Can you try connecting your PS3 via a cable to the router and having a bit of a play like that, to see if it's the wireless that's at fault ? I suspect that it probably is.
An alternative solution, if you can't have the router near the PS3, is to install a Powerline networking solution, where the network traffic is sent over your mains wiring. This is a lot faster and not prone to interference. Although it's not cheap, it'll probably set you back close to £100 for a pair of adapters (one to plug in your PS3 - or PC etc - and another to plug in to the router). This will basically act like a direct connection rather than wireless.