how can i remove the dc componente from the output of the signal from workspace?

clc; clear; close all;

stringa = '$GPGGA,123456.00,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47';

% Inizializza il vettore per la trasmissione seriale in formato 8N1

trama_gps = [];

for i = 1:length(stringa)

binaryChar = dec2bin(stringa(i), 8) - '0'; % Converte il carattere in binario (8 bit)

% Formato 8N1: 1 bit di start (0), 8 bit di dati, 1 bit di stop (1)

transmittedChar = [0, binaryChar, 1];

% Aggiunge al vettore di trasmissione

trama_gps = [trama_gps, transmittedChar];

end

% Trasforma trama_gps in un vettore colonna

trama_gps_column = trama_gps(:); % Il simbolo ": " trasforma in una colonna

% Dividi i dati in coppie di bit

% Ogni coppia di bit sarà un elemento della matrice finale

num_pairs = length(trama_gps_column) / 2; % Numero di coppie di bit

% Prepara una matrice colonna per contenere le coppie di bit

qpsk_input = zeros(num_pairs, 1);

for i = 1:num_pairs

% Ogni elemento della matrice è una coppia di bit

bit_pair = trama_gps_column(2*i-1:2*i);

% Converti la coppia di bit in un numero binario

qpsk_input(i) = bi2de(bit_pair', 'left-msb'); % Converti la coppia di bit in un numero decimale

end

% Visualizza la matrice finale

disp('Input per QPSK (in formato colonna):');

disp(qpsk_input);

bit_rate = 2720;

% Visualizza la trama

disp('Trama GPS (8N1):');

fprintf('%d', trama_gps);

fprintf('\n');

% SF = 25735;

% n = SF * length(trama_gps); % Lunghezza del vettore

% prc_1 = randi([0, 1], 1, n);

This is my code. I m trying to use the spectrum analyzer in simulink to see the spectrum of qpsk_input. I want to put qpsk input in the qpsk modulator baseband (that s why qpsk_input ha integer). The problem is that at frequency 0Hz i have i dc component that i don t want? can someone help me to remove this DC component please?

Answer 1

[Aastha]

Hi @Lorenzo,

As I understand you want to remove the DC component of the signal in Simulink. There are two methods to do this.

Method1: Mean Subtraction

You may implement this method using a “MATLAB function” block in Simulink.

For more information on “MATLAB function” block, kindly refer to the documentation link mentioned below:

https://www.mathworks.com/help/simulink/slref/matlabfunction.html

The DC component is the mean of the input signal. Since the Fourier transform is a linear operation, subtracting the mean of the input signal will remove the DC component of the signal. You can do this using the following MATLAB code snippet:

qpsk_input = qpsk_input - mean(qpsk_input);

Method 2: High Pass Filtering

To remove the DC component, you can use a high pass filter. This will give you more control over the frequencies that are suppressed. To do this you can use the “Highpass Filter” block in Simulink. You can set the parameters of the “Highpass Filter” block according to the requirements to perform filtering of the DC component.

You can find more information about the the “Highpass Filter” block in Simulink in the documentation link mentioned below:

https://www.mathworks.com/help/dsp/ref/highpassfilter.html

Hope this helps!