MATLAB: How to plot the constellation diagram for a binary FSK modulator

Communications Toolbox

I am trying to plot a constellation for a Binary FSK but this method does not seem to be available to FSK. Is there a way to generate a constellation plot for comm.FSKModulator?

Best Answer

M-FSK constellations are M-dimensional and hence the method is not available to it. But as long as you are working with binary FSK, you can use comm.ConstellationDiagram or the scatterplot function to visualize a 2-FSK constellation. Below is an example:
>> modulator = comm.FSKModulator(2, 1000);
>> data = randi([0 modulator.ModulationOrder-1],50,1);
>> modSignal = modulator(data);
>> scope = comm.ConstellationDiagram('ShowReferenceConstellation', false);
>> scope(modSignal);
However, it is important to note that even an ideal 2-FSK constellation will rotate in one direction or the other (clock- or counterclock-wise), and the direction cannot be inferred from the constellation.Therefore the constellation will not really be insightful, except for depicting the impact of impairments.