• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.6
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• pp.906-911
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• 2001

In this paper, LPI(low probability of intercept) and AJ(anti jamming) performance of the chirped BPSK system are analyzed. In the chirp method the cyclostationary of the signal is eliminated, since the instantaneous frequency is varied randomly within the whole spread bandwidth. Therefore, chirp method is considered for good LPI system against DAM(delay-and-multiplier) or SC (squaring circuit) interceptor which detects the chip rate or carrier frequency. Longer chirp duration makes the LPI performance better. From the simulation results, the chirp method has better AJ performance than DS(direct sequence) system in the PBNJ(partial band noise jammer) channel. At the same JSR(jammer to signal power ratio) level, chirped BPSK system has more robust AJ performance against MTJ(multi-tone jammer) than PBNJ.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.2
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• pp.138-141
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• 2018

In this paper, we describe the designed digital waveform of a linear frequency-modulated (FM) chirp signal using field-programmable gate arrays (FPGAs) for image radar, and this signal is modulated with an I-Q modulator, and multiplied by 24 frequency multipliers to obtain a 94-GHz W-band wideband chirp generator. The developed chirp generator is an FM signal with a 94-GHz carrier frequency and a 960-MHz bandwidth, and the flatness is less than 1.0 dB at intermediate frequency (IF) (3.9 GHz), 2.0 dB in the W-band, and it has a 0.3-W output power in the W-band.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.1
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• pp.1-7
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• 2003

A recent technology trends in synthetic aperture radar(SAR) requires the ultra high resolution performance in detecting and precisely identifying the targets. In this paper, as a technique for enhancing the radar range resolution, the wideband chirp connection algorithm is presented by stitching the several chirp modules with unit bandwidth based on the linear frequency modulated chirp signal waveform. The principles of the digital chirp signal generation and its architecture for implementation is briefly described, and the wideband chirp signal generator, modulator, and demodulator are designed. The performance analysis for the presented algorithm is given with the simulation results.

• Journal of electromagnetic engineering and science
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• v.5 no.1
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• pp.36-42
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• 2005

In this paper, the optimal position of optical phase conjugator(OPC) excellently compensating distorted WDM channels with initial frequency chirp due to both chromatic dispersion and self phase modulation(SPM) is numerically investigated. Highly-nonlinear dispersion shifted fiber(HNL-DSF) is used as a nonlinear medium of OPC in order to widely compensate WDM signal band. It is confirmed that if the OPC position was shifted from mid-way of total transmission length dependence on the initial frequency chirp as well as modulation format and fiber dispersion coefficient, it is possible to cancel the performance degradation owing to the initial frequency chirp. Using proposed configuration, it is possible to remove all in-line dispersion compensator, reducing span losses and system costs in the long-haul broadband WDM systems.

• Journal of Advanced Navigation Technology
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• v.6 no.2
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• pp.97-103
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• 2002

A recent technology trends in synthetic aperture radar(SAR) requires the ultra high resolution performance in detecting and precisely identifying the targets. In this paper, as a technique for enhancing the radar range resolution, the wide band chirp connection algorithm is presented by stitching the several chirp modules with unit bandwidth based on the linear frequency modulated chirp signal waveform. The principles of the digital chirp signal generation and its architecture for implementation is described with the wide band chirp signal generator, modulator, and demodulator. The performance analysis for the presented algorithm is given with the simulation results.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.3
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• pp.256-265
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• 2017

In this paper, an ascheme is proposed for multiuser underwater acoustic communication by using the multi-chirp rate signals. It differs from the well known TDMA (Time Division Multiple Access), FDMA (Frequency Division Multiple Access) or CDMA (Code Division Multiple Access), by assigning each users with different chirp-rate carriers instead of the time, frequency or PN code. Multi-chirp rate signals can be separated from each other by FrFT (Fractional Fourier Transform), which can be regarded as the chirp-based decomposing, and superior to the match filter in the underwater acoustic channel. VTRM (Virtual Time Reverse Mirror) is applied into the system to alleviate the ISI caused by the multipatch and make the equalization more simple. Results of computer simulations and pool experiments prove that the proposed multiuser underwater acoustic communication based on the multi-chirp rate exhibit well performance. Outfield experments carrie out in Xiamen Port show that using about 10 kHz bandwidth, four users could communicate at the same time with 425 bps with low BER and can match the UAC application.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.54 no.2
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• pp.116-123
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• 2005

Chirp spread spectrum method using both time and frequency component is fit to time varying channel such as powerline channel. The used chirp symbol based on the CEBus standard is the unit symbol which sweeps from 100kHz to 380kHz over a 25㎲. To evaluate the performance of between Chirp-SS and DSSS, we measured the bit error rate under Gaussian channel. Simulation result is shown that Chirp-SS has a about 3[dB] gain of SNR than DSSS. To verify the performance of implemented modem, it is made up the powerline channel environment. After adding several noises to it, we examined the receiving status of modem. The implemented modem is able to receive the signal over the powerline channel with having several noises and capacitive loads.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.11
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• pp.1186-1193
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• 2009

In this paper, we propose DDS(Direct Digital Synthesizer) as a new implementation method of chirp LO(Local Oscillator) for compressive receiver applied for RFID signal detection in UHF band. We designed a receiver whose input frequency range is 908.5~914 MHz, DDL(Dispersive Delay Line) bandwidth is 6 MHz, and dispersion delay time is $13\;{\mu}s$. Chirp LO based on DDS is designed to meet $26\;{\mu}s$ sweep time and 12 MHz bandwidth for complete compressive mechanism. The measured 3 dB pulse width of the compressed signal of the fabricated receiver is 260 ns and the frequency resolution for simultaneous input signals is below 200 kHz. These performances indicate that the proposed chirp LO based on DDS and the compressive receiver is suitable for RFID signal detection in UHF band.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.8
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• pp.988-995
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• 2019

In this paper, we propose the Tile Based Frequency Hopping - Chirp Spread Spectrum(TBFH-CSS) technique, which has excellent Low Probability of Intercept(LPI)/Anti-Jamming(AJ) performance. Conventional Frequency Hopping - Chirp Spread Spectrum(FH-CSS) technique uses only single chirp signal, that makes the follower jammer easy to find and jam. However, proposed TBFH-CSS uses various kind of chirp signals which are generated according to the structure of basis tile, it is composed the basis time unit and the basis bandwidth unit. The TBFH-CSS signal has variety signal period and signal bandwidth. Therefore, the follower jammer hard to find and difficult to jam the TBFH-CSS signal. We analysis the LPI/AJ performance of the TBFH-CSS technique when the follow jamming attack exist and compared with the performance of the conventional FH-CSS technique. From the analysis, we can see the proposed TBFH-CSS technique has better LPI/AJ performance than conventional technique.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.127-128
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• 2006

In this paper, we propose a novel signaling method using chirp signals in UWB radio with satisfaction of FCC regulation. Chirp signals have been used in many ranging systems such as radar because of its good correlation properties. Because it is important to use broader signal bandwidth in order to get higher precision of the ranging, according to the Cramer-Rao Lower Bound, UWB radio is extremely good as the ranging systems. But, it is very difficult to apply existing chirp signals to UWB, because FCC regulates that the systems operating in UWB radio must occupy signal bandwidth more than 500MHz on the condition of stopping the frequency sweeping. So, we propose multiple chirp signals which can satisfy the regulation of FCC while maintaining chirp signal's properties. The multiple chirp signals which are composed of the sub-chirps modulated by sub-carriers can expand the signal bandwidth with the same principle of OFDM systems. The simulation results show that the BER performance of the proposed multiple chirp signals is identical to that of conventional OFDM when it is applied to data communication, and that the correlation properties of the proposed signals are almost the same with properties as those of single chirp signals whose sweeping bandwidth is the same value with the proposed one.