doppler

Purpose

Complex Doppler signal.

Synopsis

[fm,am,iflaw] = doppler(N,fs,f0,d,v) 
[fm,am,iflaw] = doppler(N,fs,f0,d,v,t0) 
[fm,am,iflaw] = doppler(N,fs,f0,d,v,t0,c)

Description

doppler returns the frequency modulation (fm), the amplitude modulation (am) and the instantaneous frequency law (iflaw) of the signal received by a fixed observer from a moving target emitting a pure frequency f0.

Name	Description	Default value
N	number of points
fs	sampling frequency (in Hz)
f0	target frequency (in Hz)
d	distance from the line to the observer (in meters)
v	target velocity (in m/s)
t0	time center	N/2
c	wave velocity (in m/s)	340
fm	output frequency modulation
am	output amplitude modulation
iflaw	output instantaneous frequency law

The doppler effect characterizes the fact that a signal returned from a moving target is scaled and delayed compared to the transmitted signal. For narrow-band signals, this scaling effect can be considered as a frequency shift.

[fm,am,iflaw] = doppler(N,fs,f0,d,v,t0,c) returns the signal received by a fixed observer from a moving target emitting a pure frequency f0. The target is moving along a straight line, which gets closer to the observer up to a distance d, and then moves away. t0 is the time center (i.e. the time at which the target is at the closest distance from the observer), and c is the wave velocity in the medium.

Example

Plot the signal and its instantaneous frequency law received by an observer from a car moving at the speed $v=50 m/s$, passing at 10 meters from the observer (the radar). The rotating frequency of the engine is $f_0=65 Hz$, and the sampling frequency is $f_s=200 Hz$ :

     N=512; [fm,am,iflaw]=doppler(N,200,65,10,50); 
     subplot(211); plot(real(am.*fm)); 
     subplot(212); plot(iflaw);
     [ifhat,t]=instfreq(sigmerge(am.*fm,noisecg(N),15),11:502,10);
     hold on; plot(t,ifhat,'g'); hold off;

See Also

dopnoise.

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