How do I fix Double Nat (NAT Type 3) for PS3?

When I tried to setup my internet connection settings on my PS3, I got NAT type 3. I think it is a double NAT because i have a router and I have a modem, and a modem has a NAT and a router has a NAT, therefore there is a double NAT (if I am not mistaken). How do I fix this? Oh, I forgot to say that I have a D-Link DIR-655 router and I have a Gigaset 4300 modem (from Windstream). I don't want a PPPOE connection, and I really dont want to bridge the modem because one wrong mistake, there will be no internet. Somebody please help me, thank you.