Hello,
as I reported two weeks ago, deactivating bluetooth didn't solve the problem. In the mean time I visited two friends and tried the wifi stability within their network. There I had no problems, even with the same router. The difference was, that in their surrounding only a few other networks are (two or three) whereas there are up to twelve networks at my place. May be the N2230 doesn't like too much traffic around? (But as I said, all other devices like me smartphone or my other notebook doesn't have any problem, so it shouldn't be a problem.)
Now I bought a USB wifi adapter for my place to deal with the problem (and it works!) even though I don't like this solution. I'm asking myself if Intel is not competend enough to write a working driver or if this is a hardware problem.
Cheers,
vespear