I was just watching this video Tutorial on Passive Filters, Data Transmission and Equalization. In the video he shows how one can use the size of the opening in the eye pattern as a way to measure the effectiveness of per-emphasis for overcoming bandwidth limitations of a bus or transmission line.
I assume it is a standard practice to optimize pre-emphasis for known transmission lines once and then just leave the values alone.
What I would like to know is do communications circuits exist where the pre-emphasis is adjusted dynamically as the characteristics of the channel change? I am thinking here of circuits like HF radio links over hundreds or thousands of miles where things like phase distortion vary over time. I assume this would also apply to circuits between satellites and earth stations where the satellites are not in geosynchronous orbit.