• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2006.07a
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• pp.529-529
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• 2006

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.4 no.3
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• pp.18-29
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• 1993

In single mode fiber optic transmission systems(FOT's) operated at high modulation rates over long fiber spans, chromatic dispersion can produce distortion in the demodulated waveforms, resulting in intersymbol interference(ISI) in the received signal and a reduction of transmission system performance. In this paper, chromatic dispersion limitations for intensity modulation and direct detection(IM-DD) systems are studied by considering the effect of phase modulation to amplitude modulation (PM-AM) conversion noise. Laser phase noise conversion to amplitude noise due to fiber chromatic dispersion is analyzed by deriving the noise power spectral density. We first derive the noise power spectral density of the laser phase noise to intensity noise conver- sion. Next, also evaluate the system power penalty and the transmitter laser linewidth required to avoid PM-AM conversion noise penalties in long-haul nonregenerative transmission system using an external modulator and optical amplifiers. For such system with optical amplifiers, transmission sys- tem length is limited due to fiber chromatic dispersion, even if an ideal external modulator is used.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.8
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• pp.1687-1694
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• 2011

In this paper, we propose the design procedure of a digital IF system for the OFDM based WLAN system and examine its performances. Along with the decision procedure of ADC sample rate, NCO frequency and the required decimation ratio, we show the decimation ratio is accomplished through the use of a CIC filter and a MHBF. We also show that the amplitude distortion occurred in the decimation filters can effectively be compensated by a ISOP filter and an additional FIR filter, which leads to the reduction of the overall hardware complexity. Finally, we examine the BER performance of the proposed system and compare it with a theoretical one that excludes filter non-linearities.

• 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 the Korea Institute of Information and Communication Engineering
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• v.19 no.3
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• pp.697-707
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• 2015

This paper covered the design and implementation of the demodulation receiver in the ADS-B 1090ES system, which is one of the CNS/ATM's surveillance systems. This researched demodulation performed at the level required by RTCA DO-268B and EUROCAE ED-129. The single signal process method, which applies a baseline multi-sample technique among multi-amplitude sample demodulations, was suggested to improve the quality of the receiver signal, the dynamic range and so on. The suggested multi-signal level tuning method has enhanced the single-signal process method, reducing the unstable reception ratio by the transmit output level difference and manufacturing receiver hardware. The result was that the receiver suggested by the method had 0~87dBm in dynamic range and -90dBm in MTL. This shows a better performance by -3dBm less than the international standard in ADS-B 1090ES ground receiver equipment. The systems which use a similar modulation method, will be considered to be widely applied.

• Journal of the korean Society of Automotive Engineers
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• v.18 no.3
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• pp.45-54
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• 1996

최근 자동차의 안전성을 한층 강조하는 ASV 개념의 도입이 보편화되면서 이를 구현하기 위한 여러가지 기능들이 고안되어 지고 있는데, 그 중에서도 추돌경보 및 회피기능, 야간보행자 검지기능, 후측방 장애물검지 기능, 차간거리 일정유지 제어기능 등에 있어서 공통적으로 주행중 거리계측이 필요하다. 본고에서는 ASV기술에서 필요하고 또한 중요한 핵심기술인 차량탑재용 거리계측기술에 대하여 현재 실용화되어 있거나 실용가능성이 있는 기술을 수단과 방식으로 나누어 각각의 원리와 특징에 대해 소개하였다. 수단으로서는 초음파, 레이저, 밀리파를 제시하였으며, 방식으로는 펄스시간차방식, 진폭변조 및 위상복조방식, 주파수변조방식을 소개하였다. 또한 비젼은 이들과는 계측원리와 신호처리가 매우 상이하고 본특집에서 별도로 상세히 소개될 것이기 때문에 간략히 소개하였다.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.9
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• pp.6-12
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• 1999

It is difficult to realize adaptive main carrier rejection circuit in feedforward-type LPA(Linear Power Amplifier) because the gain and nonlinear characteristics of power amplifier are changed according to operating frequency, voltage, temperature. Usually, pilot tones are used for adaptive LPA operation. but in this paper, the relative phase, which in obtained through I&Q demodulator using input signals as LO signals and main-path & sub-path signals as RF signals, and the magnitude of main-path & sub-path signals are compared, so main carrier rejection is obtained. The proposed method rejects main carriers by 28.34 ~ 34.66dB (@Po=36.2 ~ 28.2 dBm/tone) with two tones at 877MHz, 882MHz and also rejects main carriers by 31.3dB despite changing condition of operating voltage.

• Journal of Advanced Navigation Technology
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• v.2 no.1
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• pp.53-60
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• 1998

This paper describes some design concepts and design parameters of RZ-SSB which allows full carrier insertion into the single side band to overcome the severe fading in aeronautical telecommunication, and it is described in ARINC Spec. in the name of AME(AM Equivalent), and the necessary transmission bandwidth of RZ-SSB is similar to that of a aeronautical telecommunication. As an amplitude limiter manage to remove the amplitude fading without degrading the quality of output signal, the receiver acts like the FM demodulators. Using the digital Signal Processing(DSP) techniques in the design of transceiver systems has become a performance enhancement of the signal quality and reliability, and making use of DSP, it's able to design low cost, compact transceiver and reduce its weight. For avionics systems is able to eliminate the inherent disadvantages in RZ-SSB, the results of experimental tests suggest that the adoption of RZ concepts is suitable for aeronautical telecommunication transceiver systems use in HF band.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.1 s.116
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• pp.15-23
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• 2007

A simple six-port direct conversion QPSK receiver which is made up of a six-port phase correlator, a signal power detector, and I/Q channel signal de-modulator is designed and implemented in this paper. The output phase signals of six-port phase correlator are also analysed. On the basis of $90^{\circ}C$ phase relation among the six-port phase correlator output signals, the QPSK de-modulation circuit is designed by a simple circuit. The six-port phase correlator is made up of $90^{\circ}$ hybrid branch line and power detector. The six-port phase correlator, which is designed in frequency range of 11.7 to 12.0 GHz, gets the phase error characteristics less than $5^{\circ}$. By considering matching network and amplitude balance in the designed fiequency range, the designed six-port direct conversion QPSK receiver demodulates the I and Q signals with performance less than $5^{\circ}$ phase error.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.9C
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• pp.831-839
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• 2006

In this paper, we present an exact and general expression involving two-dimensional Gaussian Q-functions for the bit error rate (BER) of hierarchical MPSK with I/Q phase and amplitude imbalances over an additive white Gaussian noise (AWGN) channel. First we derive a BER expression for the k-th bit of hierarchical 4, 8, 16-PSK signal constellations when Gray code bit mapping is employed. Then, from the derived k-th bit BER expression, we present the exact and general average BER expression for hierarchical MPSK with I/Q phase and amplitude imbalances. This result can readily be applied to numerical evaluation for various cases of practical interest in an I/Q unbalanced hierarchical MPSK system, because the one- and two-dimensional Gaussian Q-functions can be easily and directly computed usinB commonly available mathematical software tools.