphasis on broadband convergence, knowledge s haring, and calm services. Some people refer to this as the "ubiquitous" computing because its focus is on a high degree of connectivity between a company and its customers, suppliers, and channel partners. Ubiquitous computing technology, "RF" stands for "radio frequency"; the "ID" means "identifer". The tag itself of a computer chip and an antenna. The shortest metaphor is that RFID is like a bar-code but is read with an electromagnetic field rather than by a laser beam. Much has already been written about the use of RFID. But there is no has written about the use of RFID in the convention industry. Therefore this study have specific objectives as follows. 1. To give details on the use of RFID in convention. 2. To introduces the key concepts behind RFID technology. 3. To identify advantage & disadvantage of RFID technology using a BEXCO CASE study. 4. To study on ubiquitous convention using RFID and effective operation methods such as entrance identification system, session management, machine management, CRM management, visitor management, and contents management. This results provide into the current status of ubiquitous computing technology in convention industries. Specific advantages by using ubiquitous computing technology(RFID) are one-stop differentiate service, wireless internet service, use of visitor management system, entrance by tag, and U-logistics. On other side, disadvantages are security, stabilization of RFID system, higher price of RFID tag, and commercial scale. Convention by using of RFID technology is currently at an early stage. Convention company as BEXCO need to have the capabilities to adapt, to customize, to commercialize, and to modify technology to suit our circumstances.