EXFO PSO-200 Optical Modulation Analyzer - Manual (Page 92)

Bit Pattern Analysis and the Gearbox
84 PSO-200
Importing User-Defined Symbol Patterns
Importing User-Defined Symbol Patterns
You can import a known symbol pattern from a file and work directly with
the symbols in the constellation without having to know the Gearbox
details. This allows you to simulate a modulation scheme implementation
that is not supported by the PSO-200 or simply to read back symbols
information from a previous export.
In this mode, the IF recovery algorithm takes advantage of the known
pattern information, and is therefore more robust towards limitations in the
signal laser linewidth (phase noise).
The symbol error rate (SER) can be evaluated, but not the bit error rate
(BER), since there is no defined mapping between symbols and bits.
The symbol pattern file must have data for the same polarization(s) as the
input signal:

If the signal contains X and Y polarizations and the imported symbol
pattern contains only one, the application will automatically duplicate
these values for the Y polarization.

If the signal contains one polarization and the imported symbol pattern
contains both, the application will truncate the Y data from the pattern.
Note: When importing a symbol pattern, the application will normalize any
non-normalized value.
Note: The Gearbox is not available in this mode.