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      • HARVEST
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      DSP compensation for distortion in RF filters

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      MScThesis.pdf (1.173Mb)
      Date
      2010-04-16
      Author
      Alijan, Mehdi
      Type
      Thesis
      Degree Level
      Masters
      Metadata
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      Abstract
      There is a growing demand for the high quality TV programs such as High Definition TV (HDTV). The CATV network is often a suitable solution to address this demand using a CATV modem delivering high data rate digital signals in a cost effective manner, thereby, utilizing a complex digital modulation scheme is inevitable. Exploiting complex modulation schemes, entails a more sophisticated modulator and distribution system with much tighter tolerances. However, there are always distortions introduced to the modulated signal in the modulator degrading signal quality. In this research, the effect of distortions introduced by the RF band pass filter in the modulator will be considered which cause degradations on the quality of the output Quadrature Amplitude Modulated (QAM) signal. Since the RF filter's amplitude/group delay distortions are not symmetrical in the frequency domain, once translated into the base band they have a complex effect on the QAM signal. Using Matlab, the degradation effects of these distortions on the QAM signal such as Bit Error Rate (BER) is investigated. In order to compensate for the effects of the RF filter distortions, two different methods are proposed. In the first method, a complex base band compensation filter is placed after the pulse shaping filter (SRRC). The coefficients of this complex filter are determined using an optimization algorithm developed during this research. The second approach, uses a pre-equalizer in the form of a Feed Forward FIR structure placed before the pulse shaping filter (SRRC). The coefficients of this pre-equalizer are determined using the equalization algorithm employed in a test receiver, with its tap weights generating the inverse response of the RF filter. The compensation of RF filter distortions in base band, in turn, improves the QAM signal parameters such as Modulation Error Ratio (MER). Finally, the MER of the modulated QAM signal before and after the base band compensation is compared between the two methods, showing a significant enhancement in the RF modulator performance.
      Degree
      Master of Science (M.Sc.)
      Department
      Electrical Engineering
      Program
      Electrical Engineering
      Supervisor
      Salt, J. Eric
      Committee
      Hanson, J.; Daku, B.; Klymyshyn, D.; Lynch, D.
      Copyright Date
      April 2010
      URI
      http://hdl.handle.net/10388/etd-04052010-164240
      Subject
      Amplitude distortion
      Equalization
      FIR
      IIR
      Quasi Newton Algorithm
      Optimization
      CATV
      DSP
      DOCSIS
      RF filter
      SRRC
      BER
      Modulator
      QAM
      Conjugate symmetry
      MSE
      LMS
      MER
      Complex distortion
      Group Delay distortion
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      • Graduate Theses and Dissertations
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