Hacker News Reader

Comment by rayiner | Hacker News Reader

OFDM is orthogonal to PSK (hah). PSK is a modulation--a way of representing bits on a carrier wave. Another type of modulation is QAM. OFDM is a way of combining multiple sub-carriers (each modulated with PSK or QAM) into one signal in order to deal with multi-path distortion: https://www.csie.ntu.edu.tw/~hsinmu/courses/_media/wn_11fall....

View on HN

Still, hatsunearu is correct. The page is grossly wrong, absolutely no modern WiFi modulation technique uses 8-PSK. Have a look at http://mcsindex.com/ 11a/11n/11ac all use BPSK, QPSK, 16-QAM, 64-QAM, and (for 11ac only) 256-QAM.

I know. And not a word on forward-error correction, trellis codes, automatic gain control, beam steering or MU-MIMO. Is this for babies? They don't even touch on low-noise amplifiers. Much less DAC and ADC performance. Where's the link a primer on FFT?

Some systems even combine PSK and ASK (like QAM) but asymmetrically (called APSK), obviously though you start getting into diminishing returns; noise limiting the gains. Of course you are limited by Shannon's law. But depending on the transmission medium lower energy signals can be more resistant to noise, so you can use either probabilistic or dynamic symbol selection to reduce the effect noise has on the signal and hence increase the available error free bandwidth (error free symbol rate)[0].

[0] https://en.wikipedia.org/wiki/Constellation_shaping ; check the references and external links for more in depth explanations.

Reply on news.ycombinator.com