• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.9
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• pp.4390-4407
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• 2019

The paucity of pilot signals in Massive MIMO system is a vital issue. To accommodate substantial number of users, pilot signals are reused. This leads to interference, resulting in pilot contamination and degrades channel estimation at the Base Station (BS). Hence, mitigation of pilot contamination is exigency in Massive MIMO system. The proposed Time Shifted Pilot Signal Transmission with Pilot signal Hopping (TSPTPH), addresses the pilot contamination issue by transmitting pilot signals in non-overlapping time interval with hopping of pilot signals in each transmission slot. Hopping is carried by switching user to new a pilot signal in each transmission slot, resulting in random change of interfering users. This contributes to the change in channel coefficient, which leads to improved channel estimation at the BS and therefore enhances the efficiency of Massive MIMO system. In this system, Uplink Signal Power to Interference plus Noise Power Ratio (SINR) and data-rate are calculated for pilot signal reuse factor 1 and 3, by estimating the channel with Least Square estimation. The proposed system also reduces the uplink Signal power for data transmission of each User Equipment for normalized spectral efficiency with rising number of antennas at the BS and thus improves battery life.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.54 no.11
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• pp.654-659
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• 2005

An improved power supply for APD(Avalanche Photo Diode) with a received optical power monitoring circuit allows the received optical power increase temporary without of the degradation of the electrical signal. For the cost reduction and simple fabrication, an improved power supply has been proposed that it was designed for driving a APD as a receiving device of a wireless optical transmission system. It was demonstrated that it was possible to improve a dynamic range by compensating the temperature coefficient of the APD up to 1.0 V/$^{\circ}C$ through the power supply. Also, for an efficient transmission at the receiver end, a simple structure of a single cylindrical micro-lens configuration was used in conjunction with the laser diode to partially compensate a laser beam ellipticity. For this purpose, an astigmatism introduced by the micro-lens is utilized for the additional compensation of the beam ellipticity at the receiver end. In this paper, it is demonstrated that an efficient beam shaping is realized by using the proposed configuration consisting of the single lens attached to the laser diode.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.1656-1660
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• 2008

Internal noise level of a train running in tunnel is influenced by sound transmission coefficients of floor, side door, window and gangway as well as by the sound power levels of major noise sources. The structure of a gangway should be strong enough for the safety of passengers while it should be flexible enough for the movement of a train in curves. Due to this the sound transmission coefficients of gangways are relatively low compared to those of carbody structure. The effect of the sound transmission coefficient of the gangway is studied in this paper in regards to the existence of end doors.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.9
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• pp.898-906
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• 2002

In this paper, we investigated the improvement degree of transmission distance of the various initial frequency chirped optical pulse with 5 dBm initial power dependence on the various bit rate and fiber dispersion coefficient, when MSSI(Mid-Span Spectral Inversion) with the optimal pump power condition is adopted for the compensation method for optical pulse distortion. And we analyzed the influence of mutual relation of optical pulse frequency chirp and Kerr effect on the MSSI methods for the long-haul optical transmission through the computer simulation. We found that the compensation degree of distorted optical pulse varies as a consequence of the variation of combined phase modulation of self phase modulation(Kerr effect) and initial frequency chirp parameter dependence on the fiber dispersion coefficient. And we found that, if the transmission bit rate is increased k times, the dispersion coefficient value of dispersion shift fiber is decreased $2^k$ times so as to be almost the same performance of the transmission system with k times lower bit rate.

• Journal of electromagnetic engineering and science
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• v.11 no.3
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• pp.156-160
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• 2011

We have proposed and analyzed an equivalent circuit for a magnetically coupled wireless power transmission (WPT) system between two loop resonators by considering its coupling coefficient and radiation-related parameters. A complete formulation is provided for all the necessary circuit parameters. The mechanism of radiation loss is sufficiently explained. The circuit and electromagnetic (EM) simulation results have been shown to be in good agreement. Based on the proposed circuit formulation, a specific load impedance for maximum WPT efficiency was found to exist. The proposed modeling of the WPT in terms of circuit characterizations provides sufficient insight into the problems associated with WPT.

• Proceedings of the KIEE Conference
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• 2002.07c
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• pp.1782-1784
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• 2002

In this paper, the coefficient of friction betwee and sheath in 345kv XLPE cable was measured the simulated inclinated condition of You-Youngdeungpo transmission line. The phenomena of slipping down the simu inclination was investigated theoretically usin measured data and was analyzed from experim result. The measured and analyzed result were conside be as a reference data for real installation of XLPE Youngseo-Youngdeungpo transmission line.

• Journal of electromagnetic engineering and science
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• v.16 no.2
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• pp.112-118
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• 2016

Alternative analytic expressions for the mutual inductance ($L_m$) and coupling coefficient (k) between circular loops are presented using more familiar and convenient expressions that represent the property of reciprocity clearly. In particular, the coupling coefficients are expressed in terms of structural dimensions normalized to a geometric mean of radii of two loops. Based on the presented expressions, various aspects of the mutual inductances and coupling coefficients, including the regions of positive, zero, and negative value, are examined with respect to their impacts on the efficiency of wireless power transmission.

• Journal of Advanced Navigation Technology
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• v.23 no.4
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• pp.309-315
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• 2019

This paper proposes an implementation of unequal power divider with 1:3 and 1:4 splitting ratio in multi-section structure using CPW and offset coupled transmission line. The power divider consists of a multi-section transmission line and a circuit with parallel capacitors and resistors. A multi-section transmission line was implemented by decomposing a ${\lambda}/4$ single transmission line terminated by an arbitrary impedance and converging it with a multi-section transmission line shorter than $90^{\circ}$ electrical length, and RC parallel circuits were connected between transmission lines to obtain reflection coefficient of output port and isolation characteristics between the output port. In this way, it was confirmed that the transmission lines at the unequal power divider designed at 2 GHz were shorter than ${\lambda}/4$ and implemented at least 27% less than the conventional ones, and that the broadband characteristics could be obtained.

• Journal of Power System Engineering
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• v.11 no.1
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• pp.92-97
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• 2007

It is important to compute the structural analysis of plate structures in structural design. In this paper, the author uses the finite element-transfer stiffness coefficient method (FE-TSCM) for the structural analysis of plate structures. The FE-TSCM is based on the concept of the successive transmission of the transfer stiffness coefficient method and the modeling technique of the finite element method (FEM). The algorithm for in-plane structural analysis of a rectangular plate structure is formulated by using the FE-TSCM. In order to confirm the validity of the FE-TSCM for structural analysis of plate structures, two numerical examples for the in-plane structural analysis of a plate with triangular elements and the bending structural analysis of a plate with rectangular elements are computed. The results of the FE-TSCM are compared with those of the FEM on a personal computer.

• Journal of Electrical Engineering and Technology
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• v.11 no.6
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• pp.1735-1743
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• 2016

Insulation of valve-side windings in converter transformer withstands pulsating voltages, which will produce more serious insulation problems. In this paper, the electric breakdown experiments of oil-paper insulation specimens were executed at pulsating voltages and different temperatures. Experiment and analysis results showed that the breakdown voltage decreased with increasing temperature under pulsating voltage. The influence of temperature proves to be more significant once the temperature exceeds a limitation threshold. A fitting formula between breakdown voltage and the temperature was reported. Finally, in order to clearly understand the breakdown properties under pulsating voltage, the electric field distribution and space charge behavior under pulsating voltage at different temperature were discussed.