Which version of dl 256qam is a feature?

QAM is quadrature amplitude modulation, that is, a digital signal performs ASK modulation on two orthogonal carriers (sin and cos) respectively, and the corresponding "quadrature" amplitude can be represented by a plane constellation, that is, each point on the constellation corresponds to the combination of two orthogonal carrier amplitudes.

The so-called 256QAM is the quadrature amplitude modulation of digital signal in 16, and the constellation is 16* 16=256 points.