• The Journal of the Korea institute of electronic communication sciences
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• v.18 no.6
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• pp.1023-1030
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• 2023

FMCW LiDAR system with robust target detection capabilities even under adverse operating conditions such as snow, rain, and fog is addressed in this paper. Our focus is primarily on enhancing the performance of FMCW LiDAR by improving the characteristics of the frequency-modulated laser, which directly influence range resolution, coherence length, and maximum measurement range etc. of LiDAR. We describe the utilization of an unbalanced Mach-Zehnder laser interferometer to measure real-time changes of the lasing frequency and to correct frequency modulation errors through an optical phase-locked loop technique. To extend the coherence length of laser, we employ an extended-cavity laser diode as the laser source and implement a laser interferometer with an photonic integrated circuit for miniaturization of optical system. The developed FMCW LiDAR system exhibits a bandwidth of 10.045GHz and a remarkable distance resolution of 0.84mm.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.1
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• pp.49-56
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• 2006

In this paper, to overcome the effect of nonlinear power amplifier, CE-CPSK(Constant Envelope Continuous Phase Shift Keying)modulation method which has the constant envelope and continuous phase characteristics is proposed. The code acquisition performances of the CE-CPSK modulated system and BPSK system are analyzed. And the performance is evaluated in terms of mean acquisition time and detection probability with the output backoff of the amplifier in multiuser environment. Results performed in a channel having a high degree of AM nonlinearity(AM-to-AM conversion), have shown that the CE-CPSK signal, when passed through class C-nonlinear Amplifier, has a spectrum with greatly reduced sidelobes compared to the conventional BPSK signal. The code acquisition performance of a CE-CPSK modulation system is better than that of BPSK system with nonlinear amplified multiuser environments.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.11
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• pp.1759-1766
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• 2001

Vibration transient generated by developing localized fault in gear can be used as indicators in gear fault detection. In this paper, we propose the zoomed phase map for a fault signal using continuous wavelet transfers to detect this vibration transient. Local fault induces the abrupt fluctuation of load exciting tooth and phase lag in the vibration signal measured on the gearbox. The relatively large fault like "tip breakage" easily can be detected by the clear fluctuation of exciting load. However, minor fault like "initial pitting"cannot be detected using the load fluctuation. To defect this kind of minor fault, the phase map for a fault signal is taken into account. The phase lag by minor fault is observed well in the zoomed phase map.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.05a
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• pp.568-573
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• 2002

In this paper, the Viterbi decoder containing new branch metrics of the squared Euclidean distance with multiple order phase differences is introduced in order to improve the bit error rate (BER) in the differential detection of the trellis-coded MDPSK-OFDM. The proposed Viterbi decoder is conceptually same as the Continuous multiple phase differential detection method that uses the branch metric with multiple phase differences. Also, we describe the Viterbi algorithm in order to use this branch metrics. Our study shows that such a Viterbi decoder improves BER performance without sacrificing bandwidth and power efficiency Also. the proposed algorithm ran be used in the single carrier modulation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.11
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• pp.1190-1196
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• 2014

This paper presents the design of a Frequency Modulated Continuous Wave(FMCW) radar altimeter with wide altitude range and low measurement errors. Wide altitude range is achieved by employing the optic delay in the transmitting path to reduce the dynamic range of measuring altitude. Transmitting power and receiver gain are also controlled to have the dynamic range of the received power be reduced. In addition, low measurement errors are obtained by improving the sweep linearity using the Direct Digital Synthesizer(DDS) and minimizing the phase noise employing the reference clock(Ref_CLK) as the offset frequency of the Phase Locked Loop(PLL).

• Korean Journal of Optics and Photonics
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• v.19 no.3
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• pp.175-181
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• 2008

We develop a fiber optic acceleration sensor with LED, PD, POF, and a cantilever beam, having film grating at the edge of the beam. Light is transmitted from LED to PD through the film grating. When the cantilever beam moves by external vibration, output light is modulated as sinusoidal signals. The characteristics of output signals are dominated by the spacing of the film grating and also by the size and the elasticity of the beam. Two output signals, having constant initial phase difference, are obtained by two gratings with 90 degree phase difference. Those two signals are used to determine phase angle, which is proportional to the displacement of the beam. Finally, the acceleration is determined from conversion equation between displacement and acceleration. This sensor is designed for monitoring the vibration of large and complex building in the low frequency range of below 7 Hz, and is particularly suitable to measure acceleration in electromagnetic environments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.10C
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• pp.942-948
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• 2003

In this paper, we analyze the performance of multiple trellis coded modulation applied to continuous phase frequency shift keying (MTCM/CPFSK) for the noncoherent receiver without channel state information (CSI) on the interleaved Rician fading channel. In this system, the squared cross-correlation between the received signal and a candidate signal is used as the branch metric of the Viterbi decoder. To obtain the bit error performance of this system, we analyze the approximated pairwise error probability (PEP) and the exact PEP. We also derive the equivalent normalized squared distance (ENSD) and compare it with the ENSD of the noncoherent receiver with perfect CSI. Simulation results are also provided to verify the theoretical performance analysis.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.4
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• pp.535-543
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• 2002

In this paper, we propose $\pi$/8 shift 8PSK and trellis-coded $\pi$/8 shift 8PSK-OFDM techniques by applying $\pi$/4 shift QPSK to trellis-coded modulation (TCM), and performing signal set expansion and set partition correspondingly based on phase difference. In our Viterbi decoding algorithm, up to L phase differences from successively received symbols are employed in the new branch metrics. Such sliding multiple symbol detection (SMSD) method provides improved bit-error-rate (BER) performance in the differential detection of the trellis-coded $\pi$/8 shift 8PSK-OFDM signals. The performance improvements are achieved for different communication channels without sacrificing bandwidth and power efficiency. It thus makes the proposed modulation and sliding detection scheme more attractive for power and band-limited systems.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.6
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• pp.51-57
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• 2017

In this paper, we designed a frequency synthesizer using DDS (Direct Digital Synthesizer) for Ka-band compact Radar. DDS is applied to generate various waveform and to cover high-speed frequency sweep. In order to reduce size, waveform generator and Ka band frequency up-converter are integrated in one module. Proposed frequency synthesizer provides LFM(Linear Frequency Modulation) waveform and Phase modulated FMCW (Frequency Modulation Continuous Wave) waveform. It is observed that fabricated synthesizer performs $0.191{\mu}sec$ frequency switching time and -89.16 dBc/Hz phase noise at offset 1 kHz.

• Investigative Magnetic Resonance Imaging
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• v.7 no.1
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• pp.12-21
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• 2003

Purpose : In order to overcome limitations in the existing conventional spectrometer, a new spectrometer with advanced functionalities is designed and implemented. Materials and Methods : We designed a spectrometer using the TMS320C6701 DSP capable of 1 giga floating point operations per second (GFLOPS). The spectrometer can generate continuously varying complicate gradient waveforms by real-time calculation, and select image plane interactively. The designed spectrometer is composed of two parts: one is DSP-based digital control part, and the other is analog part generating gradient and RF waveforms, and performing demodulation of the received RF signal. Each recover board can measure 4 channel FID signals simultaneously for parallel imaging, and provides fast reconstruction using the high speed DSP. Results : The developed spectrometer was installed on a 1.5 Tesla whole body MRI system, and performance was tested by various methods. The accurate phase control required in digital modulation and demodulation was tested, and multi-channel acquisition was examined with phase-array coil imaging. Superior image quality is obtained by the developed spectrometer compared to existing commercial spectrometer especially in the fast spin echo images. Conclusion : Interactive control of the selection planes and real-time generation of gradient waveforms are important functions required for advanced imaging such as spiral scan cardiac imaging. Multi-channel acquisition is also highly demanding for parallel imaging. In this paper a spectrometer having such functionalities is designed and developed using the TMS320C6701 DSP having 1 GFLOPS computational power. Accurate phase control was achieved by the digital modulation and demodulation techniques. Superior image qualities are obtained by the developed spectrometer for various imaging techniques including FSE, GE, and angiography compared to those obtained by the existing commercial spectrometer.