How to plot constellation diagram for 8 - PSK modulation ?

I wants to plot the constellation diagram for 8 - PSK modulation. The modulation is at the baseband data. I have three signals for the same which modulated the input data stream into 8 - PSK modulation. These are I, Q & Signal waveforms. I have captured these data on Oscilloscope. But not sure how will I use these captured data to plot the constellation diagram. In oscilloscopes, there is XY mode but will be only useful to plot QPSK modulation constellation.

Can anyone help on how I can use these captured ".csv" data further in MATLAB to plot the Constellation Diagram ?

My license number is : 416213.

Regards,

Nikhil Mitaliya

Answer 1

[Yukthi S]

Hi @Nikhil Mitaliya

As per my understanding, you want to load the I, Q sample data captured in .CSV files into MATLAB and use it to plot a constellation diagram.

1. Text files such as .CSV files can be imported into MATLAB using readtable if you want to bring in the data as a table, or readmatrix if you prefer to import it as a matrix.

You can refer to the following MathWorks documentation links to know more about readtable and readmatrix:

• https://www.mathworks.com/help/matlab/import_export/ways-to-import-text-files.html#:~:text=its%20user%20interface.-,Import%20Data%20as%20Tables,-If%20your%20text
• https://www.mathworks.com/help/matlab/ref/readmatrix.html#d126e1410276:~:text=example-,A%20%3D%20readmatrix(filename),-creates%20an%20array

2. To plot constellation diagram in MATLAB, scatterplot function can be used. Before using scatterplot function, make sure “Communication Toolbox” is installed in MATLAB.

More information about scatterplot is given in this MathWorks documentation:

• https://www.mathworks.com/help/comm/ref/scatterplot.html#:~:text=example-,scatterplot(x),-creates%20a%20scatter

The code given below gives a basic idea of how it can be done:

I_data = readmatrix('I_data.csv');  % Replace with actual file name
Q_data = readmatrix('Q_data.csv');  
% Combine the I and Q data into a complex signal
complex_signal = I_data + 1j * Q_data;
figure;
scatterplot(complex_signal);

Hope this will help you to get started!