• Title/Summary/Keyword: Nonlinear chirp

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Underwater Acoustic Communication Using Nonlinear Chirp Signal (비선형 chirp 신호를 이용한 수중음향통신)

  • Lee, Chang-Eun;Kim, Ki-Man;Kim, Woo-Sik;Chun, Seung-Yong;Lee, Sang-Kook
    • The Journal of the Acoustical Society of Korea
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    • v.33 no.4
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    • pp.255-261
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    • 2014
  • This paper presents an underwater acoustic communication with nonlinear chirp modulation. The information is carried by the carrier amplitude, frequency or phase in the most common underwater acoustic communications. However, the proposed method includes the information within frequency variation of carrier wave for a symbol. Especially, as carrier wave the hyperbolic frequency modulated signal, one of the nonlinear chirp signal, is used and it is robust in the Doppler channel. The proposed method was analyzed and compared to conventional method by simulation. When the doppler shift existed, the error probability of the proposed method is reduced by 5~12 % than conventional method with linear frequency modulated signal. Sea trial was performed to analyze the performance of the proposed method.

Optimal Position of Optical Phase Conjugator for Compensation of Distorted WDM Signals with Initial Frequency Chirp

  • Lee Seong-Real;Choi Byung-Ha;Chung Myung-Rae
    • 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.

Position Estimation of Chirp Spread Spectrum Node based on Unscented Kalman Filter (Unscented 칼만 필터 기반의 chirp spread spectrum 노드 위치 추정)

  • Cho, Hyeon-Woo;Ban, Sung-Jun;Lee, Young-Hun;Joen, Young-Ju;Kim, Sang-Woo
    • Proceedings of the IEEK Conference
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    • 2009.05a
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    • pp.187-189
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    • 2009
  • Position estimation in indoor is significant problem, because GPS which is usually used for outdoor positioning cannot be utilized to indoor positioning. Sensor network can be a solution for the positioning. Recently, chirp spread spectrum(CSS) specified in IEEE 802.15.4a provides an ability of ranging. Based on the results of the ranging, a position of a CSS node can be calculated by using trilateration. In this case, Kalman filter can be applied to the trilateration because of the measurement noise. In this paper, we apply the unscented Kalman filter for the trilateration. The trilateration can be represented to a nonlinear state space equation, and the unscented Kalman filter is suitable for nonlinear state space equation. Through the experimental results. we show the accuracy of the estimated position.

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Characteristics of Compensation for Distorted Optical Pulse with Initial Frequency Chirp in 3 X 40 Gbps WDM Systems Adopted Mid-Span Spectral Inversion

  • Lee, Seong-Real;Lee, Yun-Hyun
    • Journal of electromagnetic engineering and science
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    • v.3 no.2
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    • pp.79-85
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    • 2003
  • In this paper, we investigated the degree of compensation for distorted optical pulse of wavelength division multiplexed(WDM) channel with initial frequency chirp generated in optical transmitter. The WDM channel signal distortion is due to chromatic dispersion, self phase modulation(SPM) and cross phase modulation(XPM) in fiber. The considered system is 3 ${\times}$ 40 Gbps intensity modulation direct detection(IM/DD) WDM transmission systems, which adopted mid-span spectral inversion(MSSI) as compensation method. We confirmed that the effect of initial frequency chirp on compensation for signal distortion due to a SPM is gradually decreased as a dispersion coefficient of fiber becomes gradually small. But, in the aspect of a compensation for signal distortion due to both SPM and XPM, the effect of initial frequency chirp on compensation is gradually decreased as a dispersion coefficient of fiber becomes gradually large.

Transform-Limited Optical Short Pulse Generation by Compression of Gain-Switched DFB Laser Pulses (DFB 레이저 이득 스위칭과 펄스 압축을 이용한 변환 제한된 초단 광 펄스 발생)

  • 조성대;이창희;신상영;채창준
    • Journal of the Korean Institute of Telematics and Electronics D
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    • v.35D no.6
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    • pp.92-98
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    • 1998
  • The transform limited optical short pulses are generated by compression of pulses from a gain switched distributed feedback laser at 5 GHz repetition rate. The gain-switched pulses have the minimum pulse width of 27 psec with the spectral width of 1.1 nm. Thus the output pulses have a large amount of linear chirp and nonlinear chirp. We suppress the nonlinear chirp by passing the pulses through the optical band pass filter with 3 dB band width of 0.55 nm which is narrower than spectral width of the input pulses and generate 7.1 psec pulses by compressing the output with the dispersion compensating fiber. The pulses have time-bandwidth product of 0.49 which is close to the transform limited gaussian pulse. These pulses can be utilized as optical sources in 40 Gbit/s time division multiplexed optical transmission system.

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Theoretical analysis improved cavitity design of a 10 GHz harmonically mode-locked Er-doped fiber laser (10GHz로 고조모드록킹된 고리형 어븀첨가 광섬유 레이저의 이론적 해석 및 향상된 공진기 설계)

  • 이유승
    • Korean Journal of Optics and Photonics
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    • v.11 no.5
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    • pp.353-359
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    • 2000
  • A harmonically mode-locked fiber ring laser cavlty was theoretically analyzed. The measured charactenstlcs of a 10 GHz erbium-doped fiber ring laser were used as a basis of the theoretical analysis. From the nonlinear Schroedinger equation of an actively mode-locked erblUm-doped fiber laser. the effects of the components inside the laser cavity have been analyzed includmg nonlinear effects from group-velocity dispersion (GVD) and self-phase modulation (SPM). Usmg the analysls. we have designed a laser cavity with minimum pulsewidth and chirp by changing the intracavity optical intensity and the bandwidth of the filter. In the new design, the chirp i, reduced by 2 times and the pulsewidth by 2A times. compared to the laser used in the experiment. iment.

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Influences of the Filter Effect on Pulse Splitting in Passively Mode-Locked Fiber Laser with Positive Dispersion Cavity

  • Chen, Xiaodong
    • Journal of the Optical Society of Korea
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    • v.19 no.2
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    • pp.130-135
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    • 2015
  • Based on the extended nonlinear Schr$\ddot{o}$dinger equation, the influences of the filter effect on pulse splitting in a passively mode-locked erbium-doped fiber laser with positive dispersion cavity are investigated theoretically. Numerical results show that, as the bandwidth of the spectral filter decreases, the nonlinear chirp appended to the pulse increases under the combined action of the filter effect of the super-Gaussian spectral filter and the self-phase modulation effect. On further decreasing the bandwidth, the wave breaking of the pulse takes place. In addition, by varying the pump power of the laser or the profile of the spectral filter, the influences of the filter effect on pulse splitting also change accordingly.

Doppler shift frequency estimation and compensation in underwater acoustic communication using triangle spread carrier technique (Triangle spread carrier 기법을 이용한 수중음향통신에서 도플러 천이 주파수 추정 및 보상 )

  • Chang-hyun Youn;Hyung-in Ra;Kyung-one Lee;Ki-man Kim
    • The Journal of the Acoustical Society of Korea
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    • v.42 no.3
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    • pp.169-180
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    • 2023
  • The performance of underwater acoustic communication is greatly affected by multipath propagation and Doppler spread. This paper proposes a new communication technique, the Triangle Spread Carrier (TSC) technique, by modifying the existing Sweep Spread Carrier (SSC) technique that is strong in a multipath propagation environment. The proposed TSC technique is a form in which the up-chirp and down-chirp signals have repeated carriers, and each correlation function characteristic is used to estimate and correct the Doppler shift frequency of the receiving signal. To demonstrate the performance of the proposed TSC technique, we present the results of simulations using underwater channel simulators and sea trial conducted in the East Sea. When demodulating using only the estimated Doppler shift frequency as a result of the sea trial, the uncoded bit error rate was up to 0.194, but when the proposed method was applied, the uncoded bit error rate was reduced to 0.001.

Study of RF Impairments in Wideband Chirp Signal Generator (광대역 첩 신호 발생기를 위한 RF 불균형 연구)

  • Ryu, Sang-Burm;Kim, Joong-Pyo;Yang, Jeong-Hwan;Won, Young-Jin;Lee, Sang-Kon
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.24 no.12
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    • pp.1205-1214
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    • 2013
  • Recently spaceborne SAR systems are increasing image resolution and frequency. As a high quality image resolution, the wider bandwidth is required and a wideband signal generator with RF component is very complicated and RF impairments of device is increased. Therefore, it is very important to improve performance by reducing these errors. In this study, the transmission signal of the wideband signal generator is applied to the phase noise, IQ imbalance, ripple gain, nonlinear model of high power amplifier. And we define possible structures of wideband signal generator and measure the PSLR and ISLR for the performance assesment. Also, we extract error of the amplitude and phase from the waveform and use a quadratic polynomial curve fitting and examine the performance change due to nonlinear device. Finally, we apply a high power amplifier predistortion method for non-linear error compensation. And we confirm that distortion in the output of the amplifier by intermodulation component is decreased by 15 dB.

A digital Audio Watermarking Algorithm using 2D Barcode (2차원 바코드를 이용한 오디오 워터마킹 알고리즘)

  • Bae, Kyoung-Yul
    • Journal of Intelligence and Information Systems
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    • v.17 no.2
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    • pp.97-107
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    • 2011
  • Nowadays there are a lot of issues about copyright infringement in the Internet world because the digital content on the network can be copied and delivered easily. Indeed the copied version has same quality with the original one. So, copyright owners and content provider want a powerful solution to protect their content. The popular one of the solutions was DRM (digital rights management) that is based on encryption technology and rights control. However, DRM-free service was launched after Steve Jobs who is CEO of Apple proposed a new music service paradigm without DRM, and the DRM is disappeared at the online music market. Even though the online music service decided to not equip the DRM solution, copyright owners and content providers are still searching a solution to protect their content. A solution to replace the DRM technology is digital audio watermarking technology which can embed copyright information into the music. In this paper, the author proposed a new audio watermarking algorithm with two approaches. First, the watermark information is generated by two dimensional barcode which has error correction code. So, the information can be recovered by itself if the errors fall into the range of the error tolerance. The other one is to use chirp sequence of CDMA (code division multiple access). These make the algorithm robust to the several malicious attacks. There are many 2D barcodes. Especially, QR code which is one of the matrix barcodes can express the information and the expression is freer than that of the other matrix barcodes. QR code has the square patterns with double at the three corners and these indicate the boundary of the symbol. This feature of the QR code is proper to express the watermark information. That is, because the QR code is 2D barcodes, nonlinear code and matrix code, it can be modulated to the spread spectrum and can be used for the watermarking algorithm. The proposed algorithm assigns the different spread spectrum sequences to the individual users respectively. In the case that the assigned code sequences are orthogonal, we can identify the watermark information of the individual user from an audio content. The algorithm used the Walsh code as an orthogonal code. The watermark information is rearranged to the 1D sequence from 2D barcode and modulated by the Walsh code. The modulated watermark information is embedded into the DCT (discrete cosine transform) domain of the original audio content. For the performance evaluation, I used 3 audio samples, "Amazing Grace", "Oh! Carol" and "Take me home country roads", The attacks for the robustness test were MP3 compression, echo attack, and sub woofer boost. The MP3 compression was performed by a tool of Cool Edit Pro 2.0. The specification of MP3 was CBR(Constant Bit Rate) 128kbps, 44,100Hz, and stereo. The echo attack had the echo with initial volume 70%, decay 75%, and delay 100msec. The sub woofer boost attack was a modification attack of low frequency part in the Fourier coefficients. The test results showed the proposed algorithm is robust to the attacks. In the MP3 attack, the strength of the watermark information is not affected, and then the watermark can be detected from all of the sample audios. In the sub woofer boost attack, the watermark was detected when the strength is 0.3. Also, in the case of echo attack, the watermark can be identified if the strength is greater and equal than 0.5.