Thanks everyone.

Actually, i am already minimizing scrambling. Channel selection is OK, as far as it can be in a condominium. Floor noise is there, unfortunately. But I minimized as much as I could use xirrus wifi inspector. It's good.

5GHz is indeed an option, as that is not much used here, but please consider that the garage wall/ceiling i need to go through is thick, so 5Ghz means i will have to use a bit more power.

Power line is an excellent idea, if only I had a power socket in the condominium garage. Not one.

Which is why I was thinking of a range extender and directional antenna.