www.gusucode.com > phased 案例源码 matlab代码程序 > phased/FreeSpacePropagationOfWidebandSignalsExample.m
%% Free-Space Propagation of Wideband Signals % Propagate a wideband signal with three tones in an underwater acoustic % with constant speed of propagation. You can model this environment as % free space. The center frequency is 100 kHz and the frequencies of the % three tones are 75 kHz, 100 kHz, and 125 kHz, respectively. Plot the % spectrum of the original signal and the propagated signal to observe the % Doppler effect. The sampling frequency is 100 kHz. %% % *Note:* This example runs only in R2016b or later. If you are using an earlier % release, replace each call to the function with the equivalent |step| % syntax. For example, replace |myObject(x)| with |step(myObject,x)|. c = 1500; fc = 100e3; fs = 100e3; relfreqs = [-25000,0,25000]; %% % Set up a stationary radar and moving target and compute the expected % Doppler. rpos = [0;0;0]; rvel = [0;0;0]; tpos = [30/fs*c; 0;0]; tvel = [45;0;0]; dop = -tvel(1)./(c./(relfreqs + fc)); %% % Create a signal and propagate the signal to the moving target. t = (0:199)/fs; x = sum(exp(1i*2*pi*t.'*relfreqs),2); channel = phased.WidebandFreeSpace(... 'PropagationSpeed',c,... 'OperatingFrequency',fc,... 'SampleRate',fs); y = channel(x,rpos,tpos,rvel,tvel); %% % Plot the spectra of the original signal and the Doppler-shifted signal. periodogram([x y],rectwin(size(x,1)),1024,fs,'centered') ylim([-150 0]) legend('original','propagated'); %% % For this wideband signal, you can see that the magnitude of the Doppler shift increases % with frequency. In contrast, for narrowband signals, the Doppler shift is % assumed constant over the band.