Experimental investigation of a four-dimensional 256-ary lattice-based modulation format

A four-dimensional modulation format with 256 point from the D4-lattice (256-D4) is compared to PM-16QAM in experiments. 256-D4 is more sensitive at high OSNR but with a 21.3% overhead turbo product code, PM-16QAM outperforms 256-D4.