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Multipath channels

on Jul 21, 2010

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Multipath channelsPresentation 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