EXFO PSO-200 Optical Modulation Analyzer - Manual (Page 102)

Bit Pattern Analysis and the Gearbox
94 PSO-200
Performing Detailed Bit Pattern Analysis with the Gearbox
Bit Symbol Mapping Section
Depending on the modulation scheme, there can be one to four bits per
symbol, or even more. This section contains as many lines as there are bits
per symbol in the modulation scheme. Each line represents a bit mapping
and delay.
Note: In addition to editing this section of the file with a text editor, you can also
modify its values in the Optical Modulation Analyzer application.
To better understand how this works, here is an example representation of
a DP-QPSK transmitter:
In this image, S1 is the input bit stream, X0 and X1 are the modulator inputs
for the X polarization, and Y0 and Y1 are the modulator inputs for the Y
polarization. It represents what happens when a single bit stream is split
into four modulators. The corresponding configuration file is
“DP-QPSK_OneGlobalStream.gearbox”.