Experimental performance of 4D optimized constellation alternatives for PM-8QAM and PM-16QAM

Sensitivity and reach of soft-decoded PM-8QAM was improved by 1.2-dB and 35%, respectively, by moving to a 64 point 4D constellation and iterative decoding. Replacing PM-16QAM by 256 4D points led to 0.3-dB gain only.