• ETRI Journal
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• 제41권3호
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• pp.316-325
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• 2019

Accurate suppressive jamming is a prominent problem faced by radar equipment. It is difficult to solve signal detection problems for extremely low signal to noise ratios using traditional signal processing methods. In this study, a joint sensing dictionary based compressed sensing and adaptive iterative optimization algorithm is proposed to counter suppressive jamming in information domain. Prior information of the linear frequency modulation (LFM) and suppressive jamming signals are fully used by constructing a joint sensing dictionary. The jamming sensing dictionary is further adaptively optimized to perfectly match actual jamming signals. Finally, through the precise reconstruction of the jamming signal, high detection precision of the original LFM signal is realized. The construction of sensing dictionary adopts the Pei type fast fractional Fourier decomposition method, which serves as an efficient basis for the LFM signal. The proposed adaptive iterative optimization algorithm can solve grid mismatch problems brought on by undetermined signals and quickly achieve higher detection precision. The simulation results clearly show the effectiveness of the method.

• 한국통신학회논문지
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• 제23권6호
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• pp.1562-1574
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• 1998

본 논문에서는 ATM(Asynchronous Transfer Mode) 교환기 시스템에 T1, E1 및 부분적으로 E1급 속도의 중 저속 HDSL(High-rate digital subscriber line) 정합 기능을 개발하고, 근단누화(NEXT), 임펄스. 선로 잡음(power line noise) 및 접지 임피던스(longitudinal) 잡음 같은 주요 전송 손실이 존재하는 0.4 mm 및 0.5 mm의 기존 전화가입자 선로(UTP, Unshielded twisted pair)를 사용하는 CSA(Carrier serving areas) 선로 모델을 이용하여 $10^{-7}$의 BER(Bit error rates)의 전송 성능을 만족하기 위한 가입자 서비스 전송 거리 성능을 평가하였다. HDSL은 DSI, ISDN 기본 속도 접속 및 DLC 피더에 사용될 것이며 광 케이블과 인터페이스될 것이다. 또한, HDSL 시잔 전망을 제시한다.

• 한국전자파학회논문지
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• 제14권11호
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• pp.1149-1155
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• 2003

OFDM/SFH 시스템은 OFDM통신시스템이 재밍에 잘 견디게 하기 위하여 주파수 도약(FH) 방식과 결합한 시스템이고, OFDM/DS 시스템은 PN(pseudo noise) 시퀀스에 의한 대역 확산(DS) 방식과 결합한 시스템이다. 본 연구에서는 OFDM/SFH 시스템과 OFDM/DS 시스템을 동일한 정보량을 기준으로 부분대역 재밍과 톤 재밍이 있는 채널 환경 에서 성능을 분석한다. 부분대역 재밍 에서는 JFR(jamming functional ratio)과 JSR(jamming to signal power ratio) 변화에 따른 BER성능을 분석하며, 단일 톤 또는 다중 톤 재밍에서의 JSR에 따른 BER성능을 분석한다. 그 결과 부분대역 재밍에서는 OFDM/DS 시스템이 OFDM/SFH 시스템보다 우수한 성능을 보인다. JFR=4/16이고, JSR=0 ㏈일 때 BER=$10^{-3}$을 기준으로 OFDM/DS 시스템 이 OFDM/SFH 시스템보다 약 2,5 ㏈ 정도의 SNR(signal to noise power ratio) 이득이 있다. 그러나 단일 톤이고, JSR=5 ㏈일 때 BER=$10^{-3}$을 기준으로 OFDM/SFH 시스템이 OFDM/DS 시스템보다 3 ㏈ 정도의 SNR 이득이 있다. 한편 다중 톤인 경우 OFDM/SFH 시스템의 성능 저하가 OFDM/DS 시스템에 비해 크게 나타난다.

• 한국해안해양공학회지
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• 제9권3호
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• pp.115-124
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• 1997

동일지점에 투하한 여러개 표류부표 사이의 이격거리 관측방법을 사용하여 한국 연안 여러곳에서 와동확산의 분산을 측정하고 ‘확산계수’를 산정하였다. 시간이 경과함에 따라 와동확산의 분산은 ｔ$^{m}$ 에 비례하여 증가 하였는데, 여기서 시간지수승 m은 1.5와 3.5범위의 비정수 값으로 나타났다. 실측된 분산의 시간지수승 관계는 와동확산계수를 상수로 두는 확산모델링 방법에서는 재현되지 않는다. 본 논문에서는 프랙탈 이론을 도입하여 와동확산에 에 따른 분산의 지수승 관계를 시뮬레이트하였다. 본 논문의 프랙탈 확산모델에서는 가우스소음 대신에 프랙탈 가우스소음(fGn)을 와동확산에 따른 임의행보 과정에 적용하였다. 이 모델에서 프랙탈 브라운운동(fBm)으로 표현되는 와동확산의 분산은 시간 ｔ에 대하여 ｔ$^{2H}$와 같이 나타났는데, 여기서 H는 허스트 지수(Hurst exponent)이다. 본 논문의 프랙탈 확산모델은 시간지수승이 1과 2범위인 와동확산 분산을 잘 재현하였지만, 시간지수승이 2가 넘는 경우는 재현되지 않는다. 시간지수승이 2이상인 경우는 평균류의 유속전단(velocity shear)에 기인한다.다.

• JSTS:Journal of Semiconductor Technology and Science
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• 제15권2호
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• pp.301-306
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• 2015

An ultra-compact and wideband low noise amplifier (LNA) in a quad flat non-leaded (QFN) package is presented. The LNA monolithic microwave integrated circuit (MMIC) is implemented in a $0.25{\mu}m$ GaN IC technology on a Silicon Carbide (SiC) substrate provided by Triquint. A source degeneration inductor and a gate inductor are used to obtain the noise and input matching simultaneously. The resistive feedback and inductor peaking techniques are employed to achieve a wideband characteristic. The LNA chip is mounted in the $3{\times}3-mm^2$ QFN package and measured. The supply voltages for the first and second stages are 14 V and 7 V, respectively, and the total current is 70 mA. The highest gain is 13.5 dB around the mid-band, and -3 dB frequencies are observed at 0.7 and 12 GHz. Input and output return losses ($S_{11}$ and $S_{22}$) of less than -10 dB measure from 1 to 12 GHz; there is an absolute bandwidth of 11 GHz and a fractional bandwidth of 169%. Across the bandwidth, the noise figures (NFs) are between 3 and 5 dB, while the output-referred third-order intercept points (OIP3s) are between 26 and 28 dBm. The overall chip size with all bonding pads is $1.1{\times}0.9mm^2$. To the best of our knowledge, this LNA shows the best figure-of-merit (FoM) compared with other published GaN LNAs with the same gate length.

• 한국소음진동공학회논문집
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• 제23권6호
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• pp.553-562
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• 2013

Vehicle vibrations arise from engine and road surface excitations. The engine mount system of a passenger car sustains the engine weight and insulates the excitation force from the engine system. The dynamic properties of viscoelastic material used for the vehicle engine mounts have large variation due to environmental factors such as environmental temperature and humidity etc. The present study aims to investigate the variability of dynamic characteristics in rubber engine mounts considering both environmental temperature change and material model errors/uncertainty. The engine mounts for a passenger car were modeled using finite element method. Then, the dynamic stiffness variability of the engine mounts were estimated using Monte Carlo simulation method. In order to estimate the variations in the storage and loss moduli of the viscoelastic materials, the material properties of the synthetic rubber were expressed as a fractional-derivative model. Next, in order to simulate the uncertainty propagation of the dynamic stiffness for the engine mounts due to the storage and loss moduli variations, the Monte Carlo simulation was used. The Monte Carlo simulation results showed large variation of the engine-mount stiffness along frequency axis.

• 한국소음진동공학회논문집
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• 제18권2호
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• pp.185-191
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• 2008

Optimal damping layout of the constrained viscoelastic damping layer on beam is identified with temperatures by using a gradient-based numerical search algorithm. An optimal design problem is defined in order to determine the constrained damping layer configuration. A finite element formulation is introduced to model the constrained layer damping beam. The four-parameter fractional derivative model and the Arrhenius shift factor are used to describe dynamic characteristics of viscoelastic material with respect to frequency and temperature. Frequency-dependent complex-valued eigenvalue problems are solved by using a simple re-substitution algorithm in order to obtain the loss factor of each mode and responses of the structure. The results of the numerical example show that the proposed method can reduce frequency responses of beam at peaks only by reconfiguring the layout of constrained damping layer within a limited weight constraint.

• 한국소음진동공학회논문집
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• 제25권10호
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• pp.685-691
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• 2015

In this work, to identify effective parameter for performance of piezoelectric jetting dispenser, experimental investigation is carried out based on design of experiment. After preparing jetting dispenser using two stack-type piezoelectric actuators, basic working principle of the jetting dispenser is described. Eight operating conditions are chose as main factors and it is assumed that each factor has two levels. To reduce number of experiments for performance evaluation, the experimental sets are designed based on factional factorial design method. Experimental setup is established and the weight of single dot is measured by using precision scale. The main and interaction effects of factors are analyzed using commercial statistical program and optimal operating condition for small amount and small variation of weight of dispensed single dot are determined.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2019년도 춘계학술대회
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• pp.288-289
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• 2019

This paper studies the secrecy capacity for a wireless cooperative network with perfect channel state information at the relays, and receiver. A similar assumption is also made for the instance where there exist a direct link between the transmitter and receiver. Physical Layer security techniques are employed in wireless networks to mitigate against the activity of eavesdroppers. It offers a viable alternative to computationally intensive encryption. In this paper the design of a protocol utilizing jamming (via jamming nodes) for better security and relaying (via relay nodes) for the amplify-and-forward (AF) operation, is investigated. A a signal-to-noise variant of secrecy known as secrecy gap is explored because of its use of lesser computational power - preferable for practical systems. Thus we maximize this signal-to-noise approach instead of the conventional secrecy capacity maximization method. With this, an iterative algorithm using geometric programming (GP) and semi-definite programming (SDP) is presented with appreciable benefits. The results show here highlight the benefits of using fractional components of the powers of the relays to offer better secrecy capacity.

• ETRI Journal
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• 제26권6호
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• pp.657-660
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• 2004

We propose a fine phase tuner and a rounding processor for a numerically controlled oscillator (NCO), yielding a reduced phase error in generating a digital sine waveform. By using the fine phase tuner presented in this paper, when the ratio of the desired sine wave frequency to the clock frequency is expressed as a fraction, an accurate adjustment in representing the fractional value can be achieved with simple hardware. In addition, the proposed rounding processor reduces the effects of phase truncation on the output spectrum. Logic simulation results of the NCO using these techniques show that the noise spectrum and mean square error (MSE) for eight output bits of a 3.125 MHz sine waveform are reduced by 8.68 dB and 5.5 dB, respectively, compared to those of the truncation method, and 2.38 dB and 0.83 dB, respectively, compared to those of Paul's scheme.