AM Demodulation code error

f_lo = 30e3;  % frequency of local oscillator

A_lo = 1;  % amplitude of local oscillator
y_lo = A_lo*sin(2*pi*f_lo*time');

Unrecognized function or variable 'time'.

y_demod = y_lo.*filt_received'; 

demod_sig_FD = fft(y_demod);  % calculate frequency domain of audio
demod_sig_FD_amp = abs(demod_sig_FD)/no_of_pnts;  % calculate the amplitude of frequency domain
demod_sig_FD_amp_adj = fftshift(demod_sig_FD_amp);  % adjust the frequency sides

figure;
semilogy(freq, filt_rec_sig_FD_amp_adj, 'b');
hold on;
semilogy(freq, demod_sig_FD_amp_adj, 'r');
xlim([10, freq_max]);
grid minor;
box on;
xlabel('Frequency (Hz)');
ylabel('Amplitude');
legend('Filtered Received', 'Demodulated');
title('Frequency Domain of Filtered Received and Demodulated Signals');

The Error is:

y_demod = y_lo.*filt_received';

Requested 1102840x20000 (164.3GB) array exceeds maximum array size preference (7.7GB). This might cause MATLAB to become unresponsive.

Answer 1

[Image Analyst]

time is a built in function so your use of it is not recommended.

What is filt_received? Specifically what is its size (rows and columns)? If it's a vector, or you think it is, then it might not be the same shape as y_lo. Then with the "automatic expansion" it's making a huge 2-D matrix out of it. You might try turning both factors into column vectors and then doing it.

y_demod = y_lo(:) .* filt_received(:); % Create new column vector.

These are just normal questions that any of the rest of us would ask when debugging code. To learn how to debug: Debugging in MATLAB | Doug's MATLAB Video Tutorials

[Matt]

The same issue comes up.

[Image Analyst]

@Matt, did you see the first two questions I asked? If you did, you forgot to tell us the answers.

And do you know how to step through code and check variable values and sizes in the workspace (i.e., normal debugging activities)?

[Matt]

Ah ok, I believe they're different sizes however I'm not sure how to change that.

[Image Analyst]

We don't know either. We don't know how you assigned them since you left it out of the snippet of code you posted. Even if we knew how you created those two variables, how do we know if it's right or not? You should know. Does it pass the sanity check, like the sizes seem reasonable to you?

I think you should know how many rows and columns your data should have, right? And if they're different then why do you think you can multiply them together?

[Matt]

% time Durationt = (0 : 1/Fs : 10);

Does this make more sense?

[Image Analyst]

Not to me. Why would adding in that comment change anything?

[Matt]

time has originated from my carrier signal code:

mod_ind = 1; % AM modulation index

f_carrier = 550e3; % frequency of carrier sine wave

A_carrier = std(audio)/mod_ind; % amplitude of carrier sine wave

y_carrier = A_carrier*sin(2*pi*f_carrier*time');

carrier_FD = fft(y_carrier); % calculate frequency domain of audio

carrier_FD_amp = abs(carrier_FD)/no_of_pnts; % calculate the amplitude of frequency domain

carrier_FD_amp_adj = fftshift(carrier_FD_amp); % adjust the frequency sides