Asking for a code.

How can I add and plot a gaussian noise difference in this FDM system

% Design and simulation of Frequency Division Multiplexing in MATLAB
clc;
clear all
close all

samples=1000;

% number of users
nos=4;
% modulating signal frequency in Hz
mfreq=[25 50 75 100]; 
% carrier frequency allocated to the different users in Hz
cfreq=[300 600 900 12000 1500];

% choose frequency deviation
freqdev=10;

% generate modulating signal 
t=linspace(0,1000,samples);

%initialize random number generator
rng default  
x = sin(t) + 10*rand(size(t));
windowSize = 4; 
b = (1/windowSize)*ones(1,windowSize);
a = 1;

parfor i=1:nos
    m(i,:)=sin(2*pi*mfreq(1,i)*t)+2*sin(pi*8*t);
end

% Generate the modulated signal
parfor i=1:nos
    y(i,:)=fmmod(m(i,:),cfreq(1,i),10*cfreq(1,i),freqdev);
end

% pass the modulated signal through the channel 

ch_op=awgn(sum(y),0,'measured'); 

% demodulate the received signal at the base station 
parfor i=1:nos
    z(i,:)=fmdemod(y(i,:),cfreq(1,i),10*cfreq(1,i),freqdev);
end

% display the transmitted signal  and received signal at the base station
% figure

C = {'k','b','r','g','y',[.5 .6 .7],[.8 .2 .6],[.3 .2 .2]}; 
% Cell array of colors.

for i=1:nos 
    figure (1)
    hold on 
    plot(y(i,:),'color',C{i});
    xlabel('Time index'); ylabel('Amplitude'); title('Signal from different users combined in the channel');
    figure
    subplot(3,1,1)
    plot(m(i,:))               % modulating signal
    xlabel('Time index'); ylabel('Amplitude'); title('Modulating Signal from user');
    subplot(3,1,2)
    plot(y(i,:),'color',C{i}); % modulated signal
    xlabel('Time index'); ylabel('Amplitude'); title('Modulated Signal from user');
    subplot(3,1,3)
    plot(z(i,:),'color',C{i}); % demodulated signal 
    xlabel('Time index'); ylabel('Amplitude'); title('Demodulated Signal from user at the base station');
end
figure 
plot(ch_op) % combination of all modulated signals passed through the channel
xlabel('Time index'); ylabel('Amplitude'); title('Signal after passing through the channel');


y = filter(b,a,x);
figure
plot(t,x)
hold on
plot(t,y)
legend('Input Data','Filtered Data')

Answer 1

[Samhitha]

Hi @Sean Audie,

add Gaussian noise difference in your Frequency Division Multiplexing (FDM) system and plot it, you can use following steps.

1. Generate clean combined signal (without noise)
2. Add AWGN (additive white Gaussian noise) to your combined FDM signal.
3. Compute and plot the difference (the noise added).

Code that you can add in your script:

% Combine all modulated signals (clean FDM signal) 
clean_signal = sum(y); 

% Pass through channel with AWGN 
noisy_signal = awgn(clean_signal, 0, 'measured'); 

% Compute Gaussian noise difference 
noise_diff = noisy_signal - clean_signal; 

% Plot the Gaussian noise difference 
figure 
plot(t, noise_diff) 
xlabel('Time index'); 
ylabel('Amplitude'); 
title('Gaussian Noise Difference Added to FDM Signal'); 

For more details, look into following documentation:

https://www.mathworks.com/help/comm/ref/awgn.html

Hope this helps!