RECOMMEND YOU A WIFI REPEATER (its like a device you connect it on the wall socket and you configure it with your modem or router wifi and it will repeat it), so if you have a socket near the PS3, you first configure it near the modem (to, have more signal **this is on the CDmanual, its very easy to configure.. there is a guide**) and then you put it near the PS3..
Then, the repeater comes with an Ethernet (wired) connection.. after configuring it, you connect the repeater with ps3 and works like if the repeater its the Modem
HOPE IT HELPS!!!! GOOD LUCK... its strange you cant RTEing on CEX but if you want DEX and your router is in living room.. this is the greatest solution!!