A thought occurs:
As this is quite obviously one of the best ways to use radio frequencies efficiently, and that it relies on there being many small antennae, and also that there be a wide range of paths, interference, distance, obstacles, etc. between the sender and receiver...
Is this not something we should expect an alien civilisation to use when communicating between systems?
As the receiver needs "only a single antenna" and a lot of processing, and the sender can send from 128 different antennae, surely that's perfect for a communication system from one star system to another, with antenna on different planets (or different points of the same planet), and any amount of space-stuff in between (even space warped by gravity of other planets etc.)?
Not saying we have any clue how to listen for that, or how to determine how it's arranged, but it would seem to be the no-brainer application of something like MIMO to form the basis of a deep space network from a single original star system