• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.10
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• pp.3887-3907
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• 2015

This paper introduces a full duplex single secondary user multiple-input multiple-output (FD-SSU-MIMO) cognitive radio network, where secondary user (SU) opportunistically accesses the authorized spectrum unoccupied by primary user (PU) and transmits data based on FD-MIMO mode. Then we study the network achievable average sum-rate maximization problem under sum transmit power budget constraint at SU communication nodes. In order to solve the trade-off problem between SU's sensing time and data transmission time based on opportunistic spectrum access (OSA) and the power allocation problem based on FD-MIMO transmit mode, we propose a simple trisection algorithm to obtain the optimal sensing time and apply an alternating optimization (AO) algorithm to tackle the FD-MIMO based network achievable sum-rate maximization problem. Simulation results show that our proposed sensing time optimization and AO-based optimal power allocation strategies obtain a higher achievable average sum-rate than sequential convex approximations for matrix-variable programming (SCAMP)-based power allocation for the FD transmission mode, as well as equal power allocation for the half duplex (HD) transmission mode.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.1
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• pp.69-75
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• 2011

As part of its space development program, Korea has a plan for the launch of a lunar orbiter and a lunar lander. To enable the transmission of lunar information based on multimedia, it is necessary to construct a communication system that is capable of transmitting large-volume telemetry data. The CCSDS standard recommends the deferred NAK mode as ARQ scheme for reliable long-distance deep-space communication systems. In this paper, we implement a space communication system simulator in the deferred NAK mode using models of the lunar orbiter, the earth station, and the space environment. The simulator employs modulation techniques and turbo coding schemes for transmitting large-volume telemetry data. We analyze the transmission performance of telemetry data through the simulation.

• Progress in Superconductivity
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• v.11 no.2
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• pp.106-111
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• 2010

Sapphire resonators with $YBa_2Cu_3O_{7-\delta}$ (YBCO) endplates have provided a way to realize extremely high quality factor due to the extremely low dielectric loss of sapphire and conductive loss of YBCO films, which enables to measure the low surface resistance of superconductor films at microwave frequencies. We present microwave properties of HTS sapphire resonators designed for measuring the surface resistance of HTS films at millimeter-wave frequencies by using the two-resonance mode dielectric resonator method. Despite enhanced surface resistance ($R_S$) of YBCO films due to the quadratic frequency dependence of the $R_S$, the unloaded quality factor ($Q_0$) of the $TE_{021}$ mode sapphire resonator still appears to be well above $1\;{\times}\;10^6$ at a mm-wave frequency of 38 GHz at 10 K. However, it appears that the $TE_{012}$ mode $Q_0$ is unexpectedly low despite that the corresponding resonance peak looks uncoupled with parasitic modes. We discuss possible reasons for the unexpected results using the surface resistance at the $TE_{021}$, $TE_{012}$, and $TE_{011}$ mode frequencies.

• Journal of electromagnetic engineering and science
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• v.4 no.2
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• pp.68-71
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• 2004

The limitation of telegrapher's equations for analysis of nonuniform transmission lines is investigated here. It is shown theoretically that the input impedance of a nonuniform transmission line cannot be derived uniquely from the Riccati equation only except for the exponential transmission line of a particular frequency-dependent taper. As an example, the input impedance of an angled two-plate transmission line is calculated by solving the telegrapher's equations numerically. The numerical results suffer from larger deviation from its rigorous solution as the plate angle increases.

• Journal of Advanced Navigation Technology
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• v.15 no.4
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• pp.571-577
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• 2011

This paper presents a novel balanced filter design based on a metamaterial structure applicable to differential-mode excitation. The metamaterial structure is based on a unit-cell which under a differential-mode excitation behaves like composite right/left-handed(CRLH) metamaterial with filter characteristics. In contrast, the metamaterial unit-cell is below cut-off under a common-mode excitation. Experimental results are used to verify the proposed metamaterial's differential-mode characteristics. The metamaterial is fabricated with a balanced filter design resulting in an operating frequency range of 960~1000 MHz with a insertion loss of 4.1 dB.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.26 no.2
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• pp.51-60
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• 2012

An improved method for detecting fault distance in overhead transmission lines is described in this paper. Based on single-ended measurement, propagation theory of traveling waves together with the wavelet transform technique is used. In estimating fault location, a simple, but fundamental method using the time difference between the two consecutive peaks of transient signals is considered; however, a new method to enhance measurement sensitivity and its accuracy is sought. The algorithm is developed based on the lattice diagram for traveling waves. Representing both the ground mode and alpha mode of traveling waves, in a lattice diagram, several relationships to enhance recognition rate or estimation accuracy for fault location can be found. For various cases with fault types, fault locations, and fault inception angles, fault resistances are examined using the proposed algorithm on a typical transmission line configuration. As a result, it is shown that the proposed system can be used effectively to detect fault distance.

• 제어로봇시스템학회:학술대회논문집
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• 1993.10b
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• pp.550-553
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• 1993

Methods of Alternating Noise Canceling were previously developed for the optical instrumentation;one using a dual photo sensor and another using a single photo sensor that could cancel normal mode noise on a transmission line, even if the noise was of equal status noise. But the methods could not remove noise on sensor line. This paper discusses a new method of using a photo sensor with a resistance sensordummy, effectively canceling equal status normal mode noise not only on a sensor line but also on a transmission line of an optical instrumentation. The accuracy of this method has been verified by experiments using sinusoidal wave as an equal status noise on a sensor line and/or rectangular wave as an equal status wide band noise on a transmission line respectively.

• International Journal of Precision Engineering and Manufacturing
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• v.3 no.3
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• pp.28-36
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• 2002

The continuously variable transmission (CVT) mechanism considered here is the output coupled type which combines the functions of a 2K-H I type differential gear unit and a V-belt type continuously variable unit (CVU). One shaft of the CVU is connected directly to the output shaft and another shaft of it is linked to the differential gear unit. It is shown that some fundamental relations (speed ratios, power flows and efficiencies) for twelve mechanisms previously described are valid by various experimental studies, six of them produce a power circulation and the others produce a power split. Parametric analysis is carried out in relation to the efficiency, speed ratio and power ratios in order to assist in the design of an optimum configuration. Some useful properties associated with power flow modes also are discussed in the output coupled type continuously variable transmission.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.11
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• pp.2817-2824
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• 1994

A torque split type multi-pass CVT(MPC) system consiting of CVT and planetary gear train with 4 clutches was suggested to overcome the inherent inferior acceleration performance of CVT. Also, a shifting algorithm of MPC was suggested for the two driving modes : (1) power mode and (2) economy mode. By using the shifting algorithm and the MPC vehicle dynamic model, numerical simulations were performed to estimate the performance of the MPC vehicle. Simulation results showed that comparing the performance of the conventional 4-speed automatic transmission, an improvement in acceleration can be obtained by MPC for the power mode and 31% improvement in fuel economy for the economy mode.

• Journal of electromagnetic engineering and science
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• v.2 no.1
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• pp.39-44
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• 2002

A high speed data link capability is one of the critical factors in determining the performance of the spaceborne SAR system with high resolution because of the strict requirement far the real-time data transmission of the massive SAR data in a limited time of mission. In this paper, based on the data lint model characterized by the spaceborne small SAR system, the high rate multi-channel data link module is designed including link storage, link processor, transmitter, and wide-angle antenna. The design results are presented with the performance analysis on the data link budget as well as the multi-mode data rate in association with the SAR imaging mode of operation from high resolution to the wide swath.