How to design a base band filter with MATLAB

How do I design a base band filter with MATLAB and test on a one-dimensional signal, now you can get the output of the BPSK signal.

Answer 1

[Rahul]

Hi @kia mansor,

In order to create a base band filter, you can follow the given steps:

STEP 1: Create a BPSK signal.

% Here I have created a BPSK signal variable 'bpsk_signal' using random binary data 
% I have used 'randi' and 'repelem' functions for the same

data = randi([0 1], 1, 1000);
bpsk_signal = 2*data - 1;
bpsk_signal = repelem(bpsk_signal, 10);

% NOTE: This step is not required if you have a BPSk signal available.

STEP 2: Obtain a base band filter which would essentially be a low-pass filter.

% Here I am designing the low-pass filter using 'designfilt' function.
% I have added example parameters for reference. These can be changed
% according to specific use-case.

baseband_filt = designfilt('lowpassfir', 'PassbandFrequency', 50, ...
    'StopbandFrequency', 70, 'PassbandRipple', 1, ...
    'StopbandAttenuation', 60, 'SampleRate', 1000);

% 'fvtool' function helps in visualizing the magnitude response of the filter
fvtool(baseband_filt)

STEP 3: Filter the signal using the filter created.

% Use the 'filter' function to obtained the 'filtered_signal'
filtered_signal = filter(baseband_filt, bpsk_signal);

You can further plot the signals to observe the difference between original and filtered BPSK signal.

You can refer to the following Mathworks documentations to know more about these functions:

'randi': https://www.mathworks.com/help/releases/R2022a/matlab/ref/randi.html

'repelem': https://www.mathworks.com/help/releases/R2022a/matlab/ref/repelem.html

'designfilt': https://www.mathworks.com/help/releases/R2022a/signal/ref/designfilt.html

'fvtool': https://www.mathworks.com/help/releases/R2022a/signal/ref/fvtool.html

'filter': https://www.mathworks.com/help/releases/R2022a/matlab/ref/filter.html

Hope this helps solve your query. Thanks.