Equalization can help.
Here I show an example of a fixed transmit-based
equalization scheme. This is called "pre-emphasis".
It is based on the observation that the signal after
each changing edge seems to have some initial difficulty crossing the
receiver threshold. To counteract this tendency, the transmitter
amplifies each changing edge, and then quickly reverts to a more nominal
sustaining level for the long, flat parts of the transmitted signal.
A simple fixed equalizer can often add 50% to the
attainable distance in a digital channel.
