Re: [Discuss-gnuradio] Simulated Doppler Shift

[Matt Ettus]

Ryan Rutherford wrote:
> Hello everyone,
>
> I am trying to figure out the best way to approach simulating doppler
> shift on my BPSK transmitter.  Does anyone know of how I may be able
> to approach this?
>
> Thank you in advance for any information.

Doppler shift will affect both the center frequency and modulation
frequency proportionally.  However, once you have translated the
received signal to baseband, those two are no longer proportional, so
you have to handle the effects separately.

For the center frequency delta, just use a complex mixer.  In gnuradio
that would be sending the signal into a complex mixer, and feed the
other mixer with a complex sine wave at the doppler frequency (which is
positive or negative).

For the modulation frequency, the easiest thing to do is to do
fractional sample rate conversion, using a gr_fractional_interpolator. 
However, you may not need to do this if the doppler effect on your
modulation frequency is small.  If the doppler effect on your signal
bandwidth is much smaller than the range of your symbol timing recovery,
then most would just ignore it.

Matt