Multipath channels
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Multipath channels

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    Multipath channels Multipath channels Presentation Transcript

    • Parameters of Multipath channels
              • M.Vignesh pandi
              • A.Vijayasekhar
    • Coherence Bandwidth
      • It is a measure of range frequencies over which the channel is considered flat.
      • Otherwise it is range frequencies over which two frequency component have a strong potential for amplitude correlation.
      • It is used to characterize the channel in the frequency domain
      • It is inversely proportional to the rms delay spread
      • B c =1/ σ ז
      • Two sinusoidal with frequency separation greater than Bc are affected quite differently by the channel.
      • If the frequency correlation function is above 0.9, than the correlation bandwidth is
      • B c =1/50 σ ז
      • If the frequency correlation function is above 0.5 than the coherence bandwidth is approximately B c =1/5 σ ז
      • Doppler spread and coherence time are parameters are describes the time varying nature of the channel in a small- scale region.
      • It is defined as the range of frequency over which the received Doppler spectrum is essentially non-zero
      • Doppler spread and Doppler frequency:
      • Doppler spread B d is defined as the range of frequencies over which the received Doppler spectrum is essentially non-zero.
      Doppler spread and coherence time
      • The maximum Doppler frequency f d is give by
      • f d =v/ λ
      • λ =c/f
      • f d =v/ λ = v/(c/f)
      • f d =vf/c
      • Where
      • C-velocity of light
      • V-speed of the mobile, including the speed of the mobile environment in m/s
      • λ - wavelength of the radio signal in meters and
      • F- radio frequency
      • When a pure sinusoidal tone of frequency fc is transmitted the received signal spectrum, will have components in the range fc-fd to fc+fd
      • where fd is the Doppler shift.
    • Coherence Time (T c )
      • Coherence time is the time duration over which two received signal have a strong potential for amplitude correlation
      • Distortion is occurred at the receiver, if the reciprocal bandwidth of signal is greater than the coherence time for the channel
      • The Doppler spread & coherence time are inversely proportional to each other
      • T c ≈1/f m
      • If the time correlation function is above 0.5 than the coherence time is given as
      • T c ≈9/(16 π f m )
      • where
      • f m =maximum Doppler shift
      • f m =v/ λ
      • If the digital transmission system is used,than the coherence time as geometric mean of above two equation
      • T c =√(9/(16 π f m 2 ))
      • THE END