Doppler spread is a measure of the spectral broadening caused by time-varying multipath effects in a mobile channel. It refers to the range of frequencies over which the received Doppler spectrum is essentially non-zero. The Doppler power spectrum gives the statistical power distribution of the channel versus frequency and is the Fourier transform of the autocorrelation function of the channel over time. Doppler spread (fD) is defined as the maximum Doppler shift and determines the coherence time Tc, which characterizes the time-varying nature of the channel.

2.  Doppler spread is a measure of the spectral
broadening caused by the time
or
 Range of frequencies over which the received
Doppler spectrum is essentially non-zero.
 Doppler Power Spectrum gives the statistical
power distribution of the channel v/s
frequency.

3.  The Doppler power spectrum is the Fourier
transform of At(∆t ) is given by

4.  When a pure sinusoidal tone of frequency fc is
transmitted, the received signal spectrum,
called the Doppler spectrum.
 The spectrum components in the range fc – fd
to fc + fd, where fd is the Doppler shift.
 Unlike the power delay profile, the Doppler
power spectrum is non-zero strictly for ∆f€
(-fD, fD ).

5.  fD is maximum Doppler spread or Doppler
spread. The Doppler spread fD is given by
• As long as the communication bandwidth B <<
fc, the Doppler power spectrum can be treated
as approximately constant.

6.  Coherence time Tc is used to characterize the
time varying nature of the frequency
depressiveness of the channel in the time
domain.
 Values for the Doppler spread and the
associated channel coherence time for LTE at
Pedestrian, Vehicular, and Maximum Speeds
are given in Table below for two possible LTE
frequency bands.

8. Thank You