Good day friends.. I'm using unifi 5mb. But installed in 1st floor of my house.I But my ground floor getting very weak or sometime no signal. I've read that homeplug can help me with improving signal strength but only if i install the modem or router at ground floor. all the shops unsure how to increase the signal strength if i fix the modem at the first floor as they said the signal transmission is always in upward direction. Is it possible if i place the router upside down in order to improve or boost the signal downstairs? Please advise. Thanks.

Just use a home plug.
I get full signal on the ground floor eventhough my modem is on the first floor.

homeplug is the most viable option

The best way still is using cable to cable and then wifi out