|Block Diagram||System Diagram||N/A|
|BER/SER Meter||System BER/SER Meter||N/A|
|Modulation Type||List of options||N/A|
|Statistic Type||List of options||N/A|
The measurement plots a theoretical QAM bit or symbol error probability along the y-axis and the swept variable (typically Eb/N0 or Es/N0) along the x-axis. The y-axis should normally be set to use log scaling.
The measurement generates a reference curve based on the type and settings of the meter block selected in the BER/SER Meter setting. If the BER/SER Meter parameter is set to "Auto", the measurement will compute the bit error probabilities Pb for BER meters and symbol error probabilities Ps for SER meters. Values for Pb or Ps are calculated for each power value specified in the meter's SWPTV parameter.
When M is an even power of 2 (M=2k, k is even) the following equations are used :
where Q(x) is the Gaussian integral or Q-function:
and is approximated numerically, Es is the average symbol energy, N0 is the noise power spectral density and M is the number of signal levels.
For other values of M an approximate upper bound is calculated from :
The measurement computes bit error probabilities from the symbol error probabilities using the following approximation :
This approximation assumes Gray coded square QAM constellations, which is not realizable for all values of M.