How to attenuate the signal in frequency domain without disturbing the noise floor?
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I have written a code to calculate the power spectrum of a 200Hz sinusoidal signal. In frequency domain, the strength of the 200Hz component is 24dbm and the noise floor is at -15dbm. How to attenuate the signal with out affecting the noise floor at -15dbm?
close all;
clear all;
clc;
fs = 1e3; % sample freq
f = 2e2;
D = 0.3; % pulse delay times
StopTime = 1;
t = (0 : 1/fs : StopTime-1/fs)'; % signal evaluation time
N = size(t,1);
w = 0.2; % width of each pulse
yp = pulstran(t,D,@rectpuls,w);
x = (10)*sin(2*pi*f*t);
display(size(yp));
display(size(x));
z = yp.*x;
noisy_z = z + 0.5*randn(size(z));
y = xcorr(noisy_z,'biased');
display(size(y));
subplot(2,1,1);
plot(t*(1/(f*StopTime)),z);
title('Pulsed sine signal');
subplot(2,1,2);
plot(t*(1/(f*StopTime)),noisy_z);
title('Noisy signal');
l = length(t);
%%Fourier Transform:
X1 = fft(y,l);
X2 = X1(1:l/2);
X = abs(X2)/N;
%%Frequency specifications:
dF = fs/N; % hertz
f1 = 0:dF:fs/2-dF; % hertz
display(size(f1));
display(size(X));
%%Plot the spectrum:
figure;
plot(f1,(10*log10((X).^2*1e3)));
xlabel('Frequency (in hertz)');
ylabel('Power (in dbm)');
title('Autocorrelation spectrum');
grid on;
1 Comment
Wayne King
on 20 Feb 2014
Edited: Wayne King
on 20 Feb 2014
Well, right out of the gate, how are you doing this?
fs = 1e3; % sample freq
f = 2e2;
A sinusoid with a period of 1/2000 sampled at 1/1000 is going to be aliased to be DC (all zeros for sin with zero phase and all ones for a cosine with zero phase.)
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