EXFO PSO-200 Optical Modulation Analyzer - Manual (Page 106)

Bit Pattern Analysis and the Gearbox
98 PSO-200
Performing Detailed Bit Pattern Analysis with the Gearbox
Symbol Coordinates Section
The third section of the Gearbox configuration file is used to tell the
application where, in the constellation, a “word” is supposed to be found.
This arrangement highly depends of the implementation of the transmitter.
The configuration file normalizes the constellation on both axes. To
indicate where a “word” should appear in the constellation, each line in
the file represents a bit pattern and its symbol coordinates:
For example, in a 16-QAM model, we could define that the word “0000” is
located at I
X
= –1, Q
X
= –1, and “1111” is located at I
X
= 1, Q
X
= 1, as
shown in the above diagram.
16-QAM
constellation
example
I an Q values
for polarization X
I an Q values
for polarization Y (if applicable)