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On the technical side, the patent is for Non-Uniform Constellations or NUCs. It's a modification of the modulation constellation points to match the error coding.

Traditional 64QAM:

https://www.w6rz.net/64qamrect.png

ATSC 3.0 64QAM for 9/15 code rate:

https://www.w6rz.net/64qamnuc.png

You can explore this with my open source ATSC 3.0 transmitter.

https://github.com/drmpeg/gr-atsc3

Demo clip.

https://www.youtube.com/watch?v=cmIGM0I3NE0

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I was always surprised why QAM uses a rectangular I/Q coordinate rather than a radial one like how 8PSK does it. It would seem like a radial pattern maintains better ISI margin just from inspection.

With less error coding (13/15 code rate), the constellation is more rectangular.

https://www.w6rz.net/64qamnuc1315.png

With really heavy error coding (2/15 code rate), the constellation becomes almost unrecognizable with points very close to each other.

https://www.w6rz.net/64qamnuc215.png

Wow. There must be some interesting coupling between the coding and the constellation/modulation.

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