Fig. 1. (a) Structure diagram of CMA and (b) amplitude diagram of 16-QAM signals.

Fig. 2. Extracted partial amplitudes of PS 256-QAM signal in (a) Cartesian coordinate and (b) polar coordinate systems.

Fig. 3. Decision diagram of local density and relative distance.

Fig. 4. Experimental setup of a PS 256-QAM coherent optical transmission system.

Fig. 5. Extracted partial amplitudes of a PS 256-QAM signal with marked standard radii and decision region of amplitude.

Fig. 6. Measured BER versus OSNR of 7.4 bit/symbol 256-QAM signal.