Nobody uses 512-QAM for WiFi, and for some good reasons: 1) it's not part of any current or draft standard; 2) it only encodes 9 bits vs. 8 bits for 256-QAM.

Nobody uses 512-QAM for WiFi, and for some good reasons: 1) it's not part of any current or draft standard; 2) it only encodes 9 bits vs. 8 bits for 256-QAM. Plugging this into GP's formula gives us: 1/3.6e-6 × 468 × 9 × 5/6 = 975 Mbit/s 3) current WiFi QAM constellations are all square [1,2], and there is no way to arrange 512 points into a square. 4) that would require an unrealistically clean channel, and give no advantage over lower-order modulations otherwise [3] [1] https://dsp.stackexchange.com/questions/31607/why-are-qam-constellations-regular-and-rectangular https://dsp.stackexchange.com/questions/31607/why-are-qam-co... [2] http://www.radio-electronics.com/info/rf-technology-design/quadrature-amplitude-modulation-qam/8qam-16qam-32qam-64qam-128qam-256qam.php http://www.radio-electronics.com/info/rf-technology-design/q... [3] https://upload.wikimedia.org/wikipedia/commons/thumb/6/68/QAM_Mutual_Information_in_AWGN.svg/1024px-QAM_Mutual_Information_in_AWGN.svg.png https://upload.wikimedia.org/wikipedia/commons/thumb/6/68/QA...