Jerry,
The Thetis software for the Hermes Lite, ANAN and radioberry radios has adaptive predistortion and you can examine the source files to see how it works. Thise radios have the capability of operating full duplex so they use the receiver to listen to a sample of the transmitter output and down convert it to baseband where the predistortion is calculated and applied to the baseband transmitter before upconversion.
Gary
W9TD
Gary