Changes to expect in the efficiency of sending ET comms

I think that in a decade or so the chance of sending successful messages to other lifeforms will increase due to better mapping of the galaxy. When the Square Kilometer Array radio telescopes come online the "dispersion measure" of most of the galaxy will be revealed. Dispersion measure is how much the speed of light varies for different frequencies because of free charge along the path. It causes the range of frequencies that make up a signal to arrive at slightly delayed times. It is smeared through time.

Pulsars have unique and repeatable pulse shapes. Through analysis of known pulse shapes from sources like pulsars the amount of smearing of the signal can be computed. There are lots of pulsars along many lines of sight through the galactic disk. By combining them a map of the intensity of the smear of frequencies in time can be measured. In general the denser the charge, or lower the frequency, the more smearing.

To send a simple "pulse" of a finite bandwidth hundreds of light years and have all the frequencies over the range arrive at the same time corrections have to be applied using computer digital signal processing. Anticipated dispersion is canceled out by shifting the lower frequency part of the signal to a proportionally sooner time in the transmission.