dopnoise

Purpose

Complex doppler random signal.

Synopsis

[y,iflaw] = dopnoise(N,fs,f0,d,v)
[y,iflaw] = dopnoise(N,fs,f0,d,v,t0)
[y,iflaw] = dopnoise(N,fs,f0,d,v,t0,c)

Description

dopnoise generates a complex noisy doppler signal, normalized so as to be of unit energy.

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
y	output signal
iflaw	model used as instantaneous frequency law

[y,iflaw] = dopnoise(N,fs,f0,d,v,t0,c) returns the signal received by a fixed observer from a moving target emitting a random broad-band white gaussian signal whose central frequency is 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

Consider such a noisy doppler signal and estimate its instantaneous frequency (see instfreq) :

         [z,iflaw]=dopnoise(500,200,60,10,70,128);
         subplot(211);    plot(real(z)); 
         subplot(212);    plot(iflaw);   hold; 
         ifl=instfreq(z); plot(ifl,'g'); hold; 
         sum(abs(z).^2)
         ans = 
               1.0000

The frequency evolution is hardly visible from the time representation, whereas the instantaneous frequency estimation shows it with success. We check that the energy is equal to 1.

See Also

doppler, noisecg.

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