Uh, was your father John Renshaw Carson?
Single-sideband modulation - Wikipedia says John Renshaw Carson was born 1886 and the first to patent SSB in 1915.
If you have ever used SSB it is a miserable minimalist mode. Everything sounds like Donald Duck and the slightest error in frequency makes it worse because SSB lacks a means of self-centering.
Quite often the situation with fundamental inventions such as SSB the concept can not be put into use fast enough to be useful. The patent serves as documentation which prevents anyone else from patenting it 20 years (formerly 17) in the future.
SSB took a long time to catch on because it is difficult to build mixers to transmit and demodulate. And as I said above, it is not pleasant to listen to.