Underground garage communication?

I have an undegroud garage, where low to none cell signal is picked up by my phone. It's only ≈65 ft (20m) from my home, but there's a thick concrete slab between the surface and the garage. Some ventilation grids are present in the ceiling of the garage, from which there is an almost direct sight to my house.

What protocol/antenna combo might be suitable to establish a solid connection between the two points? I'm diy inclined, so budget friendly kits are very welcome.

Thanks for your time.

Submitted by INPoppoRTUNE

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