How do i stop this lag in Call of Duty Black Ops for PS3?

I usually use a wireless connection for my PS3, but lately whenever i play, even with friends who live close to me, i start with a 4 bar (green) connection, and then it just ends up at 1 bar (red) and then just switches between 1-3 bars throughout the match. I then tried connecting my PS3 with an ethernet cable, and the same thing happened. Also, the other night, my NAT type was on strict, but i managed to fix it, and since then it has been on open, but i am still lagging like crazy when i play. Anyone know a way to fix this, or what the problem could be?