Can gravitational wave be used for data transmission? Imagine an advanced civilization which can manipulate gravity like we manipulate electromagnetic radiation. Could they already be using gravitational waves for data transmission across different galaxies? 
Unlike electromagnetic radiation which can be shielded, gravitational waves appear to travel through any medium at speed of light. Perhaps this explains why SETI is a wasted effort?
EDIT: didn't realize there was a similar question already raised:
Would it be possible to transmit information through gravitational waves?
 A: In theory, yes. The recent observation of gravitational waves is nothing but information transfer via gravitational waves captured by us, humans. The information conveyed is not an email (sorry gmail) but it tells us that two black holes merged. However, whether GW or EM waves, the source has to be unimaginably powerful to communicate over galactic distances. Also, because GW can not be shielded, therefore, they can not be pointed in a particular direction like we can do with EM waves. So, the source has to be even more powerful. But if a civilization is that advanced, it may have figured out some other more practical means of communication.
A: We can already manipulate gravity like we manipulate electromagnetic waves. Tie something at the end of a rope and swing it around your head: you're now generating gravitational waves. And yes, you can transmit information with gravitational waves in the same way you can transmit information with any other modulable wave.
The problem is not generating waves, it's generating strong enough waves; the waves you generate by swinging something around are completely undetectable by any technology we have the resources or engineering capacity to build, and so they'd be useless for transmitting readable information to someone else. It would be like trying to contact someone far away by whispering at them.
A: Can gravitational waves be used to transfer information?
Yes, the two black holes did just that.
The waveform held information allowing scientists to

*

*estimate their masses, including error bars

*estimate their location in the sky (roughly)

*estimate their distance and the time of the event

All of this information is part of the exact increase/decrease of the detected wave amplitude and frequency in conjunction with the matching data of the sister detector.
If you want to know more on the general issue, I suggest topics such as

*

*fourier transformation

*signal encoding theory

*modulation of waves (acoustic, electromagnetic)

Can aliens use GWs to transport information? If they know how to carefully swing black holes around, then yes. But I'd be skeptical. It's so much easier to use electromagnetic waves by carefully swinging electrons around. Or carve something in stone and send by snail mail, like the Voyagers do :-)
