• Title/Summary/Keyword: Nonlinear Distortion Effects

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Design and Performance Evaluation of Receiver Feedback Closed Loop Pre-Distortion System (수신기 포함 폐루프 전치왜곡기 설계와 성능 평가)

  • Bok, Junyeong;Jo, Byung Gak;Baek, Gwang Hoon;Ryu, Heung-Gyoon
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.37A no.10
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    • pp.827-833
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    • 2012
  • The receiver performance is degraded by nonlinear memory problem in communication system. The pre-distorter techniques are an effective technique to compensate for the nonlinear distortion of the HPA without memory effects. However, memory effect of HPA can no longer be ignored when data signal is transmitted in high speed. Many adaptive pre-distorter schemes have been studied to compensate for memory effect problem of HPA in transmitter. The complexity and cost of satellite will increase when using adaptive pre-distorter in satellite communication system. In this paper, we propose receiver feedback closed loop pre-distortion technique in order to compensate for nonlinear problem of HPA with memory problem. The purpose of this paper is to reduce complexity and cost of satellite design by using only pre-distorter at terrestrial station.

Performance of DS-CDMA forward Link Due to Nonlinear Power Amplifier in Multiuser Environment (다중사용자 환경에서 비선형 전력증폭기로 인한 DS/CDMA의 순방향 성능 분석)

  • 최성호;목진담;손동철;김성철;정희창;조경록
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.10 no.4
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    • pp.479-486
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    • 1999
  • In this paper the system performance degradation resulting from nonlinear transmitter power amplifier which is essential to increase the efficiency is analyzed in a forward link CDMA system. The power amplifier is modeled by power series model which includes only odd-order terms. The effects of power amplifier's nonlinearity such as intersymbol interference, phase distortion on the RF system performance were visualized by examining the distorted time domain waveforms, signal vector constellation. And through the investigation of the power spectrum density of the transmitted signal, spectral regrowth or sideband regrowth which is result from amplitude distortion can be seen. All these characteristics result in BER performance degradation due to other user interferences and intersymbol interference. The analysis technique described here applies not only to power amplifier but also to any other nonlinear components such as mixers and switches. Also the effects of adjacent channel interference and supurious emission can be analysed between different systems.

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Numerical Research on Suppression of Thermally Induced Wavefront Distortion of Solid-state Laser Based on Neural Network

  • Liu, Hang;He, Ping;Wang, Juntao;Wang, Dan;Shang, Jianli
    • Current Optics and Photonics
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    • v.6 no.5
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    • pp.479-488
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    • 2022
  • To account for the internal thermal effects of solid-state lasers, a method using a back propagation (BP) neural network integrated with a particle swarm optimization (PSO) algorithm is developed, which is a new wavefront distortion correction technique. In particular, by using a slab laser model, a series of fiber pumped sources are employed to form a controlled array to pump the gain medium, allowing the internal temperature field of the gain medium to be designed by altering the power of each pump source. Furthermore, the BP artificial neural network is employed to construct a nonlinear mapping relationship between the power matrix of the pump array and the thermally induced wavefront aberration. Lastly, the suppression of thermally induced wavefront distortion can be achieved by changing the power matrix of the pump array and obtaining the optimal pump light intensity distribution combined using the PSO algorithm. The minimal beam quality β can be obtained by optimally distributing the pumping light. Compared with the method of designing uniform pumping light into the gain medium, the theoretically computed single pass beam quality β value is optimized from 5.34 to 1.28. In this numerical analysis, experiments are conducted to validate the relationship between the thermally generated wavefront and certain pumping light distributions.

Numerical study on attenuation and distortion of compression wave propagation into a straight tube (직관내를 전파하는 압축파의 감쇠와 변형에 관한 수치해석적 연구)

  • Kim, Hui-Dong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.7
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    • pp.2315-2325
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    • 1996
  • A compression wave is attenuated or distorted as it propagates in a tube. The present study investigated the propagation characteristics of the compression waves which are generated by a train in a high-speed railway tunnel. A Total Variation Diminishing (TVD) difference scheme was applied to one-dimensional, unsteady viscous compressible flow. The numerical calculation involved the effects of wall friction, heat transfer and energy loss due to the friction heat in the boundary layer behind the propagating compression wave, and compared with the measurement results of a shock tube and a real tunnel. The present results show that attenuation of the compression wave in turbulent boundary layer is stronger than in laminar boundary layer, but nonlinear effect of the compression wave is greater in the laminar boundary layer. The energy loss due to the frictional heat had not influence on attenuation and distortion of the propagating compression waves.

Laboratory geometric calibration simulation analysis of push-broom satellite imaging sensor

  • Reza Sh., Hafshejani;Javad, Haghshenas
    • Advances in aircraft and spacecraft science
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    • v.10 no.1
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    • pp.67-82
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    • 2023
  • Linear array imaging sensors are widely used in remote sensing satellites. The final products of an imaging sensor can only be used when they are geometrically, radiometrically, and spectrally calibrated. Therefore, at the first stages of sensor design, a detailed calibration procedure must be carefully planned based on the accuracy requirements. In this paper, focusing on inherent optical distortion, a step-by-step procedure for laboratory geometric calibration of a typical push-broom satellite imaging sensor is simulated. The basis of this work is the simulation of a laboratory procedure in which a linear imager mounted on a rotary table captures images of a pin-hole pattern at different angles. By these images and their corresponding pinhole approximation, the correction function is extracted and applied to the raw images to give the corrected ones. The simulation results illustrate that using this approach, the nonlinear effects of distortion can be minimized and therefore the accuracy of the geometric position of this method on the image screen can be improved to better than the order of sub-pixel. On the other hand, the analyses can be used to proper laboratory facility selection based on the imaging sensor specifications and the accuracy.

Image Recovery Using Nonlinear Modeling of Industrial Radiography (산업용방사선영상의 비선형모델링에 의한 영상복구)

  • Hwang, Jung-Won;Hwang, Jae-Ho
    • Journal of the Institute of Electronics Engineers of Korea SP
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    • v.45 no.4
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    • pp.71-77
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    • 2008
  • This paper presents a methodology for recovering the industrial radiographic images from the effects of nonlinear distortion. Analytical approach based on the inverse square law and Beer's law is developed in order to improve a mathematic model of nonlinear type. The geometric effect due to dimensions of the radioactive source appeals on the digitized images. The relation that expresses parameters values(angle, position, absorption coefficient, length, width and pixel account) is defined in this model, matching with the sample image. To perform the search for image recovery most similar to the model, a correction procedure is designed. The application of this method on the radiographic images of steel tubes is shown and recovered results are discussed.

Power and Spectrum Efficiencies Considering the HPA Nonlinearity in OFDM Communication System (OFDM 통신 시스템에서 비선형 증폭기 특성을 고려한 전력 효율과 대역 효율)

  • 이재은;윤기후;이준서;유흥균
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.14 no.6
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    • pp.543-549
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    • 2003
  • It is important to consider the nonlinear effects of the HPA(High Power Amplifier) in the OFDM communication systems and other digital communication systems as well. In this paper, we investigate a new performance figure-of$.$merit(D) that reflects both power and spectrum efficiencies. The performance figure-of-merit is expressed to include the spectrum and power efficiencies that depend on the magnitude of IBO(Input Backoff) and the number of subcarriers. So, we analyze the variation characteristics of the power efficiency and spectrum efficiency which has the tradeoff relationship.

Dispersion-Managed Links for WDM Transmission Arranged by Linearly or Nonlinearly Incremented Residual Dispersion per Span

  • Lee, Seong-Real
    • Journal of information and communication convergence engineering
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    • v.15 no.4
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    • pp.205-211
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    • 2017
  • Combining dispersion-managed optical links with midway optical phase conjugation (OPC) is a possible method of compensating for optical signal distortion due to group velocity dispersion and nonlinear Kerr effects. Although an improvement in the performance of these optical links has been reported, the fixed residual dispersion per span (RDPS) that is typically used restricts the flexibility of link configurations. Thus, in this paper, a flexible dispersion-managed link configuration, comprising artificial distributions of linearly/nonlinearly incremented RDPS, is proposed. Simulations show that a descending distribution of RDPS before the midway OPC, and an ascending distribution of RDPS after the midway OPC, gives the best artificial distribution pattern as the number of fiber spans is increased, regardless of the RDPS incrementation method.

On the Adaptive Pre-processing Technique for the Linearization of a Third-Order Volterra System (3차 볼테라 시스템의 선형화를 위한 적웅 선행처리 기법)

  • Kim, Jin-Young;Choi, Bong-Joon;Nam, Sang-Won
    • Proceedings of the KIEE Conference
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    • 1996.07b
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    • pp.1289-1291
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    • 1996
  • In this paper, we propose a new adaptive pre-processing technique for the linearization of a weakly nonlinear system which can be modeled by a Volterra series up to third order. To compensate the nonlinear effects of a given system, an update algorithm for the linear filter coefficients of the proposed adaptive pre-processor is introduced, and to compensate the linear distortion of the given system, the linear inverse filter is also utilized. For the performance test of the proposed adaptive pre-processor, computer simulation results obtained by analyzing an ANRSS loudspeaker model are provided.

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New OFDM Schemes Robust to Doppler and PAR Effects for Satellite Communications (위성통신에서 도플러 및 PAR 효과에 강인한 새로운 OFDM 방식)

  • Hong, Sang-Wan;Lee, Byung-Seub
    • Journal of Satellite, Information and Communications
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    • v.10 no.2
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    • pp.60-69
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    • 2015
  • A new and effective Doppler effects compensation method based on constellation estimation as well as an average power saving strategy by modified modulation scheme utilizing zero point constellation are presented with theoretical analysis and relevant simulations. The suggested schemes are proved to be very effective for satellite OFDM signals relayed by power limiting transponder for the mobile terminal on high speed vehicles.