how to add velocity to the generated modulated signal?

i have generated a modulated signal with noise at the user, and this user is moving with velocity (Initial Velocity = 0, constant velocity = 20 km\hr and maximum velocity = 50 km\hr), how can it be done? any suggestions appriciated, thanks in advance.

fs = 50;

t = (0:2*fs+1)'/fs;

%Create a sinusoidal input signal.

x = sin(2*pi*t) + sin(4*pi*t);

%Set the carrier frequency and phase deviation.

fc = 10;

phasedev = pi/2;

%Modulate the input signal.

tx = pmmod(x,fc,fs,phasedev);

%Apply white Gaussian noise and plot the results.

y = awgn(x,10,'measured');

[VBBV]

Use gradient on input signal

%if true
  % code
%  end
fx = gradient(x)% input signal gives velocity
T = tx + fx;% adding velocity to modulated signal

Answer 1

[Chaitanya Mallela]

Velocity effect can be induced in the model when the input signal vary as function of both time and displacement. The function pmmod performs the phase modulation of the signal as a function of time by fixing the displacement. Translation of the source will not effect the momentum of the waves but results in Doppler effect at the receiver.