Your home signal strength, although an indication of how well your PS3 is talking to your router/internet does not mean that the same can be said for any connection to the MW3 servers which are run separately.
Have you looked at the Activision website or any of the other COD websites to see if anyone else is experiencing the same issues?
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tried putting in black ops and i was playing fine up there. so im guessing its ap roblem with the mw3 server. but when i ask my friends who are also playing they arent experiencing any problems...