said by Secyurityet:All good ideas that have been tried, except the cable which will be difficult since they are on separate floors. Signal strength at the printer is a full five bars!
Reorient the printer so the antenna is better oriented to the router
Change the channel to a (more) empty channel for your area
Make sure the signal strength on the RG is up to max
Put the printer within a cable's length of the RG and connect it via Cat5e/6 cable...