• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.7
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• pp.573-581
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• 2014

We proposed a hopping phase estimator to demodulate the received signals without any hopping information in frequency hopping spread spectrum systems. The demodulation process in this paper is as follows: hopped frequency tracking is accomplished by choosing a frequency component with maximum amplitude after taking discrete Fourier transform and a hopping frequency estimator which estimates the phase generated by hopped frequency is established through difference product and down-sampling. We obtained the probability density function and variance performance of the proposed estimator and confirmed that the analysis and the simulation results were agreed with each other.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.9
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• pp.912-918
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• 2003

In this paper, we designed and implemented the dual band monopole antenna for cellular CDMA(Code Division Multiple Access) and IMT-2000(International Mobile Telecommunication 2000) repeater. The antenna was designed by using 3D simulations program, HFSS(High Frequency Structure Simulator). Electrical characteristics were measured by using HP 8720C network analyzer and measured maximum S$\_$11/ was -10.9 dB for all frequency bands of interests in Cellular CDMA and IMT-2000. Simulation results for antenna gain at 859 MHz and 2027.5 MHz were 2.38 dBi and 4.02 dBi respectively with omni directional radiation pattern. The size of implemented antenna is compact and the antenna can be produced in low cost enough for commercialization.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.9A
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• pp.2141-2152
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• 1998

In this paper, we design and implement an indoor wireless modem using small signal of ISM band regulation, which can tranceive reliable data streams. We use direct sequence spead spectrum (DS-SS) signaling with synchronous BPSK and QPSK modulation, convolutional coding with viterbi decoding. The radio frequency module uses frequency devision duplexing in 900 MHz band, and the digital module is implemented with FPGAs for the purpose fo ASIC design. The perfomrance of our own acquistion and tracking circuit consisting digital matched filter and decision logic is proved by experiments, and the possibility of file transfer at indoor environment with the entrie system that the modem is connected the PC through RS-232C port is verified.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.2C
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• pp.99-104
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• 2011

The chirp spread spectrum (CSS) technique spreads the data signal over a frequency bandwidth wider than minimum required bandwidth. By using time overlapping, the bit rate in CSS can be increased. However, for reliable transmission of data signal, the intersymbol interference (ISI) due to overlap should be analyzed. In this paper, the relation between the degree of overlap and ISI is analyzed in direct modulation binary phase shift keying CSS systems. In some cases, the overlap does not incur ISI at all and the ISI fluctuates or monotonically increases as the number of overlaps changes. It is also shown that the simulation results closely agree with the analytic results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.11
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• pp.1124-1131
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• 2014

The chirp spread spectrum (CSS) technique that transmits data signal by using a chirp signal is often used for maritime wireless communication systems such as sound detection radar systems for submarines. However, maritime multipath environment could reduce the data rate of the CSS system. To tackle the problem, an overlap-based CSS transmission scheme is proposed and analyzed in this paper: Based on the approximated Gaussian Q function, we derive a closed form expression of the bit error rate (BER) of the proposed overlap-based CSS system and investigate the mathematical relationship between the number of overlaps and the intersymbol interference (ISI).

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.4
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• pp.8-12
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• 2003

Characteristics of optical transceiver module in radio frequency(RF) band were investigated with TO-can packaged Fabry-Perot laser diode(FP-LD). R-L-C parameters for equivalent circuit model of the LD were extracted with an impedance analyzer. With this model, impedance matching to the packaged LD could be performed by eliminating inductive components of the leads in the package by using lumped chip capacitors that have opposite reactance, while it shows resonance dip in low frequency band. The resonance dip could be removed using lumped elements for impedance matching by shifting the resonance frequency to the region out of interest.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.7
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• pp.1249-1255
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• 2008

1530nm band has been studied as pump wavelength for long-wavelength-band erbium-doped fiber amplifier (L-band EDFA). The pump source is built using a tunable light source and cascaded conventional-band (C-band) EDFA. The L-band EDFA uses a forward pumping scheme. Within the 1530nm band, 1545nm pump demonstrates 0.45dB/mW gain coefficient, which is twice better than that of conventional 1480nm pumped EDFA. The noise figure of 1530nm pump is at worst 6.36dB, which is 0.75dB higher than that of 1480nm pumped EDFA. Such high gain coefficient indicates that the L-band EDFA consumes low power.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2022.11a
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• pp.390-391
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• 2022

Recently, SpaceX, private enterprise dealing in space development company, has reported a plan for launching of low earth orbit satellites via Starlink Business, and launched 900 satellites until now. Concretely, it plans tp operate Ku/Ka band satellite, and launch 7,518 of V band satellites for broadband communication. Therefore, wireless communication service for ship will be provided, and various solutions will be offered through the low earth orbit satellites. In this work, we investigated RF characteristics of coplanar waveguide employing periodic 3D coupling structures, and examined its potential for a development of marine radio communication FISoC (fully-integrated system on chip) semiconductor device.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.12
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• pp.1359-1364
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• 2012

The C-band semi-lumped lowpass filter with broad stopband and compact size characteristic using chip inductor is proposed. To provide an additional attenuation pole in stopband by SRF, a separable inductor is added to proposed structure, and it has broad stopband characteristic. The third order elliptic function lowpass filter with chip inductor(L: 9.1 nH, SRF: 5.5 GHz, Q: 25) has insertion loss of 0.38 dB, cutoff frequency of 920 MHz, broad stopband(below 20 dB) of 1.43~7.8 GHz and the size is reduced 37.4 % compared to distributed inductor.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.346-346
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• 2009

저손실 고투자율 특성을 갖는 $\alpha$-Fe 나노결정 자심재료를 제조하기 위해 열처리 온도를 변화시켰으며 투자율과 신호전송 특성을 측정한 결과 $510^{\circ}C$에서 열처리된 자심재료에서 가장 우수한 특성을 얻었다. 저주파 대역에서의 신호전송 특성은 자심재료의 자기적 특성에 지배적인 영향을 받으며, 고주파 대역의 신호전송 특성은 임피던스 매칭으로 향상시킬 수 있었다. 에어-캡은 $500{\mu}m$ 이상 적용할 때, 100 A이상까지 안정적인 특성을 발휘하였다. 그리고 고역통과 필터의 설계와 신호결합장치에의 적용을 통해 통신대역 이외의 노이즈를 제거할 수 있었다.