Search All of the Math Forum:
Views expressed in these public forums are not endorsed by
Drexel University or The Math Forum.


anyone
Posts:
26
Registered:
12/22/12


Re: SNR script to run using Matlab
Posted:
Jan 5, 2013 11:25 PM


On Fri, 04 Jan 2013 09:27:08 +0000, Wan wrote: > anyone <ieGJnr4aQXRb!uzEL@z³> wrote in message > <50e37605$0$46968$c3e8da3$38634283@news.astraweb.com>... >> On Tue, 01 Jan 2013 20:41:08 +0000, Wan wrote: >> >> > Hi, >> > >> > I have a problem to run a script for SNR. Here the details. >> > >> > By using the given signal, the signal should be embended with noise >> > with with different Signaltonoise ration (SNR) of 0dB, 5dB, 10dB, >> > 15dB, 20dB, 25 dB and 30 dB. Details of the programming should >> > include: 1. How SNR of the noisy signal is calculated 2. Comparison >> > of time domain and Power Spectrum Density (PSD) of original signal, >> > noisy signal and filtered signal for each SNR. >> > >> > Anyone know how to write script for this SNR using given signal? >> >> Yes, I can think of a few ways one could do that. First, you should >> get started on your homework, then come back with an update on what you >> tried to do and what actually happened. > Hi, > > below is my coding: > > %< LOAD SIGNAL (FILENAME:mydata.mat) > %data = ('mydata.mat') > Fs=100; > t= 0: 1/Fs: 20; > S = load('mydata.mat'); > signal = S.td; > x= signal SNR = 0; > % Generate Gaussian Noise with zero mean and unit variance %function [y] > = add_noise (signal, SNR) > x_var=var (x); > x_lng=length(x) > > n_var=x_var/10^(SNR/10); > noise=n_var*randn(1,x_lng); > > %mix signal with noise mix = x+ noise; > > %SNR equation %SNR dB= 20 log10 (STDsignal/STDnoise) > %STDs = std(signal) > %STDn = std(noise) > %SNR_measured_dB = 20* log(STDs/STDn) > > Fc = 100 ; %cut off frequency > > w = Fc/(2*Fs); % Normalized frequency %design a low pass fitler with > above mentioned specifications [b,a]=butter(2,w,'low'); %5th order > butterworth LPF [h,w]=freqz(b,a,1024); %Frequency response of the filter > > y=filter(b,a,mix); % pass the input signal through the filter % y is > your output. > > %subplot figure (1) > figure(1); > %subplot(4,1,1); > plot(t, signal); > title('Input Signal'); > > %subplot(4,1,2); > %plot(t, noise); > %title('Generated Noise'); > > %subplot(4,1,3); > figure(2); > plot(t, mix); > title(['Signal + Noise for SNR = 30 dB']); > > figure(3); > %subplot(4,1,4); > plot(t, y); > title('Filtered Signal'); > > %Plot the Frequency response of the filter (Optional) > %subplot(5,1,5); > figure(4); > g = length(w/pi*2*Fs) > i = length(abs(h)) > plotHandle=plot(w/pi*2*Fs,abs(h)); > set(plotHandle,'LineWidth',2.5); > title('Frequency Response of a 5th Order Butterworth LPF'); > xlabel('Frequency (Hz)') > ylabel('Magnitude'); > grid; > > %plotting psd figure (5) > %subplot(4,1,1); > x = signal; > NFFT = 100; > X = fft(x, NFFT); > plot(NFFT/2:NFFT/2  1, fftshift(abs(X))) > title('PSD Input Signal'); > > figure(6); > %subplot(4,1,2); > v = noise; > NFFT = 100; > V = fft(v, NFFT); > plot(NFFT/2:NFFT/2  1, fftshift(abs(V))) > title('PSD Generated Noise'); > > %subplot(4,1,3); > figure(7); > w = mix; > NFFT = 100; > W = fft(w, NFFT); > plot(NFFT/2:NFFT/2  1, fftshift(abs(W))) > title(['PSD Signal + Noise for SNR= 30 dB']); > > %subplot(4,1,4); > figure(8); > m = y; > NFFT = 100; > M = fft(m, NFFT); > plot(NFFT/2:NFFT/2  1, fftshift(abs(M))) > title('PSD Filtered Signal');
Bunch of odd stuff in that. Was there some kind of question?



