• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권12호
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• pp.3055-3070
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• 2013

This paper proposes an improved carrier frequency offset (CFO) and sampling frequency offset (SFO) estimation scheme for orthogonal frequency division multiplexing (OFDM) based broadcasting system with cyclic delay diversity (CDD) antenna. By exploiting a periodic nature of channel transfer function, cyclic delay and pilot pattern with a maximum channel power are carefully chosen, which helps to enable a robust estimation of CFO and SFO against the frequency selectivity of the channel. As a performance measure, a closed-form expression for the achievable mean square error of the proposed scheme is derived and is verified through simulations using the parameters of the digital radio mondiale standard. The comparison results show that the proposed frequency estimator is shown to benefit from properly selected delay parameter and pilot pattern, with a performance better than the existing estimator.

• Current Optics and Photonics
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• 제2권1호
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• pp.34-38
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• 2018

An X-band microwave photonic (MWP) filter using switch-based fiber-optic delay lines has been proposed and experimentally demonstrated. It is composed of two electro-optic modulators (EOMs) and $2{\times}2$ optical MEMS-switch-based fiber-optic delay lines. By changing time-delay difference and coefficients of each wavelength signal by using fiber-optic delay lines and an electro-optic modulator, respectively, a bandpass filter or a notch filter can be implemented. For an X-band MWP filter with four channel elements, fiber-optic delay lines with the unit time-delay of 50 ps have been experimentally realized and the frequency responses corresponding to the time-delays has been measured. The measured frequency response error at center frequency and the time-delay difference error were 180 MHz at 10 GHz and 3.2 ps, respectively, when the fiber-optic delay line has the time-delay difference of 50 ps.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권9호
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• pp.2218-2230
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• 2012

In this paper, we propose an efficient channel delay estimation method for orthogonal frequency-division multiplexing (OFDM) systems, especially over doubly-selective fading channels which are selective in both the symbol time domain and subcarrier frequency domain. For the doubly-selective fading channels in single frequency network (SFN), long and strong echoes exist and thus the conventional discrete Fourier Transform (DFT) based channel delay estimation system often fails to produce the exact channel delay profile. Based on the analysis of the discrete-time frequency response of the channel impulse response (CIR) coefficients in the DFT-based channel delay estimation system, we develop a method to effectively extract the true CIR from the aliased signals by employing a simple narrow-band low-pass filter (NB-LPF). The performance of the proposed system is verified using the COST207 TU6 SFN channel model.

• 전자공학회논문지A
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• 제29A권2호
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• pp.33-40
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• 1992

The design method of signal delay line system using indirect frequency synthesizer is presented. The variable signal delay line system with 2[nsec] step of delay time at center frequency 60[MHz], bandwidth 500[KHz] and range 5.24-5.81[x10S0-6Tsec] is designed and fabricated. The results were met with good characteristics to be variable delay time of average 2.01[nsec] per step.

• 한국통신학회논문지
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• 제33권3A호
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• pp.248-255
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• 2008

OFDMA 시스템에서 주파수축에서의 다중사용자 스케줄링의 성능은 채널의 주파수 선택적 특성과 상관이 있다. 채널이 주파수축에서 평탄하면 다중사용자 스케줄링의 이득이 줄어들 수 있으며 반대로 주파수 선택적 특성이 너무 커서 할당 대역폭 내에서 채널의 변화가 심하게 일어난다면 충분한 스케줄링 이득을 얻기 어려워진다. 다중 사용자 스케줄링 이득을 최대화하기 위해서는 순환지연 다이버시티를 적용하여 채널의 주파수 선택적 특성을 조절할 수 있다. 이 논문에서는 할당 대역폭과 채널 특성을 고려하여 순환지연 다이버시티를 적용할 때의 최적의 지연값을 결정하는 방법을 제안한다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1999년도 하계종합학술대회 논문집
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• pp.29-32
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• 1999

In this study, the time delay model were simulated using the well-known AR model. Frequency response of the time delay model can be obtained by mapping AR model to JTC model in the time domain. That is, from the few measurement data in JTC model, the channel frequency response can be obtained by the estimation of AR model parameters. From this channel frequency response, the time delay model can be obtained using Fourier transformation. To prove the validity of the suggested method, three models of JTC were shown and analyzed.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 ITC-CSCC -1
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• pp.129-131
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• 2000

A new analog synchronous mirror delay to be used in the wide-bandwidth clocking circuits is proposed to overcome the frequency dependency of the negative-delay values in the conventional analog synchronous mirror delay. The scheme adopts a new dummy-delay compensation technique by adopting the comparator with inherent systematic offset to achieve the enhanced negative-delay range especially prominent at high frequency applications.

• 화약ㆍ발파
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• 제23권3호
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• pp.11-18
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• 2005

MS 지발 전기뇌관을 사용하는 발파형태에 있어 파형은 거리와 주파수 정도에 따라 인접 단차 간 간섭의 정도가 상이하다. 이 간섭의 정도는 계측지점에서 발파진동의 크기에 영향을 미친다. 본 연구에서는 40ms 간격으로 분리되어 기폭되는 MS 지발 발파의 협동장약 특성을 고찰하고 MS지발 발파에서 발파진동의 협력을 최소화 할 수 있는 주파수에 따른 시차 설계 방법을 제시하였다.

• 전자공학회논문지SC
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• 제37권3호
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• pp.44-54
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• 2000

본 논문에서는 표준 메모리 공정에 구현 가능한 주파수 적응성을 갖는 부지연 회로의 설계기법에 대해 제안한다. 제안하는 설계기법은 기본적으로 아날로그 SMD (synchronous mirror delay) 형태의 부지연 회로로서 입력클록의 주기와 구현하고자 하는 부의 지연 시간의 차이에 해당하는 시간을 아날로그 회로의 개념으로 측정하고 다음 번 주기에서 반복한다. 출력클록의 발생과 관련되는 부수적인 지연을 측정단의 앞 단인 지연모델 단에서 상쇄하는 기존의 SMB 기법과는 달리, 반복단에서 상쇄하는 새로운 기법을 통하여 넓은 부지연 범위를 구현하여 특히 고속동작에서의 부지연 특성을 원할하게 한다. 또한 넓은 범위의 주파수 동작범위를 구현하기 위해 해당하는 주파수 범위에서 아날로그 회로가 최적의 동작 조건을 갖추도록 하기 위한 새로운 주파수 감지기 및 최적조건 설정기법을 제안한다. 제안된 회로의 응용으로서 초고속 DRAM인 DDR SDRAM에 적용하는 예를 보였으며, 0.6㎛ n-well double-poly double-metal CMOS 공정을 사용하여 모의실험 함으로써 그 유용성을 입증한다.

• Journal of electromagnetic engineering and science
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• 제12권2호
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• pp.166-170
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• 2012

This paper presents a tunable composite right/left-handed (CRLH) delay line for a delay line discriminator that linearizes modulated frequency sweep in a frequency modulated continuous wave (FMCW) radar transmitter. The tunable delay line consists of 8 cascaded unit cells with series varactor diodes and shunt inductors. The reverse bias voltage of the varactor diode controlled the group delay through its junction capacitance. The measured results demonstrate a group delay of 8.12 ns and an insertion loss of 4.5 dB at 250 MHz, while a control voltage can be used to adjust the group delay by approximately 15 ns. A group delay per unit cell of approximately 1 ns was obtained, which is very large when compared with previously published results. This group delay can be used effectively in FMCW radar transmitters.