• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.9
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• pp.952-958
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• 2014

In this paper, we propose a parametric sparse recovery algorithm(SRA) applied to a radar signal model, based on the compressive sensing(CS), for the ISAR(Inverse Synthetic Aperture Radar) image reconstruction from an incomplete radar-cross-section(RCS) data and for the estimation of rotation rate of a target. As the SRA, the iteratively-reweighted-least-square(IRLS) is combined with the radar signal model including chirp components with unknown chirp rate in the cross-range direction. In addition, the particle swarm optimization(PSO) technique is considered for searching correct parameters related to the rotation rate. Therefore, the parametric SRA based on the IRLS can reconstruct ISAR image and estimate the rotation rate of a target efficiently, although there exists missing data in observed RCS data samples. The performance of the proposed method in terms of image entropy is also compared with that of the traditional interpolation methods for the incomplete RCS data.

• The Journal of the Acoustical Society of Korea
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• v.38 no.5
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• pp.580-586
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• 2019

In this paper, we propose a biomimetic communication method using a dolphin whistle to covertly transmit the communication signal. A conventional CSS (Chirp Spread Spectrum) modulation technique divides dolphin whistle into several slots and modulates with up and down chirp signals. That causes the time-frequency characteristic difference between the original dolphin whistle and the camouflage performance is degraded. In this paper, we propose a delay based modulation scheme to eliminate distortions. The simulation results show that the bit error rate of the proposed method is better performance than that of the conventional CSS modulation method by about 3.5 dB to 8 dB. And the camouflage performance that evaluated through the cross correlation in the time-frequency domain is also better than that of the CSS modulation method.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.122-122
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• 2013

In this talk, some optical properties of quantum dot based mode-locked diode lasers and photonic crystal nano lasers will be discussed. Linewidth enhancement factor, chirp and interband injection locking technique of quantum dot mode-locked lasers will be presented. Also various types of photonic crystal buried heterostructure lasers toward coherent nano laser will be covered as well.

• Aerospace Engineering and Technology
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• v.9 no.2
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• pp.105-115
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• 2010

This technical paper describes and summarizes the flight test results for the longitudinal and lateal-directional dynamic stability characteristics. The target aircraft is the 4-seat carnard type aircraft, FireFly, which has been developed by KARI. Airborne sensors and real-time telemetry system are constructed to obtain the flight test data. The dynamic stability characteristics should be analyzed and tested by estimaitng the aerodynamic parameters in the dymaic equations of motion. The maximum likelihood estimation technique has been applied to the flight data from chirp, 3211, and doublet control inputs.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.10
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• pp.91-97
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• 1998

The modulation performance of 10 Gbps electro-absorption InGaAsP/InGaAsP strain compensated MQW (Multiple Quantum Well) modulator module depends on the modulator as well as the package parasitics. The high frequency package parasitics resulting from various structural discontinuities, limit the modulation bandwidth and increase the chirp-parameter. Therefore, we propose the double bondwires embedded in dielectric materials to minimize the bondwire parasitics. Using the proposed structure with 50 $\Omega$ terminating resistor, the modulation bandwidth is greatly increased by 125 % than the bare chip and the chirp-parameter is also reduced. This technique can be used in optimizing the package of high speed external modulators.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.4C
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• pp.453-459
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• 2009

Due to its capability to resist jamming signals, chirp spread spectrum (CSS) technique has attracted much attention in the field of wireless communications. However, there has been little rigorous analysis for the performance of CSS systems in the presence of jamming signals. In this paper, thus, we present analytic results on the performance of a CSS system: specifically, symbol error rate (SER) expressions are derived for a CSS M-ary phase shift keying (MPSK) system in the presence of broadband and tone jamming signals, respectively. The numerical results show that the empirical SER closely agree with the analytic result.

• Proceedings of the IEEK Conference
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• 2001.06d
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• pp.151-154
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• 2001

In this Paper, a new harmonic imaging technique is proposed and evaluated experimentally. In the proposed method, a weighted chin signal with a hanning window is transmitted. The RF samples obtained on each array element are individually compressed by correlating with the reference signal defined as the 2nd harmonic (2f0) component of a transmitted chirp signal generated in a square-law system. The proposed method uses the compressed 2f0 component to form an image, for which the crosscorrelation term with f0 component should be suppressed below at least -60dB. After experiment, the 6dB pulse width and peak sidelobe level of the compressed 2f0 component were 0.7us and -60dB, respectively. This result shows that the proposed method can successfully eliminate the f0 component with a single transmit-receive event and therefore is more efficient than the conventional pulse inversion (PI) method in terms of frame rate. We also observed that the 2nd harmonic compont starts to decrease for source pressure higher than 210kPa in water, which implies that SNR of the 2nd harmonic imaging using short pulses cnanot be incresed beyond a certain limit.

• Journal of Biomedical Engineering Research
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• v.23 no.1
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• pp.61-72
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• 2002

In this parer, a new harmonic imaging technique is Proposed and evaluated experimentally. In the Proposed method. a weighted chirp signal with a hanning window is transmitted. The RF samples obtained on each array element are individually compressed by correlating with the reference signal defined as the 2nd harmonic component($2f_0$) of a transmitted chirp signal generated in a square-law system. The correlator output will then consist of the compressed version of the $2f_0$ component generated in tissue and the crosscorrelation sequence of the fundamental($f_0$) and 2f$_{0}$components. The Proposed method uses the compressed $2f_0$ component to form an image. for which the crosscorrelation term should be suppressed below at least -50dB. The Proposed method has two process, 2f$_{0}$-correlation and $2f_0$-correlation(PI) . $2f_0$-correlation can successfully eliminate the $f_0$ component with a single transmit-receive events and therefore is more efficient than the conventional Pulse inversion method in terms of the frame rate. 2i)-correlation(Pl) Performs pulse compression after applying pulse inversion method for the 2nd harmonic image with high resolution and SNR. Another advantage of the proposed method is that the SNR of 2nd harmonic imaging can be improved without limitation by increasing the duration of the chirp signal. The proposed method was verified through both the computer simulations and actual experiments .ts .

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.3
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• pp.292-298
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• 2013

A signal processing technique is introduced in this paper in order to estimate the lengths of missile targets. To measure the length of a target, it is necessary to know the information on the target's location and aspect angle. Chirp waveforms and stretch processing are used to estimate the location and angle of a missile as well as HRRP(High Resolution Range Profile). RELAX(relaxation) algorithm, which is one of the spectral estimation techniques, were used to find scattering centers of a missile from HRRP. From the information on the distribution of one-dimensional(1-D) scattering centers on a target, we can discriminate the length of a missile.

• The Journal of the Acoustical Society of Korea
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• v.32 no.4
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• pp.308-316
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• 2013

A set of experiments (Shallow Water 2006, SW06) was carried out in shallow water near the New Jersey shelf break in summer 2006. Significant fluctuations in direct and surface reflected arrivals were observed from the chirp data (1100~2900 Hz) measured on a vertical line array. This paper presents a geoacoustic inverssion technique for short-range acoustic data with fluctuating arrivals and inversion results of experimental data. In order to reduce effects of random sea surface on the inversion, the acoustic energy back-propagated from the array to the source through direct and bottom-reflected paths is defined as the objective function. A multi-step inversion scheme is applied to the data using VFSR (Very Fast Simulated Reannealing) optimization technique. The inversion results show a source depth oscillation period equal to the measured ocean surface wave period. The inverted bottom sound speed is 1645 m/s and is similar to that estimated by other work at the same site.