I have the same problem with my 3 week old Dell Inspiron 5521, Centrino 2230 Wifi card.
I bought the notebook and the next day I went to Dell service because of the wrong Wifi... They raplaced the card with a new one (1week)
,but the wifi problem came back (the signal strength is very good, 99% 8m away from the router. The net speed has dropped almost zero) I tried all settings in the router (probed two different routers),drivers. Now the Wifi can works only on 20mhz, Wpa-tkip. Windows 7 SP1 64-bit doesn't recognize the card driver, so I can't use MS drivers.
I invested a lot of time and energy. The Dell Service don't know anything about this driver error..., I thought it was problem only with my notebook, I was very upset. 1 week ago I found this forum and I calmed down a bit, problem that's not unique.
In 2013 ridiculous, things like this mess with people.
My other notebooks never had problem with Wifi. I'm angry...
I can't believe Intel can't fix the problem for 8months !? :@