• The Journal of the Acoustical Society of Korea
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• v.28 no.2
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• pp.148-154
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• 2009

In audio coding, SBR technology synthesizes the high-bands using patched time-frequency information from low-bands and the correction parameters, Since SBR transmits only correction parameters for high-bands, it provides a low-rate coding of high-bands, and is used as a core module of MPEG-4 HE-AAC, SBR was originally designed for audio signal and its performance for speech signal tends to decrease, and the major reason is an excessive noise floor in high-bands which is caused by incorrect tonality computation, In this paper, a new method to determine noise floor level in an adaptive fashion according to the speech characteristics is proposed in order to solve the problem of SBR for speech signal, The proposed method maintains the compatibility with the standard SBR, and the subjective performance evaluation shows that the proposed method improves the SBR performance especially for male speech signal compared with the standard SBR.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.10
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• pp.1973-1981
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• 1994

A PLDRO(Phase Locked Dielectric Resonator Oscillator) in Ku-band(10.95-11.70GHz) is designed with the concept of the feedback property of PLL(Phase Locked Loop). A series feedback type DRO is developed, and VCDRO(Voltage Controlled Dielectric Resonator Oscillator) using a varactor diode as a voltage-variable capacitor is implemented to tune oscillating frequency electrically. Then, PLDRO is designed by using a SPD(Sampling Phase Detector). This PLDRO is phase-locked voltage controlled DRO to reference source(VHF band) by SPD at 10.00 GHz for European FSS(Fixed Satellite Service). The PLDRO generates output power greater than 10dBm at 10.00 GHz and has phase noise of -80 dBc/Hz at 10 KHz offset from carrier. This PLDRO achieves much better frequency stability than conventional VCDRO.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.5
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• pp.637-644
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• 2010

A vibration-powered piezoelectric energy harvester yields the maximum power output when its resonant frequency is made equal to the excitation frequency; however, the power output is dramatically decreased when the energy harvester is operated at off-resonance frequency. It has been observed that the resonant frequency of a piezoelectric energy harvester may change with time and that the excitation frequency often varies when the energy harvester is used in real applications. Hence, in this study, we propose a piezoelectric energy-harvesting module that is suitable for excitations in a certain frequency range. The frequency characteristics of the electrical output of the module are studied through analysis and experiment. A simple frequency tuning method is also suggested for the proposed energy-harvesting module; in this method, frequency tuning is achieved by changing the electrical connections between the constituent energy-harvesting units of the module.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.2
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• pp.167-173
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• 2009

This paper proposes an electronically beam steering array antenna, consisting of single fed active element and 4 parasitic elements, operating in 5.8 GHz ISM band. Beam steering can be achieved by controlling the reactance of the variable reactance control circuit connected to the load of the parasitic elements without using the high cost phase shifters. The proposed antenna realizes ${\pm}30^{\circ}$ beam scanning of E-plane and H-plane with the below -10 dB return loss in ISM band. The gain of the $6.18{\sim}7.53\;dBi$ in E-plane and $7.022{\sim}7.779\;dBi$ in H-plane is shown in the scanning range.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.5
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• pp.383-388
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• 2018

This paper presents a 1.8 GHz six-port-based impedance modulator using CMOS technology, which can select an arbitrary load impedance with switch control. The proposed 1.8-GHz impedance modulator comprises a Wilkinson power divider, three quadrature hybrid couplers, and four SP3T switches for each load impedance selection. The measured insertion loss of -13 dB and the input/output return losses of >10 dB are achieved in the range of 1.4~2.2 GHz. The low drop output regulator for a stable 3.3 V DC power and the serial peripheral interface(SPI) for an easy digital control are integrated. The chip size, including the pads, is $1.7{\times}1.8mm^2$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.5
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• pp.510-518
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• 2010

In this paper, the designed and implemented results of CFL linearization chip which can be used in mobile radio and TRS terminal of UHF band(380~910 MHz), using $0.6\;{\mu}m$ BiCMOS process based on Si, are shown. As gain control circuits for modifying transmit power are inserted not only in feedback path but also in forward path, the stability of CFL is maintained. And, DC-offset correction function of S/H structure, which is suitable for walkie-talkie PTT operation and is easily implemented, is realized. The performance test results of transmitter show that the regulation of FCC emission mask at PEP 3 W(34.8 dBm) is satisfied when the CQPSK modulated signal is fed and more than 30 dBc improvement of 3rd order IMD is achieved when two-tone signal is inputted.

• Journal of KIISE:Information Networking
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• v.30 no.2
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• pp.179-188
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• 2003

Advances in wireless networking technology has engendered a new paradigm of computing, called mobile computing, in which users carrying portable devices have access to a shared infrastructure independent of their physical locations. Wireless communication has some restraints such as disconnection, low bandwidth, a variation of available bandwidth, network heterogeneity, security risk, small storage, and low power. Power adaptation routing scheme overcome the shortage of power by adjusting the output power, was proposed. Existing power saving routing algorithm has some minor effect such as seceding from shortest path to minimize the power consumption, and number of nodes that Participate in routing than optimal because it select a next node with considering only consuming power. This paper supplements the weak point in the existing power saving routing algorithm as considering the gradual approach to final destination and the number of optimal nodes that participate in routing.

• Korean Journal of Optics and Photonics
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• v.9 no.3
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• pp.134-141
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• 1998

A high performance afocal zoom telescope has been designed to operate in the 7.6${\mu}{\textrm}{m}$ to 10.3${\mu}{\textrm}{m}$ waveband for thermal imaging system. This IR zoom telescope is characterized by using of two movable optical element groups, variator and compensator, with mechanically compensated method and the positioning of these groups is controlled by means of a computerized program. The optical performance over the entire 4:1 zoom range and $\pm$2.31~$\pm$9.36 degrees field of view is near diffraction limit while maintaining a constant F-number. The all refracting surfaces of this system except only one aspheric surface are spherical curvature and the material for the optical elements is selected Ge and ZnSe which is used for correction of chromatic aberration.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.10 s.352
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• pp.69-78
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• 2006

High spectral efficiency can be obtained by adaptive modulation in which the modulation scheme is changed according to the channel environment. Thus it is especially suitable to mobile channel which is a typical example of time-varying channel. It is required to determine the optimum thresholds of signal-to-noise ratio(SNR) to change the modulation scheme effectively according to mobile speeds. Thus the optimum thresholds for specific mobile speeds to get the required bit error rate(BER) of $10^{-6}$ are obtained with the powerful turbo code in this paper. In addition, the optimum thresholds for the continuous mobile speed are proposed by interpolation of the obtained results. And the error performance and average spectral efficiency are investigated at various mobile speeds and channel environments.

• Journal of Satellite, Information and Communications
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• v.11 no.2
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• pp.23-28
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• 2016

In this paper, we proposed the novel algorithm which controls the resolution of the HDMI(High Definition Multimedia Interface) by the channel estimation from WiFi-AP(Access Point) in the ISM(Industry-Science-Medical) band. The 2.4 and 5 GHz channel models are widely used since they have identical RF property as RSSI(Received Signal Strength Indication). Especially, the performance degradation of signal-transmission and streaming of WiFi will be occurred by the co-channel interference between AP(Access Point) and increased number of smart devices. Therefore, the optimization scheme of video format timing was designed by HDMI-CEC(Consumer Electronics Control) which considers the transmission speed of radio channel. The HDMI resolution, video quality of home-gateway and digital TV and the decision of PIP position can be maintained by the protocols between smart devices and DLNA(Digital Living Network Alliance) via proposed technique.