Multipath channels
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Multipath channels

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Multipath channels Presentation Transcript

  • 1. Parameters of Multipath channels
            • M.Vignesh pandi
            • A.Vijayasekhar
  • 2. 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.
  • 3.
    • 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
  • 4.
    • 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
  • 5.
    • 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.
  • 6. 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
  • 7.
    • 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 ))
  • 8.
    • THE END