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Why Does my GMSK looks exactly like PSK?!

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g.hadzhiyanev

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Hi, guys!
I just noticed that my GMSK modulated signal actually looks exactly like PSK. Why? Where is the mistake?

Code: 
%----------------------GSM NETWORK SIMULATION-------------------------%
clear all;
clc

H = comm.GMSKModulator('BitInput', true, 'SamplesPerSymbol', 4);
H.PulseLength = 1;
training=randi([0 1],26,1); %Generating Training sequence
data1 = randi([0 1],61, 1); %Generating pre-training data
data2 = randi([0 1],61, 1); %Generating post-training data
Burstcol = [data1; training; data2 ];      %Assembling Burst as a single row matrix


modSignal = step(H, Burstcol);              %Signal through GMSK

t=(1:1:592);
plot(t,modSignal, 'black'), hold all;

Thanx
 

What do you mean by "my GMSK modulated signal actually looks exactly like PSK"? What is it that you are seeing in the plot? If I am not wrong, the plot function displays only the real component of 'modSignal'. If you plot the absolute value of GMSK signal, you should get 1 at all times, unlike PSK signal.

Also, I am curious why the PulseLength is set to just 1. Generally, for GMSK signals pulse length is longer. The MATLAB Help for the function says that the default is 4.
 
I changed it to 1 beacuse i changed the SamplesPerSymbol to 1. Forgot to change it back. But actually I don't know what does the PulseLength mean? Can you explain? I read the help but it was quite unclear.
 

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