• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.11
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• pp.5610-5624
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• 2017

A novel scheme based on polarization modulation and the weighted fractional Fourier transform (PM-WFRFT) is proposed in this paper to enhance the physical layer security of dual-polarized satellite systems. This scheme utilizes the amplitude and phase of the carrier as information-bearing parameters to transmit the normal signal and conceals the confidential information in the carrier's polarization state (PS). After being processed by WFRFT, the characteristics of the transmit signal (including amplitude, phase and polarization state) vary randomly and in nearly Gaussian distribution. This makes the signal very difficult for an eavesdropper to recognize or capture. The WFRFT parameter is also encrypted by a pseudo-random sequence and updated in real time, which enhances its anti-interception performance. Furthermore, to prevent the polarization-based impairment to PM-WFRFT caused by depolarization in the wireless channel, two components of the polarized signal are transmitted respectively in two symbol periods; this prevents any mutual interference between the two orthogonally polarized components. Demodulation performance in the system was also assessed, then the proposed scheme was validated with a simulated dual-polarized satellite system.

• Journal of Digital Contents Society
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• v.10 no.2
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• pp.189-198
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• 2009

In this paper, we propose a method to improve the performance of orthogonal frequency division multiplexing (OFDM) receivers by using oversampling the received signals. Demodulation of the received OFDM signals is to detect the amplitude and phase components of the subcarriers. From the oversampled OFDM signals, we can get redundant informations in frequency domain for the data, which are different in phase but the same in amplitude. By using these properties, we can obtain signal to noise ratio (SNR) gain by the oversampling ratio compared to the receivers which sampled with symbol rate. In this paper, we propose oversampled receivers whose oversampling ratio is expanded from integer to general rational number. Through computer simulations, we show the validity of the proposed methods by comparing the performance of the receivers with nonideal band-limiting filters.

• Journal of Institute of Control, Robotics and Systems
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• v.5 no.7
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• pp.787-793
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• 1999

A self-sensing magnetic suspension system utilizing a LC resonant circuit is proposed by using the characteristic that the inductance of the magnetic system is varied with respect to the air gap displacement. An external capacitor is added into the electric system to make the levitation system be statically stable system, which much relieves the control effort required to stabilize the magnetic suspension system of haying an intrinsic unstable nature. For the realization of the self- sensing magnetically levitated system, an amplitude modulation / demodulation method is used with a positive position feedback controller Experimental results are presented to validate the proposed method.

• Journal of electromagnetic engineering and science
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• v.7 no.4
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• pp.201-206
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• 2007

When the M-ary signal experiences the Rayleigh fading, the diversity schemes can reduce the effects of fading since the probability that all the signals components will fade simultaneously are reduced considerably. The symbol error probabilities for various M-ary signals, such as MDPSK, MPSK and MQAM, are mathematically derived for the SC-2(Selection Combining 2) demodulation system, whereby the two signals with the two largest amplitudes are coherently combined among the L branches. On the other hand, maximum ratio combining(MRC) requires the individual signals from each path to be time-aligned, cophased, optimally weighted by their own fading amplitude, and then summed. The propagation model used in this paper is the frequency-nonselective slow Rayleigh fading channel corrupted by the Additive White Gaussian Noise(AWGN). The numerical results presented in this paper are expected to provide information for the design of radio system using M-ary modulation method for above mentioned channel environment.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.51 no.6
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• pp.272-277
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• 2002

This paper deals with the vibration deflection shape measurement technique for a sinusoidally excited structure using a continuously scanning laser Doppler vibrometer (CSLV). The CSLV output signal is an amplitude-modulated vibration in which the excitation signal is modulated by the deflection shapes, and thus the deflection shapes of vibration defined along a scan line can be derived by the envelop and the phase information of the CSLV output signal. In this work, a Hilbert transform based approach has been proposed for measurement of deflection shapes. This technique is as simple as the demodulation technique and allows more convenient experimental settings than the Fourier transform approach. The feasibility of the proposed technique is illustrated along with results of experiment.

• Journal of the Optical Society of Korea
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• v.18 no.3
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• pp.288-291
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• 2014

This paper presents a new method for measuring the half-wave voltage $V_{\pi}$ of an electro-optic phase modulator based on a phase-modulated photonic link with interferometric demodulation. By using this method, the $V_{\pi}$ can be obtained with the RF voltage amplitude input required to achieve 1-dB gain compression of link and the differential delay of a Mach-Zehnder interferometer. We measure the $V_{\pi}$ of a commercial phase modulator by using the presented method and the carrier/the first sideband intensity ratio method. Furthermore, we compare the two measurements with the typical value provided by the manufacturer. The experiment shows that this novel measurement method is feasible, straightforward, and accurate.

• Journal of Biomedical Engineering Research
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• v.16 no.1
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• pp.95-100
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• 1995

In this study, we have evaluated the effect of amplitude and frequency perturbation of EGG signal for single vowels associated with laryngeal pathology. The normal EGG signal was properly characterized by an autoregressive model which has an optimal order of ninth using the parametric method. This can be analyzed by determining the transfer function. Perturbations in the fundamental pitch and in the peak amplitude of EGG signal measured with a four-electrode system using the modulation/demodulation techniques were investigated for the purpose of developing a decision criteria for the laryngeal function analysis. The abnormal EGG signal has nonperiodic and unstable characteristics. It can be discriminated by the calculation of opening and closing time of glottis using the EGG signal. In case of normal and abnormal subjects, m$\pm$0.5*sd was discriminating line for frequency perturbation and m$\pm$2*sd for normal amplitude perturbations, respectively. Also, The normal and abnormal cases of the subjects can be discriminated effectively using the pattern of attractor derived with Hilbert transform of EGG signal.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.10
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• pp.156-161
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• 2007

In a TDD system, the length of slots can be unequal, and the number of downlink (DL) and uplink (UL) slots per frame can be different as well. The advantage of using TDD is the capability to accommodate asymmetric high-bit-rate services for the DL and It, which will be one of the prominent features in 4G systems. This paper analyzes the performance of TDD system on mobile channel environments like indoor pedestrian and vehicular channel, and proposes optimum modulation/demodulation method in TDD system. A rectangular QAM (RQAM) used in various communication systems has good BER performance but the much more signal amplitudes also have become one of the barriers to implement receiver. While PSK receiver is implemented easily because it has a constant amplitude, but it's BER performance is worse than RQAM. APSK proposed in this paper integrates merits of RQAM and PSK, and minimizes demerits of then And a simple method is also proposed to demodulate the soft symbol. The results indicate that the proposed APSK has a little worse performance than RQAM but the dynamic range of APSK is about 4 dB, 8 dB better than RQAM at 16-ary, 64-ary modulation/demodulation respectively.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.1
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• pp.139-146
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• 2017

The ISDB-T(Integrated Service Digital Broadcasting Terrestrial) can be used in the multipath and impulsive noise, also it provide good performance over mobile reception environment since it use the OFDM(Orthogonal Frequency Division Multiplexing) based transmission technology and time interleaving technology. One segment and full segment are divided according to the number of the assigned segment. And one-segment broadcasting receiver can design and implement without high levels of technology than the full-segment broadcasting receiver using 64QAM(64 Quadrature Amplitude Modulation) since it uses QPSK(Quadrature Phase Shift Keying) modulation/demodulation. However, it has a constraint in the display size and resolution due to data-rate limits. In this paper, we design and implementation of full-segment ISDB-T receiver module which support HD resolution for set-top box, digital TV, navigation. In experimental results, the implemented full-segment ISDB-T receiver module was satisfactory for all of the desired functions.

• Journal of Broadcast Engineering
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• v.24 no.3
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• pp.485-494
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• 2019

A software-driven real-time frequency de-modulator is implemented with the aid of universal-serial-bus (USB) type software defined radio dongle. An analog stereo frequency modulation (FM) broadcast signal is down-converted to the basedband analog signal then converted to digital bit streams in the USB dongle. Computer software such as Matlab, Python, and GNU Radio manipulates the incoming bit streams with the technique of digital signal processing. Low pass filtering, band pass filtering, decimation, frequency discriminator, double sideband amplitude demodulation, phase locked loop, and deemphasis function blocks are implemented using such computer languages. Especially, GNU Radion is employed to realize the real-time demodulator.